新型可生物降解医用高分子材料-聚膦腈

聚磷腈是一族由交替的氮、磷原子以交替的单键、双键构成无机主链的新型可生物降解聚合物。聚膦腈具有独特的性质和显著的合成多样性,降解产物为磷酸、氨、氨基酸和乙醇等无毒物质。通过改变聚膦腈侧链结构和组成,可调节聚膦腈的降解速度,控制药物释放的速度。本文主要综述了聚膦腈的合成、降解及其在药物控释系统中的应用。     

Thermal degradation of copolymers based on selected alkyl methacrylates

The thermal stability and thermal degradation of copolymers based on selected alkyl methacrylates at temperatures between 250 and 400?°C have been studied using pyrolysis?Cgas chromatography. The type and composition of thermal degradation products gave useful information about the mechanism of pyrolysis of copolymers synthesized by using typical commercially available alkyl methacrylates. It was observed that the main thermal degradation products from alkyl methacrylate copolymers are monomers of alkyl methacrylates using by synthesis. Other pyrolysis by-products formed during thermal degradation were carbon dioxide, carbon monoxide, methane, ethane, methanol, ethanol, and propanol-1.     

Identification of acrylate copolymers using pyrolysis and gas chromatography

A combination of pyrolysis and gas chromatography were used to investigate thermal degradation products formed from acrylic copolymers containing alkyl acrylate and methacrylate. The method provided an analytical tool for characterizing the chemical composition and structure of the degradation products. Thermal degradation of the synthesized copolymers was analyzed using isothermal (250 °C) pyrolysis–gas chromatography. The degradation process, and the nature and amount of pyrolysis products, provides relevant information about the thermal degradation of acrylic copolymers and the mechanism of pyrolysis. During pyrolysis, the formation of corresponding olefins, alcohols, acrylates and methacrylate was observed.     

Thermal degradation of poly(alkyl methacrylates)

The thermal degradation of selected poly(alkyl methacrylates) at temperatures between 300 and 800 °C was investigated by pyrolysis gas chromatography. Quantitative characterization of the pyrolysis products yields insights into the mechanism for thermal degradation of poly(alkyl methacrylates) under these conditions. Unsaturated monomeric alkyl methacrylates, carbon dioxide, carbon monoxide, methane, ethane, methanol, ethanol, and propanol were formed during thermal degradation of poly(alkyl methacrylates).     

Thermal behavior of bismaleimide resin

The cure of a bismaleimide (BMI) neat resin modified with an aromatic diamine and a siloxane elastomer, has been studied by ¹³C solid state nuclear magnetic resonance. Two chemical reactions occur during the cure cycle; at a low temperature, Michael's reaction predominates, while at a high temperature the polymerization of the double bond maleimide creates the network. The degradation of this BMI material was characterized with isothermal and dynamic thermogravimetric analyses in air and in nitrogen. The BMI thermal stability is lower in nitrogen than in air. This behavior is an indication of oxygen participating in reactions at high temperatures. The activation energy (E_a) of thermal degradation was determined from isothermal data using an Arrhenius equation (In V vs. 1/T). The global E_a for the weight loss in air was found to be 91 kJ/mol. The nature and the evolution of the thermal degradation products were the combined analyzed by techniques of pyrolysis, gas chromatography and mass spectrometry. The major thermal decomposition products obtained in the temperature range of 300–700°C are identified as benzene, methyl formamide, aniline, toluene and isocyanate-derived products.     

Thermal degradation of α-pinene using a Py–GC/MS

Mediterranean forest fires may be accelerated, partly due to biogenic volatile organic compounds produced by vegetation, mainly monoterpenes largely represented by α-pinene. To model the propagation of biomass combustion, it is necessary to study the flammability of the produced gas mixture, and thus, necessary to identify the emitted volatile compounds. However, thermal degradation of monoterpenes is rarely experimented above 300 °C, whereas forest fires reach higher temperatures. Thus, in this work, we experimented a 2-min pyrolysis of α-pinene at temperatures from 300 to 800 °C using a Py–GC/MS device. Less than 1% of pyrolysis products were detected at 300 and 400 °C. The pyrolysis products increased then from 14 compounds at 500 °C to 31 compounds at 800 °C. Degradation of α-pinene started with its isomerization at 500 °C. At 800 °C, alkenes detected increased as well as aromatics produced through the Diels–Alder mechanism. These results are consistent with the literature on thermal degradation of α- and β-pinene presented in our article.

     

Stepwise thermal degradation of a polybenzimidazole foam

The stepwise thermal degradation of a polybenzimidazole (PBI) foam, prepared from 3,3′-diaminobenzidine and isophthaldiamide, has been studied under conditions of pyrolysis and nonflaming oxidative degradation in a thermal analyzer using gas and liquid chromatographic separation and mass spectrometric and infrared detection techniques. The recoveries of sample weight, as degradation products, were quantitative over the entire temperature ranges studied (100–300, 300–570, 570–700, and 700–1000°C for pyrolysis; and 100–570 and 570–900°C for nonflaming oxidation). In pyrolysis, 17 volatile compounds were identified with NH₃ and CH₄ accounting for 94 and 57 mole % of the total mass loss between 300–570 and 570–700°C, respectively. Above 700°C, HCN and H₂ were formed from degradation of arylnitrile-containing oligomers. The thermal and oxidative degradation of three substituted benzimidazole monomers was also studied, and the relative ratios of N₂, NH₃, and HCN that were produced from each, when compared with PBI, support a mechanism for degradation that favors cleavages that least alter the conjugation of the polymer backbone. In the presence of air, PBI formed stable oxygen-containing residues that decomposed at high temperatures to N₂, CO₂, and H₂O almost exclusively. Large quantities of H₂ and N₂ from model compounds support results from PBI that suggest that degradation begins with total erosion of the imide ring at 570°C and the formation of more condensed heterocyclic species. These quantitative techniques are generally applicable to the study of all polymeric materials.     

Direct pyrolysis mass spectrometry studies on thermal degradation characteristics of poly(phenylene vinylene) with well-defined PSt side chains

Thermal degradation characteristics of a new macromonomer polystyrene with central 4,4′-dicarbaldehyde terphenyl moieties and poly(phenylene vinylene) with well-defined polystyrene (PPV/PSt) as lateral substituents were investigated via direct pyrolysis mass spectrometry. A slight increase in thermal stability of PSt was detected for (PPV/PSt) and attributed to higher thermal stability of PPV backbone. It was almost impossible to differentiate products due to the decomposition of PPV backbone from those produced by degradation of PSt.     

Polymers with indane units by cationic polymerization

In spite of the difunctionality of the monomers, cationic polymerization of 1,3- and 1,4-diisopropenylbenzene does not lead to branched or cross-linked products. Instead, soluble polymers are obtained, containing the 1,1,3-trimethylindane system as repetitive unit along the backbone. These polymers are interesting materials because of their high glass transition temperature (200°C-250°C) and good thermal stability in air (2% weight loss at 450°C). Although the molar mass of the polyindanes seems to be limited due to a side reaction, it is possible to produce telechelic polyindanes. Substitution of an alkyl side chain onto the isopropenyl groups of 1,4-diisopropenylbenzene leads to monomers which yield substituted polyindanes with glass transition temperatures as low as 26°C. Such polymers still exhibit good thermal stability: at 340°C a weight loss of only 2% occurs. 1,4-Diisopropenylbenzene can even be anionically polymerized to linear polymers. In this case, the resulting polymer possesses isopropenyl phenyl side groups, which can be used as initiators for cationic polymerization of isobutene to obtain grafted copolymers.     

The thermal degradation and oxidation of polybutadiene

Detailed studies have been made of the successive stages in the thermal degradation in air and nitrogen of carboxy-terminated polybutadiene (CTPB). During oxidation at high temperatures, a protective surface film is first formed; this film ruptures at temperatures where pyrolysis leads to the formation of volatile products in the bulk of the polymer. Thermogravimetric curves for the degradation of CTPB in nitrogen are complex in shape; it appears that the free-radical crosslinking and cyclisation reactions cause an increase in the thermal stability of the polymer during degradation.     

Interactions observed during the pyrolysis of binary mixtures of textile polymers

The techniques of differential thermal analysis (DTA), thermogravimetry (TG), large scale pyrolysis (LSP) and hot-stage microscopy (HSM) have been used to determine the pyrolysis behaviour of three binary polymer systems: wool/Terylene, wool/Courtelle and Terylene/Courtelle. Pyrolysis was carried out in a flowing nitrogen atmosphere at a heating rate of approximately 10°C min^?1.Evidence from DTA and TG indicates that the thermal stability of the polyester fibre Terylene is reduced when pyrolysed in the presence of either wool or Courtelle. It is considered that this reduction in thermal stability is the result of chemical interactions between Terylene and degradation products arising from the breakdown of the second polymer present. Unexpectedly high residual yields (at 1213 K) have been observed from LSP experiments on the wool/Courtelle and Terylene/Courtelle systems.HSM observations for these two systems indicate the formation of a coating of the fusing polymer around the non-fusing polymer during pyrolysis. TG studies indicate that this coating of fused polymer may be effective in retaining volatile degradation products from the non-fusing polymer within the solid residue. The eventual chemical bonding of these degradation products into the solid residue thus accounts for the unexpectedly high yields of solid residue observed by LSP.     

Pore structure of pyrolyzed scrap tires

Internal structure of carbon black produced by pyrolysis (CBp) of rubber samples from the top and bottom parts of sidewall and tread of a passenger car tire was investigated in nitrogen flow at different temperatures. The pore structure (specific surface area, pore size distribution, and porosity) of CBp and commercial CB, was compared. The development of pore structure and the increase of the specific surface area were most intensive during the thermal decomposition at temperatures ranging from 300°C to 500°C. This is caused by the intensive release of volatiles during the pyrolysis. After the pyrolysis was finished, at temperatures above 500°C, further decomposition of solid matter was associated with a slight increase of the specific surface area. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Phospha-s-triazines. IV. Degradation studies of 1-diarylphospha-3,5-bis(perfluoroaliphatic)-2,4,6-triazines and 1,3,-bis(diarylphospha)-5-perfluoroaliphatic-2,4,6-triazines

Thermal and thermal oxidative stability evaluations were performed on mono- and diphospha-s-triazines at 235 and 316°C using sealed Pyrex ampoules. The specific compounds studied were: 1-diphenylphospa-3,5-bis(perfluoro-n-heptyl)-2,4,6-triazine, 1-diphenylphospha-3,5-bis(perfluoro-alkylether)-2,4,6-triazines, their respective pentafluorophenyl analogues, 1,3-bis(diphenylphospha)-5-perfluoro-n-heptyl-2,4,6-triazine and 1,3-bis(diphenylphospha)-5-perfluoroalkylether-2,4,6-triazine. All the compounds wherein phenyl groups were present on the phosphorous exhibited good thermal stability up to 316°C; the analogous pentafluorophenyl substituted materials were degraded extensively at these temperatures. The oxidative stability of both the mono- and diphospha-s-triazines was excellent at 235°C, but at 316°C some degradation was observed. This was more pronounced in compounds containing the perfluoroalkyl moiety on carbon than in the perfluoroalkylether substituted members of the series.     

Exactly alternating silarylene–siloxane polymers. VII. Thermal stability and degradation behavior of p-silphenylene–siloxane polymers with methyl,vinyl, hydrido,and/or fluoroalkyl side groups

The thermal stability and degradation behavior of a series of nine different exactly alternating silphenylene-siloxane polymers which contained methyl, vinyl, hydrido, 3,3,3-trifluoropropyl, and tridecafluoro-1,1,2,2-tetrahydrooctyl side groups, or their combinations, were investigated by dynamic and isothermal gravimetric analyses in air and in nitrogen. Two distinctly different mechanisms were observed in these atmospheres: a complex multi-step weight loss process in air and a single-step process in nitrogen. In nitrogen all polymers produced black, insoluble, highly stable degradation residues which were characterized by high carbon content. In contrast, in air the nonfluorine containing polymers degraded to pure silica, while the fluoroalkyl substituted polymers may have formed fluorosilicates of unspecified structures. There appears to be no significant molecular weight effect on the thermal stability of these polymers, at least not above an M _w value of about 35,000. Isothermal investigations indicate that 300°C in air and 350°C in nitrogen may be possible upper use temperatures for the methylvinyl substituted, exactly alternating silphenylene–siloxane polymers for extended periods of time. A strong thermostabilizing effect by vinyl side groups on the degradation behavior of these polymers was established. The extent of stabilization depends on the content of vinyl units, but it can already be clearly seen at the 5 mol % vinyl level, and it increases exponentially with increasing vinyl concentration. In contrast to this behavior, by comparison with the parent all-methyl substituted, exactly alternating silphenylene–siloxane polymers, the hydrido and fluroalkyl side groups reduce overall polymer thermal stability in terms of the degradation onset temperature, the temperature for 50% weight loss, and the amount of degradation residue. The presence of these groups also extends the later stages of the degradation processes to higher temperatures. Based on these and previous results, an order of stability is proposed as a function of the type of the substituent side groups for the thermal degradation of these polymers.     

Novel flame‐retardant thermosets: Phosphine oxide‐containing diglycidylether as curing agent of phenolic novolac resins

Phosphorus‐containing novolac–epoxy systems were prepared from novolac resins and isobutyl bis(glycidylpropylether) phosphine oxide (IHPOGly) as crosslinking agent. Their curing behavior was studied and the thermal, thermomechanical, and flame‐retardant properties of the cured materials were measured. The T_g and decomposition temperatures of the resulting thermosets are moderate and decrease when the phosphorous content increases. Whereas the phosphorous species decrease the thermal stability, at higher temperatures the degradation rates are lower than the degradation rate of the phosphorous‐free resin. V‐O materials were obtained when the resins were tested for ignition resistance with the UL‐94 test. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3516–3526, 2004     

Pyrolysis of nuclear reactor circulator oil in carbon dioxide

The ingress of circulator oil into the carbon dioxide coolant of a nuclear reactor can cause problems such as the deposition of carbon on the fuel elements.This paper describes the first stage of degradation when oil is pyrolysed, in carbon dioxide at temperatures between 600 and 900°C, and in helium at 900°C, for 20s. The degradation products were determined using gas chromatography with either a selective carbon monoxide monitor or a flame ionization detector. The chromatograph was combined with a mass spectrometer for the identification of the degradation produces.Hydrogen, carbon monoxide and a wide range of hydrocarbons are the initial degradation products. The amounts of individual reaction product, and the total amount formed (P) increased with pyrolysis temperature, T, according and the total amount = 1/T. The sensitivity to temperature of product formation varied from one product to another. Formation of carbon monoxide was least sensitive to temperature.It is clear that a chemical reaction takes place between the oil and carbon dioxide since the total amounl of product produced is much greater in carbon dioxide than in helium and the relative amounts of product produced in carbon dioxide differ considerably from those produced by pyrolysis in helium: for example, no carbon monoxide is detected when the oil is pyrolysed in helium.     

Thermogravimetric investigation ofwastes from electrical and electronic equipment (WEEE)

Two components of electronic wastes (sample A – a mixture of three types of printed circuit boards, sample B – a mixture of electronic junctions with metal wires) were investigated using thermogravimetric analysis (TG). Thermogravimetric and derivative thermogravimetric data (TG and DTG) give information on the thermal stability of A and B samples and allows finding the correct conditions for their degradation using pyrolysis in an experimental system, built on the laboratory scale for utilization of hazardous wastes. X-ray fluorescence measurements prove that brominated flame retardant is present in sample A, whilst chlorinated flame retardant is a probable component of sample B. Preliminary liquid chromatography of oil products obtained as a result of thermal waste degradation shows that the hydrocarbons released during pyrolysis could be used as a fuel.     

Thermal decomposition of metal methanesulfonates in air

The thermal decompositions of dehydrated or anhydrous bivalent transition metal (Mn, Fe, Co, Ni, Cu, Zn, Cd) and alkali rare metal (Mg, Ca, Sr, Ba) methanesulfonates were studied by TG/DTG, IR and XRD techniques in dynamic Air at 250–850 °C. The initial decomposition temperatures were calculated from TG curves for each compound, which show the onsets of mass loss of methanesulfonates were above 400 °C. For transition metal methanesulfonates, the pyrolysis products at 850 °C were metal oxides. For alkali rare metal methanesulfonates, the pyrolysis products at 850 °C of Sr and Ba methanesulfonates were sulphates, while those of Mg and Ca methanesulfonate were mixtures of sulphate and oxide.     

Evaluation of physico-chemical properties and antimicrobial synergic effect of ceftazidime-modified chitosan

The aim of this work was to study the effect of tris(3-nitrophenyl) phosphine (NPPh3), which showed a good thermal stability and carbon-forming ability, on the flame retardancy and thermal degradation mechanism of epoxy resins. A series of diglycidyl ether of bisphenol A (DGEBA) loaded with tris(3-nitrophenyl) phosphine (NPPh3) were prepared. It was found that NPPh3 can effectively improve the flame retardancy and thermal stability of the composites. When the loading amount of NPPh3 was 14%, the LOI value of the DGEBA composites was 29.2% (about 1.53 times the corresponding value of the original DGEBA resin). Thermal stability was studied by thermogravimetric analysis, and the results showed that the addition of NPPh3 can improve char formation of this system both in nitrogen and in air atmosphere. Specifically, its combustion residue at 800 °C in nitrogen atmosphere was about 4.26 times of the original resin. Differential scanning calorimetry indicated that NPPh3 slightly decreased the glass transition temperature of epoxy resins. Additionally, the gaseous degradation products were analyzed by thermogravimetric analysis/infrared spectrometry, providing insight into the thermal degradation mechanism. Scanning electron microscopy and Fourier transform infrared were brought together to evaluate the morphology and structure of the residual char obtained after combustion.     

Thermal degradation mechanism of poly(arylene sulfone)s by stepwise Py‐GC/MS

The thermal degradation of poly(ether sulfone) (PES) and polysulfone (PSF) was studied with a combination of thermogravimetric analysis and stepwise pyrolysis–gas chromatography/mass spectrometry techniques with consecutive heating of the samples at fixed temperature intervals (100 °C) to achieve narrow‐temperature pyrolysis conditions. The individual mass chromatograms of various pyrolysates were correlated with pyrolysis temperatures to elucidate the pyrolysis mechanism. The major mechanism for both PES and PSF was a one‐stage pyrolysis involving main‐chain random scission and carbonization. The major products SO₂ and phenol were released from the sulfone and ether groups in PES. The major products SO₂, phenol, and 1‐methyl‐4‐phenoxybenzene were released from the sulfone, ether, and isopropylene groups in PSF. In the PES, the thermal stability of the sulfone and ether groups was identical to the maximum thermogravimetric loss rate. In the PSF, the thermal stability was in the following order: sulfone < ether < isopropylene. The temperature of the maximum thermogravimetric loss rate was similar to the maximum evolution of phenol. However, there was a considerable difference in the thermal behavior of both polymers; the correlation of the polymer structure to the degradation mechanism is discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 583–593, 2000