Investigation on Brill transition of nylons 6/16, 4/16 and 2/16 by variable‐temperature WAXD and FTIR

Brill transition behaviour of nylons 6/16, 4/16 and 2/16 has been studied systematically by variable‐temperature wide‐angle X‐ray diffraction (WAXD) and real‐time FTIR. It is shown that all nylons investigated undergo Brill transitions before melting on heating. Brill temperatures detected by real‐time FTIR are consistent with the results of variable‐temperature WAXD measurements. In addition, Brill bands were identified based on real‐time IR spectra and further consideration of —NH— groups provided additional information for discussing the mechanism of the crystalline transition. Copyright © 2003 Society of Chemical Industry     

Thermotropic liquid crystalline main-chain polyamides containing diaza-18-crown-6-ether units

Polymers incorporating conventional mesogens and diazo-18-crown-6-ether were prepared. The crown ether unit seems to be too flexible and only weak liquid crystal character can be observed by optical microscopy except when the mesogen is terphenyl. These liquid crystalline characteristics disappeared when the polymers were complexed with potassium ions.     

Moisture absorption by various polyamides and their associated dimensional changes

The dimensional changes associated with moisture absorption were examined for various polyamides (PAs). Plaques of varying thickness were compression‐molded or injection‐molded and then immersed in water. Periodically, the plaques were removed from water and their mass and dimensions were measured. This was continued until they were completely saturated. The more polar PA46 absorbed more water than less polar PA6 and PA66 and therefore, was more susceptible to moisture‐induced dimensional growth. For a given polymer, it was found that the thicker samples took longer to reach saturation, but had the same diffusion coefficient as thinner ones. Changes in dimensions coincided with changes in mass. Sorption and swelling followed slightly different paths, but arrived at their respective equilibrium values at the same time. Within experimental error, dimensional expansion due to water absorption was the same in all directions. Injection‐molded samples absorbed slightly more water than compression‐molded ones, but their absorption rates were equal. Equilibrium water absorption data were used to approximate the dimensional changes associated with the swelling of the PAs. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Pectinlyase immobilization on polyamides for application in the food processing industry

The study concerns the immobilization of a pectinlyase (PL, EC 4.2.2.3) purified by means of a commercial enzyme for its possible applications in fruit juice and beverage processing. Results previously obtained were improved by employing polyamides, i.e. nylon 6 and nylon 11, activated by easy to perform and inexpensive methods such as direct activation with glutaraldehyde and alkylation with dimethylsulphate followed by treatment with amines and glutaraldehyde. The nylon 6 activated with glutaraldehyde gave an activity of the immobilized PL of about 200 U g^?1 (at optimum pH) and a half-life of about 190 h (at pH 3·3 and 25°C).     

A polarised μ-FTIR study on a model system for nylon 6 6: implications for the nylon Brill structure

Polarised transmission FTIR microscopy studies (μ-FTIR) have been performed on a monodisperse 3-amide oligomer. The oligomer is a model compound for nylon 6 6; it has essentially the same room temperature crystal structure, and it undergoes the same high temperature transition, the Brill transition, prior to melting. However, the oligoamide forms extended chain, rather than chain-folded, crystals, and so crystals are produced that are essentially 100% crystalline, and of μm–mm size. Consequently, this material is ideally suited for polarised μ-FTIR single crystal studies. The thermal polarised FTIR behaviour of this material provides definitive proof that the Brill transition does not involve major rearrangement of hydrogen bonds, since the strong parallel polarisation of both the NH stretch and amide I bands are retained right up to melting. Quantitative infrared dichroism measurements indicate that a maximum of 5° rotation of the N–H bonds about the extended chain axis occurs prior to melting. These results strongly suggests that the equivalent Brill transition in nylon 6 6 also proceeds without significant hydrogen bond rearrangement. In addition we have investigated the behaviour of designated ‘Brill’, ‘crystalline’, ‘amorphous’ and ‘fold’ bands that are present in our spectra.     

Influence of temperature on lattice spacings of melt‐crystallized poly(iminosebacoyl iminodecamethylene)

The variation of lattice spacings of poly(iminosebacoyl iminodecamethylene) (nylon‐10,10) with temperature was studied by wide‐angle X‐ray diffraction (WAXD) during both heating and cooling processes, which demonstrates a gradual and continuous transition with temperature. However, the crystal melts before the two peaks merge completely. Both WAXD and differential scanning calorimetry show that crystallization from molten sample results directly in the triclinic form. Additionally, this transition is thermodynamically reversible. Comparison of this transition with that of nylon‐6,6, suggests that no hydrogen‐bonded network is formed during or after the transition. We prefer to attribute this transition to asymmetrical thermal expansion in the nylon‐10,10 crystals rather than to a true first‐order phase transition. © 2001 Society of Chemical Industry     

Synthesis and characterization of polyamides X 18

Step heating melt polycondensation was adopted in the preparation of polyamides based on 1,16‐octadecane diacid and α,ω? (CH₂)_2n diamines (n = 1–6). The structure was confirmed by various spectroscopic techniques (IR, Raman, ¹H‐NMR, and ¹³C‐NMR). High molecular masses were obtained only in the presence of an excess of diamine and when the diamine possessed low volatility. The molecular masses were between (0.94 and 2.1) × 10⁴ Da for all polyamides under consideration. An excellent correlation between size exclusion chromatography and ¹H‐NMR data was demonstrated in the measurement of the degree of polymerization. The melting temperatures of the polyamides decreased from polyamide 12 18 to polyamide 2 18 as the amide density along the molecular chain declined. No significant variation was observed in the glass‐transition and decomposition temperatures of the polyamides that were obtained. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1565–1571, 2005     

“Orientation induced memory effect” in polyamides and the relationship to hydrogen bonding

The influence of molecular orientation on the “memory effect” of polyamides was investigated by differential scanning calorimetry. Melt crystallization of undrawn and drawn polyamide 6 (N6) and polyamide 66 (N66) fibers showed no difference either in the rate of crystallization or crystallization temperature. We demonstrated that hydrogen bonding does not play a major role in melt crystallization kinetics of polyamides (N6 and N66), and the “memory effect” is only retained for polymers, including N6 and N66, because of insufficient time spent above the melting temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 772–775, 2003     

Synthesis and study of new polyamides with side oxadiazole rings

A series of six new aromatic polyamides with side oxadiazole rings has been synthesized by polycondensation reaction of aromatic diamines containing pendent substituted oxadiazole groups with a silicon‐containing diacid chloride [namely, bis(p‐chlorocarbonyl‐phenylene)diphenylsilane] or with a fluorine‐containing diacid chloride [namely, hexafluoroisopropylidene‐bis(p‐benzoyl chloride)]. All polymers were easily soluble in amidic solvents, such as N‐methylpyrrolidinone and dimethylformamide, and gave thin transparent films by casting such solutions. Very thin coatings were deposited onto silicon wafers and exhibited smooth, pinhole‐free surfaces in atomic force microscopy investigations. The polymers showed high thermal stability, with decomposition temperature >400°C. Some of them did exhibit a glass transition, in the range 152–276°C, with a reasonable interval between glass transition and decomposition. Four of these polymers showed blue photoluminescence, in the range 460–480 nm, which makes them promising candidates for future use as high‐performance materials in the construction of light‐emitting devices. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 714–721, 2003     

Synthesis,characterization, and thermal studies of polyamides and polyimides containing two silarylene units in the main chain

Polyamides (PAs) and polyimides (PIs) containing two silarylene units were synthesized and characterized by their spectroscopic properties. Bis(4‐aminophenyl)methylphenylsilane was employed as a unique diamine, whereas acid dichloride and dianhydride monomers contained combinations of methyl and phenyl groups bonded to the silicon atom. The PAs were obtained in dimethylformamide solutions, and the PIs were prepared by thermal cyclization of the respective poly(amic acid)s (PAAs). The yields were low (32–51%), and the inherent viscosities for PAAs were slightly higher than the PA values. The low inherent viscosities were indicative of oligomeric species. The thermal stability was also evaluated by thermogravimetric analysis and differential scanning calorimetry analysis. In both series, the glass‐transition temperatures increased with the replacement of methyl groups by aromatic rings according to the lower mobility of the polymeric chain. On the other hand, an increase in the aromatic content also increased the thermal stability of the PAs and PIs, and this was registered through their thermal decomposition temperatures. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystalline structure and crystallization of stereoisomeric polyamides derived from arabinaric acid

The pair of stereoisomeric polyamides PA-6dAr and PA-6lAr, as well as the racemic stereocopolyamide PA-6dlAr was synthesized from hexamethylenediamine and 2,3,4-tri-O-methyl-arabinaric acid (d, l and their equimolar mixture, respectively). All these polyamides were aregic, thermally stable and display high crystallinity. The combined analysis by X-ray and electron diffraction revealed that the all three polyamides adopted the same crystal structure, which consists of a rhombic lattice with the chains in a highly contracted conformation capable of accommodating efficiently the sugar moiety in the space. The Avrami kinetic analysis revealed that copolyamide PA-6dlAr crystallized isothermally much slower than the optically homogeneous polyamides. A parallel study carried out on the racemic mixture of PA-6dAr and PA-6lAr evidenced that this mixture has a crystal structure and displays a thermal behavior similar to their separated components, and that its crystallization rate is intermediate between them and the racemic copolyamide PAdlAr.     

Computational study of thermal and mechanical properties of nylons and bio-based furan polyamides

We have investigated thermal and mechanical properties of bio-based furan polyamides and petroleum-based nylons with atomistic simulations. Glass transition temperatures estimated from a series of simulations at different temperatures were in good agreement with experimental measurements. Stress–strain relationships under uniaxial deformation conditions were also obtained and analyzed. Overall, polymers with smaller repeat units exhibited slightly higher glass transition temperatures and elastic moduli, which were attributed to higher cohesive energy densities. Furan polyamides displayed higher van der Waals cohesive energy densities and maintained more rigid planar structures near furan rings compared to nylons. As a result, bio-based furan polyamides showed higher glass transition temperatures and comparable mechanical properties despite having overall weaker hydrogen bonding than nylons.     

Crosslinked chitosan membranes: characterization and study of dimethylhydrazine dehydration by pervaporation

Crosslinked chitosan membranes were synthesized using glutaraldehyde and characterized by infra‐red (IR) and wide‐angle X‐ray diffraction (WAXD) spectroscopic methods. The membranes were applied for the pervaporation‐based dehydration of the highly hazardous and hypergolic unsymmetrical dimethylhydrazine liquid propellant. The characterization techniques were an efficient tool in identifying polymer–liquid interaction sites and the separation mechanisms involved. The crosslinked polymer was found to have good potential for the separation of the aqueous azeotrope of the propellant (20 wt%) and its enrichment to >90% purity. An equilibrium sorption study examined the preferential affinity of the membrane amongst the two penetrating liquids. The pervaporation performance of the membrane was evaluated by varying the experimental parameters of feed composition, membrane thickness and permeate pressure, and found to be promising. © 2001 Society of Chemical Industry     

改性聚芳酰胺的研究进展

聚芳酰胺是一类重要的高性能聚合物材料,因其突出的耐热性和力学性能被广泛应用于航空航天、交通运输、电子电气等领域。笔者综述了聚芳酰胺的改性途径及应用现状。     

Determination of the width of the transition layer between the crystalline and amorphous zones in nylon 1010 by SAXS

The width of the transition layer between the crystalline and amorphous zones in nylon 1010 was determined by SAXS with point collimation and long-slit collimation, respectively. The width of the transition layer, E, was found to be 1.7 nm. The results show that the width of the transition layer is independent of crystallinity.     

Molecular dynamics simulation of the structural and mechanical property changes in the Brill transition of nylon 10/10 crystal

In order to confirm the structural features in the Brill transition of aliphatic nylons, molecular dynamics calculation has been performed at the various temperatures for nylon 10/10 crystal as a model. With an increase in temperature, the torsional motions around the methylene-amide and methylene-methylene bonds were activated. These motions became more remarkable above 420 K and the interconversion between trans and gauche forms occurred frequently, resulting in the disordered conformation of the methylene sequences and the pseudo-hexagonal packing of these parts. During such a drastic structural disordering, however, the hydrogen bonds were kept alive although the bond strength became weaker. These calculations were found to be consistent with the experimental results by the temperature-dependent X-ray diffraction and infrared spectral measurements. The Young's modulus along the chain axis was also calculated as a function of temperature: it decreased remarkably from 250 GPa at 0 K to 180 GPa at 300 K due to a small contraction of the skeletal chain by only about 0.2-0.5% through the torsional motion of the skeletal chains, and the modulus decreased furthermore to 80 GPa at 550 K because of the larger conformational disordering of the skeletal chains. The Young's modulus in the direction perpendicular to the chain axis was also found to decrease remarkably in parallel to the change of the chain packing mode.     

Facile synthesis of dendronized polyamides with chloromethyl groups in the periphery and some properties

A novel dendronized aromatic polyamide with a polyamide backbone and chloromethylene‐end‐functionalized polyamide dendrons is reported for the first time. An attempt at a one‐pot synthesis of end‐functionalized dendronized polymers with a macromonomer strategy without protection and deprotection procedures is also reported for the first time. The results from Fourier transform infrared and NMR spectral analysis indicated that perfect coverage of the chloromethyl groups in the periphery of the resulting polymers was obtained. Data from gel permeation chromatography analysis showed a typical weight‐average molecular weight (M_w) of 76,678 and a polydispersity of 2.44 for the first‐generation polymers and an M_w of 41,554 and a polydispersity of 2.74 for the second‐generation polymers. The solubility in solvents for the resulting polymers was improved remarkably because of the introduction of the dendritic fragments and the existence of the periphery functional groups. Both the glass‐transition temperature and onset decomposition temperature decreased versus those of the linear aromatic polyamides, but the 50% weight loss temperature was still up to 723°C. The X‐ray diffractograms indicated only an amorphous peak in the wide‐angle region of 24–25°. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

透明聚酰胺的研究进展

主要阐述了制备透明聚酰胺所需具备的基本结构要素,指出抑制结晶能力及其尺度大小是提高聚酰胺透明性的关键。按照透明聚酰胺的分子链结构特点将其分为脂肪族透明聚酰胺和芳香族透明聚酰胺两大类。针对脂肪族透明聚酰胺,又细分为带有脂环结构、侧甲基脂环结构和直链结构3种类型,对于芳香族透明聚酰胺则细分为含有侧基、不含侧基和具有复杂结构等类型。并进一步评述每一种类型透明聚酰胺的结构特点,力学、热学、光学、耐化学性等综合性能以及各类产品的加工性与应用领域。脂肪族透明聚酰胺与芳香族透明聚酰胺两种材料中,前者具有比较优异的耐候性和耐UV性能,后者则具有较强的耐热性和力学性能。未来对此类透明聚酰胺的研究将会集中于生物降解性、普通溶剂溶解性或超高耐热性等方面。     

Synthesis and properties of silicon-containing polyamides

A series of aromatic polyamides incorporating silicon together with phenylquinoxaline or with hexafluoroisopropylidene groups has been synthesized by solution polycondensation of a silicon-containing diacid chloride with aromatic diamines having phenylquinoxaline rings or hexafluoroisopropylidene groups. These polymers are easily soluble in polar aprotic solvents, such as N-methylpyrrolidinone and dimethylformamide, and in tetrahydrofurane, and can be solution-cast into thin, transparent films having low dielectric constant, in the range of 3.26 to 3.68. These polymers show high thermal stability with decomposition temperature being above 400°C and glass transition temperature in the range of 236°C to 275°C. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1533–1538, 1997     

Structural change in the Brill transition of Nylon m/n (2) conformational disordering as viewed from the temperature-dependent infrared spectral measurements

The structural changes in the Brill transition of aliphatic Nylons m/n have been investigated by carrying out the temperature-dependent infrared spectral measurement for Nylon 6/10 -[-NH-(CH₂)₆-NHCO-(CH₂)₈-CO-]_n-, Nylon 6/12 -[-NH-(CH₂)₆-NHCO-(CH₂)₁₀-CO-]_n- and Nylon 10/10 -[-NH-(CH₂)₁₀-NHCO-(CH₂)₈-CO-]_n-. They took the crystal structure of α-form at room temperature. By heating the samples up to the Brill transition temperature region, the conformation of the methylene segments was found to change remarkably from the all trans-zigzag form to the disordered conformation constructed by shorter trans-zigzag segments combined with some gauche bonds. At the same time, the twisting motion was found to occur around the CH₂-amide bonds. During this order-to-disorder transition of molecular conformation, the intermolecular hydrogen bonds were kept alive although they were weaker gradually with increasing temperature. The methylene segments sandwiched by NH groups [NH(CH₂)_mNH] were found to be disordered more remarkably than those of CO(CH₂)_nCO sequence due to the difference in torsional energy barriers around the CH₂-NH and CH₂-CO bonds.