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.

Keywords:

• block copolymer/homopolymer
• hydrogen-bonding
• nanophase-separated structures
• self-assembly
• solvent annealing

Acknowledgments

The authors would like to acknowledge financial support of the National Science Foundation for Distinguished Young Scholars of China (Grant No. 51025517), the Innovative Group Foundation of NSFC (Grant No. 50721062), and the National 973 Project of China (2007CB607606).