适配双链与非适配单链包结γ-CD聚准轮烷嵌段共聚物合成与表征

Synthesis and Characterization of Matched Double-chain and Loose-fit Single-chain Stranded γ-CD-based Polypseudorotaxane Containing Block Copolymers

首先在精准控制摩尔投料比条件下,通过缓慢加料方式制备出以2-溴异丁酰基为端基的双三缩四乙二醇偶氮苯二甲酸酯(Br-EG_4-AZO-EG_4-Br,1)作为引发剂,然后在[γ-CD]/[1]=4的条件下,将1与γ-环糊精(γ-CD)在水溶液中进行自组装制备得到双链包结聚准轮烷(i PPR),进而用该聚准轮烷原位引发N-异丙基丙烯酰胺(NIPAAm)进行原子转移自由基聚合(ATRP)得到聚准轮烷嵌段共聚物(PPRs).分析结果表明,该类共聚物以γ-CD与偶氮苯和折叠三缩四乙二醇链自组装形成的适配双链包结结构的形式存在,而在与由1引发NIPAAm进行ATRP聚合所制备的PNIPAAm-EG_4-AZO-EG_4-PNIPAAm进行自组装包结时,γ-CD则均匀分布在整条共聚物链上生成非适配单链包结聚准轮烷嵌段共聚物(a PPRs).与引发剂1和a PPRs相比,PPRs中代表反式偶氮苯基团的紫外吸收峰发生明显红移,但紫外光照射产生的顺式异构化几乎不导致γ-CD滑脱下链,说明γ-CD与偶氮苯和折叠三缩四乙二醇包结形成的适配双链包结结构不仅稳定性高,而且还能可逆地转化为γ-CD与双三缩四乙二醇链包结形式的适配双链包结结构.

By carefully controlling the feeding ratio and slow feeding the reactants,2-bromoisobutyryl end-capped tetraethylene glycol azobenzene-4,4￠-dicarboxylic ester（Br-EG4-AZO-EG4-Br,1）was synthesized as an initiator.With n（γ-CD）/n（Br-EG4-AZO-EG4-Br）=4/1,the resulting initiator 1 was self-assembled withγ-cyclodextrin（γ-CD）in water to create first a double-chain stranded polypseudorotaxane（iP PR）as supramolecular initiator,which was then used to initiate,in situ,atom transfer radical polymerization（ATRP）of N-isopropylacrylamide（NIPAAm）to prepare polypseudorotaxane containing block copolymers（PPRs）.It was found that the addedγ-CDs accommodate both an azobenzene and a folded tetraethylene glycol chain in the block copolymers,presented as a matched double-chain stranded inclusion complexing structure.However,in the case of self-assembling with PNIPAAm-EG4-AZO-EG4-PNIPAAm prepared from ATRP of NIPAAm,γ-CD was randomly distributed along the whole copolymer chain to give access to a series of loose-fit single-chain stranded inclusion complexing structured polypseudorotaxanes（a PPRs）.Compared with Br-EG4-AZO-EG4-Br and a PPRs,the characteristic peak of ultraviolet（UV）absorption due to trans-azobenzene in PPRs was obviously red-shifted,but the unique cis-isomerization of this group appeared not leading to the threadedγ-CDs sliding off the polymeric chain.All these characterizations suggested that the matched double chain stranded inclusion complexing structure was constructed by an azobenzene and a folded tetraethylene glycol chain jointing to enter the cavity ofγ-CD,showing not only a relatively higher stability,but also a reversible transformation into the double tetraethylene glycol chain stranded inclusion complexing structure in the process of cis-isomerization of the azobenzene.