Hello,
assuming a simple solution polymerisation (batch): how can I estimate the appropiate reaction time? If I try to copolymerise differente acrylates I usually know the dissociation kinetics of the initiator, but I have only a very rough knowledge of the polymerisation kinetics.
I feel this is a somewhat ill-posed (but real-world) problem and would welcome any comments.
Oliver
The rate constants would be, besides the one for dissociation of initiator, for a polyadition (chain poymerization), the steps would be
-dissociation of initiator (generation of I*)
-attack of the I* on the monomer
-attack of the M* on another monomer (M* means a growing chain)
-coupling M* + M*
-disproportionation MCH2-CH2* + MCH2-CH2* -> MCH2CH3 + MCH=CH2
-chain transfer reactions
Depending on the conditions you are working, it is possible to rule out some steps, like chain transfer or disproportionation. Writing down the rate laws you can assmble everything in an electronic spreadsheet (ie. Excel, Starmath, Mathlab, etc...) and plot the reaction progress.
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polymerisation
Unfortunately, in solution polymerization there can be a significant amount of chain transfer to solvent; Polymer Handbook contains a very good compilation of chain transfer constants to solvents, initiators, monomers, polymers, thiols, etc.
In solution, methacrylates will have a significant amount of disproportionation, acrylates much fewer.
As a starting recipe for a new polymerization, try about 1 wt.% initiator (benzoyl peroxide, Vazo 64, etc.) and run the polymerization for at least 6 initiator half-lives. The typical conversion should be 90-98%. Continuous imitator feed may increase conversion and product molecular weight, but may increase cycle time, especially if low imitator concentration is desired at the end of the polymerization.
Since (meth)acrylates have a strong Tromsdorff effect, using bulk, suspension or emulsion polymerization will reduce the polymerization time, and increase MW significantly.
Ernie
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