Cononsolvency refers to the phenomenon in which a polymer collapses in mixtures of good solvents with specific compositions. The coil-to-globule-to-coil transitions of a zwitterionic polymer, poly(2-[(N-2-methacryloyloxyethyl-N,N-dimethyl)ammonio]acetate) (PCB2), in water, ethanol, and water–ethanol mixed solvents were investigated and compared with those of poly[2-(methacryloyloxy)ethyl phosphorylcholine] (PMPC). PCB2 showed cononsolvency in water–ethanol mixed solvents with specific ethanol volume fractions. The reentrant square well-type sharp coil–globule transition was reproduced by a statistical mechanical model involving competitive hydrogen bonding and cooperative hydration. PCB2 showed a broader cononsolvency range than PMPC because of its lower association constants of water and ethanol and the marked competition for hydrogen bonding. The zwitterion-specific cononsolvency characteristics were rationalized with the electrostatic potentials and van der Waals energies of the zwitterions.

共溶性是指聚合物在具有特定组成的良好溶剂的混合物中坍塌的现象。两性离子聚合物的线圈到小球到线圈的转变，poly(2-[( N -2-methacryloyloxyethyl- N,N-二甲基）铵]乙酸盐）（PCB2），在水，乙醇和水 - 乙醇混合溶剂中进行了研究，并与聚[2-（甲基丙烯酰氧基）乙基磷酸胆碱]（PMPC）进行了比较。PCB2 在具有特定乙醇体积分数的水-乙醇混合溶剂中表现出共溶性。通过涉及竞争性氢键和协同水合作用的统计力学模型再现了可重入方孔型尖线圈-小球转变。PCB2 显示出比 PMPC 更宽的共溶范围，因为它具有较低的水和乙醇缔合常数以及氢键的显着竞争。两性离子特定的共溶解特性与两性离子的静电势和范德瓦尔斯能量合理化。