Controlling external diphenylcyclohexylphosphine feeding to achieve cis-1,4-syn-1,2 sequence controlled polybutadienes via cobalt catalyzed 1,3-butadiene polymerization

Add time:09/10/2019    Source:sciencedirect.com

Microstructure and unit sequence are critical parameters that determine the properties of polybutadiene materials. In this contribution, we have reported the syntheses, characterization of 6-(di-tert-butyl-phosphine) amine fused 2-R-pyridine compounds (R = 1′H-oxazoline (L1); 4′,4′-dimethyl oxazoline (L2); 4′-isopropyl oxazoline (L3) supported cobalt dichloride complexes and their performances in regio-selectivity, sequence and molecular weight controlled polymerization of butadiene. In combination with MMAO, the cobalt-mediated polymerization displays many characteristics of a living and cis-1,4 polymerization system over a wide temperature window of 0–80 °C. We show it is possible to tune the number average molecular weight in the range of 152–164 kg/mol with narrow MWD values of 1.04–1.34. The steric bulkiness on the catalysts has detrimental effect on the polymerization rate, (kobs(Co1, substituent free) of 0.037 L/mol·min. >Kobs(Co3, isopropyl) of 0.030 L/mol·min. >Kobs(Co2, dimethyl) to 0.024 L/mol·min.). With diphenylcyclohexylphosphine (Ph2CyP) as in-situ additive, the cobalt catalyst is highly active in cis-1,4 and 1,2-syndiotactic tunable butadiene polymerization to produce various cis-1,4-block-syn-1,2 polybutadienes differing in block length. By continuous Ph2CyP feeding, this cobalt catalyst has been applied for the first synthesis of a regiogradient polybutadiene which starts with a cis-1,4 rich polybutadiene block and ends with an syn-1,2 rich block where the 1,2 specificity controlled between 28.7 and 88.5 mol%, moderate syndiotacticity (rr) of 49.8–64.5% and controlled molecular weight. The processing and mechanical properties were also evaluated. The phosphine dependent regio-selectivity and sequence controlled polymerization provide an simple and efficient strategy for various cis-1,4-syn-1,2 multi-block and cis-1,4-syn-1,2 regiogradient polybutadiene with tunable physical and mechanical properties.

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