ABSTRACT
A molecular weight and branching distribution (MWBD) method is presented for measuring long chain branching (LCB) as a function of molecular weight in such polymers as polyvinyl acetate and polyethylene. The method requires intrinsic viscosity (IV) and size exclusion chromatographic (SEC) data on the polymer, and a polystyrene calibration determined under the same solvent-tempera ture conditions. The MWBD method expresses the size separation with elution volume (V) as In [ η ] i M N . i = f ( Vi ) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003065081/c17910f6-7d69-4e95-a799-194ca99cfe28/content/ieq0229.tif"/> , and assumes IV to be described by a polynomial of the form - In [ η ] i = ln K + a 1n M N , i + b ln M N , i 2 + C ln M N , i 3 . https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003065081/c17910f6-7d69-4e95-a799-194ca99cfe28/content/ieq0230.tif"/> . The number-average mole cular weight and the number of branch points on a molecular basis are obtained as a function of elution volume. From this, integration across the chromatogram provides the number average molecular weight M ¯ N https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003065081/c17910f6-7d69-4e95-a799-194ca99cfe28/content/ieq0231.tif"/> and the number-average number of branch points per molecule and per 1000 carbon atoms ( B ¯ N and λ ¯ N https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003065081/c17910f6-7d69-4e95-a799-194ca99cfe28/content/ieq0232.tif"/> , respectively). As part of the MWBD method, C-13 nuclear magnetic resonance spectroscopy is used to validate the method and the theoretical assumptions made.
The utility of the MWBD method is illustrated using a series of commercial high-pressure, low density polyethylenes and poly vinyl acetates. Correlation of the LCB results are made to rheological and blown film properties and to expectations based on reaction kinetics.
