Scanning densitometric and calorimetric studies of poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) triblock copolymers (poloxamers) in dilute aqueous solution

The phase transitions of poloxamers and polyoxypropylene, in dilute aqueous solution (0.5% w/v), were detected using high sensitivity differential scanning calorimetry (HSDSC) at a scan rate of 60Khr(-1). The molecular weights of the polymer samples range from 725 to 14000. The solutions of the poloxamers with a polyoxyethylene content of greater than 10% of the overall molecular weight are optically transparent over the temperature of the phase transition and the solutions of the polyoxypropylene samples are optically transparent below the phase transition and turbid at elevated temperatures. The temperature (T-m) at which the differential excess heat capacity (Cp,m) is a maximum decreases with increasing polyoxypropylene content for both poloxamers and polyoxypropylene samples. Multiple linear regression analysis of calorimetric parameters show strong relationships to the polyoxypropylene content of the poloxamers. The observed phase transitions for both poloxamers and polyoxypropylene samples are reversible and unaffected by scan rate (10, 30 and 60Khr(-1)) and hence show no obvious kinetic limitations.