Amorphous PDA

Amorphous PDAs. The cast films of 1 were heated between two quartz panes (1 x T, 1 mm thick) at above their melting points, upon which thermal cross polymerization of DA groups took place and orange to red brown tran arent materials were obtained. It seems that simultaneous irradiation with UV light (fi om a medium pressure Hg lanq)) he s the thermal polymerization. Some of the polymers 2 only undergo thermal polymerization in the amorphous state (7P). 

Amorphous PDAs. Yu et al.(2i) prepared poly(hexa-2,4-diynylene terephthalate), which is not photosensitive, but does polymerize by heating at 150 C. A value of 3.2 X 10 ° esu (determined the degenerate four wave mixing technique at 532 nm) has been reported for this material The polymers 3 and 4 (Chart 4) are not photosensitive, but underwent cross-polymerization when heated at 180°C (in the molten state) for 2.5 hours with simultaneous UV irradiation, giving red transparent materials. The x values for these materials were found to be 1.9 - 3.5 x 10 ° esu for polymers 3 and 2.7 -2.9 x 10 esu for polymers 4. Absorption spectra of one of the polymers 4 are shown in Figure 3. The films have an absorption maximum at 400 nm and a trough at 340-350 nm, but absorption tails down towards 700 nm due to their amorphous nature. 

Z-scan experiment was carried out for some amorphous PDAs using wavel gth of 1064 nm A typical exanople is own in Figure 4. Two photon absorption coefficient, P, was found to be 2.7 cm/GW. 

H.P. Klug, L.E. Alexander XRD procedures for polycrystalline and amorphous materials 1974 Wiley Interscience The complete reference for ex situ PDA... 

Trans-PA will now be used to illustrate the kind of data that are actually obtained for a real CP, using the approaches described above. It is chosen as an example for several reasons. A large amount of work has been performed on this material, both experimental and theoretical, and in both the undoped state (considered in this chapter) and the conducting state. It has by far the largest conductivity in the doped state, up to o- 105 S/cm at room temperature [36]. So it has been used as a prototype CP. It is the most crystalline CP (except, of course, the PDAs) as much as 90% of the total mass may be in the crystalline regions [4], so interference by the amorphous CPs may be minimal. Its repeat unit is the simplest of all CPs. Figures 1 and 2 show data for trans-PA. Although it has been helpful in... 

The temperature effect on the polymerization of p-PDA Et is described in the range from —50 to 15 °C in Figs. 4 and 5. p-PDA Et, with a melting point of 100 °C (96 °C by the capillary method) and a crystal transition point of 56 °C (DSC), photopolymerizes quantitatively to a crystalline high polymer at a temperature below ca. 0°C as is obvious in Figs. 4 and 5. However, above ca. 25 °C, a partially cross-linked amorphous polymer is obtained in poor yield. 

In contrast, due to the typical temperature effect on the lattice-controlled process of a four-center photopolymerization, in the case of a few diolefin crystals such as m-PDA Me (m.p. 138 °C), only the amorphous oligomer is produced at all the temperature ranges attempted. In the polymerization of m-PDA Me higher temperatures favor chain growth. This behavior is reasonably well explained by lattice-controlled dimerization followed by random cyclobutane formation yielding the oligomer through the thermal diffusion process (Sect. IV.b.)22. ... 

From the oscillations and Weissenberg photographs, all the polymers have been found to be oriented three-dimensionally, while oligomers of m-PDA Me and CVCC Me are amorphous. 

Solid PDA have not had an extensive reaction chemistry largely due to their van der Watds tight-packed structures which effectively preclude diffusion of potentially reactive liquids and gases (. Recently (17), reactions of poly-DCH (2c) with electrophiles have led to modified materials which are homogeneous on microscopic examination. The reactions are anisotropic. Bromination resulted in a crystal-to-crystal transformation, while chlorination and nitration have led to amorphous solids to date. The scope of such reactivity is clearly of interest. 

IBM-X polyimide is the proprietary polymer used in IBM s flat panel displays. This polyimide is disordered/amorphous, while the BPDA-PDA polyimide film discussed before (Fig. 6.7) has microcrystalline domains. We note that rubbing introduces in both film surfaces the same charge anisotropy, independently of the presence/absence of locally ordered domains. 

PDA-Containing polymer films. The DA-containing polymer films were cast fi om solutions (chloroform for 1 and N-methylpyrrolidone for 2). In the case of 2 the solvent was evaporated at 60°C under reduced pressure. When a heated spin coater was used for 2, highly transparent films could be obtained, but due to their amorphous nature, no crosspolymerization took place on irradiation. In the case of 1, the transparency (crystallinity) of the films depended on the number of meth>iene units (x andy). For exanq)le, when x is 2 and is 5, the film is always conq>letefy opaque, and in other cases reasonably transparent films can be obtained, although the transparency depends on the casting conditions. 

PDA-Polymer Composite Systems. If microcrystals of PDAs can be homogeneous di ersed in an amorphous, transparent polymer, and if the crystal rize is smaller than the wavelength of the applied laser, the materials can probably have applications. An exanq)le of this was previously mentioned (72) and the x values were measured (25) for the system consisting of N,N -dioctylocta-3,5-diynylenediurethane di ersed in poly(N,N-dimethylarninoethyl methacrylate). Up to... 

These systems, which consists of microcrystals of photosensitive DAs in host polymers, are interesting materials. Very little has yet been studied on such systems. DA microcrystals dispersed in an amorphous polymer can be converted to PDA microcrystals by irradiation, and when the crystal size is small conpared with the wavelength of the laser, the materials may be usefiil for NLO applications. Systems with new combinations of DAs and host polymers are expected to appear in the fixture. 

Variation of the side-groups determines the morphology of PDAs, with coffin-shaped crystals (PTS) and fibres (DCH) as the two extreme crystal forms. More complex side-groups can also give PDAs that can form LB films or be cast as amorphous films. 

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