Effect of physical aging on the microstructure and the crystallization of amorphous poly(aryl ether ether ketone ketone) (PEEKK)

Physical aging of poly(aryl ether ether ketone ketone) (PEEKK) has been investigated. Heat flow responses were measured after annealing the amorphous samples obtained by quenching the melt into an ice-water bath close to, but below, the glass transition temperature. The extent of aging is related to the supercooling from the glass transition temperature and to the aging time. The activation energy of the aging process, which was estimated by a Williams-Watt expression, is similar in magnitude to that obtained for the cold crystallization for the aged samples. The quenched glass is a metastable glass. The conformation of molecular chains rearranges with physical aging which results in the formation of a denser packing in the amorphous phase. The dense amorphous phase may form an initial nucleus for crystallization. Isothermal cold crystallization of the aged samples was carried out. The Avrami equation was used to determine the kinetic parameters, and the Avrami constant n is about 2. An Arrhenius expression was used to evaluate the activation energy of relaxation upon physical aging and the activation energy of transportation upon isothermal crystallization. The activation energy of relaxation is similar in magnitude to that of crystallization for aged samples. Results obtained are interpreted as kinetic effects associated with the glass formation process.

Isothermal melt and cold crystallization kinetics of poly(aryl ether ether ketone ketone) (PEEKK)

Isothermal melt and cold crystallization kinetics of PEEKK have been investigated by differential scanning calorimetry in two temperature regions. During the primary crystallization process, the relative crystallinity develops with a time dependence described by the Avrami equation, with exponent n = 2 for both melt and cold crystallization. The activation energies are -544.5 and 466.7 kJ/mol for crystallization from the melt and amorphous glassy state, respectively. The equilibrium melting point T-m(o) is estimated to be 371 degrees C by using the Hoffman-Weeks approach. The lateral and end surface free energies derived from the Lauritzen-Hoffman spherulitic growth rate equation are sigma=10 erg/cm(2) and sigma(e) = 60 erg/cm(2), respectively. The work of chain folding q is determined as 3.98 kcal/mol. These observed crystallization kinetic characteristics of PEEKK are compared with those of PEEK. (C) 1997 Elsevier Science Ltd.

Variation of crystallographic parameters in PEEKK with heat treatment temperature

Using the wide-angle X-ray diffraction method, the variation of crystallographic parameters of poly(aryl ether ether ketone ketone) (PEEKK) has been studied in different heat treatment temperatures. All the reflections and their intensities as well as their Miller indices are presented in detail according to an orthorhombic system. The investigation indicates that the unit cell parameters a, b, c and the unit cell volume V systematically decrease with increasing heat treatment temperature. This variation is interpreted by the change of conformation of polymer molecular chains during thermal treatment. The results calculated from the formula of degree of crystallinity (W-c,W-x) for PEEKK, which was derived based on X-ray scattering intensity theory and the graphic multipeak resolution method, are compatible with the density measurement (W-c,W-d) and calorimetry (W-c,W-h) values. (C) 1997 Elesevier Science Ltd.

The crystal structure and drawing-induced polymorphism in poly(aryl ether ketone)s .2. Poly(ether ether ketone ketone), PEEKK

The crystal structure, morphology and polymorphism induced by uniaxial drawing of poly(ether ether ketone ketone) [PEEKK] have been studied by transmission electron microscopy (TEM), electron diffraction (ED) and wide angle X-ray diffraction (WAXD). On the basis of WAXD and ED patterns,the crystal structure of unoriented PEEKK is determined to have two-chain orthorhombic packing with unit cell parameters of a 0.772 nm, b = 0.600 nm, c = 1.004 nm (form I), A stress-induced crystal modification (form II) is identified and found to possess a two-chain orthorhombic lattice with unit cell dimensions of a = 0.461 nm, b = 1.074 nm, c = 1.080 nm. The 7.5% increase in c-axis dimension for form II is attributed to an overextended chain conformation, arising from extensional deformation during uniaxial drawing and fixed ''in-situ'' through strain-induced crystallization. The average ether-ketone bridge bond angles in form II crystal are determined to be 148.9 degrees by using standard bond lengths. The crystal morphology of PEEKK bears a great similarity to that of PEEK. The crystals grow in the form of spherulites and have the b-axis of unit cell radial. The effects of draw rate on strain-induced crystallization and induction of form II structure are also discussed.

聚醚醚酮酮（PEEKK）和含联苯结构聚醚醚酮酮（PEBEKK）共聚物的SAXS研究

应用一维电子密度相关函数方法，对含不同联苯结构的ＰＥＥＫＫ－ＰＥＢＥＫＫ共聚物样品小角Ｘ射线散射（ＳＡＸＳ）去模糊强度分析计算表明：ＰＥＥＫＫ－ＰＥＢＥＫＫ共聚物的聚集态结构明显地依赖于共聚物中联苯含量。当联苯含量ｎｂ＝０．３５时，积分不变量Ｑ，长周期Ｌ，平均结晶片层厚ｄ，电子密度差η_ｃ－η_ａ和结晶度Ｗ_（ｃ，ｘ）值为最小，比表面积Ｏ_ｓ为最大。

聚醚醚酮酮（PEEKK）－含联苯聚醚醚酮酮（PEBEKK）共聚物的T_g和T_m转变

不同联苯含量的ＰＥＥＫＫ－ＰＥＢＥＫＫ共聚物的ＤＳＣ结果表明，随着联苯含量的增加，共聚物的玻璃化转变温度几逐渐升高；共聚物的熔点Ｔｍ明显地依赖于联苯含量，当联苯含量ｎＢ＝０．３５时，Ｔｍ值最４小。热处理可以显著地改善共聚物的结晶性，并出现熔融重结晶双峰。

聚芳醚酮及聚谷氨酸苄酯的亚稳性研究

人类对凝聚态物质的亚稳性的认识已经有了相当长的时间。常温常压下，热力学上更不稳定的、而实际上存在的相，都可称之为亚稳相。由于聚合物分子尺寸很大，分子运动的时间尺度具有很宽的范围，因此，在极大多数情况下，聚合物都处于亚稳态下。研究聚合物相行为和相变中的亚稳性，了解并认识亚稳态的存在、演变和终结，对于充分理解高分子凝聚态物理学的基本问题具有极其重要的科学意义，将为高分子材料的加工和功能开发提供新的途径和理论基础。本文正是基于这样一种广义的亚稳性概念，分别研究了聚芳醚酮系列聚合物的形态多样性、物理老化现象和双熔融峰行为以及聚谷氨酸苄酯的超分子组装和构象转变。首先实现了聚醚酮酮的溶液结晶，获得了单晶状片晶，揭示了聚醚酮酮结晶时优先生成片晶的特征。研究了聚醚醚酮酮的物理老化现象，提出了“亚稳刚性非晶相”概念，指出了刚性非晶相中的局部有序性。进一步探索了聚醚醚酮的双熔融峰行为，首次引入“亚稳熔体”概念，解释了亚稳晶体向更稳定晶体的转化。首次应用AFM技术观察到聚谷氨酸苄酯的高有序化组装特征，发现其中存在着侧链苯环间的亚稳性超分子组装结构。应用高分辨核磁共振技术深入研究了聚谷氨酸苄酯在二氯乙烷／二氯乙酸混合溶剂中的构象稳定性，阐明了聚谷氨酸苄酯的构象转变是受慢反应机理控制的，其中质子对分子内氢键的破坏是一个热力学平衡过程，进而揭示了聚谷氨酸苄酯／二氯乙烷／二氯乙酸三元体系的相态稳定性与高分子链构象稳定性的密切相关性，指出聚谷氨酸苄酯存在两种亚稳构象，即无规线团构象和螺旋链构象，这两种亚稳构象的存在决定了聚谷氨酸苄酯／二氯乙烷／二氯乙酸三元体系相态的亚稳性。主要结论如下：1．PEKK(T/I)结晶时优先生成片晶织构。a轴和b轴位于晶片平面内，c轴则垂直于晶片平面；b轴方向为片晶的优先生长方向。从熔融状态等温结晶时，平躺和侧放的片晶相互交错生长构成了辐射状的球晶。从溶液中结晶时既生成“初生态”球晶，也生成单晶状片晶。利用高分辨电镜技术研究了PEKK(T/I)晶体的微区结构。发现PEKK(T/I)晶体中存在许多缺陷，这些缺陷使得品格弯折。2．淬火的PEEKK玻璃态试样处于非平衡状态下，物理老化可引起亚稳玻璃体分子链的局部调整，形成刚性非晶相(Rigid Amorphous Phase)。物理老化时间越长，PEEKK玻璃体中生成的刚性非晶相越多。刚性非晶相中分子链间存在一定的有序性，可以在随后的PEEKK的结晶中起初级晶核的作用，从而降低PEEKK的结晶活化能。3．等温结晶处理的PEEK中分布着两种不同厚度的片晶。这些片晶相互堆砌在一起形成球晶结构。从热力学稳定性和动力学稳定性两方面考虑，这些片晶是亚稳片晶。其中，厚片晶比较稳定，因而在加热至通常的熔融温度前，可稳定存在。但是薄片晶则更不稳定，在加热过程中它要转变成为亚稳熔体；亚稳熔体只能短时存在，它很快就发生重结晶转变为更稳定的晶片。亚稳熔体的结晶过程非常快，它借助样品中已有的厚晶片作为晶核，从厚晶片表面直接向外生长。4．首次应用AFM技术观察到PBLG和PBDG分子的左、右手螺旋结构。揭示了PBLG或PBDG在云母表面上的高度有序化组装。发现PBLG或PBDG分子在云母表面上通过侧向和端基间的相互作用沿着云母表面[100]方向作有组装，进而形成向列相织构。在消旋的PBG共混物中，PBLG侧链上的苯环与PBDG侧链上的苯环之间可以形成规则堆砌结构。这种有序的苯环堆砌结构的形成促成了PBLG与PBDG螺旋分子间的超分子组装。当它们从溶液中析出时可形成纳米级的超分子纤维。5．应用NMR技术研究了PBLG／DCE／DCA三组分体系中PBLG构象的相互转变。在不同的温度下，PBLG可以以无规线团构象或α-螺旋构象存在。无规线团构象和α-螺旋构象在一定的温度范围内可发生相互转变：这种转变并不是受快速的反应过程控制的，而是由非常慢的成核机理控制的一个动力学平衡过程。NMR谱中碳共振双峰和质子共振双峰的出现正是这种动力学平衡的结果。PBLG／DCE／DCA三组分体系从低温到高温分别表现出各相同性态、各相同性与胆甾液晶共存态、胆甾液晶态和高温各相同性态等不同的相态织构。这些相态织构的出现是受PBLG分子的构象决定的。PBLG分子构象表现出强烈的温度依赖性，进而使得PBLG／DCE／DCA三组分体系的相态稳定性也表现出强烈的温度依赖性。

Isothermal melt and cold crystallization kinetics of poly(aryl ether ketone ether ketone ketone)

The isothermal melt and cold crystallization kinetics of poly(aryl ether ketone ether ketone ketone) are investigated by differential scanning calorimetry over two temperature regions. The Avrami equation describes the primary stage of isothermal crystallization kinetics with the exponent n approximate to 2 for both melt and cold crystallization. With the Hoffman-Weeks method, the equilibrium melting point is estimated to be 406 degrees C. From the spherulitic growth equation proposed by Hoffman and Lauritzen, the nucleation parameter (K-g) of the isothermal melt and cold crystallization is estimated. In addition, the K-g value of the isothermal melt crystallization is compared to those of the other poly(aryl ether ketone)s. (C) 2000 John Wiley & Sons, Inc.

Melt crystallization of poly(ether ether ketone ketone) under strong electric field

In this paper, melt crystallization of poly(ether ether ketone ketone) (PEEKK) under strong electric field was investigated. In the crystal structure of PEEKK, the length of c axis was found to he 1.075 nm, increasing by 7% compared to that of PEEKK crystallized without strong electric field. The molecule chains might take a more extended conformation through the opening of the bridge bond angles by increasing from 124 degrees to 144 degrees under strong electric field in the crystal structure.

Physical aging and crystallization of amorphous poly(aryl ether ether ketone ketone)

Physical aging of poly(aryl ether ether ketone ketone) (PEEKK) was investigated. Heat flow responses were measured after annealing the amorphous samples that were obtained by quenching the melt into an ice-water bath at just below the glass transition temperature. Isothermal cold crystallization of the aged samples was carried out. The Avrami equation was used to determine the kinetic parameters, and the Avrami constant it is about 2. An Arrhenius form was used to evaluate the relaxation activation energy of physical aging and the transport activation energy of isothermal crystallization. The activation energy of physical aging was similar in magnitude to that observed for the temperature dependence of crystallization under conditions of transportation control. Results obtained were interpreted as purely kinetic effects associated with the glass formation process. (C) 1998 John Wiley & Sons, Inc.

Influence of annealing on structure of poly(aryl ether ether ketone ketone) revealed by SAXS

Structural studies of poly(aryl ether ether ketone ketone) (PEEKK) using small-angle X-ray scattering and one-dimensional electron density correlation function methods revealed that its aggregated state structure was significantly influenced by the annealing temperature. The long period L, the average thickness of the lamellae d, the electron density difference between the crystalline and amorphous regions eta(c) - eta(a), and the invariant Q increased with increasing annealing temperature, but it was opposite to the case of the specific inner surfaces O-s. A transition zone existed between the traditional "two phases" with a dimension about 0.5 nm for semicrystalline PEEKK. (C) 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1829-1835, 1998.

Studies on poly(ether ether ketone ketone) poly(ether biphenyl ether ketone ketone) copolymers and blends

We synthesized a series of polymers: poly(ether ether ketone ketone)(PEEKK), poly(ether biphenyl ether ketone ketone) (PEBEKK) and their copolymer by polycondensation, We also prepared a series of PEEKK-PEBEKK blends, By using DSC method, we found that T-g of the copolymers and the blends rose with the increasing of biphenyl contents in the polymers, T-c of the copolymers and the blends is higher than the corresponding homopolymer. From the results, we think that PEEKK-PEBEKK copolymer and blends are miscible and the copolymer is random.

Nonisothermal melt and cold crystallization kinetics of poly(aryl ether ether ketone ketone)

Analysis of the nonisothermal melt and cold crystallization kinetics of poly(aryl ether ether ketone ketone) (PEEKK) was performed by using differential scanning calorimetry (DSC). The Avrami equation modified by Jeziorny could describe only the primary stage of nonisothermal crystallization of PEEKK. And, the Ozawa analysis, when applied to this polymer system, failed to describe its nonisothermal crystallization behavior. A new and convenient approach for the nonisothermal crystallization was proposed by combining the Avrami equation with the Ozawa equation. By evaluating the kinetic parameters in this approach, the crystallization behavior of PEEKK was analyzed. According to the Kissinger method, the activation energies were determined to be 189 and 328 kJ/mol for nonisothermal melt and cold crystallization, respectively.

The crystal structure and drawing induced polymorphism in poly(aryl ether ketone)s .3. Crystallization during hot-drawing of poly(ether ether ketone ketone)

The evolution of crystallinity and polymorphism during hot-drawing of amorphous poly(ether ether ketone ketone) (PEEKK) as a function of strain rate, draw ratio, and temperature was investigated. In modification I, the competition of chain extension and molecular alignment is responsible for the strain rate and temperature dependence. Modification II crystallization is basically controlled by chain extension during stretching. The former can be transformed into the latter via relaxation during stretching or annealing at elevated temperature.