Novel polyurethane coating technology through glycidyl carbamate chemistry.

Glycidyl carbamate chemistry combines the excellent properties of polyurethanes with the crosslinking chemistry of epoxy resins. Glycidyl carbamate functional oligomers were synthesized by the reaction of polyfunctional isocyanate oligomers and glycidol. The oligomers were formulated into coatings with several amine functional crosslinkers at varying stoichiometric ratios and cured at different temperatures. Properties such as solvent resistance, hardness, and impact resistance were dependent on the composition and cure conditions. Most coatings had an excellent combination of properties. Studies were carried out to determine the kinetics of the curing reaction of the glycidyl carbamate functional oligomers with multifunctional and model amines. Detailed kinetic analysis of the curing reactions was also undertaken. The results indicated that the glycidyl carbamate functional group is more reactive than a glycidyl ether group.

Keywords: Epoxy resins, polyurethanes, mechanical properties, physical properties, thermal properties, solvent-based, thermoset, amines, amides, epoxy, isocyanate

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Thermosetting epoxy and polyurethane polymer systems are widely used in many applications, including protective coatings, composite materials, and adhesives. These systems involve the reaction of functional polymers or oligomers with other materials containing mutually reactive groups. The composition of the reactants used determines the final properties of the thermoset coatings. Epoxy coatings generally exhibit good corrosion performance while polyurethane systems result in coatings having good toughness, abrasion resistance, and durability. Glycidyl carbamate chemistry has the potential of combining epoxy and polyurethane technology into a single system and has been shown to improve toughness in epoxy-amine systems. (1)

Reactions of amine with oxirane will occur at different rates depending on reactivity of the active amine hydrogen (2) and stoichiometric concentration of the amine relative to oxirane. (3,4) Amines used with epoxy resins are primary, secondary, or tertiary amines. Tertiary amines can, in turn, catalyze epoxide homopolymerization (5) (etherification). Amine structure also plays a factor in the overall reactivity of the primary and secondary amines. Reactivity is a function of steric factors (6,7) and amine basicity. (7-13) Amine reaction mechanisms using tetraglycidyl-4,4'-diaminodiphenylmethane (TGDDM) are also established in literature. (6,14-16) TGDDM reactions demonstrate that epoxide type also influences kinetics and deviates from diglycidyl ether bisphenol A (DGEBA) resins. (4,6)

In this study, we will examine the crosslinking of trifunctional glycidyl carbamate resins with several amines. The glycidyl carbamate (GC) group is readily synthesized from the reaction of an isocyanate with glycidol (17) (Figure 1). Two types of intermolecular reactions are possible with the glycidyl carbamate group. The first is the reaction of the oxirane with the amine and the second is the self-crosslinking reaction. We have seen from earlier work that the self-crosslinking reaction in the absence of amine forms a thermoset coating with an excellent combination of properties. (18) In the presence of amine crosslinkers, the reactivity of the amine and the curing temperature will influence the relative reaction rates and may lead to different network structures and coating properties. These properties will be used to determine if a combination of different mechanisms may exist during cure. Influences of varying stoichiometry and kinetics of reaction will also be discussed for complete evaluation.

EXPERIMENTAL

Materials

Glycidol was supplied by Dixie Chemical and stored in refrigeration to minimize the formation of impurities. (19) Rhodia Inc. provided Tolonate[R] HDT-100 and Tolonate HDB-100, isocyanurate and biuret resin condensate derived from hexamethylene diisocyanate (HDI). Tolonate HDT-100 and Tolonate HDB-100 have NCO equivalent weights of 190.13 and 191.25, respectively. Isocyanate equivalent weights were based on the titrated %NCO (ASTM D 2572) and the molecular weight of an isocyanate group. Amines used as hardeners were purchased from Aldrich. Those purchased include: diethylene triamine (DETA), 4,4'-methylene dianiline (MDA), and bis(para-aminocyclohexyl) methane (PACM)--an aliphatic, aromatic, and cycloaliphatic amine, respectively. Trimethylolpro-panetriglycidylether (TMPGE), purchased from Aldrich, was used as a control trifunctional epoxy resin. For kinetic experiments, aniline, N-methyl aniline, and dimethyl aniline, (a primary amine, a secondary amine, and a tertiary amine) were also obtained from Aldrich. These amines were used to model the reaction of MDA with glycidyl carbamate (GC). D.E.R.[R] 332 (DGEBA) was supplied by The Dow Chemical Company.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

Coating Formulation

Synthesis, characterization, and self-crosslinking reactions of glycidyl functional oligomers (IGC and BGC) are described in earlier work. (17,18) Biuret glycidyl carbamate (BGC) and isocyanurate glycidyl carbamate (IGC) were synthesized through the reaction of HDB and HDT with glycidol, respectively. Epoxy equivalent weights were determined by titration with HBr (ASTM D 1652). The theoretical epoxide equivalent weight of IGC and BGC was 265, which compares with 240 and 242 g/equivalent determined by titration. Nominal structure of IGC, BGC, and TMPGE used in this study are shown in Figure 2. Structures of the amines used are shown in Figure 3.

[FIGURE 3 OMITTED]

MDA samples were melted initially at 55[degrees]C for one hour. Then, for a complete melt, the temperature was lowered and held for four hours at 35[degrees]C. This procedure allowed MDA to reach a molten state while minimizing crosslinking with the resin. PACM and DETA were mixed with the epoxy resins at room temperature (25[degrees]C). Form-ulations containing PACM were given at least 20 min of induction (sweat-in) time before application. However, DETA began to react upon mixing, thus shortening the sweat-in times to approximately 5 min. Also, reactions with DETA and carbon dioxide in the air occurred to form a carbamate salt. (10,20-22) This was evidenced by a white appearance of the coatings after casting. Toluene (based on 70% solids) and BYK-301 (0.1 wt% of solution based on total formulation) were added to reduce viscosity and improve substrate wetting.

Film Preparation

The coating formulations were applied onto iron-phosphated 22-gauge steel test panels purchased from Q-Panel Lab Products. Coating application was made using a drawdown bar for a final dry film thickness of 75 microns. The coated panels were then placed in an oven at 80[degrees]C, 120[degrees]C, and 150[degrees]C for 60 min for crosslinking.

Hardness Measurements

Hardness of films was evaluated one week after the films cured. The films were tested for Konig hardness (ASTM D 4366), with the values reported in seconds (sec).

Reverse Impact Testing

ASTM D 2794 was used as a standard test method for the resistance of organic coatings to the effects of rapid deformation via reverse impact. Films were tested one week after cure using a Gardener impact tester. The maximum drop height was 43 in. with a drop weight of four pounds. All measurements were performed in triplicate. Grazing or loss of adhesion was noted and inch-pounds were determined at film finish failure. Samples that did not fail were noted as >172 in.-lb.

MEK Double Rubs

Methyl ethyl ketone (MEK) double rubs were used to assess the development of cure. The steel test panels were cut in half and a coating was applied using a casting bar. The coated panels were then placed in an oven preheated to 40[degrees]C. At approximately 10-minute intervals, the panels were removed to determine cure by solvent resistance. A 26-ounce hammer with five layers of cheesecloth wrapped around the hammerhead was soaked in MEK. After 100 double rubs the hammer was rewet with MEK. Once mar was achieved the number of double rubs was noted. A fully cured coating was based on 400 double rubs without mar.

Viscosity Studies

A Brookfield DV-E viscometer was used to determine time of gelation. The small sample adapter with spindle S-31 was used. Viscosity standard (Fluid 5000), purchased from Brookfield, was used to check instrument calibration at 25[degrees]C before measuring sample viscosity. Viscosity was measured at 25[degrees]C or 40[degrees]C, depending on the hardener and resin reactivity. A circulating bath was used to supply a constant temperature to the sample cell holder. Rotational speed was adjusted according to the amount of torque supplied on the spindle. A percent of 30% to 80% was maintained.

[FIGURE 4 OMITTED]

Differential Scanning Calorimetry 

A TA Instruments Q1000 differential scanning calorimeter (DSC) was used to determine glass transition temperatures and curing kinetics. Glass transitions are reported as the temperature at mid-point of the inflection. Cured films were measured by placing the sample into conventional aluminum pans, then equilibrating at 0.0[degrees]C. Modulation was set at [+ or -] 3.18[degrees]C every 60 sec and held isothermally for 5 min. The samples were ramped 20[degrees]C/min to 250[degrees]C, then the first glass transition was noted ([T.sub.g]1). The sample was cooled and rescanned to determine the ultimate glass transition temperature (Tg[infinity]). The upper temperature of 250[degrees]C was chosen to be below the onset of decomposition as determined by thermogravimetric analysis (TGA).

To monitor the cure kinetics, conventional DSC was used in both scanning mode and isothermally. Hermetic aluminum pans were used to seal in GC/epoxide and curing agent for kinetic analysis. Sample sizes were weighed out to approximately 8 mg. Indium standardization was conducted for enthalpy calibration. In dynamic curing studies, scans were started at 0[degrees]C and ended at 250[degrees]C, or the point where the curing isotherm started then merged with the baseline. Measurements were performed isothermally by placing the sample pan into the DSC sample cell, then heating to the desired reaction temperature. Isothermal temperatures were held until reaction completion.

RESULTS AND DISCUSSION

Our past research in the area of glycidyl carbamate monomers and their oligomers indicates that at higher temperatures (ca. 150[degrees]C) self-crosslinking of the oligomers occurs. The self-crosslinked coatings have an excellent combination of physical properties due to the carbamate and epoxide functionality. In our earlier work we defined the GC structure, (17) characterized properties, (18) determined kinetics during self-crosslinking, (23) and investigated initial cure properties with various amines. (24) These results suggested that curing at different temperatures yields a combination of properties dependent on the stoichiometric ratio of GC to amine and also the amine reactivity.

[FIGURE 5 OMITTED]

Due to the excellent properties of the self-crosslinked glycidyl carbamate resins, it is likely that these good physical properties would carry over when the GC resins are crosslinked with amine functional crosslinkers. For use in exterior coatings, higher reactivity and excellent physical properties are needed. These physical properties are usually obtained by using polyurethanes or epoxies. The combination of these working in unison can be achieved with the GC system. Using a system designed like this allows one to achieve an excellent combination of properties at lower cure temperatures.

In these systems, it is expected that as the cure temperature is increased, the amine reactivity and amine to GC stoichiometry is reduced, and the self-crosslinking reaction may become involved in network formation. However, the effect of these parameters on physical properties is not known.

We prepared coatings from two glycidyl carbamates (BGC and IGC) and a control trifunctional epoxy, TMPGE, with diethylene triamine (DETA), 4,4-methylene dianiline, and bis(para-aminocyclohexyl) methane--an aliphatic, aromatic, and cycloaliphatic amine, respectively. Structures of the materials are illustrated in Figures 2 and 3. Stoichiometric ratios of amine to oxirane were based on amine hydrogen equivalent weight (AHEW) and on weight per epoxide (WPE). A 1:1 formulation is based on one epoxide reacted with one amine active hydrogen. Coatings formulations based on twice (2:1) and half (1:2) the amount of resin to amine active hydrogens were also prepared.

[FIGURE 6 OMITTED]

In this system, various competing reactions may be occurring. Primary amines react with oxirane to form secondary amines, which can, in turn, react to form tertiary amines. The tertiary amine may, in turn, promote poly-etherification (homopolymerization) of the epoxy groups. Amine reactivity and stoichiometry determine if amine reactive hydrogens or self-crosslinking are involved in the reaction (Figure 4).

Previous studies of difunctional glycidyl-terminated polyurethane-modified epoxy resins showed enhanced property relationships. (1) This is expected since the network is actually toughened by the carbamate linkage. Therefore, improved physical properties are expected after cure. The past work has not considered the effect of varying the amount of amine, amine reactivity, or effects of self-crosslinking. Thus, there is need to evaluate physical properties as a function of changing formulation and to understand the kinetics of the various competing reactions.

The self-crosslinking reaction of the glycidyl carbamate resins begins to occur at 120[degrees]C for the BGC resin and 135[degrees]C for the IGC resin, as illustrated in Figure 5. To examine the curing with amines, the study will examine the effects of amine structure and stoichiometry at three temperatures: (1) curing reactions without self-crosslinking (80[degrees]C), (2) curing reactions at the onset of self-crosslinking (120[degrees] or 135[degrees]C), and (3) curing reactions at fully self-crosslinked temperatures (150[degrees] and 160[degrees]C). In addition, TMPGE was used as a control epoxy resin. We have also determined kinetics of cure for the glycidyl carbamate functional oligomers with both multifunctional and model amines. Our approach is to more thoroughly elucidate the curing reaction.

[FIGURE 7 OMITTED]

As amines crosslink with epoxies, crosslink density increases as more active hydrogens of the amine react. This leads to higher crosslink density, greater solvent resistance, harder coating, and loss of segmental motion. Significant differences exist between an aromatic amine and aliphatic amines. Aromatic amines generally lead to a harder and more brittle coating than aliphatics. Anticipated results are that MDA should form a harder coating, have a higher [T.sub.g], and be less resilient to reverse impact than PACM. However, opposite findings suggest that as temperature increases the inverse holds true. Tables 1-3 list the coating compositions prepared along with their physical properties.

[FIGURE 8 OMITTED]

Properties of 1:1 Epoxy:Amine Coatings

Table 1 shows the physical property results for the resins crosslinked using the three amines at a 1:1 stoichiometric ratio. Most of the coatings had excellent cure and high pendulum hardness values. Comparison with TMPGE shows a loss of impact resistance and generally a harder coating, especially at the higher curing temperature. A key difference with the GC resins is the presence of the urethane linkage and the possibility of the self-crosslinking reaction at the higher temperature. When BGC is reacted with PACM, reverse impact follows the inverse behavior of BGC:MDA, but results in the hardest of the three 1:1 formulations with GC. Glass transitions of the cured film without additional heating ([T.sub.g]1) were highest for BGC:MDA when compared to BGC:PACM. However, glass transitions of the cured film annealed then reheated are known as the ultimate glass transition ([T.sub.g][infinity]), and were similar for BGC:MDA and BGC:PACM. It is expected that amine active hydrogens of PACM are more reactive with BGC, while more self-crosslinking is involved with the IGC:MDA reaction. This would explain why glass transition temperatures were slightly higher for BGC:PACM than IGC:PACM at temperatures of 80[degrees]C and 120[degrees]C. One explanation is higher reactivity of BGC when compared to IGC. Notably, [T.sub.g]1 were highest for TMPGE:DETA and lowest for TMPGE:MDA due to structural differences in the aliphatic and aromatic amine. For TMPGE:DETA, glass transitions were not found (NF) when determining the ultimate glass transition ([T.sub.g][infinity]). This may be due to many, if not all five, of the active hydrogens reacting to form a tightly crosslinked network.

Cure Development of the Coating Formluations

Gel times, determined using viscometry, were determined for the resins reacted with amines. All gel studies were done at 40[degrees]C, except for DETA. For DETA, the sample temperature was lowered to 25[degrees]C. The lower temperature was used due to the higher reactivity of the straight chain aliphatic amine. As seen in Figure 6, MDA is the least reactive of the three amines. The arrow in Figure 6 has been added to demonstrate how gel times were determined. This procedure was used to determine the gel times of all the coatings formulated, as plotted in Figure 8. MEK double rubs were in agreement with viscometer gel times as illustrated in Figure 7. If a cured system is based on 400 double rubs, then the amount of time for BGC, IGC, and TMPGE to cure on steel panels is 86 minutes, 213 minutes, and 291 minutes, respectively.

Gel Times when Varying Amine Type and Stoichiometry

To further evaluate cure development, we determined gel times and charted their differences. To do so, we doubled or halved amine amount in the formulations. Gel times were taken for samples that cured within 24 hours (Figure 8). Gel times not charted did not cure within the 24-hour period. No data was taken for 1:2 TMPGE:DETA. When comparing formulations, doubling the amount of amine increased gel times while decreasing the amount of amine led to shorter cure times. TMPGE proved to be the least reactive, followed by IGC, with BGC being the most reactive. Most notable cure times and reactivity differences were seen when comparing 2:1 IGC:MDA with 2:1 BGC:MDA.

Properties of 2:1 Epoxy:Amine Coatings

Physical property results for the coatings based on a stoichiometric ratio of 2:1 epoxy to amine are shown in Table 2. As in the case of the 1:1 coatings, most coatings had good solvent resistance and high pendulum hardness. Coatings based on IGC crosslinked with MDA at the two lower cure temperatures had low solvent resistance and hardness. This is consistent with the gel time data in Figure 8. The data indicates that with 2:1 BGC:MDA formulations there was an increase in impact resistance and a slight decrease in hardness with excellent solvent resistance. Doubling the resin to amine yields a more flexible thermoset due to lower crosslink density. These findings are similar when comparing the 1:1 formulation (Table 1). Doubling the amount of TMPGE shows less loss of impact resistance and generally the same hardness as the 1:1 formulation.

[FIGURE 9 OMITTED]

Also, as was found with the 1:1 formulations, when BGC is reacted with PACM, the reverse impact follows the inverse behavior of BGC:MDA. The BGC:PACM coating shows a decrease in impact resistance and an increase in hardness when the temperature is increased to 150[degrees]C, while the IGC:PACM does not show a decrease in impact resistance. A reason for this is that IGC is less reactive than BGC. In this case, amine active hydrogens are involved in the reaction to reduce the amount of self-crosslinking. The 2:1 IGC:PACM takes a longer time to react than the 2:1 BGC:PACM, as seen in Figure 8. In this case, when IGC is heated at higher temperatures the self-crosslinking reaction is involved and the coating behaves more like the self-crosslinking reaction.

Properties of 1:2 Epoxy:Amine Coatings

Coatings properties of the systems with a 1:2 epoxy to amine ratio are summarized in Table 3. As before, the coatings generally had good solvent resistance and good pendulum hardness. For BGC:MDA, impact resistance and pendulum hardness increased when compared to the 1:1 and 2:1 formulations. When comparing IGC:MDA to BGC:MDA, the impact resistance drops. This is possibly due to the more rigid nature of the triazine ring found with IGC. (25,26) TMPGE:MDA behaved similarly to IGC:MDA, but lower glass transitions were found because TMPGE has a lower reactivity towards MDA (Figure 8).

[FIGURE 10 OMITTED]

As twice the amount of PACM was added to the epoxide, the cycloaliphatic amine behaved as a toughening agent towards GC and allowed the coating to increase in reverse impact. Both BGC:PACM and IGC:PACM demonstrated an increase in reverse impact, improved solvent resistance, and good hardness. TMPGE:PACM also had good impact resistance, but at higher temperatures the coating began to degrade. TMPGE degradation upon heating and property changes was most notable when DETA was used as the amine. Overall, TMPGE:DETA, when reacted 1:1, 2:1, and 1:2 (epoxide:DETA), gave the poorest properties. The coating became tacky and degraded while heating. When twice the amount of DETA was used with BGC and IGC the surface appearance began to change and coating hardness began to drop, primarily due to coating roughness.

Kinetic Analysis

DGEBA (DER 332) was selected as a standard epoxy resin to compare thermal reactivity with IGC and BGC. Even though DGEBA differs structurally, it is worthwhile to use for comparison since a great deal of literature is available. We took DGEBA, IGC, and BGC and evaluated model reactions with dimethyl aniline (DMA), N-methyl aniline (NMA), and aniline (A)--a tertiary, secondary, and primary amine, respectively. These model compounds were then compared with MDA for fraction reacted and activation energies using the Kissinger equation. Thermal analysis of the model compounds yields degree of cure and kinetic process parameters. This information can then be used to provide insight for the reactions occurring during curing of the coatings.

Scanning DSC of the Self-Crosslinking Reaction

Scanning DSC of the polymerization reaction of BGC and IGC is shown in Figure 9. Scanning measurements were performed using heating rates of 1[degrees]C/min, 2[degrees]C/min, and 3[degrees]C/min. For the self-crosslinking reaction, there are two exotherm peaks separated by a slope going through zero (Figure 9). The separation of the two exotherms indicates that more than one reaction mechanism occurs. Similar scanning DSC data has been observed with the reaction of imidazole and epoxide. (27) Literature suggests the first exotherm is from the amine attacking oxirane and the second exotherm is due to polyetherification. This is consistent with our ongoing studies of the self-crosslinking cure mechanism of glycidyl carbamates; however, it needs to be investigated more thoroughly.

Comparing DMA Added to IGC/BGC to the Self-Crosslinking Reaction by DSC

In the absence of added amine, the first peak exotherms of IGC and BGC took place at 157.83[degrees]C and 148.55[degrees]C and the second peak exotherms took place at 179.49[degrees]C and 172.79[degrees]C, respectively (Figure 10). However, when tertiary amine (DMA) was added to the resin there is only one peak exotherm observed at 161.44[degrees]C and 135.14[degrees]C for IGC:DMA and BGC:DMA. The single peak exotherm, for the resin:DMA reaction, was from polyetherification catalyzed by the DMA.

Thermal Analysis of IGC and BGC Reacted with Amines

We then compared the reaction of IGC and BGC with aniline, MDA, DMA, and NMA. Samples were analyzed in the scanning mode from 0[degrees]C to 250[degrees]C at 2[degrees]C/min. Note that, in this experiment, aniline was used at an equimolar amount relative to oxirane. Aniline is the most reactive of the amine model compounds; however, an interesting observation was noted. When examining IGC/NMA and IGC/MDA, both exotherms were in close proximity. Yet, IGC/NMA yielded only one peak exotherm. A difference was observed with the IGC/MDA reaction. Examination of IGC/MDA showed that a ratio of 1:1 incorporated self-crosslinking into the reaction, yielding two exotherms separated by slopes going through zero (Figure 11). This signifies that amine active hydrogens are reacting but are also being followed by self-crosslinking. This is an important observation because the physical properties of the coatings cured at high temperatures demonstrate the effects of self-crosslinking. Mechanistically, the reaction proceeds from amine active hydrogen attach onto the oxirane, but as the reaction proceeds the active hydrogen is sterically hindered and etherification dominates. Therefore, MDA does not follow the model compound and behaves chemically and thermodynamically different. Further exploration is ongoing.

Fraction Reacted and Degree of Cure

We then determined the fraction reacted for IGC and BGC with model compounds and MDA. The total heat flow was calculated from the sum of the isothermal and residual heat flow. Next, fractions of the isothermal run were taken at different conversions and were divided by the total heat flow for the fraction reacted. The isothermal run was carried out at 120[degrees]C until reaction completion. Reaction completion is when residual heat flow is zero and no exotherm is present. Cure behavior of IGC and BGC allows for an understanding of processing effects. For example, degree of cure can be calculated from fraction reacted at any specific time when total heat and residual heats are known. As shown in Figure 12, the cure of IGC:aniline and BGC:aniline reached 100% conversion in the least amount of time. On the other hand, IGC and BGC self-crosslinking reactions had the lowest cure conversion, yielding 9% and 21% cure, respectively. Autocatalytic effects of IGC:MDA and IGC:DMA are apparent when comparing differences in one-hour degree of cure. IGC/MDA is cured 97% in 60 min. Yet, IGC/DMA has a longer lag time before the reaction proceeds with 95% cure in 60 min. As depicted, reactions with DGEBA require more time for the reaction to proceed to completion when compared to GC functional epoxide resins. Thus, these results indicate that the glycidyl carbamate epoxy group is more reactive than glycidyl ether epoxy groups.

[FIGURE 11 OMITTED]

[FIGURE 12 OMITTED]

Activation Energies Determined by the Kissinger Equation

In a process, one concern is kinetic parameters during the cure cycle and crosslink formation. This information is determined by activation energies via the Kissinger method. (11) The procedure follows the peak maximum ([T.sub.exo]) during different heating rates (1[degrees]C, 2[degrees]C, 3[degrees]C, 5[degrees]C, and 10[degrees]C). Next, heating rate was plotted against 1/[T.sub.exo] X [10.sup.-3]. The slope of the plotted line yields the activation energy and the intercept results in the pre-exponential factor. A concern is to keep all heating rates exact, since slower and faster heating rates may adversely affect reported activation energies. Activation energies determined using such an approach for BGC/IGC self-crosslinking and BGC/IGC:MDA are reported in Table 4. The activation energies of the self-crosslinking reaction of BGC were determined to be 78.85 and 72.61 kJ/mol for BGC peak A and BGC peak B, respectively. For IGC, the activation energies were 60.48 and 64.65 for peak A and peak B, respectively. As increasing amounts of MDA were added, the activation energy decreased and the peak exotherm decreased. The effect of stoichiometry on activation energy is believed to be due to the autocatalytic nature of the epoxy-amine reaction.

CONCLUSIONS

Coatings with an excellent combination of physical properties such as hardness and flexibility can be achieved from the reaction of glycidyl carbamate functional oligomers with multifunctional amines. Variations in cure temperature, type of amine, and amine stoichiometry result in variations in coatings' physical properties. Some key findings are as follows: First, the reaction rate of the amines is in the order aliphatic > cycloaliphatic > aromatic. This is consistent with the literature on epoxy-amine cure kinetics. Second, the reactivity of the three epoxy resins is in the order: BGC > IGC > TMPGE. Thus, the glycidyl carbamate epoxy group is more reactive than the glycidyl ether epoxy. This finding is also supported by the kinetic experiments. Third, the good combination of hardness and flexibility is maintained for the GC resins over a wide range of stoichiometry and curing temperatures. This is especially true for the PACM-cured coatings.

Kinetic experiments using model compounds demonstrate that self-crosslinking reactions of the GC resins are involved at higher cure temperatures. The amount of self-crosslinking found in the IGC:MDA reaction is sufficient to alter physical properties at higher cure temperatures. The activation energy is lower for the glycidyl carbamate:MDA reaction than the glycidyl carbamate self-crosslinking reaction. The reaction rate and degree of cure increase when GC functionality is present when compared to conventional epoxide resin. In other words, the glycidyl carbamate epoxide is more reactive than the glycidyl ether epoxide. We have not only shown that good performance properties are gained from glycidyl carbamate resins crosslinked with amines, but that they also have related physical properties to the kinetics of the crosslinking reactions. Further exploration of these effects is ongoing. In addition, we are also investigating the effect these parameters have on the crosslink density of the coating formed, as well as exploring ambient temperature curing of these coatings.

Table 1 -- Coating Properties with a 1:1 Epoxy:Amine Ratio Using a
One-Hour Cure Time

                                   MDA
Temp                 Impact       MEK            Konig Pendulum
([degrees]C)  Resin  (in.-lb)     (Double Rubs)  Hardness (sec)

 80           BGC     116         >400           168
120           BGC     120         >400           155
150           BGC    >172         >400           122
 80           IGC    >172           40            20
135           IGC     100         >400           174
160           IGC     160         >400           178
 80           TMPGE  >172          350           196
135           TMPGE  >172         >400           102
160           TMPGE    16         >400           183

                                   PACM
Temp                 Impact       MEK            Konig Pendulum
([degrees]C)  Resin  (in.-lb)     (Double Rubs)  Hardness (sec)

 80           BGC    >174         >400           172
120           BGC      24         >400           155
150           BGC      16         >400           183
 80           IGC    >172         >400           180
135           IGC    >172         >400           165
160           IGC    >172          360           169
 80           TMPGE   120         >400           178
135           TMPGE   108         >400           188
160           TMPGE    48         >400           193

                                   DETA
Temp                 Impact       MEK            Konig Pendulum
([degrees]C)  Resin  (in.-lb)     (Double Rubs)  Hardness (sec)

 80           BGC    <172         >400           190
120           BGC     108         >400           188
150           BGC      76         >400           193
 80           IGC    >172         >400           105
135           IGC    >172         >400            73
160           IGC    >172         >400           100
 80           TMPGE  Tacky        Tacky          Tacky
135           TMPGE  Degraded     Degraded       Degraded
160           TMPGE  Degraded     Degraded       Degraded

                               MDA
Temp                        [T.sub.g] 1         [T.sub.g] [infinity]
([degrees]C)  Resin         ([degrees]C)        ([degrees]C)

 80           BGC           63.7                103.8
120           BGC           64.0                 97.6
150           BGC           63.6                 87.1
 80           IGC           56.0                102.5
135           IGC           60.5                 80
160           IGC           67.3                 90.7
 80           TMPGE         46.5                 84.3
135           TMPGE         64.7                 90.9
160           TMPGE         97.8                101.7

                                PACM
Temp                        [T.sub.g] 1         [T.sub.g] [infinity]
([degrees]C)  Resin         ([degrees]C)        ([degrees]C)

 80           BGC           54.6                105.5
120           BGC           58.2                 98.4
150           BGC           60.3                 88.1
 80           IGC           65.2                 96.2
135           IGC           66.3                 87.7
160           IGC           62.7                 90.4
 80           TMPGE         41.1                101.4
135           TMPGE         43.7                 93.2
160           TMPGE         43.6                101.6

                              DETA
Temp                       [T.sub.g] 1          [T.sub.g] [infinity]
([degrees]C)  Resin        ([degrees]C)         ([degrees]C)

 80           BGC           46.7                 86.1
120           BGC           50.7                 70.9
150           BGC           59.9                 69.0
 80           IGC           47.3                 56.8
135           IGC           46.4                 58.1
160           IGC           45.9                 59.5
 80           TMPGE        120.8                 NF
135           TMPGE         93.9                 NF
160           TMPGE         95.5                 NF

Table 2 -- Coating Properties with a 2:1 Epoxy:Amine Ratio Using a
One-Hour Cure Time

                                    MDA
Temp                  Impact        MEK            Konig Pendulum
([degrees]C)  Resin   (in.-lb)      (Double Rubs)  Hardness (sec)

 80           BGC       36          >400           174
120           BGC      168          >400           170
150           BGC      172          >400           172
 80           IGC     >172            30            21
135           IGC     >172            40            31
160           IGC       92          >400           186
 80           TMPGE   >172          >400           165
135           TMPGE    120          >400           162
160           TMPGE    120          >400           178

                                    PACM
Temp                  Impact        MEK            Konig Pendulum
([degrees]C)  Resin   (in.-lb)      (Double Rubs)  Hardness (sec)

 80           BGC     >172          >400           137
120           BGC      160          >400           185
150           BGC       44          >400           169
 80           IGC     >172          >400           185
135           IGC      160          >400           190
160           IGC     >172          >400           183
 80           TMPGE    120           360            18
135           TMPGE     93           200            73
160           TMPGE   Degraded      Degraded       Degraded

                                     DETA
Temp                  Impact        MEK            Konig Pendulum
([degrees]C)  Resin   (in.-lb)      (Double Rubs)  Hardness (sec)

 80           BGC     >172          >400           137
120           BGC       80          >400           165
150           BGC       80          >400           165
 80           IGC     >172          >400           135
135           IGC     >172          >400           190
160           IGC     >172          >400           165
 80           TMPGE   >172          >400            49
135           TMPGE   Degraded      Degraded       Degraded
160           TMPGE   Degraded      Degraded       Degraded

                                      MDA
Temp                             [T.sub.g]1          [T.sub.g][infinity]
([degrees]C)  Resin              ([degrees]C)        ([degrees]C)

 80           BGC                60.4                 97.9
120           BGC                64.4                 91.8
150           BGC                68.5                 87.1
 80           IGC                58.9                106.0
135           IGC                66.8                101.1
160           IGC                95.9                 96.5
 80           TMPGE              50.0                 78.4
135           TMPGE              46.4                 55.5
160           TMPGE              48.4                 54.3

                                    PACM
Temp                            [T.sub.g]1           [T.sub.g][infinity]
([degrees]C)  Resin             ([degrees]C)         ([degrees]C)

 80           BGC                49.7                 87.1
120           BGC                63.6                 90.7
150           BGC                69.5                 94.9
 80           IGC                45.4                 87.4
135           IGC                68.7                 91.1
160           IGC                64.5                 91.0
 80           TMPGE              52.6                 42.4
135           TMPGE              50.2                 42.4
160           TMPGE              37.1                 41.9

                                 DETA
Temp                            [T.sub.g]1           [T.sub.g][infinity]
([degrees]C)  Resin             ([degrees]C)         ([degrees]C)

 80           BGC                46.9                 75.2
120           BGC                57.5                 70.9
150           BGC                63.9                 69.0
 80           IGC                47.3                 58.8
135           IGC                50.5                 60.8
160           IGC                58.8                 67.9
 80           TMPGE             116.7                 NF
135           TMPGE              91.6                 NF
160           TMPGE             121.9                 NF

Table 3 -- Coating Properties with a 1:2 Epoxy:Amine Ratio Using a
One-Hour Cure Time

                                    MDA
Temp                   Impact       MEK            Konig Pendulum
([degrees]C)  Resin    (in.-lb)     (Double Rubs)  Hardness (sec)

 80           BGC       170         >400           190
120           BGC      >172         >400           188
150           BGC      >172         >400           193
 80           IGC         8         >400           207
135           IGC         8         >400           173
160           IGC         2         >400           160
 80           TMPGE       8           10           116
135           TMPGE       8         >400           211
160           TMPGE       8         >400           183

                                    PACM
Temp                   Impact       MEK            Konig Pendulum
([degrees]C)  Resin    (in.-lb)     (Double Rubs)  Hardness (sec)

 80           BGC      >172         >400           123
120           BGC      >172         >400           176
150           BGC      >172         >400           124
 80           IGC      >172         >400           123
135           IGC      >172         >400           183
160           IGC      >172         >400           178
 80           TMPGE    >172          150            30
135           TMPGE    >172          350           128
160           TMPGE      48         >400           100

                              DETA
Temp                   Impact       MEK            Konig Pendulum
([degrees]C)  Resin    (in.-lb)     (Double Rubs)  Hardness (sec)

 80           BGC       120         >400           Bad Surface
120           BGC       170         >400            39
150           BGC        48         >400           100
 80           IGC      >172         >400           105
135           IGC      >172         >400           117
160           IGC        70         >400           113
 80           TMPGE    Tacky        Tacky          Tacky
135           TMPGE    Degraded     Degraded       Degraded
160           TMPGE    Degraded     Degraded       Degraded

                                 MDA
Temp                          [T.sub.g]1        [T.sub.g][infinity]
([degrees]C)  Resin           ([degrees]C)      ([degrees]C)
 80           BGC              61.3               86.2
120           BGC              63.6               86.8
150           BGC              66.4               87.4
 80           IGC              36.1               50.7
135           IGC              48.4               51.9
160           IGC              62.1               73.4
 80           TMPGE            43.7               90.3
135           TMPGE            47.7               97.1
160           TMPGE            84.6              106.8

                                PACM
Temp                          [T.sub.g]1        [T.sub.g][infinity]
([degrees]C)  Resin           ([degrees]C)      ([degrees]C)

 80           BGC              30.6               78.9
120           BGC              52.2               84.6
150           BGC              59.4               78.8
 80           IGC              38.1               64.9
135           IGC              62.6               73.6
160           IGC              59.9               70.4
 80           TMPGE            45.8               89.2
135           TMPGE            47.3               85.6
160           TMPGE            63.9              102.3

                                 DETA
Temp                          [T.sub.g]1        [T.sub.g][infinity]
([degrees]C)  Resin           ([degrees]C)      ([degrees]C)

 80           BGC              31.6               47.2
120           BGC              33.6               47.3
150           BGC              47.7               45.2
 80           IGC              46.7               56.3
135           IGC              60.4               56.3
160           IGC              57.2               63.1
 80           TMPGE           121.2               NF
135           TMPGE            96.8               NF
160           TMPGE           118.4               NF

Table 4 -- Activation Energies Calculated by the Kissinger Equation for
Glycidyl Carbamate Self-Crosslinking and Reaction with MDA

Resin: Hardener               [E.sub.a](kJ/mol)

BGC Peak A                    78.85
BGC Peak B                    72.61
BGC: MDA (2:1)                85.51
BGC: MDA (1:1)                61.40
BGC: MDA (1:2)                59.79
IGC Peak A                    60.48
IGC Peak B                    64.65
IGC: MDA (2:1)                75.50
IGC: MDA (1:1)                57.43
IGC: MDA (1:2)                55.72

ACKNOWLEDGMENTS

The authors would like to thank Phoenix International, Rohm and Haas, and North Dakota EPSCoR for funding.

Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, on October 27-29, 2004, in Chicago, IL.

References

(1) Hsia, H.C., Ma, C.C., Li, M.S., Li, Y.S., and Chen, D.S., "Glycidyl-Terminated Polyurethane Modified Epoxy Resins: Mechanical Properties, Adhesion Properties and Morphology," J. Appl. Polym. Sci., 52, 1134 (1994).

(2) Chean, C.S., and Woo, E.M., "Cure Kinetics and Morphology of Amine-Cured Tetraglycidyl-4,4'-diaminodiphenylmethane Epoxy Blends with Poly(Ether Imide)," Polymer, 36 (15), 2883 (1995).

(3) Schneider, N.S., Sprouse, J.F., Hagnauer, G.L., and Gillman, J.K., "DSC and TBA Studies of the Curing Behavior of Two Dicy-Containing Epoxy Resins," Polym. Eng. Sci., 19 (4), 304 (1979).

(4) Dusek, K., and Matejka, L., "Advances in Network Formation and Rheology During Curing of Epoxy Resin Systems Including Reactive Elastomers," Polym. Mater. Sci. Eng., 57, 765 (1987).

(5) Mijovic, J. and Wijaya, J., "Etherification Reactions in Epoxy-Amine Systems at High Temperature," Polymer, 35 (12), 2683 (1994).

(6) Matejka, L., and Dusek, K., "Mechanism and Kinetics of Curing of Epoxides Based on Diglycidylamine with Aromatic Amines. 2. The Reaction between Diglydidylaniline and Aniline," Macromolecules, 22, 2911 (1988).

(7) Duffy, J.V., Hui, E., and Hartman, B., "Reaction Kinetics for Hindered Amine/Epoxides by DSC," J. Appl. Polym. Sci., 33 (8), 2959 (1987).

(8) Buckley, L., and Roylance, D.K., "Kinetics of a Sterically Hindered Amine-Cured Epoxy Resin System," Polym. Eng. Sci., 22 (3) (1982).

(9) Johncock, P., Porecha. L., and Tudgey, G.F., "The Relative Reactivity of Primary and Secondary Amine Hydrogen Atoms of Aromatic Amines with Epichlorohydrin and N- and O- Glycidyl Compounds," J. Polym. Sci., Polym. Chem. Ed., 23 (2), 291 (1985).

(10) Wicks, Z. Jr., Jones, F.N., and Pappas, S.P., Organic Coatings and Science and Technology, Vol. 2, John Wiley and Sons, New York, 1992.

(11) May, C.A. and Tanaka, Y. (Eds.), Epoxy Resins Chemistry and Technology, Vol. 2, Chapt. 3., Marcel Dekker, New York, 1988.

(12) Ellis, B., (Ed.), Chemistry and Technology of Epoxy Resins, Vol. 1, Chapt. 1-2, Blackie Academic and Professional, New York, 1993.

(13) Sourour, S. and Kamal, M.R., "Differential Scanning Calorimetry of Epoxy Cure: Isothermal Kinetics," Thermochim. Acta, 14 (1-2), 41 (1976).

(14) Ginsburg, D. (Ed.), Concerning Amines, Their Properties, Preparation and Reactions, Robert Maxwell, M.C., M.P. London, 1964.

(15) Sung, C.S., Pyun, E., and Sun, H.L., "Characterization of Epoxy Cure by UV-Visible and Fluorescence Spectroscopy: Azochrophoric Labeling Approach," Macromolecules, 19, 2922 (1986).

(16) Matejka, L. and Dusek, K., "Mechanism and Kinetics of Curing of Epoxides Based on Diglycidylamine with Aromatic Amines. 1. The Reaction of Diglydidylaniline with Secondary Amines," Macromolecules, 22, 2911 (1988).

(17) Edwards, P., Erickson, J., and Webster, D.C., "Synthesis and Self-Crosslink-ing of Glycidyl Functional Oligomers," Polym. Prepr., 44 (1), 54 (2003).

(18) Edwards, P., Erickson, J., and Webster, D.C., "Synthesis and Characteriza-tion of Glycidyl Functional Oligomers," Polym. Prepr., 44 (1), 144-145 (2003).

(19) Cardillo, P. and Nebuloni, M., "Theoretical and Calorimetric Evaluation of Thermal Stability of Glycidol," J. Loss Prevention in the Process Industries, 4 (4), 242 (1991).

(20) Croll, S.G., "Atmospheric Gases and the Hardening of Amine-Cured Epoxy Coating," JOURNAL OF COATINGS TECHNOLOGY, 24, No. 664, 65 (1980).

(21) Bell, J.P., Reffner, J.A., and Petrie, S., "Amine-Cured Epoxy Resins: Adhesion Loss Due to Reaction with Air," J. Appl. Polym. Sci., 21 (4), 1095 (1977).

(22) Grahm, J.P., Gloskey, D.A., Fisher, T.G., and Garling, R.A., "Effect of Temperature and Relative Humidity on Intercoat Adhesion Failure of Aliphatic Amine Cured Epoxy Coatings," JOURNAL OF COATINGS TECHNOLOGY, 60, No. 760, 35 (1988).

(23) Edwards, P., Striemer, G., and Webster, D.C., "Kinetics and Cure of Glycidyl Carbamate Functional Oligomers," Polym. Prepr., 90, 455 (2004).

(24) Edwards, P., Striemer, G., and Webster, D.C., "Cure Properties of Glycidyl Carbamate Oligomers Reacted with Amines," Polym. Prepr., 45 (1), 935 (2004).

(25) Caille, J.P., Pascault, J.P., and Tighzert, L., "Reaction of a Diepoxide with a Diisocyanate in Bulk," Polym. Bull., 24 (1), 23 (1990).

(26) Kordomenos, P.I., Frisch, K.C., and Kresta, J.E., "Oxazolidone Coatings. Part 2: Structure-Properties Relationships and Thermal Stability," JOURNAL OF COATINGS TECHNOLOGY, 55, No. 700, 59 (1983).

(27) Ooi, S.K., Cook, W.D., Simon, G.P., and Such, C.H., "DSC Studies of the Curing Mechanisms and Kinetics of DGEBA using Imidazole Curing Agents," Polymer, 41 (10), 3639 (2000).

Peter A. Edwards, Grant Striemer, and Dean C. Webster -- North Dakota State University*

*1735 NDSU Research Park Dr., Fargo, ND 58105.