Polymerization pentadiene

Only a definite scope of monomers can be polymerized in a given host. This indicates that inclusion polymerization displays a sterically different boundary condition from other polymerizations. That is, an increase of one methylene unit of one monomer can induce an inhibition of the polymerization in a given channel (Fig. 5a,b). Moreover, the relative sizes of the channels change the polymerizabilities of the identical monomers. Even though a monomer does not polymerize in a small channel, the same monomer polymerizes in a larger channel, (Fig. 5b,c). For example, 4-methyl-1,3-pentadiene polymerized in the smaller channels of deoxycholic acid. 

FIGURE 17.14 End groups detected in poly (4-methyl-1,3 pentadiene) polymerized with CpTiCl3/MAO in the presence of A1( CH3)3 2,1-insertion (A) l,4-insertion (B) (P = polymer chain). 

SCHEME 17.1 Schematic representation of the monomer insertion process in 4-methyl-1,3-pentadiene polymerization that leads to the two different polymer end groups A and B (L = ancillary ligand). 

The soluble catalysts from an aluminum alkyl chloride and a cobalt compound are well known since they have long been used, even on an industrial scale, for polymerizing butadiene to cis-1,4 polymer. The features of pentadiene polymerization by these catalysts are more or less similar to those of butadiene polymerization. Since the latter has been widely investigated and has already been the object of various papers (See e.g. 3, 4), we shall limit ourselves here to underlining the more significant differences that we have observed between the polymerization of butadiene and pentadiene. 

When they are used in aromatic solvent (and in the case of pentadiene polymerization they must be used in aromatic solvent in order to obtain cis-1,4... 

Longo, R Grisi, R Proto, A. ZambelU, A. Chemoselectivity in 4-methyl-l,3-pentadiene polymerization in the presence of homogeneous Ti-based catalysts. Macromol. Rapid Commun. 1997, 18, 193-190. 

Ever since 1962, when Williams, Okamura, and their associates started to publish propagation rate-constants k+p for the cationic bulk polymerization of cyclo-pentadiene, isobutene, styrene, a-methylstyrene and isopropylvinyl ether by ionizing radiations, these constants have been accepted as the best, most likely, values for the k+p of unpaired cations in a medium of low-polarity, and those obtained subsequently by Stannett and his collaborators, using similar methods, enjoyed the same status, (The loci classici are Bates et al. (1962), Bonin et al. (1964), Taylor Williams (1969) and the three papers by Ueno et al. (1967), Hayashi et al. (1967) and Williams et al. (1967).)... 

The polymerization of trans-1,3-pentadiene, 149, in a chiral channel inclusion complex with enantiomerically pure perhydrotriphenylene affords an optically active polymer, 150 (236). Asymmetric polymerization of this monomer guest occurs also in deoxycholic acid inclusion complexes (237). 

Monomers with cumulated double bonds, such as substituted allenes and ketenes, produce a great variety of structures. Stereoisomerism is found both at the saturated (iso- or syndiotacticity) and at the unsaturated carbons where the substituents in the plane of the chain can be oriented in either direction (forward or backward). With regard to 1,3-disubstituted allenes, four stereoregular strac-tures, 43-46 (Scheme 10), are predicted. Porri, Rossi, and Ingrosso succeeded in polymerizing 2,3-pentadiene (1,3-dimethylallene) samples of different optical purity (87). In their experiments they recognized the existence of sequences 43. 

Further examples of polymerization of optically active monomers are concerned with 2,3-pentadiene (dimethylallene), which gives rise to a structure like 43, already examined in Section II-C (87), with chiral acetylene compounds... 

The trick used in asyrmnetric inclusion polymerization is to perform the reaction in a rigid and chiral environment. With more specific reference to chirality transmission, the choice between the two extreme hypotheses, influence of the starting radical (which is chiral because it comes from a PHTP molecule), or influence of the chirality of the channel (in which the monomers and the growing chain are included), was made in favor of the second by means of an experiment of block copolymerization. This reaction was conducted so as to interpose between the starting chiral radical and the chiral polypentadiene block a long nonchiral polymer block (formed of isoprene units) (352), 93. The iso-prene-pentadiene block copolymer so obtained is still optically active and the... 

The all-trans-all-isotactic and all-trans-all-syndiotactic structures for the 1,4-polymerization of 1,3-pentadiene are shown in Fig. 8-6. In naming polymers with both types of stereoisomerism, that due to cis-trans isomerism is named first unless it is indicated after the prefix poly. Thus, the all-trans-all-isotactic polymer is named as transisotactic l,4-poly(l,3-penta-diene) or isotactic poly( -3-methylbut-l-ene-l,4-diyl). 

For example, in the ring isomerization reaction, methylcyclopentane forms a methylcyclopentene intermediate in its reaction sequence to cyclohexane. The intermediate can also further dehydrogenate to form methylcyclo-pentadiene, a coke precursor. Bakulen et al. (4) states that methylcyclo-pentadiene can undergo a Diels-Alder reaction to form large polynuclear aromatic coke species. Once any olefinic intermediate is formed, it can either go to desired product or dehydrogenate further and polymerize to coke precursors. This results in a selectivity relationship between the desired products and coke formation as shown on the next page. 

Von 1,3-Pentadien (IT) wurden taktischc Polymere synthetisiert, deren stcrischer Aufbaii vorwiegend von der Art der verwendeten Katalysatoren aber auch von dem eingesetzten Isomcren dcs Monomcren (reines cis- bzw. trans-Isomeres oder Isomercngomischc) abhangt. Ins-... 

Of the conjugated dienes, 1,3-butadiene undergoes base-initiated polymerization but does not yield oligomers since there is no proton transfer reaction. Isoprene and 1,3-pentadiene, in contrast, give linear and cyclic dimers. 

When butadiene and 2,3-dimethylbutadiene are included in the channels of urea and thiourea, respectively, 1,4 addition invariably results to yield polymers with chemical and stereo regularities (Scheme 39). Note that addition in the 1,2 fashion is prevented sterically by the narrow channel. Similarly, high selectivity was obtained when butadiene, vinyl chloride, and styrenes were polymerized in the channels of cyclophosphazenes. Syndiotac-tic polymer alone is obtained from vinyl chloride included in urea channels this is apparently the first example of inclusion polymerization of a vinyl polymer in which control is exerted over the steric configuration of the developing tetrahedral carbon atom (Scheme 39). Highly isotactic polymer is obtained from 1,3-pentadiene when it is included in a perhydrotriphenylene matrix (Scheme 39). Note that addition could occur at either end (i.e., Q to... 

Ahnliche Untersuchungen wurden am trans-1,3-Pentadien (XCIX) beschrieben (196). Mit einem Katalysator aus (+)-Tri(2-methylbutyl)-aluminium und Titantetrabutylat entsteht ein inaktives Polymeres. Dagegen wurde mit dem System Triathylaluminium und (—)-Titantetra-menthylat eine betrachtliche optische Aktivitat erzielt. Die Polymeren wurden fraktioniert der Anteil mit dem hochsten cis-l,4-Gehalt wies auch die hochste optische Aktivitat auf. Bei der Ozonolyse dieser Polymeren wurde optisch aktive Methylbernsteinsaure erhalten damit ist bewiesen, daB die optische Aktivitat des Polymeren von asymmetrischen C-Atomen der Polymerkette herruhrt. 

Natta, Porri and co-workers have studied the stereospecific polymerization of trans 1.3-pentadiene (51,52,53,54,55). This monomer acts as a propylene vinylogue in 1.2-polymerization. It requires a cationic catalyst such as alkylaluminum dichloride to produce the 1.2 polymer. 

Fig. 7. Anionic catalysts and their effectiveness for the steric control in the polymerization of butadiene and isoprene. Cationic catalysts in the polymerization of trans- 1.3-pentadiene...

The 1,4 polymerization of trans-1.3-pentadiene has been studied by Natta, Porri and coworkers. Their results also show that the cis polymerization occurs with catalysts of ionicities in the middle region, while the trans structures come in the more ionic regions. The methyl group at the end of the diene systems shifts the transition points... 

The 1.4-cis polymerization of 1.3-pentadiene offers a second type of steric control. The methyl group of the new monomer can be sterically oriented by the methyl groups at the end of the growing polymer chain. Isotactic cis polymers can be obtained by a planar six membered ring... 

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