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, 1 H and 13 C 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 1 H-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.

The interchange reaction between poly(ethylene terephthalate) and poly(m‐xylylene adipamide)

“…On the basis of work done by Denchev et al,13, 26 the use of NMR solvents such as deuterated sulfuric acid (D 2 SO 4 ) will allow determination of the sequence lengths in the reacted (PET/MXD6) blends. For this work; therefore, their recommended procedure has been followed.…”

“…There have been significant numbers of research studies of the interchange reactions that occur between two polycondensates. These studies include polyester–polyester1–13 and polyamide–polyamide14–16 systems. Research has also included the interchange reactions between polyesters and some polyamides 17–26.…”

Chemical Structure and Microstructure of Poly(alkylene terephthalate)s, their Copolyesters, and their Blends as Studied by NMR

“…The phase morphology of this blend is noticeably affected by the occurrence of reactions between the two polymers and the effect of the catalyst on these reactions has been reviewed by Pilati et al These authors concluded that titanium alkoxides were the most effective for increasing the interchange reactions in this system. These interchain reactions can be followed by both 1 H and 13 C NMR …”

Immiscible Blends of PC and PET, Current Knowledge and New Results: Rheological Properties

“…Among the chemical techniques for the analysis of the copolymers, the combination of selective degradation of the PC blocks of the copolymers with piperidine in methylene chloride followed by intrinsic viscosity measurements in mixture of 1,1,2,2‐tetrachloroethane/phenol 60/40 wt.‐% at 25 °C has been used 29 . 1 H NMR spectroscopy was also found to provide a reliable characterization of the products of the exchange reactions after selective degradation of the PC sequences 29, 33–35. Deviation of the value of the glass transitions of the components from the Fox law was also used to assess the degree of interpenetration of the copolymers into the corresponding neat components 28, 32, 33, 36, 37…”