Graft copolymer stabilizers for non-aqueous polymer dispersions

Free-radical solution polymerization techniques have been used to prepare carboxyl-terminated poly(methyl methacrylate) and poly(2- ethyl hexyl acrylate) homopolymers. The molar masses of these prepolymers were readily controlled and they were found to be approximately monofunctional with respect to carboxy I groups. These carboxyl-terminated prepolymers were converted to methacrylate-terminated macromonomers via acyl chlorideterminated intermediates. The macromonomer functionalities obtained by this procedure were high, typically 0.90-1.05 methacrylate groups per molecule on average. The prepolymers and macromonomers were characterized using End-group analysis (EGA). Infra-red spectroscopy (IR), 1H Nuclear Magnetic Resonance spectroscopy (lH NMR) and Gel-permeation Chromatography (GPC). Polystyrene-graft-poly(methyl methacrylate) and polystyrene-graft-poly(2-ethyl hexyl acrylate) copolymers were prepared by the free-radical solution copolymerization of macromonomers (M2) with styrene (M1). A dual detector GPC method was used to estimate macromonomer conversions. Unreacted macromonomer and styrene were removed and the purified graft copolymers were characterized by Thin-layer Chromatography (TLC) , GPC, IR and 1H NMR. It was shown that efficient grafting had occurred by copolymerization of the macromonomer end-group and that ungrafted polystyrene backbone was not produced. The graft copolymer chemical compositions and physical architectures were controlled by changing the comonomer feed composition or the macromonomer molar mass. Reactivity ratios (r1) were determined by the Jaacks, Finnemann-Ross and Kelen-TUdos methods. It was shown that the reactivities of the methacrylate-terminated macromonomers were approximately similar to conventional methacrylates and independent of the macromonomer molar mass or composition within the limits investigated. The polystyrene-graft-poly(2-ethyl hexyl acrylate) copolymers have been used as stabilizers in the free-radical non-aqueous dispersion polymerization of methyl methacrylate in aliphatic hydrocarbons. The poly(methyl methacrylate) particles were characterized by Transmission Electron Microscopy (TEM) in order to determine their size, shape and state of aggregation. Ultraviolet spectroscopy (UV) was used to determine the graft copolymer content of the particles, from which an estimate of surface coverage was made. The effects of varying the polymerization method, and both the composition and concentration of stabilizers used, were studied. The average particle size, particle size distribution and the state of aggregation were found to be dependent upon these parameters.