Preparation and study of alkyl carbamylated polyrotaxanes with large hysteresis during sol–gel phase transition

Ethyl carbamylated polyrotaxane (ECPR) and propyl carbamylated polyrotaxane (PCPR) were prepared based on the reactions between ethyl/propyl isocyanate and polyrotaxane (PR) in anhydrous DMSO under an argon atmosphere. By changing the alkyl type and substitution ratio, the PR derivative with good water-solubility was obtained and its solutions showed reversible sol–gel phase transition. During the heating process, transition temperature from sol to gel decreased from 32 °C to 18 °C with increasing the solution concentration from 2.44% to 13.5%, while in the cooling process, all the gels with various concentration did not turn into sols until the temperature decreased to 1 °C, exhibiting large hysteresis between heating and cooling.