The Influence of a Phase Transition in Poly(oxyethylene)/Poly(oxypropylene)/Poly(oxyethylene) Block Copolymer Surfactants on the Properties of Material Adsorbed from Dilute Aqueous Solution

In this study the adsorption of poloxamer block copolymer surfactants to polystyrene latex has been studied at a range of temperatures. It has been noted previously that the adsorption first falls, then rises and falls again as the temperature is increased, due to the existence of a phase transition in aqueous solutions of these surfactants at specific temperatures, which may be a critical micelle temperature. The present study shows that the hydrophobicity of the surface changes in a manner related to the amount of poloxamer adsorbed (i.e. is greatly influenced by the temperature of adsorption in relation to the transition temperature). The coating layer thickness, however, is essentially unchanged by the temperature of adsorption (i.e. not related to the amount adsorbed), but is influenced by the temperature at which the sizing was undertaken. This is due to dehydration of the poly (oxyethylene) with increasing temperature. The data presented here provide a possible explanation for the changes in biological distribution of poloxamer coated particles which occur when they are injected into animals.     

The Influence of Diphenyl Siloxane on Morphology and Physical Properties in the Poly(Imide Siloxane)(PIS) Copolymer

Various numbers of diphenyl-siloxane groups were incorporated in α,ω-bis(aminopropyl)polydimethylsiloxane (APPS) to prepare α,ω-bis(aminopropyl)-polydimethyldiphenylsiloxane (APPPS) oligomers of three different number-average molecular weights(Mn = 547,772,1210 g mol⁻¹).These APPPS oligomers were than used, together with 3,3′,4,4′-bezonphenone tetracarboxylic dianhydride (BTDA) and 2-2′-bis[4-(3-aminophenoxy)phenyl] sulfone (m-BAPS), to synthesize a series of APPPS containing poly(imide siloxane) (PIS) copolymers. Microstructural studies showed that at certain APPPS content, a critical microphase separation point existed, beyond which, microphase separation began to develop. This critical point of microphase separation was found to be affected by the Mn of the APPPS oligomers (8.0, 4.3 and 2.1 mol% for Mn of 547, 772 and 1,210 g mol⁻¹, respectively). Diphenyl-siloxane significantly improved compatibility between polyimide and polysiloxane segments. Physical studies showed that the introduction of diphenyl siloxane changed the thermal stabilities and mechanical properties of the PIS copolymers. These findings have potential applications for design purposes in engineering polymers.     

Phase transition in swollen gels: 7. Effect of charge concentration on the temperature collapse of poly(N,N-diethylacrylamide) networks in water

The swelling and mechanical behaviour of gels of the copolymer of diethylacrylamide (DEAAm) with a small quantity of sodium methacrylate (mole fraction x_MNa = 0–0.067) swollen in water was investigated in the temperature range 1–80°C. For networks in the range x_MNa > 0.0095 phase transition was observed; both the critical transition temperature T_c,c and the extent of the collapse Δ_c increase with increasing x_MNa. The formation of associations in the collapsed state contributes to the overall extent of the transition; these structures give rise to stable turbid gels at elevated temperatures. Evidence for the formation of ‘associated’ structures is also supported by the observed independence of cloud temperature of the concentration of DEAAm, c, in the polymerization DEAAm-water mixture without the crosslinking agent in the range c = 0.5–80 vol%. While PDEAAm solutions are formed in the range c < 4.5–6 vol%, physical gels arise at higher concentrations.