Thermomechanical and Free-Volume Properties of Polyester–Polyol Films for Coatings Applications: Role of Diol Composition

Abstract

Because of their utility in diverse coatings applications, a model series of polyester–polyol films possessing different diol formulations and cross-linked with an aliphatic isocyanate cross-linker under two different conditions is systematically investigated to elucidate the effects of backbone chemistry and cure temperature on the ultimate thermomechanical and free-volume properties. The diol of particular interest in this study is 2,2,4,4-tetramethyl-1,3-cyclo­butanediol (TMCD). The glass transition temperature of the films, as measured by thermal calorimetry and dynamic mechanical analysis, is observed to correlate strongly with TMCD content. In the limit of 100 wt % TMCD diol, the operable temperature range for these films increases by as much as ∼60 °C. Surface mechanical properties, interrogated by nanoindentation, also depend sensitively on both TMCD content and cure conditions, and a previously reported phenomenon known as “pileup” is considered to explain some of our observations. Results from positron annihilation lifetime spectroscopy indicate that the nanoscopic free volume of films containing varying levels of TMCD is strongly dependent on chemical makeup but not on cure conditions.

Molecular Simulations of Thermoset Polymers Implementing Theoretical Kinetics with Top-Down Coarse-Grained Models

“…Similarly, simulated values of E are displayed for each crosslinked resin as a function of temperature in Figure . In general, E decreases with increasing temperature, as anticipated on the basis of experimental observations . Another experimental trend, connected to the T g values of the crosslinked material, is captured: the crosslinked materials with higher T g values undergo a decrease in Young’s modulus at higher temperatures compared to materials with lower T g s. However, the change in E with temperature does not occur as abruptly at each T g in comparison with the measured experimental behavior, which might point to some deficiencies in the simulation models.…”

“…2 to 4 GPa, depending on composition. 66 The simulated E values at this temperature in Figure 13 are slightly higher (ca. 5−7 GPa).…”

“…Another aspect of these simulations is that they can provide corresponding predictions for bulk thermal and mechanical properties. Simulated values of T g and E are compared with experimental data 66 for the same five formulations, in which T g values were measured by thermal calorimetry, in Figure 12. Two different resin cure temperatures have been investigated…”

“…In general, E decreases with increasing temperature, as anticipated on the basis of experimental observations. 66 Another experimental trend, connected to the T g values of the crosslinked material, is captured: the crosslinked materials with higher T g values undergo a decrease in Young's modulus at higher temperatures compared to materials with lower T g s. However, the change in E with temperature does not occur as abruptly at each T g in comparison with the measured experimental behavior, 66 which might point to some deficiencies in the simulation models. At temperatures below their respective T g s, the resins are glassy and, at ambient temperature (25 °C), exhibit elastic moduli (from dynamic mechanical analysis) and surface moduli (from nanoindentation) ranging from ca.…”

“…Another aspect of these simulations is that they can provide corresponding predictions for bulk thermal and mechanical properties. Simulated values of T g and E are compared with experimental data for the same five formulations, in which T g values were measured by thermal calorimetry, in Figure . Two different resin cure temperatures have been investigated in the experiments: 333 and 393 K. The T g values measured at the higher cure temperature exceed the respective T g values evaluated at the lower cure temperature, thereby following known trends.…”