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Preparation and properties of poly(hexamethylene oxamide) copolymers containing ether moiety
Abstract
To modify the properties of poly(hexamethylene oxamide) (PA62), amine-terminated polyoxypropylene glycols (PGs) were introduced into the polyoxamide main chain as soft segments. A series of PA62/PG2 copolymers were synthesized successfully by a two-step method. Fourier transform infrared spectroscopy, solution proton nuclear magnetic resonance spectroscopy (¹H-NMR), differential scanning calorimetry, thermogravimetric analysis, and wide-angle X-ray diffraction were used to analyze the structures and to investigate the properties of these copolymers. The saturated water absorption was also evaluated by gravimetric analysis for PA62/PG2 copolymers. The results revealed the incorporation of PG2 effectively modified the properties of PA62 and the copolymers with PG2 content of 10–20 mol% possessed high melting point (293°C–314°C), good thermal stability and low saturated water absorption. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers
Production processes based on CO 2 as raw material offer high scalability and sustainability. Here, a novel process cascade is introduced, combining the advantages of electrochemical CO 2 conversion with the synthetic potential of industrial biotechnology: CO 2 is electrocatalytically reduced to formic acid as substrate for the metabolically engineered bacterium Methylorubrum extorquens that produces l ‐lysine as precursor of the polymer building block 1,5‐diaminopentane (cadaverine). Cadaverine is purified through targeted downstream processing and finally used in a polycondensation process to produce polyamide materials.
A novel alternating copolyoxamide of poly (decamethylene oxamide-alt-hexamethylene oxamide) (PA102-alt-62) was synthesized by oxalate-terminated bisester–bisoxalamide (262-diester) and decamethylene diamine via solution/solid-state polycondensation (SSP). The alternating structure was confirmed by solution ¹H NMR and ¹³C NMR spectra. The thermal properties were addressed by DSC and TGA and the results revealed that PA102-alt-62 possessed quite high Tm (284 °C) and ΔHf (94 J g⁻¹) as well as excellent thermal stability (T5 = 415 °C). The high crystallinity (38%) as determined by WAXD and the extremely short t1/2 at 250 °C (10 s) calculated from analysis of isothermal crystallization demonstrated that PA102-alt-62 had outstanding crystallization properties. As to the modulus of PA102-alt-62, it was almost twice as the random counterpart at room temperature and still as high as 1 GPa at 140 °C as revealed by DMA test. All the results suggested that PA102-alt-62 was a high-performance engineering polymer.
As a representative polyoxamide, poly(hexamethylene oxamide) (PA62) has good comprehensive performance. However, the high Tm (330°C) creates an obstacle for processing. To improve the processability of PA62, poly(hexamethylene terephthalate/hexamethylene oxamide) alternating copolyamide (alt‐PA6T/62) was synthesized by hexamethylene diamine‐terminated 6T6‐diamine and dibutyl oxalate via solution/solid state polycondensation. Random copolyamide (ran‐PA6T/62) was also synthesized for comparison. The structure and properties of the copolymer were analyzed by Fourier transform infrared spectroscopy (FT‐IR), nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Wide‐angle X‐ray diffraction (WAXD) and the saturated water absorption test. The NMR results confirm the alternating structure of alt‐PA6T/62. The DSC and TGA results demonstrate that the novel alternating copolyamide alt‐PA6T/62 (Tm = 321°C, T5 = 420°C) exhibited better thermal properties than those of ran‐PA6T/62 (Tm = 294°C, T5 = 412°C). The saturated water absorption of alt‐PA6T/62 was found to be 3.2 wt%. These results revealed that the novel alt‐PA6T/62 had an alternating sequence distribution, showed a high melting point as well as good processability and thermal stability, and possessed low saturated water absorption and excellent dimensional stability.
To modify the properties of poly (hexamethylene oxamide) (PA62), m‐xylylene diamine (MXD) was introduced into the polyamide main chain. A series of high molecular weight PA62/MXD2 were synthesized via a two‐step method. The chemical structure of polymer was analyzed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy, and the results confirmed the formation of PA62/MXD2. DSC test showed that the Tm of the copolymers were decreased as the molar contents of MXD in the range of 10 to 50 mol %. TGA analysis revealed that the thermal stability of the copolymers compared well with commercial PA6. Wide‐angle X‐ray diffraction studies suggested the copolymers with MXD content of 0 to 10 mol % possessed high crystallinity. The water uptake measurements were monitored, and the saturated water absorptions were found to be lower than 2.5 wt %. These properties gave them a competitive edge for application where precise dimensional stability and high thermal resistance properties are required.
In this study, an attempt was made to prepare bio-based poly(pentamethylene oxamide) (PA52) using a novel process of spray/solid-state polycondensation. A prepolymer of relative viscosity of 1.3 was prepared by spray polycondensation, where the monomers (dibutyl oxalate and 1,5-pentanediamine) were separately injected into the nozzle, atomized simultaneously under nitrogen flow, mixed, and polymerized at room temperature. After solid-state polycondensation, PA52 with relative viscosity of 3.2, weight-average molecular weight of 4.3 × 10⁴, and melting point of 301 °C was obtained. FTIR and ¹H-NMR analysis confirmed the formation of PA52 while the DSC results suggested that the resultant polymer possessed high heat resistance and good crystallizability.
Magnetic resonance imaging (MRI) and NMR relaxation experiments are used to study the water absorption by polyamide 4,6 (PA46) plates. Despite the higher crystallinity, PA46 absorbs more water as compared to the polyamides 6 and 6,6 (PA6 and PA66). Relaxation measurements demonstrate that the volume averaged molecular mobility (T2H) of the absorbed water molecules in PA46 is higher than in PA6 and PA66. Quantitative relaxation results of water saturated PA46 further suggest fast exchange between free water and water molecules bound via hydrogen bonds to amide groups. MRI reveals a gradual decrease in the amount and the T2H relaxation behaviour of water from the surface towards the core part of PA46 plates. This can be explained by the very high crystallisation rate of PA46, which prevents the close coupling of amide groups in the amorphous phase and results in a larger mean distance between the amide groups, especially in the outer part of the PA46 plates. Density measurements (WAXS and gradient column) show an increase of the density of the amorphous phase during annealing, resulting in a lower water uptake and a lower mobility of the absorbed water molecules.
Magnetic resonance imaging (MRI), NMR relaxometry, thermal analysis and gravimetrical experiments are performed to study the water absorption by neat PA46 and copolymers of PA46 and PA4n (PA46-co-PA4n) with 4 mol% n=8, 12 and 16. The observed reduction in water uptake, ingress rate and water molecular mobility with increasing value of n is explained by a combination of several physico-chemical molecular properties. The increased [CH2]/[amide] ratio and the reduced amount of crystallinity do not completely clarify the observed trends in water uptake and water molecular mobility in the copolymer series. It is shown that the increased chain mobility of the PA46 segments in the copolymers allows an improved coupling of the amide groups in the amorphous phase, explaining the observed decrease in water uptake. The important role of the morphology of the amorphous phase for water uptake is further demonstrated by annealing results and NMR relaxation experiments as a function of temperature.
A novel bio-based polyamide, poly(pentamethylene oxamide) (PA52), with high molecular weight has been prepared from dibutyl oxalate and renewable monomer of 1,5-pentanediamine by a two-step polymerization procedure. The chemical structures are analyzed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy while the properties are evaluated by differential scanning calorimetry, thermogravimetric analysis, and water uptake measurements for the obtained PA52. The results reveal that PA52 possesses distinguished properties such as high temperature resistance, excellent crystallizability and low water absorption. POLYM. ENG. SCI., 2017.
The design of assembly components requires special attention to aspects related to their dimensions to ensure their functionality. The goal of this paper is to analyse the influence of case-based environmental conditions, including extreme hydrothermal conditions, on the dimensional stability of a component made from different polyamides throughout the component's working life. The results support the conclusion that components made from PA6 have a higher capacity to absorb humidity than those made from PA66 and, on the other hand, a higher capacity to lose this humidity, which implies a more significant effect on the average error in the dimensions considered (12% for PA6 in comparison to 3% for PA66). With regard to assembly dimensions, components remain within dimensional tolerances under average and extreme humidity conditions and average temperature conditions. Components injected with P66 are more stable for all of the situations analysed.
Difluoro-substituted monomer (N,N’-Bis(4-fluorobenzoyl) isophorone diamine (BFID) was prepared via interfacial reaction from isophorone diamine and 4-fluorobenzoic chloride. It was then conducted to react with hydroquinone (or resorcinol, 1,1-bis(4-hydroxyphenyl)-1-phenylethane (BHPPE)) to yield a series of semi-aromatic polyamides. For the synthesized semi-aromatic polyamides differential scanning calorimetry and thermogravimetric analysis confirmed high glass transition temperatures (Tg), between 217 and 239 °C and a good thermal stability with initial degradation temperatures (Td) in the range 425 - 430 oC. Tensile test and dynamic mechanical analysis (DMA) results revealed the good mechanical properties for the semi-aromatic polyamides at ambient temperature and even at 200 °C. A complex viscosities at 310 oC for the semi-aromatic polyamide in the range of 990-1350 Pa•s could be observed when measured by rheological characterization, which suggests that they were suitable for melt process. The better solubility properties for the resultant semi-aromatic polyamides compared to the commercial ones were also found. All the results indicated the good processability for the synthesized semi-aromatic polyamides. Additionally, they were found to have almost the identical optical transmittance (Tran%: 83%-85% at 450 nm) as polycarbonate (PC) in the UV-visible region.
A series of semiaromatic difluorobenzamide monomers was synthesized by the reaction of diamine and 4-fluorobenzoic chloride using a facile interfacial method. These syntheses were conducted to react the monomers with 1,1-bis(4-hydroxyphenyl)-1-phenylethane (BHPPE), so as to prepare semiaromatic polyamides containing ether units by the method of nucleophilic polycondensation. These had excellent thermal properties with glass transition temperatures (Tg) of 134.4–195.6 °C and initial degradation temperatures (Td) of 405–443 °C. The activation energies of degradation were in the range of 180.1–275.9 kJ mol−1. The resultant polymers can be dissolved in strong polar solvents and supply a tough film with a tensile strength of 89–105 MPa. Also, we found that the complex viscosities of these semiaromatic polyamides ranged from 77 to 688 Pa s at 290 °C. They had the appropriate complex viscosities for melt processing. Moreover, they had much wider processing windows than those of traditional semiaromatic polyamides such as poly(hexamethylene terephthalamide) (PA6T). Interestingly, some of the resultant polymers were found to be naturally self-retardant.
An unprecedented family of segmented polydimethylsiloxane poly(urea oxamide) (PDMS-UOx) copolymers displayed thermoplastic elastomeric behavior with improved thermomechanical properties compared to PDMS polyurea (PDMS-U) analogs. A two-step, PDMS end-capping sequence using diethyl oxalate and hydrazine generated difunctional oxamic hydrazide capped oligomers. Polymerization with HMDI provided high molecular weight copolymers, which yielded elastomeric films with monodisperse hard segments. Dynamic mechanical analysis (DMA) of PDMS-UOx copolymers revealed a broad, rubbery plateau that extended for >180 degrees C. The PDMS-UOx service window extended similar to 120 degrees C further than a PDMS-U analog, presumably due to enhanced hydrogen bonding and concomitant microphase separation. DSC and WAXD elucidated the amorphous morphology of PDMS-UOx, and DMA, SAXS, and AFM confirmed a well-defined microphase-separated morphology. Incorporation of urea oxamide groups significantly affected microphase separation and thermomechanical properties, and these copolymers offer impact in adhesive and biomedical technologies due to low temperature reaction conditions for unique hydrogen bond containing segmented copolymers.
Polyether block amide (PEBA) elastomer-organoclay nanocomposites were prepared by a melt mixing technique. The X-ray diffraction and transmission electron microscope analysis indicated that the nanocomposite formed a partially exfoliated nanostructure in which the organoclay was dispersed uniformly throughout the matrix at the nanometer scale. The effect of organoclay on the melting temperature (Tm), glass transition temperature (Tg), crystallization temperature (Tc), and heat of fusion (ΔHm) of the PEBA was determined by differential scanning calorimetry. Enhanced mechanical properties of the nanocomposites were observed from tensile and dynamic mechanical analysis. Thermal gravimetric analysis showed that the clay nanoparticles caused an increase in the thermal stability of the PEBA. Measurement of oxygen permeability and the degree of swelling in ASTM #3 oil indicated that the gas barrier properties and solvent resistance were greatly improved by the clay nanoparticles. Melt rheological studies revealed that the nanocomposites exhibited strong shear thinning behavior and a percolated network of the clay particles was formed. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers
An investigation of the structure-property relationships of poly(dimethyl siloxane) (PDMS) polyoxamide segmented copolymers reveals the impact of oxamide spacing and PDMS molecular weight on physical properties. Varying the length of the methylene spacing between the oxamide hydrogen bonding groups in the hard segment (HS), as well as the PDMS soft segment molecular weight, provides insight into the influence on thermal and mechanical properties. Bulk polycondensation of ethyl-oxalate-terminated PMDS oligomers with diamines yields optically clear, thermoplastic elastomers with excellent mechanical properties. The structure-property investigation reveals optimum mechanical properties of PDMS polyoxamide segmented copolymers occur with the smallest spacing between oxamide groups in the HS.
Poly (2-methyl-1,8-octametyleneoxamide) (nylon-MOMD-2) was prepared from dibutyl oxalate and 2methyl-1,8-octamethylenediamine. The chemical structure was investigated by C-13 nuclear magnetic resonance (C-13 NMR). The C-13 NMR spectrum revealed that the methyl groups distribute among the four beta-sites at random. The crystal structure and its temperature dependence were also investigated by molecular mechanics calculations, X-ray diffraction, and differential scanning calorimetry. The structure was determined to be monoclinic and a = 6.26 angstrom, b = 8.80 angstrom, c = 14.7 A, and beta = 50.7. The torsion angle of the NH-CH2 bonds has a skew conformation and there are the two distinct torsion angles in the crystal structure. The crystal structure of nylon-MOMD-2 has a disordered and statistical structure. The crystal structure shows no phase transition on heating until its melting point, although the unit cell expands in the a and b axis directions.
A homologous series of aliphatic polyoxamides, nylon 122, 102, 82, and 62, were prepared by the bulk polycondensation of dialkyl oxalates with diamines. Infrared spectroscopy, x-ray diffraction, differential thermal analysis, thermogravimetric analysis, and gas chromatography were used to study the structure and thermal stability of these polyoxamides. From the fiber pattern of nylon 122, a structural repeat distance of 19.5 Å was measured. This was in close agreement with the expected value for an extended planar, zigzag chain conformation. With the exception of the expected decrease in the structural repeat distance along the chain axis resulting from the different number of methylene groups, nylons 122, 102, and 82 were isostructural. Nylon 62 appeared to pack in a similar manner to the other materials studied. However, there were differences in the diffraction pattern of this polymer; these may be indicative of a different chain conformation or of strain in the crystalline regions of the polymer. The infrared spectra indicate the presence of strong hydrogen bonding in all the polymers. Thermal analysis and pyrolysis data revealed catastrophic polymer degradation between 400 and 500°C in nitrogen, with appreciable homolytic cleavage of the oxamide group.
Long chain semiaromatic polyamides with high molecular weight were synthesized by the reactions of undecanediamine with various aromatic diacids, and characterized by fourier transform infrared spectra (FT-IR) and nuclear magnetic resonance (1H-NMR). The thermal behaviors were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The solubility, dynamic mechanical, physical and mechanical properties of the polyamides were also investigated. The experimental results show that the polyamides with high molecular weights are obtained only the PH value of the polyamides salt are in the range of 7.2–7.4. The melting temperatures and the glass transition temperatures of the polyamides increase with the increase of the rigidity of aromatic diacids, and are near to those of poly(nonamethyleneterephthalamide) (PA9T).
Segmented poly(ether ester amide)s comprising glycine or β-alanine extended bisoxalamide hard segments are highly phase separated thermoplastic elastomers with a broad temperature independent rubber plateau. These materials with molecular weights, Mn, exceeding 30 × 103 g mol−1 are conveniently prepared by polycondensation of preformed bisester–bisoxalamides and commercially available PTHF diols. FT-IR revealed strongly hydrogen bonded and highly ordered bisoxalamide hard segments with degrees of ordering between 73 and 99%. The morphology consists of fiber-like nano-crystals randomly dispersed in the soft polymer matrix. The micro-structural parameters of the copolymers were addressed by simultaneous small- and wide-angle X-ray scattering. It is shown that the crystals have strictly identical thickness, which is close to the contour length of the hard segment. The long dimension of the crystals is identified with the direction of the hydrogen bonds. The melting transitions of the hard segments are sharp, with temperatures up to 170 °C. The studied polymers have an elastic modulus in the range of 139–170 MPa, a stress at break in the range of 19–31 MPa combined with strains at break of higher than 800%. The segmented copolymer comprising the β-alanine based bisoxalamide hard segment with a spacer of 6 methylene groups has a melting transition of 141 °C which is higher than the melting transition of its glycine analogue of 119 °C. Likewise, the fracture stress increased from 22 to 31 MPa when the glycine ester group in the hard segment was replaced with β-alanine. The improved thermal and mechanical properties of the latter polymers is related to the crystal packing of the β-alanine based hard segments in the copolymer compared to the packing of the hard segments comprising glycine ester groups.
The evaluation of the randomness degree and block length of polyamides after interchange reactions is a key issue to estimate the transamidation progress, which strongly influences the final properties of the materials. The polymers under examination are poly(m-xylylene adipamide) (MXD6) and poly(hexamethylene isophthalamide-co-terephthalamide) (PA6I-6T). They were blended by extrusion and then treated in differential scanning calorimeter (DSC) in order to improve transamidations and copolymer formation. The molecular structure of the final materials was analysed by means of an efficient, new and fast method based on 1H NMR analysis. The results were compared to those obtained by the more widely used 13C NMR analysis.
Long chain semiaromatic polyamides were synthesized by the reactions of decanediamine with various aromatic diacids and characterized
by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1H-NMR). The thermal behaviors were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).
The solubility, dynamic mechanical, physical and mechanical properties of the polyamides have also been investigated. The
resultant polyamides have intrinsic viscosity ranging from 1.7 dL/g to 2.1 dL/g. Their melting temperatures range from 305°C
to 343°C, and the glass transition temperatures fall in the range of 125–130°C. The tensile strength of the polyamides is
above 100 MPa.
A comparison is made between the rates of spherulitic growth in Nylon 6 and Nylon 66 polymers. Theoretical equations describing the growth rates are presented using the concept of molecular chain folding within the fibrils or lamellae comprising the spherulites. These equations adequately describe the rate of spherulite growth in these two polyamides, which occurs by a coherent two-dimensional mechanism. Crystal surface free energies are given.
Chain-folded single crystals of the seven even-even nylons: 4 8, 4 10, 4 12, 6 10, 6 12, 6 18 and 8 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 single crystals are lath-shaped lamellae. Diffraction from these crystals, at room temperature, reveals that three crystalline forms are commonly present. The crystals are composed of chain-folded, hydrogen-bonded sheets; the linear hydrogen bonds within the sheets generate a progressive shear of the chains. The sheets are found to stack in two different ways: some of the sheets stack with progressive shear, to form ‘α-phase’ crystals; other sheets stack with alternate up and down stagger, to form ‘β-phase’ crystals. Both the α- and β-crystals give two strong diffraction signals at spacings of 0.44 and 0.37 nm; these signals represent a projected inter-chain distance within a hydrogen-bonded sheet (actual value 0.48 nm) and the inter-sheet spacing, respectively. Some crystals also show an additional diffraction signal at 0.42 nm; this signal is characteristic of the pseudo-hexagonal phase, a phase usually only found at high temperatures. The melting points of solution grown crystals of this even-even nylon series decrease with decreasing linear density of hydrogen bonds. On heating, the strong diffraction signals in both α- and β-phases move together and meet, as is the case for other even-even nylons. The lowest temperature at which the two signals first have the same spacing is termed the Brill temperature. For all the nylons of the present study the Brill temperature is coincident with the melting temperature, and the two strong signals meet at the spacing (0.42 nm) of the pseudo-hexagonal phase. The behaviour of these nylons is compared and contrasted with that of nylon 6 6, where only the α-phase is found at room temperature and, on heating, the Brill temperature is found to occur in the range 95-35°C below the melting point at 265°C.
Purpose
The purpose of this paper is to investigate the electronic industry's reaction to environmental regulations specifically in terms of lead‐free solders and halogen‐free flame‐retardants (FRs).
Design/methodology/approach
This work achieves its objective by discussing the various international regulations pertaining to electronics manufacturing and relating the industry reactions to those regulations. The electronics industry is pursuing lead‐free solders and halogen‐free FRs, in part due to regulations. However, the paper includes examples of how the industry is successful in implementing environmentally friendly changes.
Findings
The authors compared regulations from Japan, the European Union, and the US. While the regulations themselves vary in scope, industry actions to find alternatives do have common purposes. Electronics manufacturers recognize that environmentally motivated changes are beneficial in terms of waste minimization. Regardless of the regulatory motivation, minimization does lead to energy and economic efficiency.
Practical implications
Electronics manufacturers that are interested in green design will benefit from understanding present regulations. They will also benefit from the included examples of product and process improvement for the purpose of environmental compatibility. The paper includes specific examples of material alternatives to banned substances.
Originality/value
This paper derives its perspective from a similar review of literature and company findings that the authors completed in 2001. As refinement of the regulations has continued, the electronics industry has developed improvements in basic materials and processes.
Purpose
This paper seeks to investigate the electronics industry's reaction to environmental regulations specifically in terms of lead‐free solders and halogen‐free flame‐retardants (FRs).
Design/methodology/approach
This work achieves its objective by discussing the various international environmental regulations pertaining to electronics manufacturing and relating the industry reactions to those regulations. It also provides the market trends related to lead‐ and halogen‐free products. The electronics industry is pursuing lead‐free solders and halogen‐free FRs, in part due to regulations. However, the paper includes examples of how the industry is successful in implementing environmentally friendly changes.
Findings
The authors compared regulations from Japan, the European Union, the USA, and China. While the regulations themselves vary in scope, industry actions to find alternatives do have common purposes. Electronics manufacturers recognize that environmentally motivated changes are beneficial in terms of waste minimization.
Research limitations/implications
Electronics manufacturers that are interested in green design will benefit from understanding present regulations. They will also benefit from the included examples of product and process improvement for the purpose of environmental compatibility.
Originality/value
This paper derives its perspective from a similar review of literature and company findings that the authors completed in 2006. As refinement of the regulations has continued, the electronics industry has developed improvements in basic materials and processes.
A series of polyoxamide homopolymers and regular copolyoxamides was prepared by liquid-liquid interfacial, gas-liquid interfacial, and solution polycondensation techniques. Thus, poly(hexamethylene oxamide) {Nylon 62}, poly(ethylene oxamide) {Nylon 22}, and poly(p-phenylene oxamide) were prepared in moderate molecular weight by reacting gaseous oxalyl chloride with aqueous solutions of 1,6-hexanediamine, N,N′-bis(2-aminoethyl) oxamide, and p-phenylenediamine, respectively, using a gas-liquid interfaciai technique developed for the continuous production of polyoxamides. A number of regular copolyoxamides were prepared by condensing various aliphatic diamine-diamides with both aliphatic and aromatic acid chlorides using both liquid-liquid interfaciai and solution polymerization procedures. Both the yield and molecular weight of the polymers produced were found to be dependent on factors such as polymerization technique, monomer solubility, reaction temperature, reactant concentration, type of solvent, and type of acid acceptor.
The structure and morphology of nylon 9,2 has been investigated using transmission electron microscopy, selected area electron diffraction, and X-ray diffraction. A unit cell with parameters a = 5.45 Å, b = 8.7 Å, c (chain axis) = 31.8 Å, and β = 47.9° was determined and a C12/c1 space group is postulated. Chain conformation is practically all-trans, but the torsion angles of the NH−CH2 bonds slightly deviate from 180° in order to optimize the hydrogen-bonding interactions between neighboring chains. A structure with two directions of hydrogen bonding is derived, although the unit cell is strongly related to that found in nylon 6,6. Crystallization from the melt and temperature-induced structural changes have also been studied.
Chain-folded single crystals of the five even−even nylons 4 4, 6 4, 8 4, 10 4, and 12 4 were grown from solution and their structures and morphologies studied using transmission electron microscopy, both imaging and diffraction. Sedimented mats were examined using X-ray diffraction. All these nylons have room temperature crystal structures that relate to that reported for nylon 6 6, yet there are differences, reflecting the differences in the amide group distribution. At room temperature, all the crystals are composed of chain-folded, hydrogen-bonded sheets; the hydrogen bonds within the sheets form a progressive shear pattern, and, in addition, the sheets themselves are sheared progressively parallel to the sheet plane so that they generate triclinic unit cells. The magnitude of this intersheet shear may differ between nylons; it is dependent on the details of the amide decoration pattern on the hydrogen-bonded sheet faces. In all five nylons studied, the two strong and characteristic diffraction signals of the room temperature triclinic structure, at spacings 0.44 nm (projected interchain/intrasheet distance) and 0.37 nm (intersheet distance), move together and merge as they do for single crystals of nylon 6 6. For each of the X 4 nylons, the Brill temperature (lowest temperature where the spacings are equal) is in the range 140−190 °C. In each case, the triclinic structure gradually transforms into a pseudohexagonal structure as the temperature rises. The melting points of solution-grown crystals of this series of even−even nylons decrease with the linear hydrogen bond density. This series of nylons is unique since in each case the chain folds must be in the diamine alkane segment.
Poly(hexamethylene oxamide) [Nylon 62] of reasonable molecular weight was prepared by a modification of the Sokolov technique for the preparation of oxamides. This polymer could be stretched and a fiber diagram of the polymer could be obtained. Nylon 62 has a structure similar to that of the α form of Nylon 66.
Poly(hexamethylene oxamide) and related polyoxamides were prepared by ring-opening polymerization of appropriate cyclic oxamides. They polymerized rapidly in the melt with ionic catalysts to form solid polymers and copolymers. Slow thermal decomposition, with evolution of CO and CO2, was observed in polymerization mixtures. Poly(hexamethylene oxamide) was also found to undergo thermal decomposition well below its melting temperature, c-62 also polymerized in the crystalline state.
Cyclic oxamides of various diamines have been prepared and characterized. From hexamethylenediamine and oxalyl chloride the first three cyclic oligomers were obtained in pure form. These are designated c-62, c-6262, and c-626262. c-22, c-43, c-82, and 4-methoxy-c-62 were prepared from ethylenediamine, tetramethylenediamine, octamethylenediamine, and 3-methoxyhexamethylenediamine with oxalyl chloride.
The crystalline structure of nylon 12 2 has been studied by means of X-ray and electron diffraction. Two structures can be obtained, depending on the preparation conditions. Both are based on a progressive stacking of hydrogen-bonded sheets, but they differ in the chain axis shift between consecutive sheets. Packing energy calculations corroborate these observations and indicate as the most stable a structure with only 1 Å shift. In the same way, theoretical calculations were also performed with nylon 6 2. Similarly, a structure with a different shift from the characteristic value of most conventional nylons is stabilized. Electron charge distributions on the oxalamide and amide groups play a fundamental role, thus favoring different stacking modes.
The phase behavior of blends containing only aromatic polyamides has been investigated, and the results compared with a predictive treatment founded upon a mean-field binary interaction model. The similarity of structure and composition of the polymers, and hence the close proximity of the respective glass transition temperatures, necessitated the implementation of the technique established by Ellis and ten Brinke to evaluate phase phenomena within the blends. Relying on the structural dependence of the kinetics of enthalpy recovery, this technique has proven to be very sensitive and provides information that is available by no other technique. The prediction of immiscibility was found to be supported in most cases and confirms the axiom that polymers of similar constitution will not form homogeneous mixtures. Noted exceptions to this rule were also found, suggesting that there exists the potential for subtle behavior that is not yet accounted for. The elements possibly contributing to this are addressed and discussed in terms of the applicability of a binary interaction model to blends of this nature.
The principle of the new gas-phase method of polycondensation consists of carrying out the polycondensation reaction of two high reactive compounds at a liquid—gas interface. The gas-phase method permits the synthesis of polyamides with rapidly hydrolyzing diacid chlorides (e.g., oxalyl chloride), which cannot be used for liquid—liquid polycondensation. The gas-phase synthesis of polyhexamethyleneoxamide from hexamethylenediamine and oxalyl chloride has been investigated in detail. The common features of gas-phase and interfacial methods of polycondensation are due to the fact that in both cases the chemical reaction proceeds in the polymeric film. The gas-phase methods can be used for the synthesis of a series of polymers.
The sorption and the desorption isotherms of water are described for several crystalline polyamides (nylons 2, 3, 6, 7, 8, 11), amorphous polyamides (poly-C-methylcaprolactam, terpolymer of caprolactam, aminoheptanoic acid and aminoundecanoic acid) and model amides (N-ethyl acetamide, Y-ethyl butyramide, N-butyl capronamide) at 27°C., with amides also at 40 and 55°C. On the basis of our own as well as reported data (on sorption isotherms, heat balance of sorption, sorption heats, infrared absorption, nuclear magnetic resonance, mechanical properties of polyamide-water systems), we propose the following mechanism for the sorption of water in polyamides (capillary condensation is not considered): In nylon 6, three molecules of water are sorbed on two neighboring amide groups in an accessible region. The first molecule forms a double H-bonds between the CO groups (firmly bound water) and the other two molecules form H-bonds between the CO and the NH groups (loosely bound water). It turns out that even in nylons 2 to 6, water is probably sorbed by this mechanism whereas in nylons 8 to 12 only one molecule of water is sorbed on two amide groups, probably as a firmly bound water. Nylon 7 stands somewhere between the two groups.
The sorption and transport of water in nylon 6,6 films as functions of the relative humidity (RH) and temperature were studied. Moisture-sorption isotherms determined gravimetrically at 25, 35, and 45°C were described accurately by the GAB equation. Water-vapor transmission rates were enhanced above ≈ 60–70% RH, primarily due to the transition of the polymer from glassy to rubbery states. The glass transition temperatures (Tg's) of nylon 6,6 were measured at various moisture contents using differential scanning calorimetry. The results showed that the sorbed water acted as an effective plasticizer in depressing the Tg of the polyamide. Fourier transform infrared spectroscopy (FTIR) was utilized to characterize the interaction of water and the nylon. Evidence from FTIR suggested that the interaction of water with nylon 6,6 took place at the amide groups. Based on the frequency shift of the peak maxima, moisture sorption appeared to reduce the average hydrogen-bond strength of the NH groups. However, an increase was seen for the CO groups. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 197–206, 1999
The synthesis of polyetheramide, containing poly(tetramethylene ether) (PTMEG) as the soft segment phase and polylactams as the hard phase was carried out in a Leistritz modular intermeshing counter-rotating twin-screw extruder in a one-step, solvent-free process. No by-product such as carbon dioxide or H2O is formed during the reaction procedure. Isocyanate-terminated telechelic PTMEG was premixed with caprolactam, and these were fed into the twin-screw extruder to form the polyetheramide triblock copolymer. This triblock copolymer has not been previously polymerized in a twin-screw extruder or continuous mixer. Subsequent to polymerization, the copolymer and PA6 homopolymer were also melt-spun into fibers. Molecular weights and molecular weight distributions were determined by GPC on trifluroacetylated samples. Thermal, rheological, mechanical, and structural properties were investigated. It appears that phase separation (arising from immiscibility between the polyether segment and the polyamide segment as the reaction proceeds) did not hinder the chemical reaction between the two reactants because of the intense mixing in the twin-screw extruder. The new triblock copolymer should have application as a rubber-toughened thermoplastic or thermoplastic elastomer depending upon the elastomer content.
The crystal structure of the -form of nylon 6 (polycaproamide) obtained by the iodine treatment of the -from of nylon 6 has been determined by x-ray diffraction. The unit cell contains four repeating units and is monoclinic with a = 9.33 A., b = 16.88 A. (fiber axis), c = 4.78 A., β = 121°. The space group is P21/a. There is considerable deviation from the planar configuration in the amide group of the chain. The plane of the CH2 chain zigzag lies nearly parallel to the (001) plane. The crystal is composed of the pleated sheets of the parallel chains joined by hydrogen bond between the adjacent chains. The chain directions are opposite in alternating sheets. The hydrogen-bond length is 2.83 A., a reasonable figure for an NH·. O chains joined by a hydrogen bond between the adjacent chains. The direction of the hydrogen bond makes an angle of 12° with the (100) plane, and the CO and NH bonds are nearly colinear. The amide groups lie at the same level in the cell.
If a solution of a fast-reacting diacid halide in a water-immiscible solvent is brought together with an aqueous solution of a diamine without stirring, a thin film of high polymer is formed at once at the interface. Polyurethanes and polyamides in particular form tough films which can be grasped and pulled continuously from the interface as a folded rope of film. This unstirred interfacial polycondensation not only provides a dramatic demonstration of polymer formation but has permitted the observation of polymerization behavior and the study of the effects of many variables upon the process. The polymer-forming reactions proceed by nucleophilic displacement, and many have rate constants of at least 102–104 1. mole−1 sec. −1. Polymers derived from diamines were found to form in the organic solvent phase. Therefore the rate of polymer formation is controlled by the transfer of diamine from the aqueous phase. It is believed that the liquid interface does not have any beneficial orienting effect on the reactants but that it provides for the regulated flow of one reactant into an excess of the other. Furthermore, the aqueous phase provides for the removal of the interfering byproduct, hydrogen halide, from the polymerization site. Some of the interrelated variables which have been studied and which are discussed in relation to the physical mechanism are the solvent sensitivity of the polymer, partition coefficients of the reactants, reactant concentration, duration of the polymerization, and the addition of monofunctional reactants, detergents, and salts. The formation of polyphenyl esters is discussed briefly.
The crystal structure of nylon 6 (NH (CH2)5CO)p has been determined by interpretation of the x-ray diffraction patterns given by drawn, rolled fibers. The determination was part of a program to investigate the relation between structure and physical properties, in particular melting point. Nylon 6 melts 50°C. lower than its isomer nylon 66 (NH (CH2)6NH·CO (CH2)4CO)p; it had been suggested that this was due to deficient hydrogen-bond formation in nylon 6 crystallites. The unit cell contains eight chemical units (NH (CH2)5CO) and is monoclinic with a = 9.56 A., b = 17.24 A., c = 8.01 A., and β = 671/2°. Calculated density = 1.23. Observed density for a drawn monofilament = 1.16. The structure consists of planar chains of CH2 groups and amide groups tilted 7° from the (001) plane. Alternate chains in this plane are oppositely directed, an arrangement which allows all hydrogen bonds to be made perfectly. The hydrogen-bonded sheets of atoms are packed in an “up-and-down” staggered configuration along the c-axis. Distances between atoms in neighboring molecules are all normal van der Waals contact distances. It appears, from a general survey of polyamide melting points published elsewhere, that the determining factor is the number of CH2 groups between the amide “anchor points”—polymers with odd numbers of CH2 groups melt lower than those with even numbers. The present work shows that the odd number of CH2 groups in this polymer does not lead to deficient hydrogenbond formation, and that the lower melting point of nylon 6 as compared with nylon 66 must be ascribed to some other cause, possibly connected with the propagation of vibrations along odd-numbered chain segments.
Water absorption at 93% relative humidity and 25°C was determined for 12 regular aliphatic/aromatic copolyoxamides. The equilibrium water absorption ranges from 7% to 30%, varied with the polymer structure and is highest in polymers with high amide concentration. The water absorption is reversible and seems to consist of a two-step process, rapid absorption of water by polymer followed by a slower second stage as equilibrium is approached. These polymers have low crystallinity and the water absorption does not occur in crystalline regions. All water is bound to the polymer; it may be freed by heating the hydrated polymer above 100°C, but rebinds completely at room temperature.
Interfacial polycondensation is a rapid, irreversible polymerization at the interface between water containing one difunctional intermediate and an inert immiscible organic solvent containing a complementary difunctional reactant. It is based on the Schotten-Baumann reaction in which acid chlorides are reacted with compounds containing active hydrogen atoms (OH, NH and SH). A large number of polymers (heat-sensitive and infusible as well as stable and meltable) can be prepared. The method has been applied to the preparation of polyurethanes, polyamides, polyureas, polysulfonamides, and polyphenyl esters. Interfacial polycondensations are run in simple, open laboratory equipment with or without stirring. With suitable agitation granular or powdered polymers with high molecular weight are prepared at room temperature and isolated within a few minutes. The intermediates need not be absolutely pure or in balance nor is a quantitative yield needed in order to obtain high polymer. The major variables in the interfacial polycondensation process are discussed and the laboratory techniques and principles are contrasted with melt polycondensation.
An attempt was made to produce a new short-chain alphatic polyamide nylon-4,2. This polyoxamide can be prepared by polycondensation of tetramethylene diamine and diethyl oxalate. A high molecular weight polymer (ηinh = 1.9 from 0.5% solutions in 96% sulphuric acid) has been obtained by employing a two-step polycondensation method; the precondensation was carried out in solution at low temperatures (20–140°C) and the postcondensation in the solid state at high temperatures (250–300°C). The effect of solvent composition and reaction temperature on the prepolymerization and the effect of reaction time and temperature on the postcondensation was studied. We also investigated the influence of moisture during washing, storing, and the solid-state reaction on the polymerizability by the postcondensation. Nylon-4,2 is soluble only in highly polar solvents such as trifluoroacetic acid (TFA), dichloroacetic acid, and 96% sulphuric acid. Films were cast from TFA. With these films we studied the IR spectrum, WAXS pattern, water absorption, and melting behavior. Nylon-4,2 was found to melt at 388–392°C, has a crystallinity of 70%, and a low water absorption (3.1% at 50% RH). The glass transition temperature of the dry sample was found to be at ∼120°C and for the wet sample at −15°C.
A modified dual-mode sorption model represents the sorption of water vapor by an amorphous polyamide at 23 °C. The Langmuir equation is used to calculate the volume fraction of chemisorbed solute and the Flory-Huggins equation is used instead of Henry's law to calculate the volume fraction of water which is not chemisorbed. This model describes the data over a range of water activities from zero to one and predicts clustering of the sorbant. Fourier Transform Infrared (FTIR) spectroscopy data and dielectric measurements of the gamma relaxation temperature suggest that the water associates with amide groups at low water activities.
- Lozano-González
D. Glasscock, W. Atolino, G. Kozielski, and M. Martens, DuPont Eng. Polym., (in press).
- D. Glasscock
- W. Atolino
- G. Kozielski
- M. Martens