Thioxanthene-9-thione Mediated MMA Polymerization

In the “cycloketyl radical mediated living polymerization” (CMP) process, a cycloketyl compound, [9,9′]bixanthenyl-9,9′diol (BIXAN) was ultilized as initiator and mediator. The cycloketyl (CK) radical was used as the dormant radical to achieve the increase of molecular weight. Herein, a series of cycloketyl thioketones were synthesised by Lawesson’s reagent by one step reaction with high yeild, and we found that, when a special cycloketyl thioketone compound, thioxanthene-9-thione (TXT), was added to a routine radical polymerization system, TXT could capture chain radical, and simultaneously formed an radical analogous to CK radical in structure, which could trigger the growth of polymer chains. This simple system was efficient to initiate the polymerization of methyl methacrylate (MMA) and in all cases the molecular weights increased with the increase of conversions. By the end-group analysis with 1 H-NMR and MALDI-TOF MS, it was confirmed that the P-STXT radical was used to control the polymerization. The re-initiating reactions were achieved when PMMA was used as the macro-initiator.