Study On Reaction Kinetics Of Controlled/living Photo Polymerization Of MMA And Synthesis Of The Functional Materials

Controlled/living photopolymerization of methyl methacrylate(MMA) mediated by bimolecular system for 4-hydroxy-2,2,6,6-tetramethyl-piperidinyl-l-oxyl(HTEMPO) and 2,2,6,6-tetramethyl-piperidinone(TMPD) have been performed under 4.6 mW/cm² at ambient temperature. The effects of HTEMPO, TMPD and their different ratio as a mediator and photo-induced oxidization in situ of TMPD in the system have been discussed respectively. The results show that the molecular weight (M_n) of MMA homopolymer increased linearly and the polydispersity index(PDI) decreases with the conversion increasing, even until the conversion up to 85 %, mediated by bimolecular system with both HTEMPO and TMPD, which is characteristic of a controlled/living free radical polymerization. It is found that the obtained MMA homopolymer prepared by the photopolymerization exhibited narrow molecular weight distribution as was characterized by GPC, the smallest value of polydispersity index is 1.2. The result also shows that the bimolecular systems with both HTEMPO and TMPD as a mediator has better controlling on kinetic performance of the photopolymerization of MMA monomer over molecular weight and polydispersity than that only mediated by HTEMPO at the same condition. When the molar ratio of HTEMPO/Initiator is 1.1 in the monomolecular systems, the same results with the bimolecular systems have been obtained. The concentration of nitroxide decreasing with time of exposure increasing is observed according to ESR monitor, and the mechanism of photopolymerization mediated by nitroxides is suggested at first time. Besidesf_d(efficient of initiator) = 0.57, K_d'(constant rate of initiator decomposing) = 2.31×10^-3 s^-1,k_l(positive constant rate of the living polymerization) = 8.94×10⁷ mL/mol·s, k_-l(negativeconstant rate of the living polymerization) = 18.15 s^-1, K_l (constant rate of the livingpolymerization) = 4.9×10⁶mL/mol, k_p (constant rate of propagation chains)= 8.4×l0⁵M^-1·s^-1 arecalculated according to the ESR results and the reaction. K_l of this systems is smaller 10⁷ times than that of thermopolymerization of styrene system, which could explain to control result in the photopolymerization of MMA system is observed but to be failed in thermopolymerization.As an applied sample, HTEMPO-functionalized central cores were formed with divinybenzene in "core first" method, and the four or five arms star polymers were build via controlled / living free radical photopolymerization. The four arms star polymers were prepared with "arm first" method via controlled / living free radical photopolymerization. The results show that the star polymers have low polydispersities and molecular weight(Mn) with the 85000 560000 g/mol range, and the reaction time was shorted from 9 days to 4 hours.As other applied sample, hydroxide group capped polylactide(PLA) was synthesized with ROH/Sn(Oct)2 as initiator at 130°C in vacuum for 12 h, the yield about 91%, then the production reacted with acryloyl chloride for 4 h, and got the polymer capped with double bonds. Using Irgacure651 as an initiator and HTEMPO as a mediator, the polymer resolved in solvents and copolymerized with acrylic acid under UV-light exposure for 80 min, at last the homopolymer were removed from the copolymers. A character of the copolymer in main chain structure is biodegradable, and a part is hydrophile and the other is hydrophobe. The copolymers capped with HTEMPO could be re-opened by the thermal reaction condition to prepare star polymers.