Melting temperature of the n-alkanes and the linear polyethylenes

Abstract

The melting behavior of n-alkanes up to carbon number 390 and molecular weight fractions of linear polyethylene up to M" = 5600 have been analyzed. Surprisingly, it is found that the melting temperature-molecular weight relation is the same for both types of chain molecules. The results are explained in terms of premelting of the n-alkanes, with the disordering of sequences of end units, so that the structure prior to melting is the same as that of the polymer. Support of this conclusion is given by theoretical considerations and experimental results. The difficulties in extrapolating the present data base to the equilibrium melting temperature of the infinite molecular weight chain are discussed.

Structure Formation in the Crystallization and Annealing of Tetracontane Nanoparticles

“…The final total energy, intermolecular and intramolecular energy at different temperatures also have a sharp increase around 365 K (not shown). The T m obtained from the present simulations lies between the experimental T m of the bulk tetracontane (354.5 K) [54] and that of bulk crystalline PE (414-419 K). [51] The surprising result that the experimental T m of bulk tetracontane is about 10 K lower than the simulated T m for the nanoparticle could be fixed by reducing slightly the size of e in the LJ potential, as described earlier in the simulation of the melting of thin films.…”

The Crystallization Behavior of Long Chain N-Alkanes and Low Molecular Weight Polyethylenes

“…!,-alkane with 168 carbon atoms (corresponding to 2350 glmol) folds after rapid crystallization. When crystallized from solution, the limiting molecular weight for the formation of folded-chain crystals is slightly lower than in the crystallization from the melt, but still very similar [22]. A limiting molecular weight for the formation of folded structures is also predicted by nucleation theory applied to finite chain molecules [4].…”

“…Since the synthesis of long chain n-alkanes containing between 100 and 400 carbon atoms [1][2][3], emphasis has been directed to the study of the nucleation [4][5][6][7][8], morphology [9][10][11][12][13][14], crystallization kinetics [15][16][17][18], thickening [19][20][21] and melting processes [16][17][18][19][20][21][22] of these ideal model systems. These studies will serve as a bridge to the crystallization behavior of polymers by comparing the characteristics of these n-alkanes with those of low molecular weight linear polyethylene fractions crystallized from either the bulk or from dilute solution.…”

“…In the high crystallization temperature region, close to the melting or dissolution of the initial folded crystals, the isothermal energy fluctuations, which initiate melting of a portion of a crystallite, will be combined with a premelting process, involving the disordering of end sequences, and known to take place in normal paraffins at these temperatures [16,22,[27][28][29]. Both processes increase with increasing temperature and, therefore, vary in the same direction as the rate of thickening.…”

Contribution to the study of thermal, biological and photo degradation of polylactide

“…It is well known that T m º may decrease at lower molar mass. For the thermal degraded samples, was calculated according to Mandelkern et al [110]. This study considers that the variation is related to the carbon units of the molecule of n-alkenes.…”