组装-聚合法制备聚苯乙烯-聚丙烯酸胶束和凝胶

通过苯乙烯和丙烯酸单体的预组装再聚合的制备方法,在不改变共聚物浓度的前提下制备了共聚物胶束溶液和凝胶,探讨了引发剂(偶氮二异丁腈)浓度对生成的共聚物的聚集体结构以及分子结构的影响.利用核磁共振氢谱、扫描电子显微镜和透射电子显微镜等表征了共聚物的分子结构和聚集行为,此外,借助耗散粒子动力学方法模拟了该体系,辅助实验阐明了不同引发剂浓度下生成的共聚物聚集体结构及相对应的共聚物分子结构,在此基础上,利用动态机械热分析和流变学的表征技术,研究了共聚物胶束溶液和凝胶的流变特性.结果表明,在单体浓度不变的情况下,高引发剂浓度时该体系趋于形成平均嵌段长度较长的两嵌段共聚物,生成稳定的胶束溶液,而低引发剂浓度时趋于形成交替共聚物,得到物理凝胶,耗散粒子动力学模拟得到了与实验一致的结果.流变学表征发现胶束体系和凝胶体系均呈现剪切变稀行为,并确定了凝胶体系的凝胶点及恢复性.

Preparation of Micelles and Gels via Polymerization of Pre-assembled Styrene and Polyacrylic Acid

Micelles and hydrogels,generally prepared at different concentrations in waters,arouse great interest due to their wide application.However,it is inconvenient and difficult to prepare the micelles and hydrogels at the same concentrations.In this work,different states of a same copolymer,such as micelle solutions and hydrogels,are prepared via the polymerization of the pre-assembled acrylic acid and styrene with the same monomer compositions at the same concentrations.The influence of initiator (azodiisobutyronitrile) concentration on the structures of the aggregates is investigated,and the corresponding molecular structures of the copolymers are studied by nuclear magnetic resonance and dynamic thermomechanical analysis,whereas the morphology of the aggregates is characterized by scanning electron microscope and transmission electron microscope.As a supplement to the experiment,dissipative particle dynamics simulation is further performed to reveal the aggregate structures and the corresponding molecular structures of the copolymers.It is found that,under the same concentration of acrylic acid and styrene,the system with a higher initiator concentration (7.0 × 10-3 moFL) tend to form stable spherical micelles of 50 nm diameter,in which the copolymers have longer blocks;while that with a lower initiator concentrations (such as 7.0 × 10-4 mol/L) tend to form network hydrogels,in which the copolymers have alternated and shorter blocks.Both the dynamic thermomechanical analysis and the simulation results demonstrate that the diblock copolymers and multiblock copolymers are synthesized at the higher and the lower initiator concentration.The different aggregate structures are originated from the different molecular structures.In addition,rheological characterization techniques are employed to investigate the rheological properties of the solutions and the hydrogels to clarify the relations between the properties and the molecular/aggregate structures.The rheological characterization showed the shear thinning non-Newtonian behaviour for both the micelle solutions and the hydrogels,and the gel-point ofhydrogels was determined to be at the concentration of 22 wt％.It is found that the hydrogels are recoverable after destruction by large amplitude oscillatory shear.The work can serve as an example to clarify the role of the polymer microstructure in determining the material properties and to provide guides for constructing materials with the similar composition but different aggregate structure.