COOPERATIVITY OF THE COIL-GLOBULE TRANSITION IN A HOMOPOLYMER - MICROCALORIMETRIC STUDY OF POLY(N-ISOPROPYLACRYLAMIDE)

The temperature-induced intramolecular coil-globule transition in poly (N-isopropylacrylamide) has been studied by microcalorimetry to invest igate the cooperativity of this transition. Measurements were performe d in the presence of sodium dodecyl sulfate (SDS) which prevents the p olymer from aggregation both in the coil and in the globule state. It has been shown that the effective (van't Hoff) enthalpy of transition of a cooperative unit is 120 times less than the calorimetric enthalpy of a polymer molecule. This means that a coil-globule transition in t his polymer is not an ''all-or-none'' process and occurs independently in cooperative units (''domains'') which are 120 times smaller than t he polymer molecule and have a molecular weight about 6 x 10(4).