Synthesis of water-soluble polyisocyanates with the oligo(ethylene glycol) side-chain as new thermoresponsive polymers†
Isocyanates with oligo(ethylene glycol) units have been designed and synthesized as 2,5-dioxaheptyl, 2,5,8-trioxadecyl, 3,6,9-trioxaundecyl, and 2,5,8,11-tetraoxatridecyl isocyanates (MeEO2IC, MeEO3IC, EtEO3IC, and MeEO4IC, respectively). The bulk polymerization of the isocyanates using n-butoxy(η5-cyclopentadienyl)dichlorotitanium(IV) at 10 °C proceeded via a living manner to produce well-defined water-soluble polyisocyanates of PMeEO3IC, PEtEO3IC, and PMeEO4IC except for PMeEO2IC. The phase transition property of the obtained polyisocyanates was estimated by their cloud point temperatures (Tcps) in an aqueous solution (40 g L−1). For PMeEO3IC, the Tcp decreased from 90.0 to 74.9 °C with the increasing molecular weight (Mn,NMR) from 1960 to 9000 g mol−1. The Tcp of 94.0 °C for PMeEO4IC (4460 g mol−1) was higher than that of 79.6 °C for PMeEO3IC (4560 g mol−1), and the Tcp decreased from 79.6 to 34.7 °C by changing from the methyl to the ethyl group in the oligo(ethylene glycol) units from PMeEO3IC to PEtEO3IC (4470 g mol−1).