末端四苯乙烯荧光团标记法研究双亲性嵌段聚合物的自组装行为

Study on Self-assembly Behaviors of an Amphiphilic Block Polymer by Terminally Grafting Tetraphenylethene-Based Aggregation-Induced Emission Active Moietys

以四苯乙烯类分子2-溴-2-甲基-丙酸-3-(4-三苯乙烯基-苯氧基)-丙醇酯(E)作为引发剂,N-异丙基丙烯酰胺和苯乙烯为原料,通过活性自由基聚合,合成了末端具有聚集诱导发光(AIE)活性发光体的双亲性嵌段聚合物G。详细研究了AIE活性引发剂E和嵌段聚合物G在不同状态下的光物理行为差异。结果表明,在相同浓度条件下,随着温度的升高,引发剂E分散液的荧光强度不断下降。而嵌段聚合物的荧光强度先上升,当温度超过37℃后,嵌段聚合物的荧光强度不断下降。同样地,通过改变引发剂E和嵌段聚合物G在四氢呋喃和水混合溶剂中的浓度发现,随着浓度的减小,引发剂E的荧光强度不断下降,而嵌段聚合物分散液在改变分散液浓度时荧光强度的变化规律和改变温度时荧光强度的变化趋势相似。通过监控双亲性嵌段聚合物末端挂接的AIE活性发光分子发光性质的变化可以间接表征其聚集态结构的变化。

Poly( N-isopropylacrylamide)( PNIPAM) is an amphiphilic thermosensitive polymer with the hydrophilic amide group and the hydrophobic isopropyl group in the side chain. A reversible phase change occurs due to intermolecular interaction with the change of outside temperature. Tetraphenylethene derivatives have advantages of easy-to-synthesize,highly efficient chemical modification feasibility,aggregation-induced emission( AIE) characteristic and high quantum yield. Therefore,a macromolecular initiator F was prepared by the polymerization of N-isopropylacrylamide through single electron transfer-living free radical polymerization with tetraphenylethene derivative as the initiator. Then styrene was used as comonomer to convert the active PNIPAM initiator to an amphiphilic block polymer G,which was characterized by gel permeation chromatography and Fourier transform infrared spectra. Using tetraphenylethene-based AIE-active initiator as the research object of reference,the photophysical properties of amphiphilic block polymer at different temperatures and concentrations were studied to correlate the AIE activity with the amphiphilic nature of the block polymer in detail. It was found that the fluorescence intensity of AIE-active initiators decreased with the increase of temperature at the same concentration of dispersion,while the fluorescence intensity of the block polymer increased firstly,and then decreased after the temperature exceeded 37 ℃. Under the same conditions,by changing the concentrations of AIE-active initiators and block polymer in tetrahydrofuran/water mixed solvents,we found that the fluorescence intensity of AIE-active initiator decreased with the decrease of concentration,while the change tendency of fluorescence intensity for block polymer was similar as those obtained from the temperature changes. It is feasible to investigate the self-assembly behaviors of the amphiphilic block polymer by grafting the AIE active moiety to the terminal of polymer.