Thermoresponsive Copolymers with Well-Defined Composition and Phase Separation Via Semi-Batch Free-Radical Polymerization in a Non-Polar Medium

Thermoresponsive polymers formulated in non-polar media are finding a plethora of applications in the oil and gas and lubricant sectors. Their great adaptability mainly comes from the possibility of tuning their cloud point (T-cp), which is achieved by copolymerizing two or more monomers. In this direction, good control over the copolymer composition is crucial to ensure a sharp phase separation and, as a consequence, a prompt and well-defined response. For this reason, controlled radical polymerizations (CRPs) are often used to synthesize these materials. However, these pseudoliving polymerization techniques are still far from industrial maturity because of their cost and low polymerization rate. On the other hand, free-radical polymerization (FRP) is notoriously affected by the compositional drift of the copolymer chains, which for thermoresponsive polymers is reflected in broad phase separations. To overcome the disadvantages of FRP and guarantee remarkable control of the copolymer composition typical of CRPs, in this work we develop a semibatch power feed process for the copolymerization of diethylene glycol methyl ether methacrylate (EG(2)MA) and lauryl methacrylate in Dectol (i.e., a mixture of decane/toluene 50:50 v/v). First, their reactivity ratios were determined by analyzing the variation in the residual monomer phase composition over time at different initial molar ratios of the two monomers. These were subsequently employed for designing the inlet flow rate of the power feed strategy. Through this approach, we demonstrated for the first time that semibatch FRP is a valuable strategy to afford compositionally well-defined copolymers with a controllable upper critical solution temperature and sharp phase separations while maintaining high productivity and avoiding CRPs.