Restriction of Molecular Mobility by Filler Surfaces

If an elastomer is really tightly bound or adsorbed to reinforcing filler surfaces, should not molecular mobility of the polymer chains be restricted accordingly In particular, should not the glass transition temperature, thermal expansion coefficient, and free volume depend upon reinforcement Surprisingly, these properties turn out to be only modest functions of filler level. 

For instance, Kraus and Gruver (1970) found that the Tg of a styrene-butadiene copolymer increased only 0.2°C for every ten parts per hundred by weight of reinforcing carbon black added, and that the coefficient of thermal expansion of the polymer component in the rubbery region was substantially unaffected by the presence of filler. While Yim and St. Pierre (1969) found that the Tg of silicone rubber increased up to 8 C with the addition of 40 parts per hundred by weight of reinforcing silica, this effect is still rather modest. 

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