Modeling the Solvent Effect on the Tacticity in the Free Radical Polymerization of Methyl Methacrylate

The control of steteochemistry in the lice iadical polymerization of methyl methacrylate (M MA) is important because the physical properties of PM MA arc often significantly affected by the main-chain tactic:ay In this study, the role of the solvent on the tact way of M MA polymerization has been investigated by considering the propa;ation rate constants for the syndiotactic and isotactic flee i adical polymerization of M MA in vacuum, in methanol (CH3OH), and in 1,1,1,3,3,3-hexalluoro-2-(trifluoromethyl)propan-2-ol ((CF3)(3)COH) All geometry optimizations have been caried out with the B3LYP/6-31+G(d) methodology The kinetics of the propagating dimer have been evaluated with the B3LYP/6-31 +GD(d)/6-311+G(3df,2p), MPWB1K/6-311+G(3df,2p), and B2PLYP/6-31+G(d) methodologies The role of the solvent has been investigated by using explicit solvent molec des and also by introducing a polarizable continuum model (I EF-PCM) with a dielectric constant specific to the solvent Experimentally, the free radical polymerization of M MA in (CF3)1C01-1 is found to be highly synchotactie (rr = 75% at 20 degrees C) the steicoefTects of fluoioalcohols are claimed to be due to the hydrogenbonding interaction of the alcohols with the monomers and mowing species This modeling study has revealed the fact that the solvents CH3OH and (CF3)(3)COH, which are H-bonded with theca' bonyl oxygcns located on the same side o the backbone hindel the foi motion of the Isola:tic PM MA to some extent Methanol is less effective in reducing the isotacticity because of its small size and also because of the relatively loose hydlogen bonds (similar to 19 angstrom) with tile carbonyl oxygens The methodologies used in this study reproduce the solvent elTect on the free radical polymerization kinetics of M MA In a satisfactory way