A STUDY OF CHAIN DYNAMICS IN WATER-SWOLLEN GELS OF POLY(ETHYLENE OXIDE) DIALKYL ETHERS USING NMR AND DIFFERENTIAL SCANNING CALORIMETRY

Water swollen gels of (unbranched) dialkyl ethers (n = 16, 17, 18, 20 and 21) of poly(ethylene oxide) (M(n)BAR = 10000, 20000 and 30000) have been investigated using NMR spectroscopy and differential scanning calorimetry (DSC). Aggregates of the alkyl segments were found to undergo a 'solid/liquid' transition at a temperature approximating the melting point of an unbranched hydrocarbon about three to four carbon atoms shorter than the alkyl chain. Below the transition temperature, the alkyl component gave a broad NMR line whose second moment was approximately one-quarter that of a crystalline alkane of similar length. The enthalpy of the transition was approximately one-third that of the corresponding unbranched alkane. These results indicate a partially crystalline structure for the 'solid' aggregates.