Co-aggregation process of poly(ethylene oxide)-b-polybutadiene/poly(acrylic acid) based on evolution of interpolymer hydrogen bonding in solutions

The co-aggregation process of a diblock copolymer poly(ethylene oxide)-block-polybutadiene (PEO-b-PB) and a homopolymer poly(acrylic acid) (PAA) in solutions was studied. The number-average molecular weights of both the PEO and PB blocks are 5100 g/mol; the weight-average molecular weight of PAA is ∼2000 g/mol. The co-aggregation was induced by adding a PB selective solvent (i.e., alkane or cycloalkane) into the THF solution of the two polymers, with the processes characterized by turbidity, 1H NMR, dynamic light scattering, and microscopy experiments. During the selective solvent titration, the solution underwent a macro-phase separation that was mainly related to PAA, followed by a micro-phase separation that corresponded to the formation of vesicles with the shell of PB block and the core of PAA/PEO complex. The experimental results indicated that the evolution of interpolymer hydrogen bonding complexation between the PAA and PEO blocks determined the co-aggregation process. The loose and soluble interpolymer complex could be formed at rather low selective solvent content (f). The complexation was enhanced with increasing f, resulting in “redissolving” the PAA-rich domains in the blend solutions. Afterwards, the more compact PAA/PEO complex chemically linked with a soluble PB block acted as the building blocks to form the vesicles at higher f.