(54) EXTRUSION PROCESS AND PRODUCT 5,677.404 A * 10/1997 Blair .......................... 526,247 5,703,185 A * 12/1997 Blair .......................... 526,247 (75) Inventors: Patrick Anthony DeFeo, West Grove, 6,103,844 A 8, 2000 Brothers PA (US); Glenn W. Heffner, 6,489,420 B1* 12/2002 Duchesne et al. ........... 526,255 Wilmington, DE (US); Niall D. McKee, 6,703,464 B2 * 3/2004 Kono et al. ... 526.247 Newark, DE (US); Sundar Kilnagar 7,105,619 B2 * 9/2006 Kono et al. ................. 526,247 Venkataraman, Vienna, WV (US)

The poly(3-alkylthiophenes) are a class of electrically conducting polymers which are of particular scientific and commercial interest due to their solubility and meltabillty. A series of poly(3-octylthiophene) (P3OT) fractions having molecular weights in the range M(w) = 30,000 to 400,000 were generated by preparative gel permeation chromatography (GPC). Although the polymer remained weakly aggregated when dissolved in pure THF, the addition of an organic salt (1 wt.% tetrabutylammonium p-toluenesulfonate) resulted in complete molecular dissolution. We were thus able to completely and consistently describe the polymer's single-chain properties using three dilute solution characterization methods: viscometry, GPC, and integrated light scattering. The molecular weight dependence of the intrinsic viscosity and the radius-of-gyration were established, and were characteristic of solutions near the theta condition, indicating poor solvent quality. Calculation of the persistence length from our data revealed that the polymer backbone is only 2 to 3 times more rigid than common flexible polymers, despite its conjugated ring structure.

The poly(3-alkythiophenes) are electrically conducting polymers which are of particular interest due to their melt-processibility. We have studied the melt properties of poly(3-octylthiophene) (P3OT) by dynamic theological measurements at temperatures between 180 and 250 degrees C. The samples investigated have molecular weights in the range M(w) = 30,000 to 400,000 and have been carefully characterized by dilute solution techniques. Residual iron chloride, a reagent used in the polymerization of these materials, was found to cause a high degree of crosslinking in the polymer melt. By contrast, samples which had been carefully purified demonstrated a negligible rate of crosslinking in a nitrogen atmosphere; however, the presence of air and higher temperatures were found to increase the rate of crosslinking substantially. The temperature dependence of the viscoelastic properties was characterized according to the principles of time-temperature superposition, and the influence of molecular weight was also evaluated. Overall, the theological behavior was determined to be similar to that commonly observed for linear flexible polymers, which is in agreement with the results of our solution characterization of these materials.

Recent theories have related the molecular-weight dependence of the conductivity of a conjugated polymer to the relative importance of interchain and intrachain charge transport processes. This prompted an experimental search for this effect using a series of fractionated poly(3-octylthiophenes). No significant molecular-weight dependence was found over the range 30 000⩽Mw⩽400 000, indicating that interchain transport does not limit the macroscopic conductivity of these samples. However, even small differences in the degree of crystallinity among the polymer samples were determined to have a profound effect on the conductivity.

A method for calculating the effect of molecular weight and orientation on the conductivity of polymers has been developed. The conductivity in the isotropic state is found to depend on the charge carrier density, the polymers persistence length, the mean lifetime of the charge on a polymer, tau(c), and the time for a charge to diffuse the length of a single polymer, tau(i). We describe a method for estimating these time constants individually by a combination of ac and dc measurements. Our prediction for the enhancement of conductivity when the polymer is stretched is in good agreement with existing experimental data. We conclude with a discussion of how the macroscopic conductivity is affected by chain stiffness, by molecular weight distribution, and by defects that can block charge diffusion along a polymer chain.

The solution processing of doped conducting polymers is a fast and simple method by which conducting articles may be formed, although aggregation of the polymer upon doping may inhibit processing. Solutions of poly(3-octylthiophene) (P3OT) doped with FeCl3.6H2O and NOPF6 were found to exhibit varying degrees of aggregation dependent upon the polymer concentration and doping level. However, we have found that coherent films with conductivities up to 1 S/cm may be cast directly from the doped solutions. The effect of doping level and other factors on the physical state of the doped solutions is discussed and related to the conductivity achieved in the solution-cast films.

Rheological and rheooptical properties of poly(di-n-hexylsilane) were investigated in oscillatory and steady-shearing experiments. The samples consisted of concentrated solutions up to 6 wt% of a very high molecular weight polymer (M(w) = 4.6 x 10(6)) dissolved in decalin. Experiments showed that the flow-induced shear and normal stresses were linearly related to the birefringence and that the constant of proportionality-the stress-optical coefficient-was larger than that of typical polymers. The enhanced stress-optical coefficient is a result of both the intrinsic rigidity of the polysilane chain and the higher polarizability of the sigma-conjugated electrons. This result is similar to that found recently for a pi-conjugated polymer. Additional results on the concentration dependence of various rheological properties are reported.

A complete molecular characterization of poly(3-hexylthiophene) (P3HT) in dilute solution was conducted by using static and dynamic light scattering, gel permeation chromatography, and viscosity measurements. The dependence of the intrinsic viscosity and the radius of gyration upon molecular weight was determined in THF for 40 000 less-than-or-equal-to M(w) less-than-or-equal-to 220 000 and found to be characteristic of a moderately good solvent. Similar solution characteristics were observed in chloroform. A comparison of the macromolecular dimensions determined by different techniques was made to demonstrate the consistency of the data, which indicate that the P3HT macromolecules exist as isolated flexible-coil chains in dilute THF solution with a persistence length of 2.4 +/- 0.3 nm.