Sequence length determination in poly(ethylene terephthalate)-bisphenol-A polycarbonate random copolymers by application of selective degradation

Abstract

Poly(ethylene terephthalate) (PET) and bisphenol-A polycarbonate (PC) are melt-mixed in equimolar ratios under various conditions to get a series of PET–PC copolymers. Samples from each copolymer are characterized by differential scanning calorimetry, 1H and 13C nuclear magnetic resonance (NMR), size exclusion chromatography (SEC), and polarizing light microscopy. The lengths of the PET sequences are determined in different copolymer samples by NMR sequential analysis before and after removal of the PC segments by selective degradation. In the former case, rather unusual results are obtained, suggesting predominant alternating order of single PET and PC repeating units. After selective elimination of the PC units, however, the NMR techniques show evidence of consecutively bonded dyads or triads of PET and PC units, which corresponds to the theoretical values in random copolymers obeying the statistics of Bernoulli. Considering the 1H-NMR and SEC results after selective elimination of the PC sequences, a possible structure of the residual PET containing segments is proposed for the first time. It is concluded that in the PET/PC copolymers studied, when sequence distribution approaches the random one, determination of the PET block lengths after elimination of the PC sequences is more reliable as compared to the cases when selective degradation is not applied. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 429–440, 1998