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We have measured by low angle X-ray scattering (SAXS) the long period of fractionated polyethylene (P.E.) quenched from the melt. The P.E. samples were annealed at different temperatures Ti above the melting temperature and for a time greater than the relaxation time defined in Part I. As for polydispersed material, the long period is given by the relationship L(Ti) = L(To) (1 + α(T i - To)) : α is equal to β/2, β being the temperature coefficient of the ideal chain in the liquid state. Three types of behaviour are distinguished according to the value of the molecular weight M of the fractionated samples : M < M1 L ∼ M (1) M1 < M < M2 L∼ M1/2 (2) M > M2 L ∼ M1/22 (3) M1 is the critical molecular weight, above which the chain has a Gaussian behaviour in the liquid state. M1 is of the order of the molecular weight M e of a portion of chain between two entanglements. The scaling law (2) is new, the long period varies like the end to end distance of the coil in the melt. Our results indicate the necessity of introducing a critical value M2 for the molecular weight, above which the long period is constant. From WAXS and SAXS measurements the crystalline core lamella thickness lc is found to be constant, of the order of 170 Å, the distance between two consecutive entanglements along a chain. The experimental scaling laws giving L and lc give information about the process of crystallization of fractionated P.E

Résumé. 2014 Nous avons mesuré les longues périodes de plusieurs polymères trempés à partir de l'état fondu. Nous donnons la relation entre la longue période mesurée dans la phase semi-cristalline et la rigidité de la chaîne dans l'état liquide juste avant la cristallisation. On montre que la mesure des longues périodes d'échantillons préala-blement recuits à l'état fondu, à différentes températures, et pendant des temps différents, nous permet de remonter à un temps de relaxation des pelottes dans le fondu.Abstract. 2014 The long spacing L of several crystalline polydispersed polymers quenched from the liquid state at various temperatures has been measured. We correlate the variations of the long period L with the variations of the dimension r0 > of the ideal coils in the melt just before the crystallization. The relationship between L and the rigidity C of the liquid chain is given. The annealing of the melt at different temperatures and for different times, and the subsequent crystallization allow us to measure the relaxation time of the coils in the liquid state.

Abstract. 2014 The crystallization of mixtures of P.E. fractions quenched from the melt has been studied by SAXS, WAXS and DTA. The laws of variation of the long period with the weight and number average molecular weights are given. It is shown that the long period, L, of the semi-crystalline state is given by the weight average of the end-to-end distance rw of the coils in the liquid state before quenching. For mixtures containing high molecular weight M > M* = 105, the long chains behave like a series of segments of chains of molecular weight M* which crystallize independently. The crystallinity measured by WAXS and DTA varies with the molecular weight and its distribution as the linear crystallinity lc/L ~ lc/rw where lc is the crystalline lamella thickness and is independent of the molecular weight. The correlations emphasized in this paper between the solid and melt states of P.E. support the contention that the structure of lamellar semi-crystalline P.E. is not controlled by the phenomenon of secondary nucleation, but by the dimensions and the rigidity of the coils just before crystallization. The results reported in this paper show that the process of crystallization of short and long chains are different ; that would explain the differences observed in studies of the kinetics of crystallization, and in the morphology of the semicrystalline state when the molecular weight is increased.

It is shown that the molten state and the semi-crystalline state of polydisperse polyethylene are interrelated. Large polydisperse fractions obtained according to Pennings' fractionation method were studied by small angle X-ray scattering and differential thermal analysis; the long period, depending on the molecular weight distribution, is shown to be given by the weight average end-to-end distance of the coils; the long chains with molecular weights M > lo5 behave as a series of "sub-chains" with molecular weight M* = lo5 which crystallize independently. The same result is found for fractions with narrow molecular weight distribution and for mixtures of polyethylene fractions.