Effective Regulation of Polycaprolactone Molecular Weight and Oligomers Content Using Tetraphenyltin Catalyst
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There is a lack of effective approaches that produce polycaprolactone materials (PCL) with a high molecular weight, narrow polymer dispersity index (PDI), and fewer formation of oligomers. The immigration of the remained oligomers predominantly causes poor PCL quality and induces odor release. This limits the extensive application of PCL materials. This study investigates the effects of different catalysts and loadings on the PCL performance along with the formation of oligomers in detail. The oligomers were successfully separated using gel permeation chromatography (GPC). This was followed by a quantitative and qualitative identification using high-resolution mass spectrometry (HRMS) and low field nuclear magnetic (L-field NMR) analysis. The results show that tetraphenyltin is an effective catalyst to promote the reaction and produce high-performance PCL that possesses the highest Mn (65000), narrowest PDI (1.37), and the lowest content of oligomers (7.466 wt.%). Density functional theory (DFT) studies that were combined with characterizing key intermediates verified that an anhydride bond was formed close to the end hydroxyl group in the PCL chain because of the special catalytic mechanism. This unusual chemical structure successfully inhibited the chain from being broken by the “back-biting” behavior, which is helpful for lowering the content of oligomers. This study can provide a scalable synthetic approach to creating high-performance polymers.