Miscible blends containing a liquid crystalline polymer via optimized hydrogen bonding: Correlation to theory

Blending a liquid crystalline polymer (LCP) with an amorphous polymer to create a molecular composite offers a method to use the desirable properties of an LCP at a more modest cost. However, very few such blends are miscible. Our earlier findings (Viswanathan, S.; Dadmun, M. D. Macromol Rapid Commun 2001, 22, 779–782; Macromolecules 2001, 35, 5049–5060; Macromolecules 2003, 36, 3196–3205) demonstrate that it is possible to create a true molecular composite by inducing miscibility in a blend containing an LCP and an amorphous polymer by slightly modifying the structure of the polymer constituents to promote hydrogen bonding between the two polymers. This result is interpreted to indicate that separation of the hydroxyl groups along the amorphous polymer chain enhances the accessibility of the ? OH to intermolecularly hydrogen bond to C?O groups and increases the miscibility of the blends. In this report, the phase diagrams for these blends are correlated to the theoretical phase diagrams that are determined using Coleman and Painter's association model, indicating excellent agreement between theory and experiment. This correlation also provides quantification of the functional group accessibility (via K) as a function of copolymer composition, which agrees very well with the previous phase behavior results and interpretation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1010–1022, 2004     

Intermacromolecular complexation in solution and complex blends

By progressively increasing the hydrogen bonding interaction, otherwise immiscible polymer blends composed of modified polystyrene and poly(alkyl methacrylate) can achieve miscibility and complexation successively. The differences in chain arrangement between the states of mere miscibility and complex can be detected by a modified NRET fluorescence technique. Immiscibility-miscibility-complexation transitions have been proved to be of generality for polymer blends with controllable hydrogen bonding.     

Influence of copolymer configuration on the phase behavior of ternary blends

The influence of copolymer configuration on the phase behavior of various ternary polymer blends containing a crystallizable polyester, a noncrystallizable polyether, and an acrylic random copolymer of different chain configuration was investigated. In these ternary blends, the acrylic random copolymer is typically added to control rheological properties at elevated temperatures. In fact, the acrylic random copolymers composed of various compositions of MMA and nBMA were found to have different miscibility with polyester as well as polyether, leading to substantially different phase behavior of ternary blends. Remarkable temperature dependence was also found. The mean-field Flory-Huggins theory for the free energy of mixing, extended to ternary polymer blends, was adopted for predicting phase diagrams where the exact spinodal and binodal boundaries could be calculated. Phase diagrams of ternary blends, predicted by the Flory-Huggins formulations and related calculations, were in good agreement with experimental phase diagrams. The differences observed in the rheological processes of various ternary blends with different acrylic copolymers were directly related to changes in miscibility, associated phase behavior, and chain configuration.     

Miscible blends through hydrogen bonding: effects on polymer properties

Miscible blends through hydrogen bonding have been intensively studied. The effects of a variety of miscible hydrogen bonded polymer blends on properties such as thermal and thermal oxidative stability, moisture sensitivity, modulus and glass transition temperature are discussed. In addition, the preparation of semi-interpenetrating polymer networks (IPNs) and studies of the effect of crosslinking on the miscibility in hydrogen bonded polymer blends are reviewed.     

Epoxy resin/poly(ethylene oxide) (PEO) and poly(ε-caprolactone) (PCL) blends cured with 1,3,5-trihydroxybenzene: miscibility and intermolecular interactions

Epoxy resin (ER)/poly(ethylene oxide) (PEO) and/or poly(e-caprolactone) (PCL) blends cured with 1,3,5-trihydroxybenzene (THB) were prepared via the in situ curing reaction of epoxy monomers in the presence of PEO and/or PCL, which started from the initially homogeneous mixtures of DGEBA, THB and PEO and/or PCL. The miscibility and the intermolecular specific interactions in the thermosetting polymer blends were investigated by means of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The two systems displayed single and composition-dependant glass transition temperatures (T _gs), indicating the full miscibility of the thermosetting blends. The experimental T _gs of the blends can be well accounted for by Gordon-Taylor and Kwei equations, respectively. The T _g-composition behaviors were compared with those of poly(hydroxyether of bisphnol A) (Phenoxy) blends with PEO and PCL. It is noted that the formation of crosslinked structure has quite different effects on miscibility and intermolecular hydrogen bonding interactions for the thermosetting polymer blends. In ER/PEO blends, the strength of the intermolecular hydrogen bonding interactions is weaker than that of the self-association in the control epoxy resin, which is in marked contrast to the case of Phenoxy/PEO blends. This suggests that the crosslinking reduces the intermolecular hydrogen bonding interactions, whereas the intermolecular hydrogen bonding interactions were not significantly reduced by the formation of the crosslinking structure in ER/PCL blends.     

Δχ effects on the miscibility of polymer blends

The Δχ effect on the miscibility of polymer blends prepared by solution-casting has been investigated using the mixture of poly(methyl methacrylate)(PMMA) with poly(vinyl acetate) (PVAc). The PMMA/PVAc blends have been prepared by casting from eleven different solutions. The Δχ effect of the solution–cast PMMA/PVAc blends was discussed in terms of Hansen's specified solubility parameters. It was found that the miscibility of the blends could be defined mainly by the solubility parameter contributed by the hydrogen–bonding of a solvent.     

Study of the miscibility and segmental motion of STMAA-PBMA polymer blends and semi-interpenetrating polymer networks by an ESR spin probe method

Linear polymer blends and semi-interpenetrating polymer networks (IPNs) with controlled hydrogen bonding interactions based on poly(styrene-co-methacrylic acid) (STMAA) and poly(butyl methacrylate) (PBMA) were studied by an ESR spin probe method. The observed composite ESR spectra with fast- and slow-motion components in all the samples were ascribed to two-phase morphology. For linear blends, the temperatures T(a) corresponding to appearance of the fast motion, T(d) corresponding to the disappearance of slow motion, T(5mT) and the rotational correlation times tau(c) increased with increasing carboxylic acid content in STMAA. It was concluded that the degree of mixing of the blends was improved with increasing carboxylic acid content, owing to the enhanced hydrogen bonding interactions between the carboxylic acids in STMAA and the ester groups in PBMA. With respect to semi-IPN samples, there existed a competition in the microphase structure between the intercomponent hydrogen bonding interactions, which improved the miscibility of the samples and the intracomponent cross-linking, which might lead to phase separation in the systems with strong specific interactions. When the semi-IPN contained 29 mol% carboxylic acid, the temperatures T(d), T(5mT) and tau(c) reached their minimum values, which indicated that the sample reached its maximum miscibility.     

Liquid-liquid equilibria of polymer solutions: a closed miscibility loop phase behavior

In the phase behavior of binary polymer/solvent mixtures, a lower critical solution temperature (LCST) and hour-glass shaped and closed miscibility loop phase behavior are encountered. The closed miscibility loop phase behavior may be mainly due to highly oriented interactions such as hydrogen bonding. The purpose of this study is to describe closed miscibility loop phase behavior in the liquid-liquid equilibria of polymer solutions. To consider highly oriented interactions (or specific interactions), we employed a secondary lattice concept as a perturbation term.     

Controllable specific interactions and miscibility in polymer blends, 2. A brief description of the main results

In this paper, we briefly report the main results of our work on the effect of introducing specific interaction on the miscibility of otherwise immiscible polymer blends. A strong proton-donating unit (CF₃)₂(OH)C- was incorporated into polystyrene (PS(OH)). A series of blends of PS(OH) with one of polyacrylates such as PBA, PMMA, PEMA and PBMA was studied. The infrared spectra of the blends present convincing evidence of the formation of hydrogen bonding. The frequency shift of the OH stretching band due to H-bonding is independent of the structure and composition of the hydroxyl-containing polymers, but clearly dependent on those of the counterpolymers. Both excimer and nonradiative energy transfer (NRET) fluorescence techniques have proved effective for monitoring the variation of the degree of molecular interpenetration with the density and strength of the hydrogen bonds in the blends. TEM observations reveal clear and regular variation in the morphology of the blends with the content of hydroxyl-containing groups. The morphological features of this kind of blends are almost controllable since the structure and/or amount of the introduced groups forming hydrogen bonding are readily adjusted in chemistry. NRET and viscosity measurements of solutions of polyacrylate and PS(OH) with relatively high hydroxyl contents in toluene provide evidence of the intermolecular complexation. In addition, the effect of introducing simultaneously crosslinking and intermolecular hydrogen bonding into blends of PS and PBA on miscibility was studied. It is concluded that single phase IPN can be prepared, but much higher content of the proton donor is needed in comparison with the blends of the corresponding linear polymers. The interlocking structure of the networks appears unfavourable to forming miscible IPN.     

On the phase behavior of blends of polymers and nematic liquid crystals

The phase behavior of mixtures of polymers and nematic liquid crystals (LC) is investigated. Two types of systems are examined. The first one deals with blends in which the polymer is made of linear chains. In this case, a systematic study of the effects of various parameters on the phase diagrams is performed. In particular, it is shown how increasing the polymer size and/or the LC molecule size increases the miscibility gap of the mixture. It also reduces the region where a single nematic phase is observed in the presence of a tiny amount of polymer. Likewise, the relative effects of the isotropic and the nematic interaction parameters on the phase diagrams are examined. The second part of this investigation deals with blends involving crosslinked polymers. Here, substantial differences are observed as compared to the case where the polymer components are made of linear chains. These differences are illustrated by showing the phase diagrams in similar conditions for both blends. Unlike the case of a linear polymer matrix, it is observed that the single nematic phase and the nematic-isotropic spinodal branches are absent from the phase diagram of crosslinked polymers. This results into significant distortions of the phase diagram. In order to highlight all these effects, examples representing hypothetical blends are considered. These examples are chosen for illustration of the results in which the choice of numerical parameters is made consistently with the existing values in the literature which makes comparison with published data possible.     

聚氨酯硬段模型聚合物和SAN的特殊相互作用研究

运用ＤＳＣ物理老化和ＦＴＩＲ谱带分离及拟合技术，对聚氨酯（ＴＰＵ）硬段模型聚合物（ＨＭ）和苯乙烯－丙烯腈共聚物（ＳＡＮ）的共混体系进行了研究。实验结果表明，ＨＭ／ＳＡＮ是一个相容体系，体系的相容性来源于两组分聚合物之间的特殊相互作用。ＳＡＮ的加入消弱了ＨＭ中羰基和氨基间的氢键相互作用，这一结果对阐明ＴＰＵ／ＳＡＮ共混体系相容性本质提供了重要的依据。     

Formation of a True Molecular Composite using Optimal Hydrogen Bonding

Guidelines for creating miscible blends containing a liquid crystalline polymer and an amorphous polymer by optimizing intermolecular interactions between the two polymers are presented. It is shown that by controlling the spacing between the functional groups that participate in hydrogen bonding along the amorphous polymer chain, the extent of intermolecular interactions between the two polymers is optimized, and this induces miscibility in the systems studied.     

Blends of some non-flexible and flexible polymers: Routes to molecular composites?

The definition of a molecular composite is a blend of a rigid rod polymer and a flexible coil polymer that is miscible at the molecular level. This concept has been tested using systems in which the chain flexibilities differ as widely as possible as judged by the difference in glass transition temperatures (δTg). The biggest variation (δT ∼360°C) was obtained by mixing poly benzimidazole with copolymers of poly(vinyl acetate-ran-vinyl alcohol). It was observed that the blends were distinctly two phase when the hydroxyl content was less than 50 mol %. Above this value clear blends were obtained with finely dispersed phases although it is doubtful if mixing at the molecular level takes place. Miscible blends could be obtained from combinations of the sodium salt of poly(phenylene terephthalamide) with poly(4-vinylpyridine) and mixtures of poly(phenyl imino-1,4-phenyleneoxyterephthalate) with poly(styrene-stat-hydroxylstyrene) where coulombic interactions and hydrogen bonding respectively promoted the miscibility.     

Phase behaviors and interactions of N-alkylated polyanilines and ethylene-co-vinyl acetate blends

Conjugated polyanilines bearing long alkyl side chains (dodecyl PANi-12 and octadecyl PANi-18) were prepared for the purpose of obtaining well-mixed conducting polymer blends with insulating flexible polymers. The miscibility of the polyanilines and ethylene-co-vinyl acetate copolymers (EV A20 with 20 wt % of vinyl acetate and EV A70 with 70 wt %) was significantly improved by long alkyl chains of the same hydrocarbon moieties as the ethylene segments in the matrix EV A, as demonstrated by microscopic observation. PANi-18/EV A20 blends exhibit a lower critical phase separation temperature (LCST). In addition, the EV A crystallinity and the side-chain crystallinity in the miscible blends were depressed, as shown by thermal analysis and x-ray scattering. The comparison of three designed blend systems indicates that the miscibility of the polymers is determined by the hydrophobic interaction between the hydrocarbon units in the both components and by the hydrogen bonding. The solvatochromic phenomena for the blends at low miscible PANi compositions was detected by UV-visible spectroscopy. The threshold conductivities exhibit sensitivity to the morphological structure of the polymeric blends, and was lowered by improved homogenous dispersion of the conducting phase. © 1995 John Wiley & Sons, Inc.     

高分子共混物中氢键的作用Ⅱ.氢键对高分子共混物性能的影响以及引入方法

高分子共混物中氢键的存在能促进共混组分具有更好的可混和性.因此,研究高分子共混物中的氢键对高分子的共混改性具有重要的理论和实用价值.本文是<高分子共混物中氢键的Ⅰ.氢键的特征描述以及影响因素>的下篇,将继续介绍高分子共混物中氢键的作用,主要包括氢键对高分子共混物性能的影响以及主要的引入氢键的方法.特别地,本文通过将高分子共混物分为合成高分子与合成高分子共混物,合成高分子与天然高分子共混物以及合成高分子与其它物质共混物,总结了氢键存在对共混物性能的影响.     

Analyse de la relations structure-proprietes des melanges PVC-PMMA

Analysis of Structure-Properties Relationship of PVC-PMMA Blends. This paper presents a study of the structure-properties relationship of PVC-PMMA blends. For that purpose, blends of variable compositions from 0 to 100 wt % were prepared. Their physico-chemical characterization was carried out by differential scanning calorimetric analysis (DSC) and Fourier Transform Infrared spectroscopy (FTIR). The analysis of thermograms showed polymer miscibility up to 60 wt % PMMA. This miscibility is due to a specific interaction of hydrogen bonding type between carbonyl groups (C+O) of PMMA and hydrogen from (CHCl) groups of PVC. The two-band deconvolution showed an increase in associated groups percentage in the domain of miscibility. The variation of mechanical properties such as tensile behaviour, hardness and impact resistance was investigated for all blend compositions. The effect of a plasticizer on the same properties was considered. The obtained results show that a range of properties can be generated according to the blend compositions.     

固体NMR研究PAA/PEO共混物中氢键相互作用与结构演化

分子间相互作用是决定材料结构和性能的关键因素之一,而如何在分子水上实现对复杂相互作用分子的检测仍然是一个挑战性课题。本工作首先在不同p H值条下以聚丙烯酸/聚环氧乙烷(PAA/PEO)的混合水溶液制备了系列的固体薄膜,然后采用多种基于连续相调制多脉冲技术的一维和二维~1H多脉冲去耦(CRAMPS)固体NMR新技术,并结合高分辨~(13)C交叉极化魔角旋转(CPMAS)、~(23)Na多量子(MQ)等多核固体NMR实验,对PAA/PEO聚合物共混物的微观结构和动力学进行了原位和系统的研究。通过不同类型的~1H高分辨CRAMPS实验检测到共混物中包含多种不同类型质子:通过氢键相互作用形成二聚体的COOH基团、自由COOH基团、与水结合的COOH基团和主链基团。随着p H值的升高,除主链质子外,大部分其它区域的信号都明显降低,这是由于PAA与PEO以及水的氢键作用减弱所致。这些CRAMPS NMR技术也被用来阐明不同p H值制备的样品中不同基团的分子运动性。此外,二维~1H-~1H自旋交换NMR实验提供了关于聚合物PAA与PEO大分子链间、以及水与聚合物的相互作用。~1H自旋扩散实验表明,在这些共混物中明显存在相微观相分离的结构,并且测定的分散相区尺寸约为17 nm。~(23)Na MQMAS实验揭示了在共混物中存在两种类型~(23)Na位,一种是自由的钠离子,另一种是与大分子相互作用的Na离子。特别是通过~1H-检测的~(23)Na-~1H CPMAS实验揭示了Na~+离子的位置远离PEO而与PAA临近。上述这些SSNMR实验结果在分子水平上提供了氢键相互作用对PAA/PEO共混物微观结构和动力学影响的详细信息,可以获得不同p H值对PAA与PEO的氢键作用、相容性、微观结构、水-聚合物相互作用和不同组分分子运动性的影响。在上述核磁共振研究的基础上,我们提出了一种新的PAA/PEO共混物的结构模型,该模型首次成功地揭示了不同的p H值对PAA/PEO共混物中微观结构和动力学的影响。本工作清楚地表明,固态核磁共振是在分子水平上研究具有复杂相互作用的多相聚合物材料的有力工具。本文的研究工作对于探索检测聚合物弱相互作用的新方法和发展基于氢键相互作用的聚合物新材料的开发具有重要意义。     

Study of the miscibility and the thermal degradation of PVC/PMMA blends

The aim of this paper is to study the miscibility and the thermal degradation of PVC/PMMA blends. For that purpose, blends of variable compositions from 0 to 100 wt% were prepared with and without plasticizer. Their physico-chemical characterization was carried out by differential scanning calorimetric analysis (DSC) and Fourier transform infrared spectroscopy (FTIR). Their thermal degradation under nitrogen at 185°C was studied and the HCl evolved from PVC was measured by the pH method. Degraded samples were characterized, after purification, by FTIR and UV-visible spectroscopy. The DSC analysis showed polymer miscibility up to 60 wt% of PMMA. This miscibility is due to a specific interaction of hydrogen bonding type between carbonyl groups (C=O) of PMMA and hydrogen from (CHCl) groups of PVC as evidenced by FTIR analysis. On the other hand, it was found that PMMA exerted a stabilizing effect on the thermal degradation of PVC by reducing the zip dehydrochlorination and by leading to the formation of short polyenes.     

Poly(styrene-co-p-(hexafluoro-2-hydroxy-2-propyl)-styrene) blends with syndiotactic and/or isotactic poly(methyl methacrylate)

A modified polystyrene, poly(styrene-co-p-(hexafluoro-2-hydroxy-2-propyl)styrene) (FPS), was blended with syndiotactic and/or isotactic poly(methyl methacrylate) (PMMA) in toluene. Blends were prepared under different conditions to control the self-aggregation of the PMMA segments. The formation of hydrogen bonding and the attendant changes in the aggregation or crystallization of PMMA segments were determined in the solid state by means of FTIR and DSC. The results indicate that for the binary blends, the aggregation of PMMA segments is diminished by hydrogen bonding interaction with either s-PMMA or i-PMMA, and that the interaction is stronger with the s-PMMA blends. For the ternary blends, FPS/s-PMMA/i-PMMA, the preference for stereocomplexation in the system with hydrogen bonding may be attributed to the “kink-nucleated” mechanism, which needs relatively short chain lengths of PMMA segments. Regardless of the order of addition of the components, the formation of crystalline stereocomplexes of s- and i-PMMA could be readily detected. Therefore, the miscibility of the polymer blends is dependent on the competition between the self-aggregation of the s- or i-PMMA segments, stereocomplexation and the hydrogen bonding interaction of PMMA segments with FPS.     

Phase behavior of polystyrene acrylonitril copolymer and polymethylmethacrylate blends under shear

Polymer blends undergo external stresses such as pressure and shear in course of processing cycles. The knowledge of their phase behavior at each step of these cycles is crucial for understanding their physical properties and eventually improves their performance in practical applications. The effects of shear on the phase diagram of binary polymer blends are considered. A theoretical formulism is used upon which the free energy is the sum of two terms. The first term is modeled with the Flory–Huggins free energy of mixing and describes the thermodynamic behavior of the system in the quiescent state. The second term represents the excess free energy stored during flow. In the presence of shear flow, the excess free energy is expressed in terms of the viscosity and the shear modulus. Both quantities depend on composition and shear rate. The curvature of the variation of viscosity versus composition has a tremendous impact upon the nature of phase separation. Phase diagrams are described by the spinodal curves and show for the case considered here miscibility enhancement with increasing shear rate. A good correlation is found with experimental data of the literature on blends of polystyrene acrylonitril copolymer and polymethylmethacrylate. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011