PMMA-containing ITX Residues and its Initiation for Synthesizing PMMA-b-PSt Copolymer

In virtue of the reversible coupling and cleaving mechanism involved isopropylthioxanthone (ITX), a precursor of poly(methyl methacrylate) ended with ITX residues (PMMA-ITXH) was firstly synthesized through the photopolymerization of methyl methacrylate (MMA) initiated by a binary system of ITX and ethyl-p-dimethyl amino benzoate (EDAB), and secondly, applying this precursor as a macroinitiator, block copolymer of poly(methyl methacrylate) and polystyrene (PMMA-b-PSt) was produced through a thermal activated radical polymerization of styrene (St) at a temperature above 80°C. The content of incorporation of the reduced ITX groups in the precursor was estimated by UV-vis spectrum analysis and the results indicated that it was greatly influenced by the ITX concentration in system. The presence of EDAB could promote the polymerization and result in high monomer conversions and low molecular weight of polymers with wide distributions, but had no evident effect on the incorporation of reduced ITX moieties in polymer. Furthermore, more monomer supplied in system was advantageous for the production of high molecular weight of polymers and provided apparently low content of reduced ITX residues in polymer. Using a selected precursor of PMMA-ITXH with a moderate level of reduced ITX residues, molecular weight and its distribution, the bulk polymerization of St was initiated. FTIR spectrum analysis and GPC measurement confirmed the formation of block copolymer of PMMA-b-PSt.