High‐temperature coupling of high‐speed GPC with continuous viscometry. II. Ethylene–vinyl acetate copolymers

Abstract

SynopsisAn application of the high temperature coupling of a gel permeation chromatograph with a home-made continuous viscometric detector is described. It concerns the comprehensive characterization of ethylene-vinyl acetate copolymers. Suitable chromatographic conditions are chosen to enable a correct use of the universal calibration concept. Through analysis of poly(viny1 acetate) fractions and commercial polyethylene samples, a comparison is made with the results of classical measurements. Average molecular weights as well as intrinsic viscosity appear to be in good agreement within experimental error, which proves the system for the characterization of random ethylene-vinyl acetate copolymers. In attempting to obtain a reliable estimate of long chain branching frequency A, a series of commercial samples has been selected, with the vinyl acetate weight fraction within the range 045%. As a rule, experimental viscosity law exhibits two parts, a straight line with a Mark-Houwink exponent 0.7 in the low molecular weight region and a curvature, well smoothed by a third-degree polynomial regression. Consequently, long chain branching does not appear before a limiting molecular weight of about 50,000. Beyond this limit, X is 0.5 X with no dependence on molecular weight, which resembles low density polyethylene.

Continuous Viscometric Detection in Size Exclusion Chromatography

“…But, when it is unknown, we have remarked, during our studies (9)(10)(11)(15)(16), that branching usually occurs only after a limiting molecular weight, which produces a linear variation in the low molecular weight region of the viscosity law. Taking the slope in this region can prcvide the visocsity law of the linear polymer (16).…”

Copolymer analysis

“…A continuous viscometer was also applied to the analysis of an EVA copolymer, in 1,2, 4-trichlorobenzene at 135°C [34]. A relationship of 10g [11] v. 10gM for EVA copolymers was composed of two parts: a straight line in the low-molecular-mass region, the limiting molecular mass (M)) being about 50000, and a curve above M) well smoothed by a thirddegree polynomial regression.…”

Data Treatment in Aqueous GPC with On-Line Viscometer and Light Scattering Detectors

“…On this basis. several viscometers were studied in different laboratories (3)(4)(5)(6)(7)(8)(9)(10)(11)(12) and now, two models are commercially available from Viscotek (13) and Waters Associates (14.16). A t t h e same time, the lowangle laser light scattering (LALLS) technique was introduced by Ouano and Kaye in 1974 (16.17) and developed by Chromatix (18) and recently, a new multi-angle light scattering technique has been commercialized by Wyatt Technology Corp. (19).…”