Cross-linking nonlinear optics, polymers

Highly efficient and stable nonlinear optical polymers via chemical cross-linking under electric field, 7. Appl. Phys. 56 2610 (1990). 

Note that the sol-gel materials based on polysiloxane have been known for their durability and good optical quality. If functionalized with azobenzene moieties, they exhibit nonlinear optical properties and photoinduced anisotropy. There are a few examples of SRG inscribed onto materials (Kim et al., 2006b Chaput et al., 2000 Frey et al., 2000 Darracq et al., 1998). The gratings could be inscribed only in freshly prepared films, whereas in aged films, the cross-linking of the polymer completely hindered SRG formation. 

While IPNs can be and have been made extremely tough and impact resistant, many of the proposed applications involve such diverse fields and sound and vibration damping, biomedical materials, and nonlinear optics. This is because the presence of cross-links in both polymers reduces creep and flow, allowing relatively stable materials with a wide range of moduli to be prepared. Thus, those materials with leathery mechanical behavior, combinations of elastomers and plastics, are especially interesting to scientists, inventors, and engineers. 

Polymers and supermolecules modified using electron push-pull chro-mophores are also of particular interest for nonlinear optics (NLO) [10-15]. NLO material has attracted much interest over the past 20 years and has been widely applied in various field (telecommunications, optical data storage, information processing, microfabrication, etc.). Chemists have developed ways to introduce NLO chromophores into many type of polymers, such as Hnear polymers, cross-linked polymers, and branched polymers, and have demonstrated their performance in NLO appHcations. 

The hb-PAEs of hb-P13 and hb-P15 contain NLO-active azo-functionalities, which are soluble, film-forming, and morphologically stable (Tg > 180 °C). Their poled films exhibited high SHG coefficients ( 33 up to 177pm/V), thanks to the chromophore-separation and site-isolation effects of the hyperbranched structures of the polymers in the three-dimensional space (Table 5) [28]. The optical nonlinearities of the poled films of the polymers are thermally stable with no drop in d33 observable when heated to 152 °C (Fig. 8), due to the facile cross-linking of the multiple acetylenic triple bonds in the hb-PAEs at moderate temperatures (e.g., 88 °C). 

The nonlinear absorption of Ptn acetylide chromophores has also continued to retain the interest of many researchers. Malmstrom and coworkers have recently investigated Pt-acetylide chromophores blended with solid-state polymer matrices [94], An example of such a complex is 4.7. They found that the photoluminescence properties of the blends agreed well with that of dilute THF solutions containing the Pt-acetylides. Optical power limiting experiments showed that the clamping levels for dyes nonbonded to the polymer host were about half that for dyes in the highly cross-linked solids at similar concentrations. 

This chapter concentrates on the design of efficient dipolar NLO chromophores and the different approaches for their incorporation in non-centrosymmetric materials, including guest-host polymer systems, chromophore-functionalized polymers (side-chain and main-chain), cross-linked chromophore-macromolecule matrices, dendrimers, and intrinsically acentric self-assembled chromophoric superlattices. The different architectures will be compared together with the requirements (e.g., large EO coefficient, low optical absorption, high stability, and processability) for their incorporation into practical EO devices. First, a brief introduction to nonlinear optics is presented. 

E. M., and Kitipichai, P., Processable cross-linked polymers for nonlinear optical applications. Mater. Res. Soc. Symp. Proc., 328, 637-642 (1994). 

Because of the versatility of the polyurethane system it is possible to introduce comonomers which can affect the physical properties of the derived polymers. For example, photo cross-linkable polyurethanes are formulated using 2,5-dimethoxy-2,4 -diisocyanato stilbene as a monomer (76). Comonomers, having an azoaromatic chromophore, are used in optical bleaching applications (77), or in the formation of photorefractive polymers (78). The latter random poljnners have second-order nonlinear optical (NLO) properties. Linear poljnners are also obtained from HDI/PTMG and diacetylenic diols. These polymers can be cross-linked through the acetylenic linkages producing a network polymer with properties similar to poly(diacetylenes) (79). 

Trollsas M, Orrenius C, Sahlen F, Gedde UW, Norin T, Hult A, Hermann D, Rudquist P, Komitov L, Lagerwall ST, Lindstrom J (1996) Preparation of a novel cross-linked polymer for second-order nonlinear optics. J Am Chem Soc 118(36) 8542-8548. doi 10.1021/ ja961309e... 

C). The nonlinear optical effects were studied at 633 nm at room temperature. In another example of substitution reactions of [NPCl2] the sodium salt of 7-(2-hydroxyethoxy)-4-methylcoumarin was used to incorporate photosensitive coumarin groups on the main phosphazene chain to obtain the cross-linkable polymer (190) (average ca. 10, Tg = 67 °C) that is stable up to 280 °C and that, under XJV irradiation, undergoes a [2 -l- 2] cycloaddition to form insoluble cross-linked curable films. The related poly[(bis(3-acetylcoumarin-o-aminoben-zoylhydrazone)phosphazene] has also been reported. ... 

The preparation of nonlinear optical (NLO) PCs via macro-cydic prepolymers has the advantage that the low viscosity oligomer mixtures make reactive processing possible. The conversion of macrocydes to polymer occurs with nonvolatile by-produds or very litde change in volume and can be done simultaneously with electric field poling and, if desired, chemical cross-linking. Kulig et prepared such PCs based on a... 

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