Branched methyl-substituted polymers

Due to this chain-migration process ethylene is polymerized to macromolecules containing multiple branches - rather than to the linearly enchained polymer obtained with classical solid-state catalysts. In propylene polymerization with these catalysts 1,2-insertions give the normal methyl-substituted polymer chains, but after each 2,1-insertion the metal centre is blocked by the bulky secondary alkyl unit and can apparently not insert a further propylene. Instead the metal must then first migrate to the terminal, primary C atom before chain growth can continue by further propylene insertions. By this process, also called 1,CO-enchainment or polymer straightening, some of the methyl or (in the case of higher olefins) alkyl substituents are incorporated into the chain. 

A series of methyl-substituted polymers, with varying numbers of methylene units between the terminal olefin and the branch point [58], demonstrated that, when there are at least two methylene units separating the olefin and branch point, there is little effect on the catalysis of the reaction. A series of poly(l,4-alkylenephenylene)s have also been prepared by ADMET with Schrock s molybdenum, Grubbs first-generation, and classical catalysts [59]. This series demonstrated that hydrocarbon dienes containing aromatic groups are readily polymerizable by ADMET, even when there is only one methylene unit between the olefin and the aromatic group. 

There has been a great deal of interest in the design of dendrimers using arene complexes of transition metals (246-252). Astruc has developed an efficient route to core molecules suitable for the synthesis of star and dendritic materials via peralkylation or allylation of methyl-substituted arene complexes of cyclopen-tadienyliron. The resulting branched polymers contained cationic cyclopentadi-enyliron moieties at the core and/or the periphery. Complexes containing aryl ethers coordinated to six CpFe+ moieties (110) were synthesized via SNAr reactions (248). 

Astruc and coworkers have reported the synthesis of highly branched polymers coordinated to cyclopentadienyliron and pentamethylcyclopentadienyl-ruthe-niiun cations." The catalytic and sensing ability of star polymers and dendrimers has also been reviewed. Multifunctional core molecules suitable for the synthesis of star and dendritic materials were synthesized by peralkylation or aUylation of methyl-substituted arene complexes of cyclopentadienyliron." The benzylic protons on these complexed arenes are acidic, which permits their facile alkylation. These branched polymers contained cationic cyclopentadienyliron moieties at the core and/or the periphery. The synthesis of a water-soluble metallodendrimers... 

A second example [IJ) is that of the anomeric spectral region of dextran B-742 fraction S, a polysaccharide for which per-methylation data indicate Structure 2, when n=0. This is an unusual polymer, as every backbone residue is 3-0-substituted. It is fortunate that this polymer exists, as the dextrans branching through 3,6-di-O-substituted residues present a problem in the anomeric spectral region, displaying only a single branching anomeric resonance in addition to the linear dextran resonance. 

Kenawy 64) immobilized ammonium and phosphonium peripheral functionalized dendritic branches on a montmorillonite supported chloromethylstyrene/methyl methacrylate copolymer (74-75). These polymer/montmorillonite-supported dendrimers were used as phase transfer catalysts (PTC) for the nucleophilic substitution reaction between -butyl bromide and thiocyanate, cyanide, and nitrite anions in a toluene or a benzene/water system. These PT catalysts could be recycled by filtration of the functionalized montmorillonite from the reaction mixture. Generally,... 

Some branching has been detected in the polymerizations of styrene and anethole (P-methyl-p-methoxystyrene), indicating intermolecular aromatic substitution by a propagating carbocation on the aromatic ring of another polymer chain [Hatada et al., 1980 Kennedy and Marechal, 1982]. 

In summary, the acid-catalyzed condensation polymerization of sugars in methyl sulfoxide results in the formation of copolymers of the sugars with formaldehyde. The glycosyl residues probably occur in blocks, instead of being evenly separated by methylene bridges. The polymers are highly branched, and the glycosyl residues appear to be substituted in a random fashion. 

Table 18 shows values of strength at break, Ob, deformation at break, 8b, and elasticity coefficient, E, of studied polymer networks. The data indicate that substitution of methyl groups by phenyl ones and variation of the distance between chain branching centers is accompanied by a significant chan-ge of deformation and strength properties of studied polymers. Note that substitution of both methyl groups by phenyl ones is accompanied by the... 

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