A Synthetic Approach for the Incorporation of Highly Efficient, Thermally Stable Second Order Nonlinear Optical Chromoph
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~N ~
~
N
CN
S
1
-
N
ON
Synthetic Aspects The methacrylate derivative of 1, (6) was synthesized as shown in Scheme 1. The starting compounds used in this sequence (i.e., aldehyde 2 and phosphonate 3) were prepared by literature methods. 2a-c, 4 b The ylide of phosphonate 3 was generated with K'BuO in TIF
517 Mat. Res. Soc. Symp. Proc. Vol. 328. ©1994 Materials Research Society
Scheme 1 OCOCH 3
R
I
I
s
I"I
KItBuO/THF
+I 2
0_Y0J
N
Chloride
PEN(Et)
-
3 /CH 2 CI2
4
a) R = OCOCH3
b) R = OH
N
Tetracyanoethylene DMF / 40'C
NC
N CN
and reacted with aldehyde 2 at 0°C to produce stilbene 4a (R = OCOCH 3). Treatment of 4a with one equivalent of KtBuO in THF at room temperature resulted in deacetylation to yield 4b (R = OH). Methacroyl chloride was reacted with 4b in the presence of triethylamine to yield methacrylate 5 This compound was reacted with tetracyanoethylene in DMF to yield the desired product 6. The structure of 6 was fully confirmed by conventional spectroscopic 6 3 techniques (IR, UV, 1H and 1 C-NMR) and by elemental analysis. Polymerization of methacrylate 6 was attempted by conventional methods using AIBN as a free-radical initiator and methylmethacrylate for copolymerization. The reaction was run under a variety of conditions using several solvents but did not yield the desired material. The polymerization yielded low molecular weight polymethylmethacrylate 8 (PMMA) as the major (95-100 %) component. The desired copolymer was produced in less then five percent yield and all attempts to improve the yields were quite unsuccessful. The lack of activity of acrylate 6 was attributed to the reactivity of the tricyanovinyl group toward the free-radicals generated from AIBN. This was shown to be the case when 1 was treated with AIBN at 60oC in chlorobenzene. The radicals generated by AIBN reacted with compound 1 and yielded an undetermined product mixture which contained none of the starting tricyanovinyl compound. In a separate experiment, it was found that compound 4a (no tricyanovinyl or acceptor)) was not reactive toward the free-radicals generated from AIBN. These two experiments led us to the theory that the presence of the tricyanovinyl group in the chromophore 6 was inhibiting the polymerization by a reaction between the radicals and the tricyanovinyl group. In an attempt to synthesize a polymer containing this highly active material (1), a polymerization was run with the methacrylate derivative 5. By using the fact that the chemical properties of polymers generally are the same as there corresponding monomers, it was anticipated that the acrylate copolymers of 5 could be "post-treated" with tetracyanoethylene to obtain the required methacrylate copolymers of 6. The polymerization proceeded smoothly and resulted in copolymers with the structure 8. The above polymerization was carried out using different initial concentrations of 5(X) and methylmethacrylate(Y) to obtain a series of copolymers (8) with varying ratios of X to Y. The results (Tg, glass transition temperature, and Mn
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