Doctor of Philosophy
Raphael M. Ottenbrite
The effect of the amide function and the carbethoxy function on the polymerization properties of maleimide are reported. The effects of these functions on homopolymerization and copolymerization (with styrene) were examined. These electron-withdrawing groups appeared to decrease the rate of homopolymerization and increase the rate of copolymerization.
N-carbamylmaleimide and N-carbethoxymaleimide were copolymerized with styrene in 1,4 -dioxane at 60.0° C at different feed ratios to high conversion. Copolymer composition, determined by elemental analysis and 1H NMR, indicated that while 1:1 copolymers were obtained with an equimolar feed ratio, the two systems were not alternating. It is of note that the copolymerizations were carried out at a very low total monomer concentration of 0.2 mol/L due to the limited solubility of N-carbamylmaleimide in the reaction solvent. If higher concentrations had been possible, 1:1 copolymer formation would have been enhanced.
Investigation of the complexation of maleic anhydride, maleimide, N-carbethoxymaleimide, N-carbamylmaleimide, N-phenylmaleimide and N-ethylmaleimide with the electron-donors styrene, furan, and 2-chloroethyl vinyl-ether was accomplished by use of ultraviolet (UV) spectroscopy and 1H NMR spectroscopy. It appeared generally that the electron-withdrawing groups increased the complexation of maleimide with the electron-donating comonomers. There was no evidence of complex formation with 2-chloroethyl vinyl ether for any of the compounds studied.
A continuous variation method using UV spectroscopy indicated that all observed charge-transfer complexes (maleic anhydride-styrene; N-carbethoxymaleimide-styrene; N-phenylmaleimide-styrene; maleic anhydride-furan; N-carbamylmaleimide-furan) had 1:1 stoichiometry. The formation constant of complexation between maleimide and styrene was increased towards the value of the complex formation constant for maleic anhydride-styrene when the electron-withdrawing groups -CONH2 and -C02Et were substituted on the maleimide N. The same effect was not observed for complexation with furan.
IR spectroscopy and 13c NMR spectroscopy indicate that the electron-withdrawing groups increase the double bond character of the maleimide carbonyl groups. The results of the complexation studies suggest that the carbonyl groups of maleimide may play a significant role in complex formation with styrene. The mechanism of complex formation with furan appears to be different from that of styrene.
It was also shown that when N-phenylmaleimide and maleic anhydride (both electron-accepting monomers) are copolymerized, a random copolymer results.
When reaction with styrene is considered, the results of this investigation indicate that electron-withdrawing N-substituents influence the polymerization properties of maleimide to be more like those of maleic anhydride.
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