Ambient Temperature Reversible Addition-Fragmentation Chain Transfer Radical Polymerization Of Styrenic Monomers Under UV-Visible Radiation

Reversible Addition Fragmentation chain Transfer (RAFT) radical polymerization merges the merits of both traditional radical polymerization and living polymerization into a single whole and has become a powerful technique for the synthesis of well-defined architecture polymers or copolymers. Ambient temperature RAFT polymerization is a facile and versatile technique, particularly in favor of the synthesis of well-defined polymers from thermo-sensitive or thermo-degradable monomers. In recent years, much effort has focused on the ambient temperature RAFT polymerization initiated with radiation, for instance,γ-ray radiation and plasma radiation. However, handling and setting up of UV lamps is facile, safer and cheaper than using eitherγ-ray or plasma radiation. UV radiation has been already used extensively in industry for several purposes. Previously studies of our group demonstrated that cutting off the chain transfer agent(CTA)-sensitive shorter-wave radiation significantly suppressed photolysis of CTA moieties in the duration of RAFT polymerization, thus remarkably improving the living behavior of these polymerizations;addition of highly efficient photoinitiator and optimizing functional groups of CTA remarkably suppress retardation effect in RAFT process, thus significantly shortening the initialization period and accelerating overall RAFT process. In this paper, based on the research on ambient temperature RAFT polymerization of styrene (St) under long-wave UV-vis radiation, we investigated ambient temperature RAFT polymerization of three styrenic-based monomers, which contain chloromethyl, tertiary amine group or hydroxymethyl, under long-wave UV-vis radiation for the first time. Furthermore, we synthesised various block copolymers with different structure by ambient temperature RAFT polymerization under long-wave UV-vis radiation.Photoinitiator, (2, 4, 6-trimethylbenzoyl) diphenylphosphine oxide (TPO) and several CTAs were investigated by UV-vis absorption characteristics in this paper. From them, we chose S-dodecyl-S'-(α,α'-dimethyl-α''-acetic acid) trithiocarbonate (DDMAT) as CTA, long-wave UV-vis radiation(λ> 365 nm) as resources to carry out ambient temperature RAFT polymerization of styrenic-based monomers. Moreover, two styrenic-based monomers, N,N-diethyl-(4-vinylbenzyl) amine (DEVBA) and 4-vinylbenzyl alcohol (VBA), were synthesized and characterized by NMR. we investigated the characteristics of ambient temperature RAFT polymerization of St, VBC, DEVBA and VBA. Making a comparison between this four systems, by UV-vis spectrophotometry, the researches on characteristics of"living"/ controlled, we discoveried that: (1) The initialization period of this four polymerization systems were short, and photolysis of CTA moieties in the duration of RAFT polymerization were weaker. (2) The rate of polymerization (Rp) of these monomers, from quick to slow is: VBA, VBC, DEVBA, St at the same conditions. The polymerizations of VBC, DEVBA, St nearly agreed with pesudo first-order kinetic characteristics, VBA with high reaction activity, agreed with pesudo first-order kinetic characteristics at lower monomer conversion. (3) The ambient polymerization of St, VBC or DEVBA, mediated by DDMAT, showed the characteristics of"living"/ controlled polymerization, while it was also a well-controlled polymerization process of VBA when the conversion was lower than 30%. In a whole, inducing chloromethyl, tertiary amine group or hydroxymethyl to the monomer, is favorable for enhancing the activity of styrenic-based monomers.Moreover, using polystyrene (PS) or poly(4-vinylbenzyl chloride) (PVBC) as macroCTA, by ambient temperature RAFT polymerization under mild light radiation, we gained various all-styrenic-based block copolymers, PS-b-PVBC, PS-b-PVBA and PVBC-b-PVBA, which can be precursor for building macromoleculars with special architecture and properties.