嵌段共聚物苯乙烯-丁二烯-苯乙烯(SBS)/苯酰化聚苯醚共混分相动力学

<正> 对高分子-高分子共混体系相分离动力学过程的研究,人们一般局限于均聚物-均聚物,均聚物-无规共聚物共混体系,对于均聚物-嵌段共聚物共混体系的分相过程很少涉及。原因其一是很难找到具有临界相行为的嵌段共聚物-均聚物共混体系,其二是嵌段共聚物存在微相分离,使得宏观相分离动力学过程研究变得复杂。Paul的工作似乎为这方面的研究工作开辟了道路。     

嵌段共聚物／均聚物共混体系的微相分离和形态结构研究

着重介绍嵌段共聚物／均聚物共混体系的微相分离，微胶束的形成，微区的形态结构以及形态的控制。     

嵌段共聚物和星型均聚物共混体系相行为的自洽场理论研究

用自洽场理论方法(Self-consistent field theory, SCFT)计算了嵌段共聚物AB和三等臂星型均聚物A共混体系的微相形态. 为了简化计算, 着重讨论了固定嵌段共聚物本体的相形态(如层状相)时, 所加入的均聚物的体积分数及均聚物与嵌段共聚物链长之比对体系相形态的影响; 并结合体系的熵和相互作用能的变化, 讨论了星型均聚物在体系微相结构中的分布.     

均聚物/共聚物共混体系的相行为研究进展

通过控制均聚物与共聚物共混过程中的相行为,能够得到许多性能优异的材料。本文从理论和实验两方面总结了影响均聚物／共聚物共混体系相容性和形态结构的因素,主要包括均聚物的分子量、浓度,共聚物的组成、结构、浓度,与均聚物相应的共聚物组分的分子量,共聚物分子内的相互作用,均聚物与共聚物分子间的相互作用等。     

微量聚四氢呋喃-聚甲基丙烯酸甲酯/聚四氢呋喃共混体系稀固体溶液中共聚物胶束的抑制成核作用

 本工作将Leibler、Whitmore和Mayes等近期关于非晶嵌段共聚物共混体系胶束理论应用于结晶嵌段共聚物共混体系的熔融态,对聚甲基丙烯酸甲酯-聚四氢呋喃两嵌段共聚物与聚四氢呋喃均聚物共混体系的结晶行为进行了研究.结果表明,很低的共聚物浓度(如1％),其胶束在共混体系的结晶过程中即可显著地起到抑制成核的作用.这对改善结晶均聚物的形态及性能有一定的应用价值.     

微量聚四氢呋喃-聚甲基丙烯酸甲酯/聚四氢呋喃共混体系稀固体溶液中共聚物胶束的抑制成核作用

本工作将Leibler、Whitmore和Mayes等近期关于非晶嵌段共聚物共混体系胶束理论应用于结晶嵌段共聚物共混体系的熔融态,对聚甲基丙烯酸甲酯-聚四氢呋喃两嵌段共聚物与聚四氢呋喃均聚物共混体系的结晶行为进行了研究.结果表明,很低的共聚物浓度(如1％),其胶束在共混体系的结晶过程中即可显著地起到抑制成核的作用.这对改善结晶均聚物的形态及性能有一定的应用价值.     

Flory状态方程理论研究PS/PMMA/SAN相行为

将改进的Flory状态方程理论(EOS)引入含“分子内链段排斥性相互作用”的高分子共混物中,研究含无规共聚物的三元共混体系聚苯乙烯(PS)/聚甲基丙烯酸甲酯(PMMA)/聚苯乙烯-丙烯腈(SAN)无规共聚物的相行为,建立相应的适用于含无规共聚物三元共混体系Spinodal方程.用PS、PMMA、PAN的特征参数及其链段间相互作用参数分别计算相应共聚物的特征参数,由二元相互作用模型计算均聚物-共聚物间的相互作用能参数.在运用EOS理论研究三元均聚物共混体系相行为基础上,进一步预测PS/PMMA/SAN体系的相行为,计算并绘制不同温度下的Spinodal曲线并进行实验验证,理论计算与实验结果吻合.结果表明,EOS理论可以克服经典平均场理论的缺陷,成功描述含分子内排斥作用共混体系相行为与共聚物组成及温度之间的关系.     

PMMA—b—PTHF／PTHF共混体系中共聚物结晶能力的增强

结晶嵌段共聚物具有一般均聚物所没有的许多特殊结晶行为。虽然,人们很早就已开始对聚氧化乙烯/聚苯乙烯诸类嵌段共聚物的结晶行为进行研究,但对这类体系相分离规律及结晶行为的认识仍很不够。这主要是因为已研究的体系非常有限,此外,大都为对体系非平衡态结构的研究。所以,尽管Whitmore和Noolandi最近提出了结晶嵌段共聚物及其共混物的平衡形态理论,但缺乏实验数据与之比较。     

聚氧化乙烯-聚苯乙烯-聚氧化乙烯三嵌段共聚物/聚苯醚共混物的相容性和结晶行为

 本工作对聚氧化乙烯-聚苯乙烯-聚氧化乙烯(PEO-PS-PEO)三嵌段共聚物与聚苯醚(PPO)均聚物共混物的相容性及结晶行为进行了研究。结果表明,共混体系的相容性与嵌段共聚物中苯乙烯段的含量有关,PS含量越高,PPO与共聚物PS段的相容性越好。共混体系的结晶行为也明显不同于一般均聚物共混体系。在DSC降温结晶过程中最多可出现三个结晶峰。     

聚氧化乙烯-聚苯乙烯-聚氧化乙烯三嵌段共聚物/聚苯醚共混物的相容性和结晶行为

本工作对聚氧化乙烯-聚苯乙烯-聚氧化乙烯(PEO-PS-PEO)三嵌段共聚物与聚苯醚(PPO)均聚物共混物的相容性及结晶行为进行了研究。结果表明,共混体系的相容性与嵌段共聚物中苯乙烯段的含量有关,PS含量越高,PPO与共聚物PS段的相容性越好。共混体系的结晶行为也明显不同于一般均聚物共混体系。在DSC降温结晶过程中最多可出现三个结晶峰。     

Thin film confinement reduces compatibility in symmetric ternary block copolymer/homopolymer blends

The thin film phase behavior of ternary blends consisting of symmetric poly(styrene) (PS)-b-poly(dimethylsiloxane)(PDMS), PS, and PDMS was investigated using X-ray reflectivity (XRR) and atomic force microscopy (AFM). This system is strongly segregated, and the homopolymers are approximately the same length as the corresponding blocks of the copolymer. The XRR and AFM data are used to quantify changes in domain spacing (L) and morphology evolution with increasing homopolymer content (Φ _H). In 100 nm thick films, from Φ _H = 0 to 0.20, the system maintains a perfect parallel lamellar structure and domains swell as predicted based on theory; however, from Φ _H = 0.30 to 0.50, a morphology transition to a “dot pattern” morphology (tentatively identified as perforated lamellae) and mixed morphologies were observed before macrophase separation. In thicker films, dot patterns were observed for a broad range of Φ _H before macrophase separation. The absence of the bicontinuous microemulsion phase reported for bulk blends and thin films of perpendicular lamellae and the presence of dot patterns/perforated lamellae are attributed to preferential migration of the PDMS homopolymer to the wetting layers located at the substrate and free air interfaces, which leads to an asymmetric composition within the film and morphology transition. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1443–1451     

Phase Behavior of Poly(Oxyethylene)–Poly(Oxypropylene)–Poly(Oxyethylene) Block Copolymer in Water and Water–C12EO5 Systems

Abstract

The binary phase diagram of a triblock copolymer poly(oxyethylene) (PEO) poly(oxypropylene) (PPO) poly(oxyethylene) (PEO), (PEO)₃₇(PPO)₅₈(PEO)₃₇ or P105 in water and the ternary system of P105, water, and pentaoxyethylene dodecyl ether (C₁₂EO₅) has been studied to understand the miscibility of a small amphiphile, C₁₂EO₅ and a copolymer, as well as the mixing effect on the formed liquid crystalline structures. Phase diagrams, small angle x‐ray scattering (SAXS) and differential scanning calorimetry (DSC) were used to characterize these systems. The phase diagram of the binary system is presented together with the characteristic parameters for founded phases, namely, cubic, hexagonal, and lamellar phases. In the ternary system it was found that the small amphiphile and the block copolymer, despite having very different chain lengths are essentially miscible forming single phases. A large amount of C₁₂EO₅ can be solubilized in the P105 aggregates whereas P105 is most difficult to dissolve in the C₁₂EO₅ aggregates because of the difference in the molecular size. The copolymer is practically insoluble in the lamellar phase of C₁₂EO₅ due to the packing constraint. Hence, two lamellar phases coexist in a surfactant‐rich region, at W _s  = 0.66, where W _s is the weight fraction of the total amphiphile in the system. This indicates that the thickness of the lipophilic part of the C₁₂EO₅ lamellar phase is too small to allocate the large lipophilic chain of the P105 triblock copolymer.     

Effect of Cyclohexane on the Phase Behavior of L64/1-Butyl-3-Methylimidazolium Tetrafluoroborate System

The triblock copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (L64, PEO₁₃PPO₃₀PEO₁₃) in 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF₄]) can form lamellar liquid crystalline (L_α). The effect of apolar cyclohexane molecules on the L_α phase was investigated by using polarized optical microscopy (POM) and small-angle x-ray scattering (SAXS). The results of POM and SAXS show that a suitable amount of cyclohexane can contribute to the formation of lamellar liquid crystals, and the ordering of L_α phase is increased. For comparison, the effect of polar water on L_α phase was explored. After adding water, both EO groups and [BF₄]^– anion can form hydrogen bonds with water molecules, which weakens the electrostatic interactions between L64 and [Bmim][BF₄] and therefore the ordering of lamellar structures is destroyed.     

Crystal phase transformations within propylene/hexene-1 copolymers films as induced by direct current discharge treatment

The effect of a direct current discharge on the films of polypropylene and copolymers of propylene and hexene-1 synthesized with an isospecific catalytic system, rac-Me₂SiInd₂ZrCl₂-polymethylaluminoxane, was investigated. The treatment of isotactic polypropylene films by the discharge did not affect the ratio of crystalline phases in the polymer to a measurable extent. However, for the plasma treated films of copolymers of propylene and hexene-1 (the hexene-1 content of 1-2 mol%), a structural transformation of γ-modification into α-modification has been noticed. The observed phase transition has no apparent relation to any changes in microstructure of the copolymer chain because melting temperature values and the stereoregularity parameters of the samples remained practically unchanged. An experimental investigation of the specific influence exerted by individual components of a direct current discharge on the crystalline structure of copolymers has been undertaken. The exposure to a quantum component of the discharge did not induce any changes in the phase composition of the irradiated samples. The heating of the samples led to a negligible change of their phase composition. It has been determined that the surface of polypropylene and propylene/hexene-1 copolymer films facing the cathode in the course of the direct current discharge treatment had an accumulated negative charge Q > 10 nC/cm² which persisted for a long time afterwards. It has been suggested that the electrical field of a negative discharge may be the main cause of the γ-into α-phase transition in propylene/hexene-1 copolymers under the plasma effect. To verify this assumption, a propylene/hexene-1 copolymer film was charged under electron beam with energy of 4 keV. The electron beam treatment of the film resulted to the negative charge value of 11 nC/cm². The electron beam irradiation has induced the phase transition which was quite similar to the transition observed as the result of plasma treatment. So, it may be concluded that the phase transition from crystal γ-modification to α-modification under the effect of direct current discharge which has been investigated for copolymers of propylene and hexene-1 is induced by electric field of the negative charge accumulated at the surface layers of the films of the copolymers.     

Blends of bisphenol-A polycarbonate and acrylic polymers: III. Effect of imide concentration on compatibility

Imide units copolymerized with MMA units have been selected in order to improve compatibility between PC and acrylics through specific interaction or internal repulsion. Good dispersion of acrylic inside a PC matrix has been observed upon melt mixing, which can be partially explained by the good rheological agreement between these two polymers. Transmission electron microscopy has shown that the system remains phase separated from 5 to 95 wt % of PC. Phase diagrams for three different imide concentrations have been drawn. Results obtained by DSC (conventional and with enthalpy relaxation) are similar to those obtained by optical cloud point detection. The phase diagrams show the raise of the PC/PMMA demixtion curve (LCST type) when percentage of imide increases in the acrylic phase. Theoretical calculations on binary interaction energy density show a slight improvement of the interaction between acrylic and PC when imide percentage increases. Cloud point measurements on 50/50 PC/acrylic blends varying the imide concentration show that the improvement of compatibility deduced from the raise of the demixtion curve (LCST type) is more related to a kinetic effect (the high T_g of imidized samples is reducing macromolecule mobility) than specific interactions. The calculated favorable interactions are probably too weak to be detected with cloud point measurements. The microstructures obtained after crystallization of the PC phase under solvent vapors in phase separated PC/acrylics blends can also be explained by T_g effects. Moreover, solvent vapor exposure could be a powerful tool to determine the real thermodynamic behavior of the blends at room temperature. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 749–761, 1997     

Synthesis of the perovskite ceramic Li3xLa2/3–xTiO3 by a chemical solution route using a triblock copolymer surfactant

The synthesis of the perovskite Li_3xLa_2/3–x□_1/3–2xTiO₃ by a chemical solution route, using a triblock copolymer surfactant, PEO_n–PPO_m–PEO_n, is described. This titanate is a non-hygroscopic fast lithium conductor and therefore is a good candidate for electrochemical applications. It is generally prepared by a conventional solid-state reaction (SSR) method. However this synthesis method does not allow the preparation of nanopowders or the formation of thin films. For these special purposes, synthesis by a chemical solution route, with the formation of a polymeric precursor during synthesis, has been investigated. By using the above-mentioned non-ionic surfactant, the preparation of nanopowders of complex oxides can be done. Furthermore, this way of synthesis leads to the formation of an intermediate polymeric precursor which can be easily spread on substrates to obtain films. We show that the formation of a pure phase of the perovskite Li_3xLa_2/3–x□_1/3–2xTiO₃ is highly dependent on the synthesis conditions, namely the presence of water in the solvent, the EO/metal ratio, the Li⁺ content in the precursor and the calcination temperature. The influence of these parameters on the microstructure of the oxide is studied by X-ray diffraction, scanning electron microscopy and granulometry. A powder of Li_3xLa_2/3–x□_1/3–2xTiO₃ (x = 0.10), with an average particles size of 200 nm, has been obtained. The ionic conductivity of this oxide is the same as the one obtained with oxide prepared by SSR (a bulk conductivity of 1.4 × 10⁻³ S/cm at 37 °C). The ceramic obtained from this powder after sintering at 1,150 °C shows a good pH response. This material can then be used as a sensitive membrane in a potentiometric pH sensor. The presence of hydrophobic PPO groups in the polymer precursor allowed preparing films of Li_3xLa_2/3–x□_1/3–2xTiO₃ with a good adherence on Pt substrate. This kind of synthesis is then very promising to prepare micro pH sensors.     

Mechanism of polymorph selection during crystallization of random butene-1/ethylene copolymer

Starting from an initial sample of butene-1/ethylene copolymer with stable form I’, we examined the nucleation of different crystalline polymorphs (here metastable form II and stable form I’) at different isothermal crystallization temperatures after being melted at different melt temperature (T _melt). When T _melt was just above the melting temperature (T _m) of the crystallites, self-seeding took place. There, residue crystallites served as nuclei leading to the crystallization of the same crystalline phase. When T _melt was a few degrees above the T _m, self-seeding was disabled due to complete melting of the initial crystals. Upon crystallization, the selection of the different polymorphs in this random copolymer was found to depend on an interplay between the domain size of segregated long crystallizable sequences and the size and energy barrier of the critical nucleus of the respective crystalline forms. Our results provide a clear understanding of the polymorphs selection during crystallization of a random copolymer as well as homo-polymers under confinement.     

Key techniques to control porous microsphere morphology in S/O/W emulsion system

A solid-in-oil-in-water (S/O/W) emulsion system has been developed to prepare porous polymeric microspheres. The obtained microspheres showed unique core–shell structure with a dense core and a surface porous layer. The emulsion system has two processes. In the first process, S/O/W₁ viscous emulsion is prepared by dropping of S/O phase in the first water phase (W₁). In the second process, the S/O/W₁ emulsion is poured to another water phase (W₂) as S/O/W₁/W₂ emulsion. During the process, S/O/W₁ droplet becomes microsphere after organic medium completely diffusion. Emulsion techniques have various effective combinations such as additive and process conditions to design microsphere morphology. With regards to the proposed S/O/W system, addition of the solid phase in the system is a key factor to form the porous structure. When the medium diffusion starts, the solid makes W₁ phase kept inside the S/O/W₁ droplet. The remained W₁ phase changes surface porous layer after purification. Affinity between the solid and oil phase should be adjusted as well. In this study, an optimization of the emulsion system was attempted considering solubility parameter and polarity. Additionally, it is found that process conditions could help to design microsphere morphology such as pore size and porous layer thickness.     

Effect of crystallization temperature on the phase transitions of P(VDF/TrFE) copolymers

A systematic study was carried out on the effect of the crystallization temperature (T_cr), on the phase transitions presented by P(VDF/TrFE) copolymers cast from dimethylformamide (DMF) solution with molar ratios 60/40, 70/30, and 80/20. The results obtained by differential scanning calorimetry (DSC) showed that two-phase transitions are observed only when the copolymer crystallizes above a certain temperature T_o, and that the temperatures at which these transitions occur are reduced slightly with T_cr increase. It also was observed that when T_cr increases, the intensity of the endotherm corresponding to the lowest temperature transition is increased, whereas the one corresponding to the highest temperature transition is reduced. In order to explain these phenomena, the existence of two ferroelectric and two paraelectric phases is suggested. The conformational differences between like phases occur due to the distinct origin of each one: the best organized phase crystallizes directly from solution, whereas the least organized is the result of a solid phase transition. Wide angle x-ray diffusion (WAXD) diffractograms corroborate this hypothesis. Phase diagrams for samples crystallized below and above T_o have been proposed. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 403–414, 1998     

HPC/H2O/H3PO4 tertiary system: a rheological study

This study characterizes the rheological behavior of the HPC/H₂O/H₃PO₄ tertiary system based on the 3-D phase diagram that was obtained in our earlier work. The effects of frequency, temperature, HPC concentration, liquid composition (H₂O/H₃PO₄ ratio), and phase status on the rheological parameters were thoroughly investigated. The most useful parameter for distinguishing the isotropic (I) and liquid crystalline (LC) phases was tanδ. Agglomeration in the cloudy suspension (CS) phase at high temperature was too severe to allow a smooth flow, so the tanδ and η* represented significant damping, which is a good indicator of the presence of the CS phase. With an increase in temperature, the viscosity of the flow with a single homogeneous phase—either the I phase or the LC phase—or a combination of two homogeneous phases in sequence, obeyed the Arrhenius model. In contrast, once the temperature rose to that of the formation of heterogeneous CS phase, the Arrhenius model was no longer valid. The activation energy E of the I phase was greater, and more sensitive to the HPC concentration, than the LC phase. Finally, the concentration of the sol/gel transition (SGT) declined as temperature increased but increased as the H₃PO₄ content increased. Furthermore, this tertiary system exhibited no clear order of the onsets of the formations of SGT phase, the LC phase, and the CS phase as HPC concentration was varied.