Melt transesterification and characterization of segmented block copolyesters containing 2,2,4,4-tetramethyl-1,3-cyclobutanediol

Conventional melt transesterification successfully produced high-molecular-weight segmented copolyesters. A rigid, high-T _g polyester precursor containing the cycloaliphatic monomers, 2,2,4,4-tetramethyl- 1,3-cyclobutanediol, and dimethyl-1,4-cyclohexane dicarboxylate allowed molecular weight control and hydroxyl difunctionality through monomer stoichiometric imbalance in the presence of a tin catalyst. Subsequent polymerization of a 4000 g/mol polyol with monomers comprising the low-T _g block yielded high-molecular-weight polymers that exhibited enhanced mechanical properties compared to a nonsegmented copolyester controls and soft segment homopolymers. Reaction between the polyester polyol precursor and a primary or secondary alcohol at melt polymerization temperatures revealed reduced transesterification of the polyester hard segment because of enhanced steric hindrance adjacent to the ester linkages. Differential scanning calorimetry, dynamic mechanical analysis, and tensile testing of the copolyesters supported the formation of a segmented multiblock architecture. Further investigations with atomic force microscopy uncovered unique needle-like, interconnected, microphase separated surface morphologies. Small-angle X-ray scattering confirmed the presence of microphase separation in the segmented copolyesters bulk morphology.