Thermal degradation of polyether-urethanes: Part 3—Polyether-urethanes prepared from methylene bis(4-phenylisocyanate) and low molecular weight poly(ethylene glycols)

Polyurethanes have been prepared by reaction of methylene bis(4-phenylisocyanate) with diethylene glycol and with poly(ethylene glycol) with a molecular weight of approximately 200. Degradation has been carried out at temperatures up to 500°C and volatile products and structural changes in the residual polymer analysed in detail. The primary degradation reaction is one of depolycondensation to form the two monomers but a large proportion of these undergo a further complex series of reactions while they diffuse from the hot reaction zone. A comprehensive mechanism for the overall process has been deduced and discussed.     

Thermal degradation of ammonium polymethacrylate and polymethacrylamide

The degradation of ammonium polymethacrylate and polymethacrylamide has been studied by a combination of thermal analysis methods (TVA and TG) and examination of volatile and involatile products by infrared analysis. It is shown that total reaction comprises an initial cyclization and further fragmentation of the modified chain at higher temperatures to yield gaseous volatiles. The partially degraded NH₄PMA contains anhydride ring and cyclic imide structures in the chain. Quantitative comparison of yields of isocyanic acid and carbon dioxide has shown that imidization is the major reaction and anhydride formation is of less importance. The mechanisms of the various reactions are discussed.     

Thermal degradation of poly(alkyl acrylates). I. Preliminary investigations

A qualitative survey of the thermal degradation reactions which occur in poly(ethyl acrylate), poly(n-propyl acrylate), poly(isopropyl acrylate), poly(n-butyl acrylate) and poly(2-ethylhexyl acrylate) has been made by using three thermal analytical methods: thermogravimetric analysis (TGA), thermal volatilization analysis (TVA), and the dynamic molecular still (DMS), all combined with infrared and mass spectrometry. Degradation in poly(isopropyl acrylate), which is a secondary ester, becomes discernible at 260°C and proceeds in two stages. The other four polymers, which are all primary esters, are more stable. They degrade in a single-stage process starting at 300°C. The principal volatile products from the primary esters are carbon dioxide and the olefin and alcohol corresponding to the alkyl group. A roughly equivalent quantity of short-chain fragments is also formed. From poly(isopropyl acrylate), carbon dioxide and propylene are the only volatile products in the first phase of the reaction.     

Thermal degradation of phenyl methacrylate-methyl methacrylate copolymers

The degradation behaviours of poly(phenyl methacrylate), four phenyl methacrylate-methyl methacrylate copolymers which span the composition range, and poly(methyl methacrylate) have been compared by using thermogravimetry in dynamic nitrogen and thermal volatilisation analysis (TVA) under vacuum, with programmed heating at 10°C/min. Volatile products have been separated by subambient TVA and identified and the cold ring fraction and partially degraded polymer have been examined by ir spectroscopy. Poly(phenyl methacrylate) resembles poly(methyl methacrylate) in degrading completely to monomer. Copolymers of phenyl methacrylate and methyl methacrylate are more stable than the homopolymers. On degradation, the major products are the two monomers. Minor products from all the copolymers include carbon dioxide, dimethylketene, isobutene and formaldehyde. Copolymers with low and moderate phenyl methacrylate contents show the formation of anhydride ring structures in the cold ring fraction and partially degraded copolymer, together with small amounts of methanol in the volatile products. Carbon dioxide is a more significant product at lower phenyl methacrylate contents.The mechanism of degradation is discussed.     

Radiation-oxidation mechanisms: Volatile organic degradation products from polypropylene having selective C-13 labeling studied by GC/MS

PP samples, in which the three unique carbon atom positions along the chain were selectively labeled with C-13, have been subjected to γ-irradiation in the presence of oxygen, and the resulting organic volatile products analyzed by GC/MS. The isotopic labeling patterns in 33 organic degradation compounds have been assigned by comparison of the four mass spectra for each compound (from unlabeled PP, and from the three labeled PP materials). The volatile products have been “mapped” onto their positions of origin from the PP macromolecule, and insights have been gained into the chemistry through which these compounds must have formed. Most products show high specificity of isotopic labeling, indicating a single dominant reaction pathway. Oxidation chemistry occurred heavily at the C(2) tertiary carbon, with chemistry also at C(1) methylene. Methyl ketones are in abundance, along with alcohols, some aliphatic hydrocarbons, and other compound types. The C(3) methyl carbon remained attached to its original C(2) position in all catenated degradation products, and underwent no chemistry. However, products containing “non-catenated” carbons (i.e., not bonded to any other carbon atom) consisted entirely of a mix of C(3) and C(1). By examination of the labeling patterns, many products could be assigned to two successive chain scission events in close proximity, while others are clearly seen to arise from cleavage, followed by radical-radical recombination reactions. Interestingly, the former products (two chain scissions) are all found to have an odd number of carbon atoms along their chain, while the latter (scission followed by radical-radical reaction) all have an even number of carbons. An explanation of this odd/even phenomenon is provided in terms of the symmetry of the PP macromolecule.     

Thermal degradation of zinc polymethacrylate and a zinc methacrylate/methyl methacrylate copolymer

Methyl methacrylate and zinc methacrylate have each been polymerised in methanol solution using azodiisobutyronitrile as initiator and a copolymer of the two monomers has been prepared in the same medium.The degradation behaviour of the three materials has been studied using TG and TVA, volatile products have been investigated by infra-red and GLC analysis and infra-red spectroscopic examination of structural changes in the partially degraded polymer has been carried out for zinc polymethacrylate (ZnPMA).The breakdown of ZnPMA shows many similarities to the behaviour of the alkaline earth polymethacrylates. The effect of introducing ZnMA units into the PMMA chain by copolymerisation is to stabilise the chain considerably and to modify the degradation behaviour of the MMA units, so that methanol and carbon monoxide, resulting from side group scission, become major products in addition to MMA monomer; the ZnMA units in the copolymer behave in the same way as in ZnPMA.This study provides support for the mechanism previously proposed for the degradation of PMMA/ZnBr₂ blends, in which the ZnMA/MMA copolymer structure was regarded as an intermediate stage in the reaction.     

Thermal degradation of bromine containing polymers—Part 4: Mechanisms of decomposition of copolymers of 2-bromoethyl methacrylate and methyl acrylate and blends of the homopolymers

The principal products of degradation of copolymers of 2-bromoethyl methacrylate (2BEM) and methyl acrylate (MA) and of blends of the two homopolymers are the two monomers, methyl bromide, 1,2-dibromoethane, methanol, acetaldehyde, methyl methacrylate, carbon dioxide, 2-bromoethanol and chain fragments. There are also a number of minor products including carbon monoxide, hydrogen and methane. Possible mechanisms of formation of these compounds are suggested and discussed in the light of the experimental evidence and an integrated reaction sequence has been drawn up.     

Oxidation of Polyisoprene Popcorn Polymer. III. Further Studies on Water and Carbon Dioxide Production

The volatile products resulting from polyisoprene popcorn polymer oxidation were analyzed quantitatively for carbon dioxide and water, and semiquantitatively for formaldehyde. The production of these three products was a linear function of the amount of oxygen consumed in the reaction. For every mole of oxygen reacted, 0.098 mole of water, 0.038 mole of carbon dioxide, and > 0.016 mole of formaldehyde were formed. Twenty-four products were detected after extensive oxidation; the major ones being water, carbon dioxide, formaldehyde, formic acid, 2,5-hexanedione, and acetic acid. No levulin-aldehyde was identified in the products. A tentative oxidation mechanism is discussed.     

Scalable Synthesis of Interconnected Porous Silicon/Carbon Composites by the Rochow Reaction as High‐Performance Anodes of Lithium Ion Batteries

Despite the promising application of porous Si‐based anodes in future Li ion batteries, the large‐scale synthesis of these materials is still a great challenge. A scalable synthesis of porous Si materials is presented by the Rochow reaction, which is commonly used to produce organosilane monomers for synthesizing organosilane products in chemical industry. Commercial Si microparticles reacted with gas CH₃Cl over various Cu‐based catalyst particles to substantially create macropores within the unreacted Si accompanying with carbon deposition to generate porous Si/C composites. Taking advantage of the interconnected porous structure and conductive carbon‐coated layer after simple post treatment, these composites as anodes exhibit high reversible capacity and long cycle life. It is expected that by integrating the organosilane synthesis process and controlling reaction conditions, the manufacture of porous Si‐based anodes on an industrial scale is highly possible.     

Measurement of Hexanal Production by Myoglobin-Induced Lipid Peroxidation Using a Miniature Incubator and Cryofocusing Inlet System with Gas Chromatography and Time-of-Flight Mass Spectrometry

A miniature incubator was used in combination with a cryofocusing inlet system and GC-TOFMS in order to determine the rate of hexanal production during myoglobin (Mb)-induced lipid peroxidation of phosphatidyl choline containing arachidonic acid. The cryofocusing inlet system allowed for rapid preconcentration of the volatile products of the peroxidation reaction, yielding a total analysis time for hexanal of less than 4 min. Each reaction was sampled repetitively, and the production of hexanal was determined in real time, as the reaction progressed. Myoglobin-induced lipid peroxidation produced hexanal linearly over 40 min, maximizing at an average concentration of 1 ppm after 60 min. In reaction mixtures containing basal levels of hexanal, presumably due to autoxidation occurring during storage, greater amounts of hexanal were formed at a faster rate of production, though the production was not linear for more than 15 min. The rapid preconcentration and nondestructive sampling are advantageous; the sampling time can be adjusted in order to detect and quantitate minor products, and the instrumentation can thus be used for full profiling of the volatile products of lipid peroxidation.     

Chlorinated products of plastic pyrolysis

The formation of various chlorinated products in pyrolysis of polymers and plastics additives was studied. Formation of chlorobenzenes (in addition to the monomers) from poly(chlorostyrene) and poly(vinylbenzyl chloride) was observed. Hydrogen chloride is only produced from these polymers at above 600 °C when the chlorine atoms are cleaved off and abstract hydrogen. A similar process takes place in aromatic chlorine-containing dyes, in which the strong aromatic molecular structure prevents the thermal cleavage of chloroaromatic volatile products. We have observed that cupric and ferric chlorides chlorinate phenolic thermal decomposition products of plastic materials which originate either from the polymer or from the stabilizer. The highest yields of chlorophenols are obtained in pyrolysis at around 700 °C.     

The thermal degradation of copolymers of vinyl acetate with methyl methacrylate and other monomers

The thermal degradation of copolymers of vinyl acetate with methyl methacrylate, styrene and ethylene has been investigated using thermal volatilization analysis and thermogravimetry, together with analysis of volatile and involatile degradation products. All three copolymer systems show some of the features characteristic of the homopolymers of the monomers concerned. There is evidence, however, for an intramolecular lactonization process in VA—MMA copolymers, involving reaction of adjacent VA and MMA units with elimination of methyl acetate. This reaction occurs less readily than the analogous process in vinyl chloride—MMA copolymers. Mechanisms of the various degradation reactions are discussed.     

Design, synthesis, and characterization of conifer-shaped dendritic architectures

An elongated structural design leading to more conical-shaped dendritic architectures by using a combination of 1-->3, 1-->(2+1), and 1-->(2+1 Me) C-branched monomers is presented. Synthesis of the conifer-shaped macromolecule was achieved by reaction between isocyanate 20 and amine 26 in dry CH2Cl2. A resultant extended focal adamantane-modified dendron was deprotected to generate the water-soluble product, which was subsequently complexed with beta-cyclodextrin in D2O to create the desired tree-like product. Host-guest interactions of the adamantane moiety with the beta-cyclodextrin cavity were monitored by 1H NMR spectroscopy. All monomers, key intermediates, and final products were fully characterized by 1H and 13C NMR spectroscopy, ESI or MALDI-TOF mass spectrometry, and IR spectroscopy.     

Degradation thermique des copolymeres methacrylate de methyle-chlorure de vinylidene

The thermal degradation, under inert atmosphere, of a set of methyl-methacrylate-vinylidene chloride copolymers prepared by free radical copolymerization with constant composition conditions, is studied by thermogravimetry coupled with titration of HCl evolved and with gas chromatographic analysis of volatile products (monomers, methyl chloride). Only the formation of methyl methacrylate can be related to the sequence distribution.     

Thermal degradation of polymers with phenylene units in the chain. IV. Aromatic polyamides and polyimides

The breakdown mechanism of an aromatic polyamide and four polyimides has been studied under vacuum in the temperature range of 375–620°C, by using techniques described earlier, involving collection and analysis of volatile products as well as analyses of residues at different temperatures. The decomposition of the polyamide up to 375°C yielded predominantly carbon dioxide, while between 375 and 450°C about equal amounts of carbon dioxide and carbon monoxide formed. Hydrogen is the major product between 450 and 550°C, along with hydrogen cyanide, methane, and carbon monoxide. The major reaction at the lower temperatures seems to be the cleavage of the linkage between the carbonyl group and the ring, with subsequent formation of a carbodiimide linkage via isocyanate intermediates, and liberation of carbon dioxide. Alternatively, cleavage between the carboxyl and the NH-group leads to the formation of carbon monoxide. Carbon dioxide and carbon monoxide are also the major volatile decomposition products of the polyimides at the lower temperatures. The primary cleavage reaction is believed to be the rupture of the imide ring between a carbonyl and nitrogen, with subsequent formation of isocyanate groups. The latter react with each other to form carbodiimide linkages and carbon dioxide, while the remaining benzoyl radical is the source for carbon monoxide.     

The mechanism for the conversion of uric acid into uroxanate and allantoin : A new base-induced 1,2-carboxylate shift

Alkaline permanganate oxidation of uric acid (1), particularly the late stages of the transformation into uroxanate (7) and allantoin (3), was studied by means of isotope-position labelling. A clear-cut degradation procedure developed for distinguishing among carbonyl and α-aminal carbon atoms in these products demonstrated conclusively that the carboxylic carbon of 7 and the 4-carbonyl carbon of 3 have their origin in C(5) of uric acid (1). None of the mechanisms that have been proposed for this reaction would have predicted this result. Isotope-labelling evidence, in combination with other data, revealed the sequence of events and identities of species involved in oxidative transformation of 1 ; the carbon-skeleton rearrangement of the first transient intermediate 4 must occur by a 1,2-carboxylate shift to give allantoin-5-carboxylate (6) which either decarboxylates to allantoin (3) or else undergoes hydrolytic ring opening to uroxanate (7).     

二氧化碳/1,2-环氧丁烷/ε-己内酯的三元共聚合和表征

以高聚物负载型双金属负离子配位化合物PBM为催化剂,通过二氧化碳(CO2),1,2-环氧丁烷(BO)与ε-己内酯(CL)的三元开环共聚合反应,得到三元共聚物,脂肪族聚碳酸酯(PBCL).对PBCL进行了FTIR1、H-NMR1、3C-NMR、DSC和WAXD等表征,并考察了反应单体比例及反应时间对共聚物性能的影响.结果表明,由于ε-己内酯开环共聚,引入了易水解的羧酸酯单元,PBCL的降解速度和玻璃化转变温度较二氧化碳-环氧丁烷的二元共聚物(PBC)得到了有效地提高.同时,PBCL相对于聚己内酯(PCL)玻璃化转变温度和降解速度明显改善,且PBCL为非晶结构.     

超临界CO2协助三单体接枝改性聚丙烯

利用超临界二氧化碳(SC CO2)作为单体的溶剂和聚丙烯的溶胀剂, 通过自由基接枝聚合合成了聚丙烯与丙烯酸、甲基丙烯酸甲酯以及马来酸酐的接枝产物PP-g-(AA-MMA-MAH). 在单体的选择上采取软、硬单体复配的方式来调节链的柔韧性. 考察了溶胀条件、接枝条件以及单体配比对接枝反应的影响, 研究结果表明, PP和单体以及引发剂在7.74 MPa、47 ℃下溶胀5 h后, 75 ℃下反应3 h时接枝率为4.31%, 接枝效率可达71.83%. 产品表征说明单体均匀地接枝到聚丙烯颗粒上; 改性后聚丙烯水润湿角降低, 亲水性能得到明显改善; 接枝单体的引入提高了PP的热稳定性.     

Thermal stability and degradation mechanisms of poly(acrylic acid) and its salts: Part 3—Magnesium and calcium salts

The magnesium and calcium salts of acrylic acid have been polymerised in aqueous solution using ammonium persulphate as initiator. Both polymers were also prepared by the neutralisation of poly(acrylic acid) with metal oxide in the same medium.

The thermal degradation behaviour of magnesium and calcium polyacrylate was studied using thermogravimetry (TG), differential thermal analysis (DTA) and thermal volatilisation analysis (TVA). Degradation products were investigated by IR spectroscopy, mass spectrometry and GC-MS techniques, the volatile product fraction having first been separated by subambient TVA.

The decompositions of these materials show some similarities to the behaviour of the alkali metal salts of poly(acrylic acid) and to that of the alkaline earth metal salts of poly(methacrylic acid), but there are also important differences. Acetone and carbon dioxide are the most important volatile products and, in addition, there are various other carbonyl containing products. More carbon dioxide, resulting from side group scission, is evolved from magnesium polyacrylate than from calcium polyacrylate, because of the lower thermal stability of magnesium carbonate.     

热重-固相微萃取/气相色谱-质谱联用研究葡萄糖/天冬酰胺模拟体系非水相Maillard反应

利用热重-固相微萃取/气相色谱-质谱(TG-SPME/GC-Ms)联用对葡萄糖/天冬酰胺模拟体系非水相Maillard反应热学性质进行了研究,并分析了模拟体系46种热解逸出挥发性产物相对含量的动态变化情况.探讨了有效减少Maillard反应产物丙烯酰胺的方法.结果表明:葡萄糖/天冬酰胺模拟体系非水相Mail-lard反...