3 5sih sivi ratio 1 3 1 3propertiescompression set 27 89heat aging sup b 2 5______________________________________ sup a in parts per million platinum sup b oven heat aging for 70 hours at 177 u00b0 c measured as change in points in hardness shore a from table 2 above it can be clearly seen that silicone compositions of the present invention having a ratio of d q of greater than 0 8 1 have significantly improved compression set and heat aging properties over those having a d q ratio of 0 8 1 or less such excellent properties makes the compositions of the present invention eminently suitable as gasket materials table 3______________________________________example 7 7a ______________________________________composition pbwmm sup vi qd sup a 25 m m sup vi q 0 67 1 d q 1 1 mqd sup vi 25 m q 0 67 1 d q 0 15 1 vinyl end stopped 75 75high viscosityorganopolysiloxaneplatinum catalyst sup b 20 20hydride crosslinker 3 5 3 5filler sup c 30 30propertiesshore durometer 58 60tensile psi 800 1100 elongation 400 600tear strength psi 130 250compression set 27 90heat aging sup d 1 12______________________________________ comparative example sup a dimethyl d units or a blend of dimethyl d units and methyl vinyl d units sup b in parts per million platinum sup c minusil alpha quartz fumed silica mixture sup d change in hardness after heat aging for 70 hours at 177 u00b0.