Vinyl absorptions

A shoulder at 950 cm."1, which might well have been vinyl absorption shifted by oxygen and chlorine, disappeared during the first 30 minutes. 

Hydrogenation led to substantial additional absorption from — CH2— groups and the elimination of the vinyl absorptions. Weak bands at ca. 2960 and 1370 cm -1 from methyl groups also occurred. 

The ketone could be reduced to two epimeric alcohols dihydro-kopsine-A (CLXXII) resulted with sodium borohydride reduction (100, 109), whereas catalytic hydrogenation gave dihydrokopsine-B (CLXXIV, 100, 104). Both formed only a monoacetate. Kopsine shows no vinyl absorption in the NMR-spectrum and could not be further reduced (except by catalytic hydrogenation of the benzene ring). The molecule therefore contains seven rings, since subsequent evidence excludes a tetrasubstituted double bond. 

The intensities of the vinyl absorption bands increase as the temperature is lowered. The crystalline bands at 1050 and 1176 cm exhibit a much narrower bandwidth at lower temperatures. Only slight changes in the amorphous bands are observed with temperatme. However, differences between slow-crystallized and quenched samples are apparent... 

Two types of NMR absorptions are typically found in alkenes vinyl absorptions due to protons directly attached to the double bond (4.5-6.5 ppm) and allylic absorptions due to protons located on a carbon atom adjacent to the double bond (1.6-2.6 ppm). Both types of hydrogens are deshielded due to the anisotropic field of the r electrons in the double bond. The effect is smaller for the aUylic hydrogens because they are more distant from the double bond. A spectrum of 2-methyl-1-pentene is shown in Figure 3.38. Note the vinyl hydrogens at 4.7 ppm and the allylic methyl group at 1.7 ppm. 

The cationic UV photo-initiator (UVI) is a triarylsulfonium hexafluoroantimonate salt in propylene carbonate. This initiator can undergo photolysis to yield radical species as well as a strong acid for cationic polymerization initiation (75). The relative degrees of conversion and ring opening of the resultant polymers were obtained from the IR spectra with emphasis on the carbonyl and vinyl absorption regions. 

Dental resin formulations were prepared by the combination of SOCM with an ethoxylated bisphenol A dimethacrylate (EBPAD, Diacryl 101, Akzo Chemie America) in a 26.6 73.4 wt ratio which corresponds to a 41.5 58.5 mol ratio. Resin samples were activated by the addition of various photo-initiators and were polymerized as unfilled films between Mylar sheets. The cured samples were stored for 24 h at 37 C and then removed from the Mylar. The degree of conversion of the combined methacrylate groups of SOCM and EBP AD as well as the conversion of the spiro vinyl group of SOCM were determined by comparison of the IR spectra of the uncured resin with those of the polymerized films. The methacrylate double bond absorption at 1637 cm and the spiro vinyl absorption at 880 cm were monitored with the aromatic band at 1585 cm utilized as an internal standard reference 14),... 

The IR spectra in Figure 4 trace the synthetic pathway to the SOCM monomer 3. The entire series is dominated by the strong IR bands characteristic of the spiro orthocarbonate group. IR absorptions associated with the shortened CO4 centr ether bonds occur near 1200 cm while the external ether bands are found near 1050 cm. Intermediates 6 and 7 produce a strong OH band around 3400 cm and 7 also yields peaks due to the oxaspiro-based double bond at 1698 and 880 cm". Addition of the methacrylate group in monomer 3 eliminates the OH band and gives rise to the carbonyl and methacrylate vinyl absorptions at 1720 and 1637 cm", respectively. 

In the latter case, D6.08 is the sum of the optical densities of the vinylidene and vinyl absorption bands in this region. An optical density ratio for these bands of approximately this value was found (1.75 to 3.3) for the products of thermal degradation of polypropylene. It is seen that only in the case of amorphous polypropylene irradiated with gamma-radiation from Co is the ratio (D11.23 + D10.99)/D6.08 close to the value calculated from the extinction coefficients of these bands. In the spectra of irradiated isotactic polypropylene, the intensity of the 6.08 pm band is greater than would be expected if only vibration of terminal double bonds contributes to absorption in this region. This increase in absorption in the 6.08-pm region can be related to absorption by the internal double bond in the allyl radical, the vibrational frequency of which is lowered by conjugation of the Jt-electrons of the double bond... 

Figure 1 shows the proton NMR spectra of 4-d-phenoi eAo]7)-styrene and its polymer prepared by free radical polymerization. For the monomer s spectrum, a doublet located at 1.64 and 1.66 ppm was assigned to CHj of the ethoxy group and the proton of its CH group had a quartet located at 5.97 to 5.99 ppm three protons of the double bond were located at 5.13 to 5.16 5.59 to 5.97 and 6.64 to 6.69 ppm two sets of aromatic protons were in the region of 6.93 to 734 ppm. FT-IR spectrum of the monomer showed a vinyl absorption at 1629 cm which, after polymerization, disappeared completely as evidenced by the FT-IR of the polymer (Figure 2.)... 

Figure Bl.22.10. Carbon K-edge near-edge x-ray absorption (NEXAFS) speetra as a fiinotion of photon ineidenee angle from a submonolayer of vinyl moieties adsorbed on Ni(lOO) (prepared by dosing 0.2 1 of ethylene on that surfaee at 180 K). Several eleetronie transitions are identified in these speetra, to both the pi (284 and 286 eV) and the sigma (>292 eV) imoeeupied levels of the moleeule. The relative variations in the intensities of those peaks with ineidenee angle ean be easily eonverted into adsorption geometry data the vinyl plane was found in this ease to be at a tilt angle of about 65° from the surfaee [71], Similar geometrieal detenninations using NEXAFS have been earried out for a number of simple adsorbate systems over the past few deeades.

Kinetic measurements were performed employii UV-vis spectroscopy (Perkin Elmer "K2, X5 or 12 spectrophotometer) using quartz cuvettes of 1 cm pathlength at 25 0.1 C. Second-order rate constants of the reaction of methyl vinyl ketone (4.8) with cyclopentadiene (4.6) were determined from the pseudo-first-order rate constants obtained by followirg the absorption of 4.6 at 253-260 nm in the presence of an excess of 4.8. Typical concentrations were [4.8] = 18 mM and [4.6] = 0.1 mM. In order to ensure rapid dissolution of 4.6, this compound was added from a stock solution of 5.0 )j1 in 2.00 g of 1-propanol. In order to prevent evaporation of the extremely volatile 4.6, the cuvettes were filled almost completely and sealed carefully. The water used for the experiments with MeReOj was degassed by purging with argon for 0.5 hours prior to the measurements. All rate constants were reproducible to within 3%. 

Fig. 4. Chemistry of poly(vinyl cinnamate) negative-acting resist. Initial light absorption by the photosensitizer is followed by energy transfer to produce a pendant cinnamate group in a triplet electronic state. This combines with a second cinnamate on another polymer chain, forming a polymer—polymer...

Acrolein is highly toxic by skin absorption. Brief contact may result in the absorption of harmful and possibly fatal amounts of material. Skin contact causes severe local irritation and chemical bums. Poly(vinyl chloride) coated protective gloves should be used (99). 

A second type of uv curing chemistry is used, employing cationic curing as opposed to free-radical polymerization. This technology uses vinyl ethers and epoxy resins for the oligomers, reactive resins, and monomers. The initiators form Lewis acids upon absorption of the uv energy and the acid causes cationic polymerization. Although this chemistry has improved adhesion and flexibility and offers lower viscosity compared to the typical acrylate system, the cationic chemistry is very sensitive to humidity conditions and amine contamination. Both chemistries are used commercially. 

Vinyl acetate has moderate acute toxicity if ingested. The LD q for oral ingestion in rats is 2.9 g/kg body weight for absorption through the skin, the LD q in rats is more than 5 mL/kg in 24 h. First-aid procedures to be followed in the event of overexposure to vinyl acetate are as foUow ... 

The nmr spectmm of PVAc iu carbon tetrachloride solution at 110°C shows absorptions at 4.86 5 (pentad) of the methine proton 1.78 5 (triad) of the methylene group and 1.98 5, 1.96 5, and 1.94 5, which are the resonances of the acetate methyls iu isotactic, heterotactic, and syndiotactic triads, respectively. Poly(vinyl acetate) produced by normal free-radical polymerization is completely atactic and noncrystalline. The nmr spectra of ethylene vinyl acetate copolymers have also been obtained (33). The ir spectra of the copolymers of vinyl acetate differ from that of the homopolymer depending on the identity of the comonomers and their proportion. 

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