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Isoprene bulk polymerization

Problem 6.15 Isoprene was polymerized in bulk at several temperatures using AIBN at an initial concentration of 0.0488 mol/L in dead-end polymerization experiments [33]. In every case, the conversion increased with time until a limiting value was obtained beyond which no further polymerization was observed. No autoacceleration eifect was observed in this system. The data of fractional degree of conversion (p) with time, including the limiting value of conversion (poo), determined at each temperature are shown in table below ... [Pg.479]

Alkali Metal Catalysts. The polymerization of isoprene with sodium metal was reported in 1911 (49,50). In hydrocarbon solvent or bulk, the polymerization of isoprene with alkaU metals occurs heterogeneously, whereas in highly polar solvents the polymerization is homogeneous (51—53). Of the alkah metals, only lithium in bulk or hydrocarbon solvent gives over 90% cis-1,4 microstmcture. Sodium or potassium metals in / -heptane give no cis-1,4 microstmcture, and 48—58 mol % /ram-1,4, 35—42% 3,4, and 7—10% 1,2 microstmcture (46). Alkali metals in benzene or tetrahydrofuran with crown ethers form solutions that readily polymerize isoprene however, the 1,4 content of the polyisoprene is low (54). For example, the polyisoprene formed with sodium metal and dicyclohexyl-18-crown-6 (crown ether) in benzene at 10°C contains 32% 1,4-, 44% 3,4-, and 24% 1,2-isoprene units (54). [Pg.4]

Copolymerizations initiated by lithium metal should give the same product as produced from lithium alkyls. Usually the radical ends produced by electron transfer initiation have so short a lifetime they can have no influence on the copolymerization. This is true for instance in the copolymerization of isoprene and styrene (50). The product is identical if initiated by lithium metal or by butyllithium. With the styrene-methylmethacrylate system, however, differences are observed (79,80,82). Whereas the butyllithium initiated copolymer contains no styrene at low conversions, the one initiated by lithium metal has a high styrene content if the reaction is carried out in bulk and a moderate one even in tetrahydrofuran. These facts led O Driscoll and Tobolsky (80) to suggest that initiation with lithium occurs by electron exchange and that in this case the radical ends are sufficiently long-lived to produce simultaneous radical and anionic reactions at opposite ends of the chain. Only in certain rather exceptional circumstances would the free radical reaction be of importance. Some of the conditions required have been discussed by Tobolsky and Hartley (111). The anionic reaction should be slow. This is normally true for lithium based catalysts in hydrocarbon solvents. No evidence of appreciable radical participation is observed for initiation by sodium and potassium. The monomers should show a fast radical reaction. If styrene is replaced by isoprene, no isoprene is found in the copolymer for isoprene polymerizes slowly by free radical initiation. Most important of all, initiation should be slow to produce a low steady concentration of radical-anions. An initiator which produces an almost instantaneous and complete electron transfer to monomer produces a high radical concentration which will ensure their rapid mutual termination. [Pg.99]

The abovementioned materials can be mixed with one another. A series of other polymers and resins can also be added if the substances listed in 1 to 4 form the bulk of the material. Additional materials are PE, PP, low molecular weight polyolefins, polyterpenes (mixtures of aliphatic and cycloaliphatic hydrocarbons produced by polymerisation of terpene hydrocarbons), polyisobutylene, butyl rubber, dammar gum, glycerine and pentaerythritol esters of rosin acid and their hydration products, polyolefin resins, hydrated polycyclopentadiene resin (substance mixtures manufactured by thermal polymerization of a mixture mainly composed of di-cyclopentadiene with methylcyclopentadiene, isoprene and piperylene which is then hydrogenated). [Pg.47]

The oxidative process is driven either by oxygen itself or by any source of free radicals. If a polymer backbone is attacked, leading to either a polymeric carbon or oxygen radical, backbone cleavage is possible. For polyethylene, polypropylene and butadiene- or isoprene-containing polymers, this may be accompanied by elimination of formaldehyde or acetaldehyde. For styrene-containing polymers, formaldehyde and benzaldehyde are products from the cleavage [74], Such reactions could take place either in the bulk oil phase or in deposits in which the polymer is physically trapped. [Pg.176]

Antioxidants based on 2,6-ditertiarybutyl- -vinylphenol or 2,6-ditertiarybutyl-l-isopropenylphenol are the only monomeric stabilizers that have been synthesized and studied. We have developed efficient synthetic methods for the preparation of such compounds and have polymerized them with styrene or methyl methacrylate in solution or in bulk with AIBN as the initiator. More importantly, we have developed a good emulsion polymerization of 2,6-ditertiarybutyl-4-vinylphenol and 2,6-ditertiarybutyl-4-isopropenylphenol with butadiene or isoprene. The copolymers of good molecular weights had comonomer contents between 6 mol and 20 mol of the vinyl or iso-propenyl monomer. The polymers were effective at a 0.1 weight percent level in retarding autooxidation of polybutadiene and polyiso-prene. [Pg.208]

Some styrene-butadiene rubber is manufactured by solution processes using alkyllithium catalysts. Production techniques resemble those used for the polymerization of isoprene (Section 18.3.3) and butadiene (Section 18.4.3). Solution styrene-butadiene rubbers have microstructures similar to those of the emulsion copolymers but show narrower molecular weight distribution, less long chain branching and lower non-rubber content. The two types of materials have very similar bulk properties. [Pg.437]

Method of synthesis - bulk precipitation polymerization of isoprene catalyzed by supported titanium catalyst TiCI MgCI ... [Pg.443]

The development of systems that operate in non-halogenated solvents at temperatures closer to ambient has been a long-standing goal in the cationic polymerization field. This is especially true in regards to the copolymerization of isobutene with isoprene to make butyl rubber industrial production is conducted as a slurry in MeCl using AlClj at low temperatures ( -100°C) [55-61]. The majority of improvements that have been made in terms of reduced energy consumption, omission of chlorinated solvents, and elimination of waste have come from developments in the chemistry of initiator systems. The bulk of these stems from research conducted in the area of IB polymerization and have been previously covered... [Pg.161]


See other pages where Isoprene bulk polymerization is mentioned: [Pg.344]    [Pg.344]    [Pg.556]    [Pg.26]    [Pg.21]    [Pg.42]    [Pg.467]    [Pg.482]    [Pg.114]    [Pg.119]    [Pg.344]    [Pg.467]    [Pg.91]    [Pg.344]    [Pg.90]    [Pg.39]    [Pg.167]    [Pg.954]    [Pg.3674]    [Pg.159]    [Pg.427]    [Pg.468]   
See also in sourсe #XX -- [ Pg.42 ]




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