MOLECULAR-STRUCTURE EFFECTS ON THE SECONDARY RELAXATION AND IMPACT STRENGTH OF A SERIES OF POLYESTER COPOLYMER GLASSES

The secondary relaxations of a series of glassy copolymers based on po ly(ethylene terephthalate) (PET) and poly( 1,4-cyclohexylenedimethylen e terephthalate) (PCT) involve cooperative motions of the cyclohexylen e rings. The cooperativity gives rise to longer range motions which cr eate significant volume fluctuations that can facilitate macroscopic s hear yielding. Comparison of the secondary loss peaks and activation e nergies by dynamic mechanical spectroscopy between the copolyesters an d poly(cyclohexyl methacrylate) and poly(1,4-cyclohexylenedimethylene 2,5-dimethylterephthalate) indicates that the secondary relaxation of the copolyesters involve motions of the cyclohexylene ring. Dipolar ro tational spin-echo C-13 NMR confirmed large amplitude motions of the c yclohexylene ring faster than 10 kHz at 300 K. By examining feasible r ing conformations, we conclude that transitions between chair and twis t-boat conformations are possible for trans-cyclohexylene rings and ci s-rings that prefer chair conformations. (Cis-rings that reside in boa t conformations are more restricted.)