Structure of a dimeric piperidone-aldehyde condensation product

The base-catalyzed condensation of benzaldehyde with 1-methyl-4-piperidone (5) gave two isomeric products which were dimers of 3-benzylidene-1-methyl-4-piperidone (7). Reactions of the dimers and their mass spectral data are examined on the basis of the X-ray structural analysis of the dibromo derivative of the dimer which was identified as 4-p-bromobenzylidene-9-p-bromophenyl-10a-hydroxy-2,7-dimethyl-2,7-diaza-10-oxa-1,2,3,4,5,6,7,8,8a,10a,-decahydroanthracene (10b).     

Thermal degradation of phosphonated polystyrenes: Part 1—Chain end condensation

Polystyrenes substituted with chloromethoxyphosphonated groups at chain ends undergo a condensation reaction at a relatively low temperature (ca. 200°C) prior to extensive degradation of the polymeric chain (280–430°C). The condensation leads to an increase in the molecular weight through the formation ofPOPbonds between phosphonated chain ends with elimination mainly of CH₃Cl. Trace amounts of CH₃OH are also evolved in this step. Mechanisms for the condensation reaction are proposed and its relevance to the fire retardant activity of these polymers is discussed.     

Thermal degradation of bisphenol a polycarbonate

Bisphenol A polycarbonate (Makrolon 3000) has been purified and fractionated. Thin films of these samples have been degraded by heating at 200° under continuous evacuation (pressure less than 0- 1 Pa) for periods of several hours. The molecular weight is observed (by gel permeation chromatography) to increase with time at 200°. Eventually gel is formed. The variation of the number- and weight-average molecular weights with heating time and the effect of the initial molecular weights of the polycarbonate samples are consistent, in the main, with the Davis-Golden mechanism of thermal degradation of bisphenol A polycarbonate; i.e. the principal reactions are condensation and trifunctional branching. Chain scission due to hydrolysis of the carbonate linkage is absent under our conditions.     

Thermal condensation of imidazole with trifluoroacetaldehyde

The title condensation occurred readily at reflux (100°C) with the methyl hemiacetal of trifluoroacetaldehyde and provided 37.3% of 4(5)-(1′-hydroxy-2′,2′,2′-trifluoroethyl)imidazole as the major product, together with 8.8% of 2-(1′-hydroxy-2′,2′,2′-trifluoroethyl)imidazole, 7.2% of 2,4(5)-bis-(1′-hydroxy-2′,2′,2′-trifluoroethyl)imidazole and 0.4% of the 4,5-bis-product. (Trifluoroacetyl)imidazoles were prepared by oxidation of these condensation products. Nitration and bromination of the condensation products gave the corresponding nitro- and bromoimidazoles, respectively.     

Thermal condensation of indoles with trifluoroacetaldehyde

The title condensations provide the corresponding (1′-hydroxy-2′,2′,2′-trifluoroethyl)indoles. Indole itself, 1-methylindole and 2-methylindole gave 3-adducts in yields of 77%, 49% and 84%, respectively. 3-Substituted indoles (3-methylindole, ethyl indole-3-acetate and indole-3-ethyl acetate) afforded 2-adducts in yields of 69%, 21% and 23%, respectively. The indole adduct eliminates water at 137°C to form a transient 3-(trifluoromethylmethylene)indolenine, which reacts rapidly with nucleophiles including indole.     

Structure elucidation of a condensation product of 4-aminopyrrole derivatives and dicyclohexylcarbodiimide

The chemical structure of the two condensation products of dicyclohexylcarbodiimide (DCC) with the precursors of the mono-pyrrole homologues of distamycin and with the mono and tri-pyrrole homologues of congocidine were established. The two products isolated were proven to be condensation products between 4-aminopyrrole derivatives and dicyclohexylcarbodiimide (DCC).     

Thermal degradation of a series of polyester polyurethanes

A series of polyester polyurethanes with a range of polyester contents was prepared from an ethylene glycol/propylene glycol/adipic acid polyster, butane diol, and methylene bis (4-phenyl isocyanate) (MBPI). They were thermally degraded under vacuum and the products of degradation were identified. The urethane linkages decompose first as the temperature is increased and the stability increases with polyester content. Reaction mechanisms were proposed which account for the principal features of the reaction and the products of degradation.     

Thermal condensation of phthalimide with malonic acid

When phthalimide is reacted with malonic acid in the presence of zinc acetate, 1-hydroxy-1-methyl-1H-3-(1-oxoisoindolin-3-ylidenemethyl)isoindole, the zinc complex of 1-hydroxy-8,1322,27-diimino-1,615,20-dinitrilotetrabenzo[b,d,l,q]eicosin, and zinc tetrabenzoporphin are formed depending on the temperature. The compounds have been characterized by their electronic absorption spectra, IR and mass spectra, and also by their x-ray photoelectron spectra. A possible scheme for the synthesis of zinc tetrabenzoporphin has been proposed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 480–484, April, 1988.     

Thermal condensation of substituted imidazoles with trifluoroacetaldehyde

The title condensation provides the corresponding (1′-hydroxy-2′,2′,2′-trifluoroethyl)imidazoles in yields dependent on the electronic nature of the substituent: ortho-para directors promote the reaction while meta directors retard it strongly. 1-Alkylimidazoles gave only 2-adducts. 2-Substituted imidazoles yielded 4(5)-adducts together with small amounts of 4,5-bis-adducts. 4(5)-Substituted imidazoles provided 5(4)-adducts as the main products together with 2-adducts and 2,5(4)-bis-adducts.     

Thermal degradation of UHMWPE

The thermal behaviour of ultra-high molecular weight polyethylene (UHMWPE) of different molecular weights was examined by thermal analysis methods. The melting temperatureT _m and the heat of melting H were measured by the DSC method. The thermooxidative degradation process was investigated by using a MOM Q-1500 D derivatograph at various heating rates in air atmosphere. The initial decomposition temperatureT _i was determined from the TG curves, and other characteristic temperatures of decomposition were calculated. It was found thatT _m and H are higher for UHMWPE than those for HDPE, i.e. 146C and 195 J g^–1 for UHMWPE as compared with 133C and 166 J g^–1 for HDPE. The thermal behaviour of the investigated UHMWPE samples is not significantly influenced by molecular weight.     

Thermal degradation of polystyrene

Molecular weight change studies have shown that the thermal degradation of random copolymers of styrene — namely HIPS, SAN, and ABS-at low temperatures and in air involves random chain scission. The dominant process in the degradation of HIPS is random chain scission due to weak links, whereas in SAN it is intermolecular chain transfer. In ABS, the degradation is initially random scission due to weak links and then mainly intermolecular chain transfer. The infrared spectra show that during degradation the labile weak links are attacked by oxygen and peroxidic free radicals are produced. Via hydrogen abstraction or autoxidation of olefinic links, these free radicals are responsible for the formation of aliphatic ketonic or peroxyester structures, and for isomerization and cyclization. The activation energies of overall degradation of HIPS, SAN, and ABS are 134, 142, and 92 kJ.mol^–1 respectively.Part of the PhD dissertation of Mrs. Jaya Nambiar, University of Gorakhpur, Gorakhpur-273001, 1980.     

Thermal degradation of Levan

The thermal degradation of the polysaccharide Levan, of various molecular weights, was studied by means of isothermal and dynamic TG, X-ray diffraction, and IR measurements. From dynamic TG traces, two main degradation stages were observed for HL-Levans (hydrolyzed) whereas, three such stages were observed for UL-Levans (unhydrolyzed). These stages were correlated with branching effects, an interpenetrating network, and ring-fragmentation and other reactions in the late stages of the thermal degradation which result in the formation of infusible material that chars on further heating. Isothermal curves obtained for the first stage indicated the possibility of a random type of thermal degradation. Anticipated linear plots were obtained, using expressions from random degradation theory, which added further support for this type of degradation for Levan (stage 1). Various parameters were obtained for the thermal degradation of Levan, e.g., activation energies, and various experimental observations have been correlated in terms of postulated microstructures for Levan and in terms of parameters such as entropy of activation.     

Thermal degradation of polyethylene

Thermal degradation of low-density polyethylene (LDPE) in the temperature range from 450 to 525°C has been studied using a sieve-bottom reactor with inert gas as heat-transferring agent bubbled through the PE melt. Temperature dependence of the degradation rate was determined. Full degradation of LDPE into gaseous and wax-like hydrocarbons (alkanes and 1-alkenes) was achieved. Temperature rise and prolonging of the contact time increased the yield of the gaseous hydrocarbons and decreased the molecular weight of the wax-like product.     

Thermal degradation of polyquinoxalines

A systematic investigation of the thermal stability of nine structurally related polyquinoxalines has been conducted. The relative oxidation resistance of these polymers is controlled by two opposing structural effects. Phenyl sidegroup substitution in the heterocycle greatly improves oxidative stability, while the introduction of oxygen into the main polymer chain, in the form of ether groups, produces a negative effect of equal magnitude. These results are discussed from a mechanistic point of view. Simultaneous, dynamic thermal analysis in vacuum up to 1400°C and analysis of volatile and nonvolatile products indicates three major decomposition regions. Between 500 and 640°C, main polymer degradation takes place involving the heterocycle. This event is followed by dehydrogenation of a stable degradation product between 640 and 690°C. Above 1360°C an exothermic reaction takes place to yield highly condensed aromatic residues.     

Thermal degradation of polybenzyl

Polybenzyl has been synthesized from the benzyl compounds, chloride, methyl ether, and isopropyl ether by using stannic chloride as the Friedel-Crafts catalyst. The detailed structures of these polybenzyls have been determined by use of methods including elemental analysis, molecular weight determination, and infrared, ultraviolet/visible, and NMR spectra. The structure of these polybenzyls is globular with a high degree of branching. Thermal degradation was studied by using DTA and stepwise and isothermal degradation with analysis of both the volatile fraction and the residue. The activation energy for scissions was determined from changes in the molecular weight of the sample with time at a range of degradation temperatures of 340–440°C. The composition of the volatile fraction changed with both temperature and time of degradation. Thermal scission is directed to internal units and depends on the presence of weak links such as substituted anthracene units.     

Thermal degradation of a styrenated unsatured polyester resin

The isothermal and non-isothermal degradation of a typical styrenated phthalic acid-maleic acid-propylene glycol polyester were measured. Non-isothermal and isothermal kinetic analyses were performed on the various degradation steps observed. The values of the non-isothermal and the isothermal kinetic parameters are in good agreement.