Control of Self-Assembled Structures in Binary Mixtures of A−B Diblock Copolymer and A−C Diblock Copolymer by Changing the Interaction between B and C Block Chains

Abstract

Self-assembled structures in solvent-cast mixtures of polystyrene-block-poly(ethylenepropylene) (PS−PEP) and polystyrene-block-(partially hydrogenated polyisoprene) (PS−HPI) were investigated by small-angle X-ray scattering and transmission electron microscopy. Various self-assembled structures were observed in the solution-cast films, depending upon the degree of hydrogenation of the HPI block of the PS−HPI. The microdomain structure of PS domains and domains composed of PEP and HPI (called “rubber domains” hereafter) was first formed at relatively low polymer concentrations during the solvent-casting process over the whole range of the hydrogenation in our experiments. Subsequently, at a higher concentration during the process, phase separation between PEP and HPI in the rubber domains was observed in mixtures with medium and high hydrogenation. For mixtures with low hydrogenation, repulsive interactions between PEP and HPI become large enough to cause the segregation between PEP and HPI, which leads first to the modulation of the interface between the PS domain and the rubber domain and eventually to the macrophase separation between PS−PEP and PS−HPI, during the solvent evaporation process. Thus, observed macrophase-separated structure is a consequence of a two-step phase separation, i.e., a microphase separation followed by a macrophase separation. The development of those patterns was controlled only by the degree of the repulsive segmental interaction between PEP and HPI, i.e., the degree of the hydrogenation of HPI.

Micro-vs.macro-phase separation in binary blends of poly(styrene)-poly(isoprene) and poly(isoprene)-poly(ethylene oxide) diblock copolymers

“…In comparison to ref. [3] our system has a relatively large interaction parameter between the A and C blocks, and therefore the governing macro-phase separation is not a surprise.…”

“…To date, there has been little experimental work on such systems. Kimishima et al [3] have investigated the phase behaviour of 50:50 blends of a poly(styrene)-poly(ethylene-co-propylene) diblock copolymer with one of a series of poly(styrene)-hydrogenated poly(isoprene) copolymers. The degree of hydrogenation of the latter was varied (100% hydrogenation corresponds to PEP), and the phase separation process studied for solvent-cast structures using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM).…”

Silica reinforced triblock copolymer gels

“…Changing the chemical nature of one or both the component blocks can have dramatic effects on the self-assembly of the resultant material. Modification of the polydiene block in polystyrene-polydiene-polystyrene block copolymers has received much attention [35][36][37][38][39][40][41], including the selective hydrogenation of the midblock. Because the transition temperature from a rubbery gel to a plastic fluid (T P ) is too low for many applications, polystyrene has been either replaced by a higher T g block [42][43][44][45] or chemically modified [46][47].…”

Evolution of Block Copolymer Lithography to Highly Ordered Square Arrays

“…In terms of modularity, simple blending of different diblock copolymers, such as A-B/B-C and A-B/C-D alloys, would seem to be attractive for combining physical properties and broadening the processing window (15)(16)(17). However, uniform long-range order has not been achieved in thin-film blends of block copolymers (18) because of the overwhelming tendency of such mixtures to exhibit macrophase separation (19)(20)(21)(22).…”