Novel Copolymers of Styrene. 8. Some Ring-Disubstituted Ethyl 2-Cyano-3-Phenyl-2-Propenoates

Electrophilic trisubstituted ethylenes, ring-disubstituted ethyl 2-cyano-3-phenyl-2-propenoates, RPhCH?C(CN)CO₂C₂H₅ (where R is 3-Br-4-CH₃O, 5-Br-2-CH₃O, 3-F-2- CH₃, 3-F-4-CH₃, 4-F-2-CH₃, 4-F-3-CH₃, 5-F-2-CH₃, 2-Cl-5-NO₂, 2-Cl-6-NO₂, 4-Cl-3- NO₂) were prepared and copolymerized with styrene. The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-disubstituted benzaldehydes and ethyl cyanoacetate, and characterized by CHN analysis, IR, ¹H and ¹³C-NMR. All the ethylenes were copolymerized with styrene (M₁) in solution with radical initiation (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, ¹H and ¹³C-NMR. The order of relative reactivity (1/r ₁) for the monomers is 5-Br-2-CH₃O (1.02) > 4-Cl-3-NO₂ (0.93) > 3-F-4-CH₃ (0.81) > 2-Cl-6-NO₂ (0.77) > 2-Cl-5-NO₂ (0.71) > 3-Br-4-CH₃O (0.66) > 4-F-3-CH₃ (0.60) > 3-F-2-CH₃ (0.38) > 4-F-2-CH₃ (0.31) > 5-F-2-CH₃ (0.16). Relatively high T_g of the copolymers in comparison with that of polystyrene indicates a decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 250–500°C range with residue (2–26% wt.), which then decomposed in the 500–800°C range.