Abstract
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, Macromolecules 2013, 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. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1261–1272
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