Synthesis and characterization of low molecular weight poly(1-butene) macromolecules prepared using metallocene catalysts

• Low molecular weight poly(1-butene) (Mw < 20,000 g mol−1) was prepared with two metallocenes.
• The studied metallocenes allowed obtaining isotacticities within 50–90%.
• Higher hydrogen pressures (>3 bar) decreased the molecular weight to 3000–4000 g mol−1.
• Higher temperatures (105 °C) decreased the molecular weight below 5000 g mol−1.
• XRD patterns and DSC of poly(1-butene) showed mostly the presence of mixed phases.

Poly(1-butene) low molecular weight macromolecules with molecular weights within 1000–20,000 g mol−1 and isotacticities around 50–90% were prepared by the polymerization of 1-butene in liquid phase with n-butane as solvent using two metallocene catalysts: rac-dimethyl-silyl-bis-(2-methyl-4,5-benzoindenyl)zirconium dichloride (A) and rac-dimethyl-silyl-bis-(2-methylindenyl)zirconium dichloride (B). Catalyst A showed higher yields and productivities than catalyst B, as well as better isotacticity values, which were ascribed to the presence of an additional aryl substituent in the indenyl moiety which increases its stability and hinders deactivation phenomena by aggregation. Kinetic experiments with catalyst A showed a continuous increase in conversion along the time so no strong deactivation was observed. With catalyst A, an increase in the hydrogen pressure at 75 °C up to 6.0 bar led towards low molecular weight macromolecules with 3000–4000 g mol−1 and a isotacticity of 75–80%. An enhancement in temperature up to 105 °C decreased the yields, molecular weights and isotacticity for both catalysts. Additionally, increasing the hydrogen partial pressure to 1.0 bar at 95 and 105 °C decreased the molecular weight within the 3000–5500 g mol−1 range. XRD patterns of the majority of low molecular weight macromolecules showed the presence of mixed phases, although some low molecular weight macromolecules with pure phase I (twined hexagonal) were obtained. Additionally, the DSC thermograms showed a decrease in the melting temperatures of the crystalline phases of poly(1-butene) low molecular weight macromolecules with regard to the corresponding ones of poly(1-butene) polymers (Mw > 100,000 g mol−1), due to their lower molecular weight.

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