Free Volume in the Melt and How It Correlates with Experimental Glass Transition Temperatures: Results for a Large Set of Polymers

There is a continuing, strong interest in making connections between the polymeric glass transition (T-g) and bulk properties. In this Letter we apply the Locally Correlated Lattice (LCL) model to study a group of 51 polymers and demonstrate two broad correlations. In the first, we show that the theoretically determined polymeric free volume in the melt, all at a single common T, P (425 K, 1 atm), correlates noticeably with the experimentally determined T-g values, and that this tend sharpens considerably when families of polymers are examined. Further, we show a strikingly linear correlation between the experimental T-g and the LCL model calculation for the percent free volume expected at the polymeric T-g. We suggest that this trend has a predictive value, acting as a boundary of T-dependent minimum-required free volume separating the melt and glassy regimes. Our theoretical estimates of free volume values at a polymer's T-g range between 4 and 16%, and their evident temperature dependence indicates an important role for temperature in glassification.