Trans-polymer polymerization

By using a transition metal chloride catalyst and an iodine modified cocatalyst, ring-opening polymerization of C5 and C8 monocyclic olefins is controlled to prepare either cis polymers or trans products that are crystallizable. In copolymerization, the cis/trans units in the copolymers are regulated by adjusting the C5/C8 olefin monomer ratio. As the comonomer is increased, the copolymer becomes less crystalline and then completely amorphous at equal amounts of cis/trans units. Polymerization results are reported from WC16 and MoCl5 catalysts. 

Cyclopentene. After Eleuterio s early disclosure (10) of cyclopentene polymerization by ring-opening catalysis, Natta and co-workers (11) reported that trans polymer forms using WC16 catalyst and the cispolypentenamer forms using MoC15. The... 

Later, Tieke reported the UV- and y-irradiation polymerization of butadiene derivatives crystallized in perovskite-type layer structures [21,22]. He reported the solid-state polymerization of butadienes containing aminomethyl groups as pendant substituents that form layered perovskite halide salts to yield erythro-diisotactic 1,4-trans polymers. Interestingly, Tieke and his coworker determined the crystal structure of the polymerized compounds of some derivatives by X-ray diffraction [23,24]. From comparative X-ray studies of monomeric and polymeric crystals, a contraction of the lattice constant parallel to the polymer chain direction by approximately 8% is evident. Both the carboxylic acid and aminomethyl substituent groups are in an isotactic arrangement, resulting in diisotactic polymer chains. He also referred to the y-radiation polymerization of molecular crystals of the sorbic acid derivatives with a long alkyl chain as the N-substituent [25]. More recently, Schlitter and Beck reported the solid-state polymerization of lithium sorbate [26]. However, the details of topochemical polymerization of 1,3-diene monomers were not revealed until very recently. 

Figure 1 summarizes the chemical structures of the topochemically polymerizable 1,3-diene monomers providing stereoregular 1,4-trans polymer (Scheme 6) [ 16]. Most of the polymerizable monomers contain benzyl, naphthylmethyl, and long alkyl-chain substituents in their chemical structures. The (ZyZ)-, (E,Z)-, and ( , )-muconic and sorbic acids as well as the other diene carboxylic acids are used as the ester, amide, and ammonium derivatives. In contrast to this, the carboxylic acids themselves have crystal structures unfavorable for polymerization while they undergo [2-1-2] photodimerization, as has already been described in the preceding sections.

Scheme 6 Solid-state polymerization of 1,3-diene compounds providing 1,4-trans polymers...

Woemer et al. 373) produced polyacetylene with locally oriented regions and an optical anisotropy of 2 x by polymerization on crystals of biphenyl. Yamashita and co-workers 374,375) have recently reported epitaxial polymerization of acetylene on crystals of anthracene, naphthalene and biphenyl where fibrils of cis- or trans-polymer formed, crystallographically aligned with the substrate. Fincher et al. 376) produced a 3 x extension which gave a 4 x optical anisotropy. 

FIGURE 3. 50 MHz 13C NMR spectrum of the 81% trans polymer obtained by the ADMET polymerization of 4,4,7,7-tetramethyl-4,7-disiladeca-l,9-diene. Reprinted with permission from Ref. 260. Copyright (1991) American Chemical Society... 

The ROMP of neat 99 is remarkable in that it proceeds to 96% conversion in 18 h at 25 °C to yield an all-HT, 97% trans polymer. Dilution of the living polymer with benzene causes neither reversion to monomer nor backbiting to form cyclic oligomers. The driving force for polymerization in this case derives from the relief of torsional strain in the monomer caused by interaction between eclipsed methyl groups on the adjacent silicon atoms300. 

The halide y-TiCl3, which offers only one coordination site at the active center, promotes the formation of trans-1,4-polymers, whereas /3-TiCl3, which provides more sites, favors the formation of a mixture of homo-cis- and homo-trans-polymers. Questions about the nature of TiCl3 structures may be answered by referring to references (6, 67) and (68) for polymerization on catalyst surfaces, refer especially to (69) and (70). 

The rotation barrier about the fi-y bond is not negligible, so that the centres exist in either the cis or trans forms (Z, E) mutual transitions between these two forms only occur under certain conditions and at a certain rate. In diene polymerizations in hydrocarbon medium with Li+ as counter-ion, monomer addition transforms a cis centre into a cis segment of the chain, and a trans centre into a trans polymer (the former case is typical for isoprene polymerization in THF the equilibrium is shifted towards the cis form over the whole of the available temperature range). A cis tram transition is, of course, not excluded (for example with butadienyllithium), and when it is more rapid than addition, chain stereospecificity is reduced. 

Kranz and Beck [268] have calculated that the enthalpies of polymerization of liquid cyclopentene to solid cis and trans polypentenamer are 4.2 and 3.2 kcal mole", in good agreement with a calorimetric value of 4.5 kcal mole for a 65% trans polymer. Other than this limited thermodynamic data the quantitative aspects of the polymerization are unknown of particular interest would be the factors influencing molecular weight and molecular weight distribution. 

This article describes the solid state polymerization of 1,i-disubstituted butadiene derivatives in perovskite-type layer structures, in layered structures of organic ammonium halide salts, and in lipid layer structures. Recent investigations by spectroscopic methods and x-ray structure analyses are described. The studies clearly indicate that the photolysis in the crystalline state leads to the formation of 1,i-trans-polymers exclusively. Crystal structure analyses of monomeric and polymeric layer perovskites demonstrate that upon y-irradiation a stereoregular polymer is obtained in a lattice controlled polymerization. 

Our investigations show that 1,4-disubsituted butadiene derivatives react in layered structures under exclusive formation of 1,i-trans-polymers. A stereoregular polymer is obtained. The structure analyses of the monomer and polymer crystals of 1 show that a lattice-controlled reaction takes place. It is certainly worthwhile studying the course of the reaction more in detail, and to compare the reaction mechanism and kinetics with those of other lattice-controlled reactions, as, for example, the polymerization reactions of diolefin 12Z) and butadiyne derivatives (23). 

While several explanations may be given for these findings, we focus here on our contention that this result supports the importance of allyl isomerization in diene polymerization. We postulate initially that the loss of bond forming stereospecificity in the diene polymerization is the result of allyl isomerization. This is particularly well supported by the completely stereorandom bond formation found for trans polymer. This is satisfactorily accounted for by rapid isomerization of the label, via primary allyls, to a random(l l) mixture of syn and anti deuterium. Any other mechanism for randomization, for example... 

Expts. Transition metal anode Aluminium anodic loss [mg] Anodic circulated charge in C Al Trans, metal Polymerization time [h] Converted ethylene [%1 Polymer yield [%I... 

A third access to soluble polyenes lies in the ROMP of cyclooctatetraene (COT) derivatives. COTs are readily polymerized by W- and Mo-based Schrock carbenes to yield substituted polyenes (Scheme 36). As evidenced by UV—Vis spectroscopy, these materials which are synthesized in a predominately cis form are highly conjugated with values for Amax of up to 538 nm (R = />octadecyl). Thermal cis—trans isomerization is possible and may be monitored via UV— Vis spectroscopy. The resulting predominately all-trans polymers show values for Xmax of up to 634 nm (R = neopentyl). Upon doping of these materials with iodine, conductivities of up to 50 S/m may be achieved.Trimethylsilyl-substituted COT forms transparent polymers, which may be casted onto n-doped silicon (n-Si). Upon treatment with iodine, surface barrier solar cells may be prepared. Soluble,... 

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