Nanophase-Separated Structures of Hydrogen-Bonded Interpolymer Complexes of AB Block Copolymer/C Homopolymer in Thin Film with Variable Blending Composition upon Solvent Annealing

Abstract

The self-assembly behavior of hydrogen-bonded interpolymer complexes of poly(styrene)-b-poly(4-vinylpyridine) (PS-b-P4VP)/poly(4,4′-oxydiphenylenepyrome llitamic) acid (POAA) in thin films with variable POAA weight content upon solvent annealing in benzene/N-methy1-2-pyrrolidone (NMP) mixture vapor was investigated. It was found that when the PS-b-P4VP/POAA thin film blends were annealed in a benzene/NMP (0.97/0.03, in volume) mixture vapor, the thin film blends with a high POAA wt%, above 40%, exhibited a mixture of spherical and rod-like microphase-separated structure, while the thin film blends with a POAA wt% lower than 40% were homogenous. For the blends in thin films with a POAA wt% of less than 40%, the benzene/NMP (0.97/0.03, in volume) vapor was highly miscible with both the PS blocks and P4VP/POAA complexes, which led to decrease of segregated repulsion between the two components and no obvious microphase separation could be achieved. When the PS-b-P4VP/POAA blends in thin films with POAA wt% of 20%, 50%, and 70% were annealed in benzene/NMP with a volume ratio of 0.99/0.01, obvious microphase separation was observed for all films due to increasing PS-selectivity of the mixture vapor. However, the phase structure of blends in thin film with POAA wt% of 50% and 70% consisted of PS microdomains dispersed within the P4VP/POAA matrix, while the blends in thin film with POAA wt% of 20% revealed an opposite phase structure with P4VP/POAA microdomains surrounded by the PS matrix. The transition could be attributed to the increasing free volume of PS domains relative to that of P4VP/POAA due to swelling by benzene vapor during annealing.