Shell-core-corona aggregates formed from poly(styrene)-poly(4-vinylpyridine) block copolymer induced by added homopolymer via interpolymer hydrogen-bonding

The solution behavior of poly(styrene)-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer with added poly(4,4′-oxydiphenylenepyromellitamic acid) (POAA) homopolymer in DMF is studied by dynamic light scattering (DLS), nuclear magnetic resonance (NMR), and transmission electron microscopy (TEM). It is found that coaggregation takes place when mixing PS-b-P4VP block copolymer and POAA homopolymer in DMF due to the strong interpolymer hydrogen-bonding between POAA chains and P4VP blocks. The coaggregation is a diffusion-controlled process and the complexation-induced aggregates are very stable. NMR measurements demonstrate that the resultant aggregates are much more swollen compared with typical amphiphilic block copolymer core-shell micelles. DLS measurements with Eu³⁺ as a probe combined with TEM observation, are employed to study the structure of the aggregates. Results reveal that the formed aggregates are core-shell spheres with the P4VP/POAA complexes as core and the PS blocks as shell when the weight ratio of POAA to PS-b-P4VP is lower. However, a core-shell-corona structure forms with a thin layer of POAA chains adsorbed on the initial core-shell aggregates with increasing weight content of POAA to 60%. Finally, possible mechanisms of the structural transitions are proposed.