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Cyclization of polyisoprene

Triflic acid has been used to induce cyclization of polyisoprene (xylene, 75°C, 5-30 min) and the various ring moieties (215-217) were identified by 1H... [Pg.716]

The dependence of the pyrolysis on the sample structure may be used in applying Py-GC to solve various physico-chemical problems. In particular, Py-GC has been used to study the kinetics of cyclization of polyisoprene rubber the results were later corroborated by other methods [268,269]. [Pg.131]

The cationic cyclization of polyisoprene with acid catalysts is well documented. The same reaction in polybutadienes requires much more severe conditions, higher temperatures and more acidic catalysts, and until recently has received much less attention. A cyclized polymer with a reduction of 35—40% of the initial unsaturation, can be prepared by treating cis-l,4-polybutadiene with an alkyl aluminium chloride-organic halide catalyst in xylene solution at >100 C."- Such polymers, containing polycyclic sequences apparently at random within the chains, have better skid resistance and tensile properties than the parent polymer. Cyclization has been reported to accompany other reactions in polydienes, for example the radiation-induced addition of carbon tetrachloride to 1,2-polybutadiene, and the direct addition of a o j unsaturated carboxylic acids (acrylic and cinnamic) to polydienes and polypentenamers. It is reported that the thermal isomerization of cis-transoidal poly(phenylacetylene) is accompanied by cyclization, and additionally chain scission and aromatization at temperatures >120°C. ... [Pg.275]

Before leaving the subject of the cyclization of polyisoprenes it may be mentioned that the 3,4-polyisoprenes have been used to produce ladder polymers. Since neither the initial nor the final product can be considered as a rubber this will not be dealt with further here. (For further details see for example the review by Golub, 1969.)... [Pg.184]

The type of alkylaluminum compound has only a secondary influence on structure in the polymerization of diolefins in contrast to its strong effect on the structure of polypropylene. An exception is AlEtCb, which, apparently in connection with its cationogenic character, with j3-TiCl3 induces polymerization to trans-1,4 polybutadiene and, even without transition metal compound, leads to formation of cyclized polyisoprene. Incidentally, this indicates that poly-butadiene is much more stable towards cyclization than polyisoprene. [Pg.151]

In summary, cationic polymerization gives polymers of structure P8a Ziegler-Natta complexes mainly lead to blocks of structure P8b. This study gives further evidence for cyclization reactions of high-molecular-weight polyisoprenes. This point of view has been confirmed by the study of the cyclization of model polyisoprene molecules with two, three, or four monomer units toward the catalysts able to initiate such a reaction (24). [Pg.166]

Acid Catalyzed Rearrangements. An example of a photoresist based on an acid catalyzed rearrangement is the diaryliodonium salt photoinduced cyclization of cis-1,4-polyisoprene shown in Equation 18. This facile cyclization which has been reported previously (11) by non-photochemical processes results in a polycyclic polymer whose physical properties and solubility characteristics are considerably different than the initial polymer. Exploitation of these differences in the exposed and unexposed regions of the polymer film permit their use as either positive or negative tone resists. [Pg.6]

Cationic cyclization of unsaturated elastomers such as poly(c -l,4-isoprene), poly(3,4-isoprene), poly(l,2-butadiene), and poly( 1,4-butadiene) usually leads to the formation of cyclized resinous products of no commercial value. An extensive review on the subject has been published by Schults et al. (1983). Cyclization of unsaturated elastomers, such as polyisoprene, can be carried... [Pg.527]

Rubber can be bromimted at 30 C. If traces of alcohol are present, the reaction appears to go on entirely by addition. " Without alcohol, substitutions take place rapidly and simultaneously with the additions to the double bonds. Exomethylene groups and intramolecular cyclic stroctures form in the process. Slow additions of bromine to vinylidene double bonds result in formations of tribromides, -C5H7B13. Also, cis and trans isomers of polyisoprene brominate differently. Substitution reactions take place in brominations with N-bromosuccinimide. They are accompanied by cyclizations. ... [Pg.408]

Cyclization reactions of polyisoprene can be catalyzed by TiCU and by sulfuric acid. 3-115,117 products appear similar in the infrared spectra with only a few minor differences. Also, there is only a small number of fused rings in the product. [Pg.417]

The modification of polyisoprene by treatment with strong acid dates, in the case of natural rubber, to at least the late 18th century. 1 It has been accepted for some time now that the resinification and loss of rmsaturation acconpanying such treatment are due, inmost instances, to acid-catalyzed cyclization. The earlier work on sudi cyclization has been reviewed thoroij lyl and only a brief overview of the main aspects will be given here. [Pg.383]

Figure 1. Acid-Catalyzed Cyclization of 1.4-Polyisoprene. (Formation of a Tetracylic S nent). Figure 1. Acid-Catalyzed Cyclization of 1.4-Polyisoprene. (Formation of a Tetracylic S nent).
In Table IV are shewn the results of our NMR analyses of 20 sanples of cyclized polyisoprene, prepared as noted in Table I. Because of the relevance bo the block copolymersl0 12 mentioned above, the bulk of the data are for cycliz lithivm polyisoprene. Ihere are, however, sene results for cyclized natural rubber, both hevea and gu yule. [Pg.398]

Finally, mention may be made of processes other than cyclization, specifically alkene isomerization. There is evidence here of at least two t es of double bond iscxnerization of polyisoprene repeat imits in the partially cyclized samples, namely, positional and cis-trans (some fraction of vhich may be positional as well). The Ir lIMk spectra, as discussed above, reveal the existence of olefinic methylene other than that associated either with 3,4-units or dischstituted SBG and assignable to iso-1,4 units. Goli > and Heller have previously conjectured that such iscmerization occurs. [Pg.405]

A reduced cis/trans ratio is seen for other partially cyclized lithium polyisoprenes (Ll-1 and 11-2). It is likely that the drop in /trais ratio represents some net cis-trans isoroerizaticm. Differential cyclizatim, even given that the distribution of micro-structures is random, 28 could occur if there were bias at initiation and/or termination and could oonceiv ly account for some of the change in cis/trans ratio. [Pg.406]

Products of cyclization of trans-l,4-polyisoprene are virtually identical to those obtained from c/5-l,4-polyisoprene. [Pg.181]

Minatti, E., Borsali, R., Schappacher, M. et al. (2002) Effect of cyclization of polystyrene/polyisoprene block copolymers on their micellar morphology. Macromolecular Rapid Communications, 23,978-982. [Pg.818]

The terpene cyclase or synthase is another class of enzyme that is capable of synthesizing new C—C bonds. Terpenoids is one of the most diverse classes of natural products. Their syntheses involve the cyclization of linear polyisoprene precursors by terpene... [Pg.435]

Fig. 5. Chemistry of cyclized mbbei—bis-a2ide negative acting resist, (a) Preparation of cyclized mbber resin from polyisoprene (b) photochemistry of aromatic bis-a2ide sensiti2ers. The primary photoproduct is a highly reactive nitrene which may combine with molecular oxygen to form oxygenated products, or may react with the resin matrix by addition or insertion to form polymer—polymer linkages. Fig. 5. Chemistry of cyclized mbbei—bis-a2ide negative acting resist, (a) Preparation of cyclized mbber resin from polyisoprene (b) photochemistry of aromatic bis-a2ide sensiti2ers. The primary photoproduct is a highly reactive nitrene which may combine with molecular oxygen to form oxygenated products, or may react with the resin matrix by addition or insertion to form polymer—polymer linkages.

See other pages where Cyclization of polyisoprene is mentioned: [Pg.601]    [Pg.517]    [Pg.528]    [Pg.498]    [Pg.509]    [Pg.667]    [Pg.238]    [Pg.601]    [Pg.601]    [Pg.517]    [Pg.528]    [Pg.498]    [Pg.509]    [Pg.667]    [Pg.238]    [Pg.601]    [Pg.879]    [Pg.240]    [Pg.786]    [Pg.140]    [Pg.786]    [Pg.461]    [Pg.384]    [Pg.384]    [Pg.390]    [Pg.390]    [Pg.402]    [Pg.404]    [Pg.405]    [Pg.406]    [Pg.184]    [Pg.106]    [Pg.115]    [Pg.348]    [Pg.349]   
See also in sourсe #XX -- [ Pg.40 , Pg.383 , Pg.384 , Pg.392 , Pg.401 , Pg.401 , Pg.403 , Pg.403 , Pg.405 ]




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