无规共聚物P(MEO2MA-co-OEGMA)的合成及其在水溶液中温度诱导相转变行为

利用原子转移自由基聚合(ATRP)方法,由单体2-(2-甲氧基乙氧基)甲基丙烯酸乙酯(MEO₂MA)和寡聚(乙二醇)甲基醚甲基丙烯酸酯(OEGMA, M_n = 500 g·mol^-1)合成了无规共聚物P(MEO₂MA-co-OEGMA).并采用动态光散射(DLS)、紫外光谱及透射电子显微镜(TEM)等技术考察聚合物在水溶液中的温度响应性聚集行为,获得其在水溶液中的最低临界溶解温度(LCST)及其随组成的变化规律.结果表明,该聚合物具有良好且可逆的温度响应行为,这主要归因于聚合物与水分子之间氢键作用,及其分子本身疏水作用之间为了保持一种微妙的动态平衡而自发对聚集形态进行的“自我调整”,从而达到新的热力学平衡状态的结果.该聚合物的LCST与聚合物中单体OEGMA所占的摩尔比例呈线性关系,可以通过改变单体的摩尔配比实现对聚合物LCST的调控.

Synthesis of P(MEO2MA-co-OEGMA) Random Copolymers and Thermally Induced Phase Transition Behaviors in Aqueous Solutions

Random copolymers of 2-(2-methoxyethoxy)ethyl methacrylate (MEO₂MA) and oligo(ethylene glycol) methacrylate (OEGMA, M_n = 500 g·mol^-1) were synthesized by atom transfer radical polymerization (ATRP). Thermally induced aggregation of the co-polymers P(MEO₂MA-co-OEGMA) in aqueous solutions was investigated with dynamic light scattering (DLS), UV-Vis absorption, and transmission electron microscopy (TEM). In addition, the lower critical solution temperature (LCST) in aqueous solutions of P(MEO₂MA-co-OEGMA), and its change with respect to the composition of the copolymer, were obtained. The results indicate that the copolymers have an appreciably reversible thermal responsivity that can be attributed to a delicate balance between hydrogen bonds between the copolymers and water molecules and hydrophobic interactions of polymer segments. If the balance is broken, the polymers attain a new thermodynamic equilibrium by spontaneously changing the extent of aggregation. The LCST correlates linearly with the mole fraction of OEGMA units in the copolymer, and can be adjusted by changing the mole ratio of the two monomers.