REACTIVE EXTRUSION OF STYRENE POLYMERS

Reactive extrusion is the term used to denote a plastics processing me thod in which an extruder is used as a reactor for the continuous synt hesis and modification of polymers. This paper describes the manufactu re of polystyrene and styrene-isoprene copolymers by a reactive extrus ion process: anionic ''living'' s-butyl lithium initiated bulk polymer ization was performed in a co-rotating closely intermeshing twin screw extruder. The results of the process analysis show that living polyme rization of styrene can be performed in a screw-type reactor, despite the high reaction temperatures of over 200-degrees-C. The polystyrene melt can be modified in bulk with comonomers or coupling reagents imme diately after polymer synthesis. Depending on the raw material, formul ation, and process parameters, the process variants developed and anal yzed (homopolymerization of styrene, copolymerization of styrene-isopr ene mixtures, sequential polymerization of styrene and isoprene) resul ted in styrene polymers with widely differing structural characteristi cs and properties. For example, the copolymerization or styrene -isopr ene monomer mixtures produced poly[(isoprene-co-styrene)-b-styrene]. T he sequential polymerization of styrene and isoprene led to poly(styre ne-b-isoprene) contaminated with partly crosslinked low molecular weig ht polyisoprene. The polyisoprene content is presumably formed by side reactions due to the high reaction temperatures.