Exploring the influence of the poly(4-vinyl pyridine) segment on the solution properties and thermal phase behaviours of oligo(ethylene glycol) methacrylate-based block copolymers: the different aggregation processes with various morphologies

Abstract

The assembly properties, thermal phase behavior and microdynamics of well-defined P(MEO₂MA-co-OEGMA)-b-P4VP, (poly(2-(2-methoxyethoxy)ethylmethacrylate)-co-poly(oligo(ethylene glycol) methacrylate))-b-poly(4-vinyl pyridine), in aqueous solution during heating are investigated in detail by dynamic light scattering (DLS), turbidity measurements, temperature-variable ¹H NMR and FTIR spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) and the perturbation correlation moving window (PCMW) technique. It is observed that the chain length of the relatively hydrophobic P4VP segment strongly affects the temperature-induced phase transition behavior of the block copolymers: the copolymers with shorter P4VP_7/10 segments exhibit an abrupt phase transition process, while the copolymer with longer P4VP₁₉ blocks presents a relatively gradual transition behavior. Moreover, the two systems with different P4VP segment lengths have different morphologies in aqueous solution: a single-chain globule for shorter P4VP_7/10 systems and a core–shell micelle consisting of a relatively hydrophobic P4VP core and a hydrophilic POEGMA-based shell for the longer P4VP₁₉ system. Analysis of spectral results clearly illustrates that the dehydration of the CO groups at the linkages between backbones and pendant chains predominates the sharp phase transition of P(MEO₂MA-co-OEGMA)-b-P4VP₁₀, while the dehydration of hydrophobic C–H groups on the side chains in P(MEO₂MA-co-OEGMA)-b-P4VP₁₉ leads to the continuous increase of the hydrodynamic diameter (D_h) upon heating.