Activation energies free radical copolymerization

Temperature has a greater influence on the ri and V2 values of ionic copolymerizations than in free-radical copolymerization because of the greater spread of activation energies for the propagation reactions involving ions. There is no general trend observable and the monomer reactivity ratios may increase or decrease with temperature in the isobutylene-styrene copolymerization ri increases by a factor of 1.5 and V2 increases by a factor of 3 when going from —94°C to —30°C... 

The reaction rate in the studied range (60-90°C) increases with temperature independently of the media. DAAH copolymerization with SO2 proceeds significantly easier in aqueous media - at lower temperatures and lesser concentrations of initiator, than in DMSO. The values of the total activation energy of DAAH copolymerization with SO2 in the water solution and DMSO, calculated from Arrenius equation, are 58,6 and 87,9 kJ/mol, respectively. It is known from reference data [9] that the values of activation energy of alternate copolymerization turn out to be lesser, than in the case of the most reactions of free-radical polymerization, effective activation energy of the latter being in the range 83,7-96,3 kJ/mol. 

The free-radical copolymerization of p-isopropyl-a-methylstyrene has been studied in chloroform solvent at 60 C, with BPO initiator. Copolymerization gave a 1 1 copolymer regardless of the feed ratios, with the highest rate of copolymerization being obtained at equimolar feed. Kinetic studies at 1 1 feed and various concentrations of BPO showed an order of 1.07 and 0.65 with respect to the concentrations of MA and BPO. The overall activation energy was of the order of 7.6 kcal/mol. The dependence of copolymerization rate on monomer concentration and feed ratio shows that the mechanism of copolymerization cannot be simply explained by the participation of charge-transfer complexes formed between the two monomers. 

Equation 10.102 is rather unwieldy. However, it can often be simplified Binary terminations as reactions of two free radicals with one another have low activation energies and large rate coefficients that, with few exceptions, are of the same order of magnitude (monomers giving strongly stabilized radicals are poorly suited for polymerization see also Section 9.4). As a result, in copolymerization ... 

Radiation-initiated copolymerizations, either bulk or in solution, exhibit no induction period for the a-methylstyrene-MA monomer pair. Standard free-radical inhibitors prevent or stopped the copolymerizations. Apparent activation energies of 6.7 and 5.4kcal/mol were obtained for the bulk (3.6 mol % MA in a-methylstyrene) and (8.0 wt. % chloroform solution of equimolar amounts of the monomer pair) copolymerizations, respectively. Composition and IR spectra studies indicated that homopolymerization of either of the two monomers did not occur, under conditions explored, and that alternating copolymerization occurred over a wide range of monomer concentration of one component. As pressures are raised from 1 bar to 3 bars, considerably enhanced rates of copolymerization are observed. Above 80 C random copolymer is obtained. 

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