Vinylene groups

That values of yj and 7r vary with the reaction and the reaction conditions is readily seen from the results reported in Table XLVIII for the rrans-vinylene group. Values of yj for this group range from 1.01 to 3.28. That the value of yj is dependent upon the reaction is no surprise. Charton has shown (251,252) that the yj values may be calculated from the Kirkwood-Westheimer equation in the form... 

The first set of dyes, so called visible set , is presented by polymethine dye PD 2630, squaraine dye SD 2243, and tetraone dye TD 2765, all with benzo[e]indolium terminal groups. The second set of dyes, so called NIR set , is presented by polymethine dye PD 2658, squaraine dye SD 2878, and tetraone dye TD 2824, all with 5-butyl-7,8-dihydrobenzo rJ furo[2,3-/]indolium terminal groups. A distinguishing feature seen from this figure is a remarkably large, 300 nm, red shift of the absorption bands for PD 2658 and SD 2878 as compared to PD 2630 and SD 2243. The absorption spectrum of TD 2824 is red-shifted by 200 nm as compared to TD 2765. Thus, the effect of the 5-butyl-7,8-dihydrobenzo[coT]furo[2, 3-/]indo-lium terminal groups is equivalent to the extension of the chain to three vinylene groups. 

Since BG-LDPEs contain mainly trans-vinylene group and vinyl one, the reactions (7-1), (7-2), (8-1) and (8-2) take place in the irradiation of these polymers. While, the reactions (7-2), (7-3), (8-2) and (8-3) take place in the irradiation of IG-LDPE containing vinyl and vinylidene groups. The lower rate of grafting onto IG-LDPE may be caused by the lower reactivity of... 

Lack of coplanarity in quaternary bipyridyls can be overcome not only by the discussed bridging but also by insertion of a vinylene group between the two pyridine rings. 

The isomeric quaternary salts 5-10 again exemplify the validity of the general stmcture A If the rings are connected to the vinylene group in 4,4 -, 2,2 - and 2,4 -positions (5- 7) fully reversible redox reactions are observed with practically equal potentials and Ksem s (Fig- 4. The smaller Ksem s compared to 7/are discussed in Sect. 5.)... 

The classical Weitz-type redoxsystem If can be transformed into 11 or by formal insertion of one or two vinylene groups. Although the ir-system is considerably enlarged by this operation, Ej and E2 and therefore Ksem are hardly changed (Fig. 5). 

Nevertheless, positions and differences of Ej and E2 allow some qualitative interpretations. The vinylene bridge in 5,6-position seems to be inert not only in ii, which resembles the 4,4 -bipyridyl system i/(c.f. 3.1) but also 13B2 and 13B3 which behave similar to the 2,2 -bipyridyl systems 2B2 and 2B3. In 13B3 the vinylene group prevents the two pyridyl units from distortion by the Ca-brit e between the nitrogen atoms compared to 2B3. Thus its Ksem stays closer to that of 13B2. 

The effect of an increasing number of vinylene groups in the general type A should be of special interest. The separation of the end groups X which carry an appreciable amount of positive charge on the level SEM and OX increases as the rr-system is enlarged. 

With increasing numbers of vinylene groups partly the positions of E, and partly those of E2 are more influenced. The reason for this phenomenon is not clear. Different solvation energies may be involved. 

In both cases the number of ir-electrons differs from that of the sp2-atoms by one. Accordingly a linear correlation is expected between the absorption maxima of cyanines and violenes, and the number of vinylene groups or 7r-electrons. 

The results of Table II are interesting from several standpoints. In the first place the vinylene groups in polyethylene (PE) are all trans,... 

To determine the concentration of cis-vinylene groups in irradiated specimens, the original cw-polybutadiene itself was used as a standard, and a value for A (assumed independent of concentration) was determined from Av and logr (I0/I)vo of unirradiated specimens. The total concentration of unsaturation was accepted (15) as 100% of theoretical and the density as 0.90 gram per cc. The cis concentration was obtained by subtracting from the total unsaturation the trans-vinylene and vinyl contents determined from the calibration curves developed as described below. The value of A so determined was 2.67 X 103 liters/mole-sq. cm. 

To use the absorbance of the band at 967 cm. 1 to determine trans-vinylene groups in the high cis-polymer, it was necessary first to correct for the overlap from the wing of the cts-vinylene band at 998 cm. 1... 

Concentrations are expressed in moles of olefin groups per liter and absorptivities in liters per mole-cm. The concentration of the side vinyl group in the sodium polymer is cvi and for the trans-vinylene group, 15.3 — Cvi similarly for the emulsion polymer, cv> is vinyl, and 15.8 — cv2 is trans concentration. Solving these equations gave molar absorptivities and concentrations from which calibration curves were constructed, relating corrected absorbance at 910 and 967 cm."1 to concentration of side vinyl and trans groups, respectively. 

Initial yields for conversion to the trans-vinylene isomer can be derived by adding to the apparent yield the rate of destruction calculated from the initial concentration of trans-vinylene groups and the first-order rate constants determined for the amorphous trans polymer. The initial yield of trans-vinylene groups is 6.8 for gamma radiation and 4.4 for the reactor. The value for gamma radiation is similar to Golub s value of 7.2 for both gamma and electrons. 

The destruction of tram-vinylene groups in the crystalline high trans polymer had upper and lower G values of 22 and 11. There was little or... 

The first-order rate constants for terminal vinyl groups and for trans-vinylene groups in linear polyethylene were observed by Dole and Williams (8) to be 20 to 30 times higher than our corresponding rates in the amorphous trans- and vinyl polybutadienes (Table III). On the other hand, the initial yields were lower than our G0 values because of the... 

Similar effects are observed in y-irradiated n-C H (530 kGy) in the molten state. Three new structures are identified as a) one-bond crosslinks (H-structure), b) trans-vinylene groups and c) long branches (T- or Y-structure)144). However, highly crystalline polyethylene y-irradiated in the solid state at low doses (up to 40 kGy) yields predominantly the branched Y-structure. A failure to detect the cross-linked H-structure could arise from a) insufficient abundance of crosslinks to give a detectable signal and b) insufficient mobility of crosslinked chains in the polyethylene gel which results in very broad resonance lines, not observable during normal data acquisition in the solution 13C NMR experiment145). 

In Fig. 7.22 are shown the theoretically most energetically favourable structures of the aluminum on poly(p-phenylenevinylene) complex. These occur in the cases when (a) two aluminum atoms interact with a vinylene group and (b) two aluminum atoms interact with a... 

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