EPDM Elastomers in Rubber Modified Plastics

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Abstract
The superior resistance of EPDM to thermal and ultraviolet degradation makes the use of this elastomer particularly attractive in rubber modified plastics. Because of difficulty in grafting onto EPDM compared to polybutadiene or SBR, conventional emulsion polymerization processes do not give products with the desired balance of physical properties. In order to obtain the necessary degree of grafting and desired rubber particle size in the plastic matrix, a solution-precipitation polymerization was developed. This process is particularly well adapted for the preparation of EPDM modified styrene-acrylonitrile. Properties are quite dependent upon the EPDM composition used to modify the plastic. The amount and choice of third monomer are the most critical parameters with 5 to 12 C = C/1000 of 5-ethylidene-2-norbornene giving the best balance of properties. Relatively poor plastics result with dicyclopentadiene or 1, 4-hexadiene EPDM. while the physical properties of the EPDM-SAN plastic compare very favorably with commercial ABS, the chief advantage is a much greater resistance to the deleterious effects of aging. This is shown by comparative tests of oxygen uptake, accelerated aging, property retention and discoloration at elevated temperatures and during outside exposure, and rheological stability under severe processing conditions.

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