Examination of the preparation of a block copolymer from macroradicals produced in viscous media

Abstract

Extensive experiments on copolymer syntheses as a type of dispersion polymerization in viscous poor solvents (e.g., silicone oil) have been reported (Seymour, R. B.; Kincaid, P. D.; Owen, D. R. Adv. Chem. Ser. 1973,129,230) which, based on a trapped-macroradical model, were taken to suggest that such conditions promoted the formation of block copolymers. Here we report the results of a series of tests devised to elucidate the mechanisms in these systems. One such test used initiation by y radiolysis of water, which allows virtually instantaneous cessation of the production of primary radicals after removal from the y source. This resulted in a very rapid drop in the polymerization rate. This observation constitutes what seems to be irrefutable evidence against the trapped macroradical model, which would predict that the polymerization should continue at a moderate rate after removal from the source. Furthermore, it is shown that in these viscous-solvent dispersion polymerizations, there is a significant rate of production of free radicals under conditions where the original interpretation implied that this would not be the case. Moreover, it is shown that the formation of graft copolymers can result from the transfer reaction of primary free radical with the preformed homopolystyrene backbone. The original erroneous interpretation (in terms of formation of block copolymers from trapped macroradicals) can thus have arisen because the distinction between block and graft copolymer was beyond the resolving power of the analytical technique used to characterize the products. The results of the present experiments and those of Seymour can be readily explained in terms of rapid termination between two long macroradicals encountering each other through reaction/diffusion and/or between an entangled macroradical and a mobile oligomeric free radical formed by transfer.

Physically Controlled Radical Polymerization of Vaporized Vinyl Monomers on Surfaces. Synthesis of Block Copolymers of Methyl Methacrylate and Styrene with a Conventional Free Radical Initiator

“…These heterogeneous radical polymerizations entrapped propagating species in insoluble polymer particles and extended their lifetime. However, Louis et al 16 reported that the entrapped macroradical model in a viscous solvent is doubtful in the dispersion polymerization of St and demonstrated that graft and statistical copolymers are formed in the process. Zhang et al 15 also did not rule out the possibility of graft copolymer formation occurring in the consecutive copolymerization in ionic liquids.…”

“…The crude copolymer sample 2-2c (56.70 mg) was extracted to remove each homopolymer at 80 °C for 24 h using selective solvents, i.e., cyclohexane for PSt and acetonitrile for PM-MA. 15,16,33,34 After the selective extraction, the residue was dissolved in CHCl3 at room temperature. The fractions (7.9, 10.9, and 80.9 wt %) were characterized with 1 H NMR (see Supporting Information), FTIR, and GPC (Table 3).…”

Controlled Radical Polymerization of Vaporized Vinyl Monomers on Solid Surfaces under UV Irradiation

“…acetonitrile for PMMA and cyclohexane for PSt, respectively. [39][40][41][42] After the selective extraction, the residual part was dissolved in CHCl 3 at room temperature. Each fraction was characterized with 1 H NMR, FT-IR and GPC.…”

“…To determine the copolymer structure, the selective solvent fractionation method [39][40][41][42] was applied to the consecutive copolymerization sample 2-1c. The as-polymerized sample 2-1c was extracted to remove each homopolymer at 80 8C for 24 h using the selective solvents cyclohexane and acetonitrile for PSt and PMMA, respectively.…”

Physically controlled, free‐radical polymerization of vaporized fluoromonomer on solid surfaces

“…These heterogeneous radical polymerizations entrapped the propagating species in insoluble polymer particles and extended their lifetime. However, Louis et al19 reported that the entrapped macroradical in a viscous solvent is a doubtful model, especially in the dispersion polymerization of St. They did this by demonstrating that graft and statistical copolymers were formed in the process.…”