大投料比下自缩合原子转移自由基共聚合中聚合物支化结构的形成与演化

研究了少量N-4-(α-溴代异丁酰氧基)苯基]马来酰亚胺(BiBPM)与大量甲基丙烯酸-N,N-二甲氨基乙酯(DMAEMA)在CuBr/N,N,N′,N″,N″-五甲基二乙烯三胺(PMDETA)催化下的自缩合原子转移自由基共聚合(SCATRCP).分别利用气相色谱、三检测凝胶渗透色谱测定了聚合反应过程中DMAEMA的转化率、所得聚合物(PDMAEMA)的分子量与分子量分布、绝对分子量和特性黏数等随着反应时间的变化.结果表明,在以上聚合过程中,PDMAEMA的分子量随着聚合的进行而不断上升,但是支化度持续下降.由此可知,在聚合早期就形成了低分子量而高支化度的PDMAEMA,在聚合后期,主要进行DMAEMA的ATRP,导致支化度随着分子量的上升而逐渐下降.

DEVELOPMENT OF BRANCHING STRUCTRUE IN SELF-CONDENSING ATOM TRANSFER RADICAL COPOLYMERIZATION WITH A LARGE COMONOMER/INIMER FEED RATIO

CuBr /N,N,N′,N″,N″-pentamethyldiethylenetriamine-catalyzed self-condensing atom transfer radical polymerization (SCATRP) of N-4-(α-bromoisobutyryloxy)phenyl]maleimide (BiBPM) with a large excess of ( N,N-dimethylamino) ethyl methacrylate ( DMAEMA) was carried out,in which the conversion,relative molecular weight ( MW) and its distribution,absolute MW and specific viscosity of the PDMAEMA were monitored by gas chromatography,gel-permeation chromatography coupled with multi-angle laser light scattering and online visometry.The results showed that with the increase of the monomer conversion,the MW and polydispersity of the PDMAEMA increases gradually.The specific viscosity of the so-obtained PDMAEMA in tetrahydrofuran ( THF) was significantly lower than that of the linear analogues with comparable MW,indicating the presence of the branched structure.The contraction factor (g′),as a function of the MW of the branched PDMAEMA,decreases with increasing MW,suggesting that the degree of branching (OB) decreased slowly.The above results suggested that the SCATRP with a large comonomer /inimer feed ratio is a multi-step process: the inimer-initiated ATRP of comonomers forms the primary chains of several repeating units and the SCATRP of the primary chains forms low-MW and high-degree of branching PDMAEMA during the early stage,and the ATRP of DMAEMA initiated by branched PDMAEMA during the later period,gives rise to the high-MW and low-degree of branching PDMAEMA.