Reversible Addition-Fragmentation Chain Transfer Polymerizations Of Styrene And Methyl Methacrylate With Different Initiation Systems

In this thesis, the effects of different initiation systems on the reversible addition fragmentation chain transfer (RAFT) polymerizations of styrene and methyl methacrylate and RAFT polymerizations of 2-(dimethylamino) ethyl methacrylate (DMAEMA) were investigated. The results were shown as below. The bulk polymerizations of styrene in the presence of 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN) and tetraethylthiuram disulfide (TETD) exhibited "living"/ controlled polymerization characteristics: the linear kinetic plots, the experimental molecular weights increasing linearly with monomer conversion and being close to the theoretical ones, narrow polydispersities (<1.3). The results indicated that the polymerizations undertook RAFT polymerization mechanism and the TETD acted as an initiator. Well-controlled polymers could be prepared when the initial molar ratios of CPDN to TETD was 2~3, and the tempreture of polymerization was 60~70 0C. About 98.2% polymer chains were end-capped with CPDN moiety in the one end, and about 75% polymer chains with TETD moiety in the other end, which was proved by the 1H NMR spectrum. As the moiety of TETD is sensitive to UV light, the obtained polymer can be extended under the irradiation of UV light. This provided an alternative way to functionalize the polymer. RAFT polymerizations of styrene and methyl methacrylate were carried out at 80 0C with five initiation systems: 2, 2'-azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), TETD, dicumyl peroxide (DCP) and BPO/DMA (N, N-Dimethylaniline). The control ability of the RAFT polymerizations was studied using these initiation systems with different decomposition rates. When the decomposition rate of the initiator increased, the polymerization rate increased and polydispersities of obtained polymer became broader, resulting an ill controlled polymerization. The possible reason was that the decomposition rate was so large that the generating rate of propagating radicals would be higher than the addition rate between the propagating radical and RAFT agent, which resulted some radicals could not be caught by RAFT agent to be dormant, resulting termination reaction and ill-controlled polymerization. Well-defined polyDMAEMA was synthesized via the RAFT polymerizations of DMAEMA using CPDN as the RAFT agent and AIBN as an initiator through optimizing the recipe of concentrations of monomer, RAFT agent, initiator and solvent. Increasing temperature accelerated the polymerization, however, had no obvious effect on the polydispersity of polymers. The well-defined amphiphilic copolymers were prepared using the obtained polymer as the macro-RAFT agent and styrene as the second monomer. Micelles of the amphiphilic copolymer formed through self-assembling in water displayed spherical shape.