EFFECTS OF HOMOPOLYMERS ON THE GEL FORMATION IN AQUEOUS BLOCK COPOLYMER SOLUTIONS

The gel formation in aqueous EO99-PO65-EO99 solutions has been studied (EO and PO being ethylene oxide and propylene oxide, respectively). In particular, the effects of the homopolymers (i.e., PEO and PPO) were investigated in detail. It was found that PEO of intermediate molecular weight causes the gel to ''melt'', at an amount of homopolymer which depends on the copolymer concentration. The efficiency of PEO in inducing the gel melting increases with its molecular weight, but at very high PEO molecular weights, phase separation, rather than gel melting, occurs. The gel melting behavior was found also for a cationic polyelectrolyte (PDADMAC). PPO, on the other hand, tends to increase the stability region of the gel, depending, however, on the PPO molecular weight. These findings are reported by means of rheological data and detailed phase diagrams, and discussed in terms of the temperature-dependent micellization occurring in this copolymer system.