Thermoplastic copolyesters occupy an important segment in the materials market, finding use in a wide range of engineering plastic applications. This fact owes itself to the versatility underlying the synthetic preparation. However, the industry relies nearly exclusively on virgin feedstocks that are derived from fossil-based resources. With a keen interest in improving the deleterious environmental impact of this material class, we combine postconsumer recycled PET (rPET) with a bioderived dimer fatty acid (DFA) building block for the synthesis of segmented thermoplastic copolyesters (TPCs) via solvent-free melt polycondensation. The influence of (i) catalyst type, (ii) hard block (i.e., PET) precursor, and (iii) soft block (i.e., DFA) content on the microstructure and mechanical properties of TPCs was assessed. Samples that exhibit equivalent mechanical strength and segment distribution are accessible using either pristine bis-hydroxy ethylene terephthalate (BHET) or rPET as starting materials. Screening of reaction conditions and composition space within this context was performed with small-scale (2 g) reactions. Further optimization of reaction conditions in terms of catalyst concentration and ethylene glycol deconstruction agent content allowed for the upscaled synthesis (100 g) of engineering-grade TPCs in a custom-built reactor. We believe that our results contribute to a new paradigm in the efforts for more responsible manufacturing practices for TPCs and provide an additional outlet for the efficient handling of end-of-life, recyclable plastics.

Thermoplastic copolyesters (TPCs) are important structural components in countless high performance applications that require excellent thermal stability and outstanding mechanical integrity. Segmented multiblock architectures are often employed for the most demanding applications, in which semicrystalline segments of poly­(butylene terephthalate) (PBT) are combined with various low T g soft blocks. These segmented copolymers are nearly always synthesized from pristine feedstocks that are derived from fossil-fuel sources. In this work, we show a straightforward, one-pot synthetic approach to prepare TPCs starting from high-molar mass poly­(ethylene terephthalate) recyclate (rPET) combined with a hydrophobic fatty acid dimer diol flexible segment. Transesterification is exploited to create a multiblock architecture. The high molar mass and segment distribution are elucidated by detailed size-exclusion chromatography and proton and carbon nuclear magnetic resonance spectroscopy. It is also shown that rPET can be chemically converted to PBT through a molecular exchange, in which the ethylene glycol is substituted by introducing 1,4-butane diol. A series of copolymers with various compositions was prepared with either PET or PBT segments and the final thermal properties and mechanical performance is compared between the two different constructs. Ultimately, PBT-based TPCs crystallize faster and exhibit a higher modulus over the range of explored compositions, making them ideal for applications that require injection molding. This represents an ideal, sustainable approach to making conventional TPCs, utilizing recyclate and biobased components to produce high performance polymer constructs via an easily accessible upcycling route.

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