Synthesis of novel photoreactive bis(dithiocarbonate) type xanthates as chain transfer agents and their use in MADIX polymerization of styrene

In this study, two novel photoactive xanthates, which bear a photoinitiator (PI) group in the middle and an S-alkyl dithiocarbonate group (–O–C(S)–S–R) at each of the two ends of the molecule, were synthesized as chain transfer agents (CTA) to be used in reversible addition-fragmentation chain transfer/macromolecular design via the interchange of xanthate (RAFT/MADIX) polymerization. Having the same central photoinitiator group, two chain transfer agents (CTA-PI-CTA 1 and CTA-PI-CTA 2) differ from each other in their R leaving groups; C6H5–CH2– and C6H5–CH(COOEt)–, respectively. The structures of CTA-PI-CTAs were elucidated via elemental analysis and spectroscopic techniques, such as 13C NMR, 1H-NMR, and FT-IR. Styrene (St) was used as the model monomer in MADIX polymerization. Its RAFT/MADIX polymerization with these chain transfer agents successfully produced mid-chain functional polystyrene macrophotoinitiators (PSt-PI-PSt 1 and PSt-PI-PSt 2) with well-defined structures. The GPC, FT-IR, 1H-NMR, UV, and fluorescence spectroscopic studies revealed that low-dispersity polystyrenes with desired photoinitiator functionality in the middle of the chain were obtained. Finally, these macrophotoinitiators were used as prepolymers in photoinitiated free radical polymerization of methyl methacrylate (MMA) to obtain polystyrene-poly(methyl methacrylate) (PSt-PMMA) block copolymers.