The drawing behavior of a series of linear polyethylene homopolymers with weight‐average molecular weight (M̄w) ranging from 67,800 to ∼3,500,000 and variable distribution (M̄w/M̄n = 5.1−20.9) has been studied. Sheets were prepared by two distinct routes: either by quenching the molten polymer into cold water or by slow cooling below the crystallization temperature (∼120°C) followed by quenching into cold water.When the samples (2 cm long) were drawn in air at 75°C using a crosshead speed of 10 cm/min it was found that for low M̄w polymers the initial thermal treatment has a dramatic effect on the rate at which the local deformation proceeds in the necked region. At high M̄w such effects are negligible. An important result was that comparatively high draw ratios (λ > 17) and correspondingly high Young's moduli could be obtained for a polymer with M̄w as high as 312,000. It is shown how some of the structural features of the initial materials (mainly studied by optical microscopy, small‐angle x‐ray scattering and low‐frequency laser Raman spectroscopy) can be interpreted in terms of the molecular weight and molecular weight distribution of the polymers. Although crystallization and morphology can be important at low M̄w, it suggested that the concept of a molecular network which embraces both crystalline and noncrystalline material is more helpful in understanding the drawing behavior over the whole range of molecular weights.

SynopsisThe drawing behavior of linear polyethylene homopolymers with weight-average molecular weights (Ml,J from 101,450 to ca. :3.500,000 has heen studied over the temperature range 75°C to the melting point. In all cases 1-cm gauge length samples were drawn in an Instron tensile testing machine a t a constant cross-head speed of 10 cm/min. With the exception of the lowest molecular weight polymer, it was found that increasing the draw temperature led to substantial increases in the maximum draw ratio which could he achieved, and that this increased monotonically with increasing draw temperature. Measurements of the Young's modulus of the drawn materials showed, however, t h a t the unique relationship between modulus and draw ratio previously established for drawing a t 75°C was not maintained to the highest draw temperatures. T h e highest draw temperature a t which this relation held was found to be strongly molecular weight dependent, increasing from ca. 80 to ca. 125°C when M,,. increased from 101,450 to 800,000, In all cases conditions could be found for drawing samples to draw ratios of 20 or more with correspondingly large values of the Young's modulus.

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The influence of the degree of crystallinity and morphology on the drawing behavior of linear polyethylene (LPE) has been investigated on three polymers with molecular weights ranging from 67,000 to over 300,000. Samples of similar crystallinity, but different morphology, were obtained by subjecting the polymers to two distinct preparations: slow cooling from the melt in one case and rapid quenching followed by annealing at 120°C in the other. The resulting isotropic products, characterized by optical microscopy and density measurements were drawn at constant speed and the deformation process monitored by recording the draw ratioldraw time relationship and the stresdstrain curves. The results indicate that crystallinity per se does not have a primary effect in determining the rate of local deformation except in the case of polymers of very low weight average molecular weight and narrow molecular weight distribution. A dominant role seems to be played by the broad features of the sample morphology as detected by optical microscopy. A comprehensive explanation of these results is based on the concept of a network structure whose nature is affected by the annealing treatment to an extent which depends on the degree ofcoupling between adjacent crystalline regions in the isotropic undrawn polymer.