摘要
两亲性偶氮苯聚合物既具有偶氮苯结构独特的光致顺反异构化行为,又具有两亲性嵌段共聚物的微相分离和纳米聚集特征,因而成为光敏感功能高分子材料的有效来源。本论文利用可逆加成断裂链转移自由基(RAFT)聚合方法开展了具有不同取代基的偶氮苯乙烯基单体的活性可控聚合研究。利用获得的偶氮苯均聚物,进行了单体甲基丙烯酸二甲胺基乙酯(DMAEMA)和甲基丙烯酸聚氧乙烯醚酯(PEGMA)单体的扩链反应,制备了相应的两亲性偶氮苯嵌段共聚物,对聚合物的溶液性质进行了考察,具体工作如下:
(1)使用α-二硫代萘甲酸异丁腈酯(2-cyanoprop-2-yl 1-dithionaphthalate, CPDN)作为RAFT试剂,偶氮二异丁腈(2,2'-azobisisobutyronitrile, AIBN)作为引发剂,分别以[6-(4-偶氮苯基)苯氧基]甲基丙烯酸正己酯(6-(4-Phenylazophenoxy)hexyl methacrylate, PHMA),(6-[4-(4-甲氧基偶氮苯基)苯氧基]}甲基丙烯酸正己酯(6-[4-(4-methoxyphenylazo) phenoxy]hexylmethacrylate,MHMA) (6-[4-(4-氰基偶氮苯基)苯氧基]甲基丙烯酸正己酯和(6-[4-(4-cyanophenylazo)phenoxy] hexyl methacrylate,CHMA)为单体,在苯甲醚中通过可逆加成-断裂链转移(RAFT)聚合方法,制备了结构精致的相应偶氮苯均聚物(PAzoMA),PPHMA、PMHMA和PCHMA。三种单体的RAFT聚合过程显示典型的“活性”/可控特征。另外,将获得的偶氮苯均聚物作为大分子RAFT试剂进行了单体DMAEMA的扩链反应,成功地合成了偶氮苯两亲性嵌段共聚物(PAzoMA-b-PDMAEMA)。聚合物的分子量和结构利用GPC和1H NMR方法进行了表征。研究了聚合物溶液的光致异构化行为、在选择性溶剂中的自组装行为和热性能等。
(2)利用RAFT方法,以制备的偶氮苯均聚物PPHMA以及类似的甲氧基(PMHMA)和腈基(PCHMA)取代的偶氮苯聚合物为大分子RAFT试剂进行PEGMA的扩链反应,成功合成了相应的两亲性嵌段共聚物PPHMA-b-P(PEGMA),PMHMA-b-P(PEGMA)和PCHMA-b-P(PEGMA),扩链反应过程表现出典型的活性可控特征。对嵌段共聚物的热行为、组装行为和溶液中的光致异构化行为等进行了研究。结果显示嵌段共聚物PPHMA-b-P(PEGMA)可以在水-THF体系中发生光照诱导的自组装,形成相应的聚集体,并出现了荧光发射行为。结果表明聚合物在溶液中的聚集态的形成和体积的变化有可能和偶氮基元的荧光性质的改变有关。
Amphiphilic azobenzene-containing block copolymer combined the properties of azobenzene and amphiphilic block copolymer, which showed interesting photo-responsive behaviors in solution. These polymers attacked more and more researching interest for their novel ability as the building block of photo-sensitive materials. In this thesis, the RAFT polymerization behavior of three azobenzene vinyl monomers containing different substitutes was investigated firstly. Then, the amphiphilic block copolymers of these azobenzene polymers with DMAEMA and PEGMA were synthesized through the chain extension method. The properties of these polymers in solution were investigated thereafter. The details were showed as following:
(1) Three well-defined azobenzne homopolymers, e.g. poly{6-[4-phenylazo -phenoxy)hexylmethacrylate} (PPHMA), poly{6-[4-(4-methoxyphenylazo) phenoxy]hexylmethacrylate} (PMHMA) and poly{6-[4-(4-cyanophenylazo) phenoxy] -hexylmethacrylate} (PCHMA), were synthesized via RAFT polymerization using CPDN as the RAFT agent and AIBN as the initiator. The polymerization showed characteristics of living/controlled behavior. Using these azobenzene homopolymers as the macro-RAFT agents, the amphiphilic diblock copolomers were prepared by chain extension using DMAEMA as the second monomer. The polymer structure was characterized via NMR technique. The light responsive behaviors of the homopolymer and their diblock copolymers in their solution were also investigated.
(2) The amphiphilic azobenzene block copolymer, poly(6-(4-phenylazophenoxy) hexylmethacrylate-b-poly((2-dimethylamino)ethyl methacrylate)) (P(PHMA)-b- (PEGMA)) was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization technique. The polymerization behavior showed that it was conducted in a controlled living manner. The obtained amphiphilic block copolymer showed strong fluorescence emission in water/tetrahydroforan(THF) solution with minor relationship with UV-vis irradiation. Further investigation showed that such copolymer emitted strong fluorescence in THF after UV-vis irradiation. The change of fluorescence emission behavior of the amphiphilic block copolymer both in water/THF and THF solution was caused by the formation and size changing of aggregation originated by the photo-isomerization of azobenzene chromophore.
引文
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