Synthesis and Characterization of Thermoresponsive Graft Copolymers of NIPAAm and 2-Alkyl-2-oxazolines by the “Grafting from” Method

Abstract

New thermoresponsive graft copolymers were synthesized by the cationic ring-opening polymerization of 2-methyl-2-oxazoline (MeOxa) or 2-ethyl-2-oxazoline (EtOxa), initiated by the random copolymers of chloromethylstyrene (CMS) and N-isopropylacrylamide (NIPAAm) using the “grafting from” method with a yield of 66−94%. The polymers were characterized by NMR, GPC, and DSC, and the conformational transition (lower critical solution temperature, LCST) of macroinitiators and graft copolymers was determined by the turbidity and DSC measurements. The transition temperature of the graft copolymers could be fine-tuned through the composition of the macroinitiator and the graft copolymer. An increasing quantity of the hydrophobic comonomer chloromethylstyrene in the macroinitiator lowered its LCST, while in the graft copolymer an increasing content of the hydrophilic segment of poly(2-methyl-2-oxazoline) or poly(2-ethyl-2-oxazoline) raised the transition temperature. For graft copolymers with a high content of long poly(2-alkyl-2-oxazoline) grafts, stabilized aggregates with a thermoresponsive core can be formed at the LCST instead of precipitation of the material.

Bioinspired Poly(2-oxazoline)s

“…Voit et al investigated graft copolymers with thermoresponsive poly(NIPAM-stat-chloromethylstyrene) backbones and hydrophilic poly(2-alkyl-2-oxazoline) side-chains. The phase transition temperatures were found to increase with increasing number and length of the side-chains [33].…”

Design Strategies for Functionalized Poly(2-oxazoline)s and Derived Materials

“…Phase transition could be altered not only via side-chain composition or structure, but also by hydrolysis of the methyl ester groups and subsequent carboxylic acid functionalization. Tailoring of the polymer properties was also reported to be feasible by the parameters macroinitiator and hydrophilic/hydrophobic segments [104]. An increasing quantity of chloromethylstyrene in the backbone lowered the LCST, while an increasing content of pMeOx or pEtOx (relative to the backbone) raised the transition temperature.…”

Dual-switchable surfaces between hydrophobic and superhydrophobic fabricated by the combination of click chemistry and RAFT

“…Each cycle lasts only several minutes. It was reported that PNIPAAm [55] shows its LCST at 32°C in aqueous solution. The hydrogen bond is formed between the water and N-isopmpylacrylamide group when the temperature under the LCST, and it will display the hydrophilic properties.…”