Highly Asymmetric Lamellar Structure in Blends of Polystyrene-b-Poly(acrylic acid) Block Copolymers and Poly(4-vinylpyridine) Homopolymers Facilitated by Polyelectrolyte Complexation

Highly asymmetric lamellar (A-LAM) structures, in which the thickness of one layer is several times larger than that of the other, have potential applications in block copolymer (BCP) nanolithography. In this work, A-LAM structures were constructed via blending polystyrene-b-poly(acrylic acid) (PS-b-PAA) BCPs with poly(4-vinylpyridine) (P4VP) homopolymers, in which the PAA block and P4VP homopolymers could form polyelectrolyte complexes (PECs). The A-LAM structure with the thickness ratio (l(PS):l(PAA/P4VP)) of as high as 4.95:1 was achieved when the blending ratio of functional groups (n(AA):n(4VP)) was only 1:0.1 and the volume fraction of polystyrene (PS) (f(PS)) was 0.832. The molecular weight of P4VP homopolymers has little effect on the formation of the A-LAM structure. However, when the molecular weight of PS-b-PAA BCPs is too low or too high, A-LAM structures cannot be formed at such a high f(PS). We proposed that the competition between chain stretching of PS chains and the electrostatic cross-linking within PAA/P4VP phase is the determining factor for the formation of A-LAM structures.