US 4,728,701 AGranted

Process for the polymerization of acrylates

OwnerMarvin A. Jarvis, Lawrence A. Testainventors

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Abstract

The continuous solution polymerization of an acrylate, particularly methyl methacrylate, is practiced in the presence of a large quantity of solvent by introducing the monomer feed into a continuous loop of recycled solvent and removing the polymerized product therefrom. The polymerization is practiced in a plurality of stages, preferably two stages wherein the bulk of the polymerization is performed in the first stage and the final stage is operated to deplete the initiator and any other polymerization modifiers, thereby forming a crude polymerizate for devolatilization. A product of superior thermal stability and optimum heat distortion temperature is achieved by the addition of some of the comonomer such as methyl acrylate, or ethyl acrylate, etc., to the final stage or stages of the polymerization. Additionally, the product quality is enhanced by addition of a portion of the chain transfer agent, such as n-dodecyl mercaptan, to the final stage or stages of polymerization. The crude polymerizate is preheated and devolatilized in a flash zone. Sufficient pressure is maintained on the crude polymerizate in the devolatilizer preheater to avoid the formation of foam encrustations on the heat exchange surfaces of the devolatilizer preheater and on the surfaces of the transfer lines.

A continuous solution process for the polymerization of monomers comprising at least 40 percent arylate esters of C.sub.1 to C.sub.8 alkanols which comprises:

(a) introducing monomer, initiator and chain transfer agent into admixture with solvent to provide a polymerization medium containing not less than 40 weight percent solvent;
(b) maintaining said polymerization medium under polymerization conditions, in at least one polymerization reactor comprising a temperature from 60 to about 130 degrees C. and sufficient residence time to effect 20 to 95 percent of the total conversion of said monomer and form a crude intermediate polymerizate;
(c) withdrawing said crude, intermediate polymerizate and passing it to at least one succeeding polymerization reactor, including a final polymerization reactor;
(d) stirring said crude intermediate polymerizate in said succeeding polymerization reactor, including said final polymerization reactor, to maintain said polymerizate intimately admixed while maintaining polymerization conditions therein comprising a temperature from 60 to about 130 degrees C., and sufficient residence time to essentially deplete the initiator in said polymerizate, thereby forming, and pumping a crude polymerizate containing solvent, unreacted monomer and less than about 50 weight percent polymer from said final polymerization reactor;
(e) heating said crude polymerizate in a devolatilzer preheater to a temperature between 200 degrees and 270 degrees C., withdrawing the preheated crude polymerizate from said preheater and passing it through a transfer line to a devolatilizer and spraying said preheated polymerizate into said devolatilizer and, flashing the polymerizate therein to remove a volatile stream comprising solvent, unreacted monomer, and oligomers therefrom;
and
(f) maintaining a pressure on the crude polymerizate in said transfer line and said devolatilizer preheater which permits vaporization therein to form a mixed two-phase system of vapor and liquid, which pressure is sufficient to prevent incipient solidification in the liquid phase, thereby avoiding formation of foam encrustations on the heat exchange surfaces of said preheater, while heating said polymerizate sufficiently in said preheater to provide a preheated crude polymerizate with sufficient heat to supply the heat of vaporization necessary to produce said molten polymer and permit it to be pumped from said devolatilizer.

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Abstract

Claims22