疏水链段对两亲性三嵌段共聚物在水中聚集行为的影响

EFFECT OF HYDROPHOBIC BLOCKS ON THE AGGREGATE BEHAVIOR OF AMPHIPHILIC TRIBLOCK COPOLYMERS IN AQUEOUS SOLUTION

以结构明确的两端为短的聚苯乙烯（PS）或聚甲基丙烯酸甲酯（PMMA）链段,中间为长的聚乙二醇（PEG）链段的PS-b-PEG-b-PS和PMMA-b-PEG-b-PMMA两亲性三嵌段共聚物为对象,研究了PS和PMMA链段对其在水中形成胶束和凝胶的影响.两种三嵌段共聚物在水中形成以PS或PMMA链段为核、PEG链段为壳的球形胶束,流体力学半径Rh,app为15.3-24.3 nm,并随PEG链段长度增长而增大.临界胶束浓度CMC均小于0.01 mg/mL,随着PS和PMMA链段长度的增加而减小.PS-b-PEG-b-PS浓度高于4.5 wt%可形成较强的疏水缔合的物理凝胶,平衡模量Ge可达到103Pa;PMMA-b-PEG-b-PMMA浓度高于7.5 wt%可以形成弱的凝胶,Ge＆lt;10 Pa.凝胶的储存模量G′和损耗模量G″均随着PS或PMMA链段的增长而增大.

The effect of hydrophobic blocks on the formation of micelle and gel for amphiphilic triblock copolymers of poly（methyl methacrylate）-b-poly（ethylene glycol）-b-poly（methyl methacrylate）（PMMA-b-PEG-b-PMMA） and polystyrene-b-poly（ethylene glycol）-b-polystyrene（PS-b-PEG-b-PS） was examined by fluorescence excitation spectra of pyrene probe,dynamic light scattering（DSL）,atomic force microscopy（AFM）,transmission electron microscopy（TEM） and rheology measurements.The core-shell micelle with hydrophobic PS or PMMA core and hydrophilic PEG loop chain corona formed in aqueous solution.The critical micelle concentration（CMC） was less than 0.01 mg/mL for all samples and decreased with increasing PS and PMMA block length,while the PEG block length had less effect on the CMC.The hydrodynamic radius Rh,app ranged from 15.3 to 24.3 nm and increased with increasing PEG block length.Increasing hydrophobic PS and PMMA block length effectively promoted the micelle formation in aqueous solution.The spherical shape of the micelle of the triblock copolymers was observed by AFM and TEM.The physical gel of PS-b-PEG-b-PS formed when the concentration was higher than 4.5 wt%.The gel formed by PMMA-b-PEG-b-PMMA when its concentration was higher than 7.5 wt%.The storage modulus G′ and loss modulus G″ increased with increasing of triblock copolymer concentration and the length of PS or PMMA blocks.The equilibrium modulus Ge was 103 Pa for PS-b-PEG-b-PS at 7.5 wt%,while less than 10 Pa for PMMA-b-PEGb-PMMA at 15.0 wt%.The stronger hydrophobicity of PS blocks comparison with PMMA block resulted in the stronger hydrophobic interaction and formation of stronger gels.