1,4-Hexadienes, polymers

MHz 1H-rWR SPECTRAL DATA OF 5-METHYL-1,4-HEXADIENE POLYMER (Et2AlCl/6-TiCl3 Catalyst, 0°C) in CC14 and C D6... 

Figure 1. GLC data for the polymerization and isomerization of trans-1,4-hexa-diene at 25°C with a Et3Al/S-TiCls catalyst (Al/Ti atomic ratio is 2). n-Hexane was used as the internal standard. Key O, trans-7,4-hexadiene , polymer A, cis-2-tzans-4-hexadiene tTans-2-trans-4-hexadiene A, 1,3-hexadiene. Reproduced, with permission, from Ref. 14. Copyright 1980, John Wiley Sons, Incorporated...

In contrast to the spectrum of isotactic trans-l,4-hexadiene polymer (Figure 5), the 300 MHz -H-NMR spectra of the 5-methylhexadiene polymer in both CCI4 and CgDg solutions exhibit only one peak for its backbone methylene protons. As in the case of cis-l,4-hexadiene polymer (14), the backbone methylene protons were not resolvable. The absence of a doublet for the methylene protons in these polymers does not necessarily preclude the possibility that they are isotactic. 

To clarify the tacticity problem, trans-l,4-hexadiene and 5-methyl-l,4-hexadiene polymers were examined by X-ray diffraction. Fiber diagrams were obtained from samples stretched to four times their original lengths. Eight reflections from the poly(trans-1,4-hexadiene) fiber pattern may be interpreted on the0basis of a pseudo-orthorhombic unit cell with a = 20.81 + 0.05 A b =... 

Most joint replacements utilize polymers to some extent. Finger joints usually are replaced with a poly(dimethylsiloxane) Insert and over h00,000 such replacements are made each year (l). More recently a poly(1, -hexadiene) polymer has been tried in this application (l). Many other parts of the hand, such as the bones, have also been replaced by silicone rubber. Other types of joints, such as the hip or the knee, often involve the contact of a metal ball or rider on a plastic surface which is usually made from high density, high molecular weight polyethylene. These metal and plastic parts are usually anchored in the body using a cement of poly(methyl methacrylate) which is polymerized in situ. Full and partial hip prostheses are implanted about... 

Isomer of 2,4-hexadiene Polymer trans, trans cis, trans... 

In special cases aHyl compounds, such as diaHyl [592-42-7] (C H q), (1,5-hexadiene) and diaHyl ether [557-40-4] (C H qO), can form high polymers... 

Ethylene—Propylene Rubber. Ethylene and propjiene copolymerize to produce a wide range of elastomeric and thermoplastic products. Often a third monomer such dicyclopentadiene, hexadiene, or ethylene norbomene is incorporated at 2—12% into the polymer backbone and leads to the designation ethylene—propylene—diene monomer (EPDM) mbber (see Elastomers, synthetic-ethylene-propylene-diene rubber). The third monomer introduces sites of unsaturation that allow vulcanization by conventional sulfur cures. At high levels of third monomer it is possible to achieve cure rates that are equivalent to conventional mbbers such as SBR and PBD. Ethylene—propylene mbber (EPR) requires peroxide vulcanization. 

The terminal double bond is active with respect to polymerisation, whereas the internal unsaturation remains in the resulting terpolymer as a pendent location for sulfur vulcanisation. The polymer is poly(ethylene- (9-prop5iene- (9-l,4-hexadiene) [25038-37-3]. 

Kinetic studies using 1,9-decadiene and 1,5-hexadiene in comparison widi catalyst 14 and catalyst 12 demonstrate an order-of-magnitude difference in their rates of polymerization, widi 14 being the faster of the two.12 Furdier, this study shows diat different products are produced when die two catalysts are reacted widi 1,5-hexadiene. Catalyst 14 generates principally lineal" polymer with the small amount of cyclics normally observed in step condensation chemistry, while 12 produces only small amounts of linear oligomers widi die major product being cyclics such as 1,5-cyclooctadiene.12 Catalyst 12, a late transition metal benzylidene (carbene), has vastly different steric and electronic factors compared to catalyst 14, an early transition metal alkylidene. Since die results were observed after extended reaction time periods and no catalyst quenching or kinetic product isolation was performed, this anomaly is attributed to mechanistic differences between diese two catalysts under identical reaction conditions. 

Similar divergences are found for lithium poly-2,4-hexadiene solution (1 10-3 M in living polymers) for which a sixfold decrease of viscosity upon protonation corresponding to a degree of association of 1.7 was reported 113), whereas only a threefold decrease, i.e. a degree of association of 1.4 was indicated earlier 1,8). The difference between the 1.7 and 1.4 values was tentatively attributed to a slow decomposition of the active ends over a period of two weeks U8) notwithstanding their reported good... 

Polymerization/lsomerization. The polymerization of 5-methyl-1,4-hexadiene (>99% pure) was carried out in n-pentane with a (5-TiCl3/Et2AlCl catalyst at 0°C according to the procedure described previously (14). To assess monomer disappearance and identify isomerization products, samples were withdrawn at specified intervals from the reaction mixture for GLC analysis (14). The final polymer conversion was determined by precipitation in excess methanol. 

Hydrogenation. Hydrogenation of poly(5-methyl-l,4-hexadiene) was carried out with p-toluenesulfonyl hydrazide (20) in refluxing xylene (2il molar ratio of the hydrazide to the polymer repeat unit). 

We have reported earlier (14) that during the polymerization of trans-l,4-hexadiene with a Et3Al/6-TiCl3 catalyst (Al/Ti atomic ratio = 2) at 25°C, a major portion of the consumed monomer was converted to isomerized products, thereby accounting for the relatively low conversion to isotactic 1,2-polymer (Figure 1). The relative amounts of the hexadiene isomerization products were in the following order cis-2-trans-4-hexadiene> trans-2-trans-4-hexadiene> 1,3-hexadiene > 1,5-hexadiene >cis-2-cis-4-hexadiene. 

The 1,2-polymerization of 5-methyl-l,4-hexadiene was further confirmed by ozonolysis of the polymer. The resulting solution, after triphenylphosphine treatment, contained only acetone and no detectable formaldehyde by GLC. As shown below in Scheme 1, the volatile products expected by the above chemical treatment of poly(5-methyl-l,4-hexadiene) are acetone and formaldehyde if the polymer was formed by 1,2- and 4,5-polymerization, respectively. 

Further confirmation of the structure and tacticity of poly/5-methyl-l,4-hexadiene)was obtained from X-ray diffraction and u-NMR data of its hydrogenated polymer (Scheme 2). The hydrogenated polymer sample showed a highly crystalline pattern (Figure 7), with diffraction spots that were well defined. This pattern was identical to that of isotactic poly(5-methyl-l-hexene) as reported in the literature (26) (measured identity period, 6.2 A lit., 6.33 A). 

The polymers of 1,4-hexadienes have unusually wide molecular weight distributions. This is illustrated by the gel permeation chromatogram of the methanol-insoluble fraction of poly(5-methyl-1,4-hexadiene) in tetrahydrofuran (Figure 9). The polymer was obtained in 82% conversion and had an inherent viscosity of 2.1 dl./g. in toluene at 25°C. 

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