Method of producing mercaptan terminated polymers with increased

Details Method of producing mercaptan terminated polymers with increased Method of producing mercaptan terminated polymers with increased

1987-01-22

1988-03-01

Marquis, Melvyn I.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From reactant having at least one -n=c=x group as well as...

528 55, 528 86, 528374, 528375, 528376, 528373, 528388, C08G 1810

Patent

active

047287128

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

Of increasing commercial value are mercaptan terminated liquid polymers exemplified by the early polysulfide material produced under U.S. Pat. No. 2,466,963. More recent polymers include the mercaptan terminated polyethers of U.S. Pat. No. 3,431,239, and the mercaptan terminated urethane modified polyethers of U.S. Pat. Nos. 3,923,748, 3,446,780, and German Pat. No. 0,066,167. Mercaptan terminated polythioethers are disclosed in U.S. Pat. No. 4,366,307.
The mercaptan terminated polymers are typically supplied as liquid materials which are applied to various surfaces and cured to form solid elastomeric sealants. All of these liquid materials contain small quantities (0.5 to 3 weight percent) of low molecular weight mercaptan compounds which produce undesirable odors that generally limit application of the sealants to well ventilated areas. Attempts have been made to reduce the odors by heating batches of the liquid material under vacuum, with or without the presence of an inert gas. However, the polymers frequently depolymerize, oxidize or otherwise decompose before a low odor product is obtained.
It would be desirable to provide a method for treating the liquid mercaptan terminated polymer materials to reduce the level of odor causing low molecular weight mercaptan compounds in the liquid material without decomposing or otherwise adversely affecting the material.
Most of the presently available single component sealants based upon mercaptan terminated liquid polymers cure from the polymer surface inwards into the body of the polymer at a rate of around 1 mm per day. The cure rate may be increased using various additives, such as catalysts and promoters. Also curing conditions may be controlled in order to increase cure rates. Shortened cure times are desirable since it reduces the amount of time that the applied sealant exists in a tacky, non-solid form. Accordingly, there still is a present need to provide methods for increasing the cure rate of the liquid mercaptan polymers without adversely affecting the quality of the cured elastomer sealant.


SUMMARY OF THE INVENTION

In accordance with the present invention, a method is disclosed in which the level of odor producing mercaptan compounds present in liquid mercaptan terminated polymers is reduced without adversely affecting the liquid polymer. In addition, we surprisingly discovered that the cure rate for mercaptan terminated liquid polymers treated by our method is substantially increased over untreated mercaptan terminated liquid polymers.
The present invention is based on the discovery that mercaptan terminated polymers containing from about 0.5 weight percent to about 3 weight percent low molecular weight mercaptan compounds can be heated under certain conditions for short periods of time to remove at least 50 weight percent of the low molecular weight mercaptan compounds without decomposing the polymer to thereby produce a liquid mercaptan terminated polymer having an increased cure rate and a reduced obnoxious mercaptan odor.
The method of the present invention basically involves heating the mercaptan terminated polymer to a sufficient temperature and for a sufficient length of time to vaporize at least about 50 weight percent of the low molecular weight obnoxious smelling mercaptan containing compounds. The heating of the mercaptan terminated polymer is carried out for a sufficiently short time and under specific conditions as will be described below to prevent decomposition of the liquid mercaptan terminated polymer while providing the desired vaporization of at least 50 weight percent of the mercaptan compounds. The mercaptans which are vaporized or stripped from the liquid mercaptan terminated polymer are separated from the polymer to produce a stripped liquid mercaptan terminated polymer having the desired reduced obnoxious mercaptan odor and the additional unexpected benefit of an increased cure rate. The increase in cure rate for compositions incorporating polymers treated in accordance with the present inventi

REFERENCES:
patent: 2466963 (1949-04-01), Patrick et al.
patent: 3431239 (1969-03-01), Morris et al.
patent: 3912758 (1975-10-01), Weaver
patent: 3923748 (1975-12-01), Hutt et al.

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