Measurement of the absolute molecular weight and molecular weight distribution of polyolefins using low‐angle laser light scattering

Abstract

SynopsisBy connecting a low-angle laser light scattering photometer (LALLSP) on line with a high-temperature gel permeation chromatograph (GPC), molecular weight distributions were determined for three polyethylene standards (two high density and one low density) without resorting to column calibration procedures. In addition, the absolute weight-average molecular weight and second virial coefficients of four polyethylene standards (three high density and one low density) were obtained using low-angle laser light scattering. The molecular weights measured were in excellent agreement with those specified by the National Bureau of Standards, For the low density material, a microgel fraction was detected by the on-line LALLSP but not by the conventional GPC detector. This resulted in a z-average molecular weight of over 3 X 106 daltons, an order of magnitude greater than that determined by conventional GPC techniques.

High molecular weight tail and long-chain branching in SRM 1476 polyethylene

“…The detection of a second peak at small elution volumes is consistent with earlier reports. 6,10,18,20 This secondary peak was not present in the response of the DRI and VD detectors, which is consistent with earlier on-line viscometer and SEC studies. [3][4][5][6][7]9,10 The difference in response between the LSD and the VD detectors is not surprising because it reflects the difference in sensitivity.…”

“…18 Grinshpun et al described the 3.4 ϫ 10 6 value of M z that they observed as arising from spikes in their LS chromatogram and attributed them to supermolecular aggregates. 17 Because no spikes were observed in the light scattering chromatogram in Figure 1, the presence of undissolved aggregates can be ruled out in our work.…”

“…Particularly striking, however, are the values of z-average molecular weight (M z ) obtained by SEC-LSD, which can be up to an order of magnitude higher than the value obtained by SEC-VD. 12,17,18 It was these differences in molecular weight averages that first led some authors 6,7,10,18,19 to suggest the presence of a high molecular weight tail in the polymer.…”

Molecular chain heterogeneity of a branched polyethylene resin using cross-fractionation techniques

“…In literatures, the molecular weight and molecular weight distribution (MWD) of SRM1476 have been reported, and its long-chain branching (LCB) effect has been also studied. For example, Wagner, Beer, Penlidis, Wild, et al estimated its branch structures and MWD [29][30][31][32][33][34][35][36]. Moreover, Beer et al investigated its high molecular weight tail and LCB effect [33,35].…”

Measurement and modeling of poly(vinyl acetate)–solvent viscosity mixtures

“…Osmotic pressure6, 7 and intrinsic viscosity ([η])8–12 methods are used for the determination of M n 13, 14. Sedimentation,15, 16 diffusion,17–19 and light scattering20–24 methods are suitable for the determination of M w . These methods of molecular weight determination are primary methods, and other methods, such as high‐performance liquid chromatography25 and electrophoresis,26, 27 are considered secondary methods 13…”