Polynorbornene structure

The first report of ROMP activity by a well-characterized Mo or W species was polymerization of norbornene initiated by W(CH-t-Bu)(NAr)(0-f-Bu)2 [122]. In the studies that followed, functionality tolerance, the synthesis of block copolymers, and ring-opening of other monomers were explored [30, 123]. Two important issues in ROMP concern the cis or trans nature of the double bond formed in the polymer and the polymer s tacticity. Tacticity is a consequence of the presence of two asymmetric carbons with opposite configuration in each monomer unit. The four ROMP polymers (using polynorbornene as an example) that have a regular structure are shown in Scheme 3. 

Scheme 3. The four possible regular structures of polynorbornene prepared by ring-opening metathesis polymerization...

Concurrent with the development of the mechanistic explanations for the chemistry has been the creation of new polymers based on ROMP chemistry. While a wide variety of strained cyclic monomers have been polymerized with a significant emphasis on monomer structure/reactivity relationships, three ring structures deserve special attention, since they are or have been produced on a commercial scale. These polymers are polyoctenamer (from cyclooctene), polynorbornene (from... 

FIGURE 16.2 Structure of a polynorbornene containing alternating l-exo,l -syn- and 2-exo,l -exo-enchainments in the main chain and 2-exo,2 -exo-]ivksd norbomyl branches. 

Ivin and Rooney recognized that an indirect method could be used to distinguish between isotactic and syndiotactic structures in ROMP polynorbornenes. - "" This method exploits the... 

Similar to most conventional catalysts, tungsten alkylidene complex 12 (without GaBra) selectively polymerizes the anti isomer of 7-MeNB from a 1 1 mixture of the syn and anti isomers. The resulting poly(fl ti-7-MeNB) contains less than 5% 7-iy -MeNB incorporated. This polymer is atactic and contains 41% trans C=C structures. The hydrogenated polymer (poly-H-(anft-7-MeNB)) is semicrystalline despite its atactic stereochemistry. This is similar to the partial crystallinity of the atactic hydrogenated polynorbornene previously described. The DSC curve for poly-H-(a ti-7-MeNB) displays an endothermic melt transition with a peak maximum at Tm = 176 °C (A// = 26 J/g) (there is an additional minor peak at 137 C). This result shows that partial... 

In 2011, Meille, Porri, and co-workers characterized the crystalline form of a vinyl-type polynorbornene (PNB). Fully saturated vinyl polymers or oligomers with a 2,3-exo-disyndiotatic ((is) structure were obtained using an AlEt2Cl-TiCl4 catalyst with a ratio monomer/TiCU of 18 or 250, respectively. A fractionation method was used for the purification. These polymers formed a molecular tube-shape that contained some different types of small molecules like toluene, as shown in Figure 5.23 (red circles). This... 

As of the steric hindrance and the possibility to form allylic intermediates, cyclopentene inserts by metallocene catalysts with a 1,3-structure while polynorbornene shows a 1,2-structure (structure (64)) [544]. 

Nickel-0- and palladium-O-complexes are very active catalysts for the polymerization of norbornene and also for cyclopentene [552-554], Nickel catalysts produce soluble polymers with a molecular weight of over one million while polymers obtained with palladium or metallocene complexes are insoluble. The soluble polymers have an atactic structure. The microstructure of the polynorbornene depends on the catalyst used and is isotactic by synthesis with chiral metallocenes. 

All prepared polymers were used for searching correlations between their structures and gas permeability. Along with mono-silyl substituted polynorbornenes and polynorbornadienes, they showed the dramatic influence of SiMe-containing substituents on gas permeation properties (Table 5). 

The C-nmr spectrum of poly(5-norbornene-2-nitri-le) had three sets of peaks at 30 -48 ppm, about 120 ppm and 128 - 135 ppm from tetramethylsilane, which were assigned to the carbons of the cyclopentane ring, the cyano group and the C=C bond, respectively. The quantitative analyses of these peaks, using polynorbornene, poly(methyl 5-norbornene-2-carboxylate) and poly(dimethyl 5-norbornene-2,3-dicarboxylate) as references, gave the proportion of each isomer in the three structural isomerism. The results are summarized in TABLE V. 

The topology of this product with a bulk hydrophobic structure inside and a hydrophilic part outside makes it particularly attractive for applications such as unimo-lecular micelles. On using the same procedure, norbor-nyl-poly(ethylene oxide)-polystyrene macromonomer was polymerized to polynorbornene-poly(ethylene oxide)-polystyrene block copolymer (121) [Eq. (53)]. 

Polynorbornenes may be grouped into two classes those that are soluble in toluene and those that precipitate during polymerization. WAXS and C-NMR investigations, as well as high-temperature high-resolution C-NMR investigations of the soluble polymers, confirm the different structures of the polymers and enable a further classification. 

Shiono and coworkers investigated by C-NMR spectroscopy the structure of the P-N copolymer produced with catalyst dimethyl IV-5. They observed several signals for each carbon due to the different comonomer sequences and stereoisomers of the norbornene unit. The signals around 26-30.4 and 30.26-35.42 ppm were tentatively assigned to carbons C5/C6 and C7, respectively. In particular, a broad resonance with several peaks at 31.2-32.1 ppm, which disappeared in the spectrum of polynorbornene, could be assigned to the C7 carbon of the norbornene unit in alternating and/or norbornene diad sequences. The signals at... 

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