Polymethylene-b-poly (acrylic acid) diblock copolymers: Aggregation and crystallization in the presence of CaCl2

Crystalline block copolymers tend to display a peculiar and intriguing behavior upon the external additives. In this work, we systematically investigated the self-assembly and crystallization behavior of polymethylene-b-poly (acrylic acid) crystalline diblock copolymer (PM-b-PAA, M(93)A(94)) in the presence of calcium chloride (CaCl2). When molar ratio between CaCl2 and constituent deprotonated carboxyl group (COO-) of M(93)A(94) (n, n = n(CaCl2)/n(COO)(-)) increased from 1:2 to 5:1, M(93)A(94) micelle gradually formed hexagonal and reticular aggregation. Further investigation of PM-b-PAA crystalline feature indicated that the crystallization of PM block was initially restrained by coordination interaction between calcium ion (Ca2+) and carboxylate anion (COO-), and then the crystallization of PM block was promoted when more Ca2+ was added (n(CaCl2)/n(COO)(-) reach to 5:1 and 13.5:1). Moreover, the conductivity measurement indicated that, when n (n(CaCl2)/n(COO)(-)) = 4, the coordination interaction between Ca2+ and COO- was saturated, namely CaCl2/PAA formed tetradentate complex, and this information concerning the coordination geometry was highly consistent with the simulative calculation.