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Vinyl groups, pendant

The close structural similarities between polychloroprene and the natural rubber molecule will be noted. However, whilst the methyl group activates the double bond in the polyisoprene molecule the chlorine atom has the opposite effect in polychloroprene. Thus the polymer is less liable to oxygen and ozone attack. At the same time the a-methylene groups are also deactivated so that accelerated sulphur vulcanisation is not a feasible proposition and alternative curing systems, often involving the pendant vinyl groups arising from 1,2-polymerisation modes, are necessary. [Pg.295]

The chemical structure of SBR is given in Fig. 4. Because butadiene has two carbon-carbon double bonds, 1,2 and 1,4 addition reactions can be produced. The 1,2 addition provides a pendant vinyl group on the copolymer chain, leading to an increase in Tg. The 1,4 addition may occur in cis or trans. In free radical emulsion polymerization, the cis to trans ratio can be varied by changing the temperature (at low temperature, the trans form is favoured), and about 20% of the vinyl pendant group remains in both isomers. In solution polymerization the pendant vinyl group can be varied from 10 to 90% by choosing the adequate solvent and catalyst system. [Pg.586]

Diene-based polymers such as polybutadiene have other structural distinctions. The linear versions of these polymers have one residual double bond for each mer. When the double bonds are in the polymer chain, the cis and trans stereoisomers are possible. The double bonds can appear as pendant vinyl groups, which can then exhibit tacticity. [Pg.469]

Silastic LS 420, possessing approximately Q.6%-0.9% pendant vinyl groups, was blended with Kynar 7201, a vinylidene fluoride copolymer with tetrafluoroethylene (Atochem), in the presence of triallylisocyanurate (TAIC) and DAP containing a small amount of benzoyl peroxide in the DAP fraction. [Pg.334]

Thus, whether the remaining ethylenic bond of a given unit is incorporated within the chain (V) or in a pendant vinyl group (VI) external to the chain is governed by the manner of addition of the succeeding unit. The 1,4 unit may occur as either the cis or the trans isomer, i.e. [Pg.238]

The term branched refers to the over-all pattern of the polymer molecule as depicted schematically above, rather than to the nature of the structural unit. The 1,2 unit of butadiene, for example, may be regarded as branched inasmuch as it possesses a pendant vinyl group, but the polymer should be considered linear nevertheless, provided that these units are connected in a single linear sequence. [Pg.258]

The chloromethyl derivatives of 1 and 2 can be converted to the corresponding phosphonium salts by treatment with triphenyl-phosphine.19 A subsequent phase transfer catalysed Wittig reaction of these salts with formaldehyde introduced pendant vinyl groups. [Pg.8]

II) (Figure 1) as determined by C NMR and IR (Figure 2). The C NMR peak at 50,0 indicates that PPDMA also contains a small amount of 6-membered ring imide (III). No pendant vinyl groups yere found. This is in agreement with PPDMA prepared by Xi and Vogel. PPDMA was soluble in DMF, DMSO and chloroform, but was insoluble in water. [Pg.293]

Andrianov and Zhdanov have developed a method for the synthesis of polymers containing heterochain and carbon-chain units by free-radical copolymerization of metal-containing polyorganosiloxanes bearing a pendant vinyl group with vinyl monomers. The copolymers thus obtained display increased thermal stability and can be used for the production of laminated plastics, adhesives and other valuable materials 53),... [Pg.119]

Re A3. High energy radiation causes some cyclization of the pendant vinyl groups (.29). This should cause a stiffening of the chain and thus an increase in of the free network strands. The modulus should then be decreased by the ratio / (30 ). However, the effect is apparently too small to cause a significant decrease in the modulus. [Pg.448]

Radical polymerizations have three important reaction steps in common chain initiation, chain propagation, and chain termination. For the termination of chain radicals several mechanisms are possible. Since the lifetime of a radical is usually less than 1 s, radicals are continuously generated and terminated. Each propagating radical can add a finite number of monomers between its initiation and termination. If a divinyl monomer is in the monomer mixture, the reaction kinetics changes drastically. In this case, a dead polymer chain may grow again as a macroradical, when its pendant vinyl groups react with radicals, and the size of the macromolecule increases until it extends over the whole available volume. [Pg.180]

Two possible reactions of a pendant vinyl group may be distinguished, shown schematically in Fig. 34 ... [Pg.181]

Intermolecular crosslinking between pendant vinyl groups and radical centers located on different macromolecules produce crosslinks that are responsible for the aggregation of macromolecules, which leads to the formation of a macrogel. It must be remembered that both normal and multiple crosslinks may contribute to the rubber elasticity of a network, whereas small cycles are wasted links. [Pg.181]

The divinyl monomers can thus be found in macromolecules as units which bear pendant vinyl groups or which are involved in cycles, crosslinks or multiple crosslinks. Since the number of crosslinks necessary for the onset of macrogelation is very low [64], pendant vinyl groups in RCC are mainly consumed in cycles and multiple crosslinks. Therefore, the reaction rate of pendant vinyl groups is a very sensitive indicator for the formation of cycles and multiple crosslinks in finite species [100,147,157-160]. [Pg.181]

The conversion of pendant vinyl groups, x3, may be defined as the fraction of divinyl monomer units with both vinyl groups reacted... [Pg.181]

Fig. 35. Graphical representation of variation of the conversion of pendant vinyl groups x3 with the monomer conversion x for various types of intramolecular reactions [157]. [Pg.182]

Fig. 37. Conversion of pendant vinyl groups x3 versus monomer conversion x for different degrees of initial dilution in RCC of 1,4-DVB. Monomer concentration in toluene are 5 ( ), 2 (A), 1 (O), and 0.5 g/100 mL (+). Initiator (AIBN) concentration = 8X10 3 M temperature = 70 °C. [Reprinted with permission from Ref. 209, Copyright 1995, American Chemical Society]. Fig. 37. Conversion of pendant vinyl groups x3 versus monomer conversion x for different degrees of initial dilution in RCC of 1,4-DVB. Monomer concentration in toluene are 5 ( ), 2 (A), 1 (O), and 0.5 g/100 mL (+). Initiator (AIBN) concentration = 8X10 3 M temperature = 70 °C. [Reprinted with permission from Ref. 209, Copyright 1995, American Chemical Society].
It is well-known that the coil density of macromolecules decreases with increasing molar mass. Due to cyclization this decrease in density becomes less or even disappears because the macromolecules of higher molar mass are more strongly contracted than those of lower molar mass. After a certain conversion of pendant vinyl groups, the influence of the intermolecular reaction on [r ]... [Pg.188]

Fig. 40. A Relation between [-r ] and Mw during crosslinking of PVS. B Increase of Mw with the conversion of pendant vinyl groups during crosslinking of PVS. Molar mass of starting PVS, Mw0 = 135000 g/mol. Temperature = 70 °C. The PVS concentrations are shown in the figures [217]. Fig. 40. A Relation between [-r ] and Mw during crosslinking of PVS. B Increase of Mw with the conversion of pendant vinyl groups during crosslinking of PVS. Molar mass of starting PVS, Mw0 = 135000 g/mol. Temperature = 70 °C. The PVS concentrations are shown in the figures [217].
The solvating power of the solvent used in polymerization also strongly influences the rate of cyclization. Batzilla crosslinked PVS in a series of toluene/ methanol mixtures of increasing content of the non-solvent methanol and measured the initial conversion rate of pendant vinyl groups, which corresponds to the rate of cyclization [217]. As seen in Fig. 41, this rate increases very rapidly... [Pg.191]

Fig. 41. Initial rate of the conversion of pendant vinyl groups during crosslinking of PVS shown as a function of the volume fraction of methanol in the toluene/methanol mixture [217]. PVS concentration = 0.30-0.35 mass %, initial molar mass of PVS = 170000 g/mol, temperature = 70 °C. Fig. 41. Initial rate of the conversion of pendant vinyl groups during crosslinking of PVS shown as a function of the volume fraction of methanol in the toluene/methanol mixture [217]. PVS concentration = 0.30-0.35 mass %, initial molar mass of PVS = 170000 g/mol, temperature = 70 °C.
Dusek [385] found that on crosslinking of these soluble polyunsaturated polymers, the crosslink densities were much lower than those of corresponding polymers obtained by direct polymerization of the monomer mixtures. This result indicates a strong sterical hindrance of pendant vinyl groups. [Pg.196]

Hiller and Funke obtained easily dissolvable linear macromolecules of PVS by anionic polymerization of 1,4-DVB up to conversions of 80-90% [230,231]. In these experiments very low concentrations of n-butyl lithium (n-BuLi) were used and tetrahydrofuran (THF) as solvent. The reactions were carried out at -78 °C and for 7 min. The contents of pendant vinyl groups in the polymer were determined by infrared spectroscopy, mercury-II-acetate addition and catalytic... [Pg.196]

Hiller and Funke extensively investigated the change of the polymer structure as a function of the monomer and the initiator concentration in various solvents [231]. The content of pendant vinyl groups in the polymer was about 100% for n-BuLi concentrations below 2 mol % and for the whole range of the monomer concentration studied (20-100 g/1). The content of pendant groups decreased when the n-BuLi concentration increased and approached 80% in the transition region of a soluble polymer to a macrogel. As seen in Fig. 45, the decrease of pen-... [Pg.197]

Fig. 45. [t ] and content of pendant vinyl groups of polymers shown as a function of the initial n-BuLi concentration in the anionic polymerization of 1,4-DVB in THF. Initial 1,4-DVB concentration = 20 g/L. Reaction temperature = -78 °C. Reaction time = 7 min. [Reproduced from Ref. 231 with permission, Hiithig Wepf Publ., Zug, Switzerland]. [Pg.197]


See other pages where Vinyl groups, pendant is mentioned: [Pg.440]    [Pg.766]    [Pg.222]    [Pg.201]    [Pg.242]    [Pg.138]    [Pg.141]    [Pg.150]    [Pg.150]    [Pg.180]    [Pg.181]    [Pg.181]    [Pg.182]    [Pg.183]    [Pg.184]    [Pg.184]    [Pg.185]    [Pg.186]    [Pg.189]    [Pg.191]    [Pg.191]    [Pg.192]    [Pg.196]    [Pg.197]    [Pg.198]   
See also in sourсe #XX -- [ Pg.93 , Pg.98 ]




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Poly pendant vinyl groups

Vinyl group

Vinylic groups

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