Thermoresponsive Properties of Poly[oligo(ethylene\nglycol) sorbate]s Prepared by Organocatalyzed Group Transfer Polymerization

Abstract

The\ncurrent contribution presents the synthesis of poly­[oligo­(ethylene\nglycol) sorbate]­s (PREG_mSs) by the <i>t</i>-Bu-P₄-catalyzed group transfer polymerization (GTP) method, their\npostpolymerization modification at the backbone double bond, and thermoresponsive\nproperties in aqueous solution. Four oligo­(ethylene glycol) sorbate\nmonomers (REG_mSs), including 2-(2-methoxyethoxy)­ethyl sorbate\n(MeEG₂S), 2-(2-(2-methoxyethoxy)­ethoxy)­ethyl sorbate (MeEG₃S), 2-(2-(2-ethoxyethoxy)­ethoxy)­ethyl sorbate (EtEG₃S), and 2-(2-(2-(2-methoxyethoxy)­ethoxy)­ethoxy)­ethyl sorbate (MeEG₄S), are newly designed to study the thermoresponsive properties\nof their related polymers. The <i>t</i>-Bu-P₄-catalyzed GTP of REG_mS only proceeds in a 1,4-regioselective\naddition manner to quantitatively produce the backbone <i>trans</i>-rich (<i>ca.</i> 80%) PREG_mS. The complete\nhydrogenation and epoxidation of the backbone double bonds result\nin hydrogenated and epoxidized polymers (PREG_mS-H₂ and PREG_mS-epoxy, respectively), which have different\nmain-chain structures and rigidity from their parent PREG_mS. Given the 1,4-substituted structure of a sorbate monomer, the\nchemical structure determination of PREG_mS-H₂ by ¹³C NMR spectra demonstrates that the above polymers\nhave an <i>erythro</i>-rich (<i>ca.</i> 60%) structure\nin diastereochemistry and a diisotactic/disyndiotactic ratio around\n1:1 in stereoregularity. The thermoresponsive properties of PREG_mS, PREG_mS-H₂, and PREG_mS-epoxy\nin aqueous solutions are studied in detail from various aspects in\nterms of polymer mass concentration, molecular weight, length and\nend group of the oligo­(ethylene glycol) side chain, and main-chain\nstructure by turbidity, ¹H NMR spectroscopy, and dynamic\nlight scattering (DLS) methods, which are discussed below.