Hydrogen-bonding induced abnormal microphase separation behavior of poly(ethylene oxide)-b-poly(tert-butyl acrylate-co-acrylic acid) block copolymers

Hydrogen (H)-bonding interaction was introduced into a poly(ethylene oxide)-b-poly(tert-butyl acrylate) (PEO-b-PtBA) block copolymer (BCP) by partial hydrolysis of tBA units into acrylic acid (AA) ones, in order to compete with the segregation force between the PEO and PtBA blocks. It was found that, as the hydrolysis degree (D-hyd) of the PtBA block increased, the structure of the PEO-b-P(tBA-co-AA) BCPs underwent the change from hexagonally packed cylindrical (HEX) into body-centered cubic spherical (BCC), then into HEX. The first HEX-to-BCC transition at lower D-hyd arose from the enhanced compatibility between the PEO and P(tBA-co-AA) blocks induced by the H-bonding interaction. When a PEO-b-P(tBA-co-AA) BCP with a HEX structure was heated, the BCC-to-HEX order-order transition (OOT), which was opposed to that in the common BCPs with an upper critical ordering temperature (UCOT) phase diagram, could be achieved because the H-bonding interaction was weakened at higher temperature. The second BCC-to-HEX at higher D-hyd was interpreted in terms of the enhanced chain rigidity and the chain arrangement approximately parallel to the microdomain interface induced by H-bonding interaction. The variation of the H-bonding interaction with temperature and the conformational change of the PEO block induced by H-bonding interaction were verified with FT-IR. (C) 2016 Elsevier Ltd. All rights reserved.