Modeling Equilibrium Behavior of Nylon 6, Nylon 6,6 and Nylon 6/6,6 Copolymer

Nylon 6 and nylon 6,6 reaction equilibria depend in a complex way on water concentration and temperature. For example, data sets from six research groups reveal that the apparent equilibrium constant for polycondensation increases with water at low water concentrations, reaches a maximum, and then decreases as the water concentration rises further. In this article, semi‐empirical expressions are proposed to describe the experimentally observed equilibrium behavior for the five main reactions that occur during nylon 6 and nylon 6,6 polymerization. Nine side reactions involving amidine ends, cyclopentanone ends, and hydrated carboxyl ends are used to develop expressions that account for the influence of both water and temperature on these equilibrium constants. Excellent fit to the data, over the entire range of the available nylon 6 and nylon 6,6 literature data, suggests that the proposed equations will be helpful for modeling reaction equilibria for nylon 6/6,6 copolymerization.     

Mathematical Modeling of Nylon 6/6,6 Copolymerization in Batch Reactor: Investigating Recipes without Water and with Cyclic Dimer

A model is used to simulate batch copolymerization of caprolactam with hexamethylene diamine (HMD) and adipic acid (ADA) to produce nylon 6/6,6. Four different recipes are considered: a recipe containing caprolactam and an aqueous solution of HMD and ADA, a recipe containing caprolactam and dry HMD/ADA salt, and two recipes with a portion of the caprolactam replaced by nylon 6 cyclic dimer (CD). Consuming CD would be advantageous because CD is an undesirable side product from nylon 6 production. Simulation results lead to three important findings: (i) operation using dry salt rather than aqueous salt solution leads to higher degree of polymerization, (ii) substantial quantities of CD can be consumed to produce nylon 6/6,6 copolymer, and (iii) including water in the recipe is beneficial for achieving improved consumption of CD. The results of this study will be helpful in designing experiments aimed at improving industrial nylon 6/6,6 copolymerization processes.     

Mathematical Modeling of Nylon 6/6,6 Copolymerization: Beneficial Influence of Comonomers on Degree of Polymerization in Batch Reactor

A model is developed for hydrolytic copolymerization of caprolactam with hexamethylene diamine (HMD) and adipic acid (ADA) in a batch reactor to produce nylon 6/6,6 copolymer. The reaction mechanism includes hydrolysis of caprolactam and cyclic dimer, polycondensation, polyaddition, transamidation, and ring formation via end biting and back biting. The catalyzing effect of carboxyl groups is accounted for using kinetic parameters from the literature. Model predictions are compared with low‐temperature literature data before simulating reactor conditions of industrial interest. The model predicts a higher degree of polymerization (DP) for nylon 6/6,6 copolymer compared to nylon 6 and 6,6 homopolymers produced using the same reactor conditions. Dynamic changes in concentrations of water, caprolactam, HMD, ADA, and end groups are tracked and used to explain the positive influence of comonomers on reaction rates and DP. Insights gained from this model will form a useful basis to build future models of continuous industrial reactors.

     

Water penetration in nylon 6,6: Absorption,desorption, and exchange studied by NMR microscopy

The uptake of water by nylon 6,6 [42DB Adipure (trade name of Dupont Canada Inc.)] at 100°C has been monitored by a combination of one-dimensional proton NMR spectroscopy, relaxation time (T₁ and T₂) measurements and proton microscopic NMR imaging techniques. The relaxation times of the water absorbed into the nylon matrix are very short at room temperature, (T₂ < 1 ms and T₁ ≈ 1 s) indicating that the water is located in a highly restricted environment and suggesting that strong interactions exist between the absorbed water and the polymer. The diffusion profiles measured at room temperature indicate that the diffusion of water into nylon 6,6 at 100°C is Case I Fickian diffusion. The spatial dependence of the T₂ relaxation time constant and its variation with the water content was also examined. The results reveal that both T₂ and T₂^* decrease toward the center of the sample in samples that have a concentration gradient of sorbed water. In fully saturated samples, no spatial dependence was observed. The overall values of T₂ and T₂^* are also observed to increase as a function of exposure time. An evaluation of the desorption process at room temperature and at 100°C was performed. A continuous, exponentially decreasing solvent profile was observed for the desorption process which again indicates Case I Fickian kinetics. The exchange process of external bulk and atmospheric water with deuterium oxide (D₂O) saturated nylon rods has also been studied using the microscopic imaging technique. © 1993 John Wiley & Sons, Inc.     

Thermal and mechanical properties of electrospun PMMA,PVC, Nylon 6, and Nylon 6,6

Poly(methyl methacrylate) (PMMA), poly(vinyl chloride) (PVC), Nylon 6, and Nylon 6,6 have been electrospun successfully. The nanofibers have been characterized by scanning electron microscopy (SEM), confirming the presence of bead free and fiber‐bead free morphologies. Thermogravimetric analysis (TGA) indicated differences between the thermal stability of PMMA nanofibers and PMMA powder. However, no significant differences were observed between the starting physical form (powder or pellet) of PVC, Nylon 6 and Nylon 6,6, and their corresponding electrospun nanofibers. Differential scanning calorimetry (DSC) demonstrated a lower glass transition temperature (T_g) and water absorption for PMMA electrospun nanofibers. Furthermore, electrospun Nylon 6 and Nylon 6,6 had a slight decrease in crystallinity. Tensile testing was performed on the electrospun nanofibers to obtain the Young modulus, peak stress, strain at break, and energy to break, revealing that the non‐woven mats obtained had modest mechanical properties that need to be enhanced. Copyright © 2007 John Wiley & Sons, Ltd.     

Method for grafting poly(acrylic acid) onto nylon 6,6 using amine end groups on nylon surface

Several methods have been developed for grafting materials to the surface of polymers to alter their surface characteristics. This article reports a procedure for grafting poly(acrylic acid) (PAA) onto nylon 6,6 films via the naturally occurring amine end groups of nylon 6,6 using N‐hydroxy‐succinimide in conjunction with 1‐ethyl‐3‐ (3‐dimethylaminopropyl)carbodiimide hydrochloride (EDC) facilitated amidazation. Reaction conditions were investigated with respect to PAA molecular weight, activator concentrations, reaction temperature, and time. X‐ray photoelectron spectroscopy showed that surface coverage of more than 50% was consistently achieved for 250 kD PAA. The maximum grafting occurred at room temperature with a large excess of EDC with a reaction time of 30 min. The same level of grafting can be achieved using smaller amounts of EDC at 60 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 719–728, 2002; DOI 10.1002/pola.10149     

尼龙6,6膜的电驱动透过性

电驱动条件下膜分离性能的研究对膜在微流控芯片等微小器件中的应用具有重要的指导意义.研究了界面聚合的尼龙6,6膜的电驱动分离性能,并考察了电场强度、通电时间和温度等操作条件对SO42-和Cl-离子透过性能的影响.结果表明尼龙6,6膜具有较好的SO24-和Cl-离子透过性能,并且透过性能差异不大,离子透过百分比随电场强度和通电时间的增加而增加,而随温度的增加基本保持不变.而对FITC标记的甘氨酸和赖氨酸则能完全截留,截留分子量在500左右,具有部分纳滤膜性质.该膜可望应用于微型器件中氨基酸等有机与生物大分子的电驱动分离和浓缩.     

Carbon Nanotube‐Adsorbed Electrospun Nanofibrous Membranes of Nylon 6

Summary: A simple and mass‐producible method was developed to densely assemble multiwalled carbon nanotubes (MWNTs) onto electrospun nylon 6 nanofibrous membranes. The process consists of dispersing the acid‐treated MWNTs in surfactant solutions or organic solvents, and dipping the nanofibrous membranes in the resulting dispersion for only 60 seconds, followed by the extraction of the surfactants in pure water and drying. The conductivity of the MWNT‐adsorbed nanofibrous membranes ranges from 2.2 × 10⁻² to 1.5 × 10⁻¹ S · cm⁻¹, as determined by the four probe method, which implies that the MWNTs are adsorbed uniformly and densely along the nanofibrous membranes. Furthermore, the results suggest that there is a strong interaction between the acid‐treated MWNTs and nylon 6. We also investigate the amount of MWNTs present in the membranes using thermogravimetric analysis.

SEM images of the non‐woven fibrous nylon 6 membranes after dip‐coating in a dispersion of the MWNTs in surfactant‐containing water.     

Unusual Crystallization Behavior in Nylon‐6 and Nylon‐6/Montmorillonite Nanocomposite Films

Summary: The crystallization behavior of nylon‐6 and nylon‐6/montmorillonite nanocomposite films with different heat histories was investigated by wide‐angle X‐ray diffraction (WAXD). For nylon‐6 films isothermally crystallized above 170 °C or annealed at 200 °C and then quenched in ice water, a crystalline peak appeared at 2θ = 28.5°. This crystalline peak was strong in intensity for the former and weak for the latter. However, for nylon‐6 films cooled in air after isothermal crystallization or annealing, no crystalline peak at 2θ = 28.5° was observed in the WAXD patterns. For nylon‐6/montmorillonite nanocomposite films annealed above 140 °C, a crystalline double peak was observed between the α1 and α2 peaks. The possible origins of the peak at 2θ = 28.5° and the crystalline double peak are discussed.

WAXD patterns of isothermally crystallized nylon‐6/montmorillonite nanocomposite films.     

Mechanism of glycolysis of nylon 6,6 and its model compound by ethylene glycol

The degradation mechanism of nylon 6,6 and its model compound hexamethylenebis(hexamide) (HMHA) by ethylene glycol (EG) was studied in detail. Glycolysis of both model compound and nylon 6,6 was carried out with stoichiometric excess of EG at high temperature (250 and 275 °C, respectively) in an autoclave reactor as a closed system. Samples were collected at predetermined intervals and characterized by FT-IR, GC-MS, and GPC. FT-IR studies of model compound glycolysis showed no significant increase in the ester band after 11 h indicating that the glycolysis reaction may have reached equilibrium. GC-MS data revealed the presence of ester as well as unreacted model compound. GC-MS data for nylon 6,6 revealed the presence of compounds having β-hydroxyethylester group, bis(β-hydroxyethyl)adipate, and δ-valerolactone as the degradation products. From GPC data, as the glycolysis time of nylon 6,6 increased, both the number average and weight average molecular weights decreased indicating that the main chain of nylon 6,6 was broken into low molecular weight compounds during glycolysis.     

Polyamide‐6,6‐based blocky copolyamides obtained by solid‐state modification

Copolyamides based on polyamide‐6,6 (PA‐6,6) were prepared by solid‐state modification (SSM). Para‐ and meta‐xylylenediamine were successfully incorporated into the aliphatic PA‐6,6 backbone at 200 and 230 °C under an inert gas flow. In the initial stage of the SSM below the melting temperature of PA‐6,6, a decrease of the molecular weight was observed due to chain scission, followed by a built up of the molecular weight and incorporation of the comonomer by postcondensation during the next stage. When the solid‐state copolymerization was continued for a sufficiently long time, the starting PA‐6,6 molecular weight was regained. The incorporation of the comonomer into the PA‐6,6 main chain was confirmed by size exclusion chromatography (SEC) with ultraviolet detection, which showed the presence of aromatic moieties in the final high‐molecular weight SSM product. The occurrence of the transamidation reaction was also proven by ¹H nuclear magnetic resonance (NMR) spectroscopy. As the transamidation was limited to the amorphous phase, this SSM resulted in a nonrandom overall structure of the PA copolymer as shown by the degree of randomness determined using ¹³C NMR spectroscopy. The thermal properties of the SSM products were compared with melt‐synthesized copolyamides of similar chemical composition. The higher melting and higher crystallization temperatures of the solid state‐modified copolyamides confirmed their nonrandom, block‐like chemical microstructure, whereas the melt‐synthesized copolyamides were random. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5118–5129     

Preparation of a superhydrophobic rough surface

The relationship between the contact angles, surface tension, and surface roughness is reviewed. Numerical formulas related to the superhydrophobic rough surfaces of polymers are predicted with two approaches, the Wenzel and Cassie–Baxter models. With these models as a guide, an artificial superhydrophobic surface is created. Rough nylon surfaces mimicking the lotus leaf are created by the coating of a polyester surface with nylon‐6,6 short fibers via the flocking process. Poly(acrylic acid) chains aregrafted onto nylon‐6,6 surfaces, and this is followed by the grafting of 1H,1H‐perfluorooctylamine onto the poly(acrylic acid) chains. Water contact angles as high as 178° are achieved. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 253–261, 2007.     

Properties of Nylon‐6/Na+‐Montmorillonite Nanocomposites Obtained by Hydrolyzed Ring‐Opening Polymerization

Summary: Nylon‐6/Na⁺‐montmorillonite (MMT) nanocomposites (NNNs) are synthesized by a hydrolyzed ring‐opening polymerization. At a loading of only 2 wt.‐% MMT, the tensile modulus, the flexural modulus, and the heat distortion temperature of the NNNs exhibit increases of nearly 20%, 60%, and 63 °C, respectively. Compared with that of neat nylon‐6, the temperature of the main α‐relaxation (T_α) of the NNNs is shifted 3.6 °C toward higher temperatures and two β‐relaxation peaks are observed. Another interesting phenomenon is that there is a new melting peak (at about 206 °C) for the NNNs.

DSC second heating curves of neat nylon‐6 (N6), nylon‐6/Na⁺‐MMT nanocomposites with highly swollen Na⁺‐MMT (NHM), and nylon‐6/Na⁺‐MMT nanocomposites with slightly swollen Na⁺‐MMT (NSM) with various amounts of Na⁺‐MMT.     

Structural characteristics and moisture sorption behavior of nylon‐6/clay hybrid films

The structure of nylon‐6 hybrids with synthetic or natural clays was investigated for melt‐pressed films with Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, and differential scanning calorimetry in comparison with the nylon‐6 homopolymer. In contrast to the development of familiar α‐form crystals in plain nylon‐6 film, the hybrid films produced γ‐form crystals when nylon‐6 was conjugated with synthetic mica, whereas the hybridization with natural montmorillonite gave rise to both α‐ and γ‐crystalline modifications. The degree of crystallinity of the nylon‐6 hybrid with synthetic mica was the highest of the three series. Moisture sorption isotherms obtained for these nylon‐6‐based films were all typically sigmoid‐shaped, although the prevalence of a higher crystallinity in the hybrid samples lowered the degree of moisture regain. The sorption behavior was analyzed well in terms of the parameters of a Brunauer–Emmett–Teller multiplayer adsorption model and a Flory–Huggins treatment. It was also observed that the cluster formation of the water adsorbed into the nylon‐6 matrix tended to be restricted by the hybridization with clay. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 479–487, 2002; DOI 10.1002/polb.10106     

Tensile deformation of electrospun nylon‐6,6 nanofibers

Nylon‐6,6 nanofibers were electrospun at an elongation rate of the order of 1000 s^?1 and a cross‐sectional area reduction of the order of 0.33 × 10⁵. The influence of these process peculiarities on the intrinsic structure and mechanical properties of the electrospun nanofibers is studied in the present work. Individual electrospun nanofibers with an average diameter of 550 nm were collected at take‐up velocities of 5 and 20 m/s and subsequently tested to assess their overall stress–strain characteristics; the testing included an evaluation of Young's modulus and the nanofibers' mechanical strength. The results for the as‐spun nanofibers were compared to the stress–strain characteristics of the melt‐extruded microfibers, which underwent postprocessing. For the nanofibers that were collected at 5 m/s the average elongation‐at‐break was 66%, the mechanical strength was 110 MPa, and Young's modulus was 453 MPa, for take‐up velocity of 20 m/s—61%, 150 and 950 MPa, respectively. The nanofibers displayed α‐crystalline phase (with triclinic cell structure). © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1482–1489, 2006     

树枝状尼龙6的合成与研究

用单羧基封端的尼龙6分别与树枝状聚酰胺-胺(PAMAM)的G1代和G2代外围活泼氨基进行缩聚反应,合成出具有规整结构的由核心向外发散增长的树枝状尼龙6,采用红外光谱、扫描电镜、DSC和TGA对缩聚物进行了分析。     

Nylon 610/functionalized multiwalled carbon nanotube composite prepared from in‐situ interfacial polymerization

Pristine multiwalled carbon nanotubes (P‐MWNTs) were functionalized with 4‐chlorobenzoic acid via “direct” Friedel‐Crafts acylation in polyphosphoric acid (PPA)/phosphorous pentoxide (P₂O₅) medium. The resultant 4‐chlorobenzoyl‐functionalized MWNTs (F‐MWNTs) were soluble in chlorinated solvents such as dichloromethane, chloroform, and carbon tetrachloride. A large scale of nylon 610/F‐MWNT composite could be conveniently prepared by in situ interfacial polymerization of 1, 6‐hexamethylenediamine (HMDA) in an aqueous phase, and sebacoyl chloride with F‐MWNTs in an organic phase. Similarly, nylon 610/P‐MWNT composite was also prepared for comparison. The state of F‐MWNTs dispersion in nylon 610 matrix was distinctively better than that of P‐MWNTs, which could be clearly discerned by both naked eye and scanning electron microcopy (SEM). As a result, the tensile strength of nylon 610/F‐MWNT composite was 4.9‐fold higher than that of nylon 610/P‐MWNT composite. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6041–6050, 2008     

A new process of fabricating electrically conducting nylon 6/graphite nanocomposites via intercalation polymerization

A new process was developed to fabricate electrically conducting nylon 6/graphite nanocomposites via intercalation polymerization of ϵ‐caprolactam in the presence of expanded graphite. The transition from an electrical insulator to an electrical semiconductor for nylon 6 occurred when the graphite volume content was 0.75, which was much lower than that of conventional conducting polymer composites. The electrical conductivity reached 10⁻⁴ S/cm when the graphite content was 2.0 vol %. The TEM microphotographs suggested that the low percolation threshold and the great improvement of electrical conductivity could be attributed to the high aspect ratio (width‐to‐thickness), the high expansion ratio in c axis of the graphite sheets and the homogeneous dispersion of the nanoscale graphite particles in the nylon 6 matrix. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1626–1633, 2000     

Investigation on nonisothermal crystallization kinetics of the high‐flow nylon 6 by differential scanning calorimetry

The crystallization kinetics of the high‐flow nylon 6 containing polyamidoamine (PAMAM) dendrimers units in nylon 6 matrix was investigated by differential scanning calorimetry. The Ozawa and Mo equations were used to describe the crystallization kinetics under nonisothermal condition. The values of Avrami exponent m and the cooling crystallization function F(T) were determined from the Ozawa plots, which showed bad linearity, and were divided into three sections depending on different cooling rates. The plots of the m and log F(T) values versus crystallization temperatures were obtained, which indicated that the actual crystallization mechanisms might change with the crystallization temperatures. The high‐flow nylon 6 has higher values of m and log F(T) than those of pure nylon 6, which implied that the high‐flow nylon 6 had more complicated crystallization mechanisms and slower crystallization rate than those of pure nylon 6. The good linearity of the Mo plots verified the success of this combined approach. The activation energies of the high‐flow nylon 6 ranged from 157 to 174 kJ/mol, which were determined by the Kissinger method. The ΔE values were lower than those of pure nylon 6, and the ΔE values were affected by both the generation and the content of PAMAM units in the nylon 6 matrix. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2201–2211, 2008     

New Chiral Ligand N—Toluenesulfony1—2,2‘—dimethoxy—6,6’—di—aminobiphenyl for Catalytic Asymmetric Transfer Hydrogenation of Ketones

A new chiral ligand N‐p‐toluenesulfonyl‐2,2′‐dimethoxy‐6,6′‐diaminobiphenyl (Ts‐DMBDPPA) was prepared from 2,2′‐dimethoxy‐6,6′‐diaminobiphenyl via N‐tosylation. Its Ru(II) complex was effective catalysts for catalytic asymmetric transfer hydrogenation of aromatic ketones (with ee's up to 69.3%).