Structure and thermal properties of ethylene/4-methyl-1-pentene copolymers: Effect of comonomer and monomer sequence distribution

• A series of ethylene/4-methyl-1-pentene (E/4M1P) copolymers is synthesized and characterized.
• The copolymers structure depends on composition and monomer sequence distributions.
• E/4M1P copolymers show a multimodal crystallization and melting behavior.
• 4M1P units were not homogeneously distributed along the polymer chain.
• The chain heterogeneity was studied by successive self-nucleation and annealing technique.

A series of ethylene/4-methyl-1-pentene (E/4M1P) copolymers is synthesized, using the Ti(IV) diisopropoxy complex bearing a dianionic [O−, S, O−] bis(phenolato) ligand, in combination with methylalumoxane, as catalyst system. The semicrystalline copolymers are characterized by NMR, DSC, WAXD and SAXS. The structure and the thermal behavior of the copolymers are strongly influenced by composition and monomer sequence distribution. The copolymer crystallinity decreases as a function of 4M1P content, while an increase of the periodicity due to the enhancement of the amorphous interlamellar thickness is registered. The non-homogeneous distribution of the 4M1P units along the polymer chains is evidenced by the multimodal crystallization and melting behavior. The chain heterogeneity of the copolymers is investigated by successive self-nucleation and annealing thermal fractionation evaluating the methylene sequence length, the short chain branching and the lamellar thickness. In order to get more information on the comonomer distribution in the copolymers, solvent extraction is performed and all the fractions are characterized by thermal and X-ray techniques.

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