Controlled Radical Polymerization Mediated by Constrained Geometry Construction Trivalent Titanium Complex
Controlled radical polymerization has aroused considerable attentions during the past decades due to its ability to adjust the polymer chain structure such as molecular weight,molecular weight distribution,composition,and topology.Transition metals compounds such as copper,iron,ruthenium,nickel,etc have been extensively explored.While the effect of the auxiliary ligands on the polymerization behaviour was rarely investigated.Especially for titanium complexes,only metallocene titanium chloride Cp2TiCl2 was examined under the reduction by Zinc.Herein,the binary systems composed by constrain geometry construction trivalent titanium complex(1)and 1-bromo-1-phenylethane(I1),(2-bromo-2-propanyl)benzene(I2)and 1-iodo-1-phenylethane(I3),respectively,were employed to catalyzed radical polymerization of methyl methacrylate(MMA).The influence of initiators on the molecular weight and molecular weight distribution was assayed.The kinetic study of MMA polymerization initiated by 1/I1 indicated linear relationship between MMA conversion and polymerization time,suggesting zero order dependent on MMA concentration.While with the increase of monomer conversion,the molecular weights of the afforded polymers have no obvious change.In addition,with the increase of the ratio of MMA to I1 while keeping the MMA concentration as constant,the molecular weight of the corresponding polymer increased despite the MMA conversion decreased.Meanwhile,with the decrease of the polymerization temperature,the molecular weight of the afforded polymer increased.These results suggested that the polymerization performed in slow initiation,fast propagation.This is consistent with the typical radical polymerization mechanism,but different from those of atom transfer radical polymerization(ATRP)and organometallic mediated radical polymerization(OMRP)which are mediated by organometallic complexes.The above results indicated that the auxiliary ligand has a significantly effect on a radical polymerization process.bromo-2-propanyl)benzene(I2)and 1-iodo-1-phenylethane(I3),respectively,was employed to catalyze radical polymerization of methyl methacrylate.The influence of initiator on the molecular weight and molecular weight distribution was assayed.The kinetic study of MMA polymerization initiated by 1/I1 was carried out.The influence of reaction conditions,such as the ratio of MMA to 1,temperature,was also investigated.Combined with the results of monitoring the reaction between 1 and I1 by nuclear magnetic resonance(NMR)and electron paramagnetic resonance(EPR),the mechanism was proposed.
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