Effect of Composition Distribution on Microphase-Separated Structure from BAB Triblock Copolymers

Abstract

The effects of composition distribution on microphase-separated structures formed by monodisperse BAB triblock copolymers were investigated. Monodisperse nine parent BAB triblock copolymers consisting of polystyrene for A and poly(2-vinylpyridine) for B were prepared by anionic living polymerization. These nine copolymers were designed such that polystyrene volume fraction, φs, ranged from 0.1 to 0.9, and they were blended to produce samples with various composition distributions but with constant average composition at φ s of 0.5. Periodic simple alternating lamellar structures were observed for solvent cast and well-annealed blend films as long as composition distribution is relatively low. It has been found that microdomain spacing increases with increasing composition distribution of copolymer samples up to 1.25 in terms of M w(S)/Mn(S), where Mw(S) and Mn(S) are weight-average and number-average molecular weights of polystyrene blocks, respectively, as was the case of the AB diblock copolymer system, though the increment is larger for triblock than diblock. Furthermore, it was clarified that triblock copolymer tends to macrophase separate into several regular microphase-separated structures more easily than diblock copolymer.

Polydispersity effects in poly(isoprene-b-styrene-b-ethylene oxide) triblock terpolymers

“…Listak et al 42 recently reported that polydispersity stabilized a hexagonally perforated lamellar mesostructure in poly͑styrene-b-methyl acrylate͒ diblock copolymers; this structure is considered metastable in nearly monodisperse materials. 45,46 Polydispersity may also induce macrophase separation into multiple coexisting morphologies, 22,25,30 as reported in homopolymer/ polydisperse diblock 10 and multicomponent diblock/diblock blends, [35][36][37] and as predicted for some polydisperse materials with continuous molecular weight distributions ͑MWDs͒.…”

“…A flurry of theoretical [25][26][27][28][29][30][31][32][33][34] and a͒ Authors to whom correspondence should be addressed: Electronic addresses: hillmyer@umn.edu and bates@cems.umn.edu. experimental 11,27,[35][36][37][38][39][40][41][42][43] studies of polydispersity effects in AB block copolymers followed Bendejacq et al's report. This topic recently has been reviewed, 44 and only a brief summary is provided below.…”

“…The reduction in elastic free energy is also accompanied by an increase in the height of end-grafted polymer brushes 17 and an increase in the domain period in the melt. [27][28][29]31,33,[35][36][37]43 Furthermore, the distribution of chain lengths present in polydisperse materials may stabilize additional ordered mesostructures. Listak et al 42 recently reported that polydispersity stabilized a hexagonally perforated lamellar mesostructure in poly͑styrene-b-methyl acrylate͒ diblock copolymers; this structure is considered metastable in nearly monodisperse materials.…”

Neutron Reflectometry on Interfacial Structures of the Thin Films of Polymer and Lipid

“…The previous morphological observation for polydisperse block copolymers in composition and molecular weight clarified that lamellar domain spacing increases linearly with increasing the polydispersity in molecular weight or composition. [25][26][27] However, these results suggested only speculation on spatial distribution of the component block chains in microdomains. Thus, the segmental distribution of the component chains in block copolymer blends was directly examined by neutron reflectometry.…”

“…The evaluated segmental distribution in the block copolymer blend supported the previous morphological observations well. [25][26][27] Interdiffusion Behavior of a Cyclic Polystyrene Compared with a Linear Homologue A cyclic polymer has attracted much attention from the aspects of polymer physics due to its unique feature in molecular architecture with no chain ends. The existence of chain ends is essential for polymer dynamics such as diffusion and relaxation of a linear polymer chain in melt in the context of reptation theories.…”