A new class of silicone resins for coatings.

Abstract A new class of silicone has been developed for coatings or as coating additives. Cycloaliphatic silane monomers were prepared and reacted into more easily handled cyclic oligomers. These cyclic oligomers were-ring-opened into siloxane polymers. The polymers were functionalized with a variety of groups, including: amino, glycidyl epoxide, cyclohexene epoxide, acrylic, and alkoxysilane. The cycloaliphatic silicones have been designed for a number of different curing conditions: (1) ambient temperature-cure (amino and glycidyl epoxide), (2) cationic ultraviolet (UV)-cure (cyclohexene epoxide), (3) redical UV-cure (acrylic), and (4) moisture-cure (alkoxysilane). The end usages thus far have been focused on silieone coatings; however, usage as coating additives will be a focus for future research. The cycloaliphatic silicone has been UV-cured with mixed sol-gel precursors for usage as aerospace coatings. The cycloaliphatic silicones have also been ambient temperature-cured for release coatings, and have application as anti-fouling coatings. The inherent low surface energy makes the cycloaliphatic silicones prime candidates for surface tension additives.

Keywords Silicones, Differential scanning calorimetry, Gel permeation chromatography, Hardness, Scratch resistance, Crosslinking, Cure, Photoinitiators, Silicones, Silicates, Mechanical properties, Thermal properties, Coating formulation, VOC control. High-solids. Adhesion, Reaction mechanisms, Formulation, Aluminum

Introduction

Silicones were named as the silicon analogs to ketones. In retrospect, a more appropriate name may be "silicals" as the analog of a ketal. Like much of prespectroscopic chemistry and common names, however, marketing wins out, and silicones sounds better than silicones. The flexibility of silicone is attributed to the free, almost unhindered, rotation around the silicon oxygen bond. In the coating industry, silicone resins make up a small specialty resin market. Because of inherent surface tension properties however, silicones are ubiquitous as coating formulation additive. Indeed, one would be hard pressed to find an older formulation without a silicone additive of some sort.

Chlorosilanes are the basic building blocks of a silicones and polysiloxanes. Chlorosilanes are utilized in hydrosilation where the addition of a SiH compound to a multiple bond, often an alkene or alkyne, is the pathway to synthesizing a veriety of unique polysiloxane systems. Typically, platinum complexes are used as hydrosilation catalysts due to activity at relatively low concentrations. The most common platinum catalyst is chloroplatinic acid (Speier's catalyst) which is reduced to a platinum (0) species in the presence of a silane or siloxane. During these reactions, an induction period was observed, but this can be reduced by using a platinum (0) complex such as Karstedt's catalyst. Other metal-based catalysts can be used, such as the rhodiumbased Wilkinson's catalyst, although higher catalyst concentrations are usually required for efficiency.

Processes that involve the synthesis of linear siloxane polymers can be divided into two general classifications according to the pathway in which the polymer chain is formed: polymerization of difunctional silanes and ring-opening polymerization of cyclic oligosiloxanes. (1) Hydrolytic polymerixation involves the polymerization of halosilanes (mainly chlorosilanes) through the incorporation of water, and is often employed for the synthesis of both linear siloxane polymers and cyclic siloxane oligomers--the latter of which can be further used as substrates in ring-opening polymerization. A polysiloxane chain is most often formed as the result of two types of polymerization: homofunctional polymerization of a difunctional silane such as silanediols or dichlorosilanes; and heterofunctional polymerization involving a silanol and another functional group. A heterofunctional polymerization approach is useful for a hydrolytic polymerization step. As a result, both steps--hydrolysis and polymerization--usually occur simultaneously during the reaction.

Polysiloxanes possess a variety of applications, both medical and nonmedical. Polysiloxanes and silsesquioxanes have been functionalized with various reactive groups (1-octene. substituted phenyl groups (6), (7) to achieve the desired property. Applications of siloxanes include high-performance elastomers, membranes, electrical insulators, water repellants, anti-foaming agents. mold release agents, adhesives, and protective films. (8), (9) Furthermore, the ability to synthesize monomers, that increase the glass transition temperature could be copolymerized with other polymers such as polyurethanes, polyimides, or other silicone monomers.

Polysiloxanes are known for their thermal stability and extreme flexibility.(10) The high bond strength demonstrated by the Si-O bond accounts for the high thermal and oxidative stability of siloxanes, and is a result of the partial ionic character of the Si-O bond. Polysiloxanes have been blended with polyimides and have shown synergistic improvement in thermal stability. (5), (11) Epoxy and amine-functionalized PDMS are commercially available for blending, but may offer limited compatibility with many coating resins. Chemically modified silicone fluids with broader ranges of compatibility have been reported.(12) Cycloaliphatic diepoxy/caprolactone polyol-based coatings were blended with siloxane-functionalized caprolactone polyols, and an increase in mechanical properties was observed in addition to a reduction in potlife stability. (13)

In this work, we proposed to prepare the cyclohexyl and cyclopentyl silane monomers, polymerize the monomers into oligomers or polymers, and functionalize the oligomers or polymers into synthons for thermosetting silicone resins or as additives. The synthesis and functionalization of poly(dicyclo pentylsiloxane-co-cyclopentylhydrosiloxane), hydride terminated, and poly(dicyclohexylsiloxane-co-cyclohexylhydrosiloxane), hydride terminated, was performed in a method comparable to the methyl-and hydrogen-substituted polysiloxane. The synthetic route for the cycloaliphatic-substituted siloxance differs from that of methyl-substituted siloxane in that the cyclic species needs to be synthesized via hydrolytic polymerization of cycloaliphatic-substituted silanes. The synthesis of amine-functionalized poly(dicyclopentylsiloxane-co-cyclopentylhydrosiloxane) and poly(dicyclohexylsiloxance-co-cyclohexylhydrosiloxance) was performed via the base-catelyzed ring-opening polymerization of cyclic oligomers of the cycloaliphatic-substituted polysiloxance. The monomers, oligomers, and polymers were characterized using. (1) H-NMR. (29) Si-NMR, FTIR, and mass spectroscopy. From the monomers and oligomers, polysiloxanes homopolymers were prepared. Some end usages have also been explored, such as UV-curable cycloaliphatic epoxides, ambient temperature curable amine epoxite systems for reclease, and aerospace coatings.

Experiment

Materials

Octamethylcyclotetrasiloxane, 1,3,5,7-tetramethlcyclotetrasiloxane, 1,1,3,3-tetramethyldisiloxane, dichlorosilane, and vinyl triethoxysilane were purchased from Gelest, Inc. and were used as supplied. Wilkinson's catalyst (chlorotris(triophenylphosphine)rhodium(I). (99.99%). Karstedt's catalyst (platinum(0)-1.3-divinyl-1,1,3,3-tetramethyldisiloxane complex, 3% w/w solution in xylenes), cyclopentene, cyclohexene, Amberlyst 15 ion-exchange resin, and 4-vinyl-1 cyclohexene 1,2-epoxide were purchased from Aldrich and used as supplied. Toluene (99.5%), supplied by Aldrich Chemical Co., was distilled to eliminate any impurities and stored with molecular sieves (4A, beads, 8-12 mesh). 1,3-bis (3-aminopropyl)tetramethyldisiloxane was purchased from Gelest, Inc., tetramethylammonium hydroxide, 25 wt% solution in methanol was purchased from Aldrich Chemical Company, and used as supplied. SS4177 was obtained from GE Silicones. Irgacure 250 was supplied by Ciba Specialty Chemicals and used as received. Air-sensitive materials were transferred and weighed in a dry box under argon. Aluminum mill finish 2024-T3 (3 x 6 [in.sup.2]) panels were obtained from Q-Panel. Unsaturated polyester paste for the fiberglass panels was obtained from Bondo Incorporated.

Instruments

Proton NMR spectra were obtained from a Gemini-300 spectrometer (Varian), silicon NMR spectra were recorded on a Gemini-400 spectrometer (Varian). All NMR samples were prepared in [CDCL.sub.3] and recorded at 20[degrees]C. Chemical shifts are given relative to a tetramethylsilane internal standard. Fourier transform infrared (FTIR) spectroscopy spectra were obtained on a Mattson Genesis Series FTIR and a Waters system was used for gel-permeation chromatography analysis. Mass spectroscopy was performed on a Saturn 2200 (Varian) in EI mode with an ion trap read-out. Absorption spectra were recorded on a Hewlett-Packard 8453 diode-array spectrophotometer. Contact angles were measured on an oscillating bubble rheometer equipped with an image capture video system. Thermal analysis was performed on a DSC Q-1000 with a heating rate of 20.00[degrees]C/min under a nitrogen purge. Taber abrasion tests were conducted on a Taber Industries 5130 Abraser using a CS-10 test wheel.

Synthesis of cycloaliphatic dicholorosilane

A dry, sealed, and evacuated stainless steel bomb, cooled via a duty ice/acetone bath, was charged with chilled cycloalkene (5 g, ~30 mmol) and Wilkinson's catalyst (0.15 g, 0.16 mmol) and purged with nitrogen. In a chilled (< 10[degrees]C) calibrated tube, dichlorosilane (5 mL, 0.06 mol) was condensed and then distilled into the bomb through the inlet valve via a canula. The inlet valve was sealed and the bomb was then allowed to warm to room temperature and then heated for 24 h at 120[degrees]C by means of an oil bath. The bomb was then allowed to cool and the reaction produced a clear, light yellow liquid. After distillation, any unreacted cycloalkene and side products were removed via vaccum (2-3 mm Hg) to yield pure cycloaliphatic dichlorosilane (~88% yield). Product characterization was performed by (29) Si-NMR, (1) H-NMR, FTIR, and mass spectroscopy.

General synthesis of cyclic oligomers of polycycloaliphatic hydrosiloxane

Saturated aqueous sodium bicarbonate (10 mL) and diethyl ether (5 mL) were added to a three-neck, round-bottom flask, equipped with a reflux condenser, nitrogen inlet/outlet, and dropping funnel. A solution of cycloaliphatic dichlorosilance (4.43 g, ~0.03 mol) in ethyl ether (5 mL) was then added dropwise via the dropping funnel, and the solution was allowed to stir for several minutes at room temperature. The ether layer was separated, passed through a filter, and any remaining traces of ether removed via vacuum distillation (3-5 mm Hg) to yield a clear, viscous oil. Average molecular weight was obtained for both the cyclopentyl- and cyclohexyl-substittuted cyclic oligomers from gel permeation chromatography (GPC). The polycyclopentlylhydrosiloxane oligomers had a [M.sub.n] = 1800 and a Polymeric Dispersity Index (PDI) = 2.44, the polycyclohexylhydrosiloxane oligomers had a [M.sub.n] of 2230 and a PDI of 2.53. Oligomer characterization was performed via (29) Si-NMR, (1) H-NMR, FTIR, and mass spectroscopy.

Synthesis of cyclic oligomers of polydicycloaliphaticsiloxane

The cyclic oligomers of the desired polycycloaliphatichydrosilxane (5 g), the preferred cyclo- alkene (15 g), and Karstedt's catalyst (0.1 mL, 0.22 mmol) were added to a single-neck, round-bottom flask equipped with a reflux condenser. The reaction was held at 110[degrees]C in an oil bath and magnetically stirred. The disappearance of the SiH functionality was monitored through FTIR and the disappearance of the peak at ~2160 [cm.sup.-1] indicated that the reaction was complete (>48h). Any unreacted cycloalkenes were removed under vacuum (3-1 mm Hg) to yield a clear, viscous oil. Products were characterized by (29) Si-NMR, (1) H-NMR, FTIR, and mass spectroscopy.

Synthesis of poly (dimethylsiolxane-co-methylhydrosiloxane), hydride terminated

Octamethylcyclotetrasiloxane (90.00 g, 0.30 mol), 1,3,5,7-tetramethylcylotetrasiloxane (5.33 g, 22.1 mmol), 1,1,3,3-tetramethyldisiloxane (0.67 g, 5.3 mmol), and Amberlyst 15 (20 wt%) were added to a three-neck, round-bottom flask equipped with a reflux condenser and nitrogen inlet/outlet, and stirred at 70[degrees] C, under nitrogen, for 15 h. The viscous solution was then filtered to obtain poly(dimethylsiloxane-co-methylhydrosiloxane), hydride terminated of various molecular weight ranges. Vacuum filtration was performed (<1 mm Hg) to remove low-molecular weight oligomers and unreacted starting materials. Average molecular weight obtained from GPC analysis was [M.sub.n] = 45,000 and PDI = 1.66. Polymer characterization and SiH functionality was confirmed/analyzed through (29) Si-NMR, (1) H-NMR, FTIR analysis, and titration. The cyclohexyl and cyclopentyl polysiloxanes were produced in the same manner.

Cycloaliphatic epoxide and alkoxy silane functionalization of prepared poly (dialkyllsiloxane-co-alkylhydrosiloxane), hydride-terminated polymers

Hydride-terminated dialkylpolysiloxane (30 g), 4-vinyl 1-cyclohexene diepoxide (20 g, 0.18 mol), vinyl triethoxysilane (2 g, 0.01 mol), and Wilkinson's catalyst (0.004 g, 4.3 [micro]mol) were added to a three-neck, round-bottom flask, equipped with a reflux condenser and nitrogen inlet/outlet. Dry, distilled toluene (30 g) was added via a canula. The reaction was held at 75[degrees]C in an oil bath and mechanically stirred under nitrogen. The disappearance of the SiH functionality was monitored through FTIR and the disappearance of the peak at ~2160 [cm.sup.-1] indicated that the reaction was complete. Any solvent and unreacted starting materials were removed under vacuum (3-5 mm Hg). Cycloaliphatic epoxide and alkoxy silane functionalization were confirmed/analyzed through (1) H-NMR, FTIR analysis, and titration. (14)

Synthesis of amine-terminated poly(dicycloaliphaticsiloxane-co-cycloaliphatichydrosiloxane)

Tetramethylammonium hydroxide, 25 wt% solution in methanol (3 g, 0.033 mol), was added to a three-neck, round-bottom flask equipped with a reflux condenser and nitrogen inlet/outlet. The temperature was raised to 100[degrees]C to remove the solvent. Once the solvent was removed, cyclic oligomers of poly(dicyclopentylsilox-ane-co-cyclopentylhydrosiloxane) or poly(dicyclo hexylsiloxane-co-cyclohexylhydrosiloxane) (30 g), 1,3-bis(3-aminopropyl)tetramethyldisiloxane (1.0 g, 4.02 mmol), and toluene (10 g) were added and stirred at 80[degrees]C, under nitrogen, for 5 h. In the end, the temperature was raised to 150[degrees]C for 1 h, to inactivate the catalyst. The solution was then filtered to obtain amine-terminated poly(dicycloaliphaticsiloxane-co-cycloaliphatichydrosiloxane) of various molecular weight ranges. Vacuum filtration was performed (100[degrees]C at <1 mm Hg) to remove low-molecular weight oligomers and any unreacted starting material. Average molecular weight obtained from GPC analysis was:

* amine-terminated poly(dicyclopentylsiloxane-co-cyclopentylhydrosiloxane) [M.sub.n] = 9465, PDI = 1.32, amine equivalent weight = 4324 [+ or -] 23 g/equivalent

* amine-terminated poly(dicyclohexylsiloxane-co-cyclehexylhydrosiloxane) [M.sub.n] = 8532, PDI = 1.53, amine equivalent weight = 4198 [+ or -] 23 g/equivalent

Polymer characterization was analyzed through (29) Si-NMR, (1) H-NMR, and FTIR analysis. (1) H-NMR ([delta] (ppm). CDC[l.sub.3]]): 4.53 (s, C[H.sub.3]-Si-H), 1.24 (s, C[H.sub.2]N[H.sub.2]). (29) Si-NMR ([delta] (ppm), TMS): -38.19 (s, R-Si-H), 7.70 (s, [R.sub.3]-Si-O). FT-Ir ([cm.sup.-1], KBr Plate): 1625 (s, N-H), 2150 (s, Si-H), 3200-3400 (d, N-H).

Film preparation/mechanical testing

For general coating properties, a ratio of 1 g of amine-functionalized, cycloaliphatic-substituted polysiloxane to 11 g of cycloaliphatic epoxy-functionalized cycloaliphatic-substituted polysiloxane were combined, throughly mixed, and cast over aluminum Q-panels with a 3 mil gauge draw-down bar. The films were allowed to stand for 48 h before testing in a dust-free curing chamber. Pull-off adhesion (ASTM D 4541-02), reverse impact (ASTM D 5420-04), and Taber abrasion (ASTM D 4060-95) were performed on the cured films.

For adhesion testing on the release coatings, a solution of polymer and 3% (w/w) photoinitiator, Irgacure 250, was prepared and wiped onto gel-coated fiberglass composite panels. A Fusion UV-curing chamber with a belt speed of 55 ft/min was used to cure the coatings with a UV source (mercury are 'H' bulb, 150 mW/[cm.sup.2]). Anthracene (0.05% w/w) was added as a photosensitizer to the prepared solution to cure the film with visible light. A 150 W bulb was placed 6 in. above the substrate and was exposed for 15 min. All samples were allowed to stand for approximately 1 h to allow for dark cure to complete before testing began. A polyester resin/curing agent (Bondo) was mixed and generously applied (3-5 g) to the cured film to simulate a molding compound, and allowed to cure for 24 h before adhesion testing. Tests were conducted on the mold release while the simulated mold cured under pressure. The mold was pressed between two coated fiberglass composite panels with a force of 90 N and allowed to cure.

Visible light-cured coatings with a thickness greater than 1 mil were placed under a 150 W light bulb for 6 h to assure a complete cure. The films were then allowed to stand for an additional hour once the light source was removed. Taber abrasion was performed on 3 mil films with a CS-10 standardized abrasion wheel and 250 g of weight, and conformed to ASTM D 4060-95. Pencil hardness (ASTM D 3363-00), and conical mandrel bend (ASTM D 522-93a), were performed on 3 mil thick films cured on aluminum Q-panels (3 X 6 [in.sup.2].). The thermosetting siloxanes were cast (1 mil) on aluminum Q-panels (3 X 6 [in.sup.2]) and placed in an oven at 110[degrees]C for 5 h to fully cure the sample.

Functional group analysis

The SiH bond is polarized depending to some degree on the substitutents of the silicon. (15) The reactivity of the SiH bond makes it possible to analyze this group with qualitative or quantitative chemical tests. The SiH was titrated via reduction of a mercury (II) salt, as shown in equation (1):

-SiH + 2Hg[Cl.sub.2][right arrow]-SiCl + H[g.sub.2][Cl.sub.2] + HCl (1)

which can be titrated with a base to find the %SH in a given sample. (16)

A mercuric chloride solution (4% w/v in 1:1 chloroform-methanol) was inserted (20 mL) into an Erlenmeyer flask using a pipette. The sample to be titrated was added and agitated before adding the calcium chloride solution (15 mL, saturated solution in methanol). Phenolphthalein indicator was added (15 drops) after 5-6 min, and the solution was titrated with 0.1 N alcoholic potassium hydroxide. Blanks were titrated in the same manner before and after the analysis. The calculation for %H is shown in equation (2):

%H = [[V.sub.1] - [V.sub.2])]([N.sub.KOH])(1.008/2000)(100)/sample wt (g) (2)

where [V.sub.1] is the endpoint, [V.sub.2] is the averaged blanks, and N is the normality of the basic titrant.

Photopolymerization procedure

On average, 2-3 mg of the sample (polymer and 3% photoinitiator w/w) was placed in an uncovered, hermetic, aluminum differential scanning calorimetry (DSC) pan. An empty pan was used as a reference. The chamber of the DSC was purged with nitrogen before the polymerization and continued throughout the reaction. The samples were photocured with UV light (150 mW/[cm.sup.2] for various exposure times (1, 5, and 15 s) and temperatures (-10, 25, and 60[degree]C). The heat flux as a function of reaction time was monitored under isothermal conditions, and the rate of polymerization was calculated. (17), (18) The heat of reaction ([DELTA]H.sub.R] used for the epoxy group was 23.13 kcal/mol. (19)

The rate of propagation ([R.sub.p]) is directly proportional to the rate at which heat is released from the reaction. As a result, the height of the DSC exotherm can be used in conjunction with other sample information to quantify the rate of polymerization. The rate formula used in the analysis of the photopolymerization data was:

[R.sub.p] = ((Q/s)*M)/(n*[DELTA][H.sub.R]*m) (3)

where (Q/S) is the heat flow per second released during the reaction in J/s, M is the molar mass of the reacting species, n is the average number of epoxy groups perpolymer chain, and m is the mass of the sample.

Results and Discussion

The objective of this work was to prepare a new class of silicone based on polysiloxanes with cyclopentyl and cyclohexyl groups. The principle silane monomers have traditionally been methyl and phenyl, and hitherto cycloaliphatic silane monomers have not been reported because of steric hindrance of the cyclic alkenes. The route used in the preparation of the cycloaliphatic substitution was taken due to the difficulties of reaction the internal alkene with the available silane group. The initial hydrosilation between dichlorosilane and the cycloalkene was performed to control the amount of silane functionality along the polysiloxane backbone. The reaction of the mono- and disubstituted cycloaliphatic substituted cyclic oligomers is similar to that of the methyl-substituted polysiloxane (see Fig. 1).

Synthesis and characterization of cycloaliphatic monomers, oligomers, and polymers

A synthetic diagram of the functionalization of poly (dimethylsiloxane-co-methylhydrosiloxane), hydride terminated is presented in Fig. 1. The pendant alkoxy silane aids in miscibility during formulation and provides a site for interaction with the metal/silicon-oxo-cluster, while the cycloaliphatic epoxide provides a crosslinking site for cationic UV-induced cure. The overall silicone structure will be a block copolymer composed of mostly 'D' units (R-Si-R) and the desired functionalities. The silicone backbone substitution (R) could be methyl (as shown) or cycloaliphatic groups as latter depicted.

[FIGURE 1 OMITTED]

A diagram of the synthesis of poly(dicyclopentylsiloxane-co-cyclopentylhydrosiloxane), hydride terminated is presented in Fig. 2.

The cycloaliphatic substitution along the polysiloxane backbone was chosen for raising the glass transition of the polysiloxane, while not contributing to UV absorption and ultimately yellowing. The characterization of the monomers is presented in preliminary report including IR, NMR, MS data. (20) It is important to note that since the publication of the preliminary report, Gelest now sells both cycloaliphatic monomers. Once the cyclic oilgomers of the polydicycloaliphaticsiloxanes were prepared, they could be combined with the cyclic oligomers of the polycycloaliphatichydrosiloxanes to yield poly(dicycloaliphaticsiloxane-co-cycloaliphatichydrosiloxane), hydride terminated in a similar method as the methyl-substituted silicone (see Fig. 1). An ion exchange resing (A-15) with an end-capper are used to control the molecular weight of the ring opening polymerization to form linear siloxanes. Without the end-capper the chains will terminate randomly. The %SiH analysis results for the cyclopentyl and cyclohexyl silicones were 11.5% [+ or -] 1.1% and 10.8 [+ or -] 0.9%, respectively. GPC showed that both cycloaliphati-substitued silicones had average molecular weights of ~35,000 g/mol.

[FIGURE 2 OMITTED]

Functionalization of cycloaliphatic silicone backbone with amino, alkoxysilances, cycloaliphatic epoxide, and glycidyl groups

The spectral evidence has also been previously reported for the cycloaliphatic epoxide and alkoxysilane functionality. (19) The cycloaliphatic epoxide was attached via a hydrosilylation reaction, either as a difunctional terminator of the low-molecular silicone (-4000 m/e) or as a trifunctional epoxide with one of the epoxides attached randomly with the interior of silicone backbone. The alkoxysilane functionality was also prepared via a hydrosilylation reaction. Lt was attached as pendent off the silicone backbone with cycloaliphatic epoxides in the terminal positions.

Utilizing the route of anionic polymerization makes possible to prepare amino functional-terminated polysiloxane chains because the basic conditions will not affect the amine functionality. This option was not possible with acid-induced polymerization due to neutralization of the functional group. In general, during the early stages of anionic polymerization, polymerization is predominant due to the overabundance of cyclic siloxanes. As polymerization continues and the concentration of linear polysiloxanes increases, depolymerization (back-biting) and redistribution become more and more frequent. (21) Catalysis such as tetraalkylammonium and tetraalkylphosphonium hydroxides have special advantages because their reactivity can be destroyed upon vigorous heating after the polymerization is completed. (22)

A synthetic diagram of the preparation of the amine-terminated, cycloaliphatic-substituted polysiloxane is presented in Fig. 3. Although not depicted in Fig. 3, it is important to note that the cyclic oligomers were prepared to possess a small amount of hydrogen (RSiH) groups along the backbone. This was performed to prevent crystallization of the final polysiloxane. With the incorporation of hydrogen groups along the polymer backbone, the ability for the polymer to form ordered domains k inhibited and low-viscosity liquid polymer is obtained.

[FIGURE 3 OMITTED]

For brevity, only the spectroscopy of the substituted cyclopentyl is presented here. A more detailed spectroscopic evaluation, including all the cyclohexyl data, will be published as a separate paper. To confirm the proposed structure, FTIR was used in conjunction with H and (29) Si-NMR. FTIR spectroscopy will allow for the conformation of the amine functionality and confirm the presence of the Sill group. FTIR spectroscopy reveals that both the cyclopentyl- and cyclohexyl-substituted polysiloxanes have been functionalized with an amine group due to presence of the characteristic double peak in the 3300 [cm.sup.-1] and at -1640 [cm.sup.-1] Further investigation of the FTIR spectra reveals the SiH peak at -2100 [cm.sup.-1]. The structure of the polysiloxane was also characterized through (1)H-NMR spectroscopy, as shown in Fig. 4. Figure 4 shows resonances at 3 2.65 ppm and d 0.57 ppm, which are representative of the propyl chain protons. The methyl group protons of the chain terminating 1,3-bis (3-aminopropyl) tetramethydisiloxane are observed at ~[delta] 0.04 ppm. The SiH proton is also observed at the expected region between [delta] 3 and 6 ppm. (5)

[FIGURE 4 OMITTED]

As shown in Fig. 5, the (29) Si-NMR reveals three distinct peaks at [delta] 7.70, [delta] -38.19 ppm. respectively. The prominent peak at [delta] - 19.10 ppm is indicative of linear chains and, when compared to PDMS (~[delta] -21 ppm), (5) show that cycloaliphatic groups deshield the silicon nucleus and cause a downfield shift. The resonance for the hydrogen-substituted silicon atom is upfield at [delta] -38.9 ppm. The upfield shift occurs due to hydrogen increasing the electron density around the silicon atom. The terminal silicon atom is also observed at [delta] 7.70 and Fig. 5 shows the same three prominent peaks.

The NMR spectrum (Fig. 5) does not show resonances in the regions of ~[delta] -65 ppm and ~[delta] -107 ppm. This indicates that the polymer backbone does not have any branching and is accepted as linear.

[FIGURE 5 OMITTED]

Photo and differential scanning calorimetry

Photo-initiated cationic polymerization of functionalized polysilolxanes yields highly crosslinked networks. In addition, it is important to understand the relation- ship between the polymer structure and reaction conditions with the properties of the networks formed. Photo-differential scanning calorimetry (PDSC) makes it possible to investigate the polymerization behaviors, and especially the kinetics of photopolymerization reactions, due to their highly exothermic reaction characateristic upon exposure to UV light. As a result, the reaction rate may be measured by observing the rate at which the heat is released from the sample subject to polymerization. Profiles of reaction heat releases versus time can be utilized to characterize the reaction kinetics. (22-24) The kinetics vary from system to system and is generally complex; therefore, a generalized kinetic expression is not available for cationic polymerizations. (25) This is due to the reactivity of the carbocationic center being heavily dependant on the proximity of the counterion.

The degree of cure, or conversion, can be estimated from the ratio of the amount of heat evolved from the partial conversation after time t at a specific temperature ([H.sub.t]); to the total heat evolved from the reaction, [[DELTA][H.sub.p]]:

[alpha] = ([H.sub.l]/[DELTA][H.sub.p]) (4)

If equation (4) is a function of conversion, but not temperature--as in photo-induced experiments--the activation energy (E) can be obtained by plotting In [(1/[[DELTA][H.sub.p]]) (d[H.sub.0]/dt)] vs. (1/T), where (d[H.sub.0]/dt) is the heat of polymerization at the maximum peak of the exotherm. Calculating the slope of this plot will yield the activation energy for the polymerization (see Table 1). Previous measurements (26) analyzed the kinetic activity of photosensitizers and showed that the photosensitizers were not completely consumed until after the reaction had progressed. This indicated that the active center concentration had continued to increase after the peak maximum, which was where the reaction rate was measured.

Increasing the size of the substituent has a dramatic effect on the rate of polymerization and total conversion (Table 1). The rates of polymerization were decreased by an overall average of 50% when comparing a methyl-substituted polysiloxane to a cycloaliphatic-substituted polysiloxane. This could be attributed to the large bulky substituents hindering molecular motion during the reaction, and preventing the active species from further polymerization. As expected, the longer exposure to UV light yields a higher conversion due to the production of more active species. The percent conversion calculation is taken from the moment the exotherm begins to when the slope of the thermogramis equal to zero. The effects of "post cure" are not taken into account in the final calculation. The consequence of pose cure would undoubtedly increase the final percent conversion value.

The activation energies for the cycloaliphatic-substituted polysiloxanes are lower than the methyl-substituted polysiloxane value. The higher average molecular weight ([M.sub.n]) of the methyl-substituted polysiloxane reduces the mobility of the epoxy groups, which leads to a higher activation energy. (27), (28) The dependence on activation energy with viscosity could also account for the slight difference in activation energy in the cycloaliphatic-substituted polysiloxanes.

Table 1:Effect of substituent and temperature on the rate of
polymerization

Substituent  Average molecular   Temperature  Exposure  Heat flow
             weight ([M.sub.n])  ([degree]C)  time (s)  per second
                  (g/mol)                                 (J/s)
Methyl            45,500             -10         5        9.456
                                      25         5       14.900
                                      60         5       19.646
Cyclopentyl       34,530             -10         5        8.223
                                      25         5        5.892
                                      60         5       11.723
Cyclohexyl        38,290             -10         5        8.113
                                      25         5        5.932
                                      60         5       16.890

Substituent  [R.sub.p] (/s)  Conversion      Activation
                                 %         energy (kJ/mol)
Methyl           0.0093         99.6     144.8 [+ or -] 8.1
                 0.0110         99.5
                 0.0125         99.7
Cyclopentyl      0.0025         90.4     111.0 [+ or -] 9.2
                 0.0055         97.2
                 0.0057         97.4
Cyclohexyl       0.0054         91.2     125.7 [+ or -] 8.5
                 0.0047         96.7
                 0.0068         98.2

Figure 6 illustrates that the glass transition temperature can be tailored by being able to add on the desired pendant group through hydrosilation. The pendant group could be chosen from a number of alkene functionalized systems. Figure 6 also shows that as the size of the pendant group is increased, the glass transition temperature increases. This has an effect upon the reaction kinetics. Unfortunately, the molecular weight of the systems could not be controlled enough to compare the effect of substitution alone.

[FIGURE 6 OMITTED]

Mold release coatings

New visible and UV-curable silicone were prepared with cycloaliphatic epoxide functional silicones. Because the purpose of the coating was mold release, surface tension and durability were especially important. The surface tension for the contact angle of 103[degree] (using 72.8 mJ/[m.sup.2] as the liquid-vapor interface) was found to be 10.93 [+ or -] 0.05 mJ/[m.sup.2] for the UV-cured film. The visible light-cured system had a similar surface tension of 11.42 [+ or -] 00\.05 mJ/[m.sup.2] because its contact angle was 102 [degree]. Table 2 compares the surface tension of the photo-cured polysiloxanes to other coatings. (29, 30)

When the above results are compared to Teflon (18 mJ/[m.sup.2]), the surface tension of the photo-cured polysiloxanes is considerably less.

Pull-off adhesion tests were performed to quantify the release and multiple release potential of the cured film. The tests were performed by using the simulated mold as the bond between the substrate and the test dowel. Subsequent testing over the same area showed that the samples cured with UV and visible light had consistent results after 30 test cycles, as a result of the thorough cure of the film and the low surface tension (Table 2). It is important to note that the sample with no coating experienced mechanical failure, in that the gel coat was cleaved cleanly from the glass composite. Adhesion tests were also performed using the standard ASTM epoxy resin as the adhesive between the substrate and dowel. Results reveal that both the UV-and visible light-cured systems performed similarly in that both produced an average of 0.21 [+ or -] 0.08 MPa of normal force to remove the dowels on through to the 30th subsequent trail.

Table 2: Surface tension of common coatings

Coating                           Surface tension
                                  (mJ/[m.sup.2])
Epoxy                                   47
Polyurethane                            43
Polyvinylchloride                       39
Alkyd                                   38
Polyester (powder coating)              33
Polyethylene                            31
Teflon                                  18
SS4177 (GE Silicones)                   14
UV-cured polysiloxane                   11
Visible light-cured polysiloxane        11

Figures 7 and 8 show the results of the required amount of normal force required to remove the panel from the compressed mold.

The mold released from the panel with virtually the same amount of force required to release the noncompressed sample. The Taber abrasion and pencil hardness were performed on the coatings to determine their resistance to abrasion and hardness. The results of the test are shown in Table 3 and reveal that both the visible light-cured and the UV-cured coatings perform equally in both aspects.

[FIGURE 7 OMITTED]

[FIGURE 8 OMITTED]

Reverse impact and conical mandrel test results (Table 3) show that both the UV-cured coating and visible light-curved coating have extreme flexibility, which was expected due to their flexible nature. Although the mechanical tests for both the UV - and visible - light-cured system do demonstrate the characteristic properties of polysiloxanes, such as flexibility and adhesion, the fact that the visible light-curved system takes hours to develop a cured film is now addressed. The visible light source intensity may not be strong enough to generate protons fast enough to initiate a rapid cure of the system. Other factors that may affect the coatings cure are the photo-initiator concentration, photo sensitizer efficiency, exposure time, and/or thickness.

The ability to cure mold release agents with UV and visible light allows for a cheap and straightforward method for applying the coating to a substrate. The UV-light curing method does offer a more rapid cure time that the visible light-curing route. The verification that both methods of cure yield the same mechanical properties confirms that various cure methods are possible. The high surface tension on the coating and multiple release capabilities will permit many cycles of injection molding to be completed without having the mold stick or the need for reapplication. The durability of the coatings will also extend the life of the coating by resisting scratches and other wear produced by everyday use. The ability to make the curable mold release agent sprayable will allow for more complex molds to be considered for application--and, with an extensive potlife, long-term storage is applicable. The synthesis makes production of the fuctionalized polysiloxane unproblematic in that the hydrosilation of the cycloaliphatic epoxide is straightforward and relatively inexpensive.

Epoxy-amine systems

To observe the unique properties this amine-terminated, cycloaliphatic-substituted polysiloxane may offer, blends were prepared with a cycloaliphatic epoxy-functionalized cycloaliphatic-substituted polysiloxane (cyclopentyl-substituted epoxy equivalent weight = 236 [+ or -] 3 g/Eq, cyclohexyl-substituted epoxy equivalent weight = 265 [+ or -] 3 g/Eq). (10) Once cured, the glass transition temperature ([T.sub.g]) of the material was measured and the mechanical properties were evaluated (see Table 4). Thermal analysis revealed that the presence of cycloaliphatic groups dramatically increases the glass transition temperature of the material when compared to PDMS ([T.sub.g]~ -127 [degrees] C). (31) This is due to the rigid cycloaliphatic groups hindering the ploysiloxanes flexibility.

Table 3: Results of mechanical property testing (a)

Sample                Pencil    Reverse       Conical        Taber
                     hardness   impact        mandrel       abrasion
                               (ft/Ibs.)  (% elongation)  (cycles/mil)

UV light cured        2H/4H       38           Pass           1327
Visible light cured   2H/4H       34           Pass           1285

(a) Pencil hardness (ASTM D 3363-00), Reverse impact (ASTM D 5420-04),
conical mandrel bend (ASTM D 522-93a), Taber ASTM D 4060-95

Table 4: Thermal analysis and mechanical properties

Substituent   Reverse     Taber      Pull-Off    [T.sub.g]
              impact     abrasion    adhesion  ([degrees] C)
             (in-Ibs)  (cycles/mil)    (MPa)

Cyclopentyl      4         853          0.5    29.5 [++or--]
Cyclopentyl      5         819          0.5    38.6 [++or--]

The lack of flexibility is attributed to the [T.sub.g] of the polymers, in that the cycloaliphatic groups inhibit much of the molecular freedom of the polymer chain. The numerical difference between the surface tension of a film and the surface tension of a substrate has dramatic effect on the strength of the adhesive bond between the substrate and the dry film. If the surface tension of the coating is greater that the surface tension of the substrate, then the film will not spread out and form a film. As the surface energy is increased, a stage is reached where the coating will spread out and form a film but, when dry, has poor adhension. The surface tension for pure PDMS is ~20 mN/m, while the surface tension for aluminum is ~40 mN/m. (32)

Sol-gel hybrid coatings

Functionalized silicones based on telechelic cycloaliphatic epoxide with pendent alkoxyl silane functionality (see Fig. 1) were UV -cured with TEOS oligomers to form films for evaluation. A schematic of the network is depicted in Fig 9. Figure 10 shows the comparison of the thermal stability of the ceramer and DC 93-500 coatings. Thermal gravimetric analysis was also used to evaluate the thermal degradation of the coatings. Thermal gravimetric analysis was performed to observe the thermal stability of the ceramer coating compared to DC 93-500. (33) Irreversible changes to the crosslinked structure of silicone polymers unavoidably occur at high temperatures due to chain scission or oxidative crosslinking. (10) In an inert atmosphere, deploymerization occurs with the loss of volatile products--mostly low-molecular weight cyclic oligomers--but is often catalyzed by traces of acids, bases, water, or residual catalysts used in the polymer's original production. (34) Typically, depolymerization occurs near 400 [degrees] C for reasonably pure polydimethysiloxane. (35)

[FIGURE 9 OMITTED]

[FIGURE 10 OMITTED]

General applications

Until now, only two classes of silicones have been available on a commercial basis. There are methyl- orphenyl - substituted silicones in various degrees of substitution, and mixtures thereof. The methyl-substituted silicones have an extremely low [T.sub.g], and phenyl - substituted silicones have a higher [T.sub.g], but absorb UV light. The absorption of UV light is not a benefit for some applications. The ability to synthesize polysiloxanes with cycloaliphatic pendant groups will be beneficial by providing more monomers to be considered for new coatings, blocks or co-reactants for new coating binders, and as building blocks for additives. The cycloaliphatic silicones do not absorb UV light, and have an intermediate [T.sub.g] with respect to the methyl and phenyl analogs. The capability to modify and/or tailor the pendant groups could also solve miscibility and grafting issues by making the groups similar in structure and/or polarity to a specific type of organic binder within a coaling system.

The functionalization of the cycloaliphatic silicones would allow diverse use of the cycloaliphatic silicone in coatings formulations. Although many modifications are possible, amino, glycidyl, alkoxysilane, and cycloaliphatic epoxide have been prepared thus far and are reported herein. These functionalities are important for usage as adhesion promoters (alkoxysilane), latent moisture curing (alkoxysilane), ambient thermosetting coatings (glycidyl epoxide-amino), or as cat ionic UV-curable coatings (cycloaliphatic epoxide). It is anticipated that as time permits, further exploitation of this chemistry will be forthcoming

Although not touched upon specifically in this paper, the cyclohexyl or cyclohexyl silicone units could be easily incorporated as a flexible unit in a wide variety of coating systems via direct reaction of functional groups, including polyurethanes, Bis-Phe-nol-A (BPA) epoxides, acrylics, UV-curable systems, and latexes. Tailoring the cycloaliphatic polysiloxanes for low coefficient-of-friction coatings may be valuable for antifouling or easy-to-clean coatings. (28) (29) The ability to adjust the glass transition temperature through the variation of the pendant groups may also be beneficial for specialized applications such as wetting agents and temperature sensitive coagulating agents for latexes. (31)

Conclusions

A synthetic route was employed to prepare cationically polymerizable methyl-, cyclopentyK and cyclohexyl-substituted polysiloxanes. A synthetic route was developed to prepare amine-terminated, cycloaliphatic-substituted polysiloxanes. The base catalyzed ring-opening polymerization of cycloaliphatic-substituted cyclic oligomers allowed for molecular weight control and maintained the amine functionality. The DSC results showed that the bulky pendant groups affect the glass transition temperature, as compared to the methyl-substituted polysiloxane. (ASTM D 3363-00), reverse impact (ASTM D 5420-04), and conical mandrel bend (ASTM D 522-93a) photo-DSC exotherms showed that the cyclohexyl and cyclopenlyl groups affect the kinetics by lowering both the rate of polymerization and overall conversion, when compared to the methyl-substituted polysiloxane. Photocurable systems afforded release coatings with low surface tension, extreme flexibility, and durability, allowing for multiple releases. The solgel/cycloaliphatic silicone coatings had excellent thermoxidative stability, abrasion resistance, and hardness.

References

(1.) Mowers. WA, Rajarman, SK, Liu, S, Crivello, JV. 'The Design and Photopolymerization of Monomers Bearing Epoxy and Vinyl Ether Groups." Technical Conference Proceedings. Baltimore, MD, US, April 9-12. 2000, pp. 45-60. New York State Center for Polymer Synthesis, Department of Chemistry, RPI (2000)

(2.) Crivello. JV, Lee, J, 'The Synthesis. Characterization, and Photoinitiated Cat ionic Polymerization of Silicon-Contain-Lug Epoxy Resins." J. Polym, Sci.: Part A: Polym. Chem. Ed., 28 479-503 (1990)

(3.) Oishi. M, Kawakami, Y, Synthesis of Stereoregular and Optically Active Polysiloxanes Containing l,3-Dimelhyl-l,3-diphenyldisiloxane as a Constitutional Unit," Macromolecules, 33 (6) 1960-1963 (2000)

(4.) Belfield, KD, Chinna, C, Najjar, O, "Synthesis of Novel Polysiloxanes Containing Charge Transporting and Second-Order Nonlinear Optical Functionalities with Atom Economical Construets." Macromolecules, 31 (9) 2198-2124 (1998)

(5.) Chojnowski, I, Cypryk, M, Fortuniak. W, Scibiorek, M, Rozga-Wijas, K, "Synthesis of Branched Polysiloxanes with Controlled Branching and Functionalization by Anionic Ring-Opening Polymerization.'' Macromolecules. 36 (11) 3890-3897 (2003)

(6.) Crivello, JV, Malik, R, '"Synthesis and Photoinitiated Cat-ionic Polymerization of Monomers Containing the Silsesquioxane Core." Silicone and Silicone-Modifited Materials, pp. 284-295. ACS Symposium Series 729 (2000)

(7.) Laine, R. Brick, C, Kim, $, Tamaki, R, Chen. H, Choi. J, "Silsesquioxane Nanocomposites and Phenylsitsesquioxane Derivatives." Abstracts of Papers, 225th ACS National Meeting, New Orleans, LA, March 23-27 (2003)

(8.) Arkles, B, "CHEMTECH, Look What You Can Make Out of Silicones." CIIEMTECH. 13 (9) 542-555 (1983)

(9.) Soucek, MD, Wu, S. Chakrapani, S, Synthesis, Characterization, and Evaluation of Siloxane-Containing Modifiers for Photocurable Epoxy Coaling Formulations." Silicones and Silicone-Modified Materials, pp. 516-532, ACS Symposium Series 729 (2000)

(10.) Smith, AL, The Analytical Chemistry of Silicones. Wiley Interscience, New York. NY (1991)

(11.) Tiwari A, Nema. AK, Das, CK. Nema, SK. "Thermal Analysis of Polysiloxanes, Aromatic Polyimide and their Blends. Thermochim. Acta, 417(1) 133-142 (2004)

(12.) Fink. F. Heilen. W. Berger. R. Adams, J, "Development of New Additives to Improve Scratch Resistance and Impart Slip to Solvent-Based Coatings Systems." J. Coat. Technol, 62(791)47-56(1990)

(13.) Wu. S, Sears. MT, Soucek, MD, "Siloxane Modified Cycloaliphatic Epoxide UV Coatings.'" Prog, Org. Coat, 36 89-101 (1999)

(14.) ASTM D 1652-97, "Standard Test Methods for Epoxy Content of Epoxy Resins." June 1997

(15.) Eaborn, C, Organosilicon Compounds. Butters worth. London (1960), p. 530

(16.) Smith. RC, Angelotti, NC, Hanson, CL, Chemical Analysis of Organosilicon Compounds. Chemical Analysis (New York, NY, United States) 41 (Anal. Silicones): 113-168 (1974)

(17.) Anseth, KS. Wang, CM, Bowman, CN, "Kinetic Evidence of Reaction Diffusion During the Polymerization of Multi(Meth)Acrylate Monomers." Macromolecules, 27 (3) 650-655(1994)

(18.) Guymon. CA. Bowman, CN, "Polymerization Behavior and Kinetics during the Formation of Polymer-Stabilized Ferro-electric Liquid Crystals." Macromolecules, 30 1594-1600 (1997)

(19.) Shinohara. K, Kasamatsu, T, "Radiation-Induced Cross-Linking of Epoxy Resins." Nippon Aisotopu Kaigi Hobunshu. 4 337-380 (1961)

(20.) Dworak, DP. Soucek. MD. "Synthesis of Cycloaliphatic Substituted Silance Monomers and Polysiloxanes for Photo-Curing." Macromolecules, 37 (25) 9402 (2004)

(21.) Fleischmann, G. Eck, H, Wenzler, P, "Catalysts for Polymerization and Crosslinking." European Patent 302, 492. 1989

(22.) Kirk, N, "Continuous Process for Making Silicones." J. Ind. Eng. Chem.. 51 515-518 (1959)

(23.) Doornkamp, AT, Tan. YY. "Kinetic Study of the Ultraviolet -Initiated Polymerization of a Polyester Urethane Diacrylate by Differential Scanning Calorimetry." Polym. Commun., 31 362-365 (1990)

(24.) Chen. J, Soucek, MD, Simonsick. WJ, Celikay, RW, "Synthesis and Photopolymerization of Norbornyl Epoxidized Linseed Oil." Polymer. 43 5379-5389 (2002)

(25.) Kennedy. JP. Marechal, E, Carbocationic Polymerization. Wiley. New York (1982). p. 510

(26.) Shin, H, Choi, S, Kim, J, Park. I. Lee. S, No, J. Kang, D, "Permeation Behavior of Olefin/Nitrogen Gases Through Siloxane Based Polymeric Membranes." Memburein, 13 (4) 246-256 (2003)

(27.) Patra, M, Sinha, BK, "Polymerization of Acrylamide Initiated by V(V)-Cyclohexanone Redox System in Micellar Phase: A Kinetic Study." J. Macromol. Sci, Pure Appl. Chem., A36 (10) 1459-1473 (1999)

(28.) Doornkamp, AT. Tan, YY, "Kinetic Study of the Ultraviolet-Initiated Polymerization of a Polyester Urethane Diacrylate by Differential Scanning Calorimetry." Polym. Commun., 31 (9) 362-365 (1990)

(29.) Mori, K, Sasaki, Y. Hirahara. H. Oishi, Y. "Development of Polymer-Molding-Releasing Metal Mold Surfaces with Perfluorinated-Group-Containing Polymer Plating." J, Appl. Polym. Sci., 90 (9) 2549-2556 (2003)

(30.) Zhao, Y, Carey. JD, Knoops, N, Maetens. D. Hopkinson, J, Hay, JN, Keddie, JL, "Inhibition of the Surface Leveling of Thermosetting Polyester Powder Coatings Caused by Surface Tension Gradients." J. Mater. Sci., 37 (22) 4759-4768 (2002)

(31.) Lee WA, Rutherford RA. "The Glass Transition Temperatures of Polymers." In: Brandrup J, Immergut EH (eds) Polymer Handbook, 2nd edn. Wiley Interscience: New York, NY, (1997)

(32.) Trade Literature, Additives for Surface and Substrate. p, 2. Munzing Chemie GMBH (2001)

(33.) Dworak, D, Banks, B, Karniotis. CA. Soucek, MD, "Evaluation of Protective Silicone/Siloxane Coatings in Simulated Low-Earth-Orbit Environment." J. Spacecraft Rockers. 43 (2) 393-401 (2006)

(34.) Kang, DW, Rajendran, GP, Zeldin, M, "Kineties of Thermal Depolymerization of Trimethylsiloxy End-Blocked Poly (dimenthylsiloxane) and Poly (dimethylsiloxane)-N-phenylsilazane Copolymer." j. Polym, Sci, Part A Polym. Chem., 24 1085 (1986)

(35.) Grassie, N, Macfarlane, IG, "The Thermal Degradation of Polysiloxanes. I. Poly (dimethylsiloxane)." Eur. Polym, J., 14 875-884 (1978)

Presented at the 2006 Future Coat! Conference sponsored by the Federation of Societies for Coatings Technology, in New Orleans, LA, on November 1-3, 2006.

M. D. Soucek, D.P. Dworak, R. Chakraborty

Department of Polymer Engineering, University of Akron. Akron. OH 44325, USA

e-mail: [e-mail]