9-BBN chain transfer agent

Table 7 Summary of metallocene-mediated ethylene (1 atm) polymerization in the presence of 9-BBN chain transfer agent, using [Cp 2ZrMe] [MeB(C6F5)3] (I), [Cp 2ZrMe] [B(C6F5)4] (II), [(Ind)2ZrMe] [MeB(C6F5)3] (III), and [Cp2ZrMe] [MeB(C6F5)3] (IV) catalysts...

The other approach to eliminating the concerns about the B-H chain transfer agent is to use trialkylborane (without B-H moiety), e.g., methyl-substituted 9-BBN (Me-B-9-BBN) and trimethylborane (TMB) that have a B-CH3 moiety. Table 8 summarizes Cp2ZrCl2/MAO mediated ethylene polymerization in the presence of the Me-B-9-BBN chain transfer agent. For comparison, triethylborane (TEB) was also used as the chain transfer agent under similar polymerization... 

Figure 32 The dimeric organoborane chain-transfer agent, 9-BBN dimer (49), used for the in situ incorporation of B-containing group in polyolefins during the termination of a metallocene-catalyzed polymerization. (Adapted from ref. 71.)...

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. 

Fig. 15.4 Plot of 1/DP against the ratio of concentrations of chain-transfer agent (CTA) and cycloocta-1,5-diene (COD), (a) CTA = 6-(9-BBN)-hex-l-ene (b) CTA = 6-(9-BBN)-dec-5-ene (9-BBN = 9-borabicyclononane) (Chung 1992a).

Table 8 Summary of Cp2ZrCl2/MAO-mediated ethylene polymerization in the presenee of Me-B-9-BBN and TEB chain transfer agents at 50°C...

TABLE 19.3 Metallocene-activated Styrene Polymerization in the Presence of 9-BBN as Chain Transfer Agent ... 

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