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.     

Mixed Organo/Oxide Chromium Polymerization Catalysts

Supported chromium oxide catalysts are activated by calcination in dry air at 400–900°C, which dehydrates the carrier and binds chromium(VI) to the surface. A reduction by ethylene then provides the active species. Alternatively, the carrier can be calcined alone and afterward impregnated with an organochromium compound. Both procedures can produce an active catalyst for ethylene polymerization, but the two types differ considerably in their behavior. A third type is made by reacting an organochromium compound with the activated chromium oxide catalyst. This “mixed” catalyst displays some of the characteristics of both parents, but is not a simple combination of the two.     

Primary thermal degradation processes occurring in poly(phenylenesulfide) investigated by direct pyrolysis–mass spectrometry

The thermal degradation Processes which occur in poly(phenylenesulfide) (PPS) have been studied by direct pyrolysis-mass spectrometry (DPMS). The structure of the compounds evolved in the overall temperature range of PPS decomposition (400–700°C) suggests the occurrence of several thermal decomposition steps. At the onset of the thermal degradation (430–450°C) this polymer decomposes with the formation of cyclic oligomers, generated by a simple cylization mechanism either initiated at the—SH end groups or by the exchange between the inner sulfur atoms along the polymer chain. At higher temperature (> 500°C) another decomposition reaction takes over with the formation of aromatic linear thiols. The formation of thiodibenzofuran units by a subsequent dehydrogenation reaction occurs in the temperature range of 550–650°C; in fact, pyrolysis products with a quasi-ladder structure have also been detected. Ultimately, above 600°C, extrusion of sulfur from the pyrolysis residue occurs with the maximum evolution at the end of decomposition (about 700°C). It appears, therefore, that the residue obtained at high temperature tends to have a crosslinked graphite-like structure from which the bonded sulfur is extruded. © 1994 John Wiley & Sons, Inc.     

Chemical reactions occurring in the thermal treatment of polymer blends investigated by direct pyrolysis mass spectrometry: Polycarbonate/polybuthyleneterephthalate

The chemical reactions occurring in the thermal treatment of polycarbonate/polybuthyleneterephthalate (PC/PBT) blends have been investigated by gradual heating (10°C/min) using thermogravimetry and direct pyrolysis into the mass spectrometer. Exchange reactions occur already in the temperature range below 300°C but the transesterification equilibrium is affected by the evolution of thermal degradation products. Buthylenecarbonate, was detected in the first decomposition stage (320–380°C), which is evolved together with a series of cyclic compounds containing units of PC and PBT, in varying ratios. The overall thermal reaction evolves towards the formation of the most thermally stable polymer, i.e., a totally aromatic polyester (polymer III , Table I), which was found to be the end-product of the thermal processes occurring in the system investigated. The thermal decomposition products obtained from the PC/PBT blends in the range 320–600°C have mass sufficiently high to be structurally significant, since they contain at least one copolymer repeating unit. The reactions occurring in the thermal treatment of the PC/PBT blend are discussed in detail. © 1993 John Wiley & Sons, Inc.     

A Rheological Approach to the Analysis of Plastication Influence on Fibers Breakage of LGF-filled Polypropylene

Summary: Long glass fiber-filled polypropylene composites are widely used in industry because of their low cost and high performance. To investigate the rheological properties of such composites in the molten state an in-line slit-die rheometer was developed and mounted on an injection molding machine. The shear viscosity of filled PP determined by the in-line rheometer was found to strongly depend on the fiber length distribution. In particular, a linear correlation was determined between the viscosity at a constant temperature and shear rate and the average fiber length equation proposed by Huq and Azaiez. The developed model and the in-line rheometer were then used to assess the effects of the main plastication parameters (i.e. screw rotation speed and backpressure) on fibers damage. The experiments were carried out according to a central composite design and optimal plastication conditions were determined by means of the response surface method.     

Degradation of Poly(methyl methacrylate) Model Compounds at Constant Elevated Temperature Studied via High Resolution Electrospray Ionization Mass Spectrometry (ESI‐MS)

The products of the thermal degradation at 95 °C over 10 months of ω‐saturated and non‐saturated poly(methyl methacrylate) (pMMA) model compounds were identified with high accuracy via quadrupole ion trap and quadrupole ion trap‐time of flight (Q‐ToF) mass spectrometry. Analysis of the samples taken via these techniques indicated that degradation of vinyl terminated pMMA proceeds via the incorporation of oxygen via the formation of ethylene oxide type end groups, which subsequently rearrange under the expulsion of formaldehyde and 2‐oxo‐propionic acid methyl ester. The corresponding saturated model compounds were demonstrated to be stable over the same time period. The present findings highlight for the first time that poly(methyl methacrylate) degradation does not necessarily and exclusively proceed via radical intermediates.

     

Chemical reactions occurring in the thermal treatment of PC/PMMA blends

The chemical reactions occurring in the thermal treatment of bisphenol-A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) blends have been investigated by nuclear magnetic resonance (NMR), mass spectrometry (MS), size exclusion chromatography (SEC), and thermogravimetry (TG). Our results suggest that in the melt-mixing of PC/PMMA blends, at 230°C, no exchange reactions occur and that only the depolymerization reaction of PMMA has been observed. In the presence of an ester-exchange catalyst (SnOBu₂), an exchange reaction was found to occur at 230°C, but no trace of PC/PMMA graft copolymer has been observed. Instead, an exchange reaction between the monomer methyl methacrylate (MMA), generated in the unzipping of PMMA chains, and the carbonate groups of PC has been suggested. This is due to the diffusion of MMA at the interface or even into the PC domains, where it can react with PC producing low molar mass PC oligomers bearing methacrylate and methyl carbonate chain ends and leaving the undecomposed PMMA chains unaffected. The TG curves of PC/PMMA blends prepared by mechanical mixing and by casting from THF show two separated degradation steps corresponding to that of homopolymers. This behavior is different from that of a transparent film of PC/PMMA blend, obtained by solvent casting from DCB/CHCl₃, which shows a single degradation step indicating that the degradation rate of PC is increased by the presence of PMMA in the blend. The thermal degradation products obtained by DPMS of this blend consist of methyl methacrylate (MMA), cyclic carbonates arising from the degradation of PMMA and PC, respectively, and a series of open chain bisphenol-A carbonate oligomers with methacrylate and methyl carbonate terminal groups. The presence of the latter compounds suggests a thermally activated exchange reaction occurring above 300°C between MMA and PC. The presence of bisphenol-A carbonate oligomers bearing methyl ether end groups, generated by a thermally activated decarboxylation of the methyl carbonate end groups of PC, has also been observed among the pyrolysis products. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1873–1884, 1998     

The thermal expansion of the monoclinic unit cell of isotactic polypropylene

The lattice parameters of a highly stereoregular metallocene polypropylene crystallized at 145°C were obtained after cooling and heating cycles in a temperature interval between 25°C and 165°C. The b dimension undergoes a large thermal expansion with temperature (0.6 Å) while the change of the a axis is relatively small (0.1 Å). The unit cell dimension along the molecular (c) axis appears less sensitive to temperature than are the intermolecular distances. The difference in dimensions between the a and c axis at low and high crystallization temperatures is small, varying from 2.3 to 3.5%. This small difference allows the formation of daughter, crosshatched lamellae in the complete interval of crystallization temperatures. The thermal expansion coefficient of the unit cell specific volume is also reported. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2945–2949, 1997     

环氧丙烷聚醚三元醇/左旋聚乳酸三枝链嵌段共聚物的结晶行为

采用DSC对环氧丙烷聚醚三元醇/左旋聚乳酸三枝链嵌段共聚物(PPO-b-PLLA)的熔体结晶行为进行了研究. 在388～407 K范围内, 分别采用Avrami方程和Arrhenius方程进行了结晶动力学计算. Avrami指数n值约为2.2, 表明共聚物以二维生长方式进行晶体生长. 基于LH结晶理论, 对三枝链嵌段共聚物的结晶机理进行了探讨. 实验发现该体系共聚物的Regime II和Regime III转变温度随着n(PO)∶n(LA)的增大而变化, Kg (III)/Kg (II)＝2.0～2.2, 与LH理论预期值吻合. 实验结果表明三枝链的PPO链段对PLLA链段的结晶有很大影响, 使其成核较均聚物困难. 链折叠自由能σe和链折叠功q均高于PLLA的值.     

Synthesis and analysis of thermal characteristics of polybenzoxazine based on phenol and 3‐Amino phenyl boronic acid

In this work, 3‐amino phenyl boronic acid (AB) was used as an aniline derivative in the preparation of polybenzoxazine based on phenol. In order to investigate the effect of boronic acid on thermal characteristics, polybenzoxazines based on pure aniline and 50% aniline and AB mixture were also prepared and analyzed. Significant improvements in thermal characteristics, increase in thermal stability and char yield, was recorded for the polymers based on AB or its mixture. This behavior was associated with crosslinked structures generated by condensation reactions of B? OH groups. Morphologic and thermal characteristics of polybenzoxazines samples were investigated by NMR, FTIR, DSC, TGA, and direct pyrolysis mass spectrometry (DP‐MS) techniques. Application of DP‐MS technique also supplied additional information on crosslinked structures produced by boronic acid units. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1711–1716     

Glycidyl Tosylate: Polymerization of a “Non‐Polymerizable” Monomer permits Universal Post‐Functionalization of Polyethers

Glycidyl tosylate appears to be a non‐polymerizable epoxide when nucleophilic initiators are used because of the excellent leaving group properties of the tosylate. However, using the monomer‐activated mechanism, this unusual monomer can be copolymerized with ethylene oxide (EO) and propylene oxide (PO), respectively, yielding copolymers with 7–25 % incorporated tosylate‐moieties. The microstructure of the copolymers was investigated via in situ ¹H NMR spectroscopy, and the reactivity ratios of the copolymerizations have been determined. Quantitative nucleophilic substitution of the tosylate‐moiety is demonstrated for several examples. This new structure provides access to a library of functionalized polyethers that cannot be synthesized by conventional oxyanionic polymerization.     

Zero‐order kinetics of the thermal degradation of polypropylene/clay nanocomposites

The thermal degradation kinetics of polypropylene/clay microcomposites and nanocomposites were studied by thermogravimetric analysis. In comparison with pure polypropylene, the reaction order of the degradation of the composites became zero‐order, and the activation energy increased dramatically. The zero‐order kinetics were associated with the acidic sites (H⁺) created on the clay layers, whereas the increase in the activation energy was coupled with the shielding effect of clay. The kinetic analysis could provide additional mechanistic clues concerning the thermal stability and flammability of polymer/clay nanocomposites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3713–3719, 2005     

聚苯胺及聚邻甲基苯胺的直接裂解质谱研究

本文用直接裂解质谱和裂解色谱/质谱研究了不同氧化程度聚苯胺(PAn)和聚邻甲基苯胺(POT)的裂解过程及链结构,并用碰撞诱导解离(CID)和联合扫描(B/E)等技术探讨了链的断裂机理。结果表明,聚苯胺及其衍生物在650℃下裂解时产生5个单元的线状齐聚物,PAn及POT中苯二胺和醌亚胺两种结构单元共存。并提出了PAn和POT的自由基过渡态热解机理。     

Determination of primary bond scissions by mass spectrometric analysis of ultrasonic degradation products of poly(ethylene oxide‐block‐propylene oxide) copolymers

Ultrasonic degradation of poly(ethylene oxide‐block‐propylene oxide) copolymers consisting of a hydrophilic and a hydrophobic portion was studied with the aim to determine the location of bonds involved in the initial scission of the copolymers. LC–APCI‐IT‐MS and LC–APCI‐orbitrap‐MS were used for the detailed structural analysis of degradation products. The results indicated that initial bond scissions occurred principally at the boundary regions between backbones of polyethylene oxide (PEO) and polypropylene oxide (PPO) chains. Further structural analysis revealed the presence of oxygen adducts in the degradation products. Comparison with a thermal degradation carried out in helium atmosphere, one can conclude that the oxygen adducts are formed by radical reaction with water or dissolving oxygen molecules. The study demonstrated that chemical reactions as well as physical bond stress scissions are involved in the ultrasonic degradation of the copolymers. Copyright © 2010 John Wiley & Sons, Ltd.     

Aminotelechelics: A convenient synthesis and characterization of primary amino-terminated telechelic poly(propylene glycol) and polyisobutylene

The synthesis of amino-terminated telechelic poly(propylene glycol) and polyisobutylene from their corresponding dihydroxy-terminated derivatives was studied. The synthesis of these aminotelechelics was achieved by the coupling of imidazolylformates with ethylenediamine. The structure of the resulting amino-functionalized polymers was determined by ¹H NMR, ¹³C NMR, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. On the basis of the spectroscopic and spectrometric results, a complete conversion of dihydroxy termini into diamino end groups was observed; that is, the number-average functionality was found to be 2. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 587–596, 2004     

Critical Role of Spherulite Structure on Behavior of Stabilizers in Poly(propylene) Stabilization

Summary: We found that the spherulite structure of polypropylene (PP) significantly influences the stability of PP by affecting the behavior of stabilizers. Smaller spherulites resulted in more homogeneous dispersion of stabilizers and their slower release into air, so as to elongate the lifetime of PP. Moreover, chemically and physically weak spherulite boundaries were selectively oxidized in the presence of stabilizers. The significance to control higher order structures on the stabilization of PP is reported.     

聚苯乙烯负载聚乙二醇在合成碳酸亚丙酯上的应用

用金属钾、金属钠以及氢氧化钠水溶液等方法制备聚苯乙烯负载聚乙二醇，结果表明，采用金属钾比金属钢具有更好的接枝效果，并能使反应在较低的温度下较快进行。在氢氧化钠溶液中添加少量相转移剂，如Bu4NBr，接枝效果也有所提高。以聚苯乙烯负载聚乙二醇和KI一起为催化剂，研究了溶剂、温度等因素对CO2与环氧丙烷合成碳酸亚丙酯催化活性的影响。结果表明，以甲醇为溶剂催化活性较高。研究还表明，聚苯乙烯负载聚乙二醇具有较好的热稳定性，可以在150℃下重复使用至少5次。     

聚碳酸亚丙酯-聚醚聚氨酯的合成与性能

本文报道用CO2与环氧丙烷共聚产物聚碳酸亚丙酯和环氧丙烷均聚物来制备聚氨酯（PPCPOPU）弹性体。探讨了这类弹性体的最佳合成方法，考察了异氰酸酯基与羟基的比值；扩链交联剂用量等因素对弹性体的力学性能的影响。研究了弹性体的形态结构及其性能对配比的依赖关系。发现聚碳酸亚丙酯的耐热性因聚氨酯的形成而得到较大的改善，并发现该类弹性体具有优异的耐水性能。     

聚丙撑碳酸酯的辐射效应

研究了室温条件下聚丙撑碳酸酯(PPC)在钴-60和电子加速器辐照过程中的响应行为。结果表明,聚丙撑碳酸酯是一种辐射裂解型聚合物,其分子量随着辐射剂量的增加而减小。1mm厚PPC片材在室温和N2气保护条件下,其裂解G值为Gs,γ-ray=10.81;Gs,EB=4.9。不同的裂解G值表明,O2气在聚丙撑碳酸酯的辐射裂解过程中有重要影响。红外光谱研究表明,辐射后聚丙撑碳酸酯在3474cm-1处的峰宽峰高增加,表明其裂解后端—OH基增加。由于裂解作用,辐射后聚丙撑碳酸酯的抗张强度和断裂伸长率均下降。在通常的辐射消毒剂量范围内(25~50kGy),PPC的保留抗张强度大于23MPa,断裂伸长率大于4%,裂解后试样的力学性能依然能够满足实际应用需要,因此PPC可以经受辐射消毒。