Optimization of poly(1,4-cyclohexylidene cyclohexane-1,4-dicarboxylate) (PCCD) preparation for increased crystallinity

A key factor, which affects the crystallization temperature on cooling (Tc) of PCCD is the cis/trans isomer ratio of the cyclohexyl diester in the polymer. Isomerization of pure dimethyl-trans-1,4-cyclohexanedicarboxylate can occur during the polymerization, and the Tc on cooling decreases along with the trans content. The isomerization reaction is enhanced with temperature, time and catalyst amount, and these variables should be minimized to prepare PCCD polymers with high Tc. However, these same variables also control the molecular weight growth of the polymer, and so a compromise between the best conditions for high Tc and those for high Mw must be made. A set of optimized conditions were obtained leading to PCCD polymers with Mw of 75,000-80,000 and Tc on cooling of 164-167 °C. Solid state polymerization was used to prepare high molecular weight PCCD with a high level of crystallinity (Tc on cooling ∼193 °C). It was also shown that adding small amounts of supplementary diols facilitates PCCD preparation by ensuring that high molecular weight PCCD polymers will be obtained even when the stoichiometry of monomer feed is off by >3%, i.e. conditions which would otherwise lead to low Mw. Finally, less crystalline PCCD's have been prepared via either incorporation of diethylene glycol or increasing the cis-diester amount in the polymer.