Reversible melting of polyethylene extended‐chain crystals detected by temperature‐modulated calorimetry

Abstract

ABSTRACT:The melting and crystallization of extended-chain crystals of polyethylene are analyzed with standard differential scanning calorimetry and temperature-modulated differential scanning calorimetry. For short-chain, flexible paraffins and polyethylene fractions up to 10 nm length, fully reversible melting was possible for extendedchain crystals, as is expected for small molecules in the presence of crystal nuclei. Up to 100 nm length, full eutectic separation occurs with decreasingly reversible melting. The higher-molar-mass polymers form solid solution crystals and retain a rapidly decreasing reversible component during their melting that decreases to zero about 1.5 K before the end of melting. An attempt is made to link this reversible melting to the known, detailed morphology and phase diagram of the analyzed sample that was pressure-crystallized to reach chain extension and practically complete crystallization.

Solvent Effects on Environmentally Coupled Hydrogen Tunnelling During Catalysis by Dihydrofolate Reductase from Thermotoga maritima

“…Figure 11 illustrates the other extreme of melting behavior—complete irreversibility. The example is the analysis of extended‐chain crystals of polyethylene 37. A supercooling of about 10 K is necessary to regrow the once‐melted crystals, but after the regrowth, the crystals are chain‐folded and melt at a lower temperature.…”

Synthesis of 1,128‐Octacosahectanediol and Its Sharp Thermoresponse in Solution with Concomitant Structural Change

“…Thermal hysteresis indicated the formation of supersaturated solutions during cooling, and high stability of the metastable states was noted in the relaxation by precipitation (Figures and S5). A solution of 1 in toluene‐ d 8 was heated to 80 °C, and no 1 was observed by 1 H‐NMR.…”

Thermodynamics and kinetics of crystallization of flexible molecules

“…At this molar mass it is easy to grow extended-chain crystals. 79 Similarly, extended-chain crystals of high molar mass polyethylene 83 and sharply once-or twice-folded poly (oxyethylene)s of high crystallinity show practically no reversible melting. 84 Completely different classes of polymers are precisely-branched or -interrupted copolymers.…”