Side-chain, nonlinear optical polymers

Figure 2. Schematic structure of side chain liquid crystal polymers with dichroic dyes (imparting nonlinear optical properties) and mesogenic side groups.

Part of the rationale for investigating liquid crystal polyphosphazenes is for nonlinear optical (NLO) applications. In general, for NLO activity, polymers must either contain noncentrosymmetric side chains (eg., side-chain liquid crystal polymers) or highly delocalized (conjugated) backbones (16). Alternatively, polymers can be doped with low molar mass compounds to obtain NLO activity. 

Side-chain liquid-crystalline polymers with controlled molecular weights have been obtained by the polymerization of FM-25 with 1-22 (X = Br)/CuBr/ L-3 in the bulk at 100 °C, to examine the thermotropic transition as a function of the MWD.324 Second-order nonlinear optical materials with branched structure were prepared by the copper-catalyzed radical polymerization of FM-26 and FM-27 using hyperbranched poly[4-(chloromethyl)styrene] as a multifunctional initiator.325... 

As discussed earlier, while the scale of the fillers is substantially different, nanocomposite materials concepts and technology are very similar to those of conventional composite materials. This is clearly demonstrated in the case of new thermosets for nonlinear optical (NLO) applications, " " where nanocomposite of liquid crystalline thermosets, IPNs, and simple filled thermosets are evaluated. Tripathy et al. discussed four different ways to prepare nonlinear optical polymers. (1) The polymer matrix is doped with NLO moieties in a guest/host system (2) In side-chain polymer systems, NLO polymers with active moieties are covalently bonded as pendant groups (3) In the main chain polymer, the chromo-phores are incorporated as parts of the main polymer backbone to enhance the temporal stability of the NLO properties and (4) Stability of the optical noninearity in sol-gel-based thermosets is related to... 

Side chain liquid crystalline and nonlinear optical polymers (e.g. 37 and 38), which are conventionally produced by multi-step processes, are also available very easily via active ester synthesis. A unique feature of the active ester method for this purpose is that a single activated polymer intermediate can be used for the synthesis of any number of macromolecular structures, all by a simple single-step reaction pathway. Synthesis of such polymers by copolymerization of the... 

Chapter V of this Handbook is entirely devoted to the potential applications of the side chain liquid crystal polymers, but it is interesting to mention here the main areas where FLCPs could play a role. As far as we know, the following applications can be considered for SmC LCPs nonlinear optics, pyroelectric detectors, and display devices. 

Kimura, et al. synthesized polymers bearing oligo-aromatic esters as side chains to form second-order nonlinear optical active polymers on the basis of architecture. The cut-off wavelength ( co) of these polymers is shorter than the visible region, i.e., kco ca. 330-370 nm, which are much shorter than the typical second order nonlinear optics polymer containing chromophores like azobenzene. These polymer films exhibit good transparency in the visible region. The second-order nonlinear optical coefficient, is 2.2-9.S pm.V... 

Liquid crystals and main-chain/side-chain liquid-crystalline polymers have gained scientific and technical importance due to their applications as display materials, their exceptional mechanical and thermal properties, and their prospective applications for optical information storage and nonlinear optics, respectively [1-13],... 

Novel Side Chain Liquid Crystalline Polymers for Quadratic Nonlinear Optics... 

P. N. Prasael and D. J. Williams, Introduction to Nonlinear Optical Effects in Molecules and Polymers (John Wiley Sons, Inc., New York 1991) see also G. R. Mohlman and C. P. J. M. van der Vorst, in Side Chain Liquid Crystal Polymers (Blackie and Son, London, 1989), chapter 12. 

These materials are compatible with semiconductor technology. Low-oost thin films or waveguiding structures of polymers can be fabricated easily by fomiliar spincoating processes which meet the requirements of integrated nonlinear optics. Polymers and. in particular, side-chain polymers, liquid crystalline or amorphous ones, offer a high potential for molecular engioeering. 

Liquid crystal polymers are also used in electrooptic displays. Side-chain polymers are quite suitable for this purpose, but usually involve much larger elastic and viscous constants, which slow the response of the device (33). The chiral smectic C phase is perhaps best suited for a polymer field effect device. The abiHty to attach dichroic or fluorescent dyes as a proportion of the side groups opens the door to appHcations not easily achieved with low molecular weight Hquid crystals. Polymers with smectic phases have also been used to create laser writable devices (30). The laser can address areas a few micrometers wide, changing a clear state to a strong scattering state or vice versa. Future uses of Hquid crystal polymers may include data storage devices. Polymers with nonlinear optical properties may also become important for device appHcations. 

Optically active polymers are potentially very useful in areas such as asymmetric catalysis, nonlinear optics, polarized photo and electroluminescence, and enantioselective separation and sensing.26 Transition metal coupling polymerization has also been applied to the synthesis of these polymers.27 For example, from the Ni(II)-catalyzed polymerization, a regioregular head-to-tail polymer 32 was obtained (Scheme 9.17).28 This polymer is optically active because of the optically active chiral side chains. 

Van der Vorst CPJM, Picken SJ (1996) Electric field poling of nonlinear optical side chain polymers. In Shibaev VP (ed) Polym Electroopt photoopt Act Media. Springer, Berlin Heidelberg New York, p 173... 

---