Self-Assembling Functionalizable Polydiacetylenes and their Optical Properties
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"**Physicsand Applied ABSTRACT
The alkoxycarbonylmethylurethanes of 9-(N-methyl-N-phenylamino)-5,7-nonadiyn-l-ol were synthesized and polymerized by 60 Co gamma radiation. The resulting polydiacetylenes (PDA) are soluble, processable, and self-assemble into an acentric array. These PDAs are susceptible to postpolymerization functionalization via its dialkylaniline and ester groups, and hence comprise the most versatile PDA system for systematic chemical modification reported to date. Dialkylaniline functionalization via tetracyanoethylene and diazonium salt coupling led, respectively, to materials with interesting second order nonlinear optical properties and that exhibit directly photofabricated regular surface relief gratings. The latter materials provide the first example of a rigid rod polymer (lacking a detectable glass transition) to exhibit such phenomena. Moreover, these PDAs can form self-assembled multilayer structure in water by ester hydrolysis.
INTRODUCTION We have recently reported soluble, processable, and the most versatile PDA system
reported to date, in terms of chemical richness and diverse optical properties [1]. Over at least the last decade, there has been considerable interest in the introduction of specific side groups into polydiacetylenes to control properties such as polymer chemical reactivity [2,3], electronic structure [2-7], spectroscopy [8-10], second order nonlinear optical (NLO) properties [11-15], and chromic phenomena [16,17]. In recent reports from our laboratories [18-21], the synthesis, acentric self-assembly, and second order properties of the PDA of the n-butoxycarbonylmethylurethane (BCMU) of 1-(5-pyrimidyl)-1,3-octadiyn-8-ol (BPOD) point to a design paradigm that merits elaboration. In particular, we note three design features: 1) a conjugated backbone; 2) one side group as a chromophore; 3) the other side group with both aliphatic and hydrogen-bonded urethane groups to promote solubility and processability. The polymer was found to spontaneously self-assemble into an acentric order with significant second order optical nonlinearity. We now report the synthesis of the alkoxy carbonyl-methyl urethanes of 9-(N-methyl-N-phenylamino)-5,7-nonadiyn-l-ol (la, b, c) and their polymerization. We find that the polymers are soluble and processable, and that the benzenoid ring group is susceptible to many of the substitution reactions expected for aromatic amines making it a more versatile system for chemical modification than the previously investigated systems. We further describe novel self-assembling and linear and nonlinear optical properties of the modified polymer. These polymers, in addition to possessing the unusual assembly properties of PDA-BPOD, present some unique processing features [7]. The azobenzene functionalized PDA from la, for example, was photofabricated 677
Mat. Res. Soc. Symp. Proc. Vol. 488 0 1998 Materials Research Society
to produce regular surface relief gratings. Also, lb can be hydrolyzed [22] after polymerization and give water solubility to fabric
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