SCANNING CALORIMETRIC STUDIES OF POLY(ETHYLENE OXIDE) POLY(PROPYLENE OXIDE) POLY(ETHYLENE OXIDE) TRIBLOCK COPOLYMERS (POLOXAMERS) AND POLY(PROPYLENE OXIDE) IN DILUTE AQUEOUS-SOLUTION

The phase transitions of poloxamers and polyoxypropylene, in dilute aq ueous solution (0.5% w/v), were detected using high sensitivity differ ential scanning calorimetry (HSDSC) at a scan rate of 60Khr(-1). The m olecular weights of the polymer samples range from 725 to 14000. The s olutions of the poloxamers with a polyoxyethylene content of greater t han 10% of the overall molecular weight are optically transparent over the temperature of the phase transition and the solutions of the poly oxypropylene samples are optically transparent below the phase transit ion and turbid at elevated temperatures. The temperature (T-m) at whic h the differential excess heat capacity (Cp,m) is a maximum decreases with increasing polyoxypropylene content for both poloxamers and polyo xypropylene samples. Multiple linear regression analysis of calorimetr ic parameters show strong relationships to the polyoxypropylene conten t of the poloxamers. The observed phase transitions for both poloxamer s and polyoxypropylene samples are reversible and unaffected by scan r ate (10, 30 and 60Khr(-1)) and hence show no obvious kinetic limitatio ns.