If equal concentrations of acrylonitrile and methyl methacrylate were each polym

Question

If equal concentrations of acrylonitrile and methyl methacrylate were each polymerized radically at 600C with equal concentrations of the same initiator, which polymer would have the higher molecular weight and by how much? Assume polyacrylonitrile undergoes termination only by radical combination and poly(methyl methacrylate) by disproportionation, that no chain transfer occurs, and that initiator efficiencies are the same for both reactions. Use data from Table on the next page to solve the problem. Pay attention how to read the data from the table. For example Kp for acrylonitrile is equal 1.96 x 103 L/(mol s).

Explanation / Answer

Although,the polymerisation reaction is thermodynamically favored,the kinetic feasibility of polymerisation varies considerably from one monomer to another depending on the stability of monomer radical and polymer radical.The molecular weight of radical chain polymerisation is complicated because several possible terminations-disproportions,coupling and various transfer reactions are involved.Molecular weight changes with % conversion,due to the changes in concentrations of monomer and catalyst, and the rate constant of propogation and termination.

At low conversion where all of the kinetic parameters ( [M],[I],kd,kp,kt )are approximately constant, the polymer molecular weight does not change with conversion.

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