Thermoresponsive behaviors of novel polyoxyethylene-functionalized acrylamide copolymers: Water solubility, rheological properties and surface activity

Abstract

Herein, a series of polyoxyethelene-functionalized polymers were synthesized using acylamide (AM), acryl acid (AA), various allyl polyoxyethelene ethers as monomers via facile redox-initiated free radical copolymerization. The polyoxyethylene chains contributed to improving solubility, while the introduction of alkyl prolonged the dissolution time of polymers. Heating and addition of electrolyte caused alkyl-containing polymers to dissolve worse due to the weakening of hydration of oxyethylene units. Subsequently, in rheological studies, alkyl-capped polyoxyethylene-functionalized polymers showed strong thickening ability, excellent shear resistance and viscoelasticity. Obviously, polymer with more oxyethylene units was prone to achieve better rheological properties. Alkyl-containing polymers exerted better elasticity, and the intersections of elastic and viscous moduli was at lower oscillation frequency (around 0.01 Hz), owing to intermolecular association. Besides, the response of alkyl-containing polymers to temperature presented thermothickening behavior, differing from monotonous downward of conventional polymers. Their viscoelasticity was improved in the range of 20–50 °C, especially for polymers with more oxyethylene groups. Importantly, alkyl-capped polyoxyethelene chains endowed polymers with surface activity, which reduced surface tension to about 40 mN/m and maintained emulsification rate above 50% after 30 h at the polymer concentration of 2000 mg/L. This study provides valuable guidance for the design and application of fast-dissolving and temperature-resistant polymers.