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。     

Miscibility and isothermal crystallization behavior of polyamide 6/poly(vinyl alcohol) blend

An investigation of miscibility and isothermal crystallization behavior of Polyamide 6 (PA6)/Poly(vinyl alcohol) (PVA) blends was conducted. Fourier transform infrared spectra (FTIR) analysis indicated that the interactions between the carbonyl groups of PA6 and hydroxyl groups of PVA increase as the weight ratios of PA6 to PVA of PA6/PVA specimens increase. This interaction between PA6 and PVA leads to their miscibility in the amorphous region and even some extent effects on their crystal phase, respectively. Further isothermal crystallization behavior of PA6/PVA indicate that the miscibility of PVA in PA6 leading difficulty in crystallization of PA6. Several kinetics equations are employed to describe the effects of PVA on the crystallization properties of PA6 in PA6/PVA blends in detail. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1360–1368, 2008     

Molecular modeling simulations to predict compatibility of poly(vinyl alcohol) and chitosan blends: a comparison with experiments

Molecular modeling simulations are the most important tools to predict blend compatibility of polymers that are otherwise difficult to predict by experimental means. Conflicting reports have been reported on the blend compatibility of poly(vinyl alcohol), PVA, and chitosan, CS polymers. Since both the polymers are widely used in pharmaceutics as drug-loaded particulates and as separation membranes, we felt it necessary to investigate their compatibility over the practical range of compositions. In this paper, we attempt to study the compatibility of PVA and CS polymers using molecular modeling strategies to understand the interactions between CS and PVA polymers to predict their compatibility from atomistic simulations. Flory-Huggins interaction parameter, chi, was computed at 298 K to assess the blend compatibility at different ratios of the component polymers. Miscibility was observed for blends below 50% of PVA, while immiscibility was prevalent at compositions between 50 and 90% PVA. Computed results confirmed the experimental findings of dynamic mechanical thermal analysis, suggesting the validity of modeling strategies employed. Plots of Hildebrand solubility parameter and cohesive energy density calculated at 298 K supported these findings. The chi values for blends, which satisfied the criteria of miscibility of polymers computed by atomistic simulations, agreed with the solubility criteria related to order parameters calculated from mesoscopic simulations. Miscibility between PVA and CS polymers is attributed to hydrogen bond formation and to an understanding of which of the interacting groups of CS, i.e., -CH2OH or -NH2, are responsible in blend miscibility. This was further confirmed by molecular dynamics simulations of radial distribution functions for groups or atoms that are tentatively involved in interactions. These results are correlated well to obtain more realistic information about interactions involved as a function of blend composition. Computed free-energy from the mesoscopic simulation for blends reached equilibrium, particularly when the simulation was performed at higher time step, indicating stability of the blend system at certain compositions.     

Miscibility and hydrogen-bonding interactions in biodegradable polymer blends of poly(3-hydroxybutyrate) and a partially hydrolyzed poly(vinyl alcohol)

Miscibility and hydrogen-bonding interactions, as well as the morphological properties, of biodegradable polymer blends of poly(3-hydroxybutyrate) (PHB) and a 80% hydrolyzed poly(vinyl alcohol) (PVA80) were studied using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). It was found that PHB is miscible with PVA80 in the amorphous phase over the whole composition range. PVA80 or PHB assumes the amorphous state when its content in the blend is lower than 30 or 20 wt %, respectively. Due to the heavy overlapping of C=O stretching bands from both PVA80 and PHB and the nonmeasurable peak shift in the OH stretching band region, hydrogen-bonding interactions between the OH group of PVA80 and the C=O group of PHB were not detectable at room temperature, but were observed at a higher temperature of 180 degrees C. This is because hydrogen-bonding interactions are promoted above the melting points of these two crystalline polymers, by increasing the mixing entropy and reducing the Deltachi effect. Blending PHB with PVA80 does not have a significant effect on the OH groups of PVA80 that are hydrogen bonded with each other. Instead, the C=O groups of PHB dispossess some of the OH groups that are hydrogen bonded to the C=O groups of PVA80, which gives rise to the miscibility between PVA80 and PHB in the amorphous phase.     

聚环氧乙烷(PEO)与聚醋酸乙烯酯(PVA)的共混研究

动态力学谱研究表明熔融共混PVA/PEO体系的无定形态中存在着纯PEO及PVA/PEO的相容或部分相容相。相容或部分相容相的T_g随共混物组成的变化远高于按照FOX方程的计算值。用结晶和分子间相互作用解释了这种对FOX方程的偏离。应用FTIR差示光谱技术对PVA/PEO共混物和PVA/DGDE浓溶液的研究证实了PVA分子链上酯基和PEO分子链存在着强的相互作用。     

Comblike poly(ethylene oxide)/hydrophobic C6 branched chitosan surfactant polymers as anti-infection surface modifying agents

A series of structurally well-defined poly(ethylene oxide)/hydrophobic C₆ branched chitosan surfactant polymers that undergo surface induced self assembly on hydrophobic biomaterial surfaces were synthesized and characterized. The surfactant polymers consist of low molecular weight (M_w) chitosan backbone with hydrophilic poly(ethylene oxide) (PEO) and hydrophobic hexyl pendant groups. Chitosan was depolymerized by nitrous acid deaminative cleavage. Hexanal and aldehyde-terminated PEO chains were simultaneously attached to low M_w chitosan hydrochloride via reductive amination. The surfactant polymers were prepared with various ratios of the two side chains. The molecular composition of the surfactant polymers was determined by FT-IR and ¹H NMR. Surface active properties at the air–water interface were determined by Langmuir film balance measurements. The surfactant polymers with PEO/hexyl ratios of 1:3.0 and 1:14.4 were used as surface modifying agents to investigate their anti-infection properties. E. coli adhesion on Silastic^® surface was decreased significantly by the surfactant polymer with PEO/hexyl 1:3.0. Surface growth of adherent E. coli was effectively suppressed by both tested surfactant polymers.     

Viscosity enhancement of complexed solutions formed through the complexation of nonionic water‐soluble polymers with chemically complementary structures in aqueous media

The intermacromolecular complexation of polymers with chemically complementary structures in aqueous media is a new approach to modifying polymer solutions, especially to enhance solution viscosity. In this study, complexed solutions formed through the hydrogen‐bonding complexation of several nonionic water‐soluble polymer pairs—poly(acrylic acid) (PAA) with polyacrylamide (PAM), PAM with poly(ethylene oxide) (PEO), PAA with poly(vinyl alcohol) (PVA), and PEO with PVA—were prepared, and the viscosity enhancement of the complexed solutions were studied with vision spectrophotometry and viscometry. The effects of the polymer concentration, polymer molecular weight, and pH value of the polymer solution on the intermacromolecular interactions were investigated through a comparison of the viscosity enhancement factor R of different complexed solutions. The results show that the viscosity of the PAA/PAM complexed solution is much higher than that of its constituents, whereas that of the PAM/PEO and the PAA/PVA complexed solutions are between the viscosities of their constituents but are higher than the theory values calculated from the blending rule of two polymer solutions. These results indicate that in the complexed solutions there exist interactions between the macromolecules with chemically complementary structures, although the interactions are quite different for the different complexed systems. It is the interactions that lead to an association of the polymers and, hence, an obvious enhancement in the solution viscosity and the resistance of the polymer solutions to shearing. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1069–1077, 2000     

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     

Strength of hydrogen bonding in the novolak-type phenolic resin blends

The specific interaction strength of novolak-type phenolic resin blended with three similar polymers [i.e., poly(ethylene oxide) (PEO), poly(ethylene glycol) (PEG), and poly(vinyl alcohol) (PVA)] were characterized by means of glass transition temperature behavior and Fourier transform infrared (FTIR) spectroscopy. The interassociation formed within phenolic blends with the addition of a modifier not only overcomes the effect of self-association of the phenolic upon blending, but also increases the strength of phenolic blend. The strength of interassociation within the phenolic blend is the function of the hydrogen bonding group of a modifier, in increasing order, is phenolic/PVA, phenolic/PEG, and phenolic/PEO blend, corresponding to the result of “q” value in the Kwei equation. The FTIR result is in agreement with the inference of T_g behavior. In addition, the fact that the specific strength of hydrogen bonding of hydroxyl–hydroxyl is stronger than that of hydroxyl–ether can also be concluded. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1721–1729, 1998     

聚环氧乙烷(PE0)与聚双酚A羟基醚(PBHE)共混体系的研究

 用偏光显微镜(PLM)、扭辫(TBA)、IR及WAXD对PEO/PBHE共混体系结晶形态进行了研究。结果表明,PEO含量在50％以上的共混体系,几乎完全被PEO球晶充满,非晶态PBHE作为微区分散在大球晶之间或球晶之中。PEO含量为40％和30％的照片上呈现树枝晶。PEO含量为20％以下时照片中不再看到结晶出现,PEO与PBHE形成单一非晶相。PEO/PBHE共混体系的组分之间存在着氢键相互作用,这种作用强于PBHE分子间的氢键作用。共混体系的结晶度及T_g随PBHE组分含量的增加,前者减小后者增加并符合FOX方程揭示的规律。PEO与PBHE具有很好的相容性。     

聚环氧乙烷(PE0)与聚双酚A羟基醚(PBHE)共混体系的研究

用偏光显微镜(PLM)、扭辫(TBA)、IR及WAXD对PEO/PBHE共混体系结晶形态进行了研究。结果表明,PEO含量在50％以上的共混体系,几乎完全被PEO球晶充满,非晶态PBHE作为微区分散在大球晶之间或球晶之中。PEO含量为40％和30％的照片上呈现树枝晶。PEO含量为20％以下时照片中不再看到结晶出现,PEO与PBHE形成单一非晶相。PEO/PBHE共混体系的组分之间存在着氢键相互作用,这种作用强于PBHE分子间的氢键作用。共混体系的结晶度及T_g随PBHE组分含量的增加,前者减小后者增加并符合FOX方程揭示的规律。PEO与PBHE具有很好的相容性。     

Morphology, crystalline structure and thermal properties of PEO/MEEP blends

Poly(ethylene oxide) and poly[bis[2-(2′-methoxyethoxy) ethoxy] phosphazene], PEO/MEEP, polymer blends were investigated by thermal analysis, X-ray diffraction, and atomic force microscopy. MEEP is an amorphous polymer and its semicrystalline blends with PEO showed two distinct glass transitions, whose composition dependence was analysed by the Lodge and McLeish self-concentration model. It appears that an amorphous miscible phase is present in these blends. Excess melting enthalpy was observed for blends with high MEEP concentration. PEO lamellar characteristics exhibited changes as a function of MEEP content, both in X-ray patterns and AFM images that indicated the intercalation of MEEP side chains in the lamellar crystalline structure.     

Molecular modeling simulation and experimental measurements to characterize chitosan and poly(vinyl pyrrolidone) blend interactions

Blends of chitosan and poly(vinyl pyrrolidone) (PVP) have a high potential for use in various biomedical applications and in advanced drug‐delivery systems. Recently, the physical and chemical properties of these blends have been extensively characterized. However, the molecular interaction between these two polymers is not fully understood. In this study, the intermolecular interaction between chitosan and PVP was experimentally investigated using ¹³C cross‐polarization magic angle‐spinning nuclear magnetic resonance (¹³C CP/MAS NMR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). According to these experimental results, the interaction between the polymers takes place through the carbonyl group of PVP and either the OH? C₆, OH? C₃, or NH? C₂ of chitosan. In an attempt to identify the interacting groups of these polymers, molecular modeling simulation was performed. Molecular simulation was able to clarify that the hydrogen atom of OH? C₆ of chitosan was the most favorable site to form hydrogen bonding with the oxygen atom of C?O of PVP, followed by that of OH? C₃, whereas that of NH? C₂ was the weakest proton donor group. The nitrogen atom of PVP was not involved in the intermolecular interaction between these polymers. Furthermore, the interactions between these polymers are higher when PVP concentrations are lower, and interactions decrease with increasing amounts of PVP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1258–1264, 2008     

自旋标记法研究STVPh/PEO共混体系的链运动

利用自旋标记法将氮氧自由基连接在聚氧化乙烯分子末端,测得其与不同羟基含量的苯乙烯-4-乙烯基苯酚共聚物组成高分子共混体系的ESR波谱,研究了各组分的分子链运动.自旋标记聚氧化乙烯的ESR谱图在整个温度范围内只显示快运动或慢运动的一种运动成分,表明氮氧自由基处于单一的环境中.高分子共混体系的ESR谱在一定温度范围内同时存在快运动和慢运动的两种运动成分,且两成分相对比例随温度的变化而变化,表明体系中氮氧自由基处于不同的微相环境中.由ESR谱得到的T_5mT,τ_c,E_a的值都随着体系中羟基含量的增加而变大,显示标记分子的链运动在共混体系中的活动逐步受阻.与此同时,随着该共混物中酚羟基和醚氧基间氢键相互作用强度的增大,共混物的相容性得到逐步改善.     

Structure and interactions in homopolymers and blends as studied by the methods of vibrational and nmr spectroscopy

The combination of IR, Raman and NMR spectroscopy was used in the study of the blends of semicrystalline and amorphous polymers with considerably different strength of intermolecular interactions: poly(ϵ-caprolactam)/polystyrene (PCL/PS), poly(ethylene oxide)/poly(methyl methacrylate) (PEO/PMMA) and poly(N-methyllaurolactam)/poly(4-vinylphenol) (PNMLL/PVPh). In the vibrational and NMR spectra of the blends composed of non-interacting polymers (PCL/PS) and weakly interacting polymers (PEO/PMMA), no band changes were observed which would indicate changes of the conformational structures. ¹H NMR relaxation of the PCL and PS components in the blends is the same as in the respective homopolymers similarly treated. In the blends of weakly interacting polymers (PEO/PMMA), the crystallinity of PEO is influenced by the presence of PMMA and is negligible in the blends with less than 30 wt.-% of PEO. The rotating-frame spin-lattice relaxation time for protons T^H_1p of PMMA indicates close contact of the PMMA and PEO chains. In the blends PNMLL/PVPh with strong hydrogen-bonding interactions, both components are intimately mixed on a scale of 3–4 nm and significant shifts of some bands both in vibrational and in NMR spectra reveal changes of structure.     

Morphology of ultrathin polymer films based on poly(ethylene oxide) blends

The structure of ultrathin (15–200 nm) films of two types prepared from polymer blends based on PEO (the crystallizable component), namely, PEO-poly(arylene sulfone oxide) (the amorphous component) and PEO-PB (the amorphous component), has been studied by atomic force microscopy. The content of PEO in both blends is 76 wt %. Ultrathin blend films have been applied on a Si substrate via substrate dipping into dilute solutions of polymer blends in chloroform at room temperature. The rate of the substrate lift has been varied from 0.1 to 1 mm/min. The amorphous-amorphous separation takes place during formation of ultrathin films of the above blends in the course of the substrate lift at the stage of gelation. The crystallization of PEO and dewetting in the resulting two-phase blend gels depend on the rate of the substrate lift and the rigidity of macromolecules of the amorphous component. Moreover, the predominant interaction of the substrate with one of the components plays a significant role in structure formation of ultrathin films of both polymer blends.     

Peculiarities of Formation of Intermolecular Polycomplexes Based on Polyacrylamide,Poly(vinyl alcohol) and Poly(ethylene oxide)

The phenomenon of self-assembly of aggregates formed by relatively short chains of poly(vinyl alcohol) (PVA) on the long macromolecules of polyacrylamide (PAA) in aqueous medium are discussed. PVA and PAA form intermolecular polycomplexes (InterPC) of a constant composition independently on a ratio of polymer components. The complex formation between high-molecular-weight PAA and relatively low-molecular-weight poly(ethylene oxide) (PEO) are considered also. PEO with M ⩽ 4·10⁴ g.mol⁻¹ weakly interacts with PAA. The polymer-polymer interaction can be intensified when the part of amide groups (∼20 mol %) on PAA chain to transform into the carboxylic groups. InterPCs formed by PEO and initial or modified PAA have associative structure with friable packing of the polymer segments. They are stabilized by the hydrogen bond system.     

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.     

Poly(ethylene oxide)/poly(methyl methacrylate) (semi-)interpenetrating polymer networks: Synthesis and phase diagrams

Interpenetrating polymer networks (IPNs) of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) were prepared by simultaneous network formation. The PEO network was produced by acid-catlayzed self-condensation of α,ω-bis(triethoxysilane)-terminated PEO in the presence of small amounts of water. The PMMA network was formed by free radical polymerization of MAA in the presence of divinylbenzene as crosslinker. The reaction conditions were adjusted to obtain similar crosslinking kinetics for both reactions. An attempt was made to construct a phase diagram of the IPNs by measuring the composition of the IPNs at the moment of the appearance of the phase separation, as indicated by the onset of turbidity. This composition could be determined because the siloxane crosslinks of the PEO network could be hydrolyzed in aqueous NaOH with the formation of linear, soluble PEO chains. The phase diagram was compared with phase diagrams of blends of linear polymers and of semi-IPNs (crosslinked PMMA and linear PEO), obtained under similar conditions, i.e. polymerization of MMA in the presence of varying amounts of PEO. It was observed that the form of the phase diagrams of the linear polymers is similar to that of the IPNs, but is quite different from that of the semi-IPNs. Thus, homogeneous transparent materials containing up to 60% of PEO could be prepared in the blends and the IPNs, but in the semi-IPNs, phase separation occurred with PEO contents as low as 10%.     

Poly(N-phenyl-2-hydroxytrimethylene amine): Its blends with poly(ϵ-caprolactone) and water-soluble polyethers

A new polymer with pendant hydroxyl groups, namely, poly(N-phenyl-2-hydroxytrime-thylene amine) (PHA), was synthesized by a direct condensation polymerization of aniline and epichlorohydrin in an alkaline medium. The new polymer is amorphous with a glass transition temperature (T_g) of 70°C. Blends of PHA with poly(ϵ-caprolactone) (PCL), as well as with two water-soluble polyethers, poly(ethylene oxide) (PEO) and poly(vinyl methyl ether) (PVME), were prepared by casting from a common solvent. It was found that all the three blends were miscible and showed a single, composition dependent glass transition temperature (T_g). FTIR studies revealed that PHA can form hydrogen bonds with PCL, PEO, and PVME, which are driving forces for the miscibility of the blends. © 1997 John Wiley & Sons, Inc.