Bis-hydroxyethylterephthalamide (HETP) and dimethyl terephthalate (DMT) are readily accessible depolymerization products via aminolysis and methanolysis of polyethylene terephthalate (PET), respectively. The transesterification copolymerization of HETP and DMT yields a polyesteramide nylon hybrid having a much higher glass transition temperature (125 °C) than that of PET (72 °C), presumably because of amide hydrogen bonding. It has a melting temperature (262 °C) comparable to that of PET (265 °C). Note that the weak-link of this polyesteramide is an ester linkage—the same one present in PET itself. Because of that, the aminolysis of this copolymer with aminoethanol affords a single monomer, HETP—in double the molar quantity employed to synthesize the original polymer. Hence, this polymerization/depolymerization cycle represents an expanding loop chemical recycling strategy that doubles in scale with each revolution. Conceptually, the polyesteramide can be made from PET alone, or from PET combined with the HETP generated from depolymerized polyesteramide. Thus, as the demand for the polyesteramide increases, increasing amounts of post-consumer PET can be assimilated into this chemical recycling loop. We applied our standard PET aminolysis conditions to this polyesteramide and demonstrated facile and coherent ester scission, affording un-optimized yields of 30–56% isolated HETP. The expanding loop chemical recycling of PET will be further discussed in the context of related polymers.

Each cycle of exp<i>anding loop </i>chemical recycling incorporates additional DMT from PET—thereby doubling the quantity of polyesteramide produced. This nylon hybrid has a <i>T</i><sub>g</sub> value of 125 °C and a <i>T</i><sub>m</sub> of 262 °C.

Each cycle of expanding loop chemical recycling incorporates additional DMT from PET—thereby doubling the quantity of polyesteramide produced. This nylon hybrid has a T_g value of 125 °C and a T_m of 262 °C.

Parker Boeck

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