PHASE-BEHAVIOR STUDIES WITH POLY(ETHYLENE-CO-METHACRYLIC ACID) AT HIGH-PRESSURES

Experimental cloud-point data are reported for poly(ethylene-co-3.9 mo l% methacrylic acid) (EMAA(3.9)) in ethylene, propane, butane, butene, and dimethyl ether (DME) to 250 degrees C and 2500 bar. The cloud-poi nt data for both EMAA(3.9) and poly(ethylene-co-3.9 mol% acrylic acid) are virtually identical suggesting that the structural differences be tween these two acid copolymers does not have a significant effect on phase behaviour. Cloud-point data are presented that demonstrate the i mpact of methacrylic acid (MAA) content for EMAA copolymers with 0, 3. 1, 3.9, and 5.4 mol% MAA in butane, butene, and DME. The region of mis cibility in butane and butene decreases significantly with temperature and with increasing copolymer acid content due to dimerization of the acid groups. However, the region of miscibility in DME increases slig htly with MAA content due to the cross association with the acid repea t units. Cloud-point data are reported on the impact of DME and ethano l on the phase behaviour of poly(ethylene-co-3.1 mol% methacrylic acid ) (EMAA(3.1)) in butane. At low concentrations, ethanol is a more effe ctive cosolvent since it has two sites that can participate in hydroge n bonding with MAA. The impact of both cosolvents diminishes rapidly w ith increasing cosolvent concentration once all the acid sites in EMAA are saturated with cosolvent. (C) 1997 Elsevier Science Ltd.