Semi-crystalline polymethylene-b-poly(acrylic acid) diblock copolymers in selective solutions: Morphological and crystallization evolution dependent on calcium chloride

Although crystallization-driven self-assembly (CDSA) of semi-crystalline block copolymers (BCPs) affords one of the most promising approaches to tailor novel asymmetric nanostructures, crystalline BCPs' response to external interactive additives remains less understanding. In the present work, the interactive disturbance effect of CaCl2 additive on CDSA of semi-crystalline polymethylene-b-poly(acrylic acid) diblock copolymers (PM-b-PAA) was systematically studied. It was found that pre-formed crystalline disklike BCP micelles obtained from CDSA could be drawn closely and bridged by Ca2+ cations, leading to merging and crystallization of PM cores as well as BCP morphological evolution. Particularly, an increasing epitaxial crystallization together with morphological transition from disklike BCP micelles to worm-like micelles, incomplete networks, and reticulate aggregates was successively observed as the stoichiometric ratio of [Ca2+]/[COOH] increased from 0 to 2. The complexation between Ca2+ and ionized carboxylic groups on the PAA segments was evidenced by Fourier transform infrared (FTIR) measurement, and could be tuned by manipulating solvent quality, solution pH, and block composition. In addition to interactive disturbance effect, pronounced saltingout effects, displayed at excessive amount of CaCl2 salt, resulted in dehydration and serious aggregation of BCPs.