Structures for monodisperse oligoamides. A novel structure for unfolded three-amide nylon 6 and relationship with a three-amide nylon 6 6

Three-amide oligomers of nylon 6 and nylon 6 6 have been investigated using electron microscopy (imaging and diffraction), X-ray diffraction, and computational modeling. A new crystal structure has been discovered for the three-amide oligomer of nylon 6. This material crystallizes from chloroform/dodecane solutions into an unfolded crystal form that has progressively sheared hydrogen bonding in two directions between polar (unidirectional) chains. This structure is quite different from the usual room temperature α-phase structure of chain-folded nylon 6 crystals, in which alternatingly sheared hydrogen bonding occurs between chains of opposite polarity in only one direction. The occurrence of this new structure illustrates the extent to which progressively sheared hydrogen bonding is preferred over alternatingly sheared hydrogen bonding. Indeed, the progressive hydrogen bonding scheme occurs in the three-amide nylon 6 material even though it requires a disruption to the lowest potential energy all-trans conformation of the chain backbone, and requires all the chains in each hydrogen-bonded layer to be aligned in the same direction. We believe the presence of chain folding, which necessarily incorporates adjacent chains of opposite polarity into the crystal structure, prevents the formation of this new crystal structure in the nylon 6 polymer. In contrast, the three-amide nylon 6 6 crystal structure is analogous to the polymeric nylon 6 6 α-phase structure, found in both fibers and chain-folded crystals, and consists of progressive hydrogen-bonded sheets which stack with a progressive shear. In both structures, the molecules (≈ 3 nm in length) form smectic C-like layers with well-orchestrated stacking of 2.2 nm to form a three-dimensional crystal. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2849–2863, 1998     

Nylon 6 9 can crystallize with hydrogen bonding in two and in three interchain directions

Nylon 6 9 has been shown to have structures with interchain hydrogen bonds in both two and in three directions. Chain-folded lamellar crystals were studied using transmission electron microscopy and sedimented crystal mats and uniaxially oriented fibers studied by X-ray diffraction. The principal room-temperature structure shows the two characteristic (interchain) diffraction signals at spacings of 0.43 and 0.38 nm, typical of α-phase nylons; however, nylon 6 9 is unable to form the α-phase hydrogen-bonded sheets without serious distortion of the all-trans polymeric backbone. Our structure has c and c^* noncoincident and two directions of hydrogen bonding. Optimum hydrogen bonding can only occur if consecutive pairs of amide units alternate between two crystallographic planes. The salient features of our model offer a possible universal solution for the crystalline state of all odd–even nylons. The nylon 6 9 room-temperature structure has a C-centered monoclinic unit cell (β = 108°) with the hydrogen bonds along the C-face diagonals; this structure bears a similarity to that recently proposed for nylons 6 5 and X3. On heating nylon 6 9 lamellar crystals and fibers, the two characteristic diffraction signals converge and meet at 0.42 nm at the Brill temperature, T_B · T_B for nylon 6 9 lamellar crystals is slightly below the melting point (T_m), whereas T_B for nylon 6 9 fibers is ≅ 100°C below T_m. Above T_B, nylon 6 9 has a hexagonal unit cell; the alkane segments exist in a mobile phase and equivalent hydrogen bonds populate the three principal (hexagonal) directions. A structure with perturbed hexagonal symmetry, which bears a resemblance to the reported γ-phase for nylons, can be obtained by quenching from the crystalline growth phase (above T_B) to room temperature. We propose that this structure is a “quenched-in” perturbed form of the nylon 6 9 high-temperature hexagonal phase and has interchain hydrogen bonds in all three principal crystallographic directions. In this respect it differs importantly from the γ-phase models. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1153–1165, 1998     

Temperature-induced changes in chain-folded lamellar crystals of aliphatic polyamides. Investigation of nylons 2 6, 2 8, 2 10, and 2 12

Four members of the even-even nylon 2 Y series, for Y = 6, 8, 10, and 12, have been crystallized in the form of chain-folded lamellar single crystals from 1,4-butanediol and studied by transmission electron microscopy (imaging and diffraction), x-ray diffraction, and thermal analysis. The structures of these 2 Y nylons are different from those of nylon 6 6 and many other even-even nylons. At room temperature, two strong diffraction signals are observed at spacings 0.42 and 0.39 nm, respectively; these values differ from the 0.44 and 0.37 nm diffraction signals observed for nylon 6 6 and most even-even nylons at ambient temperature. Detailed analyses of the diffraction patterns show that all these 2 Y nylons have triclinic unit cells. The diamine alkane segments of 2 Y nylons are too short to sustain chain folds; thus, the chain folds must be in the diacid alkane segments in all cases. On heating the crystals from room temperature to the melt, the triclinic structures transform into pseudohexagonal structures and the two diffraction signals meet at the Brill transition temperature which occurs significantly below the melting point. The room temperature structures of these 2 Y nylons are similar to the unit cell of nylon 6 6 at elevated temperature, but below its Brill temperature. The room temperature structures and behavior on heating of the nylon 2 Y family is noticeably different from that of the even-even nylon X 4 family, although the only difference between these families of polyamides is the relative disposition of the amide groups within the chains. The results show that in order to understand the structure, behavior and properties of crystalline nylons, especially as a function of temperature, the detailed stereochemistry needs to be taken into account. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 675–688, 1997     

Structures of X 34‐nylons in chain‐folded lamellae and gel‐spun fibers

Structural studies and morphological features of a new family of linear, aliphatic even–even, X 34‐nylons, with X = 2, 4, 6, 8, 10, and 12, are investigated with X‐ray diffraction and electron microscopy. Solution‐grown crystals were obtained by isothermal crystallization from N,N‐dimethylformamide solutions. The thickness of lamellar‐like crystals was orders of magnitude less than the chain lengths of the polymer samples used, implying that the chains fold to form chain‐folded lamellae. The results bear a close resemblance, with the noticeable exception of 2 34‐nylon, to those reported for nylon 6 6 and other even–even nylon chain‐folded lamellar crystals. The basic structure of the straight‐stem lamellar core is similar to that of the classic nylon 6 6 triclinic α structure, and the chains tilt ≈42° relative to the lamellar normal. In the case of 2 34‐nylon, the structure resembles the 2 Y nylon series, and the chain tilt angle reduces to 36.6°. These combined results suggest that, even with a relatively low frequency of amide units along the backbone of these molecules, hydrogen bonding is still the dominant element in controlling the behavior, structure, and properties of these polymers. In addition, gels were prepared in concentrated sulfuric acid, and gel‐spun fibers were studied using X‐ray diffraction. The data are interpreted in terms of a modified nylon triclinic α structure that bears a resemblance to the structure of even–even nylons at elevated temperatures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2685–2692, 2002     

Effect of silver nanoparticles on the dynamic crystallization behavior of nylon‐6

The effect of introducing silver nanoparticles on the rheological properties and dynamic crystallization behavior of nylon‐6 was investigated. The nanocomposites showed slightly higher viscosity than pure nylon‐6 in the low‐frequency range even at an extremely low loading level of the silver particles (0.5–1.0 wt %). The nanoparticles had a more noticeable effect on the storage modulus than on the loss modulus of a nylon‐6 melt and reduced its loss tangent. They increased the crystallization temperature of nylon‐6 by about 14 °C and produced a sharper crystalline peak. The silver nanoparticles promoted the crystallization of nylon‐6, and their effect on the dynamic crystallization of nylon‐6 at 200 °C was more notable at a lower shear rate and at 190 °C at a higher frequency. Nylon‐6 produced large spherulitic crystals, but the nanocomposites showed a grainy structure. In addition, the silver nanoparticles reduced the fraction of the α‐form crystal but increased that of the γ‐form crystal. The nanocomposites crystallized at 190 °C showed a lower melting temperature than nylon‐6 by about 3 °C, whereas the nanocomposites crystallized at 200 °C showed almost the same melting temperature. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 790–799, 2004     

On the crystal structure of odd–even nylons: Polymorphism of nylon 5,10

The structure of nylon 5,10 has been investigated using electron microscopy and X‐ray diffraction. Nylon 5,10 shows polymorphism with two different structures related to the γ form obtained by either solution or melt crystallization. Packing differences may be attributed to a change in the hydrogen bonding system. In addition, a structure related to an α‐like phase can be found by precipitation from strong acid solutions and their mixtures with chloroform. A model with two hydrogen bonding directions is given for this form, in a similar way to that recently postulated for polyamides derived from odd diamine or odd diacid units. Temperature‐induced structural changes have also been studied for nylon 5,10 fibers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2383–2395, 1999     

Structure and morphology of nylon 46 lamellar crystals: Electron microscopy and energy calculations

A detailed electron microscopy study of the structure and morphology of lamellar crystals of nylon 46 obtained by crystallization from solution has been carried out. Electron diffraction of crystals supported by X‐ray diffraction of their sediments revealed that they consist of a twinned crystal lattice made of hydrogen‐bonded sheets separated 0.376 nm and shifted along the a‐axis (H‐bond direction) with a shearing angle of 65°. The interchain distance within the sheets is 0.482 nm. These parameters are similar to those previously described for nylon 46 lamellar crystals grown at lower temperatures. A combined energy calculation and modeling simulation analysis of all possible arrangements for the crystal‐packing of nylon 46 chains, in fully extended conformation, was performed. Molecular mechanics calculations showed very small energy differences between α (alternating intersheet shearing) and β (progressive intersheet shearing) structures with energy minima for successive sheets sheared at approximately 1/6 c and 1/3 c. A mixed lattice composed of a statistical array of α and β structures with such sheet displacements was found to be fully compatible with experimental data and most appropriate to describe nylon 46 lamellar crystals. Annealing of the crystals at temperatures closely below the Brill transition induced enrichment in β structure and increased chain‐folding order. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 41–52, 2000     

Relations between dynamic mechanical properties and melting behavior of nylon 66 and poly(ethylene terephthalate)

Nylon 66 films exhibiting form I melting behavior show the γ mechanical relaxation at ?140°C. Samples which have form II melting behavior do not show this relaxation. The γ relaxation disappears when material having form I behavior is converted to material having form II behavior by annealing or by cold drawing. The form I and form II types of melting behavior are also found in poly(ethylene terephthalate); the interconversions and thermal behavior of the forms are analogous to the nylon 66 case. In poly(ethylene terephthalate), the β relaxation at ?40 to ?60°C is present only when form I melting behavior is found. Conversion to form II melting behavior by annealing or drawing (80°C) again causes the relaxation to disappear. No β relaxation was found in amorphous polymer. The γ dispersion in nylon 66 and the β dispersion in poly(ethylene terephthalate) can therefore be associated with the crystalline structure responsible for form I melting behavior. Form I melting behavior has been associated with foldedchain crystals based on previous work. It is therefore postulated that the γ dispersion in nylon 66 and the β dispersion in poly(ethylene terephthalate) are associated with motions in the chain folds. This assignment is not inconsistent with the change in the γ dispersion of nylon 66 with the number of backbone CH₂ units, since these will affect the fold structure.     

Temperature‐induced structural changes in even‐odd nylons with long polymethylene segments

Structural transitions of nylons 8 9 and 12 9 heating and cooling processes were investigated using calorimetric, spectroscopic during and real time X‐ray diffraction data. These even‐odd nylons had three polymorphic forms related to structures where hydrogen bonds were established in two planar directions. Heating processes showed a first structural transition at low temperature where the two strong reflections related to the packing mode of the low temperature structure (form I) disappeared instead of moving together and merging into a single reflection, as observed for conventional even‐even nylons. The high temperature structure corresponded to a typical pseudohexagonal packing (form III) attained after the named Brill transition temperature. Structural transitions were not completely reversible since an intermediate structure (form II) became clearly predominant at room temperature in subsequent cooling processes. A single spherulitic morphology with negative birefringence and a flat‐on edge‐on lamellar disposition was obtained when the two studied polyamides crystallized from the melt state. Kinetic analyses indicated that both nylons crystallized according to a single regime and a thermal nucleation. Results also pointed out a secondary nucleation constant for nylon 12 9 higher than that for nylon 8 9, suggesting greater difficulty in crystallizing when the amide content decreased. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2494–2506     

Crystalline structure and thermal behavior of nylon‐10,14

The structure and morphology of a novel polyamide, nylon‐10,14, and its lamellar crystals from dilute solution were examined by transmission electron microscopy and wide‐angle X‐ray diffraction (WAXD). Both the electron‐diffraction pattern and WAXD data demonstrated that nylon‐10,14 adopts the structure of a triclinic lattice similar to that of the traditional nylon‐66 but with a corresponding increase of the c parameter to 3.23 nm. In addition, the thermal behavior of melt‐crystallized nylon‐10,14 was investigated by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The glass‐transition temperature of nylon‐10,14 determined by the DMA data was 46.6°C. DSC indicated that the multiple melting behavior of isothermally crystallized nylon‐10,14 probably results from the melt and recrystallization mechanism. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1422–1427, 2003     

Morphology and structure of nylon‐2,14 single crystals from dilute solution

A perfect single crystal of nylon‐2,14 was prepared from 0.02% (w/v) 1,4‐butanediol solution by a “self‐seeding” technique and isothermal crystallization at 120 and 145 °C. The morphology and structure features were examined by transmission electron microscopy with both image and diffraction modes, atomic force microscopy, and wide‐angle X‐ray diffraction (WAXD). The nylon‐2,14 single crystal grown from 1,4‐butanediol at 145 °C inhabited a lathlike shape with a lamellar thickness of about 9 nm. Electron diffraction and WAXD data indicated that nylon‐2,14 crystallized in a triclinic system with lattice dimensions a = 0.49 nm, b = 0.51 nm, c = 2.23 nm, α = 60.4°, β = 77°, and γ = 59°. The crystal structure is different from that of nylon‐6,6 but similar to that of other members of nylon‐2Y. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1913–1918, 2002     

Potential of two-dimensional near-infrared correlation spectroscopy in studies of pre-melting behavior of nylon 12

This review paper discusses the potential of generalized two-dimensional (2D) near-infrared (NIR) correlation spectroscopy in studies of pre-melting behavior and hydrogen bonds of nylon 12. A 2D NIR study on dissociation and hydrogen bonds of N-methylacetamide (NMA) is also reviewed here as a model compound study of nylon 12. Fourier transform (FT)-NIR spectra in the region of 9000–5000 cm⁻¹ of nylon 12 were measured over a temperature range of 30–150°C where gradual weakening of inter- or intramolecular associative interactions and decrease of local order leading to the eventual fusion of nylon 12 crystals are observed. The 2D correlation analysis provided the following conclusions for the pre-melting behavior of nylon 12. (i) There are at least eight bands in the 6800–6100 cm⁻¹ region assignable to free- and hydrogen-bonded NH groups of nylon 12 in various environments. The asynchronous 2D correlation spectrum in the above region indicates that the amide groups with free carbonyl oxygen appear first and then the unassociated free amide and amide groups with free NH follow as the temperature is increased. (ii) The asynchronous spectrum in the 6000–5500 cm⁻¹ region, where the first overtones of the CH₂ stretching modes are expected to appear, indicates that substantial amount of disordered or dissociated components start appearing before the disappearance of more ordered components. It seems that they appear as the pre-melting precursors (or even possibly as the indirect cause) to the precipitous decrease of the ordered components associated with melting of nylon 12 occurring at a much higher temperature.     

Investigation of solution‐grown,chain‐folded lamellar crystals of the even‐even nylons: 6 6, 8 6, 8 8, 10 6, 10 8, 10 10, 12 6, 12 8, 12 10, and 12 12

Chain‐folded lamellar crystals of the ten even‐even nylons: 6 6, 8 6, 8 8, 10 6, 10 8, 10 10, 12 6, 12 8, 12 10, and 12 12 have been grown from solution and their morphologies and structures studied using transmission electron microscopy, both imaging and diffraction. Sedimented mats were examined using X‐ray diffraction. The solution‐grown crystals are lath‐shaped lamellae and diffraction from these crystals, at room temperature, reveals that three crystalline forms are present in differing ratios. The crystals are composed of chain‐folded, hydrogen‐bonded sheets, the linear hydrogen bonds within which generate a progressive shear of the chains (p‐sheets). The sheets are found to stack in two different ways. Some p‐sheets stack with a progressive shear, to form the “α_p structure”; others sheets stack with an alternate stagger, to form the “β_p structure”. Both the α_p and β_p structures give two strong diffraction signals at spacings of 0.44 nm and 0.37 nm; these signals represent a projected intrasheet interchain distance (actual value 0.48 nm) and the intersheet spacing, respectively. Preparations of nylons 6 6, 8 6, 8 8, 12 6, and 12 8 consisted almost entirely of α_p‐structure material, with only a trace of β_p‐structure material being present. In contrast, nylons 10 6, 10 8, 10 10, 12 10, and 12 12 contained substantial quantities of both α_p‐ and β_p‐structure material, with α_p‐structure material always being in the majority. Preparations of nylons 10 8, 12 10, and 12 12 also showed an additional diffraction signal at 0.42 nm; this signal is characteristic of the pseudohexagonal (high temperature) structure. The melting temperature of solution‐grown lamellae of these even‐even nylons decreases with decreasing linear amide density. On heating, the strong diffraction signals (0.44 nm and 0.37 nm) gradually moved together and merge at the Brill temperature to form a single diffraction signal (0.42 nm), characteristic of the pseudohexagonal structure. This single diffraction signal remained until melting. For nylons 6 6, 8 6, 8 8, 10 6, and 12 6, the Brill temperatures were substantially below the respective melting temperatures and the single 0.42 nm diffraction signal was stable over temperature ranges of 14 °C to 56 °C, depending on the nylon. Conversely, nylons 10 8, 10 10, 12 8, 12 10, and 12 12 had coincident melting and extrapolated Brill temperatures. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1209–1221, 2000     

Structural studies on the polymorphism of nylon 3

The structure and morphology of crystalline nylon 3 [poly(β-alanine)] have been studied by electron microscopy and x-ray diffraction. Two clearly defined forms are detected. Form I appears as spherulites made up of ribbonlike lamellae upon crystallization at high temperature from a solution in phenol–butanediol-1,4. They have monoclinic unit cell with a = 9.60 Å, c = 8.96 Å, and β = 122.5°. The hydrogen-bonded planes run parallel to the long dimension of the crystals. Form II is observed when the samples are prepared from formic acid solution at room temperature. A second type of spherulite with a microfibrillar structure is formed in this case. The isolated crystalline structures obtained from Form II appear to grow along the intersheet direction rather than along the hydrogen bond direction, which constitutes anomalous behaviour. Our results for this second form are consistent with an orthorhombic lattice with a = 9.56 Å and c = 7.56 Å. No clear information is obtained on the b dimension of the unit cell (chain axis) in either case. We assume a value of 4.78 Å, which corresponds to fully extended chains. The two forms coexist in films prepared from a formic acid–water solution as well as in samples recovered immediately after polymerization.     

Dynamic rheo-optical characterization of uniaxially oriented polyamide 11

Dynamic mechanical analysis, coupled with polarized step-scan FTIR transmission spectroscopy, has been used to monitor the submolecular motional behavior of uniaxially oriented polyamide 11. The dynamic in-phase spectra depend upon the morphology of the samples as well as on the polarization direction of the infrared radiation. The lineshape features of the dynamic in-phase spectra and their relationship to sample deformation are analyzed on the basis of changes of the internal coordinates, the reorientation movement of several functional groups, and the thickness change of the film during the stretching cycle. Dynamic infrared spectra are helpful for deconvolution of overlapping bands on the basis of their different responses to the external perturbation, which sometimes cannot be resolved well by derivative spectroscopy or curve-fitting analysis. The lineshape features have been used to follow microstructural changes after isothermal heat treatment. Near the N H stretching frequency, two bands at 3270 cm⁻¹ and 3200 cm⁻¹ are resolved and analyzed in terms of Fermi resonance between the N H stretching fundamental mode and the overtone and combination modes of the amide I and II vibrations. The dynamic response of the N H stretching mode correlates with the modulation of hydrogen bond strength in uniaxially oriented PA-11. After thermal treatment at the highest temperature (190°C), the dynamic response in this region is mainly caused by the modulation of crystals. In amide I region, three bands at 1680 cm⁻¹, 1648 cm⁻¹, and 1638 cm⁻¹ are separated and assigned to hydrogen bond-free, hydrogen-bonded amorphous, and hydrogen-bonded crystalline regions, respectively. The dynamic responses of the hydrogen-bonded regions are more sensitive to external perturbation. Two components are found in the amide II region, and the band at 3080 cm⁻¹ is assigned to the overtone resonance of the component with perpendicular polarization. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2895–2904, 1998     

Multiple melting and crystallization of nylon‐66/montmorillonite nanocomposites

Nylon‐66 nanocomposites were prepared by melt‐compounding nylon‐66 with organically modified montmorillonite (MMT). The organic MMT layers were exfoliated in a nylon‐66 matrix as confirmed by wide‐angle X‐ray diffraction (WAXD) and transmission electron microscopy. The presence of MMT layers increased the crystallization temperature of nylon‐66 because of the heterogeneous nucleation of MMT. Multiple melting behavior was observed in the nylon‐66/MMT nanocomposites, and the MMT layers induced the formation of form II spherulites of nylon‐66. The crystallite sizes L₁₀₀ and L₀₁₀ of nylon‐66, determined by WAXD, decreased with an increasing MMT content. High‐temperature WAXD was performed to determine the Brill transition in the nylon‐66/MMT nanocomposites. Polarized optical microscopy demonstrated that the dimension of nylon‐66 spherulites decreased because of the effect of the MMT layers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2861–2869, 2003     

Crystal Structure of Nicotinic Acid·3,5-dinitrobenzoic Acid Organic Adduct

1INTRODUCTIONThedevelopmentofhighlyefficientnonlinearoptical(NLO)crystalsforvisibleandultraviolet(UV)regionsisextremelyimportantforbothlaserspectroscopyandlaserprocessing.Themainmeritsoforganicmaterialscomparedwithinorganiconesforsuchsecond-harmonicgenera…     

MULTIPLE MELTING AND CRYSTALLIZATION BEHAVIOR OF NYLON 1212

The wide-angle X-ray diffraction (WAXD) patterns of isothermally crystallized Nylon 1212 show that γ-form crystals form below 90℃ and the α-form crystals can exist above 140℃. In the temperature range of 90-140℃, the α-form and γ-form crystals coexist. Variable-temperature WAXD exhibits that the nylon 1212 γ-form does not show crystal transition on heating, while α-form isothermally crystallized at 160℃ exhibits Brill transition at a little higher than 180℃ on heating. The multiple melting behaviors of Nylon 1212 isothermally crystallized from melt come from a complex mechanism of different crystal structures, dual lamellar population and melting-recrystallization. In polarized optical microscope (POM) observations, Nylon 1212 isothermally crystallized at 175℃ shows the ringed banded spherulites. However, at temperatures below 160℃ the ringed banded image disappears, and cross-extinct spherulites are formed.     

Solution crystallization of nylon 12

Electron microscopy and x-ray diffraction data have been obtained on nylon 12 crystallized from 1-hexanol, 1,6-hexanediol, and hexylene glycol. Ribbonlike lamellar crystals of the γ form are obtained by crystallization from all the solutions and elongated flat crystals of the α form by crystallization from the 1-hexanol and hexylene glycol solutions. The direction of the hydrogen bond in these crystals is almost parallel to that of maximum crystal elongation. α- and γ-form crystals both grow from 1-hexanol and hexylene glycol at appropriate crystallization temperatures. γ-form crystals alone are obtained from 1,6-hexanediol solution at every crystallization temperature. The long periods measured by small-angle x-ray diffraction for the solution-grown crystals are in the range 7.6–10.6 nm. The melting behavior of the solution-grown crystals is examined and discussed. The melting temperatures of the γ form may be lower than that of the α form. An equilibrium melting temperature of 208.4°C for γ-form crystals is obtained by using a relation between thickness of lamellar crystals and their melting temperatures observed by differential scanning calorimeter measurements. Solvents affect the growth of the two crystalline forms in solution crystallization.     

Polymorphism in nylon‐11/montmorillonite nanocomposite

The polymorphism behavior in nylon‐11/montmorillonite (MMT) nanocomposite was investigated by wide‐angle X‐ray diffraction (WAXD) and variable‐temperature infrared spectroscopy. The results of WAXD and IR confirmed the presence of the γ‐crystalline form of nylon‐11, which is induced and stabilized by MMT. However, the hydrogen bond in the nanocomposite and its temperature dependence also exhibited some differences from neat nylon‐11. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 253–259, 2004