Copolymerising polyethylene terephthalate (PET) and polycaprolactone (PCL) could provide a cost-effective method to recycle PET waste into a compostable plastic. In this work we investigated the relationship between formulation, microstructure, and mechanical properties during catalytic transesterification. It was found that the wt.% PCL was most effective in reducing the average PET block length and determining the copolymer's microstructure at equilibrium. Catalytic transesterification is a random process and can only give a narrow distribution when the average homopolymer block length is less than three, as determined by 1H NMR spectroscopy. A statistical copolymer marks reaction equilibrium where the average PCL block length is greater than one, contradicting the theoretical limit of a single PCL block length. It was proposed that the number of PCL ester groups available for reaction diminishes as transesterification progresses, leading to a favouring of the more abundant PET ester groups to undergo neutral or reverse reactions, resulting in equilibrium. As a result of the imbalance in the availability of PET and PCL ester groups at equilibrium, secondary factors, such as increasing the catalyst amount, were ineffective in further propagating transesterification. Copolymers formed in this study were either amorphous or semi-crystalline. The mechanical properties had minimal correlation with crystallinity and instead was mainly influenced by the ratio between the “hard” (PET) and “soft” (PCL and copolymer) segments in the microstructure and the molecular mass. In this study it was demonstrated that the microstructure of aromatic-aliphatic copolymers, synthesized through catalytic transesterification, can be manipulated to tailor physical properties to meet application requirements.

中文翻译：

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催化酯交换合成统计芳香族-脂肪族共聚酯的微观结构和力学性能


聚对苯二甲酸乙二醇酯 (PET) 和聚己内酯 (PCL) 共聚可以提供一种经济有效的方法，将 PET 废物回收成可堆肥塑料。在这项工作中，我们研究了催化酯交换过程中配方、微观结构和机械性能之间的关系。结果发现，重量% PCL 在降低平均 PET 嵌段长度和确定共聚物平衡状态下的微观结构方面最有效。催化酯交换是一种随机过程，只有当平均均聚物嵌段长度小于 3 时（通过 1H NMR 光谱测定）才能给出窄分布。统计共聚物标志着平均 PCL 嵌段长度大于 1 的反应平衡，这与单个 PCL 嵌段长度的理论极限相矛盾。有人提出，随着酯交换反应的进行，可用于反应的 PCL 酯基数量减少，导致更丰富的 PET 酯基发生中性或逆反应，从而达到平衡。由于平衡状态下 PET 和 PCL 酯基团的可用性不平衡，次要因素（例如增加催化剂用量）对于进一步进行酯交换反应无效。本研究中形成的共聚物是无定形的或半结晶的。机械性能与结晶度的相关性很小，而主要受微观结构中“硬”（PET）和“软”（PCL 和共聚物）链段之间的比例和分子质量的影响。 这项研究证明，通过催化酯交换合成的芳香族-脂肪族共聚物的微观结构可以进行控制，以调整物理性能以满足应用要求。