Synthesis of Sulfur-containing Polymers of Uniform Molecular Weight

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The present research is to develop a novel method for the synthesis of sulfur-containing polymers with uniform molecular weights.The results include the (1) development of novel living polymerization of three-membered cyclic thioethers (episulfides) to give polythioethers with uniform molecular weights, and (2) the first example the photo-induced copolymerization of episulfide and epoxide, achieved by using (N-methyltetraphenylporphinato) zinc propanethiolate. Although episulfides have been known to be polymerizable with anionic and coordinate anionic initiators, no example which demonstrates the living nature of polymerization has been reported due to the concomitant side reactions such as a facile desulfuration of the monomer. Therefore, the result (1)is the first clear example of living polymerization of episulfides. As for the result (2), copolymerization of episulfides and epoxides is usually very difficult due to the much higher polymerizability of the former than the latter, and no success has been reported. On the other hand, when (N-methyltetraphenylporphinato) zinc propanethiolate is used as initiator, the copolymerization of episulfides and epoxides takes place under the irradiation with visible light, affording the corresponding copolymers. Under appropriate conditions, the produced copolymers have narrow molecular weight distributions. In sharp contrast, the copolymer of block sequences and/or the mixture of the homopolymers with very broad molecular weight distribution is formed. Therefore, this is the first example of photoenhanced copolymerizability of comonomers with very different polymerizabilities.