Polyimides side chains

Fig. 2.6 The rubbing effect on the polyimide side chains is schematically represented. The rubbing direction corresponds to the x-direction. Reproduction by permission from [38].

Chyi-Ming Leu Y-TC, Wei K-H (2003) Polyimide-side-chain tethered polyhedral oligomeric silsesquioxane nanocomposites for low-dielectric film applications. Chem Mater 15(19) 3721-3727... 

Thermal stability. The presence of side chains, cross-linking, and benzene rings in the polymer s "backbone increase the melting temperatures. For example, a spectrum of polymers with increasing melting temperatures would be polyethylene, polypropylene, polystyrene, nylon, and polyimide. 

There remains one very curious feature of the polyimide films discussed above. Some of the side chains removed contain in excess of 16 carbon atoms and are therefore relatively massive. Neverthless, they appear to diffuse through a tightly packed polymer multilayer consisting of up to 200 monolayers. Undoubtedly this process takes place, but it is hard to understand the mechanism. 

Spontaneous resolved two chiral domains are formed in equal probability. In other words, enantiomeric excess (ee) is zero. We now ask whether ee can be controlled or not. The answer is yes. Several methods used in bent-shaped mesogenic phases will be introduced. The direct method is of course an addition of chiral dopant. Actually this has been shown to be a viable method [6, 61]. Use of chiral surface is also effective [62], By using polyimide with chiral side chains at both substrate surfaces, imbalance of two chiral domains (10% ee) has been achieved. Another method using macroscopic helical structure was demonstrated by Jakli et al. [63]. They used a nonchiral polymer network, which was formed in the N phase. After the polymerization, N compounds were washed out, then bent-core mesogens were introduced. Because of the polymer helical fibers, bent-core mesogen shows a chiral domain. 

Although rigid-rod poly(p-phenyleneterephthalamide) analogues having alkyl side chains did not contain cyclic polymers, the polycondensation of silylated m-phenylenediamine and aliphatic dicarboxyhc acid chloride afforded cyclic polyamides predominantly (Scheme 49) [187]. Furthermore, cyclic polymers were also produced in polycondensations for polyesters, poly(ether ketone)s, polyimides, and polyurethanes [183]. These examples are the products in polycondensation of AB monomers or in A2 + B2 polycondensations, but cyclization of oligomer and polymer was also confirmed in polycondensation of AB2 monomers [ 188-195] and in A2 + B3 [ 196-202] and A2 + B4 polycondensations [203-206], which afford hyperbranched polymers. 

Kawakami Y, Yu SP, Abe T (1992) Synthesis and gas permeability of aromatic polyamide and polyimide having oligodimethylsiloxane in main chain or in side chain. Polym J (Tokyo) 24( 10) 1129... 

Polyimide esters, (IV), prepared Buchecker [3], containing a photoactive side chain were used as orientation layers for liquid crystals and in the construction of both unstructured and structured optical elements. 

To study the polymer structural effects on PAP, including the size of the chromophore and the mode of connection of the chromophore to the main chain, SHG-PAP studies have been performed both on a true side hain polyimide system in which the chromophore is attached to the polymer backbone via flexible tedier (PI-3a in Figure 8.4 Tg = 228 C), and on donor-embedded polyimide syst s (PI-1 and PI-2 in Figure 8.4 Tg = 350 and 252°C, r pectively), in which the azo chromophore is incorporated into the polymer backbone through the donor substituent without any flexible connector or tether. Details of SHG-PAP can be found in reference 14. In both the side-chain and the donor-embedded polyimides, polar order can be generated by thermal poling... 

In PI-3a, PAP produces a relatively small polar order as opposed to the efficient poling achieved by PAP in true side-chain NLO polymers, such as PMMA or polyimides with Tgs in the 120-265°C range, which are flexibly tethered by DR 1-type chromophores. The molecular size of the diaryiiSne azo chromophore of PI-3a is substantially larger than that of the DRl-type mokcules in the polymers studied previously (see PI-3b in Figure 8.4), a feature that requires more free volume for chromophore movement thereby decreasing... 

NLO chromophore-functionalized polyimides have attracted a lot of interest thanks to their high T., and excellent temporal stability. Verbiest et al. [72,73] and Miller et al. [74] reported several highly stable aromatic polyimides (Fig. 4.3), including the synthesis of the PI-1 polymer, which is the first reported example of a processable donor-embedded side-chain polyimide having a very high Tg of 350°C, and a chemical stability at temperatures as high as 350°C. Poled samples of polymer PI-1 have an EO coefficient of 4-7 pm/V (at 1.3 im) and a much higher orientational... 

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