1. Field of the Invention
The present invention relates to a selective catalytic process for preparing N-halothiosulfonamide modified terpolymers of ethylene-alpha olefin-diene, and catalyst compositions suitable for use in this process.
2. Description of Information Disclosures
Modified polymers of the type of interest herein, specifically rubbery polymers, are described in U.S. Pat. No. 3,915,907 and U.S. Pat. No. 3,970,133 (R. J. Hopper) incorporated herein by reference. The desirability and advantages of such polymers was additionally disclosed in articles authored and co-authored by R. J. Hopper (Rubber Chemistry and Technology, Vol. 49, p. 341-352 (1976) and International Conference on Advances in the Stabilization and Controlled Degradation of Polymers, Lucerne, Switzerland, May 23-25, 1984).
These references describe the reaction of various N-chlorothioamides, and particularly N-chlorothio-sufonamides with various ethylene propylene diene monomer (EPDM) rubbers in solutions (see, e.g., Examples I-XII of U.S. Pat. No. 3,915,907) as well as by mixing in a Banbury.RTM. type internal mixer (Examples XIII-XVI of U.S. Pat. No. 3,915,907). Furthermore, in Example XVII of the same reference, there is disclosed in a solution reaction the use of powdered anhydrous zinc chloride (this is referred to as a catalyst in Table I, footnote g and page 346 of the cited Rubber Chemistry and Technology article). The references contain no further disclosure concerning the effect of zinc chloride nor do they suggest the use of other catalytic agents.
U.S. Pat. No. 4,820,780 issued Apr. 11, 1989 discloses a method of preparing a N-chlorothiosulfonamide-modified terpolymer of ethylene, alpha olefin containing from 3 to 6 carbon atoms and a diene in the presence of a saturated aliphatic carboxylic acid containing from 6 to 30 carbon atoms, such as stearic acid. Calcium carbonate may also be added to the reaction as a scavenger for the HCl by-product. It does not suggest the use of metal salts of weak acids as catalysts.
It would be desirable to improve the rate of reaction, the conversion and product quality produced by known processes to achieve commercially useful conditions. It would be particularly useful to improve the melt phase process so as to enhance the addition reaction while minimizing the crosslinking reaction.
It has now been found that certain catalyst compositions comprising zinc salts or iron salts of weak acid in combination with a metal salt of certain metals (other than zinc or iron) of weak acids (i.e., co-catalyst) are selective catalysts in the preparation of N-halothiosulfonamide modified terpolymers of ethylene-alpha olefin-diene. By "selectively," it is intended herein that the desired addition reaction is increased while the undesired crosslinking reaction, which leads to increased Mooney viscosity and to gelation, is minimized.
Mixtures of blends of low-unsaturation rubbery polymers, particularly EPDM, with highly unsaturated rubbery polymers are of practical importance because of the superior ozone resistance imparted to the blend by the low-unsaturation EPDM rubber. Unfortunately, the presence of the low-unsaturation rubber also affects the mechanical and hysteresis characteristics of the vulcanizates in an adverse manner, as evidenced by lower tensile strength and modulus values, and by higher dynamic heat build-up and permanent set. These undesirable responses are contributed to by the mutual incompatibility of the two types of rubber, the substantially slower cure rate of the low-unsaturation rubber, and the greater affinity of the typically polar curvatures for the high-unsaturation rubber. As a result, the vulcanized blend is a heterogeneous dispersion of poorly cured and/or largely uncured low-unsaturation rubber in well cured high-unsaturation rubber. The resulting poorer mechanical and hysteresis properties severely limit, or preclude, the use of such blends in articles subjected to severe service requirements such as tires. A method for improving the physical and dynamic properties of such rubbery polymer vulcanized blends is of considerable commercial and practical importance.