Characterization of long chain branching in poly(vinyl acetate) and (polyvinyl alcohol) polymers by independent size measurements.

摘要

The branching parameter, g, is used to describe the long chain branching in polymers. It can be measured either in terms of the ratio of the radii of gyration of the branched to linear polymer at the same molecular weight, or the ratio of the intrinsic viscosities of the linear polymer to the branched polymer at the same molecular weight.; Methods of branching analysis involving size exclusion chromatography (SEC) usually depend on the validity of the universal calibration. The use of the on-line multi-angle laser light scattering detector (MALLS) avoids the use of the universal calibration because both the molecular weight and also the radius of gyration can be measured on-line directly. Thus the g values are independent of a calibration curve.; In this study, branched polyvinyl acetate (PVAC) was polymerized to different extents of conversion. Linear polymer at low conversion was also made. As expected, branching was found to increase with percent conversion. The corresponding polyvinyl alcohol (PVOH) samples were made by hydrolysis to give greater than 85% hydrolysis of the PVAC. All of these polymers were measured by SEC with on-line viscometry and on-line light scattering detectors.; {dollar}sp{lcub}13{rcub}{dollar}C-NMR was used to provide a measure of the number of branch points (B{dollar}sb{lcub}rm n{rcub}){dollar} in the PVAC so that a theoretical g could be calculated from the Zimm-Stockmayer equations. For PVAC the g calculated from NMR results, g{dollar}sb{lcub}rm NMR{rcub},{dollar} was found to give values equal to the size based branching parameter determined from MALLS at low conversions. The slope of the plot of size versus molecular weight has an inverse relationship to the branching density defined by {dollar}rm Bsb{lcub}n{rcub}/Msb{lcub}n{rcub}.{dollar} The g{dollar}spprime{dollar} values for PVAC determined by intrinsic viscosity measurements were found to follow g{dollar}sp{lcub}1/2{rcub}{dollar} in which g was measured directly by MALLS. This relationship to g{dollar}spprime{dollar} was found to increase in a linear fashion from low to high conversions. The g{dollar}spprime{dollar} values for the hydrolyzed PVAC indicated that most or all of the branching was removed by the hydrolysis reaction. The limitation was the extent of hydrolysis.