LYOTROPIC LIQUID CRYSTALLINITY IN AMPHIPHILIC BLOCK-COPOLYMERS - TEMPERATURE EFFECTS ON PHASE-BEHAVIOR AND STRUCTURE FOR POLY(ETHYLENE OXIDE)-B-POLY(PROPYLENE OXIDE)-B-POLY(ETHYLENE OXIDE) COPOLYMERS OF DIFFERENT COMPOSITION

The phase behavior and structure of binary amphiphilic polymer-water s ystems have been studied as a function of polymer concentration and te mperature for three poly(ethylene oxide)-b-poly(propylene oxide)-b-pol y(ethylene oxide) (PEO-PPO-PEO) copolymers of different composition, O )(6)(PO)(34)(EO)(6)(L62),(EO)(13)(PO)(30)(EO)(13) (L64), and (EO)(37)( PO)(58)(EO)(37) (P105), by using H-2-NMR and small-angle X-ray scatter ing (SAXS). The number of lyotropic liquid crystalline (LLC) phases fo rmed increases with the poly(ethylene oxide) content and the molecular weight of the polymers in the order L62 < L64 < P105. Only a lamellar LLC phase is formed by L62, while P105 is capable of self-assembling with increasing polymer concentration into (body-centered close-packed ) cubic, hexagonal, and lamellar LLC phases. Upon heating, the LLC pha ses of the L62-water and L64-water systems swell with water; no such s welling is detected for the P105-water system. The thermal stability o f the LLC regions increases in the order cubic < hexagonal < lamellar and L62 < L64 < P105. An increase of the temperature results in a decr ease in the interfacial area and an increase in the periodicity of the L62 and L64 lamellae. In the P105-water system, the structural dimens ions in the lamellar and hexagonal LLC regions are not much affected b y temperature. Both the lamellar periodicity and the block copolymer i nterfacial area decrease with increasing polymer content, for all poly mers. The factors influencing the self-assembly mode of amphiphilic co polymers are discussed, and the phase behavior of the PEO-PPO-PEO copo lymers in water is compared to that of nonionic surfactants.