Nonlinear synthetic polymers

Advancements in synthetic polymer chemistry have allowed a remarkable range of new nonlinear block copolymer architectures to be synthesized. The result is a wide variety of new materials with the capacity to form self-assembled phases in bulk and in solution. At present our synthetic capabilities exceed our understanding, both theoretical and experimental, of the properties of such macro-molecular systems. We anticipate that a better understanding of structure-property relationships for these materials will lead to impressive new polymers with applications such as structural plastics, elastomers, membranes, controlled release agents, compatibilizers, and surface active agents. From the synthetic standpoint it seems likely that recent advances in living free radical polymerization will make the syntheses of many non-linear block copolymers more commercially appealing. 

Since not all RNA molecules replicate equally well, faster mutants gradually take over. At each mutation, the front propagates faster. Evolution can be directly observed in a test tube. Propagating polymerization fronts of synthetic polymers may be useful for making new materials, and they are interesting because of the rich array of nonlinear phenomena they show, with pulsations, convection, and spinning fronts. Finally, we will consider photopolymerization systems that exhibit spatial pattern formation on the micron scale, which can be used to control the macroscopic properties. 

RECENT SYNTHETIC DEVELOPMENTS IN MAINCHAIN CHROMOPHORIC NONLINEAR OPTICAL POLYMERS... 

Dai DR, Hubbard MA, Park J, Marks TJ, Wang J, Wong GK. Rational design and construction of polymers with large second-order optical nonlinearities. Synthetic strategies for enhanced chromophore number densities and frequency doubling temporal stabilities. Mol Cryst Liq Cryst 1990 189 93-106. 

The architecture of macromolecules is another important synthetic variable. New materials with controlled branching sequences or stereoregularity provide tremendous opportunity for development. New polymerization catalysts and initiators for controlled free-radical polymerization are driving many new materials design, synthesis, and production capabilities. Combined with state-of-the-art characterization by probe microscopy, radiation scattering, and spectroscopy, the field of polymer science is poised for explosive development of novel and important materials. New classes of nonlinear structured polymeric materials have been invented, such as dendrimers. These structures have regularly spaced branch points beginning from a central point—like branches from a tree trunk. New struc-... 

The driving force in polymer synthesis is the search for new polymers with improved properties to replace other materials of construction. Polymers are lightweight and can be processed easily and economically into a wide range of shapes and forms. The major synthetic efforts at present are aimed at polymers with high temperature, liquid crystal, conducting, and nonlinear optical properties [Maier et al., 2001 Sillion, 1999]. There is an interrelationship between these efforts as will become apparent. 

Synthetic strategy has been developed that permits the efficient preparation of organometallic polymers which have structural characteristics necessary for nonlinear optical behavior. Complex t 5-C5H4CH20H - i 5-C5H4CH=C(CN)C02Et Fe (4) was prepared and homopolymerized through a thermally induced transesterification-polycondensation reaction. 

However, the particular synthetic requirements in the preparation of conjugated polymers have thus far severely limited the number of similarly hierarchically structured examples. Pu et al. reported different types of conjugated polymers with fixed main-chain chirality containing binaphthyl units in their backbone which exhibited, for example, nonlinear optical activity or were used as enantioselective fluorescent sensors [42—46]. Some chirally substituted poly(thiophene)s were observed to form helical superstructures in solution [47-51], Okamoto and coworkers reported excess helicity in nonchiral, functional poly(phenyl acetylenejs upon supramolecular interactions with chiral additives, and they were able to induce a switch between unordered forms as well as helical forms with opposite helical senses [37, 52, 53]. 

---