Poly , trans

On the contrary, butadiene and methacryloyl monomers (1,3,4, 10,11) can also be polymerized in the liquid expanded phase. The butadiene lipids have previously been shown to form 1,4-trans-poly(butadiene)s (40j in the monolayer (Eqn. II.). 

Stereoselective ROMP has been reported with monomer (213). Initiator (211) affords highly stereoregular polymer with >98% trans C=C bonds in the polymer backbone.534 However, when (210) is used, >98% cis-poly-(213) is obtained.535 A similar situation occurs for the diester monomer (214). Furthermore, a rapidly equilibrating mixture of (210) and (211) can be used to allow intermediate cis/trans contents to be manipulated by the stoichiometry of the initiator mixture. 13C NMR536 and dielectric analyses537 suggested that trans-poly-(213) is highly syndio-tactic (92% r dyad content). The ROMP of other fluorinated olefins has been recently reviewed.538... 

All the possible line repetition groups for cis and trans poly dienes compatible with the isotactic or syndiotactic configurations are reported in Figure 2.15,47,68 In order to consider only the possible conformations assumed in the crystalline state, the torsion angle of the central single bond is assumed to be 180° trans) in both the cis and trans polydienes. This condition produces conformations sufficiently extended to be packed in a crystalline lattice for each value of the torsion angles 0i and 02 (Figure 2.15). 

Examples of ditactic polydienes are provided by a class of crystalline polymers derived from the alkyl-esters of the trans-trans isomer of sorbic acid.101,102 For example trans-poly (methyl sorbate) (-CH(CH3)-CH =... 

Kun E, Kirsten E, Ordahl CP (2002) Coenzymatic activity of randomly broken or intact double-stranded DNAs in auto and histone HI trans-poly(ADP-ribosylation), catalyzed by poly(ADP-ribose) polymerase (PARP I). J Biol Chem 277 39066-39069 Kun E, Kirsten E, Mendeleyev J, Ordahl CP (2004) Regulation of the enzymatic catalysis of poly(ADP-ribose) polymerase by dsDNA, polyamines, Mg2-F, Ca2-F, histones HI and H3, and ATP. Biochemistry 43 210-216... 

The trans-poly-1,4-butadiene isomer is a harder and less soluble rigid crystalline polymer than the cis isomer. As shown by the skeletal structures for the trans isomer (Figure 1.11), chain extensions on opposite sides of the double bonds allow good fitting of adjacent polymer chains, and this, results in a rigid structure. In contrast, the os-poly-1,4-butadiene isomeric polymer units do not permit such interlocking of alternate units. Even so, chain... 

Allowing for rotation about the Ca—C bond (/.e., variation of ijr) and for some degree of freedom about the peptide bond [i.e., small variation of ro), the characteristic ratios of the form / (crs) and form II [trans) poly(L-proline) chain are calculated by a Monte Carlo method in which the conformational energies are used as weighting factors. The Monte Carlo method enabled short-range interactions (beyond those involved in a single residue) to be taken into account. 

An analysis of the ionic factors for the polymerization of dienes to cis and trans structures is possible in the same way as for isotactic mono-enes. The mechanism which controls the steric structure of poly 1,4 dienes is parallel to that we have already seen for the mono-olefins. Roha (2) listed the catalysts which polymerize dienes according to the polymer structures produced. It was shown that the highly anionic as well as the highly cationic catalyst systems with increasing ionic separation produced trans-poly-1,4-dienes. This is analogous to the production of syndiotactic polyolefins. 

A plot of the effect of ionicities of the catalyst and the structures which are produced and the requirements for the production of cis polybutadiene, cis polyisoprene and cis pentadiene is shown in Fig. 14. Cis and trans poly-1.3-dienes are produced according to the balance of ionicities of the catalyst. 

Finter, J. and Wegner, G. The relation between phase transition and crystallization behavior of l,4-trans-poly(butadiene). Makromol. Chemie 182, 1859 (1981) (see here and Ref. 3 for older data)... 

Tabelle 4. Schmelzpunkte von kristallinen trans-Poly alkena-meren )... 

Fig. 13. Progression of linearly re-conjugated all-carbon backbones from trans-polyacetylene (PA) through trans-poly(diacetylene) (PDA), trans-poly(triacetylene) (PTA), to carbyne.

Poly (2-methyl-l,3-butadiene), trans Poly (2-methyl-1,3-butadiene), cis Polyethylene, high density low density... 

Stereoisomerism. The first trials to use the XPS valence band spectra to distinguish between two stereoisomers were unsuccessful. Cis- and trans- poly(isoprene) - with short branched chain and small substitution effects-, as well as cis- and trans-poly(l,4dichloro-2,3epoxybutene) - with longer branched chain and more intense substituent effects- did not show in our first measurements significant differences in their valence band spectra that could be attributed to the searched effect. Before... 

Figure 4.8-2 Optical absorption of conjugated polymers with a degenerate ground state (trans-poly(acetylene)) (a), according to Suzuki et ah, 1980 and a non-degenerate ground state (poly(thiophene)) (b), according to Danno et ah, 1993 in various doping states. Doping concentrations are indicated in % in (a) and by the applied potential in (b).

Figure 4.8-4 Raman spectra of trans-poly(acetylene) excited by different laser lines, according to (Itnhoff, 1983) (a), and a schematic representation of the dispersion effect in conjugated polymers. The continuous and the dashed arrows, respectively, refer to a red and a blue laser (b).

An LCAO (linear combination of atomic orbitals) local-density functional approach was used to calculate the band structures of a series of polymer chain conformations unsubstituted polysilane in the all-trans conformation and in a 411 helical conformation, and all-trans poly(dimethylsilane). Calculated absorption spectra predict a highly anisotropic absorption for the all-trans conformation of polysilane, with the threshold absorption peak arising strictly from polarizations parallel to the chain axis. The absorption spectrum for the helical conformation is much more isotropic. Results for the dimethyl-substituted polysilane chain suggest that the states immediately surrounding the Fermi level retain their silicon-backbone a character upon alkyl-group substitution, although the band gap decreases by I eV because of contributions from alkyl substituent states both below the valence band and above the conduction band to the frontier states. 

Figure 3. Calculated absorption spectra for all-trans unsubstituted polysilane (a), all-trans poly(dimethylsilane) (b), and helical unsubstituted polysilane (c). Solid lines denote absorption for polarizations parallel to chain axis, dashed-and-dotted lines denote absorption for polarizations perpendicular to the plane of the silicon backbone (for the all-trans conformations), and dashed lines denote the remaining polarization. All curves have been broadened with a 0.7-eV full width at half-maximum Gaussian.

It is not clear that the experimental results are for pure all-trans-poly-methineimine, as other cis-transoid and trans-cisoid structures are possible. In fact, Hirao and Iwata recently stated that the experiment results are for cis-transoid-polymethineimine, and reported DFT results with the L3YP functional [87]. To clarify this issue, we are calculating the MBPT(2) structures and vibrational frequencies for other isomers of polymethineimine. Further experiments are also needed to compare with theory. 

Polymers of 1, lA and show relatively little HT bias but a complete range of bias has been observed in polymers of 13, 14 and 15, the effect with a given catalyst being greater for than for 14 (3,8). Thus (HT -t TH)/(HH -t- TT) ratios in the high-trans poly- mers made with RUCI3 and IrCl3 as catalysts are 2,4 and (fully biased) respectively for and 1.0 (unbiased) and 3.0 respectively for 14. 

Figure 2. Chemiluminescence at 25°C from a film of trans-poly-pentenamer (0.0152 g) containing 5.0 X I O 5 g of dibenzanthrone after different irradiation times...

Figure 18 Transition states for formation of c/s and trans-poly (1,3-butadiene)...

In order to examine possible conformational differences between the different classes of poly(RCOT)s, both force-field (MM2) [132] and semiempirical quantum mechanical (AMI) [133] calculations on model polyene oligomers were employed (Fig. 10-23) [34]. Using either routine, it is observed that the single bonds adjacent to the trisubstituted double bond (0] and 2) both strongly deviate from planarity in the models of the soluble polymers. In contrast, in the model of trans- poly (terr-butoxyCOT), an insoluble polymer, j is large, but 2 is not. The good correlation between polymer solubility and calculated chain twist is indicated... 

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