Synthesis of water-soluble polyisocyanates with the oligo(ethylene glycol) side-chain as new thermoresponsive polymers

Abstract

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 (T_cps) in an aqueous solution (40 g L⁻¹). For PMeEO₃IC, the T_cp decreased from 90.0 to 74.9 °C with the increasing molecular weight (M_n,NMR) from 1960 to 9000 g mol⁻¹. The T_cp 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 T_cp 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).