Micro‐FT‐IR study of stretching a single filament: Polymorphic transition in nylon 6

The polymorphic transition (γ → α conversion) in a single nylon 6 filament under stretching has been explored for the first time by using micro‐FT‐IR spectroscopy. The content of γ‐form deceases with straining while the amount of α‐form gradually increases, suggesting γ → α conversion. A two‐step mechanism, that is, melting and recrystallization, seems pertinent for the γ → α conversion considering that the γ‐form shows somewhat reversible and the α‐form keeps nearly intact upon unloading. Moreover, stress‐induced γ → α conversion at large strain can be well correlated with the molecular orientation in the amorphous phase and thus a serial arrangement between the γ crystals and amorphous phase along the stretching direction is proposed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 898–902, 2009     

Interaction of water in polymers: Poly(ethylene‐co‐vinyl acetate) and poly(vinyl acetate)

We studied the interaction of water in poly(ethylene‐co‐vinyl acetate) of various vinyl acetate compositions and poly(vinyl acetate), on the basis of the infrared spectrum of the water dissolved therein. The spectrum shows a very sharp and distinct band at about 3690 cm^?1 (named as A), and less‐sharp two bands around 3640 (B) and 3550 cm^?1 (C), the A band being outstanding especially at a low vinyl acetate composition. As the vinyl acetate composition increases, the A band decreases in intensity relative to the C band, whereas the B band increases contrarily. Analysis of the spectral change has elucidated that one‐bonded water (of which one OH is hydrogen‐bonded to the C?O of an ester group and the other OH is free) and two‐bonded water (each OH of which is hydrogen‐bonded to one C?O) coexist in the copolymer and that two‐bonded water increases in relative population with increasing vinyl acetate composition. Dissolved water is entirely two‐bonded in poly(vinyl acetate), in which C?O groups are densely distributed in the matrix. We proved that dissolved water in polymers is hydrogen‐bonded through one or two OH groups to the possessed functional groups but does not cluster. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 777–785, 2005     

The effect of compatibilization on the dynamic properties of polypropylene/nylon‐6 blends studied by broad band dielectric spectroscopy

Polypropylene (PP) and polyamide‐6 (Ny‐6) blends with a 70/30 composition have been studied by broadband dielectric spectroscopy. The unmodified blends are immiscible, and 10% of PP functionalized with maleic anhydride was added as a compatibilizer. The influence of the compatibilizer on the water sorption and on the molecular dynamics of the Ny‐6 phase is followed by the changes induced in the dielectric loss spectra of these blends in both wet and dry states. The shortest range motions are unaffected by the compatibilizer in the dry state, but a higher water sorption is observed in the unmodified blend. Higher activation energies are found for the β relaxation in the dry blends than for the Ny‐6 homopolymer, showing the existence of constraints on these longer scale motions. During increasing temperature experiments, two segmental modes are recorded, the lower temperature mode corresponding to the plasticized material; as the temperature is raised, a second cooperative mode is found, originating in the dry Ny‐6 amorphous phase, rigidized by the loss of moisture. The comparison of the dielectric strengths of the modes shows that the unmodified blend absorbs more water than the compatibilized blend. The segmental dynamics are unaffected by compatibilization. At high temperatures, the high temperature tail of the segmental mode is much higher in the absence of the compatibilizer. The contribution of a peak due to interfacial polarization is lowered by the presence of the compatibilizer, which makes the interface more diffuse and the trapping of free carriers less effective. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1408–1420, 2005     

Polymorphism of nylon‐6 in multiwalled carbon nanotubes/nylon‐6 composites

The effects of pristine and amino‐functionalized multiwalled carbon nanotubes (MWNTs) on the crystallization behaviors of nylon‐6 were investigated by differential scanning calorimetry and X‐ray diffraction. The results indicate the presence of polymorphism in nylon‐6 and its composites, which is dependent on the MWNTs concentration and the cooling rate. More MWNTs and slow cooling from the melt favors the formation of α crystalline form. With the increase in cooling rates, the crystallinity of neat nylon‐6 decreases, and that of the composites decreases initially but increases afterward. Moreover, the degree of crystallinity of the composites is higher than neat nylon‐6 under high cooling rates, counter to what is observed under low cooling rates. The heterogeneous nucleation induced by MWNTs and the restricted mobility of polymer chains are considered as the main factors. Furthermore, addition of MWNTs increases the crystallization rate of α crystalline form but amino‐functionalization of MWNTs weakens this effect. The influence of thermal treatment on the crystalline structure of MWNTs/nylon‐6 composites is also discussed. A γ–α phase transition takes place at lower temperature for MWNTs/nylon‐6 composites than for nylon‐6. The annealing peaks of the composites annealed at 160 °C are higher than that of neat nylon‐6, and the highest annealing peak is obtained for amino‐functionalized MWNTs/nylon‐6 composites. This phenomenon is closely related to the different nucleation and recrystallization behaviors produced by various MWNTs in confined space. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1499–1512, 2006     

New interpretation of progression bands observed in infrared spectra of nylon‐m/n

A series of progression bands observed in the infrared spectra of nylon‐m/n and their model compounds have been interpreted in a new manner on the basis of simply coupled oscillator models of zigzag alkyl chains. Nylon‐m/n possesses the methylene sequences of (CH₂)_m and (CH₂)_n?2, and so the effective models of m and n ? 2 coupled oscillators, respectively, had previously been assumed for the methylene rocking–twisting mode, for example. However, the spectral patterns of progression bands predicted by this previously proposed model have been found to be inconsistent with those observed for many kinds of nylon samples with various m and n values. It is rather reasonable to assume that the effective numbers of oscillators should be m ? 2 and n ? 4 for the methylene rocking, twisting, and wagging modes of the (CH₂)_m and (CH₂)_n?2 sequences, respectively. In other words, the infrared progression bands observed for methylene local modes of nylon‐m/n may be interpreted reasonably with the data of n‐alkane molecules with the chemical formulae CH₃(CH₂)_m?2CH₃ and CH₃(CH₂)_n?4CH₃. For the C? C stretching modes, the equivalent n‐alkanes are CH₃(CH₂)_m?1CH₃ and CH₃(CH₂)_n?3CH₃, respectively. In the simply coupled oscillator model, the vibrational mode of one methylene group is represented by an oscillator, for example. Our new concept is to isolate the terminal oscillator adjacent to the amide group from the other oscillators in the inner parts of the methylene zigzag sequence. This corresponds to a physical situation in which the methylene group adjacent to the amide group shows a different vibrational behavior of larger amplitude than those of the inner methylene sequence, as supported by broad‐line NMR data and molecular dynamics calculations reported in the literature. Another possibility is a difference in the electron structure of the methylene unit adjacent to the amide group from that of the inner methylene sequence, resulting in a difference in the force constant and giving a vibrational decoupling between these two types of methylene units. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1294–1307, 2003     

Blends of nylon‐6 with phenol‐containing polymers

The miscibility of nylon‐6 with poly(4‐vinylphenol) (PVPh) or poly(1‐hydroxy‐2,6‐methylphenylene) (p‐Cl‐novolac) was studied with differential scanning calorimetry and small‐angle X‐ray scattering techniques. Both PVPh and p‐Cl‐novolac are miscible with nylon‐6 at the molecular level. The presence of the phenolic polymers affects the crystallization of nylon‐6 and suppresses its melting point. PVPh increases the long space order in crystalline nylon‐6 because it increases the thickness of the amorphous layers. In contrast, a small quantity of p‐Cl‐novolac tends to decrease the long space order. It seems that p‐Cl‐novolac distributed in the amorphous regions introduces more order in these regions and makes the amorphous layers thinner. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 841–850, 2001     

Infrared spectroscopic study on the crystallization of water in poly(vinyl methyl ether) aqueous solution during heating

The Fourier transform infrared (FTIR) results are consistent with the differential scanning calorimetric results and verify the anomalous crystallization of water in 50% poly(vinyl methyl ether) aqueous solution during heating. Below about ?34 °C, the water/polymer complex was not damaged, and the water still associated with the polymer. When heating to about ?34 °C, the associated water started to free from the unpolar (methyl group) and polar‐site (ether‐oxygen group) interaction fields of polymer gradually. Then crystallization of water was induced in this system at temperatures ranging from ?34 to ?24 °C. The FTIR data also indicate that the structure of water started to change first upon forming strong H bonds among water molecules, and then the dehydration of the polymer began to proceed subsequently when the anomalous crystallization of water occurred. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2772–2779, 2002     

Toughening of nylon‐6 with epoxy‐functionalized acrylonitrile‐butadiene‐styrene copolymer

Glycidyl methacrylate (GMA) functionalized acrylonitrile‐butadiene‐styrene (ABS) copolymers have been prepared via an emulsion polymerization process. The epoxy‐functionalized ABS (e‐ABS) particles were used to toughen nylon‐6. Molau tests and FTIR results showed the reactions between nylon‐6 and e‐ABS have taken place. Scanning electron microscopy (SEM) displayed the compatibilization reaction between epoxy groups of e‐ABS and nylon‐6 chain ends (amine or carboxyl groups), which improve disperse morphology of e‐ABS in the nylon‐6 matrix. The presence of only a small amount of GMA (1 wt %) within the e‐ABS copolymer was sufficient to induce a pronounced improvement of the impact strength of nylon‐6 blends; whereas further increase of the GMA contents in e‐ABS resulted in lower impact strength because of the crosslinking reaction between nylon‐6 and e‐ABS, resulting in agglomeration of the ABS particles. SEM results showed shear yielding of the nylon‐6 matrix and cavitation of rubber particles were the major toughening mechanisms. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2170–2180, 2005     

Synthesis of nylon‐6 triblock copolymers with bifunctional polymeric activators

ABA‐type copolymers were synthesized by the anionic polymerization of hexanelactam with the sodium salt of hexanelactam as an initiator and amino‐terminated polytetrahydrofuran telechelic functionalized with diisocyanates. Two types of diisocyanates, hexamethylene diisocyanate (1,6‐diisocyanatohexane) and isophorone diisocyanate (IF; 5‐isocyanato‐1‐isocyanatomethyl‐1,3,3‐trimethylcyclohexane), were used as precursors for polymeric activators (PACs). IF was used for the first time. It was proven that the PACs were incorporated as soft, flexible midblocks in the chains of hard nylon‐6 segments. The polymers were isolated and characterized with various spectroscopic techniques. The effects of the central PAC block (according to the type, molecular weight, and content) and the polymerization conditions on the kinetics, activation energies, molecular weights, and structures of the triblock copolymers were investigated. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4154–4164, 2000     

The Temperature‐Dependent Hydrogen‐Bonding Signature of Lipids Monitored in the Far‐Infrared Domain

Phospholipids are studied by means of Fourier transform infrared (FTIR) spectroscopy in the mid‐ and far‐infrared spectral ranges, thereby establishing the hydrogen‐bonding continuum as a function of the temperature. The well‐known mid‐infrared spectrum of the phospholipid layer clearly shows a temperature‐dependent phase transition. In the far‐infrared region (from 300 to 50 cm^?1), an alternation of the interaction between the phospholipids and water molecules is found. The hydrogen‐bonding network ensemble and bound water molecules can be monitored in this spectral region. The lipid structure is found to strongly influence the intermolecular hydrogen‐bonding interplay. Thus, studies in the far‐infrared region provide significant information—at the molecular level—about the intermolecular hydrogen‐bonding signature of self‐assembled phospholipids.     

应用光谱和分子模拟法研究一种聚酰亚胺聚合物与人免疫球蛋白的相互作用

本文利用荧光猝灭法、红外光谱法及计算机模拟技术研究了一种聚酰亚胺聚合物(2,6-Bis(4-amino-2-trifluoromethyl phenoxy-4’- benzoyl)-pyridine,简称BAFP )与人免疫球蛋白（HIgG）的相互作用。同步荧光的结果定性地说明了BAFP影响水溶液中HIgG二级结构的情况。而判定BAFP影响HIgG二级结构的定量依据来自红外光谱,实验数据表明α螺旋结构的含量相比未加入药物时增加了约2.6～10.2%,,β折叠增大了约13.6～27.7%,,而β转角则减小了约23.8～30.3%。分子模拟的结果显示BAFP与HIgG的键合作用很强,并且有四个氢键在BAFP与HIgG分子的色氨酸Trp 170, 缬氨酸Val 105, 甲硫氨酸Met 139 及天冬酰胺Asn 52之间形成;同时也显示出维持药物与蛋白质的相互作用力主要是疏水作用,这与实验所得到的热力学参数判定作用力的结果相一致（依据范德霍夫公式计算得 与 的值分别为-6.70KJ.mol-1 和 71.93 J.mol-1.K-1）。     

毛冬青皂苷甲的18,19-脱水皂苷元二甲酯的红外光谱分子内氢键效应的研究

有机化合物稀溶液的红外光谱用来研究分子内氢键是否存在,存在的形式等,以确定分子的构型和构象。毛冬青皂甙甲 IlexsaponinA 是从民间治疗冠心病有效药物毛冬青Ilex     

Preparation and characterization of protein‐free natural rubber

Protein‐free natural rubber was prepared by incubation of natural rubber latex with urea and polar organic solvent in the presence of surfactant. Effect of the polar organic solvent on the removal of the proteins was investigated with respect to chemical affinity and concentration of the solvents. Under a suitable condition, nitrogen content of the deproteinized natural rubber (DPNR) was 0.000 wt%, which was less than that of natural rubber deproteinized with proteolytic enzyme or urea in the presence of surfactant. The removal of all proteins from natural rubber was proved through FT‐IR spectroscopy. Changes in morphology of the DPNR were also investigated by transmission electron microscopy. Copyright © 2011 John Wiley & Sons, Ltd.     

Rose‐Like Microstructures of Polyaniline by Using a Simplified Template‐Free Method under a High Relative Humidity

3‐D rose‐like microstructures of polyaniline (PANI), which are self‐assembled from 2‐D nanosheets consisted of 1‐D nanofibers, were synthesized by a template‐free method in the presence of ammonium peroxydisulfate (APS) as both oxidant and dopant under a high relative humidity of 80% for the first time. When the relative humidity increases from 25 to 80%, not only morphology of the micro/nanostructured PANI undergoes a change from 1‐D nanofibers to 2‐D nanosheets to 3‐D rose‐like microstructures, but also increase in crystallinity. It is proposed that a cooperation effect of the oriented water molecules at the vapor–water interface and difference in hydrogen bonding energies between the interface and the bulk induced by the relative high humidity results in the formation of the 3‐D rose‐like microstructures self‐assembled from 2‐D nanosheets. Moreover, the method reported may provide a simple approach for understanding self‐assembly of complex micro/nanostructures of PANI.

     

Crystallographic study of self‐organization in the solid state including quasi‐aromatic pseudo‐ring stacking interactions in 1‐benzoyl‐3‐(3,4‐dimethoxyphenyl)thiourea and 1‐benzoyl‐3‐(2‐hydroxypropyl)thiourea

1‐Benzoylthioureas contain both carbonyl and thiocarbonyl functional groups and are of interest for their biological activity, metal coordination ability and involvement in hydrogen‐bond formation. Two novel 1‐benzoylthiourea derivatives, namely 1‐benzoyl‐3‐(3,4‐dimethoxyphenyl)thiourea, C₁₆H₁₆N₂O₃S, (I), and 1‐benzoyl‐3‐(2‐hydroxypropyl)thiourea, C₁₁H₁₄N₂O₂S, (II), have been synthesized and characterized. Compound (I) crystallizes in the space group P , while (II) crystallizes in the space group P 2₁/c . In both structures, intramolecular N—H…O hydrogen bonding is present. The resulting six‐membered pseudo‐rings are quasi‐aromatic and, in each case, interact with phenyl rings via stacking‐type interactions. C—H…O, C—H…S and C—H…π interactions are also present. In (I), there is one molecule in the asymmetric unit. Pairs of molecules are connected via two intermolecular N—H…S hydrogen bonds, forming centrosymmetric dimers. In (II), there are two symmetry‐independent molecules that differ mainly in the relative orientations of the phenyl rings with respect to the thiourea cores. Additional strong hydrogen‐bond donor and acceptor –OH groups participate in the formation of intermolecular N—H…O and O—H…S hydrogen bonds that join molecules into chains extending in the [001] direction.     

Fracture toughness of nylon‐6 blends with maleated rubbers

The fracture toughness of blends of nylon‐6 with maleated ethylene–propylene rubber and maleated styrene/hydrogenated butadiene/styrene triblock copolymer was investigated with a single‐edge‐notched three‐point‐bending instrumented Dynatup test. The blends for which the rubber particle size was less than 0.7 μm fractured in a ductile manner over the whole range of ligament lengths, whereas the blends with particles larger than 0.7 μm showed a ductile‐to‐brittle transition with the ligament length. In this regime, ductile fracture was observed for specimens with short ligaments, whereas brittle fracture was seen for those with long ligaments. The ductile fracture behavior was analyzed with the essential‐work‐of‐fracture model, whereas linear elastic fracture mechanics techniques were used to analyze the brittle fracture behavior. The fact that the ductile fracture energy was larger for the blends with the styrene/hydrogenated butadiene/styrene triblock copolymer than for those with ethylene–propylene rubber was due to the larger dissipative energy density of the blends based on the styrene/hydrogenated butadiene/styrene triblock copolymer. Both the critical strain energy release rate (G_IC) and the plane‐strain critical stress intensity factor (K_IC) increased as the rubber particle size decreased for both blend systems. The G_IC and K_IC parameters had similar values, regardless of the rubber type, when the rubber particle size was fixed. The transition ligament length was near the size criterion for plane‐strain conditions for both blend systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1739–1758, 2004     

On the induced‐fit mechanism of substrate‐enzyme binding structures of nylon‐oligomer hydrolase

We present a detailed computational investigation of the induced‐fit motion in a nylon‐oligomer hydrolase (NylB) upon substrate binding. To this aim, we resort on the recently introduced parallel cascade selection molecular dynamics approach, allowing for an accelerated access to the set of conformational changes from an open‐ to a closed‐state structure to form the enzyme‐substrate complex in a specific induce‐fit mechanism. The structural investigation is quantitatively complemented by free energy analyses within the umbrella sampling algorithm accompanied by weighted histogram analysis. We find that the stabilization free energy is about 1.4 kcal/mol, whereas the highest free energy barrier to be overcome is about 2.3 kcal/mol. Conversely, the energetic contribution for the substrate binding is about 20 kcal/mol, as estimated from Generalized Born/Surface Area. This means that the open‐close induced‐fit motion could occur frequently once the substrate binds to the open state of NylB. © 2014 Wiley Periodicals, Inc.