Boosting thermal stability and crystallization of closed-loop-recyclable biodegradable poly(p-dioxanone) by end-group regulation

A chemically closed-loop-recyclable biodegradable polymer, poly(p-dioxanone) (PPDO), is one of the ideal candidates for single-use plastic products due to its suitability for different application scenarios. Fascinatingly, when PPDO wastes can be collected, its monomer p-dioxanone (PDO) will be obtained through chemical recycling of these wastes; when cannot be collected, the wastes are able to be biodegraded into harmless substances. However, unsatisfied thermal stability and low crystallization rate of PPDO restrict its wider applications. Herein, based on end-group regulation, we simultaneously realized the significant enhancement of thermal stability and crystallization of PPDO through the simple melt processing with tributyl phosphite (TBP) or triphenyl phosphite (TPP). The model reactions were conducted to investigate the reaction mechanism and theoretical products during the preparation of PPDO/phosphite compounds. Two kinds of phosphites were proved to act as the end-capped reagent and chain extender in the melt processing, while TBP presented better reactivity. As a result, the activation energy of thermal decomposition was largely elevated, and the unprecedented T-5% (the temperature at a weight loss of 5%) and T-ma (the temperature at a maximum rate of weight loss) of PPDO were obtained, i.e., T-5% of similar to 330 degrees C and T-max of similar to 385 degrees C in N-2 atmosphere,T-5% of similar to 240 degrees C and T-max of 317 degrees C in air atmosphere, respectively. Furthermore, the increased crystallization rate, crystallinity, crystalline orderliness, and realizable monomer recovery (yield >90%, purity >99.9%) of PPDO/phosphite compounds were confirmed.