Synthesis and characterization of low- and medium-molecular-weight hyperbranched polyethylenes by chain walking ethylene polymerization with Pd¨Cdiimine catalysts

详细信息    查看全文

• 作者：Peng Xiang ; Zhibin Ye  ; ;   ; ^{zye@laurentian.ca} ; Ramesh Subramanian
• 关键词：Hyperbranched ; Polyethylene ; Polymerization
• 刊名：Polymer
• 出版年：2011
• 出版时间：13 October 2011
• 年：2011
• 卷：52
• 期：22
• 页码：5027-5039
• 全文大小：992 K

文摘

We report in this article the synthesis and characterization of a range of hyperbranched polyethylenes having various low and medium molecular weights by chain walking ethylene polymerization with Pd¨Cdiimine catalysts of reduced ligand steric crowdedness, which are intended for potential applications as novel synthetic base stocks. Four Pd¨Cdiimine catalysts featured with different ligand crowdedness, ([(RC₆H₃NC(R?¨CC(R?NC₆H₃R)Pd(CH₃) (NCMe)]SbF₆) (1, R?=?2,6-(iPr)₂, R¡ä??CH₃; 2, R?=?CH₃, R¡ä??H; 3, R?=?2,6-(iPr)₂, R¡ä??H; 4, R?=?CH₃, R¡ä??CH₃), were employed herein for ethylene polymerizations at different conditions. Generally, reducing ligand steric crowdedness (in the order 1?>?4?>?3?>?2) leads to decreased catalyst activity and dramatically reduced polymer molecular weight. As opposed to high-molecular-weight polymers (weight-average molecular weight (M_w): about 150?kg/mol) obtained with catalyst 1, low-molecular-weight polymers (M_w: below 1.0?kg/mol) were obtained with 2 and 3, and medium-molecular-weight polymers (M_w: about 25?kg/mol) were produced with 4. Despite their various reduced molecular weights, the polymers are all featured with highly branched chain structures with a total branching density of above 100 branches per 1000 carbons. The low- and medium-molecular-weight hyperbranched polymers synthesized with 2?b xmlns="""">4 display good potential for applications as synthetic base stocks. In comparison with three commercial poly(¦Á-olefin) based synthetic base stocks, they exhibit similar thermal and viscosity properties. Meanwhile, it is also discovered that a subsequent one-pot hydrogenation step can be incorporated in the process after the Pd¨Cdiimine catalyzed polymerization step to render nearly fully saturated hyperbranched polymers without the use of additional hydrogenation catalysts.