Effect of composition on performance properties in cationic UV-curable coating systems.

Cycloaliphatic epoxides have been widely studied in the coatings industry because of the excellent mechanical properties of films prepared using these monomers and various diluents. In this study, polyol was studied as a diluent for formulations containing cycloaliphatic epoxide and oxetane in order to evaluate the effect on coatings properties and curing kinetics. The addition of polyol was shown to have an effect on both mobility of the cation as a chain transfer agent, along with the more general effect of flexibility, as evidenced by the hardness data, which increased when a small amount of polyol was added, but decreased as more polyol was included in the formulation. In terms of crosslinking kinetics, it was found that the inclusion of polyol resulted in an increase in conversion during UV irradiation. The level of polyol also had an effect on other properties, such as [T.sub.g] and crosslink density.

Keywords: Differential scanning calorimetry, dynamic mechanical properties, FTIR, ATR, photocalorimetry, UV, EB, radiation cure, mechanical properties, thermal properties, epoxy, reaction kinetics

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Coatings incorporating cationic UV-curable cycloaliphatic epoxides have gained widespread acceptance due to their excellent mechanical properties, good adhesion to a variety of substrates, and good heat and chemical resistance. (1,2) These monomers are also reported to have a low degree of volume shrinkage (< 5%) after cure, which is quite unique in the realm of UV-curable coatings. These systems are also uninhibited by oxygen, but do suffer with respect to humidity sensitivity. (3) Cycloaliphatic epoxides have the ability to form a highly crosslinked network during UV curing, but this tightly bound network can result in coatings with a high degree of surface cure or coatings that are too brittle for most applications. For this reason, formulations must be carefully designed to overcome this effect.

The use of diluents or flexibilizers in the formulation of cycloaliphatic epoxide coatings is essential, due to the brittle films that result from formulation without these components. (4) Polyols are commonly used to incorporate additional flexibility into these formulations, which also contribute to other properties, such as viscosity, cure rate, [T.sub.g], and toughness. (5) These oligomers act as a chain transfer agent, (6) and thus become incorporated into the crosslinked network during the UV-curing process, resulting in a more elastic network and a flexible coating. However, polyols can inhibit the UV-cure rate of coatings formulated with such oligomers. Thus, there is a drive to incorporate other reactive components into the formulation that will not only enhance properties, but will result in high conversion of functional groups. (7)

Another more recently developed class of diluents used in cycloaliphatic epoxide formulations is oxetanes. These types of monomers are similar in structure to epoxides, having a four-membered cyclic ether structure. Oxetanes also have been reported to have a similar reactivity to that of epoxides, owing to their similar ring strain energy and higher basicity. (8,9) This reactivity similarity can also be attributed to the mechanism of oxetane polymerization, which is a ring-opening reaction, (10) as is that of cycloaliphatic epoxides. When incorporated into a formulation, these monomers are expected to aid in relieving internal stress of the resulting films, (11) which is beneficial in achieving more pliable coatings. By utilizing these monomers along with polyols in cycloaliphatic epoxide formulations, the resulting coatings should possess the outstanding properties of the epoxide, along with a reduction in some of the negative attributes of formulations containing the epoxide alone. (12)

EXPERIMENTAL

Materials

Oxetane monomers (OXT-101 (3-ethyl-3-(hydroxymethyl) oxetane) and OXT-221 (bis{[1-ethyl(3-oxetanyl)]methyl} ether) were provided by Toagosei Co., Ltd. Photoinitiator UVI-6974 (mixed triarylsulfonium hexafluoroantimonate salt in propylene carbonate), TONE [TM] 0301 ([epsilon]-caprolactone polyol), and cycloaliphatic epoxide UVR-6110 (3,4-epoxycyclohexylmethyl-3-4-epoxycyclohexane carboxylate) were supplied by The Dow Chemical Company. All materials were used as received without further purification.

[FIGURE 1 OMITTED]

Formulations

All formulations consisted of cycloaliphatic epoxide, oxetane, cationic photoinitiator, and various amounts of polyol. The epoxide and initiator used in this study are shown in Figure 1. The structures of the diluents used, oxetane and polyol, are shown in Figure 2. The formulations were prepared by mixing together cycloaliphatic epoxide, oxetane, and polyol (if used), with gentle heating (40[degrees]C) to obtain an optically clear sample. After the sample was allowed to cool to room temperature, the photoinitator (4 wt% of solution based on total formulation) was added. The actual amounts used for each formulation are shown in Tables 1 and 2, where the R value was calculated using equation (1):

R = Epoxide Equivalents/Hydroxyl Equivalents (1)

The values for epoxy equivalents and hydroxyl equivalents were obtained using the amount of each material divided by the epoxy equivalent weight (EEW) or hydroxyl equivalent weight (HEW), respectively, that were given by each material's manufacturer. The EEW for UVR-6110 is 131-143, and the HEW for TONE 0301 is 98-103. The wt% polyol for each R value is as follows: 9.9 (R = 4), 8.1 (R = 5), and 6.8 (R = 6), which is used for ease of comparison for certain data. Oxetane functional groups were not included in the calculations for simplicity. The ratio of oxetane to epoxide was kept at 0.40 (based on weight), since this ratio gave films with the best properties based on preliminary studies.

Film Preparation

In order to obtain films of each formulation for testing, samples were cast onto a substrate at 4 mil wet thickness, then cured at ambient temperature using ultraviolet (UV) radiation for one minute. Aluminum substrates were used in order to test hardness and other basic properties; glass substrates were used to obtain free films for dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC). The UV light source used to cure films was a Dymax 200 EC silver lamp (UV-A, 365 nm) with an intensity of 35 mW/[cm.sup.2], measured with an International Light digital radiometer (Model IL1400A). Following curing, films were allowed to equilibrate for 24 hours before testing. The samples that were annealed were done so after this time for one hour at 150[degrees]C, and allowed to equilibrate for another 24 hr before testing.

Hardness Measurements

Hardness of films was evaluated using a BYK-Gardner pendulum hardness tester 24 hr after the films were cured onto aluminum substrates. The films were tested for Konig hardness, with the values reported in oscillations (osc).

Real-Time FTIR Measurements

Real-time FTIR measurements were performed using a Nicolet Magna-850 FTIR spectrometer. In order to facilitate UV curing in-situ, a LESCO Super Spot MK II UV curing lamp equipped with a fiber optic light guide was used. Uncured resin was spin-coated onto a KBr crystal at 3000 rpm, which was then exposed to UV light for 60 sec at an intensity of 35.8 mW/[cm.sup.2]. The radiation intensity was measured using an International Light digital radiometer (Model IL1400A). The end of the fiber optic light guide was positioned 15 mm from the sample in order to obtain adequate intensity. To keep humidity at 17%, a constant-humidity chamber was used to enclose the sample. Omnic FTIR software was employed for data acquisition and spectral calculations. All the samples were cured at room temperature.

The reaction progression was followed by monitoring the change in absorption of the epoxide and oxetane bands at 752-740 [cm.sup.-1] and 995-970 [cm.sup.-1], respectively. In order to calculate conversion from the absorption data, equation (2) was used:

% Conversion = [[[[A.sub.x]][.sub.o] - [[A.sub.x]][.sub.t]]/[[A.sub.x]][.sub.o]]] X 100% (2)

where [[A.sub.x]][.sub.o] represents the absorption of the epoxide or oxetane peak initially, and [[A.sub.x]][.sub.t] represents the absorption at time t.

Differential Scanning Calorimetry

Differential scanning calorimetry measurements were performed using a TA Instruments Q1000 series DSC. Samples were tested using a heat-cool-heat cycle from -20 to 200[degrees]C, at a heating rate of 10[degrees]C/min, with the exception of the samples tested immediately following photo-DSC, which were subjected to a single heat cycle (-20 to 200[degrees]C, 10[degrees]C/min). PhotoDSC measurements were obtained using the Q1000 DSC equipped with a photocalorimetric accessory (PCA). The sample and reference pans were irradiated for 300 sec at an intensity 40 mW/[cm.sup.2] from an identical UV source via fiber optic light guides. The samples were irradiated for 300 sec at a constant temperature (30[degrees]C). All DSC measurements were performed under a nitrogen atmosphere.

Dynamic Mechanical Thermal Analysis

Viscoelastic properties of crosslinked films were evaluated using a dynamic mechanical thermal analyzer (DMTA 3E, Rheometric Scientific). All samples were evaluated at a frequency of 10 rad/sec, with a heating rate of 5[degrees]C/min over a range of -75 to 300[degrees]C. Testing was performed using rectangular tension/compression geometry with a sample gap of 3 mm (length). The rectangular samples were cut to a width of 5 mm, with thicknesses in the range of 0.06-0.1 mm.

RESULTS

Konig Pendulum Hardness

One of the initial tests used to decide whether to proceed with a particular formulation is that of pendulum hardness. All coatings were subjected to this test 24 hours after UV curing, allowing for the completion of dark cure reactions, along with equilibration and relaxation of the films. As shown in Figure 3a, the addition of polyol has an enhancing effect on the hardness of the films containing cycloaliphatic epoxide and OXT-101. The films containing no polyol have a hardness of 139 [+ or -] 1.00 osc, but the addition of a small amount of polyol (R = 6, 6.8%) resulted in an increase in hardness (161 [+ or -] 1.15 osc), with a further addition of polyol (R = 4 and R = 5) resulting in lower values. The lower values of hardness for formulations with R = 4 and R = 5, 155 [+ or -] 1.00 and 149 [+ or -] 0.577 osc, respectively, are both greater than that of the films containing no polyol.

[FIGURE 2 OMITTED]

A similar trend in hardness is seen for the films containing cycloaliphatic epoxide and OXT-221. As demonstrated in Figure 3b, addition of 6.8% polyol (R = 6) again results in a significant increase in hardness, from 146 [+ or -] 1.15 to 159 [+ or -] 1.00 osc, respectively. As the amount of polyol is increased to 8.1% (R = 5), there is a decrease in hardness to 148 [+ or -] 0.577 osc. Further increasing the amount of polyol to 9.9% (R = 4) results in a further decrease in hardness, 145 [+ or -] 0.577 osc, which is within error of the value obtained for the films containing no polyol.

[FIGURE 3 OMITTED]

Real-Time FTIR

Real-time FTIR can be a powerful tool in understanding the chemistry that is occurring during many types of reactions. (13) In this study, the disappearance of epoxide and oxetane groups was monitored during a UV-curing reaction, since the concentration of these groups will only change due to reaction into the network. The % conversion was calculated using the equation described above, yielding plots of % conversion versus time for each formulation. An example of the plots obtained using this method is shown in Figure 4. In Figure 4a, the % conversion of oxetane groups is plotted for formulations containing cycloaliphatic epoxide, OXT-221, and varying amounts of TONE 0301 polyol. Figure 4b illustrates the corresponding conversion of epoxide groups for the same formulations.

The disappearance of epoxide and oxetane groups was monitored using real-time FTIR during the UV-curing reaction (60 sec UV irradiation), since the concentration of these groups will only change due to reaction into the network. The % conversion was calculated using the equation described above, yielding plots of % conversion versus time for each formulation. To gain a more complete understanding of the effect of polyol addition on the conversion of oxetane and epoxide groups, the overall conversion of each group is plotted against percent polyol in Figure 5. As shown in Figure 5a, the addition of polyol to formulations containing cycloaliphatic epoxide and OXT-101 does not have a significant effect on the conversion of oxetane groups. This is not the case for the conversion of epoxide groups; when polyol is introduced (R = 6, 6.8%), the conversion increases from 54.5% to 65.7%. A similar effect is seen when the amount of polyol is further increased (R = 5, 8.1%), but this effect levels off when the amount of polyol is increased to 9.9% (R = 4).

The real-time FTIR data for the OXT-221 formulations, shown in Figure 5b, shows a similar trend for the conversion of both oxetane and epoxide groups. For the oxetane group conversion, as polyol is introduced into the formulation the % conversion is not significantly affected. As before, as polyol content is increased (R = 6 to R = 4), the epoxide conversion is increased. Comparing epoxide and oxetane conversion, the oxetane conversion is significantly greater for all formulations, with the difference decreasing as polyol content is increased.

Differential Scanning Calorimetry: Crosslinking Kinetics

DSC was used to determine the effect of formulation variables on the crosslinking reaction and subsequent network development. This was done by determining the exotherms during UV irradiation and during subsequent heating. To do so, liquid samples were irradiated in the DSC for 300 sec with UV, immediately followed by a standard DSC experiment (-20 to 200[degrees]C) in order to determine the magnitude of the exotherms under these conditions.

The introduction of polyol into systems containing cycloaliphatic epoxide and oxetane can have a dramatic effect on the overall conversion of the system. The photoDSC and DSC exotherms for all formulations are shown in Figures 6 and 7, respectively. Typically, the photoDSC data is analyzed based on a % conversion calculated using the theoretical enthalpy of the system. For these systems, however, the use of polyol does not allow for such a calculation, due to the fact that heat of reaction data is not available for the chain transfer reaction, resulting in the absence of theoretical enthalpy data for this diluent. Because of this, an alternative method was used to characterize the data obtained from DSC.

The DSC data was analyzed using the total area obtained from both the photoDSC and DSC exotherms as the total enthalpy for each system and considering the enthalpy during photoDSC and DSC to represent % conversion. As shown in Figure 8, this leads to a significant trend for the addition of polyol into the system. For both oxetanes, the inclusion of increasing amounts of polyol results in an increase in the % conversion during UV curing, with a corresponding decrease in conversion during heating. Comparing the different formulations, those containing OXT-101 have a greater percentage of the total area from UV curing.

For formulations containing OXT-101, shown in Figure 8a, the introduction of a small amount of polyol (R = 6) results in an increase in conversion from 80.5 to 86.3% during UV curing. The corresponding % conversion during heating decreases from 19.5 to 13.7%. As the amount of polyol is increased further (R = 5), the % conversion during UV curing increases to 88.2%, with the conversion during heating decreasing to 11.8%. The maximum amount of polyol (R = 4) causes an increase in conversion during UV irradiation to 89%, with a decrease in conversion during heating to 11%. A similar trend is seen for formulations containing OXT-221.

[FIGURE 4 OMITTED]

As Figure 8b depicts, the % conversion obtained during UV curing is significantly lower for formulations containing OXT-221, but the same trend is apparent. As polyol is introduced (R = 6), the % conversion obtained during UV exposure increases from 57.9 to 68.3%. As before, the conversion obtained during heating decreases, from 42.1 to 31.7%. When polyol is increased further (R = 5), the % conversion during UV curing increases again to 68.8%, with a further decrease in conversion during heating to 31.2%. A further increase in polyol (R = 4) results in an additional increase in conversion during UV irradiation (69.1%), with a final decrease in conversion during heating (30.9%).

Differential Scanning Calorimetry: [T.sub.g] Determination

Because the samples exhibit an exotherm following UV curing, films were annealed at 150[degrees]C to determine the effect of an external heat cycle on the [T.sub.g]. As demonstrated by Table 3, the addition of a heat cycle to the films resulted in a significant increase in [T.sub.g] for all formulations. As stated above, there is additional curing that takes place during the heating of the films after UV curing, which is further exemplified by the [T.sub.g] increase shown in Table 3. Another point illustrated by Table 3 is the change in [T.sub.g] as the polyol content was increased. The inclusion of increasing amounts of polyol results in a decrease in [T.sub.g] for formulations containing either OXT-101 or OXT-221. Another point to note is the difference in [T.sub.g] between the different oxetanes. Formulations containing OXT-221 have a [T.sub.g] significantly higher than those containing OXT-101.

[FIGURE 5 OMITTED]

Dynamic Mechanical Thermal Analysis

Dynamic mechanical thermal analysis was used not only to obtain [T.sub.g] values to compare against those obtained using DSC, but also as a measure of the crosslinked network that was formed for each formulation. In order to do so, equation (3) was used to calculate crosslink density:

E' = 3[v.sub.e]RT (3)

where E' is the storage modulus at temperature T, [v.sub.e] is the crosslink density in moles per cubic meter, and R is the ideal gas constant. (14) The E' value was chosen 50[degrees]C above the [T.sub.g], so as to obtain the storage modulus in the rubbery plateau. An example of the DMTA data obtained is shown in Figure 9 for a film containing cycloaliphatic epoxide, OXT-221, and [epsilon]-caprolactone polyol (TONE[TM] 0301) (R = 5).

The overall data obtained from DMTA is shown in Figure 10 for all formulations. As demonstrated by Figure 10a, the inclusion of polyol did not have a significant effect on the [T.sub.g] of the coatings for those containing OXT-101 or OXT-221. This does not agree with the DSC data discussed above, which demonstrated a reduction in [T.sub.g] as polyol content increased. Figure 10b shows the effect of polyol amount on crosslink density of the formulations. As shown in the figure, the crosslink density tends to decrease as the polyol concentration increases.

DMTA was also used to investigate the effect of annealing on films and as a comparison with the results obtained from the DSC discussed above. As shown in Table 4, the addition of an external heating cycle to the films resulted in an increase in the [T.sub.g] for essentially all formulations, as was shown by DSC. The two exceptions to this were formulations containing cycloaliphatic epoxide, OXT-221, and [epsilon]-caprolactone polyol. When R = 4, the [T.sub.g] remained constant before and after annealing at 150[degrees]C. For the sample for which R = 5, the [T.sub.g] decreased following annealing. The crosslink density (XLD) also showed an overall trend for all formulations, decreasing following annealing. The exception to this was for the formulation containing OXT-101 at R = 4. For this formulation, there was a slight increase in crosslink density, from 2.1 X [10.sup.-5] to 3.2 X [10.sup.-5] mol/[cm.sup.3] after annealing.

DISCUSSION

The effect of formulation variables on network structure and ultimate coatings properties can be quite significant in the case of UV-curable coatings. By changing the components in a formulation, the overall network that is formed is affected, thus resulting in a change in overall properties. The use of reactive diluents in a cycloaliphatic epoxide formulation can increase the conversion of epoxide groups, which become trapped in the glassy polymer network, which forms quickly in UV-curable systems. (15) This lack of physical mobility, which is a direct result of the fast increase in [T.sub.g] that occurs in these systems, can strongly affect the rate of reaction. (16) In this study, formulations containing cycloaliphatic epoxide, [epsilon]-caprolactone polyol (TONE 0301), and oxetane were investigated in order to determine the effect of formulation variables on coating properties. The corresponding changes in conversion that accompany this addition were also studied in order to gain a further understanding of the change that may be occurring with the crosslinked network that is formed.

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

One of the most apparent effects of polyol addition can be seen when looking at the DSC data in Figure 8. For all formulations, the inclusion of increasing amounts of polyol results in an increase in the conversion that occurs during UV irradiation, with a corresponding decrease in the reaction that occurs during heating. Since the polyol is a chain transfer agent, the mobility of the cation is increased, which results in a greater degree of reaction before the system becomes vitrified. (6) The polyol also increases the flexibility of the system, also contributing to an increase in reaction during UV irradiation. This effect is demonstrated to a greater degree for formulations containing OXT-101, which has a greater percentage of conversion occurring during UV irradiation than that of formulations containing OXT-221. This can be attributed to the fact that OXT-101 is a smaller, more mobile molecule with only a single oxetane functionality, whereas OXT-221 is a larger molecule with two oxetane groups that can react. Not only is OXT-221 less mobile, but once one of the oxetane groups has reacted, it is tied into the network and loses even more mobility, thus making the second oxetane functionality even less likely to react before vitrification sets in.

[FIGURE 8 OMITTED]

The real-time FTIR data in Figure 5 gives some more insight into how the network is being built during UV irradiation, since the conversion of each functional group is monitored individually. Comparing the conversion of oxetane groups, the larger OXT-221 has lower % conversions than that of formulations containing OXT-101. This larger group also slows down the reaction of epoxide groups, resulting in all formulations containing OXT-221 to have lower % conversions. The increase in epoxide group conversion with increasing polyol can be attributed to both an increase in cation mobility due to chain transfer, (6) along with the polyol having a greater propensity to react with epoxide, resulting in a greater contribution to the activated monomer mechanism. (17) In contrast, the oxetane group conversion appears to be independent of polyol content, remaining constant as the amount of polyol was increased.

The hardness data shown in Figure 3 reflects not only the differences in conversion, but the physical effect of incorporation of a flexible diluent such as TONE 0301 polyol. For R = 6, the data indicates that polyol inclusion increases reaction due to chain transfer, exhibited by an increase in hardness for formulations containing either oxetane. This increase in reaction is verified by the DSC data above. As more polyol is added, however, the effect of cation mobility achieved by chain transfer becomes muted by the increasing flexibility of the polyol. This is demonstrated by a decrease in hardness when additional polyol is added into the system. Comparing the formulations containing the greatest amount of polyol (R = 4) with that of no polyol further demonstrates the fact that polyol influences crosslinking kinetics as well as physical properties. Even though there is a substantial amount of flexible polyol in the system, the hardness is still greater than that without polyol. This further verifies the fact that polyol incorporation leads to an increase in conversion.

The contribution of the polyol to both flexibility and conversion is further demonstrated by the DMTA data shown in Figure 10. The [T.sub.g] was not significantly affected by the introduction of polyol for the case of either oxetane. If the conversion were increasing as a result of increased cation mobility in the system, it is expected that the [T.sub.g] would increase as a result of a more developed crosslinked network. Conversely, the increase in flexibility of the coatings due to polyol inclusion would result in a decrease in the [T.sub.g]. The fact that there is not a significant change in the [T.sub.g] supports the fact that the introduction of polyol not only increases the conversion of functional groups, but increases the amount of flexibility at the same time. The crosslink density, however, does show a change as the amount of polyol is increased in the system. Overall, the crosslink density decreases as the amount of polyol is increased in the system. As with [T.sub.g], as the conversion is increased, it is expected that the amount of crosslinking in a given volume would increase. Because the opposite effect is seen, it is expected that it is not only the amount of conversion that is important but the type of linkages that are formed. Addition of polyol into the system may cause an increase in conversion, but it also leads to the incorporation of a larger group into the network, decreasing the amount of linkages in a given volume, resulting in a decrease in the crosslink density. Another factor that was studied for its effect on mobility and overall properties is temperature, which can be an important variable in terms of cure development and kinetics. (18)

[FIGURE 9 OMITTED]

[FIGURE 10 OMITTED]

Films were annealed to determine the effect of heating on the film properties. The DSC data in Table 3 shows the trends in [T.sub.g] for films before and after annealing. All formulations resulted in an increase in the [T.sub.g] following annealing at 150[degrees]C. This can be attributed to the fast network development that occurs during UV curing, which leads to entrapment of active sites such as functional groups and initiator. Heating these films above their [T.sub.g] allows for mobility to be restored, resulting in the reaction of active groups. This leads to further network development, which causes an increase in [T.sub.g]. Comparing the formulations in terms of type of oxetane, those containing OXT-101 showed a greater increase in [T.sub.g] following annealing compared to those containing OXT-221. This may be attributed to the fact that OXT-221 has two oxetane groups per molecule, which results in this monomer becoming pinned down once one functional group has reacted. This causes annealing to be less effective than for formulations containing OXT-101. The effect of annealing was further studied using DMTA, which gives some further insight into the effect of heat on the network structure.

The DMTA data in Table 4 shows a similar trend for the films following annealing. In general, the [T.sub.g] increased following annealing, which is in agreement with the DSC data. As stated above, heating the films above their [T.sub.g] increases physical mobility, allowing for the reaction of groups that may have become locked in place during UV curing. In addition, the crosslink density shows a decrease for most films following annealing. This may be attributed to a reorganization of the network, which results from heating these films above their [T.sub.g]. This data thus verifies the fact that not only does UV curing lock reactive species in place, but heating results in restoring mobility to these groups. The decrease in crosslink density further defines the likelihood of groups becoming locked into place, which are then reorganized once the temperature of the film is raised above its [T.sub.g].

CONCLUSIONS

The effect of composition was studied for formulations containing cycloaliphatic epoxide, TONE 0301 polyol, and oxetane. The inclusion of a diluent such as a polyol can increase mobility, which can be exhibited in a variety of ways. One of the more obvious effects is that of mechanical flexibility, which was demonstrated by the hardness data, where increasing amounts of polyol resulted in decreased hardness. The [T.sub.g] values obtained using DSC reinforce this effect, decreasing with increasing polyol content. The DSC data during UV irradiation demonstrated the effect of mobility, with conversion increasing with increasing polyol content. This effect can be of importance when formulating a coating to have the maximum amount of curing during UV irradiation, with little reaction occurring at later stages. This information is also useful for identifying formulations that will have maximum curing during UV irradiation, without sacrificing performance properties. As evidenced above, such variables may affect a formulation in a number of ways, so understanding the relationships of these components in detail is essential to obtaining an optimal UV-curable coating system.

Table 1--Formulations Containing Oxetane Monomer A, OXT-101

                                        [epsilon]-Caprolactone
Formulation    UVR-6110, g  OXT-101, g  Polyol, g               R Value

A4                 4.2         2.8              0.77              4
A5                 4.2         2.8              0.62              5
A6                 4.2         2.8              0.51              6
A                  4.2         2.8               --              --

Table 2--Formulations Containing Oxetane Monomer B, OXT-221

                                        [epsilon]-Caprolactone
Formulation    UVR-6110, g  OXT-221, g  Polyol, g               R Value

B4                 4.2         2.8              0.77              4
B5                 4.2         2.8              0.62              5
B6                 4.2         2.8              0.51              6
B                  4.2         2.8               --              --

Table 3--DSC Results for Samples Before and After Annealing at
150[degrees]C

Sample   [T.sub.g']      [T.sub.g']
         [degrees]C (a)  [degrees]C (b)    % Increase

A4           57              73               21.9
A5           66              80               17.5
A6           70              81               13.6
A            84              94               10.6
B4          100             109                8.3
B5          108             117                7.7
B6          110             121               11.0
B           133             150               11.3

(a) Before annealing.
(b) After annealing at 150[degrees]C for one hour.

Table 4--DMTA Results for Samples Before and After Annealing at
150[degrees]C

Sample  [T.sub.g'] [degrees]C (a)     [T.sub.g'] [degrees]C (b)

A4                115                            120
A5                120                            125
A6                120                            125
A                 115                            130
B4                165                            165
B5                175                            165
B6                170                            175
B                 175                            190

Sample  XLD, mol/[cm.sup.3] (a)    XLD, Mol/[cm.sup.3] (b)

A4       2.1 X [10.sup.-5]       3.2 X [10.sup.-5]
A5       4.7 X [10.sup.-5]       3.9 X [10.sup.-5]
A6       1.7 X [10.sup.-4]       4.7 X [10.sup.-5]
A        1.4 X [10.sup.-4]       4.3 X [10.sup.-4]
B4       3.8 X [10.sup.-5]       1.9 X [10.sup.-5]
B5       1.4 X [10.sup.-4]       4.9 X [10.sup.-5]
B6       1.5 X [10.sup.-4]       5.7 X [10.sup.-5]
B        3.5 X [10.sup.-4]       2.0 X [10.sup.-4]

(a) Before annealing.
(b) After annealing at 150[degrees]C for one hour.

ACKNOWLEDGMENTS

The authors would like to thank the Defense Microelectronics Activity (contract #DMEA90-02-C-0224) for funding this project.

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Heather A. Nash, Heidi J. Docktor, and Dean C. Webster ([dagger])--North Dakota State University*

Presented at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, on November 12-14, 2003, in Philadelphia, PA.

* Dept. of Polymers and Coatings, P.O. Box 5376, Fargo, ND 58105.

([dagger]) Author to whom correspondence should be addressed.