Michael G. Mikhael

N-substituted maleimides as thermal stabilizers for plasticized poly(vinyl chloride)

Abstract N -Substituted maleimides have been investigated as thermal stabilizers for plasticized PVC at 180°C in air by measuring the rate of dehydrochlorination and the extent of discoloration of the degraded polymer. The results reveal a higher stabilizing efficiency of the products investigated compared with basic lead carbonate, dibutyl tin maleate, and barium-cadmium stearate stabilizers which are commonly used industrially. The induction period (Ts) is influenced by the nature and position of substituents in the aryl ring together with the nature of the plasticizer used. Moreover, it has been found that the stabilizers investigated impart better color stability to the degraded samples compared with the stearate stabilizer. A synergistic effect was achieved when the products investigated were used as mixtures with the reference stabilizer in equimolar ratios. A radical mechanism is proposed which illustrates the stabilizing action of the products investigated.

Synthesis and thermal behaviour of poly(N-acryloyl,N′-cyanoacetohydrazide) and some of its metal complexes

Abstract N -Acryloyl, N ′-cyanoacetohydrazide (ACAH) has been synthesized for the first time as a new water soluble chelating monomer. Its structure was elucidated by both elemental and spectral analyses. This new monomer readily undergoes free radical polymerization in both aqueous and non-aqueous media. The thermal behaviour of poly( N -acryloyl, N ′-cyanoacetohydrazide) (PACAH) and its copper and nickel complexes was investigated using thermogravimetric (TGA) and differential thermal analysis (DTA) techniques. The data obtained showed that the thermal behaviour of PACAH-metal complexes is significantly different from that of PACAH itself. Spectral analysis (IR) was used to follow the structural changes accompanying the thermal degradation process. A mechanism for the degradation reaction of PACAH has been proposed.

N-substituted maleimides as photo-stabilizers for rigid poly(vinyl chloride)

Abstract N -substituted maleimides have been investigated as photo-stabilizers for rigid PVC by measuring the rate of dehydrochlorination, the extent of discoloration, the amount of gel formation as well as the intrinsic viscosity of the soluble fractions of the degraded polymer. The results reveal a higher stabilizing efficiency for the products investigated relative to the industrially used phenyl salicylate UV absorber. A greater efficiency is similarly observed on comparison with dibutyl tin maleate which was originally used as a thermal stabilizer. The stabilizing efficiency is influenced by the nature and position of substituents in the aryl rings of the maleimide derivatives. A synergistic effect is achieved when the maleimides are mixed with the UV absorber phenyl salicylate in equimolar ratios. A radical mechanism is proposed to account for the stabilizing action of the products investigated.

Polymerization and chelating behavior of N-acryloyl, N-phenylthiourea

SummaryThe title monomer has been prepared for the first time. It has been polymerized by a free radical mechanism in different solvents. Only oligomers were obtained so far. The dependence of the rate of polymerization on monomer and initiator concentrations has been measured and was found to follow the usual free radical scheme. The overall activation energy of polymerization has been measured in two solvents and was found to be 21.2 and 15.03 K.Cal/mol in tetrahydrofuran (THF) and N,N-dimethyl formamide (DMF) respectively. The prepared monomer has excellent chelating ability with different metal cations. The stability constant of the monomer with copper (II) ions has been measured in acetone as well as in dioxane. The complexes have no tendency for free radical polymerization.

Thermal degradation behaviour of acrylonitrile-indene copolymers

Abstract A thermal degradation study has been carried out on polyacrylonitrile, polyindene and three of their copolymers using thermogravimetry and differential thermal analysis techniques. Spectral analysis (FTIR) was carried out on some of the samples before and after heating at various temperatures. Activation energy calculations for the thermal degradation process in air and under nitrogen were made using the thermogravimetry curves. The thermal analysis data showed that there was an increase in the initial decomposition temperature with increasing indene content in the copolymers, which reflects the blocking effect of indene units on the nitrile oligomerization reaction in polyacrylonitrile. A mechanism for the role of the indene comonomer in the cyclization process has been proposed.

Effect of lithium perchlorate on the spontaneous copolymerization of 4‐vinylpyridine with various electron‐rich vinyl monomers

The spontaneous copolymerization of 4-vinylpyridine (4-VP) activated with lithium perchlorate (LiClO 4 ) with various electron rich monomers (p-methoxystyrene, MeOSt; p-methylstyrene, MeSt; styrene, St) was investigated in various solvent systems at 75°C. Increasing the LiClO 4 concentration and the nucleophilicity of the electron rich monomer increased the copolymer yields. Both 1 H-NMR and elemental analysis confirmed the almost 1:1 copolymer structure for VP/MeOSt system which possessed high molecular weight and narrow polydispersity (PDI). Compared to 4-VP activated with zinc chloride, LiClO 4 systems showed slightly lower yields and much narrower PDI. We also investigated the spontaneous copolymerization of 4-VP activated with various protic acids in the reaction with various electron rich comonomers. However, generally protic salt forms showed less solubility in organic solvents and showed low molecular weight polymer products with low yields. The proposed initiation mechanism exhibits the formation of a σ-bond between the β-carbons of the two donor-acceptor monomers, creating the 1,4-tetramethylene biradical intermediate initiating the copolymerization.

Effect of ZnCl2 on the copolymerization of acrylonitrile with N-2-chlorophenylmaleimide

SummaryThe effect of ZnCl2 addition on the reactivity ratios of the system acrylonitirle (AN)-N-2-Chlorophenylmaleimide (2CMI) has been investigated. It has been found that the addition of small amount of ZnCl2 doubles the reactivity of AN while drastically decreasing that of the 2CMI. The viscosity of the copolymers has been measured and was found to decrease with increasing the maleimide and the ZnCl2 concentrations.