AB_2型星形杂臂偶氮液晶聚合物的合成及表征

通过原子转移自由基聚合(ATRP)与ATRP衍生物化学修饰结合的方法,合成了一系列AB2型星形杂臂偶氮液晶聚合物.其中,A为聚苯乙烯,B为聚6-4-(4′-甲氧基苯基)偶氮苯氧基己酯](PMMAZO).合成分三步进行.首先,以ATRP方法得到ω-溴聚苯乙烯活性链PS(Br).然后对PS(Br)进行化学改性,得到带两个末端溴原子的聚苯乙烯活性链PS(Br)2·最后,以PS(Br)2作为双官能团大分子引发剂,引发6-4-(4′-甲氧基苯基)偶氮苯氧基]己酯(MMAZO)发生ATRP聚合,得到星形杂臂PS(PMMAZO)2聚合物.进一步对聚合产物进行了GPC和1H-NMR分析.结果表明合成产物是预期的星形杂臂聚合物,产物分子量可控且分子量分布狭窄.同时,以DSC和POM表征了星形杂臂聚合物的液晶性.

SYNTHESIS AND CHARACTERIZATION OF AB2-TYPE MIKTOARM STAR AZOBENZENE LIQUID CRYSTALLINE POLYMERS

A series of AB_2-type miktoarm star azobenzene polymers carrying one polystyrene (PS) arm and two poly6-4-(4′-methoxyphenylazo)phenoxy hexyl methacrylate｝(PMMAZO) arms were prepared by combination of atom transfer radical polymerization (ATRP) and chemical modification of the termini of ATRP derived polymers.The synthesis involved three steps.The first step involved the preparation of ω-bromopolystyrene (PS) chain by ATRP using ethyl 2-bromoisobutyrate as initiator.Next,the bromo end groups of the resulting PS chains were derivatized into ω,ω-bis(bromo)-PS chains.The last step consisted of growing two PMMAZO arms by ATRP in chlorobenzene.These precursors and miktoarm star polymers were characterized by proton nuclear resonance ( ~1H-NMR), and gel permeation chramatograpy (GPC).The information of PS(Br)_2 and PS(PMMAZO)_2 star polymers confirmed the expected structure.The liquid crystailline (LC) behavior of these copolymers was studied by DSC and POM.It was found that the miktoarm star copolymers had LC properties similar to PMMAZO those of homopolymer,and their thermal stability of the mesophases was improved,while the phase transition enthalpies were reduced.