Long Chain Branching in Polyethylene

Abstract

Long chain branching frequency in polyethylene has been measured. Molecular weights determined directly by low angle laser light scattering of eluting species in gel permeation chromatography were compared with those estimated by universal calibration. Erroneous values for long chain branching frequency are produced if care is not taken to disrupt polyethylene aggregates in the GPC solvent. Ethyl and hexyl aide chains do not register as long branches in this analysis but sixteen carbon sidechains are counted. In low density polyethylene the long chain branching frequency is generally highest at low molecular weights. This is because these polymers are produced in a non-isothermal free radical polymerization. Chain transfer to dead polymer, which produces long branches, occurs most frequently under the reaction conditions that also yield low molecular weight polyethylene.