(pT hiobenzy1idene)malononitrile starting from p-[ (2-hydroxyethyl)thio

namate (2) and [p-[ (2-hydroxyethyl)thio]benzylidene]- malononitrile (31, respectively, as outlined in Scheme I. Methacryloylations of 2 and 3 were ca...
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Macromolecules 1991,24, 2100-2102

Scheme I

Poly(meth)acrylates Containing t h e NLO-Phores pThio-a-cyanocinnamate a n d

F

(pThiobenzy1idene)malononitrile ZHENDE NI,t THOMAS M. LESLIE,! ANNE BUYLE PADIAS, AND H. K. HALL, JR.'

CHO

CHO

I Yc-cnI-x

C. S. Marvel Laboratories, Department of Chemistry, The University of Arizona, Tucson, Arizona 85721 Received March 26, 1990; Revised Manuscript Received October 10, 1990

6

Introduction Polymers with highly dipolar units have recently been the subject of much interest because of their exceptionally high second-order nonlinear optical (NLO) properties (high P value). In preceding papers, the synthesis of monomers and polymers containing nitrogen' and oxygen2 donoracceptor dipolar units in the main chain of polyesters, with all the dipolar units lined up in the same direction in a given chain, was described. In the third paper of this series: polyesters containing the p-thio-a-cyanocinnamateunit in the main chain were synthesized. NLO-phores containing sulfur should have a more polar excited state than the corresponding NLOphore containing the alkoxy group, but may be less dipolar in the ground state. As a consequence, by a solvatochromic method, it has been shown that the sulfides have a higher 0 value than the corresponding ether^.^ The introduction of sulfide linkages is also expected to increase solubility and processability of the polymers.

YYA

-0CO

Nc?

/

/ I

-

2

x

3

X - C N

COOYI

X Cn*.CW-COCI

Y

S

-0

C0 - C H C H2

NC X

-

X

4

X

5

X - C N

COOU#

-

6

X

7

x - c n

COOYa

so excess MMA was used. The conditions described in

+s+-

-

The question remains as to whether it is preferable to line up all the dipoles in the main chain, with accompanying processability problems but better mechanical properties, or whether these NLO-phores can be attached as side groups for equivalent activity. In this paper, the synthesis of (meth)acrylate monomers and polymers containing p-thio-a-cyanocinnaate and (pthiobenzy1idene)malononitrile units in the side chain is described. An overview of our research in this area, including some of the results described in this paper, has been described p r e v i ~ u s l y . ~ Results Synthesis. The new monomers were synthesized starting from p-[(2-hydroxyethyl)thio]benzaldehyde3 (l), which was condensed with methyl cyanoacetate or malononitrile to yield p-[ (2-hydroxyethyl)thio]-a-cyanocinnamate (2) and [p-[(2-hydroxyethyl)thio]benzylidene]malononitrile (31, respectively, as outlined in Scheme I. Methacryloylations of 2 and 3 were carried out by ester interchange with an excess of methyl methacrylate to give methyl p-[ [(methacryloyloxy)ethyl]thiol-a-cyanocinnamate (4) and [p-[[(methacryloyloxy)ethyl]thiolbenzylidenelmalononitrile (5), respectively. Magnesium/methanol and 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO) were used as reaction catalyst and polymerization inhibitor, respectively. Compound 2 has an active ester group, which can undergo self-transesterification to form a polyester,3 Visiting scholar from Chemistry Institute, Chinese Academy of Sciences, Beijing, People's Republic of China. Hoechst-Celanese Research Co., 86 Morris Ave., Summit, NJ 07961.

0024-9297/91/2224-2100$02.50/0

the Experimental Section are the preferred ones after various catalysts, inhibitors, solvents, and ratios of MMA to 2 were tried. Acryloylation of 2 and 3was done using acryloyl chloride. Methylp-[ [(acryloyloxy)ethyl]thio]-a-cyanocinnamate(6) and [p-[ [ (acryloyloxy)ethyl]thio] benzylidenelmalononitrile (7) were prepared by the reaction of acryloyl chloride with 2 and 3, respectively. Monomers 6 and 7 were purified by recrystallization from toluene. Monomer Characterization. The proposed monomer structures were completely in agreement with the analytical and spectroscopic data (see Experimental Section). On the basis of earlier NMR data! the ester group is E relative to the phenyl substituent. The assignment of the peaks in the NMR spectra of the new monomer was made by comparison with the model compound p-[(P,o-dicyanovinyl)thio]anisole (8): the single peak around 8 ppm was assigned to the benzylidene proton, and the double peaks a t 7.4 and 7.8 ppm were assigned to the aromatic protons. The peaks around 5.8 and 6.4ppm were assigned to the acrylate vinyl protons. 13C NMR spectra showed that the nitrile carbons absorbed around 115 ppm, and the aromatic carbons a t 126, 128, 130, and 146 ppm, analogous to the resonances in 8. By comparison with the model compounds 8 and p - [(a,@,/3-tricyanovinyl)thio]anisole (9), the resonances at 80 and 154ppm in the monomer spectra can be assigned to the benzylidene 0- and a-carbons, respectively. The IR spectra of the monomers 4-7 showed sharp peaks around 2224 cm-l, which is common for monomers containing conjugated nitrile groups. Polymerizations. As shown in Table I, monomers 4, 6, and 7 homopolymerized in benzene solution with AIBN as initiator at 60 "C. For monomer 5, DMF or chlorobenzene was used as solvent; in benzene only very low yields of poly-5 could be obtained (