Process for producing impact resistant polymer

Claim 1

A continuous process for producing impact resistant styrene polymer comprising: a. forming a solution consisting essentially of an effective amount of not more than 15 parts by weight of polybutadiene or styrene-butadiene rubber, from 0 to about 5 parts of internal lubricant and antioxidant, and at least 85 parts of styrene monomer; b. pumping the solution into a first reactor comprising a horizontal cylindrical vessel surrounded by a cooling jacket and containing a plurality of internal cooling elements disposed in a general vertical plane transverse to the central horizontal axis of the reactor, a plurality of impeller blades interspaced between the cooling elements and mounted on and extending outward from a shaft positioned along the central horizontal axis of the reactor, and a means to rotate the shaft; c. forming a first reacting mass in the first reactor by initiating polymerization in the solution; d. establishing a first temperature zone within the first reactor of from 200° to 260°F. while slowly stirring the first reactor mass by the impeller blades such that a substantially homogeneous temperature is maintained throughout the reacting mass; e. continuously passing the first reacting mass through the first reactor, in a general horizontal direction while maintaining plug flow, at a rate such that an effluent comprising a 10 to 35 weight percent of polymer solution is withdrawn continuously from the first reactor; f. transferring the effluent from the first reactor into a second reactor of similar configuration to the first reactor to form a second reacting mass; g. establishing a second temperature zone within the second reactor of from 240° to 285°F. while slowly stirring the second reacting mass by the impeller blades such that a substantially homogeneous temperature is maintained throughout the reacting mass; h. continuously passing the second reacting mass through the second reactor, in a general horizontal direction while maintaining plug flow, at a rate such that an effluent comprising a 35 to 60 weight percent solution of polymer is withdrawn continuously from the second reactor; i. transferring the effluent from the second reactor into a third reactor of similar configuration to the first and second reactors to form a third reacting mass; j. establishing a third temperature zone within the third reactor of from 250° to 480°F. while slowly stirring the third reacting mass by the impeller blades such that a substantially homogeneous temperature is maintained throughout the reacting mass; k. continuously passing the third reacting mass through the third reactor, in a general horizontal direction while maintaining plug flow, at a rate such that an effluent comprising more than 95 weight percent of polymer is withdrawn continuously from the third reactor; and l. devolatilizing the styrene polymer withdrawn from the third reactor to remove unreacted styrene monomer, whereby the devolatilized styrene polymer contains less than 0.5 weight percent of uncombined styrene monomer, has a heat distortion temperature greater than 155°F., an Izod impact strength (unannealed) greater than 0.9 ft-lb/in, a melt index between 1 and 10 grams/10 minutes, and an elongation greater than 25 percent, and contains styrene-rubber copolymer particles having a particle size between 1 and 10 microns.