Homogeneous alkylation of poly(m-phenylene isophthalamide)

Homogeneous alkylation of poly(m-phenylene isophthalamide) (PMIA) was carried out in N-methyl-2-pyrrolidone. Alkyl halides such as benzyl bromide and allyl bromide were reacted with sodium-metallated PMIA. When the Taft equation was applied to this substitution reaction, the linear relationship was apparently obtained between log k/k₀ and σ^*. The molecular weight of alkylated PMIA decreased by sodium-metallation and alkylation reactions. The weight loss of PMIA derivatives on heating increased with an increasing degree of substitution of the benzyl group, but it was improved by the reaction of the unsaturated alkyl group with 1,2-ethanedithiol.     

Block copolymer of polyurethanes with poly(m-phenylene isophthalamide)

In this study,we modified two kinds of conventional polyurethane (PU) by the low molecular weight diamine-terminated wholly-rigid aromatic polyamide poly(m-phenylene isophthalamide) (PmIA) (Nomex). Two molecular weights (1000 and 2000) of poly(tetramethylene glycol) (PTMG) with 4,4-diphenylene methane diisocyanate (MDI) and with three different ratios of low molecular weight diamine-terminated PmIA prepolymer with different molecular weight of 346, 584, 823 were synthesized to form six PmIA-PU block copolymers. Various block copolymers were also obtained by different ratios of wholly-rigid PmIA prepolymers. Inherent viscosity results indicated that the block copolymers are more viscous than conventional polyurethanes, suggesting that the block copolymers had sufficiently high molecular weights. Moreover, results obtained from differential scanning calorimetry (DSC) and dynamic mechanical properties analysis (DMA) demonstrated that the block copolymers not only exhibited a glass transition temperature (T_g) under 0 °C, but also had a higher storage modulus (E) than those of the conventional PU. Opitical microscopy (OM), phase contrast microscopy (PCM), and transmission electron microscopy (TEM) analyses confirmed that all of the block copolymers had a dispersed phase structure. The mechanical properties, tensile strength and 300% modulus of the block copolymers were found to be better than those of conventional PU.     

Modification of nylon-6 with semirigid poly(p-diphenylmethyl terephthalamide)

In this research, flexible nylon-6 was reinforced by semirigid aromatic polyamide poly(p-diphenylmethyl terephthalamide) (PMA) through physical polyblending and chemical copolymerization using p-aminophenylacetic acid (P-APA) as a coupling agent. From the DSC measurement, it was shown that the T_g of the polyblends was increased with the increase of PMA content. It was discovered that the T_g and T_m of multiblock copolyamides would be higher than those of polyblends and triblock copolyamides. The multiblock copolyamides exhibited a homogeneous texture rather than an aggregated one. Scanning electron microscopy revealed that the polyblends were a dispersed-phase structure. We found that from the wide-angle X-ray diffraction pattern the triblock copolyamides and polyblends had two diffraction peaks, i.e., 2θ = 20° and 24°. However, the multiblock had only one at 2θ = 20°, which evidently indicates that a new crystal structure of multiblock copolyamides was formed. As for the mechanical properties, the multiblock copolyamides were found to have more significant reinforcing effects than those of polyblends and triblock copolyamides. © 1993 John Wiley & Sons, Inc.     

界面缩聚法制备间位芳香族聚酰胺的研究

采用界面缩聚的方法制得了比浓对数粘度较高的聚间苯二甲酰间苯二胺(PMIA)聚合物。对聚合过程中有机溶剂的选择、两种反应单体在各自相中的起始浓度、搅拌速率、缚酸剂的选择等进行了研究。最佳工艺为:以THF为有机溶剂,常温下,CMPD/CIPC比值约为1∶1.1,搅拌速率为750 r/min,以2-甲基吡啶为缚酸剂,制得的聚合物ηinh最大,可达到1.8 dL/g。利用热重法对PMIA的热稳定性进行了分析,结果表明,聚合物具有较好的热稳定性,符合高温使用的要求。     

聚间苯二甲酰间苯二胺树脂的合成研究

以间苯二胺为原料,在溶剂N,N-二甲基乙酰胺中与间苯二甲酰氯反应,聚合成间苯二甲酰间苯二胺树脂。通过在微通道反应器中进行聚合反应时,反应物配比有效控制在1.005~1.000,反应温度0~10℃,溶剂水份300×10~(-6)g/g以下,两种单体进料速率5∶4~5∶3,此条件下,聚合物粘度1.9~2.1,分子量分布稳定。     

干法纺丝用聚间苯二甲酰间苯二胺溶液的流变性能

研究了聚间苯二甲酰间苯二胺溶液的固体质量分数、相对分子质量、温度对溶液流变性能的影响。结果表明:聚间苯二甲酰间苯二胺溶液的流变性能受溶液固体质量分数、相对分子质量、温度的影响明显,聚合物相对分子质量增大、溶液固体质量分数增加均使溶液表观黏度增大,温度升高使溶液表观黏度减小,溶液表观黏度随剪切速率的变化幅度较小。试验结果表明:适合干法纺丝的聚间苯二甲酰间苯二胺溶液的固体质量分数为31%³5%,特性黏度为1.6 dL/g左右,纺丝时原液温度范围为5035%,特性黏度为1.6 dL/g左右,纺丝时原液温度范围为50¹20℃。     

Modification of nylon-6 with semi-or wholly-aromatic polyamides

In this study, flexible Nylon-6 was reinforced by semi-or wholly-aromatic polyamides; poly(m-phenylene isophthalamide) (PmIA), poly(4,4′-diphenylmethane terephthalamide) (PMA), and poly(4,4′-diphenylsulfone terephthalamide) (PSA). Various high molecular weight block copolyamides were synthesized by solution polymerization using p-aminophenylacetic acid (p-APA) as a coupling agent. Their thermal properties have shown that the block copolyamides exhibit higher T_g and T_m, and better thermal stability than those of Nylon-6, especially PmIA modified Nylon-6. The order of their thermal properties of aromatic modified Nylon-6 copolyamides is PmIA > PMA > PSA. Moreover, the T_g and T_m of multiblock copolyamides are higher than those of triblock copolyamides. From the wide-angle X-ray diffraction pattern, it is found that the triblock copolyamides have two diffraction peaks, i.e., 2θ = 20.5° and 24°. However, the multiblock has only one peak at 2θ = 20°, indicating a different crystal structure for multiblock copolyamides. For the mechanical properties, it is found that the multiblock copolyamides have a more significant reinforcing effect than the triblock copolyamides. Also, the order of the physical properties of aromatic modified Nylon-6 copolyamides, such as tensile strength, is PmIA > PMA > PSA, but for the elongation PSA > PMA > PmIA.     

Some studies on polyblends of poly(p-phenyleneterephthalamide) and nylon-6

Polyblends of poly(p-phenyleneterephthalamide) (PPTA) and nylon-6 have been prepared by coprecipitation from solutions of the polymers in concentrated sulphuric acid. The behaviour of solutions of the polyblends in concentrated sulphuric acid was investigated. The polyblends were characterized by differential scanning calorimetry, X-ray diffraction and density measurements. The polymers were found to form a miscible blend with the composition 62.7 wt% nylon-6 and 37.3 wt% PPTA. The blends could be compacted to hard dense solids by high pressure compaction.     

Synthesis and structural study of poly(isophthalamide)s

The synthesis of a series of soluble 5-alkoxy substituted isophthalamides is described. Condensation of 1,3-diaminobenzene or 2,6-diaminopyridine with alkoxy substituted isophthaloylchlorides yields the title polyaramides. The influence of the alkyl chain length on the supramolecular structure of the polymer is investigated by X-ray diffraction experiments. Initial results indicate a lamellar type solid lattice for the polymers studied here.     

Detection of glass transition in poly(ethylene terephthalate) and nylon-6 by positron annihilation

Positron annihilation lifetime spectroscopy (PALS) was used to investigate the phase transitions, mainly the glass transition, of poly(ethylene terephthalate) (PET) and nylon-6 during the thermal treatment of these polymers. The longest-lived component lifetime and intensity, indicative of ortho-positronium pick-off, exhibit thermal dependencies that can be attributed to the free-volume changes associated with structural transitions. Glass transition temperatures and the volume of intermolecular-space holes among polymer chains were obtained from the lifetime, τ₃ and intensity of formation, I₃, of the long-lived component of ortho-positronium. For PET, the free-volume fraction and thermal expansion coefficients related to the free-volume fraction were also obtained. Double glass transition behavior was noted in the analyzed polymers, which was consistent with their semicrystalline nature as revealed by differential scanning calorimetry. Increases in the slope of the lifetime-temperature plots for nylon-6 and PET were interpreted to suggest that glass transitions are followed by an increased free-volume cavity expansion as temperature is increased. The intensity response for PET was consistent with the association of glass transition with the reduction of crystalline consraint on segmental mobility in the amorphous phase. In contrast, the intensity behavior during the thermal treatment of nylon-6 seems to be governed more by the electronic effects occurring when the polymer chains acquire mobility than by free-volume changes. Since the sensitivity of PALS is in the order of nanometers, it is expected to give an alternative novel technique to estimate phase transitions and relaxations in polymers from the point of view of the free volume. © 1996 John Wiley & Sons, Inc.     

Morphology and organizational characteristics of poly(m-phenylene isophthalamide-b-ethylene oxide) systems

A series of essentially triblock poly(m-phenylene isophthalamide-b-ethylene oxide) with sequence PEO-(MPD-I)-PEO or (MPD-I)-PEO-(MPD-I) and their admixtures with (PEO)_n were studied as solution cast films. Experimental techniques included transmission optical microscopy, transmission electron microscopy, electron diffraction, and X-ray diffraction. Characterization of these systems showed that structure could develop in two ways. The first way was the development of a typical polycrystalline structure of the (MPD-I) segment by the action of such agents as formic acid. In a second manner, however, a non-typical development was manifested by the appearance of crosses In the polarized opticial microscope. These samples showed only an amorphous halo when subjected to wide angle X-ray diffraction measuremfents. Their small angle pattern suggested scattering by dispersed particles. Other experiments indicated the crosses would form only under an unusually restrictive set of conditions, principally that the PEO present must be above a certain molecular weight and concentration and, furthermore, that the solvent must contain a salt such as LiCl. These observations led us to speculate that optical activity of the films showing crosses could occur either by chain orientation near the interface of a spherical particulate second phase or from stress induced bond polarization resulting from the film formation process.     

Differential refractometry and light scattering on nylon-6 and poly(methyl acrylate) in mixed solvents

Investigations have been made of solvent systems for potential use in characterizing nylon-6/poly (methyl acrylate) copolymers. To this end, measurements involving differential refractometry (at constant composition and also constant chemical potential of solvents) and light scattering have been conducted on solutions of nylon-6, poly(methyl acrylate) and a mixture of these two polymers. From refractometric and solubility considerations the most suitable solvents are binary mixtures of o-chlorophenol (o-CP) and 2, 2′, 3, 3′-tetrafluoropropanol. In particular, the binary solvent containing 73% (by volume) of o-CP yields the molecular weight of the nylon-6 constituent of the polymer mixture directly, since the light scattering from the other polymer constituent is thereby eliminated. Preferential adsorption of o-CP occurs to both polymers, the maximum extents corresponding to 1 mol $\text{o-}\text{CP}\text{1.4}$ segments nylon and 1 mol $\text{o-}\text{CP}\text{5.7}$ segments poly(methyl acrylate). This is attributed to a breakdown of intramolecular hydrogen-bonding in o-CP and subsequent formation of hydrogen bonds with the carbonyl groups in the polymers.     

RIM-pultrusion of nylon-6 and rubber-toughened nylon-6 composites

Unidirectionally reinforced thermoplastic composites of Nylon-6 and polypropylene oxide-Nylon-6 block copolymers have been prepared by the reaction injection molding (RIM)-pultrusion process. This process takes advantage of both the RIM and the pultrusion techniques, while avoiding their inherent shortcomings. It also represents a novel way of incorporating toughening rubber domains into a thermoplastic composite. The composites produced exhibit excellent mechanical integrity with essentially zero void content. The chemical and physical states of the composites produced by the process were probed in terms of mechanical relaxation behavior using a dynamic mechanical spectrometer. Due to the simultaneous occurrence of both polymerization and crystallization processes in the reacting system, the resulting material is in a thermodynamically nonequilibrium state. An annealing effect is shown to correspond structurally to an increase in matrix crystallinity and the degree of phase separation, Izod impact tests were used to compare Nylon-6 and rubber-toughened Nylon-6 RIM-pultruded composites. The potential of secondary processing was, demonstrated by compression molding of the RIM-pultruded composite rods.     

Modification of poly(vinyl chloride) by IPN formation with poly(ethyl acrylate)

Semi‐1 and semi‐2 interpenetrating polymer networks (IPNs) of poly(vinyl chloride) (PVC) and in situ formed poly(ethyl acrylate) (PEA) have been synthesized using diallyl phthalate and ethylene glycol dimethacrylate as the crosslinkers of PVC and PEA, respectively. These two types of IPNs have been compared with respect to their physical, mechanical, and thermal properties and an endeavor has been made to find a correlation of these properties with the morphology generated in these systems. The semi‐1 IPNs displayed a decrease in their tensile strength and modulus while in contrast; the semi‐2 IPNs exhibited a marginal increase with increasing crosslinked PEA incorporation. The semi‐1 and semi‐2 IPNs containing 10 and 30 wt % of PEA displayed a two‐stage degradation typical of PVC in their thermogravimetric and DSC studies while confirming the increased stability of the samples with higher percentages of PEA. The softening characteristics as detected by the extent of penetration of the thermomechanical probe as has been detected by thermomechanical analysis are in conformity with their mechanicals. The biphasic cocontinuous systems as explicit from the morphological studies reveal fibrillar characteristics in both the systems. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of poly(styrene-co-maleic anhydride) on physical properties and crystalline behavior of nylon-6/PEBA blends

This study investigated the effect of blending poly(styrene-co-maleic anhydride) (SMA) on the mechanical and thermal properties of nylon-6/polyether block amide (PEBA) blend. In these blends, nylon-6 was toughened with PEBA using SMA as the compatibilizer. All the blends were prepared via direct melt compounding using a co-rotating twin screw extruder. The amount of PEBA added affected the crystallization characteristics and the relative ratio of γ and α crystalline phases of Nylon 6. The crystallization rate of Nylon 6 was also affected by the cooling rate and the amount of PEBA added. The results of mechanical tests showed that the tensile properties, flexural properties, and impact strengths of the nylon-6/PEBA were all increased when blended with 1 wt% of SMA, at both 23 and ?20 °C. However, for neat nylon-6, the impact strength was not affected despite that both tensile and flexural properties were increased by the blending of SMA. The results indicated that SMA can increase the compatibility between nylon-6 and PEBA, thus expanding the usage of nylon-6/PEBA blend in low-temperature applications.     

Ductile fracture of rigid poly(vinyl chloride)

The fracture processes which take place in rigid poly(vinyl chloride) have been investigated. Under tension, crazes are formed and when necking occurs they pass almost unaltered through the neck. The crazes have the fibrillar structure generally observed with other plastics. After necking, fracture occurs either by the propagation of a crack from the edge of the test-piece or by the formation of a diamond-shaped cavity which initiates from a surface craze. The characteristic form of the diamond-shaped cavity appears to be controlled by the yield behaviour of the deformed polymer. At low temperatures (?40°C) it is possible to apply the methods of fracture mechanics to notched specimens and a value of 1·05 × 10^?3MN/m is obtained for the energy of formation of a new surface in undrawn material.     

A rigid poly(vinyl chloride) compound with improved combustion characteristics

By means of compounding, we have developed a rigid poly(vinyl chloride) (PVC) formulation with improved overall combustion properties. Newly developed analytical methods indicate a considerable reduction in the level of gases released during combustion, in addition to excellent flammability characteristics and low visible smoke emission levels. The analytical methods discussed are expected to aid in the selection of a feasible protocol for biological testing and in the interpretation of results obtained from such testing. The under-lying compounding technology is currently restricted to normal impact rigid PVC cube compounds but expected to be expanded into high impact PVC, flexible PVC, PVC powder compounds and cellular PVC.     

Modification of gel-drawn poly(vinyl alcohol) fibers with formaldehyde

Poly(vinyl alcohol) fibers which were drawn from dried gels were chemically treated with formaldehyde to induce crosslinking in the amorphous phase. The room temperature storage modulus decreased early in the treatment, to an almost constant value of 50–60% of the initial modulus of the fiber. This behavior was independent of the concentration of formaldehyde used. The modulus at low temperature was also reduced, and no T_g peak could be seen in heavily treated fibers. The modulus above the original T_g, 70°C, was much less affected. The crystallinity determined by DSC fell by one third as the room temperature modulus decreased, and X-ray diffraction indicated a reduction in the crystal length along the chain direction at the same time. Thus, under the conditions of treatment used, the loss of properties due to destruction of crystals outweighs the stiffening and reduced water sensitivity of the crosslinked amorphous phase.