The use of low unsaturation level polyols made from double metal cyanide catalysts in combination with chain extenders in the preparation of thermoplastic elastomers is disclosed in U.S. Pat. Nos. 5,096,993 and 5,185,420 both to Smith et al., incorporated herein by reference. Prior to the use of double metal cyanide catalysts for the preparation of high molecular weight polyols, the thermoplastic polyurethane elastomers produced had poor physical properties such as being too hard due to high levels of terminal unsaturation in the polyols used in their production.
The thermoplastic polyurethane elastomers of the '993 and '420 patents to Smith et al. describe the preparation of thermoplastic elastomers made with polyols have less than 0.04 meq/g of end group unsaturation, particularly, thermoplastic elastomers characterized by enhanced softness.
Because of their softness, thermoplastic elastomers are frequently used in the construction of automotive interior trim components. Automotive manufacturers frequently specify that the elastomers used to produce interior trim components have adequate long-term stability and resistance to degradation by ultra violet light and that the elastomers must also meet specific manufacturing specifications for resistance to ultra violet light exposure.
Commonly, in order to achieve the manufacturing specifications for resistance to ultra violet exposure, antioxidants, ultra violet light stabilizing agent(s), and pigment(s) are added to elastomers.
However, to date, soft thermoplastic polyurethane elastomers have not been produced which are able to meet or exceed manufacturers requirements for withstanding prolonged levels of artificial weathering which simulates exposure to the heat and ultra violet radiation and sunlight. Additionally, due to the previous presence of end group unsaturation of polyols with molecular weights greater than 2,000, soft (low durometer) aliphatic thermoplastic urethane elastomers were not available in a dry castable powder or spheroidal particle forms.