Chain Architecture and Hydrogen Bonding Induced Co-Ordering and Segregation of Block Copolymer/Graft Copolymer Blends

Abstract

We investigated the effects of chain architecture and hydrogen-bonding interaction on the phase behavior of binary mixtures containing nearly symmetric polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer and highly asymmetric polystyrenegraf t-poly(acrylic acid) (PS-g-PAA) graft copolymer. When PS-g-PAA was added to PS-b-P2VP, hydrogen bonds between PAA and P2VP chains improved the miscibility of the copolymers and facilitated localization of PS-g-PAA at the PS-b-P2VP interface, which reduced the interfacial free energy of the blends. However, positioning PS-g-PAA with one PS main chain and two PAA grafted chains at the PS-b-P2VP interface increased the stretching free energy of PS-b-P2VP. Consequently, the interfacial coverage of PS-g-PAA reached saturation. Residual PS-g-PAA was segregated into the PS microdomains formed by PS-b-P2VP to regain translational entropy and reduce the stretching free energy. When the molecular weight ratio of PS-b-P2VP to PS-g-PAA (R) was smaller than 8, PS-g-PAA could not swell the PS microdomains formed by PS-b-P2VP. Therefore, the morphology of PS-b-P2VP/PS-g-PAA blends remained lamellar. By contrast, when R > 8, PS-g-PAA effectively swelled the PS microdomains formed by PS-b-P2VP. This behavior amplified the asymmetry effect caused by the branched-chain architecture of PS-g-PAA on altering the interfacial curvature of PS-b-P2VP. Consequently, the morphology of the blends transformed into a cylindrical structure.

Impact of Composition and Placement of Hydrogen-Bonding Groups along Polymer Chains on Blend Phase Behavior: Coarse-Grained Molecular Dynamics Simulation Study

“…Similar morphological transitions between ordered phases from lamellar to cylindrical were also noted in experiments on blends of polystyrene- block -poly­(2-vinylpyridine) (PS- b -P2VP) block copolymers and polystyrene- graft -poly­(acrylic acid) (PS- g -PAA) graft copolymers at high PS- g -PAA molecular weights . These were linked to the segregation of the PS- g -PAA polymer at the interface of PS- b -P2VP lamellar phase caused by H-bonding between PAA and P2VP as well as localization of excess PS- g -PAA in the PS microdomain leading to a change in interfacial curvature to form cylindrical phases …”

“…Further, both the strength and density of hydrogen bonds dictated the formation of hierarchical microstructures such as parallel and perpendicular lamellae-in-lamellae in theoretical studies of binary AB and B′C diblock copolymer blends, where BB′ hydrogen bonds were modeled as electrostatic dipole–dipole interactions using the Yukawa potential . Similar morphological transitions between ordered phases from lamellar to cylindrical were also noted in experiments on blends of polystyrene- block -poly­(2-vinylpyridine) (PS- b -P2VP) block copolymers and polystyrene- graft -poly­(acrylic acid) (PS- g -PAA) graft copolymers at high PS- g -PAA molecular weights . These were linked to the segregation of the PS- g -PAA polymer at the interface of PS- b -P2VP lamellar phase caused by H-bonding between PAA and P2VP as well as localization of excess PS- g -PAA in the PS microdomain leading to a change in interfacial curvature to form cylindrical phases …”

“…76 Similar morphological transitions between ordered phases from lamellar to cylindrical were also noted in experiments on blends of polystyrene-blockpoly(2-vinylpyridine) (PS-b-P2VP) block copolymers and polystyrene-graf t-poly(acrylic acid) (PS-g-PAA) graft copolymers at high PS-g-PAA molecular weights. 77 These were linked to the segregation of the PS-g-PAA polymer at the interface of PS-b-P2VP lamellar phase caused by H-bonding between PAA and P2VP as well as localization of excess PS-g-PAA in the PS microdomain leading to a change in interfacial curvature to form cylindrical phases. 77 The above studies demonstrate that hydrogen-bonded polymer blends offer a rich phase space where the polymer segregation strength (via the choice of polymer chemistries) as well as the strength and placement of H-bonding groups can alter the blend structure and properties.…”

“…77 These were linked to the segregation of the PS-g-PAA polymer at the interface of PS-b-P2VP lamellar phase caused by H-bonding between PAA and P2VP as well as localization of excess PS-g-PAA in the PS microdomain leading to a change in interfacial curvature to form cylindrical phases. 77 The above studies demonstrate that hydrogen-bonded polymer blends offer a rich phase space where the polymer segregation strength (via the choice of polymer chemistries) as well as the strength and placement of H-bonding groups can alter the blend structure and properties. However, in these experimental studies, the individual role of polymer segregation strength and the strength and placement of H-bonding groups toward the resulting structure and morphology in hydrogenbonded polymer blends has not been isolated.…”

Competitive Effects of Hydrogen Bonds and Molecular Weights on the Phase and Crystallization Behaviors of Binary Block Copolymers

“…This limitation can be solved by adjusting the intermolecular forces between distinct components. For example, self-assembly of block copolymer blends that contain hydrogen bonds has attracted substantial attention. − The enthalpic contribution outweighs the entropic penalty resulting from chain packing and distribution, leading to the formation of well-organized nanostructures in which dissimilar chains share common microdomains. Furthermore, the intermolecular interaction can serve as another parameter for creating a new structure or expanding the phase boundary of a specific microdomain morphology.…”