Local free volume and glass transition in propylene/alpha- olefin copolymers with a defined length and number of branches

The local free volume size v, the glass transition temperature Tg and the specific volume have been estimated for propylenes branched with a defined amount (0 to 20 mole-%) of various α-olefins (C4 to C16). From the specific volume the fractional free volume was calculated and from this the number density of holes has been estimated. It is observed that Tg decreases and the hole size v increases linearly with both the number and length of branches. From this a linear relation between Tg and v follows. For polyethylene, an increasing number and size of holes with increasing degree of branching was observed.