US EPA

8704880 

Journal Article 

Polymerization of Methyl Methacrylate Photoinitiated by 4, 4′-Bis(N, N-diethylamino)benzophenone. 1 

Mcginniss, VD; Provder, T; Kuo, C; Gallopo, A 

1978 

1 

Macromolecules
ISSN: 0024-9297
EISSN: 1520-5835 

11 

2 

393-404 

English 

10.1021/ma60062a022 

Polymerization of methyl methacrylate (MMA) photoinitiated by 4, 4′-bis(N, N-diethylamino)benzophenone (DEABP) was shown to have unusual kinetic behavior attributable to primary radical termination reactions. This deviation from normal kinetic orders in light intensity, photoinitiator, and monomer concentrations qualitatively parallels observed concentration effects on quantum yield for the photochemical disappearance of Michler's ketone in cyclohexane. Increasing the DEABP concentration, beyond certain limits, lowers the rate of photopolymerization for MMA analogous with lowering of the quantum yield for disappearance of Michler's ketone with increasing concentrations of reactant. Molecular weights of the photopolymerized samples are significantly lower than for thermally initiated polymerizations using azodiisobutyronitrile (VAZO-64) as initiator. It is also shown that DEABP (ground state) does not influence the rate of polymerization or the molecular weight distribution of VAZO-64 thermally initiated polymerization of methyl methacrylate. Multiple detector GPC/IR/UV examination of thermally polymerized MMA showed no fragments of DEABP attached to the polymer backbone thus eliminating the possibility of growing polymer radical chain transfer to the ground state photoinitiator. Analysis of the photopolymerized MMA by GPC/IR/UV multiple detection does show photoinitiator or photoproduct fragments attached to the polymer backbone and accounts for the observed lowering of molecular weights (initiation as well as primary radical termination). Broadening of the molecular weight distribution (monomodal to almost bimodal) for the photopolymerized MMA between narrow DEABP concentration ranges indicated a change in photoinitiation mechanism. Drastic solvent effects (nonpolar-polar) were observed for the photoinitiated polymerization of MMA using DEABP initiator. Polymer formation decreased as the polarity and reactivity of the solvent-MMA mixtures were changed from benzene (polymer formed), cyclohexane (little polymer formation), and methanol (no polymer formed). These results are attributable to the decrease in the quantum yield for intersystem crossing efficiency (øst) of aminoaromatic ketones (Michler's ketone) as the polarity and reactivity of the solvent changes. Reaction mechanisms and kinetic schemes, consistent with the experimental observations, are presented and discussed. 1978, American Chemical Society. All rights reserved.