Poly , cis

As we did in the case of relaxation, we now compare the behavior predicted by the Voigt model—and, for that matter, the Maxwell model—with the behavior of actual polymer samples in a creep experiment. Figure 3.12 shows plots of such experiments for two polymers. The graph is on log-log coordinates and should therefore be compared with Fig. 3.11b. The polymers are polystyrene of molecular weight 6.0 X 10 at a reduced temperature of 100°C and cis-poly-isoprene of molecular weight 6.2 X 10 at a reduced temperature of -30°C. 

The polymer in natural rubber consists almost entirely of ci -poly(isoprene) (1.6). The molecules are linear, with relative molar mass typically lying between 300 000 and 500 000. The macromolecular nature of rubber was established mainly by Staudinger in 1922, when he hydrogenated the material and obtained a product that retained its colloidal character, rather than yielding fragments of low relative molar mass. 

A similar comparison can be made with cis-poly(isoprene), natural rubber, by taking advantage of the fact that the polymer is very slow to crystallize [164], Consequently, the comparison can be made between the supercooled, noncrystalline polymers at 0°C and the semi-crystalline polymer (31% crystalline) at the same temperature. The Tlc values for each of the five carbons involved were again found to be the same for the completely disordered polymer and the semicrystalline one, so that a similar conclusion can be made with regard to their chain structure. 

Stereoselective ROMP has been reported with monomer (213). Initiator (211) affords highly stereoregular polymer with >98% trans C=C bonds in the polymer backbone.534 However, when (210) is used, >98% cis-poly-(213) is obtained.535 A similar situation occurs for the diester monomer (214). Furthermore, a rapidly equilibrating mixture of (210) and (211) can be used to allow intermediate cis/trans contents to be manipulated by the stoichiometry of the initiator mixture. 13C NMR536 and dielectric analyses537 suggested that trans-poly-(213) is highly syndio-tactic (92% r dyad content). The ROMP of other fluorinated olefins has been recently reviewed.538... 

First, new "living" initiators have been discovered (although not always as efficient), which respond to other mechanisms, i.e. cationic (5) or even radical ones (6), and can accordingly accomodate other types of monomers. A recent typical example is the coordination polymerization of butadiene by bis (n3-allyl-trifluoro-acetato-nickel) to yield a "living" pure 1.4 cis-poly-butadienyl-nickel, able to initiate in turn the polymerization of monomers like isoprene or styrene (7). 

Figure 6.12 Plot of the Bingham yield stress versus the concentration of cis-poly (iso-prene) added to a latex in dodecane (system HK4 with

Both the naturally occurring Hevea brasiliensis (NR) and synthetic cis poly-l,4-isoprene have the following repeating unit ... 

Schumacher et al. (4) prepared adhesives for polyvinyl chloride (PVC) pipes having a T range from —60 to — 20°C and consisting of Ci-Cis poly-... 

Figure 6. High molecular weight polyisobutylene in cis-poly butadiene. Differential swelling in styrene at —25°C. Blends cured 30 minutes at 300° F.

Figure 10. Electron micrographs of (a) a 50/50 blend of IR and high-cis polybutadiene and (b) a 50/50 blend of medium-cis poly butadiene and high-vinyl polybutadiene. See Table 111 for details of diene microstructures.

Poly (1,3-butadiene), trans Poly (1,3-butadiene), cis Poly (propylene oxide)... 

TABLE 2. Physical properties of l,4-cis-poly(polybutadiene-co-urethane) prepared at 70°C using the stoichometry described in Table 1. 

Figure 4.8-7 Raman spectra obtained in situ during electrochemical doping of cis-poly(acetylene) in acetonitrile/LiClOa at 3.8 V vs. Li. Doping times are indicated in hours, according to Meisterle et al., 1984.

Lemieux has given a detailed account of a possible mechanism for this reaction. It is suggested that absorption of a 1,2-cis-poly-O-acetylglycosyl bromide on the silver chloride facilitates the formation of carbonium ions which are stabilized (immediately they are formed) by assuming a 1,2-cyclic structure. Reaction of this cyclic intermediate with chloride ion then yields the 1,2-[Pg.220]

Reaction of dineopentylosmium dioxide with 2 equiv. of Ta(CHR)(CH2R)3 was reported to result in the formation of osmium dineopentylbisneopentylidene [269, 270]. Interconversion of the two isomeric forms [syn-anti and anti-anti) of this compound was postulated to proceed via an osmium tris(neopentyl)neo-pentylidene. So far, no reports on the ROMP activity of these complexes have been given. Similar to OsCls [271] and (p-cyrnene)OsCl2P(c-H,.) j [272], (/z-H)20s3(CO)io was reported to be active in the ROMP of NBE to yield all cis-poly-NBE [273]. 

An enhanced importance of 02 quenching cannot be excluded in pigmented PO, polydienes and coatings. An efficient protection against 02 induced photooxidation of cis-poly(l,4-butadiene) by HAS was confirmed [212], Oligomeric HAS 34 and 35a imparted a good stability to the polydiene in the presence of the sensitizer Rhodamine 6G. 

The tran5-poly-l,4-butadiene isomer is a harder and less soluble rigid crystalline polymer than the cis isomer. As shown by the skeletal structure for the trans isomer (Figure 1.11), chain extensions on opposite sides of the double bonds allow good fitting of adjacent polymer chains, and this, results in a rigid structure. In contrast, the ci>poly-l,4-butadiene isomeric pplymer units do not permit such interlocking of alternate units. Even so, chain... 

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