NLO polymers

Several polymeric confignrations have been examined for the production of NLO polymers, but the two basic approaches are ... 

The first generation NLO polymers were side chain polymers, usually made by copolymerisation of a monomer bearing the chromophore bridged by a flexible spacer group with a co-monomer, commonly methacrylates. This is a flexible process allowing a wide range of co-polymers to be made. A typical example of this type of polymer is the methyl methacrylate azo dye co-polymer (5.9). 

Another successful approach involves the cross-linking of the side chain NLO polymer, after poling, at multiple sites by a different type of polymerisation mechanism. Subsequent curing and hardening produces a lattice that locks in the poled dipole. . One such process is outlined in Figure 5.32. 

Novel thermoset nonlinear optical (NLO) polymers 283 and 284 are synthesized through the hydrosilylation of NLO chromophores such as 281 and 282 and dicyclopentadiene... 

Experiments arc underway to fabricate a waveguide phase modulator-using the thermoset poled NLO polymers described in Section IV. So far, metal bottom electrode / polymer buffer layer / NLO polymer layer /... 

Figure 6. Schematic of a cross linked NLO polymer. The NLO chromophores are represented by the D-tc-A boxes and the arrow represents the charge-transfer axis.

Figure 7. Schematic of thermal processing and poling procedure for a thermoset NLO polymer.

Compound 4 was also attached to chloromethylated polystyrene through the hydroxyl moiety to afford a pendant-type ferrocenyl NLO polymer. 

I would like to thank Professor Larry R. Dalton for many helpful discussions on the problems of NLO polymer design, and Dr. David W. Polis for collaborating on copolymer design and synthesis. 

NLO polymers are designed by incorporating nonlinear chromophores into a polymer matrix. The simplest approach is the use of polymer solutions, so-called guest-host systems, in which the nonlinear chromophore is dissolved in a compatible polymer matrix. Unfortunately, the solubility of guest molecules in a polymer matrix is usually low, which limits the magnitude of the NLO response. This problem is solved by attaching the chromophores covalently to the polymer backbone (side chain polymers) or by incorporating them into the backbone of the polymer (main chain polymers). 

Charge transfer NLO polymers offer the promise of truly unique properties properties that mimic the performance of photorefractive materials, but on ultrafast (picosecond) time scales. Such materials would enable ultrafast photonic applications (e.g. ultrafast optical switching and ultrafast image processing) that are impossible today with any known class of materials. 

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... 

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... 

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