聚碳酸酯热降解与稳定性的研究进展

综述了聚碳酸酯(PC)热稳定性影响因素;阐述了聚碳酸酯热降解产物和热降解机理;介绍了聚碳酸酯端基、摩尔质量及其分布、添加剂等对聚碳酸酯热稳定性的影响;并讨论了提高聚碳酸酯热稳定性的途径及方法.     

热氧老化对氮气气氛下聚碳酸酯热稳定性的影响

采用热空气加速聚碳酸酯(PC)老化的方式进行不同时间下的老化实验,然后在氮气气氛下进行热失重分析,并用Coats-Redfern法和Freeman-Carroll法进行热分解动力学分析。结果表明:老化初期,PC起始分解温度、半失重温度和最大失重温度以及热降解活化能均呈下降趋势;PC的热稳定性下降,主要发生断链和端基脱落;老化后期,PC的起始分解温度、半失重温度和最大失重温度以及热降解活化能又均增大,因PC的交联可使其热稳定性有所提高。     

含抗氧剂聚碳酸酯的制备及降解性能研究

通过在聚碳酸酯(PC)中加入不同抗氧剂以提高其热稳定性,研究了抗氧剂的种类、用量、环境条件对PC热稳定件能和降解动力学的影响.结果发现,加入复配抗氧剂能显著提高PC的热稳定性能.在有氧气情况下,抗氧剂的质昔分数增至0.6%时,起始降解温度(以降解率达到5%时的温度计)从原来的472.1℃增加至500.4℃,而最大降解温度(降解速率最大温度)也从原来的530.3℃增加至546.4℃,并应用改良Coats-Redfem法对PC降解动力学做了分析.     

聚碳酸酯热分解特性及其与热释放的关系

研究了多种聚碳酸酯材料的热分解特性,考察了其热分解特性与热释放的关系。结果表明,在空气条件下聚碳酸酯材料都表现出了两个阶段分解的特性,氧气会导致聚碳酸酯材料热稳定性降低和炭层氧化。溴系阻燃剂的加入会导致聚碳酸酯的热失重峰值温度(DWPT)提高,这意味着峰值出现的时间将延后,效果以溴系阻燃剂PBBC最为明显。硅氧烷成分的加入有助于提高聚碳酸酯的耐热性和成炭性,显著降低热释放,但是会提高质量热损失峰值速率(DWPV)。碳酸钙的加入不但会降低聚碳酸酯的耐热性和成炭性,而其同时降低DWPV。硅氧烷成分和碳酸钙同时加入对降低DWPV具有显著的协同作用。添加20%溴系阻燃剂PBBC可以显著降低聚碳酸酯热释放峰值(PHRR)、2min热释放总量(THR)和DWPV,添加碳酸钙能够使DWPV进一步降低,但是对降低热释放没有任何帮助,反而会导致THR显著增加。这也说明,DWPV的降低并不一定导致材料的PHRR和THR也同时降低。     

PC/纳米SiO2复合材料的热降解行为

采用熔融共混法制备了聚碳酸酯(PC)/纳米二氧化硅(SiO2)复合材料。采用X射线衍射和扫描电子显微镜研究了PC和PC/纳米SiO2复合材料的结构,采用热重分析了PC和PC/纳米SiO2复合材料的热降解行为,用Kissinger-Akahira-Sunose法研究了PC和PC/纳米SiO2复合材料的热降解动力学。结果表明:PC的内部结构没有发生变化,且纳米SiO2在基体中分散均匀;加入纳米SiO2能显著改善PC的热稳定性,且PC和PC/纳米SiO2复合材料的热降解温度均随升温速率提高呈线性增加;PC和PC/纳米SiO2复合材料的热降解活化能均随转化率升高而增加,且PC/纳米SiO2复合材料的活化能明显高于PC。     

塑料降解与稳定化（Ⅱ）：热降解与热稳定（中）

2塑料热稳定 2．1提高塑料热稳定性的可能途径 2．1．1添加热稳定剂 大量研究和实践表明,对于常规的使用条件．添加“热稳定剂”是抑制塑料热降廨、提高其热稳定性的最经济有效方法。显然,由于不同塑料的具体热降解机理不同,因此热稳定剂也各不相同。但是概括起来,塑料热稳定剂至少应具有以下三种功能之一：     

二氧化碳／环氧氯丙烷共聚物的热降解动力学研究

二氧化碳（ＣＯ２）和环氧氯丙烷（ＥＣＨ）在稀土络合催化体系作用下共聚反应,合成出脂肪族聚碳酸酯（ＥＣＨＣＯ２）。采用热重分析法研究了共聚物ＥＣＨＣＯ２热降解反应的动力学,测定了不同升温速率下共聚物的热降解过程,并计算出其降解反应级数和活化能。     

浅析聚甲基丙烯酸甲酯的热降解研究

概述了有关PMMA热解研究的情况,着重阐述了PMMA在无氧及有氧条件下的热解机理,介绍了近年来有关PMMA热解动力学和稳定性方面的研究内容以及今后的发展方向。     

铝试剂热氧降解历程的研究

本文采用热重法（ＴＧ）、微分热重法（ＤＴＧ）和差热分析法（ＤＴＡ）研究铝试剂（Ｃ２２Ｈ２３Ｎ３Ｏ９）在空气流中的热氧降解历程，从而发现铝试剂的热氧降解历程由四个紧连步骤组成。     

含氯聚合物的热稳定和热降解

综述了部分含氯聚合物的热稳定性和热降解研究进展，着重介绍了氯化聚乙烯、聚偏氯乙烯、氯磺化聚乙烯、氯丁橡胶、氯化天然橡胶、氯化聚丙烯等受热脱氯化氢的过程和机理，针对上述含氯聚合物材料的热稳定和热降解，运用现代分析方法，如：差示扫描量热法、差热分析、热重分析法等进行了研究。     

Thermal degradation of bisphenol A polycarbonate by high-resolution thermogravimetry

Thermal degradation of bisphenol A polycarbonate (PC) has been studied in nitrogen and air from room temperature to 900 °C by high-resolution thermogravimetry (TG) with a variable heating rate in response to changes in the sample's degradation rate. A three-step (in nitrogen) or four-step (in air) degradation process of the PC, which was hardly ever revealed by traditional TG, has been found. The initial thermal degradation temperature of the PC is higher in nitrogen than in air, but the three kinetic parameters (activation energy E, decomposition order n, frequency factor Z) of the major degradation process are slightly lower in nitrogen. The average E, n and lnZ values determined by three methods in nitrogen are 154 KJ mol⁻¹, 0.8 and 21 min⁻¹, respectively, which are almost the same as those calculated by traditional TG measurements. © 1999 Society of Chemical Industry     

Thermal degradation kinetics and lifetime estimation for polycarbonate/polymethylphenylsilsesquioxane composite

The thermal degradation behaviors of polycarbonate/polymethylphenylsilsesquioxane (FRPC) composites were investigated by thermogravimetric analysis (TGA) under isothermal conditions in nitrogen atmosphere. The isothermal kinetics equation was used to describe the thermal degradation process. The results showed that activation energy (E), in the case of isothermal degradation, was a quick increasing function of conversion (α) for polycarbonate (PC) but was a strong and decreasing function of conversion for FRPC. Under the isothermal condition, the addition of polymethylphenylsilsesquioxane (PMPSQ) retardanted the thermal degradation and enhanced the thermal stability of PC during the early and middle stages of thermal degradation. It also indicated a possible existence of a difference in nucleation, nuclei growth, and gas diffusion mechanism in the thermal degradation process between PC and FRPC. Meanwhile, the addition of PMPSQ influenced the lifetime of PC, but the composite still met the demand in manufacturing and application.     

Synthesis,characterization, and degradation of a novel L‐tyrosine‐derived polycarbonate for potential biomaterial applications

A novel class of pseudo‐poly(amino acid)s was synthesized with a cyclic dipeptide as new diphenole. Nonpeptide bonds alternating with a peptide bond structure were introduced into the backbone of the pseudo‐poly(amino acid)s. The cyclic dipeptide in this study was obtained from natural L ‐tyrosine. L ‐Tyrosine is a major nutrient amino acid with a phenolic hydroxyl group, so a polycarbonate derived from the cyclic dipeptide should possess more optimum mechanical properties, bioactivity, and biocompatibility. The hydrolytic specimen of the resulting polycarbonate was prepared by a modified solvent evaporation process. Under strongly alkaline conditions, degradation testing was performed. The tyrosine‐derived polycarbonate possessed a low glass‐transition temperature value and a high thermal decomposition temperature value, which formed a broad mean thermal processing range. The most important results of our study were the effects of the polycarbonate degradation on the local pH values, which were smaller than those of other biodegradable polymers [e.g., poly(lactic acid), poly(glycolic acid), and poly(lactic glycolic acid)]. The synthesized polymer and cyclic dipeptide were characterized with Fourier transform infrared, ¹³C‐NMR, and ¹H‐NMR spectroscopy to determine their chemical structures; by differential scanning calorimetry and thermogravimetric analysis to determine the thermal properties of the polymer; by gel permeation chromatography to determine the polymer's molecular weight; and by X‐ray diffraction to determine the polymer's morphology. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Exactly alternating silarylene—siloxane polymers: 6. Thermal stability and degradation behaviour

The thermal stability and degradation behaviour of a series of twelve different exactly alternating silarylene—siloxane polymers were investigated by several different methods including thermal gravimetric analysis (t.g.a.) in air and in nitrogen, long term (up to 48 h) high temperature (600° and 900°C) isothermal degradation in nitrogen, and rapid pyrolysis in helium. No weight loss was observed by t.g.a. until about 400°C, and two distinctly different mechanisms were observed, one for degradation in nitrogen (a single step process), and the other in air (a three step process). Under nitrogen, black, insoluble, carbon-hydrogen-silicon containing degradation products were obtained, which were stable in pure oxygen to at least 1100°C. In air, pure SiO₂ was obtained after heating to above 730°C. Isothermal investigations revealed that at temperatures of 600°C and above, weight loss by thermal degradation under a nitrogen atmosphere was completed in less than an hour, and the polymeric products which remained thereafter did not change any further even after 48 h at 900°C.     

Thermal stability and degradation mechanism of C60 fullerene-based polymers

In this paper, the thermal stability and degradation mechanisms of C₆₀ fullerene-based polymers, obtained by click polymerization between dialkyne-substituted C₆₀ derivative monomers and 1,3,5-tris(dodecyloxy)benzene-based diazide comonomers, were evaluated. The activation energy of the fullerene polymer C₆₀P2 with an ethylene spacer, determined under peak degradation rate conditions, was lower than that of the counter polymer C₆₀P1 with a methylene spacer, suggesting lower thermal stability of C₆₀P2. The combined technique of thermogravimetric analysis—mass spectroscopy and Fourier transform infrared spectroscopy revealed that the thermal decomposition onset of the analyzed samples is accompanied by C C cleavage of the dodecyloxyside chain groups, followed by the decomposition of the 1,2,3-triazole, dicarboxylate and benzoate moieties. It was found that no thermal decomposition of the fullerene carbon cage occurs up to 670°C. Molecular modeling with Hyperchem software version 7.5 confirmed that C₆₀P1 is more thermally stable than C₆₀P2.     

Noncovalent functionalization of boron nitride and its effect on the thermal conductivity of polycarbonate composites

Polycarbonate (PC) is an engineering thermoplastic with excellent insulation and mechanical properties. However, the low thermal conductivity restricted its application in electronic devices. Hexagonal boron nitride (h ‐BN) microparticle, a promising material with high thermal conductivity, was functionalized with cationic polyacrylamide (CPAM) and introduced into PC matrix to improve the thermal conductivity. SEM and XRD analysis showed that the modified BN (CBN) particles oriented and formed thermal conductive pathways within PC matrix. The formation of large‐area oriented CBN significantly improved the thermal conductivity and thermal stability of composites. At 20 wt % CBN loading, the thermal conductivity of 0.7341 Wm^?1 K^?1 and the temperature for 5% weight loss (T ₅) of 498.6 °C were obtained, which was 3.1 times and 77 °C higher than that of pure PC, respectively. Furthermore, outstanding electrical insulation property of matrix was retained in the composites. These results revealed that PC/CBN composite was a promising material for thermal management and electrical enclosure. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44978.     

A structural model of an accessibility of polycarbonate melt to thermooxidative degradation processes

It is shown that the “accessibility” of a polymer for oxidation is the only structural factor and quantitative estimate within the framework of the fractional derivation. The oxidation rate of the “accessible” part of a macromolecular coil is independent on its structure, which allows to assume its dependence only on the chemical constitution of polymer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 3765–3768, 2006     

Novel intumescent flame retardants: synthesis and application in polycarbonate

Novel phosphorus‐containing and nitrogen‐containing intumescent flame retardants, bis‐aminobenzyl spirocylic pentaerythritol bisphosphonate (BASPB) and arylene‐N,N′‐bis(2,2‐dimethyl‐1,3‐propanediol phosphoramidate) (ABDPP), were synthesized, and their structures were characterized with Fourier transform infrared spectroscopy and ¹H and ³¹P nuclear magnetic resonance. The phosphorus compounds were used to impart flame retardancy to polycarbonate (PC). Combustion behaviors and thermal degradation properties of the flame‐retarded‐PC composites were assayed by limiting oxygen index (LOI), vertical burning test (UL‐94), cone calorimeter test, and thermogravimetric analysis. PC/5 wt.% BASPB and PC/5 wt.% ABDPP composites passed UL‐94 V‐0 rating; their LOI values were 35.5% and 34.7%, respectively. Scanning electron microscopy revealed that the char properties had crucial effects on the flame retardancy. The mechanical properties and water resistance of the PC/BASPB and PC/ABDPP composites were also measured. After water resistance test, PC/5 wt.% BASPB and PC/5 wt.% ABDPP composites kept V‐0 rating, and the mass loss was only 1.0%. Copyright © 2012 John Wiley & Sons, Ltd.