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

Abstract

The use of NMR spectroscopy in solution to investigate the chemical structure of engineering poly(alkylene terephthalate)s such as poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and poly(butylene terephthalate) (PBT) is reviewed. Chemical defects present in the polyester chain, such as oxydialkylene units, as well as accompanying side products such as cyclic oligomers generated in the polycondensation, are well detected in 1H NMR spectra. The technique is also demonstrated to be effective for identifying, and even for quantifying in certain cases, the end groups of these polyterephthalates, including those that are generated in small amounts as a consequence of thermal degradation. The application of NMR to the study of the chemical microstructure of copolyesters derived from such polyterephthalates is also reviewed for its unique ability to determine comonomeric sequence lengths and degree of randomness (R). Copolyesters synthesized by either melt polycondensation or entropically driven ring opening polymerization, in addition to those prepared by solid‐state modification or melt blending, are the object of this review.

Single‐step solution polymerization of poly(alkylene terephthalate)s: synthesis parameters and polymer characterization

“…Average molar mass values ranging between 12 000 and 20 000 g mol −1 with relatively narrow dispersity values Đ = 1.6 − 2.4 were recorded by GPC (see Table ). It should be highlighted that the low Đ values indicated a limited occurrence of side reactions and polymer degradation during the solution polycondensation …”

“…As a direct result, the reaction kinetics and rates may be influenced enabling an increase in side reactions such as chain defects, chain scission, end group modification reactions (e.g. carboxyl or vinyl end groups) and/or cyclic oligomer formation . In an attempt to solve some of these problems, antimony‐, tin‐ or titanium‐based catalysts have been applied during the polymerization process.…”

“…However, due to the limited availability of cyclic derivatives, only a few semi‐aromatic polyesters have been synthesized to date by ring opening polymerizations. Extraction and cyclo‐depolymerization result in the formation of cyclic derivatives. Nevertheless, these procedures also imply the use of solvents and catalysts which result in additional cost and toxicity issues.…”

“…carboxyl or vinyl end groups) 15,16 and/or cyclic oligomer formation. 17 In an attempt to solve some of these problems, antimony-, tin-or titanium-based catalysts have been applied during the polymerization process. However, titanium-based catalysts impart a yellow colour, while antimony catalysts were found to lead to possible toxicity issues.…”

Step‐Growth Polymerization in the 21st Century

“…Muñoz-Guerra et al discuss advanced characterization possibilities of poly(alkylene terephthalate)s, an important class of industrially relevant polyesters. [ 1 ] This review refl ects the very deep knowledge on structure-property relationships for these long-known materials, but is also important in view of the mentioned transition to Andrew P. Dove,* Michael A. R. Meier* thiol-ene chemistry for further grafting-onto reactions. Last but not least, the remaining two papers deal with sulphur-containing polymers.…”