Influence of long‐chain branching on the viscoelastic properties of low‐density polyethylenes

Abstract

Melt How data has been determined for a series of fractionated and whole low density polyethylenes which has been characterized in terms of their molecular weights and degree of long‐chain branching, (LCB). The resulting data indicate that low LCB influences melt flow both through a reduction in molecular size and an increased level of intermolecular interaction. Die swell measurements on whole polymers indicate an increase in melt elasticity with increase in degree of LCB for samples of similar melt flow (MI). Comparison of GPC data with observed die swell characteristics indicates that die swell is a molecular size dependent property and independent of intermolecular entanglement effects, suggesting that the measurement of elastic properties of LDPE melts will provide a means of determining relative degrees of LCB for commercial resins.

Characterization of Metallocene Epdm Terpolymers with High Diene and Propylene Content Crosslinked by Dicumyl Peroxide and β‐Radiation

“…The molecular weights of the polymers were estimated following the standard calibration procedure using monodisperse polystyrene samples and the corresponding Mark-Houwink coefficients for polystyrene and linear polyethylene in TCB. [12,13] The corresponding coefficients for EPDM in TCB were not found in the bibliography, so the molecular weights must be only considered qualitatively.…”

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

“…Wild et al [46] explained these features by pointing out the predominant effect of entanglements at low degrees of LCB (differences in g are not noticeable and the polymers are 'essentially linear') and the molecular size reduction effect at medium and high degrees of LCB (values of g < 1). Using this approach, Bersted [47,50] developed a model that predicts a Newtonian viscosity peak at a branching level of approximately 2.5 LCB/10 4 C and a subsequent decrease at higher LCB density, as a consequence of the decrease in molecular size (see Fig.…”

“…[7] When the LCB content is very low (less than 1 LCB /10 4 C), its effect on the radius of gyration goes unnoticed and values of g ≈ 1 are obtained [42]. The effect of such a low amount of LCB has been explored in LDPE and in modified linear polymers of ethylene/α-olefins and propylene (PP) by irradiation, electron-beam treatment, peroxide reaction, and thermal/mechanical degradation [7,10,17,[44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59]. In principle, lowpressure processes (chromium-based and Ziegler-Natta type catalysts, developed in the 1950s and 1970s, respectively) yield linear species.…”

Influence of shearing history on the rheological properties and processability of branched polymers. V. Effect of molecular structural parameters on die swell of low‐density polyethylenes

“…This object is readily achieved by comparing the swell ratio of sample A-0 with that of In conclusion, we can say that the swell ratios of the solvent-treated materials increase with increase in M , and MWD but decrease with increase in A. By the way, classifying the swell ratios on the basis of the MI range, i.e., [3][4][5][7][8]22-24, the swell ratios increase with increase in A as shown by the solid lines in Figure 1. This finding seems to be in conflict with the conclusion already mentioned.…”