as represented by adiprene and vibrathane trademarks of crompton corporation various features and aspects of the present invention are illustrated further in the examples that follow while these examples are presented to show one skilled in the art how to operate within the scope of the invention they are not intended in any way to serve as a limitation upon the scope of the invention vibrathane 8523 a commercially available mdi terminated polyester prepolymer crompton corporation with 6 9 wt reactive nco content was used to evaluate elastomers containing two non reactive polydimethylsiloxane pdms additives the additives were wacker sws 101 10 000 w 10 and wacker sws 101 60 000 w 60 the 10 000 and 60 000 refer to the viscosity cst of the fluids each additive was added to a container of vibrathane 8523 at a level of 1 3 and mixed in thoroughly a third container was carried along as a control with vibrathane 8523 but no additive the three containers were allowed to remain at 158 u00b0 f 70 u00b0 c overnight 16 hours each container was inspected in the morning before elastomer preparation no evidence of separation or increase in viscosity was found the mixture was placed in a vacuum chamber and less than 10 millibars of vacuum was applied no appreciable gas evolution was noted indicating that the additive had been dry and that there had been no other source of moisture contamination to each container was added sufficient 1 4 butanediol to react with 98 of the available isocyanate the contents of the containers were mixed thoroughly and air entrained during mixing was removed.