Inverted Cylindrical Microdomains from Binary Block Copolymer Blends Capable of Hydrogen Bonding

Abstract

A binary blend of polystyrene-block-poly(2-vinylpyridine) copolymer (PS-b-P2VP) and polystyrene-block-poly(4hydroxystyrene) copolymer (PS-b-PHS) was studied to obtain an inverted cylindrical morphology with cylinders consisting of the major block. Both neat block copolymers with slightly asymmetric volume fraction of the PS block ( f PS ∼ 0.65) showed lamellar microdomains. The blends showed phase transformation from lamellae to inverted cylinders because of hydrogen bonding between nitrogen in P2VP and hydroxyl group in PHS chains. The formation of the inverted cylinders depends on f PS in the blend and the molecular weight ratio (r) of PS-b-P2VP to PS-b-PHS because both parameters affect the interfacial curvature arising from the hydrogen bonding and chain stretching near the interface.

Truly “Inverted” Cylinders and Spheres Formed in the A(AB)3/AC Blends of B/C Hydrogen Bonding Interactions

“…How to expand the spherical and cylindrical phase regions to significantly larger f is of particular interest, especially leading to the formation of "inverted" cylinders or even spheres with f > 0.5. 26,27 Much attention has been paid both experimentally and theoretically to enlarging the spherical and cylindrical region in block copolymers. One simple way is to introduce an additional factor to amplify the effect of spontaneous curvature bending toward one block, for example, asymmetric architecture.…”

“…47 An efficient way to suppress the occurrence of macrophase separation is to introduce attractive interactions between the two different copolymers such as hydrogen bonding. 26,27,48,49 Kim and co-workers have prepared a series of AB/AC binary blends composed of long polystyrene-bpoly(2-vinylpyridine) copolymers (PS-b-P2VP) and short polystyrene-b-poly(4-hydroxystyrene) copolymers (PS-b-PHS) with hydrogen bonding interaction between P2VP and PHS blocks. 27,50−53 The hydrogen bonds between B and C blocks make the long B blocks compressed and the short C blocks stretched to favor the interaction energy, leading to an amplified effect of spontaneous curvature toward A blocks.…”

“…As a result, the "inverted" cylinder with f A ≈ 0.65 was successfully obtained, and a volume fraction of spheres approaching 0.5 was achieved. 27,50 Because of the low intrinsic spontaneous curvature of linear diblock copolymer, the enlargement of the spherical and cylindrical regions in the binary AB/AC blend is still limited. For example, a truly "inverted" spherical phase has not been achieved in the binary blend.…”

“…To be specific, the maximal f of BCC and C 6 of AB diblock copolymer is about 0.15 and 0.31, respectively, when χN = 50. How to expand the spherical and cylindrical phase regions to significantly larger f is of particular interest, especially leading to the formation of “inverted” cylinders or even spheres with f > 0.5. , …”

“…The previous studies have demonstrated that the smaller the ratio of the short copolymer to the long copolymer, the more the effect of spontaneous curvature is raised. , However, at the same time, the possibility for the macrophase separation to occur is enhanced by the increasing ratio . An efficient way to suppress the occurrence of macrophase separation is to introduce attractive interactions between the two different copolymers such as hydrogen bonding. ,,, Kim and co-workers have prepared a series of AB/AC binary blends composed of long polystyrene- b -poly­(2-vinylpyridine) copolymers (PS- b -P2VP) and short polystyrene- b -poly­(4-hydroxystyrene) copolymers (PS- b -PHS) with hydrogen bonding interaction between P2VP and PHS blocks. ,− The hydrogen bonds between B and C blocks make the long B blocks compressed and the short C blocks stretched to favor the interaction energy, leading to an amplified effect of spontaneous curvature toward A blocks. As a result, the “inverted” cylinder with f A ≈ 0.65 was successfully obtained, and a volume fraction of spheres approaching 0.5 was achieved. , …”