Comb-like thermoresponsive polymeric materials: Synthesis and effect of macromolecular structure on solution properties

A series of comb-like block and random copolymers based on acrylamide (AM) and N-isopropylacrylamide (NIPAM) have been prepared by atom transfer radical polymerization (ATRP). The number of side-arms, the length of the AM and NIPAM blocks as well as the distribution of the two monomers (block or random) were systematically varied. The aqueous solution properties, i.e. the solution viscosity as a function of shear rate and temperature and the critical micelle concentration (CMC) of the different copolymers were evaluated. Particular emphasis is dedicated to the thermoresponsiveness of the aqueous copolymer solutions as measured by the rheological behaviour. The CMC is a function of the molar ratio between the AM and NIPAM, as well as the distribution (block or random). The surface tension of the block copolymers is close to the value for pure poly(NIPAM), while that of the random copolymers is a function of the composition. The block copolymers tend to precipitate from the solution at temperatures above the Lower Critical Solution Temperature (LCST) of poly(NIPAM), indicating the formation of strong aggregates. Random copolymers of AM and NIPAM do not precipitate from the solution (up to 80 °C). In addition, depending on the composition, thermothickening behaviour is observed. The thermothickening behaviour is only present at low shear rates (γ ≤ 10 s−1). This, in connection with the ease of the synthesis, makes these copolymers especially interesting for application in Enhanced Oil Recovery (EOR).