结晶性芳香聚酯高压结晶行为研究进展

运用高压极限手段研究聚合物的结构、形态和性能是20世纪60年代以来兴起的一项聚合物前沿课题。本文主要结合作者自己的研究工作，重点叙述聚对苯二甲酸乙二醇酯(PET)的高压结晶行为研究，包括温度、压力、时间及分子量对PET高压结晶行为的影响，高压结晶PET的形态。以及对PET伸直链晶体结晶机理的探讨，同时简要介绍了对其它结晶性芳香聚酯诸如聚对苯二甲酸丁二醇酯(PBT)及聚对萘二甲酸乙二醇酯(PEN)的高压结晶行为研究，反映了该领域的研究概况和最新进展。并对今后的研究提出了展望。     

Some Comments on a Recent Article Dealing with Three Aliphatic-Aromatic Polyesters and Their Spectral Identification

This work discusses the results appearing in Wu et al.’s (2014) article dealing with three aliphatic-aromatic polyesters based on terephthalic acid and their spectral identification. Using an instrument equipped with a switch that allows ions with masses below 5 kDa to be discarded (ion deflector), the authors report the MALDI spectrum of a commercial poly(ethylene terephthalate) with signals up to 80 kDa. I plot the spectral intensities and fit them with a Gaussian curve. The result is carefully examined. Thereafter, attention is moved to the MALDI spectra obtained when the ion deflector is turned off. A computation that gives the number-average and the weight-average molar mass (Mn and Mw) was performed, but the result was Mn = 1362 g/mol and Mw = 1416 g/mol. These values are much too low and they cannot be used. In order to explain this failure, I modified a model developed for poly(pentylene adipate). This hypothesis is discarded and the correct explanation is found. I also discuss other types of instrumentation, for instance, Py-GC/MS combined with library-search and also NMR spectroscopy, with specific reference to the chemical shifts of the -CH2- protons in aliphatic-aromatic polyesters.     

Mechanism of Xylan Pyrolysis by Py-GC/MS

In order to investigate the decomposition behavior of hemicellulose, xylan was chosen as the representative of hemicellulose to study the fast pyrolysis on the combination system of analytical pyrolyzer and gas chromatograph coupled with mass spectrometer(Py-GC/MS). The main condensable products of xylan pyrolysis consisted of acids, aldehydes, and ketones; while gas products contained CO₂, CO, CH₄ and H₂. Acetic acid and furfural were the most abundant products with the highest contents of 20.11% and 20.24% respectively. While furfural and acetic acid were formed competitively with residence time and temperature increases, the distribution of xylan pyrolysis products did not vary with the residence time and temperature, while the total content of several kinds of products changed a lot. According to the analysis of experimental data, a reaction pathway of xylan decomposition was deduced so as to illustrate the formation mechanism of main products.     

PBT／PET共混体系非晶区的相容性

利用ＰＢＴ、ＰＥＴ的特性参数，通过不同组份比ＰＢＴ／ＰＥＴ共混体系的混合自由能△Ｇｍ，从理论上预测其相容性。在一定的条件下△Ｇｍ＜０，ＰＢＴ、ＰＥＴ可以相容。对不同组份比共混体系的玻璃化转变过程从分子链段运动的角度进行分析。     

Isothermal melt-crystallization and melting behavior for three linear aromatic polyesters

Isothermal crystallization and subsequent melting behavior for three different types of linear aromatic polyester, namely poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and poly(butylene terephthalate) (PBT), were investigated (with an emphasis on PTT in comparison with PET and PBT). These polyesters were different in the number of methylene groups (i.e. 2, 3, and 4 for PET, PTT, and PBT, respectively). Isothermal crystallization studies were carried out in a differential scanning calorimeter (DSC) over the crystallization temperature range of 182-208 °C. The wide-angle X-ray diffraction (WAXD) technique was used to obtain information about crystal modification and apparent degree of crystallinity. The kinetics of the crystallization process was assessed by a direct fitting of the experimental data to the Avrami, Tobin, and Malkin macrokinetic models. It was found that the crystallization rates of these polyesters were in the following order: PBT>PTT>PET, and the melting of these polyesters exhibited multiple-melting phenomenon. Lastly, the equilibrium melting temperature for these polyesters was estimated based on the linear and non-linear Hoffman-Weeks (LHW and NLHW) extrapolative methods.     

利用Py-GC/MS研究温度和时间对生物质热解的影响

以稻壳为原料,采用Py-GC/MS装置对其在不同热解条件下进行快速热解,并对热解气进行在线检测分析,考察了热解温度和时间对生物质热解性质的影响.结果表明,低于450 ℃,随着温度的升高,生物质热解产物种类及其产率均增加,但低温条件下产物种类较少,有利于产物的分离提纯;高于450 ℃,生物质热解产物种类基本稳定,仅在产率上有所变化,当550 ℃时,收率最大.随着热解温度的升高,其对应的最佳热解时间缩短,且生物质低温热解时间延长时热解比高温解热时间缩短时热解更充分.     

Inhibited transesterification of PET/PBT blends filled with silica nanoparticles during melt processing

The blends of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) undergo transesterification reactions between PET and PBT during melt processing. In this research, PET/PBT transesterification has been investigated in the presence of nano-fillers, including pure SiO₂ and silane-coupling-agent-modified SiO₂. The results show that the incorporation of SiO₂ nanoparticles inhibits PET/PBT transesterification, and the influence of pure SiO₂ is higher than modified SiO₂. The inhibition of SiO₂ on transesterification is explained by the fact that the hydroxyl end groups of PET and PBT react with the surface hydroxyl groups of SiO₂ before transesterification due to the high activity of surface hydroxyl groups of SiO₂, and the reduction of hydroxyl end groups of PET and PBT leads to the inhibition of transesterification between PET and PBT. This has been demonstrated by the experimental data of TGA, FTIR, and XPS. And the reactivity of hydroxyl end groups of PBT is higher than that of PET.     

Poly(10-undecene-1-ol) characterized by MALDI-TOF MS and NMR spectroscopy

Poly(10-undecene-1-ol)s were synthesized by metallocene-catalyzed polymerization. MALDI-TOF MS allows obtaining detailed information on the monomer units in the polymer chains and the nature of the head and end groups of these polymers in dependence on the Al alkyl triisobutyl aluminum (TIBA) as well as methylalumoxan (MAO), both used as protecting agent for the hydroxyl groups of the monomer. The peak-to-peak distances of the main peaks could be distinctly assigned to the monomer unit 10-undecene-1-ol. Evaluating the MALDI-TOF peak distributions, polymers with -H, -C₄H₉, -CH₃ head groups in combination with vinylidene and saturated (–CH₃) end groups could be detected. By ¹H NMR spectroscopy, it was verified that with the used catalysts polymers with vinylidene end groups were obtained predominantly. The presence of saturated end groups could be proved qualitatively by combination of ¹H and ¹³C NMR spectroscopy for polymers produced by TIBA protection, which strikingly confirm the results from MALDI-TOF MS. For the polymers prepared with only MAO protection, saturated groups are also proved but discrimination between head and end groups was not possible. A polymerization mechanism corresponding to the detected different head and end groups is proposed.     

碳纳米管对聚酯相容共混体系酯交换反应的影响

采用熔融共混制备了聚对苯二甲酸丙二酯(PTT)/聚对苯二甲酸丁二酯(PBT)共混体系以及碳纳米管(C NTs)填充改性的三元复合体系,通过核磁共振波谱仪(NMR)研究了CNTs对共混基体组分间酯交换反应的影响,并结合透射电子显微镜( TEM)、沉降实验等多种测试结果初步探讨了影响的机理.研究结果表明,PTT/PBT为典...     

PTT/PET共混体系晶体形态与结晶性能的研究

用差示扫描量热仪(DSC)、广角X射线衍射(WAXD)和正交偏光显微镜研究了聚对苯二甲酸丙二酯(PTT)和聚对苯二甲酸乙二酯(PET)共混体系的晶体形态与结晶性能.结果表明,共混体系结晶性能与PTT的含量有关.PET的加入,使共混体系的球晶尺寸减小.球晶完善性降低.当PTT含量为40wt%～60wt%时,共混物分别出现了双重熔融峰和双重结晶峰.双重熔融峰是加热过程中熔融重结晶造成的,双重结晶峰说明不完善的晶体产生的次级结晶.     

Thermal and crystallization characteristics of poly(trimethylene terephthalate)/poly(ethylene naphthalate) blends

Poly(trimethylene terephthalate) (PTT)/poly(ethylene naphthalate) (PEN) blends were miscible in the amorphous state in all of the blend compositions studied, as evidenced by a single, composition-dependent glass transition temperature (T_g) observed for each blend composition. The variation in the T_g value with the blend composition was well predicted by the Gordon-Taylor equation, with the fitting parameter being 0.57. The cold-crystallization peak temperature decreased with increasing PTT content, while the melt-crystallization peak temperature decreased with increasing amount of the minor component. The subsequent melting behavior after both cold- and melt-crystallization exhibited melting point depression, in which the observed melting temperatures decreased with increasing amount of the minor component. During melt-crystallization, both components in the blends crystallized concurrently just to form their own crystals. The blend with 60% w/w of PTT exhibited the lowest total apparent degree of crystallinity.     

Structure and properties of new polyester elastomers composed of poly(trimethylene terephthalate) and poly(ethylene oxide)

Series of PTT-b-PEO copolymers with different composition of rigid PTT and PEO flexible segments were synthesized from dimethyl terephthalate (DMT), 1,3-propanediol (PDO), poly(ethylene glycol) (PEG, M_n = 1000 g/mol) in a two stage process involving transesterification and polycondensation in the melt. The weight fraction of flexible segments was varied between 20 and 70 wt%. The molecular structure of synthesized copolymers was confirmed by ¹H NMR and ¹³C NMR spectroscopy. The superstructure of these polymers was characterized by DSC, DMTA, WAXS and SAXS measurements. It was observed that domains of three types can exist in PTT-b-PEOT copolymers: semi-crystalline PTT, amorphous PEO rich phase (amorphous PEO/PTT blended phase) and semi-crystalline PEO phase. Semi-crystalline PEO phase was observed only at temperature below 0 °C for sample containing the highest concentration of PEO segment. The phase structure, thermal and mechanical properties are effected by copolymer composition. The copolymers containing 30÷70 wt% of PEO segment posses good thermoplastic elastomers properties with high thermal stability. Hardness and tensile strength rise with increase of PTT content in copolymers.     

聚对苯二甲酸丁二酯/聚对苯二甲酸乙二酯固态缩聚的研究

研究了聚对苯二甲酸丁二酯(PBT)/聚对苯二甲酸乙二酯(PET)共混物的固态缩聚反应,从反应动力学过程的测定结果,表明与纯PET或PBT不同,其反应速度较快,并呈超加和的相对分子质量(以特性粘数[η]表征)增长。从反应发生在液相的基本观点出发,说明温度、共混等使液相增多,将加速反应的进行,加上共混物之间的相互缩聚和酯交换,生成嵌段共聚物的结果,导致超加和效应。     

Characterization of cross-linking structure in terephthalate polyesters formed through material recycling process by pyrolysis-gas chromatography in the presence of organic alkali

Typical terephthalate polyesters such as poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) were characterized by pyrolysis-gas chromatography (Py-GC) in the presence of tetramethylammonium hydroxide in terms of the cross-linking structure formed during their material recycling. In the pyrograms of PBT and PET thermally treated at 270 °C for 1 h, which were prepared as model polymers containing cross-linking structures, an additional peak was commonly observed as well as the main reactive pyrolysis products for the original polyesters such as dimethyl terephthalate. Based on the observed spectra obtained by Py-GC/mass spectrometry and Py-GC/Fourier transform infrared spectrometry measurements, this peak was assigned to the product reflecting a biphenyl-type cross-linking structure. Furthermore, in the pyrograms of kneaded PBT and PET samples also at 270 °C for a total of 1 h, which were prepared to simulate material recycling, the same peak for the cross-linking structure was also observed, although its intensity was slightly lower than that in the samples thermally treated in air. This fact verified that the biphenyl-type cross-linking structure would be considerably formed during the recycling of PBT and PET, which might in turn contribute to the deteriorated properties of the recycled materials from waste polyesters. Moreover, difference in the formation of the cross-linking between PBT and PET is discussed on the basis of the observed results.     

Accelerated and Natural Aging of Cellulose-Based Paper: Py-GC/MS Method

Samples of papers artificially (2 to 60 days) and naturally (10, 45, and 56 years) aged were studied by the Py-GC/MS method to identify decomposition products. Possible reaction scenarios for cellulose degradation were developed. One of the degradation products is acetic acid, which can (auto)catalyze the cleavage of cellulose β(1→4)-glycosidic bonds of cellulose polymer chains. However, during 20 s of Py-GC/MS analysis, temperatures of up to 300 °C did not significantly increase or modify the formation of decomposition products of paper components. At 300 °C, the amount of several cellulose decomposition products increased regularly depending on the number of days of artificial aging and natural aging, demonstrated mainly by the generation of 2-furancarboxaldehyde, 5-hydroxymethylfurfural, and levoglucosan and its consecutive dehydration products. No correlation between the amount of lignin decomposition products and the time of aging was found when the pyrolysis was performed at 300 °C and 500 °C. Compounds present in the products of decomposition at 500 °C bear the imprint of the chemical composition of the sampled paper. Pyrograms taken at 300 °C using the Py-GC/MS method can give additional information on the changes in the chemical structure of paper during natural or artificial aging, mainly about the cleavage of β(1→4)-glycosidic bonds during aging.     

磷酸三苯酯对PBT／PET共混体系结晶行为的影响

用广角Ｘ－角线衍射法和差法扫描量热法研究了磷酸三苯酯对ＰＢＴ／ＰＥＴ共混体系结晶行为影响，结果表明：ＴＰＰＷ作为该共混体系的稳定剂，只能延长在熔融状态下酯交换反应发生的时间，ＴＰＰ含量一定时，熔融时间增加，ＰＢＴ，ＰＥＴ之间的酯交换反应同样会发生，不同熔融时间，就要求ＴＰＰ的用量也不相同。ＴＰＰ在ＰＢＴ／ＰＥＴ共混体系中没有结晶成核剂的作用，它也不改变ＰＢＴ，ＰＥＴ的结晶结构。     

MALDI-TOF/TOF CID study of 4-alkyl-substituted polystyrene fragmentation reactions

MALDI-TOF/TOF CID experiments were conducted on a variety of hydrogen-terminated poly(4-methylstyrene), hydroxylated poly(t-butylstyrene), and polystyrene precursor ions: n = 10, 15, 20, 25, and 30, where the number of repeat units n corresponds to the oligomer mass number. The influences of structure, molecular weight, and effective collision kinetic energy on degradation mechanisms were examined to test the generality of our multi-chain fragmentation model developed for polystyrene. Each depolymerization mechanism is presented in detail with experimental and computational data to justify/rationalize its occurrence and effective kinetic energy dependence. These processes show the complex interrelationship between the various pathways along with preferred production of secondary radicals, which suppresses the appearance of primary radicals. Additionally, Py-GC/MS experimental data are presented, for comparison of the multimolecular free radical reactions in pyrolysis with the unimolecular fragmentation reactions of MS/MS. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A comparative study on transreactions induced phase changes in blends of poly(trimethylene terephthalate) and poly(ethylene naphthalate) upon annealing

By using wide-angle X-ray diffraction (WAXD), thermal analysis, scanning and optical microscopy, and nuclear magnetic resonance (NMR) analyses, this study has demonstrated that blends of two semicrystalline polyesters, poly(trimethylene terephthalate) and poly(ethylene naphthalate) (PTT/PEN), were initially immiscible in as-blended state. The process of blend phase/morphology changes upon extended heating/annealing at elevated temperatures was monitored and probed. With reactions induced at heating/annealing at high temperatures (300°C) for long enough times, the original two phases quickly merged into a single phase. NMR analyses have shown that the products of the transreactions are identified as the random copolyesters (termed as EN-TT). From the NMR results, statistical analyses revealed that the average sequence lengths decreased upon heating, and the degree of chain randomness increased with time of heating at the fixed temperature. Upon extended heating, all PTT and PEN chains could be fully transformed into random copolymers of higher randomness with only a single but amorphous phase. Results are compared to another blend system comprised of PEN and a homologous polyester, PPT, of different structure. Influence of polyester structure on transreactions and phase homogenization process is analyzed.     

Transreactions in poly trimethylene terephthalate/bisphenol-A polycarbonate (PC) blends analysed by pressure-volume-temperature measurements

The effect of annealing on the miscibility and thermal properties of poly trimethylene terephthalate (PTT)/bisphenol-A polycarbonate (PC) blends was examined using pressure-volume-temperature (PVT) measurements. The PTT/PC blends were thermally annealed at 260 °C for different times to induce various extents of transesterification reactions between the two polymers. The non-annealed blends are immiscible and exhibit the thermal properties of the blend components. Upon annealing, the original semi-crystalline morphology transforms to an increasingly amorphous nature. PVT and WAXS analysis confirmed that the PTT/PC blends completely lost their crystallinity when annealed at 260 °C for a period of 120 min or longer, indicating the formation of random co-polyesters due to chemical transreactions between the PTT and PC. The further increase in the specific volume with annealing time also indicates that after reaching a completely amorphous co-polymer the transesterification continuous until a fully random copolymer is formed.     

用X-射线衍射法测定聚对苯二甲酸乙二醇酯/聚对苯二甲酸丁二醇酯共混体系的结晶度

结晶度是表征聚合物性质的重要参数,它对聚合物的物理和机械性能有很大影响,在测定聚合物的结晶度的各种方法中,X-射线衍射法的意义明确且应用最为广泛。然而,用X-射线衍射法测定聚合物结晶度绝大部分只限于单组份体系,用于共混体系的报道尚不