Simultaneous measurement of the molecular weight distribution and 5‐ethylidene‐2‐norbornene content across the molecular weight distribution of ethylene–propylene–diene terpolymer via a new size exclusion chromatography–ultraviolet–refractive index method

Abstract

ABSTRACTA size exclusion chromatography (SEC)–UV–refractive index (RI) method was developed to measure the 5‐ethylidene‐2‐norbornene (ENB) content across the molecular weight distribution (MWD) in ethylene–propylene–diene terpolymer (EPDM) at room temperature. The ratio of the UV and RI signals at the same effective elution volume was converted to ENB content. The feasibility of using this method to measure the ENB content across the MWD in EPDM at high temperature was also demonstrated. Prior understanding was that ENB had insufficient UV absorbance relative to high‐temperature SEC solvents to allow for useful measurements. We demonstrated this by using high‐boiling‐point solvents, such as decalin, with a low UV absorbance in the UV wavelength range of interest for ENB. These solvents also gave rise to a high enough specific RI increment (dn/dc) for EPDM that a suitable RI detector response was obtained. Additionally, this methodology could be readily applied to other polymers soluble at high temperature as long as the polymers contained a UV chromophore. These include polymers containing vinyl, conjugated vinyl, aromatic ring, carbonyl, or halocarbon groups. This UV‐absorption‐based detection concept might also be extended to high‐temperature thermal‐gradient interactive chromatography‐UV, high‐temperature solvent‐gradient interactive chromatography‐UV (high‐temperature liquid chromatography‐UV), temperature‐rising elution fractionation‐UV, crystallization analysis fractionation‐UV, and crystallization elution fractionation‐UV. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43911.