Extremely fragile glass-formers? Calorimetric and rheological determinations

We use calorimetry and rheology to investigate reports of extremely fragile polymers and the speculation that d,l-lactic acid should be extremely fragile. The dynamic fragilities of lactic acid, polysulfone, bisphenol-A polycarbonate, and poly(vinyl chloride) were studied. The polymers were used as received and after a wash-precipitation treatment. The current dynamic fragility findings are not in agreement with those reported by C. Evans, H. Deng, W. Jager, J. Torkelson, Macromolecules2013, 46 (15), 6091-6103 of extremely high fragilities for the mentioned polymers. We also found no sample preparation history effect on the dynamic fragility values. The calorimetric and rheological results for the d,l-lactic acid show dynamic fragility values that are consistent with each other and are not extremely fragile. Calorimetric measurements that use a broad range of cooling rates gave smaller dynamic fragility values than those obtained from a limited range at higher cooling rates. The importance of the results is discussed. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1261-1272