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Effect of temperature in the free radical polymerization of acrylic acid
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Michael Smith
Effect of temperature in the free radical polymerization of acrylic acid
Yes, this is expected.
With higher temperature, there is a larger concentration of radicals in the polymerization mixture, and initially the polymerization goes faster than at lower temperatures. This leads to a faster increase in viscosity, which slows the ability of molecules to diffuse in solution. This means it is more difficult for unreacted monomer to find growing radicals, and for unreacted initiator to find monomer. Radicals are highly reactive so when they can't react the have a habit of engaging in termination reactions which are nonproductive regarding conversion.
This is normally called autoacceleration, and is fairly well described in Odian's 'Principles of Polymerization'. Generally, you do not need to heat radical polymerizations beyond the bare minimum to decompose your thermal initiator.
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Yes, this is expected.
With higher temperature, there is a larger concentration of radicals in the polymerization mixture, and initially the polymerization goes faster than at lower temperatures. This leads to a faster increase in viscosity, which slows the ability of molecules to diffuse in solution. This means it is more difficult for unreacted monomer to find growing radicals, and for unreacted initiator to find monomer. Radicals are highly reactive so when they can't react the have a habit of engaging in termination reactions which are nonproductive regarding conversion.
This is normally called autoacceleration, and is fairly well described in Odian's 'Principles of Polymerization'. Generally, you do not need to heat radical polymerizations beyond the bare minimum to decompose your thermal initiator.
Thanks @Karl for the response. Actually, we do not consider viscosity into account in the simulations. But as a fact, we know that viscosity increases as the polymerization progresses.More
You are going much too fast. At higher temperature, the initiator decays much more rapidly, increasing the radical concentration and thereby also the rate of recombination. The radical chain reaction itself is not so very much influenced by the temperature (being exothermic, it actually slows down at some point). The result is leftover, unreacted monomer, and very few radicals left to work on them. What you describe is the "Trommsdorff-Norrish effect", btw. Ill doubt that this "simulation" takes viscosity into account. Does it?More
Thanks a lot for the response and clear explanations. The thing which I still do not understand is that, in the simulations, the concentration of the monomer, under the conditions which I have pointed in the question, increases. If by increasing the temperature, the concentration of the monomer would remain constant, it would be more understandable for me. Can you imagine that this behavior is correct? Thanks in advance,More
Yes, this is expected.
With higher temperature, there is a larger concentration of radicals in the polymerization mixture, and initially the polymerization goes faster than at lower temperatures. This leads to a faster increase in viscosity, which slows the ability of molecules to diffuse in solution. This means it is more difficult for unreacted monomer to find growing radicals, and for unreacted initiator to find monomer. Radicals are highly reactive so when they can't react the have a habit of engaging in termination reactions which are nonproductive regarding conversion.
This is normally called autoacceleration, and is fairly well described in Odian's 'Principles of Polymerization'. Generally, you do not need to heat radical polymerizations beyond the bare minimum to decompose your thermal initiator.
Yes, this is expected.
With higher temperature, there is a larger concentration of radicals in the polymerization mixture, and initially the polymerization goes faster than at lower temperatures. This leads to a faster increase in viscosity, which slows the ability of molecules to diffuse in solution. This means it is more difficult for unreacted monomer to find growing radicals, and for unreacted initiator to find monomer. Radicals are highly reactive so when they can't react the have a habit of engaging in termination reactions which are nonproductive regarding conversion.
This is normally called autoacceleration, and is fairly well described in Odian's 'Principles of Polymerization'. Generally, you do not need to heat radical polymerizations beyond the bare minimum to decompose your thermal initiator.
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