New styrenics toughen & compatibilize.

The newest player in the field of impact modifiers is Dexco Polymers, the Houston-based partnership between Exxon Chemical Co. and Dow Chemical Co. Earlier this year, Dexco introduced seven grades of styrenic block copolymers, trade named Vector, that double as compatibilizers and aid in alloying dissimilar plastics. Dexco is producing these thermoplastic elastomer products at its new 70-million-lb/yr plant in Plaquemine, La. The plant's capacity can be increased to more than 150 million lb/yr if necessary.

Initial TPE development was in styrene-isoprene-styrene (SIS) and styrene-butadiene-styrene (SBS) copolymers for pressure-sensitive and hot-melt adhesives. Now, Dexco is developing a Vector 6000 series of SBS copolymers for modifying polyolefins, styrenics, engineering thermoplastics, recycle blends, and alloys. In Europe, the company is also devoting some effort to compoundable resins for shoe markets.

NEW RESIN TECHNOLOGY

These new materials are being produced by a proprietary technology that Dexco says allows an unprecedented level of control over polymerization. The process reportedly offers several advantages over the traditional method used to produce almost all other styrenic block copolymers on the market.

Unlike other processes, the Dexco method can achieve 100% conversion to triblock copolymer, eliminating uncoupled diblock that can adversely affect the tensile strength and elastic modulus of a neat polymer, as well as cause a negative effect on the degree of compatibilization of dissimilar materials.

This unique polymerization process also makes it easier to predict precise molecular weights, Dexco says, and eliminates the byproduct production of halide salts, cutting out the risk of future discoloration or property degradation. Polymerization control makes it feasible, Dexco says, to tailor the polymer block interfaces, opening up the possibility of improving blending compatibility with other polymers. (CIRCLE 65)