(Thio)urea/base systems have been widely used in the ring‐opening polymerization (ROP) of lactones based on their superior performance in activity and selectivity. Herein, a pyridyl‐urea (6C‐PU)/7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene catalytic system is used to prepare the polyesters with cyclic topology via the ROP of lactones in the absence of initiator under solvent‐free conditions. The catalytic system shows high activity in the ROP of δ‐valerolactone (δ‐VL) and cyclic polyvalerolactones (PVLs) with high molecular weights and narrow molecular weight distribution are obtained despite the existence of some linear products generated during the precipitation process. The structure of the resulting polymers is determined by proton and carbon nuclear magnetic resonance spectra, matrix assisted laser desorption/ionization time of flight mass spectrometry, and intrinsic viscosity studies. A possible mechanism is proposed on the basis of NMR analysis and characteristics of polymerization. Thermal and mechanical properties of cyclic PVLs are investigated through differential scanning calorimetry, thermogravimetric analysis, and tensile test.

中文翻译：

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内酯与吡啶脲/ MTBD的无溶剂开环聚合反应制得的高分子量环状聚酯

（硫代）脲/碱体系因其在活性和选择性方面的优异性能，已广泛用于内酯的开环聚合（ROP）中。此处为吡啶基脲（6C-PU）/ 7-甲基-1,5,7-三氮杂双环[4.4.0] dec-5-烯催化体系用于在无溶剂条件下在没有引发剂的情况下通过内酯的ROP制备具有环状拓扑结构的聚酯。该催化体系在δ-戊内酯（δ-VL）的ROP中表现出高活性，尽管沉淀过程中存在一些线性产物，但仍获得了高分子量和窄分子量分布的环状聚戊内酯（PVL）。所得聚合物的结构由质子和碳核磁共振光谱，基质辅助激光解吸/电离飞行时间质谱以及特性粘度研究确定。根据NMR分析和聚合特性提出了可能的机理。