Polyquinolines: Multifunctional Polymers for Electro-Optic and Light-Emitting Applications
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Mat. Res. Soc. Symp. Proc. Vol. 558 ©2000 Materials Research Society
Friedlinder condensation and an ether-forming reaction. In this paper, the excellent thermal, electrochemical and EL results obtained from these polymers will also be reported. RESULTS AND DISCUSSION Synthesis and Characterization of Polyquinolines for E-O Application * Synthesis of NLO Polyquinolines. Previously, there were two principal routes for attaching NLO chromomphores onto the polymer backbones to obtain NLO side-chain polyquinolines. One approach involved the synthesis of polyquinoline precursor polymers, and then tricyanovinylation of these polyquinolines in solution
F3
mF
n
3
OH
OH
1 m=0.625 n=0.375
PPh3 / DEAD
R-H
THF/R. T.
2a-g
3a-g m=0.625 n=0.375 R:
NN
N N
ON
ON
e-
f "NN -N(-.
CN N
N
N
NN
N
N
Scheme 1. Synthesis of NLO Side-Chain Aromatic Polyquinolines 470
to activate the side-chain NLO chromophores[8a]. However, this approach was limited to the synthesis of side-chain NLO polyquinolines with only tricyanovinyl-containing chromophores. The other approach to NLO side-chain polyquinolines involved the synthesis of a NLO chromophore-containing bis(ketomethylene) monomer and a polymerization between the bis(ketomethylene) monomer and a bis(o-amino ketone) monomer[8b]. Many chromophores, (DCM) type including 4-(dicyanomethylene)-2-methyl-6-(p-(dimethylamino)styryl)-4H-pyran chromophores, could not survive the relatively harsh chemical conditions of the acid-catalyzed polymer-forming process. Accordingly, the general applicability of this methodology was severely limited. Our present strategy for the synthesis of NLO side-chain aromatic polyquinolines was to covalently bond the chromophore onto the pendent phenyl moieties of a preformed polyquinoline via a mild Mitsunobu reaction[ 11], by which the harsh acidic polymerization processes previously employed were avoided so as to preserve the NLO chromophores (Scheme 1). This methodology allowed us to synthesize NLO side-chain aromatic polyquinolines with a broad variety of polymer backbones and flexibility in selecting NLO chromophores. In addition, by locating the hydroxyl group on the pendent phenyl side group instead of on the polyquinoline backbone, a higher efficiency of chromophore attachment could be achieved. It is also noteworthy that a phenyl spacer between the polymer backbone and the NLO chromophores facilitated the process for high electric field poling of the NLO polyquinolines compared to polyquinolines with chromophores directly attached on the polymer backbone. The high efficiency of chromophore attachment allowed us to adjust the loading level of the side-chain chomophores and fine-tune the electro-optic and the thermal properties of the final NLO polymers. The chromophore loading levels of these polyquinolines were controlled to be in the range of 20 wt% to 30 wt% in order to prevent potential chromophore aggregation which may lead to the increase of optical loss in the polymers due to light scattering. Moreover, the very mild conditions of t
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