Low modulus, thermally conductive silicones were evaluated as soft mount adhesives for substrate attachment. It was determined that due to the existence of a crystalline phase, above the glassy transition temperature (T(g)approximate to -125 degrees C), the modulus of the adhesives can be orders of magnitude higher than at room temperature. Differential scanning calorimetry shows that at a cooling rate of 5 degrees C/min the crystallization temperature, T-c, is -75 degrees C, which shifts to -66 degrees C under a slower ramp rate of 0.5 degrees C/min. Correspondingly, a sharp increase in modulus also occurs at T-c when the adhesive undergoes the same thermal processes. When the temperature is held isothermally below the crystalline melting temperature (T-m= -42 degrees C), the modulus increases simultaneously with the increase in the degree of crystallization. The growth rate of the modulus increases exponentially as the temperature approaches -75 degrees C from T-m. Once the silicones are in the high modulus state, the temperature must be increased above T-m to melt the crystalline phase and recover the normal low modulus phase. If the heating rate is faster than about 0.5 degrees C/min, the recovery temperature can pass over T-m to about -35 degrees C