The radical ring-opening polymerization (RROP) of thionolactones provides access to thioester backbone-functional copolymers but has, to date, only been demonstrated on acrylic copolymers. Herein, the thionolactone dibenzo[c,e]oxepane-5-thione (DOT) was subjected to azobisisobutyronitrile (AIBN)-initiated free-radical homopolymerization, which produced a thioester-functional homopolymer with a glass-transition temperature of 95 °C and the ability to degrade exclusively into predetermined small molecules. However, the homopolymerization was impractically slow and precluded the introduction of functionality. Conversely, the reversible addition–fragmentation chain-transfer (RAFT)-mediated copolymerization of DOT with N-methylmaleimide (MeMI), N-phenylmaleimide (PhMI), and N-2,3,4,5,6-pentafluorophenylmaleimide (PFPMI) rapidly produced well-defined copolymers with the tendency to form alternating sequences increasing in the order MeMI ≪ PhMI < PFPMI, with estimated reactivity ratios of r_DOT = 0.198 and r_PFPMI = 0.0078 for the latter system. Interestingly, defects in the alternating structure were more likely caused by (degradable) DOT–DOT sequences rather than (nondegradable) MI–MI sequences, which was confirmed through the paper spray mass spectrometric analysis of the products from aminolytic degradation. Upon the aminolysis of backbone thioesters, maleimide repeating units were ring-opened, forming bisamide structures. Conversely, copolymer degradation through a thiolate did not result in imide substitution but nucleophilic para-fluoro substitution on PFPMI comonomer units, indicating the ability of DOT–MI copolymers to degrade under different conditions and to form differently functional products. The RROP of thionolactones has distinct advantages over the RROP of cyclic ketene acetals and is anticipated to find use in the development of well-defined degradable polymer materials.

中文翻译：

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通过硫代羰基加成-开环RAFT自由基聚合制备的可完全降解的硫酯官能均聚物和交替共聚物

硫代内酯的自由基开环聚合（RROP）提供了接近硫酯主链官能共聚物的途径，但迄今为止，仅在丙烯酸共聚物上得到证明。在此，将硫代内酯二苯并[ c，e ]氧杂环戊烷-5-硫酮（DOT）进行偶氮二异丁腈（AIBN）引发的自由基均聚反应，制得的硫酯官能均聚物的玻璃化转变温度为95°C，专门降解为预定小分子的能力。然而，均聚是不切实际的缓慢并且阻止了官能团的引入。相反，DOT与N-甲基马来酰亚胺（MeMI），N的可逆加成-断裂链转移（RAFT）介导的共聚-苯基马来酰亚胺（PhMI）和N -2,3,4,5,6-五氟苯基马来酰亚胺（PFPMI）迅速生产出定义明确的共聚物，并形成交替序列的趋势按MeMI≪ PhMI <PFPMI的顺序增加，并具有估计的反应率的ř _DOT = 0.198和- [R _PFPMI对于后一个系统= 0.0078。有趣的是，交替结构中的缺陷更有可能是由（可降解的）DOT-DOT序列而不是（不可降解的）MI-MI序列引起的，这是通过对氨解降解产物进行纸喷雾质谱分析证实的。在主链硫酯的氨解后，马来酰亚胺重复单元被开环，形成双酰胺结构。相反，通过硫醇盐降解共聚物不会导致酰亚胺取代，而是亲核对位在PFPMI共聚单体单元上进行氟取代，表明DOT-MI共聚物在不同条件下降解并形成不同功能产品的能力。硫代内酯的RROP较环状烯酮缩醛的RROP具有明显的优势，并有望在开发可明确定义的可降解聚合物材料中找到用途。