Trans-vinylene

Results of Correlations with trans-Vinylene Sets... 

We have reported the first example of a ring-opening metathesis polymerization in C02 [144,145]. In this work, bicyclo[2.2.1]hept-2-ene (norbornene) was polymerized in C02 and C02/methanol mixtures using a Ru(H20)6(tos)2 initiator (see Scheme 6). These reactions were carried out at 65 °C and pressure was varied from 60 to 345 bar they resulted in poly(norbornene) with similar conversions and molecular weights as those obtained in other solvent systems. JH NMR spectroscopy of the poly(norbornene) showed that the product from a polymerization in pure methanol had the same structure as the product from the polymerization in pure C02. More interestingly, it was shown that the cis/trans ratio of the polymer microstructure can be controlled by the addition of a methanol cosolvent to the polymerization medium (see Fig. 12). The poly(norbornene) prepared in pure methanol or in methanol/C02 mixtures had a very high trans-vinylene content, while the polymer prepared in pure C02 had very high ds-vinylene content. These results can be explained by the solvent effects on relative populations of the two different possible metal... 

Third, it is acknowledged that the metathesis step itself is responsible for the formation of both cis and trans vinylene configurations (18). The steric course in olefin metathesis has been scrutinized by several researchers. Two basic phenomena are recognized ... 

Taking the trans-vinylene or vinylidene group as Z, the values of oi, era and <7e for the appropriate dienyl group can be calculated from the estimation equations 24a, 26a and 27a given above. 

The IR-spectrum of the polymer was measured with a Nippon Bunko Model DS-403G infrared spectrometer. The concentration of the unsaturated groups in the polymer (number of unsaturated group per 1000 carbons) was determined from the absorbances at 966 cm l (trans-vinylene), 910 (vinyl) and 890 (vinylidene) in the IR-spectrum by the method reported by Cernia et al. (7). 

As discussed kinetically in detail (9), the reactivity of each unsaturated group in the cross-linking reactions (7-l)-(7-3) was in the order, vinylidene> vinyl> trans-vinylene. 

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... 

A second important reaction observed in irradiated polyethylene and certain other polymers as well as paraffins is the formation of trans-vinylene. This product is far less influenced by such factors as temperature or radical scavengers than is crosslinking, and it is therefore often assumed to be formed directly by a molecular process—i.e., molecular detachment of hydrogen. Even this simple explanation cannot be fully sustained. Long after radiation has ceased, the frarw-vinylene concentration continues to rise or fall, whether the specimen is exposed to oxygen or not. This behavior may possibly be correlated with the reaction of trapped alkyl and allylic radicals, which, being slightly mobile, can add to frarw-vinylene or each other over a period of days. 

Infrared analysis (6) of irradiated film showed an increase in the yield of trans-vinylene unsaturation (Figure 2). The calculation from the... 

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 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... 

Table II. Extinction Coefficients for trans-Vinylene Unsaturation in Various Ethylene Homo- and Copolymers...

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). 

The band at 1018 cm 1 is due to the presence of occulted oxygen in PE film (thickness, 22-24 pm). The bands at 452 and 456 cm"1 appear only for LDPE (thickness, 22-24 pm) which are attributed to the P (C=C-H). The disappearance of a small band at 888 cm"1 is possibly due to >CH2 out of plane deformation. This may be explained on the basis of evolution of hydrogen gas as a result of the degradation. The intensity of IR absorption bands at 1017, 1113, 1131, 1175, 1241 cm"1 is shown to increase with increasing irradiation dose. The intensity of the bands 1069 cm 1 (C-C stretching), 1287 cm 1 (OH bending), 1377 cm"1 (symmetrical deformation of CH3) (which are initially present in IR spectra of unirradiated films) increase with absorbed dose of radiation, whereas the intensity of the sharp band at 1456 cm"1 is not affected at all. The small band at 965 cm 1 is attributed to C-H out of plane deformation of trans-vinylene groups trans RCH=CHR). 

The above examples show that the ring-opening metathesis polymerisation of cycloolefins, even simple substituted bicyclic olefins, gives rise, in principle, to polymers with a very wide range of microstructures defined by the frequency and distribution of cis and trans vinylene units, m and r diads and h-h, t-t or h-t arrangements of cycloaliphatic units. 

Mesogenic Groups Containing Trans-Vinylene Links.113... 

Figure 1. Depth profile of trans-vinylene absorbance, 2 months from the irradiation. Dotted line represents the depth profile of stopping power calculated with SR1M-2003.

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