Borane chain transfer agents

Xu, G. Chung, T.C. Borane chain transfer agent in metallocene-mediated olefin polymerization synthesis of borane-terminated polyethylene and diblock copolymers containing polyethylene and polar polymer. J. Am. Chem. Soc. 1999,121, 6763. 

In the presence of a borane chain transfer agent containing a B-H (or B-CH3) group, the metallocene-mediated propagating PP chain (1 in Scheme 7) engages in a facile ligand exchange reaction (11) between C-M (where M indicates transition... 

Lin W, Dong JY, Chung TC (2008) Synthesis of chain end functional isotactic polypropylene by the combination of metallocene catalyst and Borane chain transfer agent. Macnnnolecules 41 8452... 

In a recent development, a new process of preparing borane-terminated isotactic polypropylene (z -PPs) via an in situ chain-transfer reaction was achieved by a styrene/hydrogen consecutive chain-transfer reagent, which avoids the use of a B—H containing chain-transfer agent.74 This has resulted in the utilization of milder polymerization conditions due to the use of the alkylaluminoxane cocatalyst (MAO) (50) (Fig. 33), which cannot normally be used in the presence of a B—H chain-transferring... 

It was also reported that terminally borane-containing POs is available as another macroinitiator to prepare block copolymers (Fig. 4). These polymers were prepared by (1) the metallocene-catalyzed (co)polymerization of olefin(s) with organoborane compounds, for example, 9-borabicyclononane (9-BBN), as chain transfer agents [32], or by (2) the hydroboration of terminally unsaturated polyolefins with BBN [33-36]. 

Block copolymers can be produced from terminally borane-containing polyolefins. These borane-containing POs can be synthesized by the metallocene-catalyzed (co)polymerization of olefin(s) monomer with 9-BBN as a chain transfer agent or by the metallocene catalyzed copolymerization of olefins with allyl-9-BBN [55,56], as referred to above. Alternatively, borane-containing POs were prepared by hydroboration of terminally unsaturated PO, for instance, terminally vinyl PE and terminally vinylidene PP [33-35,57]. Such method could produce diblock copolymers, such as polyethylene-block-poly(methyl methacrylate) (PE-fo-PMMA), polypropylene-foZock-poly(methyl methacrylate) (PP-fc-PMMA), polypropylene-foZock-poly(butyl methacrylate) (PP-fc-PBMA), and PP-fc-PS. 

SCHEME 11.7 Boranes as chain transfer agents (R = alkyl M(L)n = metallocene). 

Scheme 7 Synthesis of chain functional polyolefin using borane eharn transfer agent M transition metal...

Functionalization and Block/Graft Reactions of Syndiotactic Polystyrene Using Borane Comonomers and Chain Transfer Agents... 

As dectron-delident or neutral chain transfer agents, silanes, boranes, and alanes are known and extensively investigated in single-site-catalyzed olefin polymerization in order to obtain heteroatom-ftmctionalized chain ends. Electron-rich chain transfer agents, such as phosphines and amines, have also been smdied on organolantharride-mediated polymerization systems. ... 

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