Dynamic relaxation behavior of solvent-crystallized poly(ether ether ketone)

The dynamic relaxation behavior of solvent-crystallized poly(ether ether ketone) (PEEK) has been investigated in the region of the glass-rubber (α) relaxation using dynamic mechanical and dielectric methods. Amorphous PEEK films were exposed to saturated methylene chloride and acetone vapor, with solvent-induced crystallization observed for both penetrants. Sample desorption at elevated temperatures (under vacuum) resulted in virtually complete removal of residual penetrant, thus providing for the measurement of relaxation characteristics independent of plasticization. Both dynamic mechanical and dielectric studies indicated a marked positive offset in the isochronal relaxation temperatures of the solvent-crystallized samples relative to thermally crystallized specimens of comparable bulk crystallinity, and a higher apparent activation energy in the solvent-crystallized case. These results are consistent with the evolution of a tighter crystalline morphology (i.e., smaller crystal long spacing) in the solvent-crystallized samples, the crystallites imposing a greater degree of constraint on the long-range motions of the amorphous chains inherent to the glass-rubber relaxation. © 1994 John Wiley & Sons, Inc.     

The effect of ions irradiation on the thermal properties of poly(ether ether ketone)

The effect of irradiating amorphous poly (ether ether ketone), PEEK, with ions, 11 MeV proton (H⁺), and 25.6 MeV helium (He²⁺), has been investigated focusing on the changes in thermal properties. The extent of chain scission and crosslinking was evaluated using the Charlesby‐Pinner equation. Crosslinking increased the glass transition temperature (T_g) in line with the DiBenedetto equation from which the crosslinking constant for each ion was calculated. The effect of irradiation on the thermal degradation kinetics was studied in an argon atmosphere at a constant heating rate by mean of the Chang and the second Kissinger methods. Irradiation significantly reduced the thermal stability of the polymer and its service lifetime. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2212–2221, 2008     

Development of the crystallinity and rigid amorphous fraction in cold‐crystallized isotactic polystyrene

The phase structure of crystalline isotactic polystyrene (iPS) has been investigated with temperature‐modulated differential scanning calorimetry (TMDSC), wide‐angle X‐ray scattering (WAXS), and Fourier transform infrared (FTIR) spectroscopy. Quenched amorphous samples have been cold‐crystallized at 140 or 170 °C for various crystallization times. The degree of crystallinity obtained from WAXS, with the ratio of the crystal peak intensity to the total peak intensity, shows excellent agreement with the crystallinity determined from TMDSC total heat flow endotherms. For the first time, FTIR results show that the absorbance peak ratio (I/I) has a linear correlation with the crystalline mass fraction (χ_c) for cold‐crystallized iPS according to the following relation: I/I = 0.54χ_c + 0.16. This relationship allows the crystallinity of iPS to be determined from infrared spectroscopy analyses in cases in which it is difficult to perform thermal or X‐ray measurements. On the basis of the measurements of the heat capacity increment at the glass transition, we find that a significant amount of the rigid amorphous fraction (RAF) coexists with the crystalline and mobile amorphous phases in cold‐crystallized iPS. The RAF increases systematically with the crystallization time, and a greater amount is formed at a lower crystallization temperature. A three‐phase model (crystalline phase, mobile amorphous phase, and rigid amorphous phase) is, therefore, appropriate for the interpretation of the structure of cold‐crystallized iPS. The origin of the low‐temperature endothermic peak (annealing peak) has been investigated with TMDSC and FTIR spectroscopy and has been shown to be due to irreversible relaxation of the RAF. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3026–3036, 2003     

Surface Plasticization of Poly(ether ether ketone)

This paper describes a study of the surface plasticization and antiplasticization of an amorphous and a semicrystalline poly(ether ether ketone) (PEEK) in solvent environments using nanohardness method. A range of solvents (octane, chloroform, tetrachloroethane, acetone, dichlorobenzene, polyethyleneglycol (PEG), methanol and water) based on the Hilderbrand’s Solubility Parameter were selected as solvent environments. The results of the nanoindentation hardness experiments performed on the virgin and the solvent immersed polymeric surfaces are reported. The surface plasticization or antiplasticization is reported on the basis of the softening or the hardening of the near surface layers (?1 μm) after immersion of the polymeric surfaces in the solvent environments. Surface plasticization of the amorphous PEEK has been observed in organic solvents. The chlorine containing solvents have severely degraded the hardness of the amorphous polymer. A surface hardening of the amorphous PEEK has been observed after immersion in water. Semicrystalline PEEK was seen to exhibit a considerable inert behaviour to common organic solvents but chlorinated organic solvents and water have caused a decrease in the surface mechanical properties.     

Functionalization of poly (aryl ether ether ketone): Synthesis of bromomethylated PEEK and its functionalization

Bromomethyl poly (aryl ether ether ketone) has been prepared from methyl poly (aryl ether ether ketone) (MePEEK) and has been used as the precursor to many forms of functionalized PEEK. MePEEK was brominated directly with bromine. Bromination takes place exclusively at the methyl group. The reaction conditions for bromination have been studied. The bromination level can be controlled by the amount of bromine used, up to 90% of the methyl groups can be brominated to mono-bromo and di-bromo methyl PEEK. Modification reactions have been carried out on the brominated methyl PEEK. The bromomethyl group has been converted to different functional groups, such as ? CH₂OH, ? CH₂OCH₃, ? COOCH₃, ? CH₂CN, ? CH₂COOH ? CH₂OCOCH₃, ? CH₂N⁺H (CH₂CH₃)₂Br^?, ? CH₂N (CH₂CH₃)₂, ? CH₂N⁺ (CH₂CH₃)₃ Br^?. Published 1994 John Wiley & Sons, Inc.     

Effects of methylene chloride sorption on the properties of poly(ether ether ketone)

Sorption of methylene chloride by poly(ether ether ketone) (PEEK) has been studied for both amorphous and highly crystalline polymer. After the determination of sorption and desorption curves, the crystallinity of the two materials after desorption was determined both by density and X-ray measurements. The experimental results indicate the existence of solvent-induced crystallization in initially amorphous PEEK and a virtual lack of this process in highly crystalline PEEK. In the latter case, the observed density increase is attributed to solvent compression and a decrease in free volume. The mechanical behavior of both PEEKs is consistent with their crystallinity levels. The mechanical behavior of both PEEKs before and after sorption allows us to discern the separate effects of the two processes to which the presence of methylene chloride in PEEK gives rise, i.e., plasticization and solvent-induced crystallization. © 1994 John Wiley & Sons, Inc.     

Mechanism of thermal decomposition of poly(ether ether ketone) (PEEK) from a review of decomposition studies

A review of the literature on the flammability and decomposition of poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene) (PEEK) is presented. This paper provides an overview of the flammability of PEEK and its decomposition mechanisms. Based on this literature, mechanisms have been suggested which attempt to explain the products formed at each stage of PEEK decomposition and indicate the intermediates which should be formed at each of these stages.     

Surface modification of poly(aryl ether ether ketone) (PEEK) film by covalent coupling of amines and amino acids through a spacer arm

Using the wet-chemistry technique, we selectively reduced the surface of the PEEK film (PEEK-OH), and covalently fixed hexamethylene diisocyanate by addition onto the hydroxyl functions. The resulting PEEK-NCO film displayed free isocyanate termini, the basic hydrolysis of which gave the PEEK-NH₂ film in 85% extent of derivatization. The PEEK-NCO film reacted with trifluoroethylamine in toluene, trifluoroethylamine in PBS buffer, GABA, and lysine in PBS buffer to furnish, respectively, the PEEK-CF₃(A), PEEK-CF₃(B), PEEK-CO₂H, and PEEK(NH₂)CO₂H films in 80%, 45%, 30%, and 25% extents of derivatization, as determined from the F/C and N/C atomic ratios recorded in the corresponding XPS spectra. The surface reactivity of the PEEK-NH₂ and PEEK-NCO films was assayed by coupling with appropriate ³H labels followed by liquid scintillation counting of the sample-associated radioactivity. The PEEK-NH₂, PEEK-CO₂H, and PEEK-(NH₂)CO₂H films were used as substrates for the cultivation of CaCo₂ epithelial cells; the presence of surface amine and carboxyl functions significantly improves the cellular adhesion and growth. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3779–3790, 1997     

Melting behavior of poly(ether ether ketone) in its blends with poly(ether imide)

We detail the melting behavior of poly(ether ether ketone) (PEEK) and investigate its melting behavior in miscible blends with poly(ether imide) (PEI). The determination of the equilibrium melting point (T_m⁰) of PEEK is discussed by considering its inhomogeneous morphology. T_m⁰ is obtained by a long extrapolation of a Hoffman–Weeks plot to 384°C. Hindrance of PEEK crystal reorganization induced by PEI during heating is observed over the blend composition investigated (20–75 wt % PEEK). This behavior is correlated with the incorporation of PEI in the interlamellar zones of PEEK crystals. The interaction parameter χ of PEEK/PEI blends is estimated by the equilibrium melting point depression. This gives the interaction density B = ?1.2 cal/cm³, and x = ?0.40 at 400°C. © 1993 John Wiley & Sons, Inc.     

UV-induced Self-initiated Graft Polymerization of Acrylamide onto Poly(ether ether ketone)

Photo-grafting of hydrophilic monomer was used to enhance the hydrophilicity of poly(ether ether ketone) (PEEK) with the aim of extending its applications to biological fields. PEEK sheets were surface modified by grafting of acrylamide(AAm) with ultraviolet(UV) irradiation in the presence or absence of benzophenone(BP). The effects of BP, irradiation time and monomer concentration on the surface wettability of PEEK were investigated. Characterization of modified PEEK using scanning electron microscopy(SEM), energy-disperse spectrometer(EDS) and water contact angle measurements shows that AAm was successfully grafted on PEEK surface both in presence and absence of BP. With the increase in irradiation time and monomer concentration, contact angles decrease to as low as 30°, demonstrating a significant improvement of surface hydrophilicity. In agreement with the decrease in contact angle, under identical conditions, the nitrogen concentration increases, suggesting the increase in grafting degree of the grafting polymerization. This investigation demonstrates a self-initiation of PEEK due to its BP-like structure in the backbone of the polymer. Though the graft polymerization proceeds more readily in the presence of BP, the self-initiated graft polymerization is clearly observed.     

Physical background of the endurance limit in poly(ether ether ketone)

In this study, it is demonstrated that the apparent endurance (fatigue) limit for plasticity-controlled failure in poly(ether ether ketone) is related to an evolution of the yield stress. The increase of the yield stress has two separate causes: (a) stress- and temperature-accelerated physical aging of the amorphous phase and (b) strain hardening as a result of texture development. Yield stress evolution is monitored using thermomechanical treatments during which the material is exposed to temperature and load. The combined contributions of both temperature and applied stress to yield stress evolution (below T _g) can be effectively modeled using an effective time approach employing an Arrhenius temperature-activation as well as Eyring stress activation. Combination of the yield stress evolution with a previously developed model for plasticity-controlled failure allows prediction of time-to-failure under both static and cyclic load, quantitatively capturing the observed apparent endurance limit.     

具有液晶性新型聚芳醚酮的合成与表征

通过联苯二酚(介晶基元)、取代对苯二酚(破坏结晶基元)与4,4'-二氟二苯酮的亲核取代反应合成了一系列具有液晶性的新型聚芳醚酮,采用DSC、PLM和WAXD等方法对聚合物的研究表明:联苯含量为70%时聚合物表现为向列相,联苯含量为50%时聚合物出现近晶相,在外力场作用下,向列相液晶容易形成明暗交替的条带织构.     

Molecular dynamics in ion‐irradiated poly(ether ether ketone) investigated by two‐dimensional correlation dielectric relaxation spectroscopy

This paper reports the first use of temperature–temperature 2D correlation dielectric relaxation spectroscopy (2D COS‐DRS) to study the molecular relaxation dynamics in ion‐irradiated poly(ether ether ketone) (PEEK). With the help of the high resolution and high sensitivity of 2D COS‐DRS, it was possible to locate the position of the motion of water molecules in the dielectric spectrum of PEEK. This occurred at −20°C and increased in intensity on increasing water contents. On irradiation, a new relaxation was observed at −75°C and −85°C for proton and helium ion‐irradiated samples, respectively. This increased in intensity on increasing radiation dose and was assigned to main‐chain phenyl motions of the cross‐linked units of the polymer. 2D COS‐DRS was also successfully applied to resolve the overlap in molecular events in the region of glass transition. Three processes that change in different directions with respect to ion irradiation dose were identified. These were at 160°C, 175°C, and 240°C and were assigned to the α relaxation, second α relaxation, and the onset of conductivity, respectively. In addition, hybrid 2D COS‐DRS was used to investigate the effect of the so‐called linear energy transfer effect, and the results showed that helium ions were more effective in cross‐linking PEEK. Copyright © 2013 John Wiley & Sons, Ltd.     

4,6-二甲基-N-苯基-2-嘧啶胺的低温热容和热力学性质

通过小样品精密自动绝热量热计测定了合成并提纯的 4,6 二甲基 N 苯基 2 嘧啶胺 (嘧霉胺 )在 78～ 3 91K温区的摩尔热容 .量热实验发现 ,该化合物在 3 63～ 3 72K温区 ,有一固 -液熔化相变过程 ,经三次重复测量 ,得其熔化温度、摩尔熔化焓及摩尔熔化熵分别为 :( 3 70 78± 0 0 8)K ,( 2 1 2 3 3± 0 0 13 )kJ·mol-1 和 ( 5 7 2 7± 0 15 )J·mol-1 ·K-1 .通过分步熔化法得到该物质绝对纯样品的熔点为 3 71 0 3 1K .用差示扫描量热 (DSC)技术对该物质的固 -液熔化过程作了进一步研究 ,结果与绝热量热法一致     

Synthesis and properties of poly(aryl ether ether ketone) copolymers with pendant methyl groups

Polyether ether ketone and polyether ether ketone copolymers were prepared by the nucleophilic substitution reaction of 4,4′-difluorobenzophenone with hydroquinone and with varying mole proportions of hydroquinone and methyl hydroquinone using sulfolane solvent in the presence of anhydrous K₂CO₃. The polymers were characterised by different physico-chemical techniques. The crystallinity of the polymers was found to decrease with increase in concentration of the methyl hydroquinone units in the polymer. Thermogravimetric studies showed that all the polymers were stable upto 430 °C with a char yield above 49% at 900 °C in N₂ atmosphere. The glass transition temperature was found to increase and the crystalline melting temperature and activation energy were found to decrease with increase in concentration of the methyl hydroquinone units in the polymer.     

The sulfonation of crosslinked poly(ether ether ketone)—Diffusion‐controlled kinetics

The effect of crosslinks introduced by ion irradiation with 11.7 MeV proton and 30 MeV helium ions on the reactivity of poly(ether‐ether‐ketone) (PEEK) to sulfonation have been investigated following the kinetics of the reaction at room temperature. Concentrated sulfuric acid was used as a swelling and sulfonating agent and the reaction was followed by changes in the FTIR spectrum. The rate of reaction decreased with the degree of crosslinking and the progress with time was consistent with diffusion control of the sulfuric acid into the crosslinked matrix. The results were consistent with the efficiency of the ions in crosslinking PEEK and in particular with the differences in their linear energy transfer (LET). © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 775–783, 2009     

Thermochemistry of the binary system nitrocellulose+2,4-dinitrotoluene

Melting enthalpy and mixing enthalpy of binary system 2,4-dinitrotoluene and nitrocellulose were determined by DSC method. The maximum value of mixing enthalpy was H _max ^M=1.38 kJ mol⁻¹ for molar fraction x _w24DNT = 0.501. The Flory-Huggins parameter (c) was estimated. The solubility curves and glass transition temperatures were predicted and compared with the experimental results. The measurements were performed for the samples with different times of storage at room temperature. The analysis of melting peaks for the mixture leads to the conclusion that for the long periods of storage the melting of 2,4-dinitrotoluene takes place in the confined spaces (pores) and unconfined space (bulk). The crystallization and melting is observed during the short time of storage in mixtures with low nitrocellulose content and in the case of mixtures with a large amount of NC the glass transition is additionally observed. This revised version was published online in July 2006 with corrections to the Cover Date.     

一种新型聚芳醚酮的热致液晶行为

聚芳醚酮具有优异的耐热性和环境稳定性 ,作为特种工程塑料在宇航、军工等高技术领域得到了广泛的应用 [1 ] .但其熔融温度较高 ,熔体粘度较大 ,在加工中存在一定困难 .热致液晶高分子 ( TLCP)具有较低的粘度 ,复合在热塑性高分子基体中的 TL CP在剪切力或拉伸应变流的作用下发生取向、变形成纤 ,其强度比热塑性基体高 1～ 2个数量级 ,另外 TL CP微纤提供了极大的纤维粘附表面积 ,因此 ,TL CP与聚合物共混具有广阔应用前景 .本文通过联苯二酚、 2 -叔丁基 - 1 ,4-对苯二酚与 4,4′-二氟二苯酮的亲核取代反应合成了一种具有热致液晶性…