Automatic Control of Polymer Molecular Weight during Synthesis
2016
McAfee, Terry | Leonardi, Natalie | Montgomery, Rick | Siqueira, Julia | Zekoski, Thomas | Drenski, Michael F. | Reed, Wayne F.
The continuous record of monomer and polymer concentrations, Cₘ and Cₚ, and cumulative weight-average mass, Mw, furnished by automatic continuous online monitoring of polymerization reactions (ACOMP) has been harnessed to provide feedback to control reactor monomer flow in order to follow a target trajectory Mw,ₜ(t) during linear chain growth free radical polymerization. This was achieved without a detailed kinetic model. Two proportionality parameters to pilot the controller, α and p, result from (i) reaction rate = αCₘ and (ii) Mw,ᵢₙₛₜ = pCₘ, where Mw,ᵢₙₛₜ is instantaneous Mw. Using Ansatz values for α and p, the controller periodically recomputes these, based on the ACOMP data stream, in order to follow Mw,ₜ(t). A histogram of concentration vs Mw,ᵢₙₛₜ estimates the molecular weight distribution width. Invoking an instantaneous distribution provides polydispersities. Results are compared to GPC analysis on end products. The concept of “isomorphic reaction pair” is introduced: two reactions that follow the same trajectory under different reaction variables, e.g., varying T at constant [initiator] and varying [initiator] at T = constant. The controller can be used, as is, for high solids reactions, and extended to copolymerization, including for possible control of composition gradients in controlled radical polymerization.
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