Polymeric Capsules Prepared by in Situ Synthesis and Cross-Linking of Amphiphilic Copolymer by Atom Transfer Radical Polymerization

A technique for encapsulation of polar organic solvents using atom transfer radical polymerization (ATRP) by suspension polymerization was developed to encapsulate diphenyl ether (solubility parameter δ = 20.9 MPa1/2) for the first time. An amphiphilic terpolymer was prepared by suspension polymerization, by first preparing poly(methyl methacrylate-co-poly(ethylene glycol) methacrylate), P(MMA-co-PegMA), oligomers in solution conditions, followed by addition of a cross-linking monomer, diethylene glycol dimethacrylate, to the polymerization solution, and then transfer of this oil phase to a stirred aqueous phase. The thermodynamic requirement for encapsulation of polar core oils is that the polymer has low interfacial tensions with both the oil phase and the water phase. Therefore, increasing the polarity of the copolymer by increasing its PegMA content (0−31 mol %) led to a transition in suspension particle morphology from matrix to multihollow and hollow particles. Furthermore, particles prepared with similar monomer feed ratios by conventional free radical polymerization (CFRP) did not exhibit a multihollow structure. We attribute this difference in ATRP and CFRP suspension particle morphology to the slow rate of the ATRP reaction which allows sufficient time for diffusion of the forming polymer chains to the oil−water interface, resulting in the thermodynamically favored hollow particle morphology.