Vinyl/vinylidene 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... 

The vast majority of commercial polymers based on the vinyl group (H2C=CHX) or the vinylidene group (H2C=CX2) as the repeat unit are known by their source-based names. Thus, polyethylene is the name of the polymer synthesized from the monomer ethylene poly(vinyl chloride) from the monomer vinyl chloride, and poly(methyl methacrylate) from methyl methacrylate. 

Both P-hydride transfers result in polypropene molecules with one vinylidene and one n-propyl end group. The two transfers are zero- and first-order, respectively, in monomer. P-Hydride transfer yields vinyl end groups in ethylene polymerization. 

The most characteristic vibrational modes of alkenes are the out-of-plane C—H bending vibrations between 1000 and 650 cm-1. These bands are usually the strongest in the spectra of alkenes. The most reliable bands are those of the vinyl group, the vinylidene group, and the trans-disubstituted alkene. Alkene absorption is summarized in Appendix Tables D-l and D-2. 

The effects of irradiation damage on polymers has also been followed using FT-IR 219,235,236), by obtaining difference spectra after specific exposure durations in a variety of environments. For polyethylene 219), the difference spectra revealed an increase in the vinyl end groups and an increase of ketonic carbonyl and trans-vinylidene double bonds. It was found that for every free radical formed approximately 10 carbonyl groups and 2 carbon-carbon double bonds were formed 236 ... 

Data on the significant role of the transfer reaction of the polymer chains with a monomer are in agreement with the number of vinyl and vinylidene groups in polyolefins 29.n8.n9)... 

The terminal vinyl groups appeared to be those responsible for crosslinking, rather than the fra s-vinylene or vinylidene groups known to be present in LLDPE. This conclusion has been supported by results from later studies on y-initiated crosslinking (Bracco et al, 2005). 

Vinyl groups are formed by chain transfer to monomer and j8—hydride transfer, that is, the equivalent of Eqs. (9.9)-(9.11). The formation of vinylidene and trans-vinylidene end groups is less clear. One possibility is participation of vinyl end groups in chain transfer analogous to Eq. (9.10). Transfer to the methylene and methine protons of vinyl end groups would generate frans-vinylene and vinylidene end groups, respectively. 

Vinyl chloride has also been reacted with other monomers containing carboxyl, hydroxyl, acetate, maleate, and vinylidene groups. Some of these reactive groups permit cross-linking with other polymers such as alkyds and melamines. Typical solubility characteristics are shown in Figure 3. 

An IR spectroscopic technique for the study of kinetics of radical copolymerisation of acryl and vinyl monomers was developed. The technique is based on monitoring the conversion curves and determining copolymerisation rates in the course of the process separately for each monomer by measuring variations in the intensity of IR absorption bands of reacting vinylidene groups. A comparative study of the copolymerisation of model monomer pairs using monofunctional and polyfunctional compounds provided data on the role of structural-physical transformations, involved in the formation of crosslinked polymers, on the copolymerisation kinetics and on the non-uniformity of distribution of crosslinks in the copolymers formed. 17 refs. 

Various termination reactions are possible in Ziegler polymerizations. At polymerization temperatures below 60° C, every polymer chain contains a metal atom. Thus, no thermal termination takes place at this temperature, although it does at higher temperatures, where vinyl and vinylidene groups have been found ... 

The great number of possible elementary reactions in free radical polymerizations explains why only a fraction of the many thermodynamically polymerizable groups can be converted free radically to un-cross-linked high-molar-mass polymers. Vinyl, vinylidene, and acrylic compounds, as well as some strained saturated rings, belong to this fraction. Allyl compounds only polymerize to branched oligomers, but diallyl and triallyl compounds produce high-molar-mass cross-linked networks. 

Types within group Cellulose acetate, cellulose acetate butyrate, cellulose nitrate, polyvinyl acetate, vinyl vinylidene, polyvinyl acetals, polyvinyl alcohol, polyamide, acrylic, phenoxy Cyanoacrylate, polyester, urea formaldehyde, melamine formaldehyde, resorcinol and phenol-resorcinol formaldehyde, epoxy, polyimide, polybenzimidazole, acrylic, acrylate acid diester Natural rubber, reclaimed rubber, bulyl, polyisobutylene, nitrile, styrene-butadiene, polyurethane, polysulfide, silicone, neoprene Epoxy-phenolic, epoxypolysulfide, epoxy-nylon, nitrile-phenolic, neoprene-phenolic, vinyl-phenolic... 

Vinylidene vI- ni-lo- den [ISV vinyl + -ene] (1898) n. Indicating a bi-substituted ethylene in which both hydrogen atoms on one carbon atom have been replaced, i.e., H2C=CXY, or the vinylidene group, H2C=C=. X and Y are usually the same element. 

An empirical rule which has been observed for many polymers is that Tg 2/3T m, where the temperatures are in Kelvin. This rule is applicable to most vinyl, vinylidene, and condensation polymers. This ratio is lower for pol5uners with unsubstituted backbones and higher for polyCa-olefins) with long alkyl side groups. Tac occurs in crystalline and semicrystalline polymers and is ascribed to an oscillation about the chain axes within the chain-folded crystals or a translation along the axis. Tac is related to I m by... 

Most LLDPE chains have at least one methyl (—CH3) group at one chain end. Other chain ends can be a methyl group from termination from chain transfer, or a vinyl group (CH2=CH=) or vinylidene group (CH2=C —) from termination from -hydride transfer (1). 

Based on H NMR analysis of low molecular weight polypropylene formed by 40b/MAO at 25 C with a propylene concentration of 0.5 M (in toluene solution), the predominant chain termination pathway appears to be f)-H elimination (i.e., vinylidene end groups are present). The primary kinetic isotope effect observed for 35b/MAO (vide supra) is also indicative of P-H elimination operating as the predominant chain termination pathway. No fl-CH3 elimination was observed for these catalysts specifically, no vinylic end groups are present in the H NMR spectra. For 35a-c and 40c, chain transfer was found to be primarily unimolecular, derived from f)-H elimination. For 40b, a small bimolecular contribution (chain dansfer to monomer) was also suggested, owing to the less than first order dependence of molecular weight on propylene concentration. 

Vinyl group (1,2-addition) Vinylidene group t/.(-vinylene (cis 1,4-addition)... 

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