Borane monomer copolymerization

In addition, borane-containing POs can be prepared by copolymerization of olefin with borane monomers or by hydroboration of polyolefins including unsaturated groups, such as olefin-divinylbenzene copolymer and olefin-diene copolymers. Many kinds of graft copolymers, such as poly-elhylene-gra/f-poly( vinyl alcohol), PE-g-PMMA, polypropylcnc-gra/f-poly-(maleicanhydride-co-styrene), polypropylene-gra/f-poly(methacrylic acid), polypropylene-gra/f-poly(vinyl alcohol), polypropylene-gra/f-polycaprolac-tone (PP-g-PCL), polypropylcnc-gra/f-poly(methyl methacrylate) (PP-g-PMMA), poly( ethylene-co-propylene)-gra/f-poly(methyl methacrylate) (EPR-g-PMMA), and poly(ethylene-co-propylene)-gra/f-poly(maleic anhydride-costyrene), have been synthesized by such a method resulting in controllable composition and molecular microstructures [63-66]. 

Another possibility in the functionalization of polyolefins results from the copolymerization of olefins with boran monomers. Chung and Rhubrigut... 

FUNCTIONALIZED POLYOLEFINS via COPOLYMERIZATION OF BORANE MONOMERS IN ZIEGLER-NATTA PROCESS... 

A comonomer that contains a reactive group should exhibit three essential properties (1) good stability with metallocene catalyst, (2) good solubihty with the reaction media, and (3) facile interconversion of reactive group into functional (polar) groups, such as OH and NH2 groups, after polymerization [3, 34]. In previous years, we had identified three suitable reactive comonomers, i.e., borane monomer, p-methylstyrene (p-MS), and divinylbenzene (DVB), as illustrated in Scheme 1. In concert with the selected metallocene catalysts, the copolymerization reactions take place to form well-controlled reactive polyolefin copolymers with various reactive sites in the side chains. Subsequently, the incorporated reactive... 

Chung TC, Rhubright D (1993) Kinetic aspects of the copolymerization between o-olefins and Borane monomers in Ziegler-Natta catalyst. Macromolecules 26 3019... 

In a continuous polymerization process, this observed activity behavior directly influences the obtained microstmcture of the polymer. Thus, a copolymerization of propene and the borane monomer leads to a copolymer, because of the preferred incorporation of propene, with long propene sequences. This copolymer forms crystalline phases similar to those obtained in pure isotactic PP. The borane groups are located in the amorphous part of the copolymer and so even under heterogeneous and mild conditions a modification of the borane groups (e.g., conversion to alcohol functionalities) can be performed quantitatively. This behavior leads to a polar modified polymer that can co-crystallize with pure isotactic PP and thus be used in polymer blends in order to optimize the PP adhesion to other materials such as aluminum and glass. 

A radical initiator based on the oxidation adduct of an alkyl-9-BBN (47) has been utilized to produce poly(methylmethacrylate) (48) (Fig. 31) from methylmethacrylate monomer by a living anionic polymerization route that does not require the mediation of a metal catalyst. The relatively broad molecular weight distribution (PDI = (MJM ) 2.5) compared with those in living anionic polymerization cases was attributed to the slow initiation of the polymerization.69 A similar radical polymerization route aided by 47 was utilized in the synthesis of functionalized syndiotactic polystyrene (PS) polymers by the copolymerization of styrene.70 The borane groups in the functionalized syndiotactic polystyrenes were transformed into free-radical initiators for the in situ free-radical graft polymerization to prepare s-PS-g-PMMA graft copolymers. 

Controlled radical polymerization (CRP) is an attractive tool, because of the resultant controllability of polymerization, and because of it being a versatile method to synthesize of well-defined polymer hybrids. The three main radical polymerization techniques, ATRP, NMP, and RAFT polymerization, have thus been employed. Other techniques, such as the oxidation of borane groups, have also been studied. In general, using CRP techniques, block copolymers can be synthesized from terminally functionalized PO as PO macroinitiator, and block copolymers can be prepared from functionalized PO produced by the copolymerization of olefins with functional monomers. 

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. 

Chiral oxazoborolidine systems have been regularly used as catalysts for the enantioselective Diels-Alder reaction [173]. Such a catalyst has been immobilized by copolymerization of a sulfonamide-modified styrene monomer to produce polystyrene beads and subsequently reacted with borane to furnish catalyst 49 (Scheme 4.77). A column of 49 was cooled to —30 °C and a 1 1.5 methylacrolein cyclopentadiene solution was flowed in. Following aqueous workup and column chromatography, the desired product 50 was isolated to yield 138 mmol of product in 95% yield and 71% ee by using only 5.7 mmol of catalyst. This result was found to be comparable with the heterogeneous batch reactions that were also attempted [174]. 

Yet another methodology involves the metallocene-catalyzed copolymerization of olefins with borane containing monomers (466,467). The incorporated borane group can be quantitatively converted to a hydroxy group or transformed into a stable poljnneric radical suitable for free radical grafting of acrylates. 

Direct copolymerization of aromatic a-olefins and borane-containing monomers with early tmnsitlon metal catalysts Beside the early transition metal-catalyzed copolymerization of aliphatic a-olefins with borane-containing monomers. 

An extensive study of the copolymerization of bicyclo[2.2.1]heptadiene with vinyl monomers has been described (170). Radical initiators such as trialkyl-boranes with oxygen were employed and products well into the useful molecular weight range were obtained. On the basis of infrared evidence, all of the bicyclo[2.2.1]heptadiene was stated to be present in the polymers as nortricyclene units. Vinyl chloride copolymers were studied most extensively, but most of the other commercial vinyl monomers were also examined 170). 

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