Ethylene a-olefin copolymers differ from other polyethylenes in that: -there is no long chain branching; -short chain branching is determined by the comonomer unit; -the molecular mass distribution is sharp; -the side chain distribution on different molecules is broad; -the sequential distribution of branching is very broad along the molecular chains, which becauses a multi-peak lamella distribution, and a multi-peak melting heat.With the help of a cross-fractionation method we interpreted the differences of the experimental data, according to the molecular mass fractionation and the branching received.The thermal history has a great influence on ethylene-a-olefin copolymers, evidenced in the crystallization time for the same branching type, but with extremely varied branching percentages.

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