Preparation Of NR-g-PMMA By ATRP With One-step Method

At present, graft modification of natural rubber is mainly through conventional radical polymerization. It's hard to obtain graft copolymer with well-defined structure. Applying atom transfer radical polymerization (ATRP) to graft copolymerization, the molecular weight of graft chains will be controllabled. And because the graft copolymerization only takes place on initiation point, the graft copolymer has a clear structure. There are two ways to graft polymer chain onto NR; one is to insert the chain in the a-H position of NR molecule chain, the other in the double-bond position. In this thesis, the first way was taken, using one-step method to prepare macroinitiator from NR, ie. NR-Br, by reacting with N-bromobutanimide (NBS) for its highly selective bromination of the allylic hydrogen. And then NR-Br was used to initiate polymerization of methyl methacrylate (MMA) and to obtain NR-g-PMMA, where the grafts locate in the a-H position of the backbone.In the section of preparing macroinitiator, the effect of bromination time, temperature and the amount of NBS on the reaction process was investigated to determine the reaction conditions. And the FTIR and1H-NMR were used to analyze the structure of the product so as to study the relation between reaction conditions and the bromination site and side reactions. Results show that the main reaction is bromination of the allylic hydrogen when conducted in ambient temperature, where the NR-Br obtained has initiating activity of ATRP. However, when conducted in high temperature side reactions as addition of Br2in double bond and cyclization happened, resulting a low content of allylic Br. The suitable conditions of NR-Br preparation is as following. The mole ratio of NBS to isoprene unit (I) is0.1; reaction time is12h in ambient temperature.In the section of ATRP grafting, NR-g-PMMA were prepared using NR-Br as initiator, CuBr/bpy or PMDTA as catalyst, toluene as solvent. The structure and molecular weight and distribution of grafted polymer were analyzed by FTIR,1H-NMR and GPC. The results show that the weight of product has no change after acetone extraction when grafted rate was less than100percent, indicating no homopolymer to proceed. While grafted rate improved, we discover the structure of nature rubber (analyzed by1H-NMR) in the extraction buffer of acetone. The results are that the solubility of NR-g-PMMA improves in acetone with improved graft rate of PMMA. The influence of polymerization conditions on grafted polymer grafting rate and monomer conversion was investigated. Grafting rate of more than400%can be achieved under conditions of allylic bromine content of4.41%, n(NBS): n(CuBr):n(PMDTA/bpy):n(MMA)=1:1:3:100. Study on kinetics of polymerization indicates of a first-order kinetic reaction when using PMDTA as ligand. The molecular weight of NR-g-PMMA increased as the increment of the conversion of monomer. This paper studied the structure of grafted copolymerization NR-g-PMMA, basing on the research of NR graft modification by ATRP. It revealed a new idea for using ATRP in chemically modification of NR.