4-Methyl-1,3-pentadiene polymers

Inomata 211) studied the H-NMR spectra of poly(penta-1,3-diene) and concluded that with hexane as polymerization medium the polymers were about 49% cis-1,4 and 40% trans-1,4 enchained. The polymer derived from the cis monomer had 12% of 1,2-units which were exclusively trans that from the trans monomer had some 10 % of 1,2-units, two thirds of which were trans. Aubert et al.2I6) made a more extensive study of pentadiene polymers using both1H and 13C-NMR spectroscopy and modified the cis and trans-1,4 methyl resonance assignments made by Inomata 2U). 

Although the use of pendant drops is a robust method and produces interfacial tensions of acceptable accuracy, it is dependent on there being a sufficient difference in density between the two polymers. When the densities become very similar, a true axisymmetric pendant drop may not be obtainable. Figure 2.5 shows an example of a distorted drop of polybutadiene surrounded by poly(2-methyl pentadiene). In some of these cases a sessile drop usually conforms more to the desirable profile than would a pendant one. 

One of the most important results of inclusion polymerization is the synthesis of optically active polymers from nonchiral compounds. Asymmetric polymerization of /ra 5-pentadiene in PHTP has been reported. The optical purity of the polypentadiene is about 7%. DCA and ACA, as natural hosts, induce a greater asymmetric polymerization. The cis and rra/i5-2-methyl-pentadiene gave the highest asymmetric polymerization values [88]. The optical rotatory power disappeared with temperatures higher than 70°C, indicating that this process is reversible and results from a conformational transformation. 

In one example, the Tics of the non-crystalline methyl, methine and methylene carbons of iPP, 70% crystalline, were compared at room temperature with those of model atactic poly(propylene), hydrogenated poly(2-methyl-l,3-pentadiene) [163]. It was found that, within the experimental error, the Tic values of each of the carbons were the same in both polymers. The conclusion can then be reached that the fast segmental motion, at or near the Larmor frequency of... 

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... 

When polymerizing 1.3-pentadiene, the optical activity of the isotactic cis-1.4-polymer obtained in the presence of catalysts prepared from (—)-titanium tetramenthoxide and aluminum triethyl, is far higher than that of the analogous polymers obtained with catalysts prepared from titanium tetrabutylate and (+)-tris-[(S)-2-methyl-butyl]-aIumin-um (05). 

Diene Polymers Polymerization of a 1,3-diene yields a polymer having true asymmetric centers in the main chain and ozonolysis of the polymer gives a chiral diacid compound (12) whose analysis of optical purity discloses the extent of chiral induction in the polymerization (Scheme 11.2) [12,35-39], The polymerization of methyl and butyl sorbates methyl and butyl styrylacrylates and methyl, ethyl, butyl, and /-butyl 1,3-butadiene-1-carboxylates using (+)-2-methylbutyllithium, butyllithium/(-)-menthyl ethyl ether, butyllithium/menthoxy-Na, butyllithium/bomeoxy-Na, butyllithium/Ti((-)-menthoxy)4, and butyllithium/bomyl ethyl ether initiators [35-37] and that of 1,3-pentadiene in the presence of... 

I, 3-diene polymerization. Monomer molecules are included in chiral channels in the matrix crystals, and the polymerization takes place in chiral environment. The y-ray irradiation polymerization of trans- 1,3-pentadiene included in 13 gives an optically active isotactic polymer with a trans-structure. The polymerization of (Z)-2-methyl-1,3-butadiene using 15 as a matrix leads to a polymer having an optical purity of the main-chain chiral centers of 36% [47]. 

So Cataldo et al. [101] have focused their studies on polymers like 1-2 polybutadiene, 3-4 polyisoprene and poly(4-methyl-l,3 pentadiene). These polymers are very sensitive to ozone, and their own tacticity seems to have a very low influence on their reactivity. In a usual way, substituents make... 

The polymers obtained from unsymmetrically terminally disubstituted butadiene such as 4-methyl-1,3-pentadiene are made up of 1,2 monomeric units only, irrespective of the catalyst used this is due to the presence of two methyl substituents at the C4 atom in the monomer. Two stereoregular polymers have so far been obtained from 4-methyl-l,3-pentadiene, one with a 1,2-isotactic structure and one with a 1,2-syndiotactic structure. The isotactic polymer has been yielded by heterogeneous Ziegler-Natta catalysts, e.g. TiCU—AlEt3 and a — TiCl3— [AlEt3 [182]. The factors that determine the orientation of the coordinating monomer in this case are not, however, completely clear [41]. 

Syndiotactic l,2-poly(4-methyl-l,3-pentadiene) has been formed by polymerisation with homogeneous catalysts, e.g. TiBz4—[Al(Me)0]x and CpTiCl3—[Al (Me)0]x [41,43]. The coordination of the monomer as an s-trans-t/2 ligand rather than an s-cis-r A ligand at the Ti atom has been postulated to be involved in the polymerisation. The s-cis-r A monomer coordination is less favoured for steric reasons in the case of 4-methyl-1,3-pentadiene. A possible scheme for the formation of the 1,2-syndiotactic polymer from this monomer is presented in Figure 5.7 [41,43],... 

It is interesting that the polymerisation of 4-methyl-1,3-pentadiene proceeds faster at —20 °C than at 20 °C. It has been suggested [43] that at a temperature below 0°C this monomer coordinates as an s-trans-t]2 ligand. At a higher temperature it can probably coordinate either as an s-trans-tf ligand or as an s-cis-tf ligand, but monomeric units in the polymer are derived mainly from the... 

Monomers such as E-l,3-pentadiene (piperylene) and E-2-methyl-l,3-pentadiene give 1,4-polymers with an asymmetric carbon atom. Therefore, these monomers in principle will result in polymers with an isotactic, syndio-tactic or atactic structure. 

Early studies on the homopolymerization of E-l,3-pentadiene yielded polymers with a high cis-1,4-content and an isotactic structure, whereas E-2-methyl-l,3-pentadiene resulted in a polymer with a mixed czs-1,4/transit-structure [487-492]. Investigations on the polymerization of E-1,3-pentadiene with the system NdN/TIBA/DEAC partially support these findings as a poly(l,3-pentadiene) with a cis- 1,4-threo-disyndiotactic structure was obtained [492]. A somewhat lower cis- 1,4-content of 70% was obtained when the polymerization of E-l,3-pentadiene was catalyzed by (CF3COO)2NdCl/TEA [493,494]. When 2,3-Dimethyl-1,3-butadiene is polymerized with the catalyst NdN/TIBA/EtAlC the resulting poly(2,3-dimethyl-butadiene) predominantly contains cis-1,4-units [495,496]. 

E-3-Methyl-l,3-pentadiene was polymerized using NdO/TIBA/DEAC and isotactic polymers with a high crystallinity were obtained. The polymers essentially consisted of cis-1,4 units (> 80%). Isotactic czs-l,4-poly(3-methyl-1,3-pentadiene) co-exists in two morphological structures [497]. 

A study on the homo- and copolymerization of a variety of dienes such as 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, E-l,3-pentadiene, E-l,3-hexadiene, E-l,3-heptadiene, E-l,3-octadiene, E,E-2,4-hexadiene, E-2-methyl-l,3-pentadiene, 1,3-cyclohexadiene mainly focused on mechanistic aspects [139]. It was shown that 1,4-disubstituted butadienes yield frans-1,4-polymers, whereas 2,3-disubstituted butadienes mainly resulted in cis- 1,4-polymers. Polymers obtained by the polymerization of 1,3-disubstituted butadienes showed a mixed trans-1,4/cis-1,4 structure (60/40). The microstructures of the investigated polymers are summarized in Table 26. 

In later studies on the homopolymerization of E-l,3-pentadiene with NdO/ TIBA/DEAC crystalline polymers with cis- 1,4-contents in the range 84-99% and a high isotacticity were obtained. It was found that the cis- 1,4-content increases when the polymerization temperature is decreased from room temperature to -30°C. The polymerization of E-2-methyl-l,3-pentadiene resulted in polymers which almost exclusively comprised cis- 1,4-units and no dependence of the cis- 1,4-content on polymerization temperature was observed. The obtained poly(2-methyl-l,3-pentadiene) was composed of various polymer fractions with different stereo regularities [165,166]. 

As was found for the polymerization of styrene, CpTiCT/M AO and similar half-sandwich titanocenes are active catalysts for the polymerization of conjugated 1,3 dienes (Table XX) (275). Butadiene, 1,3-pentadiene, 2-methyl-l,3-pentadiene, and 2,3-dimethylbutadiene yield polymers with different cis-1,4, trans-1,4, and 1,2 structures, depending on the polymerization temperature. A change in the stereospecificity as a function of polymerization temperature was observed by Ricci et al. (276). At 20°C, polypen-tadiene with mainly ds-1,4 structures was obtained, whereas at -20°C a crystalline, 1,2- syndiotactic polymer was produced. This temperature effect is attributed to a change in the mode of coordination of the monomer to the metallocene, which is mainly cis-rf at 20°C and trans-rj2 at -20°C. 

As found for the polymerization of styrene, CpTiCl3/MAO and similar half-sandwich titanocenes are active catalysts for the polymerization of conjugated 1,3-dienes (Table 25) [218], Butadiene, 1,3-pentadiene, 2-methyl-l,3-pentadiene and 2,3-dimethylbutadiene yield polymers with different... 

In an attempt to prepare polycyclopentadiene which would be stable in toluene solution, the polymer was hydrogenated over a platinum oxide catalyst in a Parr bomb immediately after the completion of the polymerization reaction. Infrared analysis indicated the presence of residual unsaturation and the polymer became insolubilized on standing. An attempted copolymerization of cyclo-pentadiene with propylene gave a product whose infrared spectrum indicated the presence of C-methyl groups but which was still insoluble in toluene. No attempt was made to determine whether copolymerization had occurred. 

Bulk polymerization of frons-2-methyl-l,3-pentadiene lead only to i,4-trans addition polymer, however it allows randomization of the trans structure, leading to an atactic polymer. The polymerization of the clathrate of fr(Ms-2-methyl-l,3-pentadiene yielded an isotactic l, 4-trans addition polymer. The polymer formed from the bulk had a molecular weight of 20,000 (240 monomer units), and that formed from the clathrate had a molecular weight of lOOO (l2 monomer units). Similar results were obtained for other dienes, and the results are summarized in Table 4. it can be concluded that polymerization of dienes in the clathrate lead exclusively to a i,4-trans addition polymer, except in the case of 1,3-cyclohexadiene. For this monomer, although the polymer is formed entirely by 1,4-addition, the polymer formed is essentially atactic. In bulk polymerization, the polymerization proceeds in most cases through 1,4-addition (both trans and cis), but in the case of butadiene and 1,3-cyclohexadiene 1,2-additions were also observed. Actually, in the case of the bulk y-induced polymerization of 1,3-cyclohexadiene the 1,2-addition process was favoured over the 1,4-addition process by a ratio of 4 3. 

Et(Ind)2ZrCl2/MAO gives copolymers of ethylene or propylene with nonconjugated dienes, such as 2-methyl-1,4-pentadiene, 7-methyl-1,6-octadiene and 1,7-octadiene, (Eq. 23) [103]. rac-Et(Ind)2ZrCl2/MAO also catalyzes copolymerizations of asymmetrically substituted linear dienes, 6-phenyl-1,5-hexadiene, 7-methyl-1,6-octadiene, and R-(+)-5,7-dimethyl- 1,6-octadiene. The copolymerization of R-(+)-5,7-dimethyl-l,6-octadiene with propylene to give the polymer with ca. 15% diene incorporation. The ratio of the diene-derived part is ca. 15% of the polymer [104]. 

In 1961, Natta reported one of the first examples of enantioselective catalysis using a transition metal catalyst. In this reaction, an optically active polymer was formed from 1,3-pentadiene using a chiral organoaluminum/VClj catalyst [62]. The optical activity of this polymer results from the main-chain chiraHty of polymer, where the methyl-substituted stereogenic centers are predominantly of one absolute configuration. Since this initial study, significant advances in the enantioselective synthesis of main-chain chiral polymers have been reported using ionic and metal-based techniques. 

Matthews and Strange [42] reported a similar reaction of isoprene with sulfur dioxide in the presence of hydrogen chloride. Seyer and King [Id] reported that 1,3-cyclohexadiene reacted with sulfur dioxide to give a white amorphous compound, as earlier reported by Hofmann and Damm [43]. 2-Methyl- and 4-methyl-1,3-pentadiene were reported by Morris and Van Winkle [44] to react with sulfur dioxide to yield a cyclic sulfone and some hydrocarbon polymer. Starkweather [45] in 1945 reported that chloroprene (2-chloro-l,3-butadiene) reacted with sulfur dioxide in an emulsion system to give a copolymer. Poly-sulfone is the major product when radical initiators are used. Cyclic products predominate when radical inhibitors (hydroquinone) or temperatures in excess of the ceiling temperature are used. For example ... 

Some work has also been reported on the polymerizations of various 1-substituted and 1,4- and 2,4-disuhstituted 1,3-hutadienes. Many more different stereoregular stmctures are possible for these monomers (Sec. 8-le). The result is that very few of the completely stereoregular polymers have been obtained in high yield coupled with high stereoregularity. For example, ( )-2-methyl-l,3-pentadiene (LIII) was polymerized by neodymium(III) octanoate to a polymer consisting of 98-99% cis 1,4-structure but different fractions differed in isotac-ticity [Cabassi et al., 1988]. Similar results were found for other monomers [Pasquon et al., 1989 Porri and Giarrusoso, 1989 Takasu et al., 2001]. 

Tacticities of the polymers were estimated. For example, poly (1.3-pentadiene) was highly isotactic in the channels of perhydrotriphenylene, while it was preferentially isotactic (mesoiracemic = 2 1) in the channels of deoxycholic acid. A completely isotactic polymer was utilized to prepare a unique polymer, hemitactic polypropylene, by hydrogenation of a completely 1,4-trans isotactic poly(2-methyl-1,3-pentadiene). 

Asymmetric synthesis cyclopolymerization of 1,5-pentadiene (261) was performed with an optically active metallocene catalyst. The polymer (262) obtained by (S)-ethylenebis(tet-rahydroindenyl)zirconium (S)-binaphtholate ([a] 435+1848°) in the presence of methyl aluminoxane (MAO) showed molecular rotation [(p] 4os-49.3°, and NMR analysis showed that the polymer had -68% tram structure. An optically active copolymer consisting of cyclic 262 units and linear units formed by 1,2-insertion shows LC phases. ... 

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