Poly double-bond concentration

As a class the aliphatic polyalkenamers have low values due to a combination of low chain stiffness and low interchain attraction. The presence of double bonds has the effect of increasing the flexibility of adjacent single bonds (see Chapter 4) and overall this leads to a reduction in. Thus in the sequence from polydecenamer down to polypentenamer an increase in the double bond concentration leads to a lowering of Tg. On the other hand the Tg of polybutenamer, i.e. poly butadiene, is somewhat higher than that of polypentenamer, presumably because the proportion of stiff links, i.e. double bonds, becomes sufficiently high to override the flexibilising effect on adjacent chains. Consequently the polypentenamers have the lowest Tg values known for hydrocarbon polymers (cis- -114°C, trans- -97°C). 

Maleimides Alkyl and aryl maleimides in small concentrations, e.g., 5-10 wt% significantly enhance yield of cross-link for y-irradiated (in vacuo) NR, cw-l,4-polyisoprene, poly(styrene-co-butadiene) rubber, and polychloroprene rubber. A-phenyhnaleimide and m-phenylene dimaleimide have been found to be most effective. The solubihty of the maleimides in the polymer matrix, reactivity of the double bond and the influence of substituent groups also affect the cross-fink promoting ability of these promoters [82]. The mechanism for the cross-link promotion of maleimides is considered to be the copolymerization of the rubber via its unsaturations with the maleimide molecules initiated by radicals and, in particular, by allyfic radicals produced during the radiolysis of the elastomer. Maleimides have also been found to increase the rate of cross-linking in saturated polymers like PE and poly vinylacetate [33]. 

Regioselective crosslinking of the core domain of cylindrically shaped, wormlike micelles composed of poly[(butadiene)45-b-(ethylene oxide)55] and assembled in aqueous solution at < 5% block copolymer concentrations, was performed using radical coupling of the double bonds throughout the poly(butadiene) phase [27] (Figure 6.3b). This resulted in a 13% reduction in the core diameter, from 14.2 to 12.4 nm, as measured by small-angle neutron scatter-... 

Emulsion polymerization is used for 10-15% of global polymer production, including such industrially important polymers as poly(acrylonitrile-butadiene-styrene) (ABS), polystyrene, poly(methyl methacrylate), and poly (vinyl acetate) [196]. These are made from aqueous solutions with high concentrations of suspended solids. The important components have unsaturated carbon-carbon double bonds. Raman spectroscopy is well-suited to address these challenges, though the heterogeneity of the mixture sometimes presents challenges. New sample interfaces, such as WAI and transmission mode, that have shown promise in pharmaceutical suspensions are anticipated to help here also. 

Hydroperoxide concentrations such as 0.2, 0.35 and 0.85 mol kg 1 were measured that corresponds to a conversion of 25, 35 and 9 % of double bonds for VIST, POLY and VEST respectively. The hydroperoxide content can be increased by repeating the procedure of hydroperoxidation twice12. 

When the catalyst is not fully regioselective, chain release by a /3-H transfer after a secondary insertion with formation of internal double bonds is often observed. This has been reported for ethylene/a-olefin co-poly-mers, PP, and other polyolefins, as well as for 1-hexene polymerization with dialkoxide catalysts. The reaction is shown in Scheme 14 for the case of propylene, where kinetic studies have shown it to be a bimolecular process, following the rate law s/J/ -h=s / -h[sZr][m].217,257 [sZr] refers to the concentration of active Zr centers bearing a growing chain having a secondary propylene unit linked to the metal. 

None-the-less, a number of thorough studies of cross-linking in high poly(ole-tin)s have been reported. In early work, Randall et a/. - studied irradiated high-density poly(ethylene)s (HOPE) using - C NMR, and identified a number of new structures, including internal double bonds and Y-type cross-links. The materials under consideration contained initially a high concentration of vinyl end... 

No such relationship was observed in the case of polyethylene mixtures with butyl rubber (Fig. 6). We came to the conclusion that the activity of polyacrylonitrile as a filler can be connected with EDA interactions between electrons of double bonds and -C E N groups. No such complex type has so far been detected in polymer mixtures. In the given instance an EDA complex could appear only at the interphase boundary and its concentration would be quite low. However, certain symptoms of its existence have been observed. PAN added in the amount of 30 phr raised the cis-1,4-poly-butadiene Tg towards higher temperature region by 4-15 K. This was observed by means of thermomechanical analysis under dynamic as well as under static conditions (Figs. 7 and 8). The presence of the immobilized layer of PB on the PAN domains was also established in studies carried out by the method of pulse NMR. In the mixtures of PB with PAN there appeared additional compliances of the relaxation time T2 "spin-spin" (Fig. 9), as well as relaxation time T "spin-network" (Fig. 10). This indicates that part of the elastomer has... 

Asturias et al noted that overoxidized poly aniline will gradually degrade toward the emeraldine structure (in 80% acetic acid solution) due to the hydrolysis of -C=N- double bonds). We find, however, that fully oxidized poly aniline is stable in concentrated sulfuric acid (97%). 

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