Phase Behavior of Double Zwitterionic Block Copolymers in Water: Morphology Transition through Concentration Dependent Selectivity of Water Partitioning

Abstract

Phase behavior of double zwitterionic diblock copolymers composed of a poly(carboxybetaine methacrylate) (PCB2) and a poly(sulfobetaine methacrylate) (PSB4) (PCB2 n -b-PSB4 m ) has been mapped out in aqueous solutions. Phase diagrams are constructed with polymer concentration, ϕ, ranging from 0.08 to 0.80 and PSB4 volume fraction in the PCB2 n -b-PSB4 m s, f PSB4 , ranging from 0.23 to 0.93 at 25 °C. PCB2 n -b-PSB4 m aqueous solutions show symmetric phase diagram above ϕ = 0.55, indicating that water is nearly neutral with respect to PCB2 and PSB4. The morphology transforms from columnar with PCB2 cylinders to lamellar to columnar with PSB4 cylinders with decreasing ϕ, and the phase boundaries exhibit a negative slope below ϕ = 0.45. The morphology transition is rationalized in terms of interfacial curvature modulation through the volume expansion of the PCB2 phase due to the selective water partitioning. The lyotropic mesophase of double hydrophilic block copolymers is a unique molecular compartment for hydrophilic molecules with low interfacial tension.

Cononsolvency-Induced Microphase Separation of Double Hydrophilic Poly(2-ethyl-2-oxazoline)–Polycarboxybetaine Diblock Copolymers in Water–Ethanol Mixtures

“…DHBC assemblies can offer biocompatibility, permeability for hydrophilic substances, and degradability compared to the assemblies of amphiphilic block copolymers . We reported a new type of DHBCs composed of two distinct zwitterionic polymers of poly­(carboxybetaine methacrylate) (PCB2) and poly­(sulfobetaine methacrylate) (PSB4). – The double zwitterionic block copolymers produced well-ordered mesoscale lattice structures in water through microphase separation while exhibiting morphology transition depending on the polymer concentration owing to selective water partitioning due to the difference in the water affinity of individual blocks. The microphase separation of concentrated block copolymer solutions and their concentration-dependent morphology transition using selective solvents have been extensively studied. – However, for aqueous solutions, these studies remained limited to Pluronic block copolymers comprising PEO and poly­(propylene oxide); thus, studying the microphase separation and morphology transition of zwitterionic polymer systems may offer a unique material class for biologically relevant applications.…”