Model block-graft copolymer via anionic living polymerization: Preparation and characterization of polystyrene-block-[poly(p-hydroxystyrene)-graft-poly(ethylene oxide)]-block-polystyrene

摘要

A model graft copolymer in which position of graft points was set to the center of a backbone molecule was prepared via anionic living polymerization. Polystyrene-block-poly(p-tert-butoxystyrene)-block-polystyrene (PSt-b-PBSt-b-PSt) was prepared by three-stage sequential addition. The tert-butyl group was removed from PBSt by hydrogen bromide to yield PSt-b-PHSt-b-PSt, having a poly(p-hydroxystyrene) (PHSt) block. The hydroxyl group of PHSt was reacted with dimeric potassium dianions of 1,1-diphenylethyl ene (DPE-K) or cumyl potassium (cumyl K) to yield the corresponding macromolecular initiators of PSt-b-PHSt(-)K(+)-b-PSt containing the potassium alkoxide ion of PHSt. The newly formed alkoxide groups and remaining initiators of DPE-K or cumyl K are capable of initiating the additionally introduced ethylene oxide (EO). Thus, two block-graft copolymers of polystyrene-block-[poly(p-hydroxystyrene)-graft-poly(ethyl oxide)]-block-polystyrene (PSt-b-(PHSt-g-PEO)-b-PSt) were prepared by a "grafting from" process (backbone initiation). A PSt-b-PHSt-b-PSt backbone (M-n = 1.7(5) x 10(5) by osmometry and M-w/M-n = 1.0(8) by GPC), and two PSt-b-(PHSt-g-PEO)-b-PSt block-graft copolymers (M-n = 2.4(5) x 10(5) by osmometry and M-w/M-n < 1.1(o) by GPC) had narrow molecular weight distributions. A relationship between nonquantitative metallation and spacing of the graft points on a backbone molecule was discussed in detail. Two benzene-cast films formed clear microphase-separated structures of lamellar structure. The dependence of composition on the morphology of the block-graft copolymers was found to differ from that of common block copolymers. A degree of crystallinity of PEO segment and lamellar thickness of PEO phase serving as graft molecule were also found to differ from those of homo PEO and/or PEO segment in common block copolymer. (C) 1998 John Wiley & Sons, Inc. [References: 50]