荧光标记法研究水含量对两亲性超支化共聚物组装体形貌的影响

Investigation on the Effect of Water Content on the Morphology of Hyperbranched Polymer Aggregates in Solution through a Fluorescence Labeling Approach

合成了丹磺酰基(DNS)标记的两亲性超支化共聚物,DNS-PEHO-star-PEO.用荧光标记法研究了DNS-PEHO-star-PEO在四氢呋喃(THF)/H2O混合溶剂中不同水含量下的自组装行为.结果表明,水含量对DNS-PEHO-star-PEO形成的组装体形貌影响显著.含水含量小于20 vol%时,DNS-PEHO-star-PEO组装成纳米尺寸的球形胶束;随着水含量增加到?75 vol%时,DNS-PEHO-star-PEO组装成"多胶束聚集体";纯水中(水量100 vol%),DNS-PEHO-star-PEO形成微米尺寸的聚合物大囊泡.利用不同形貌聚集体中DNS的荧光发射谱不同的特性,我们绘制了不同聚集体中DNS的荧光最大发射峰波长与水含量的关系图,直观地反映了水含量对DNS-PEHO-star-PEO组装体形貌的影响.

Water content is one of crucial factors affecting the morphology of polymer aggregates in solution. In the present work, we synthesized an amphiphilic hyperbranched copolymer（DNS-PEHO-star-PEO） with a hydrophobic poly[3-ethyl-3-（hydroxymethyl）oxetane]（PEHO） core and hydrophilic poly（ethylene oxide）（PEO） arms, in which the PEHO core was labelled with dansyl（DNS） fluorophore. The degree of branching（DB） of the hyperbranched polymer was around 0.4 and the molar fraction of the PEO arms was ca. 0.7. Through a fluorescence labeling approach coupled with transmission electron microscopy（TEM）, dynamic light scattering（DLS） and photoluminescence（PL） spectrometry analyses, etc., we studied the effect of water content on the morphology of the hyperbranched polymer aggregates in solution. Interestingly, it was found that in tetrahydrofuran（THF）/H2 O mixed solvents with 〈20 vol% water content, DNS-PEHO-star-PEO self-assembled into spherical micelles with diameters of 〈20 nm, which possessed a DNS labeled PEHO core and a PEO corona; when the water content increased to ca. 75 vol%, the hyperbranched copolymers organized into ＂multi-micelle aggregates（MMAs）＂ with diameters in the range of 300 , 400 nm, which consisted of a large amount of small spherical micelles; while in pure water, the hyperbranched copolymers aggregated into micrometer-sized giant vesicles, which emitted green photoluminescence upon excitation under fluorescence microscope. The DNS-PEHO-star-PEO aggregates of different morphologies show different PL emission spectra in THF/H2 O solutions, owing to the variation of the molecular conformation of the DNS fluorophore in the hyperbranched polymer assemblies of various morphologies. Such a unique PL feature allows the plotting of a morphological phase diagram by water content as a function of the wavelength at the PL emission maximum. The phase diagram clearly shows the effect of water content on the morphology of the PEHO-star-PEO aggregates in THF/H2 O solutions. The fluorescence labeling approach is expected to be a powerful tool in monitoring the morphological transition of polymer aggregates in solution.