Measurement and Modelling of Long Chain Branching

Abstract

<p>The measurement and modelling of long chain branching (LCB) in free-radical chain growth polymerization is examined. A new method, the "instantaneous" property method, is presented for the calculation of the full molecular weight distribution(MWD) of branched polymers when the branching is due to chain transfer to polymer. The method is shown to be accurate and consistent with the method of moments, the method that is generally used to calculate molecular weight averages. The method can give additional detail about the MWD of the various branched families in the polymeric mixture. Such information can be quite useful in correlating processing properties with molecular structure. Two polymers that produce LCB when polymerized were examined. Bulk polymerization of vinyl acetate (VAc) and p-methyl styrene were carried out. Gel permeation chromatography. intrinsic viscosity and low angle laser light scattering measurements were used to measure molecular weight averages and LCB frequencies. Two methods were used to calculate LCB frequencies and they both gave results that were consistent with the method of moments. The "instantaneous" method was applied to the data from the polymerization of PPMS since for this polymer LCB is due to chain transfer to polymer. The predictions from the "instantaneous" method, when compared to the method of moments and the experimental data, were shown to be of acceptable accuracy.</p>