Thermosensitive supramolecular hydrogels from atom transfer radical polymerization of polypseudorotaxanes self-assembled by triblock copolymer and α-cyclodextrins

We report novel thermosensitive supramolecular hydrogels with tunable crosslinking networks by using polypseudo-rotaxanes (PPRs) as macroinitiators in atom transfer radical polymerization and polyethylene glycol diacrylate (PEGDA) as bridge units. The PPRs were prepared by supramolecular self-assembly of α-cyclodextrin or 2-bromoisobutyryl bromide modified α-cyclodextrin (α-CD-BIBB) and triblock copolymer of F127 with bromopropionyl bromide terminals. The supramolecular hydrogels possess the crystal structure of inclusion complexes (ICs) and thermo-sensitive properties. The addition of mono-functional 2-hydroxyethyl methacrylate (HEMA) can enhance gelation. The swelling ratio (SR) was mainly influenced by the concentration of α-CD or modified α-CD, HEMA and PEGDA. The introduction of α-CDs was found to decrease the SR of hydrogels, while the introduction of α-CD-BIBBs could improve the SR. Meanwhile, gelation was tuned by regulating the concentration of HEMA. The SR of hydrogels was increased with the increase of the concentration of PEGDA, but decreased with the increase of that of HEMA. In the temperature range from 20 to 50 °C, the temperature sensitivity of hydrogels was mainly controlled by the state of gels. The introduction of PHEMA chains decreased the temperature responsivity of networks. The hydrogels prepared with α-CD-BIBBs threading onto the F127 chains showed the high thermo-sensitivity. The thermosensitive mechanism of hydrogels is due to the aggregation of PPO blocks in the networks.