Polyamide Homopolymer Research Articles

Novel pH sensing redox wire based on a polyamide homopolymer of L-tryptophan

The redox profile obtained from an electrochemically oxidised polyamide homopolymer containing L-tryptophan is shown to serve as a versatile molecular wire for monitoring pH. The transformation of the polypeptide is examined and the optimisation of the electrode-redox wire interface was conducted in order to enhance the electrochemical signature. Voltammetric interrogation of the modified polymer reveals the creation of quinoid functionality which can be efficiently addressed through interaction with nanofractured carbon surfaces. Preliminary voltammetric and XPS characterisation was conducted and a Nernstian response (−0.060 V/pH) was observed (pH 3–8) and as such could be used as a key component in the design of new pH probes.

Synthesis and characterization of polyisobutylene-b-polyamide multi-block copolymer thermoplastic elastomers

A series of polyisobutylene (PIB)-polyamide (PA) multi-block copolymers was synthesized via an amidation reaction to form novel thermoplastic elastomers (TPEs). A two prepolymer approach was taken in which a difunctional primary-amine-terminated polyisobutylene (NH2-PIB-NH2) was synthesized as the soft block and a difunctional carboxylic acid-terminated polyamide (HO2C-PA-CO2H) was synthesized separately as the hard block. The two prepolymers were reacted in the bulk under nitrogen at 220 °C to form the multiblock copolymer TPEs. Various copolymers were synthesized from combinations of two different PIBs (either 1000 or 2000 g/mol), and four different PAs (PA-11 and PA-6, each at either 1000 or 2000 g/mol). 1H and 13C NMR spectroscopies were used to confirm the structure of the individual prepolymers and the copolymers. Prepolymer molecular weights were determined by gel-permeation chromatography (GPC), end-group titration, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS); the latter also provided confirmation of end-group functionality of prepolymers. For GPC of PA homopolymers and PIB-PA copolymers, trifluoroacetylation of the secondary amide groups of the PA blocks was necessary to obtain solubility of the copolymers in the THF mobile phase. Copolymer number–average molecular weights varied from 8100 to 20,630 g/mol.

Melting behavior of a poly(ether‐block‐amide) copolymer melt‐crystallized under quiescent, isothermal conditions

AbstractSegmented poly(ether‐block‐amide) copolymers are typically known as polyamide‐based thermoplastic elastomers consisting of hard, crystallizable polyamide block and flexible, amorphous polyether block. The melting characteristics of a poly(ether‐block‐amide) copolymer melt‐crystallized under various quiescent, isothermal conditions were calorimetrically investigated using differential scanning calorimetry (DSC). For such crystallized copolymer samples, their crystalline structures under ambient condition and the structural evolutions upon heating from ambient to complete melting were characterized using ambient and variable‐temperature wide‐angle X‐ray diffractometry (WAXD), respectively. It was observed that dependent of specific crystallization conditions, the copolymer samples exhibited one, two, or three melting endotherms. The ambient WAXD results indicated that all melt‐crystallized copolymer samples only exhibited γ‐form crystals associated with the hexagonal habits of the polyamide homopolymer, whereas variable‐temperature WAXD data suggested that upon heating from ambient, a melt‐crystallized copolymer might exhibit so‐called Brill transition before complete melting. Based on various DSC and variable‐temperature WAXD experimental results obtained in this study, the applicability of different melting mechanisms that might be responsible for multiple melting characteristics of various crystallized PEBA copolymer samples were discussed. It was postulated that the low (T m1) endotherm was primarily because of the disruption of less thermally stable, short‐range ordered structure of amorphous polyamide segments of the copolymer, which was only formed after the completion of primary crystallization via so‐called annealing effects. The intermediate (Tm2) and high (Tm3) endotherms were attributed to the melting of primary crystals within polyamide crystalline microdomains of the copolymer. The appearance of these two melting endotherms might be somehow complicated by thermally induced Brill transition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2035–2046, 2008

Phase morphology development and stabilization in polycyclohexylmethacrylate/polypropylene blends: uncompatibilized and reactively compatibilized blends using two reactive precursors

The phase morphology developed in immiscible polypropylene (PP)/polycyclohexylmethacrylate (PCHMA) blends has been studied using an in situ reactively generated polystyrene-graft-polypropylene compatibilizer from maleic anhydride grafted polypropylene (MA- g-PP) and amine end-capped polystyrene (PS-NH2) reactive precursors during melt-blending. The imidation reaction responsible for the formation of the compatibilizer is similar to the reaction occurring in polyamide/MA-PP (MA-EPR or MA-EPDM) blends which are industrially important. In the present blend PP/PCHMA/(PP-MA-PS-NH2), no undesired reaction occurs between the maleic anhydride groups and the backbone of the PCHMA chain, as is usually the case with polyamide homopolymer. This type of reaction, although considered non significant, has consequences on the phase morphology development as it affects the viscosity of the polyamide matrix when chain scission takes place. PP/PCHMA blends covering the whole range of compositions were prepared. The composition window at which the blends exhibit a droplet-in-matrix phase morphology and that where the two phases are co-continuous were determined using a selective phase extraction in combination with scanning electron microscopy. The generation in situ of the PP- g-PS compatibilizer substantially changed the state of the phase morphology developed. In the blends having a droplet-in-matrix type of morphology, the particle sizes were significantly reduced (by a factor of more than 10). Two types of MA- g-PP reactive copolymers differing in maleic anhydride content (1 and 8 wt%) have been separately employed with the same grade of PS-NH2. Emphasis was put on a detailed investigation of the behaviour and structural stability of the blends exhibiting a co-continuous phase morphology when the compatibilizer is generated. Significant differences were found in relation to the maleic anhydride content of the MA-PP reactive compatibilizer precursor.

Solution 13C NMR spectroscopy of polyamide homopolymers (nylons 6, 11, 12, 66, 69, 610 and 612) and several commercial copolymers

Well-resolved 13C NMR spectra of nylons 6, 11, 12, 66, 69, 610, and 612 dissolved in 4:1 TFE/CDCl3 allowed complete assignment of all major backbone peaks. In addition, several low intensity peaks were identified representing cis amide groups, acid end-groups and amine end-groups. Several peaks associated with the trans amide units in the spectra of each polyamide homopolymer were identified as uniquely characteristic of that polymer. Using these unique peaks, all the polyamides studied could be distinguished from each other as homopolymers and as repeat units in copolymers. For example, three unknown polyamides (supplied by a colleague) were identified as nylon 6, nylon 66 and nylon 610 using only solution 13C NMR spectroscopy. Based on these results, several commercial polymers were examined. Using solution 13C NMR spectroscopy, the copolymer compositions, molecular weights, end-group and cis amide contents, plus the amount of residual ε-caprolactam were all determined. For example, Spiderwire Super Mono® fishing line was found to have a number average molecular weight of 25,333g/mol and to contain 82mol% nylon 6 repeat units and 18mol% nylon 66 repeat units. The residual ε-caprolactam, acid end-group and amine end-group contents were calculated as 1.25, 0.61 and 0.0mol%, respectively. The cis amide contents were calculated to be 1.2mol% for nylon 6 units and 0.61mol% for nylon 66 segments.

Phase modification and polymorphism in two poly(ether- block-amide) copolymers

The crystalline polyamide phase in two representative poly(ether- block-amide) copolymers has been shown to be polymorphic in nature via an analysis by X-ray diffraction and solid-state 13C nuclear magnetic resonance. In both polymers, this phase was found to adopt α and γ structures analogous to those that exist in the corresponding polyamide homopolymers. Furthermore, it has been shown that phase transformation between crystal types is possible using chemical modifications.

Crystallization kinetics of J-1 polymer under different thermal treatments

A bis-para-amino cyclohexylmethane (PACM)-based polyamide homopolymer (J-1 polymer produced by Du Pont), utilized as a matrix for composites, was subjected to different thermal treatments in order to investigate its crystallization thermodynamics and crystallization kinetics. Various J-1 samples, quenched, annealed from the glassy state, isothermally crystallized from the melt and slowly cooled, were studied by differential scanning calorimetry (DSC). A thermodynamic melting temperature of 352.6 °C was determined from a Hoffman-Weeks diagram of polymer samples annealed at different temperatures between the glass transition and melting temperature. By using DSC isothermal crystallization data from the melt, the existence of two crystallization regimes, already found in a previous investigation, was confirmed, and a transition temperature between the two regimes, equal to 262.2 °C was determined, in good agreement with 260.5 °C, obtained by depolarized light measurements, reported elsewhere. Moreover, the ratio between the crystallization kinetics factor of two crystallization regimes is 1.87, very close to the value of 2 predicted by the Huffman theory. Crystallization of samples from the melt, at different cooling rates, was also performed. The Arrhenius plot of data indicated that the crystallization process proceeds with two distinct activation energies (589 and 244 kJ mol−1), below or above a cooling rate of 2.67 °C min−1, corresponding to a temperature of 253.9 °C. This result is in good agreement with the two crystallization regimes reported above.

Isothermal phase behavior of Nylon‐6, ‐66, and ‐610 polyamides in formic acid–water systems

AbstractConcentration‐dependent ternary interaction parameters are experimentally determined for the polyamide homopolymers, Nylon‐6, ‐66, ‐610, and for the Nylon‐66/610/6 terpolymer in formic acid‐water systems. The binodal envelope, the tie lines, and the crystallization isotherms at 25°C are given for each of the ternary systems. © 1994 John Wiley & Sons, Inc.

Mechanical properties and morphology of liquid crystalline copolyester‐amide and amorphous polyamide blends

AbstractBlends of an amorphous polyamide (PA) and a liquid crystalline copolyesteramide (LCP), poly(naphthoate‐aminophenoterephthalate) were prepared in a twin‐screw extruder. Specimens for mechanical testing were prepared by injection molding. Morphological, thermal, mechanical, and rheological properties were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X‐ray diffractometry, capillary rheometry, and a tensile tester, respectively. The tensile mechanical behavior of the LCP/PA blends was found to be affected by their compositions and specimen thickness. Tensile testing revealed that the tensile mechanical behavior of the LCP/PA blends was very similar to that of polymeric composite and the tensile strength of the LCP/PA (50/50) blend was approximately two times of the value of PA homopolymer and exceeded that of pure LCP. The morphology of the LCP/PA blends was also found to be affected by their compositions. SEM studies revealed that the liquid crystalline polymer (LCP) formed finely dispersed spherical domains in the PA matrix and the inclusions were deformed into fibrils from the spherical droplets with increasing LCP content. It has been found that droplet and fiber formations lead to low and high strength material, respectively. In particular, at specific LCP content (50 wt%), the tensile strength of the LCP/PA blend exceeded that of pure LCP. The improvement in tensile properties is likely due to the reinforcement of the PA matrix by the fibrous LCP phase as observed by SEM. A distinct shell‐core morphology was found to develop in the injection molded samples of these blends. This is believed to have a synergistic effect on the tensile properties of the LCP/PA blends. The rheological behavior of the LCP/PA blends was found to be very different from that of the parent polymers and significant viscosity reductions were observed for the LCP/PA (50/50) blend. Based upon DSC, these blends have shown to be incompatible in the entire range of concentrations.

Characterization of structure and morphology in two poly(ether-block-amide) copolymers

XRD, NMR, and DSC results indicate that both block poly(ethylene oxide-co-nylon 6) and poly(ethylene oxide-co-nylon 12) are separated, multiphase systems that include a well-defined polyamide crystalline phase, a polyamide amorphous phase, and a predominantly amorphous polyether phase. The DSC data suggest the existence of polyether-based crystallites in both cases. However, a polyether crystalline phase was not detected by XRD, indicating either that it is a minor component or that the crystallites are very poorly defined compared to the homopolymer. In addition, the NMR and XRD results reveal that the crystalline polyamide phase in both polymers adopts a structure (α or γ) similar to that found in the corresponding polyamide homopolymer

Crystallization in J-1 polymer/carbon-fibre composites: bulk and interface processes

The process of crystallization, during isothermal treatments from the melt, of a composite of a J-1 polymer (a polyamide homopolymer produced by Du Pont) containing a single carbon fibre was studied. Two main crystalline morphologies develop in the polymer, depending on the temperature. This was directly observed during the treatment of the sample in a hot-stage chamber placed under a light microscope, and confirmed by both X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses. Moreover, a transcrystalline layer grows at the interface with the carbon fibre. The kinetics of bulk and interface crystallization were evaluated and compared by measuring, at different temperatures, the radii of crystals and the thickness of the transcrystalline layer with time. Moreover, bulk crystallization kinetics, measured by the depolarization of the light passing through the polymer sample during the isothermal treatment, indicated the apparent presence of two regimes of bulk crystallization.

Crystallization and processing behaviour of the polyamide J-1 polymer and composites reinforced with Kevlar fibre

The influence of thermal processing on the crystalline behaviour of J-1 polymer, a PACM-based polyamide homopolymer used as a matrix for advanced composites, was studied using differential scanning calorimetry (DSC), cross polarized microscopy, wide angle X-ray scattering (WAXS), and dynamic mechanical analysis (DMA). A double melting peak appears in DSC thermograms of neat polymer processed at cooling rates above 60°C min −1, accompanied by an additional crystallization peak above the glass transition. As the cooling rate is decreased, only a single melting peak occurs. This single peak corresponds to the lower temperature peak of two appearing in fast cooled J-1 polymer. Slower cooling rates produce a more ordered semicrystalline structure in the neat polymer, providing higher tensile strength and greater solvent resistance than the rapidly quenched material. WAXS patterns show the slow cooled J-1 polymer to have higher crystallinity than the quenched material. The equilibrium extent of crystallinity was determined to be about 20%, and the heat of fusion for 100% crystalline material is 150 J g −1. The density of the crystalline and non-crystalline phases are approximately 1.09 and 1.04 g cm −3 respectively. In order to study the behaviour of the composite, Kevlar fibre tows melt impregnated with J-1 polymer were wound into sheets and laminated into unidirectional composites in an autoclave process. Cracks due to internal stresses appeared in thin composite panels cooled at 10°C min −1. A thermal expansion differential was determined to be the primary cause of these stresses. By cooling the laminates slowly from the melt temperature, thin, crack-free composite panels were produced by permitting greater stress relaxation of the polymer and decreasing thermal gradients in the laminates.

Thermosensitive dielectric properties in polyamide–phenol hybrid compounds and their application to the temperature‐sensing wire

AbstractThermosensitive dielectric properteis in polyamide–phenol hybrid compounds have been studied. The polyamide–phenol hybrid compounds are constituted of p‐hydroxybenzoate–formaldehyde condensation oligomer dispersed molecularly in nylon 12 and polyamide copolymer. These materials are less hygroscopic than nylon 12 which is the least hygroscopic among polyamide homopolymers. It will be because the phenol group coordinates to amide group as the less hygroscopic “pseudo‐water” instead of water. One of these materials has also shown an intrinsic hydrophobic effect of hydrogen bond segment due to the “hybrid effect” between polyamide and phenol. The thermosensitive dielectric properties are based on the temperature dependence of intermolecular hydrogen bond behaviors by amide and phenol groups, which have been discussed in relation with the molecular behaviors. The relationship with polarizations constituting dielectric constant and hydrogen bonding molecular segments, and ac hopping conduction behaviors by proton carriers have also been discussed. These materials are applied as a temperature‐sensing material in a flexible thermosensing heater wire, which has three functions, that is, thermosensing, heating, and fusing for safe in the case of an abnormal overheat. As the features for a sensing material, these materials show the humidity low‐dependence and highly thermal stability, and will be situated as one of the high‐performance sensing material useful for the electric warmer such as an electric blanket.

Glass-Transition Temperatures of Polyamide Textile Fibers

The glass-transition temperatures (Tg) of thirty-one polyamide homopolymers and copolymers of widely differing molecular structure have been determined by differential scanning calorimetry or, as fibers, by dynamic tensile property measurements, and the results have been related to molecular structure. The effect of water on Tg has been determined, and it is shown that the extent to which saturation with water lowers Tg of a dry polyamide fiber depends only on the average spacing of amide groups in the monomeric unit. From the value of Tg for the water-saturated fiber, the dyebath temperature at which a sudden increase in color yield occurs can be predicted for one disperse-dye system. Finally a procedure is outlined that allows the calculation of each of the above quantities with a precision that averages about 7°C, from a knowledge of the structure of the polyamide monomeric unit.

Physicochemical characterization of some fully aromatic polyamides

AbstractThe characterization of eight fully aromatic polyamides are described with the procedures required to yield film‐ and fiber‐forming materials. Solutions of these aromatic polyamides in dimethylacetamide were characterized by NMR and the effects of dissolved lithium chloride on these spectra investigated. The NMR resonances for specific protons in these polymers are assigned. The IR spectra of thin films and fibers of these polyamides are also reported, together with glass transition temperatures as measured by differential scanning calorimetry (DSC). The value of NMR and IR to identify specific polyamide homopolymers and copolymers is discussed.