Process for producing impact resistant polymer

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.degree. to 260.degree.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maintaining plug flow, at a rate such that an effluent comprising a 10 to 35 weight percent of polymer solution is withdrawn continuously from the first reactor;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.degree. to 285.degree.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maintaining plug flow, at a rate such that an effluent comprising a 35 to 60 weight percent solution of polymer is withdrawn continuously from the second reactor;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.degree. to 480.degree.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.degree.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.