MOLECULAR STRUCTURE AND PROCESSING CHARACTERISTICS OF METALLOCENE EPDM RUBBERS WENBIN LIANG,* SOLOMON T ANG, RAJAN V ARA, SHERRIKA DANIEL THE DOW CHEMICAL COMPANY , ELASTOMERS R&D, FREEPORT, TX, 77541 SANDRA WATSON THE DOW CHEMICAL COMPANY , ELASTOMERS R&D, PLAQUEMINE, LA, 70765 CRISTIANO BETTE, TIM CLAYFIELD THE DOW CHEMICAL COMPANY , ELASTOMERS R&D, HORGEN, SWITZERLAND ABSTRACT We report the molecular structure and processing characteristics of a series of metallocene-based EPDM rubbers. The relationships between molecular weight and composition distributions and the ENB content of the polymers, and their effects on network structure development are investigated. Experimental data and Monte Carlo simulation results reveal that, compared to EPDM of broad MWD, EPDM rubbers with narrow MWD can achieve faster cure and higher degree of cure at equal or lower ENB level during vulcanization. The processing behaviors and mechanical properties of rubber compositions and formed articles based on EPDM grades of different manufacturing technologies are evaluated. The combination of high MW and narrow MWD of the metallocene EPDM polymers enables fast cure rate, high cure efficiency, and improved scorch safety during processing, and good mechanical strength of fabricated articles of the for- mulations. Specific examples will be given in the paper. INTRODUCTION EPDM applications and their performance requirements are highly influenced by the poly- mer molecular structure and processing conditions. In recent years, we have seen increased use of EPDM, especially in automotive applications, resulting from its unique molecular structures and versatility in manipulating the structure through catalyst and processing technologies. Metallocene-based EPDM rubbers are known to exhibit well-defined molecular architecture and product consistency. Combining metallocene catalyst technology with the gas phase reaction process, two of the most important leading trends in EPDM technology advancement, yielded EPDM rubbers with additional attributes, which include: 1,2 • Granular friable form (instead of bale) • High degree of structure control • Consistency of product composition • High MW capability without need for oil extension • High catalyst efficiency, low catalyst residues, low odor and low gel. As a result of these unique attributes, the gas-phase process EPDM products show shorter mix times and better filler dispersion compared to conventional (baled or pelletized, oil extend- ed or non-oil extended) EPDM grades. They can also be highly extended to produce low cost compounds with good physical properties and low compression set. The granular form of these products also allows for use directly in a continuous process such as profile extrusion. 3 Currently, around half of the global EPDM demand finds use in automotive applications. Flexible thermoset sealing profiles, solid or foamed, are among the most important and techni- cally challenging automotive applications. There is a wide belief that high ENB content is required for fast cure rate during profile production. However, there is generally lack of mecha- 506 * Corresponding author. Ph: 979-238-9326; Fax: 979-238-0235; email: liangw@dow.com