Poly-l,6-heptadiyne

The polymers which have stimulated the greatest interest are the polymers of acetylene, thiophene, pyrrole and aniline, poly-p-phenylene, polyphenylvinylene and poly-l,6-heptadiyne. Of these materials polypyrrole has been available from BASF under the trade name Lutamer P160 since 1988. 

Pochan et al. 585) have studied poly(l,6-heptadiyne), a polyacetylene analogue, which forms dense continuous films. They find oxygen doping follwed by degradation in a manner similar to polyacetylene, except that the rate of degradation is much larger. 

The physical properties of other poly(l,6-heptadiynes) prepared by classic catalytic systems have been summarized elsewhere [103] and need to be treated carefully in view of the poor definitions of these materials. 

The utility of classical antioxidants such as hindered amines, phenols, and nitrones for the stabilization of pristine polyacetylene (29), poly(methyl acetylene) (30), and poly(l,6-heptadiyne) (31) has been examined. Poly(methyl acetylene), although dopable to only low conductivities (10" S/cm), has similar oxidative behavior to polyacetylene and serves as a good model for other polyenes. In general, the improvement in stability of poly(methyl acetylene) was limited, but combinations of hindered phenols and hydroperoxide scavengers resulted in a factor of 5 decrease in the oxidation rate (30) as monitored by the appearance of IR absorption bands attributable to carbonyl groups. These degradation rates are still too high for the use of these polyenes in an unprotected environment. The compatibility of such stabilizers with the dopants commonly used for polyacetylene was not studied. 

A few polyacetylen s with liquid crystalline side groups have been reported. For instance, a polymer (Mw 16 x 10" ) is obtained in high yield with WCl6 from cholesteryl 4-pentynoate. The polymer shows a transition to a thermotropic liquid-crystalline phase at 89 °C and a transition to the isotropic phase at 189 °C. Other examples are poly(l,6-heptadiynes) with mesogenic side groups. Studies on their applications are under way. 

Poly(l,6-heptadiyne)s obtained were dark red or black, which indicates a high order of conjugation in the polymer. Even though a head-to-tail internal propagation would be expected, there are three possible cyclic recurring units (1—3) and structure 4... 

The attempted polymerization of 1,6-heptadiyne with NbCls and TaCls yielded a mixture of cyclotri-mer (15%) and polymer (25% for NbCls, 20% for TaCls), having a relatively low conversion (40% for NbCls, 35% for TaCls). In most cases, the resulting poly(l,6-heptadiyne)s, besides a low molecular weight of oligomers, were insoluble in any organic solvents... 

A differential scanning calorimetry (DSC) thermogram of poly(l,6-heptadiyne) showed two irreversible... 

Figure 3. IR spectra for oxidation stability to air at room temperature of poly(diphenyldipropargylmethane poly(l, 6-heptadiyne).

Figure 4. Differential scanning calorimetric (DSC) traces for poly(l,6-heptadiyne).

Table 14. Comparison of the Exothermic Peak Temperature of Poly(l,6-heptadiyne) and Its Homologues...

The isomerization temperature of linear polyacetylene is reported as 155 The higher temperature process is assumed to be due to the exo to endo rearrangement and/or the thermal decomposition reaction. Poly(l,6-heptadiyne) homologues also showed similar two exothermic peaks in the DSC thermogram, as shown in Table 14. 

Figure 5. Electrical conductivity of poly(l,6-heptadiyne) films as a function of time after exposure to iodine at 25 °C in a vacuum.

The typical electrical conductivity of a poly(DP-DPM) pellet, a substituted poly(l,6-heptadiyne), is displayed as a function of exposing time in Figure... 

In 5 h, the polymer pellet exhibited a maximum in the conductivity and then began to decrease slowly. When film-type polymer was exposed to iodine vapor, it changed from dark violet to blue-black and the electrical conductivity increased from 10 ° Q cm to 10 Q cm . The maximum electrical conductivity of iodine-doped poly(DPDPM) is smaller than that of iodine-doped poly(l,6-heptadiyne), which is reported to have a value of 10 —10 2 Q cm . ° The activation energy for conduction was derived from the temperature, T, dependence of conductivity. For the undoped poly(DPDPM), the activation energies have... 

Table 15. Linear and Nonlinear Optical Properties for Poly(l,6-heptadiyne)s...

Figure 10. Intensity of phase conjugated beam (/J vs intensity of incident beam (Ip) of DFWM experiment on a reference and 0.05 M of poly(l, 6-heptadiyne) (see poly-86 in Scheme 22) in THF.

The intensity of the DFWM signal for the poly(l,6-heptadiyne)s increased linearly with intensity of the incident beam, as shown in Figure 10. From the direct comparison between the intercepts of the V axis of the polymers and the carbon disulfide reference. the values of the polymers were obtained. And also, as the concentration of the polymer solution was increased, the values of the polymers were increased (Figure 11). The third-order nonlinear optical properties were enhanced with an increase in the bulk of the substituents at the 4-position, which is in accord with the bathochromic shift of Amax in the UV—vis spectra. From these results, it was concluded that the incorporation of bulky substituents into the 4-position of 1,6-heptadiynes enforces the TT-conjugated polyene into the more planar conformation. resulting in a red shift and the increment of the values of the polymers. Recently, Schrock... 

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