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

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 P4VP7/10 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 P4VP7/10 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 (Dh) upon heating.