Influence of <i>n</i>-Alkyl Branches on Glass-Transition Temperatures of Branched Polyethylenes Prepared by Means of Metallocene- and Palladium-Based Catalysts

Abstract

Branched polyethylenes with controlled molecular architectures were prepared by means of metallocene-catalyzed copolymerization of ethylene with 1-olefins such as propylene, 1-butene, 1-hexene, and 1-octene and by means of migratory-insertion-type ethylene homopolymerization using methylpalladium diazadiene borate as catalyst. Glass-transition temperatures, Tg, as determined by means of dynamic mechanical analysis (DMA), were correlated with propylene and 1-butene weight fractions of ethylene copolymers over the entire composition range. Several correlations between degree of branching and Tg were evaluated for ethylene-rich copolymers and branched ethylene homopolymers. The conventional degree of branching is defined as the number of branched tertiary C atoms per 1000 C atoms of the methylene units or 1000 C atoms of the entire polymer chain. We propose a new degree of branching that is defined as sum of the number of branched tertiary C atoms in the polyethylene chain and the C atoms of the n-alkyl branch, referred to 1000 C atoms of the polyethylene backbone, that gives excellent correlation with Tg of branched polyethylene, independent of the branch type and the synthetic route used to prepare branched polyethylene.