Influence of n-alkyl branches on glass-transition temperatures of branchedpolyethylenes prepared by means of metallocene- and palladium-based catalysts

Branched polyethylenes with controlled molecular architectures were prepare d by means of metallocene-catalyzed copolymerization of ethylene with l-ole fins such as propylene, l-butene, l-hexene, and 1-octene and by means of mi gratory-insertion-type ethylene homopolymerization using methylpalladium di azadiene berate as catalyst. Glass-transition temperatures, T-g, as determi ned by means of dynamic mechanical analysis (DMA), were correlated with pro pylene and l-butene weight fractions of ethylene copolymers over the entire composition range. Several correlations between degree of branching and T- g were evaluated for ethylene-rich copolymers and branched ethylene homopol ymers. The conventional degree of branching is defined as the number of bra nched tertiary C atoms per 1000 C atoms of the methylene units or 1000 C at oms 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 polyeth ylene chain and the C atoms of the n-alkyl branch, referred to 1000 C atoms of the polyethylene backbone, that gives excellent correlation with T-g of branched polyethylene, independent of the branch type and the synthetic ro ute used to prepare branched polyethylene.