Structure and properties of polyimide‐g‐nylon 6 and nylon 6‐b‐polyimide‐b‐nylon 6 copolymers

Polyimide‐g‐nylon 6 copolymers were prepared by the polymerization of phenyl 3,5‐diaminobenzoate with several diamines and dianhydrides with a one‐step method. The polyimides containing pendant ester moieties were then used as activators for the anionic polymerization of molten ε‐caprolactam. Nylon 6‐b‐polyimide‐b‐nylon 6 copolymers were prepared by the use of phenyl 4‐aminobenzoate as an end‐capping agent in the preparation of a series of imide oligomers. The oligomers were then used to activate the anionic polymerization of ε‐caprolactam. In both the graft and copolymer syntheses, the phenyl ester groups reacted quickly with caprolactam anions at 120°C to generate N‐acyllactam moieties, which activated the anionic polymerization. All the block copolymers had higher moduli and tensile strengths than those of nylon 6. However, their elongations at break were much lower. The graft copolymers based on 2,2′‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]propane dianhydride and 2,2′‐bis[4‐(4‐aminophenoxy)phenyl]propane displayed elongations comparable to that of nylon 6 and the highest moduli and tensile strengths of all the copolymers. The thermal stability, moisture resistance, and impact strength were dramatically increased by the incorporation of only 5 wt % polyimide into both the graft and block copolymers. The graft and block copolymers also exhibited improved melt processability. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 300–308, 2006     

Mechanism and kinetics of adiabatic anionic polymerization of ϵ-caprolactam in the presence of various activators

Nylon 6 was prepared by adiabatic anionic polymerization of ?-caprolactam using hexamethylene dicarbamoyl dicaprolactam (HDC), cyclohexyl carbamoyl caprolactam (CCC), or phenyl carbamoyl caprolactam (PCC) as activators and sodium caprolactamate (NaCL) as a catalyst at various initial reaction temperatures ranging from 130 to 160°C. Adiabatic temperature rise was recorded as a function of polymerization time to investigate polymerization kinetics. Kinetic parameters for polymerization, which are more accurate than data reported to date, could be obtained by fitting the temperature rise data with a new polymerization kinetic equation involving crystallization exotherm and thermal conduction. The polymerization rate highly depended on the chemical structure of the activator used, which indicates that the initiating step where the activator is attacked nucleophilically by NaCL is a very important reaction step, affecting the overall polymerization rate. CCC showed the fastest polymerization rate, whereas HDC and PCC showed the medium and the slowest rate, respectively. The contributions of crystallization exotherm and thermal conduction to the resultant temperature rise during polymerization were significant, when the initial reaction temperature was lower than 140°C. In all cases, the molecular weight obtained from intrinsic viscosity measurement was greater than the expected molecular weight. This may be attributed to the branching and/or crosslinking reaction through Claisen-type condensation reactions. © 1995 John Wiley & Sons, Inc.     

Kinetics of adiabatic anionic copolymerization of ϵ-caprolactam in the presence of various activators

Adiabatic temperature rise has been recorded as a function of polymerization time to investigate an adiabatic copolymerization kinetics of ϵ-caprolactam (CL) in the presence of several activators, considering different initial copolymerization temperatures ranging from 130 to 160°C. The copolymerization of CL and PEG-diamine has been performed using activators such as tolylene dicarbamoyl dicaprolactam (TDC), hexamethylene dicarbamoyl dicaprolactam (HDC), and cyclohexyl carbamoyl caprolactam (CCC), and sodium caprolactamate as a catalyst. The effect of PEG-diamine on the overall rate of polymerization of CL has been studied by fitting the experimental temperature rise with a new polymerization kinetic equation involving the polymerization exotherm, polymerization-induced crystallization exotherm, and the heat loss due to nonideal adiabatic condition in the experimental situation. Like homopolymerization, the net copolymerization rate is influenced by the variation of activator types in the initiation step. The temperature rise due to polymerization-induced crystallization in copolymerization is drastically decreased with the increasing initial polymerization temperature in the course of polymerization. The high molecular weight and large polydispersity index of copolymers using bifunctional activators indicate that the Claisen type condensation can occur in the course of polymerization processes. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1195–1207, 1997     

High‐flow nylon 6 by in situ polymerization: Synthesis and characterization

A new synthetic strategy for high‐flow nylon 6 was developed in this article. Generation 1, 2, 3 (G1, G2, G3) polyamidoamine (PAMAM) dendrimers reacted with p‐phthalic acid by equimolar terminal groups in water solution, respectively, and mother salt solution was then prepared. The high‐flow nylon 6 was prepared with suitable quantity of mother salt solution, end‐capping agent, and ?‐caprolactam by in situ polymerization. Blue shifts are found for the peaks of NH (γN? H and 2δN? H) of the high‐flow nylon 6 compared with pure nylon 6 in the IR spectra. Comparing with the pure nylon 6, the high‐flow nylon 6 containing low content of PAMAM units, has high‐flow property and almost the same mechanical property. The high‐flow nylon 6 with low content of PAMAM units has greater melt‐flow index (MFI) (the value of MFI increased by 70–90%). Hardly any decrease in the tensile strength is observed with the elongation at break decreasing by 20–35%. But the izod impact strength of the high‐flow nylon 6 increases. The SEM images show that the high‐flow nylon 6 presents brittle fracture with conglomeration‐like structure, while pure nylon 6 exhibits plastic fracture with island‐like structure. DSC thermograms of nonisothermal crystallization exhibit that the peak of high‐flow nylon 6 broadens compared with pure nylon 6, and the broader peak means the wider processing temperature. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Morphology and thermal behavior of MCPA6/SAN blends prepared by anionic ring‐opening polymerization of ϵ‐caprolactam

In this article, a series of blends of monomer casting polyamide 6 and styrene‐co‐acrylonitrile (MCPA6/SAN) were prepared by in situ anionic ring‐opening polymerization of ?‐caprolactam. Their morphology and thermal behaviors were investigated by means of scanning electron microscope, differential scanning calorimeter, and wide‐angle X‐ray diffraction (WAXD), respectively. The SAN phase had much finer domain in MCPA6/SAN than that in the PA6/SAN blends prepared by melt blending of PA6 and SAN. All the melting and crystallization parameters of MCPA6/SAN blends decreased gradually with the increase of SAN content, while the melting temperature was almost unchanged. These results were due to the hydrolysis reaction of SAN that occurred during the anionic polymerization of ?‐caprolactam. In addition, WAXD results showed that only α crystal forms existed in the MCPA6/SAN blends. In addition, the mechanical property of MCPA6 was improved obviously by incorporating a certain amount of SAN. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1357–1363, 2006     

Preparation and properties of monomer casting nylon‐6/PEO blend prepared via in situ polymerization

A series of MC nylon‐6/ polyethylene oxide (PEO) blends were prepared via in situ polymerization. It was found that addition of PEO delayed the polymerization process of caprolactam. The apparent activation energy and pre‐exponential factor increased, indicating that the polymerization reaction became difficult with increasing PEO content. The stress–strain curves of the blends presented strain hardening behavior and increasing elastic deformation stress plateau at low PEO content. Nonisothermal DSC and XRD tests indicated that addition of PEO led to a decrease of the crystallization ability of the nylon‐6 matrix by reducing crystal grain size and crystallinity, whereas the crystallization ability of the PEO phase was improved. No co‐crystal formed between the two phases. PEO with low content only existed as amorphous state, while with increasing PEO content, PEO can crystallize gradually, forming interfibrillar segregation first, and then forming interspherilute segregation of the blend independently. By addition of PEO, the fracture surface of the blend became rough, displaying character of tough fracture. The interface between nylon‐6 phase and PEO phase was diffused, and the nylon‐6 matrix around the PEO particles presented fibrous structure, indicating the good compatibility between them. The toughening mechanism of the blend corresponded to the crazing‐shear banding mechanism. POLYM. ENG. SCI., 55:589–597, 2015. © 2014 Society of Plastics Engineers     

Polyamide 6/ethylene‐butylene elastomer blends generated via anionic polymerization of ε‐caprolactam: Phase morphology and dynamic mechanical behavior

This paper reports about the polymerization of ε‐caprolactam monomer in the presence of low molecular weight hydroxyl or isocyanate end‐capped ethylene‐butylene elastomer (EB) elastomers as a new concept for the development of a submicron phase morphology in polyamide 6 (PA6)/EB blends. The phase morphology, viscoelastic behavior, and impact strength of the polymerization‐designed blends are compared to those of similar blends prepared via melt‐extrusion of PA6 homopolymer and EB elastomer. Polyamide 6 and EB elastomer were compatibilized using a premade triblock copolymer PA6‐b‐EB‐b‐PA6 or a pure EB‐b‐PA6 diblock reactively generated during melt‐blending (extrusion‐prepared blends) or built‐up via anionic polymerization of ε‐caprolactam on initiating ? NCO groups attached to EB chain ends (polymerization‐prepared blends). Two compatibilization approaches were considered for the polymerization‐prepared blends: (i) the addition of a premade PA6‐b‐EB‐b‐PA6 triblock copolymer to the ε‐caprolactam monomer containing nonreactive EB? OH elastomer and (ii) generation in situ of a PA6‐b‐EB diblock using EB? NCO precursor on which polyamide 6 blocks are built‐up via anionic polymerization of ε‐caprolactam. The noncompatibilized blends exhibit a coarse phase morphology, either in the extruded or the polymerization prepared blends. Addition of premade triblock copolymer (PA6‐b‐EB‐b‐PA6) to a EB? OH /ε‐caprolactam dispersion led to a fine EB phase (0.14 μm) in the PA6 matrix after ε‐caprolactam polymerization. The average particle size of the in situ reactively compatibilized polymerization‐prepared blend is about 1 μm. The notched Izod impact strength of the blend compatibilized with premade triblock copolymer was much higher than that of the neat PA6, the noncompatibilized, and the in situ reactively compatibilized polymerization blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2538–2544, 2004     

Isothermal crystallization of copolyamides. I. Kinetics of crystallization of nylon 6–piperazine adipate and nylon 6–piperazine terephthalate random copolyamides

The kinetics of primary crystallization from the melt of nylon 6–piperazine adipate and nylon 6–piperazine terephthalate copolyamides were measured dilatometrically. It was found that the crystallization rate of the samples under investigation decreases with increase in the percentage comonomer content and rigidity of molecules over the entire temperature range investigated. The Avrami exponent n varied with temperature, values being from 2 to 4.     

Synthesis and characterization of nylon 6/clay nanocomposites prepared by ultrasonication and in situ polymerization

Nylon 6 nanocomposites were prepared by the in situ polymerization of ε‐caprolactam with ultrasonically dispersed organically modified montmorillonite clay (Cloisite 30B®). Dispersions of the clay platelets with concentrations in the range 1–5 wt % in the monomer were characterized using rheological measurements. All mixtures exhibited shear‐thinning, signifying that the clay particles were dispersed as platelets and forming a “house of cards” structure. Samples with Cloisite concentrations above 2 wt % showed a drop in viscosity between the initial shearing and repeated shearing, indicative of shearing breaking down the initial “house of cards” structures formed on sonication. DMTA measurements of the samples showed an increase in the β‐relaxation temperature with increasing clay concentration. The bending modulus, at temperatures below T_g, showed an increase with increasing clay concentration up to 4 wt %. X‐ray diffraction measurements showed that all nylon 6/Cloisite 30B samples were exfoliated apart from the 5 wt %, which showed that some intercalated material was present. The nylon crystallized into the α‐crystalline phase, which is the most thermodynamically stable form. Preference for this form may be a consequence of the long time associated with the postcondensation step in the synthesis or the influence of the platelets on the nucleation step of the crystal growth. DSC measurements showed a retardation of the crystallization rate of nanocomposite samples when compared with that of pure nylon 6, due to the exfoliated clay platelets hindering chain movement. This behavior is different from that observed for the melt‐mixed nylon 6/clay nanocomposites, which show an enhancement in the crystallization rate. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanical relaxations of nylon–polyurea block copolymers

Dynamic mechanical analysis from ?150 to +150°C has been carried out on seven block copolymers that were prepared by the in situ anionic polymerization of caprolactam in the presence of a preformed polyurea. The various relaxations have been identified and activation energies calculated. Some polymer–polymer miscibility of the polyurea and amorphous nylon copolymer segments is indicated by the compositional dependence of the α relaxation.     

Preparation and characterization of polyimide‐g‐nylon 6 copolymers from nonfunctionalized polyimides

In this research, the anionic polymerization of ?‐caprolactam was carried out in the presence of small amounts of several different polyimides to generate polyimide‐g‐nylon 6 copolymers. The polyimides, which were prepared from 2,2′‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]propane dianhydride and commercially available diamines with a one‐step method, were first dissolved in molten ?‐caprolactam. Phenylmagnesium bromide was then added at 120°C. Under these conditions, caprolactam anions were formed that attacked the five‐membered imide rings to form N‐acyllactam moieties, which activated the anionic polymerization of caprolactam. In essence, nylon 6 chains grew from the polyimide backbones. Probably because of a high activation energy, the process was relatively slow, requiring 1 h at 120°C. The introduction of 5 wt % polyimide into the graft copolymers produced significant increases in the tensile modulus and tensile strength in comparison with those of low‐ and high‐molecular‐weight nylon 6. The elongation to break, however, was reduced. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 292–299, 2006     

Monomer casting nylon‐6‐b‐polyether amine copolymers: Synthesis and antistatic property

MC nylon‐6‐b‐polyether amine(PEA)copolymers were synthesized with macroinitiator based on amino‐terminated PEA functionalized with isocyanate via in situ polymerization. It was found that introduction of PEA delayed the polymerization process of caprolactam, resulting in the decrease of molecular weight of the copolymer. With increasing content of PEA, the melting peak started declining and widening, while the crystallinity and crystal grain size decreased, indicating weakening of the crystallization ability of nylon‐6 matrix. The fracture surfaces of the copolymer changed from irregular mosaic to the striation, presenting tough fracture characteristic, and the notched impact strength of the copolymers were improved dramatically. The electrical resistivity of the copolymers was increased by three orders of magnitude, and kept stable with prolonging storage time, indicating a permanently antistatic ability. The improved antistatic mechanism was deduced by the increase of concentration of oxygen atom and C? O group on the surface of the copolymers with increasing PEA content. The water contact angle decreased and surface tension increased, and finally the hydrophilicity of the copolymers was enhanced, resulting in the fairly good antistatic behavior of the copolymers by absorbing moisture from air. POLYM. ENG. SCI., 56:817–828, 2016. © 2016 Society of Plastics Engineers     

Polymorphic behavior of nylon 6/saponite and nylon 6/montmorillonite nanocomposites

X‐ray diffraction methods and DSC thermal analysis have been used to investigate the structural change of nylon 6/clay nanocomposites. Nylon 6/clay has prepared by the intercalation of ε‐caprolactam and then exfoliaton of the layered saponite or montmorillonite by subsequent polymerization. Both X‐ray diffraction data and DSC results indicate the presence of polymorphism in nylon 6 and in nylon 6/clay nanocomposites. This polymorphic behavior is dependent on the cooling rate of nylon 6/clay nanocomposites from melt and the content of saponite or montmorillonite in nylon 6/clay nanocomposites. The quenching from the melt induces the crystallization into the γ crystalline form. The addition of clay increases the crystallization rate of the α crystalline form at lower saponite content and promotes the heterophase nucleation of γ crystalline form at higher saponite or montmorillonite content. The effect of thermal treatment on the crystalline structure of nylon 6/clay nanocomposites in the range between Tg and Tm is also discussed.     

Isothermal crystallization kinetics of high‐flow nylon 6 by differential scanning calorimetry

The isothermal crystallization kinetics have been investigated with differential scanning calorimetry for high‐flow nylon 6, which was prepared with the mother salt of polyamidoamine dendrimers and p‐phthalic acid, an end‐capping agent, and ε‐caprolactam by in situ polymerization. The Avrami equation has been adopted to study the crystallization kinetics. In comparison with pure nylon 6, the high‐flow nylon 6 has a lower crystallization rate, which varies with the generation and content of polyamidoamine units in the nylon 6 matrix. The traditional analysis indicates that the values of the Avrami parameters calculated from the half‐time of crystallization might be more in agreement with the actual crystallization mechanism than the parameters determined from the Avrami plots. The Avrami exponents of the high‐flow nylon 6 range from 2.1 to 2.4, and this means that the crystallization of the high‐flow nylon 6 is a two‐dimensional growth process. The activation energies of the high‐flow nylon 6, which were determined by the Arrhenius method, range from ?293 to ?382 kJ/mol. The activation energies decrease with the increase in the generation of polyamidoamine units but increase with the increase in the content of polyamidoamine units in the nylon 6 matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A novel approach to the preparation of thermoplastic polyurethane elastomer and polyamide 6 blends by in situ anionic ring‐opening polymerization of ε‐caprolactam

Blends of thermoplastic polyether‐based urethane elastomer (TPEU) and monomer casting polyamide 6 (MCPA6) were prepared using ε‐caprolactam as reactive solvent, with caprolactam sodium as a catalyst in the presence of TPEU, with TPEU content varying from 2.5% to 10% by weight. In situ anionic ring‐opening polymerization and in situ compatibilization to prepare TPEU/MCPA6 blends were carried out in one step. The TPEU chains, which underwent thermal dissociation in amine solvents to bear isocyanate groups, acted as macroactivator to initiate MCPA6 chain growth from the TPEU chains and form graft copolymers of TPEU‐co‐MCPA6 to improve compatibility between TPEU and MCPA6. The structure and thermal properties were characterized by means of Fourier transform infrared spectroscopy, ¹H‐NMR spectroscopy, differential scanning calorimetry and scanning electron microscopy. Copyright © 2006 Society of Chemical Industry     

Kinetics of the in situ polymerization and in situ compatibilization of poly(propylene) and polyamide 6 blends

In previous articles, we reported on a novel reactive extrusion process to obtain a compatibilized blend of polymer A and polymer B. It consisted in polymerizing the monomer of polymer A in the presence of polymer B. A fraction of the latter contained initiating sites from which the polymerization of monomer A took place. As such, both polymer A and a graft copolymer of polymer A and polymer B were formed in the process. That process was called in situ polymerization and in situ compatibilization of polymer blends. Its feasibility was illustrated for in situ polymerized and in situ compatibilized poly(propylene) and polyamide 6 (PP/PA6) blends. The latter were prepared by activated anionic polymerization of ?‐caprolactam (CL) in the presence of PP in a batch mixer and a twin‐screw extruder, respectively. A fraction of the PP contained isocyanate groups from which PA6 grafts were formed. Sodium caprolactam (NaCL) was used as the catalyst and a diisocyanate compound was used as the activator. In this study, we report on the effects of various parameters on the kinetics of the anionic polymerization of CL in the presence of PP. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1498–1504, 2004     

Preparation of polyimide/nylon 6 graft copolymers from polyimides containing ester moieties: Synthesis and characterization

Polyimide‐g‐nylon 6 copolymers were prepared by the polymerization of phenyl 3,5‐diaminobenzoate with several diamines and dianhydrides with a one‐step method. The polyimides containing pendant ester moieties were then used as activators for the anionic polymerization of molten ?‐caprolactam. In the graft copolymer syntheses, the phenyl ester groups reacted quickly with caprolactam anions at 120°C to generate N‐acyllactam moieties, which activated the anionic polymerization. The thermal stability and chemical resistance were dramatically increased by the incorporation of only 5 wt % polyimide in the graft copolymers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 309–318, 2006     

Solvent induced phase separation in a nylon 6-b-polyimide-b-nylon 6 triblock copolymer

A series of new nylon 6-b-polyimide-b-nylon 6 (triblock) copolymers have been synthesized via condensation polymerization of the polyimide component and anionic polymerization of the nylon 6 component. The polyimide component is prepared from bisphenol-A dianhydride (BisA-DA) and bisaniline-P diamine (BisP) with end-capped functional groups. After the polyimides are dissolved in caprolactam, the nylon 6 anionic polymerization is initiated by the functional groups of the polyimides. The triblock copolymers can be dissolved in both m-cresol and 1,6-hexanediol. Of the two components present in the copolymers, nylon 6 crystallizes partially and BisA-DA/BisP is amorphous. Based on differential scanning calorimetry, dynamic mechanical analysis, wide angle X-ray diffraction, small angle X-ray scattering and transmission electron microscopy experiments, the copolymer films prepared from the 1,6-hexanediol solution are phase separated. The BisA-DA/Bis P and the nylon 6 components show little miscibility in the inter-lamellar amorphous region. However, in the films prepared from the m-cresol solution both components are largely miscible in the inter-lamellar amorphous region. This is due to the different solvation power of the two solvents with respect to the polyimide and nylon 6.     

Reactive blending of functionalized polypropylene and polyamide 6: In situ polymerization and in situ compatibilization

Compatibilized polypropylene/polyamide 6 blends were prepared with polypropylene, ε‐caprolactam and maleic anhydride grafted polypropylene via in situ polymerization and in situ compatibilization in a batch mixer. Scanning electron microscopy and differential scanning calorimetric analysis showed that the compatibilizing effect was significantly enhanced through use of this method compared to the classic method of blending premade polymers. The optimum processing parameters were obtained for the reactive blends and the effect of maleic anhydride grafted polypropylene content, and the effect of relative weight fraction of maleic anhydride grafted polypropylene to ε‐caprolactam on the overall morphology of the blend system was investigated. It was found that the domain sizes of the polypropylene and polyamide components in the blends could be easily controlled through proper management of the polymerization and compatibilizing reactions during processing. Polym. Eng. Sci. 44:648–659, 2004. © 2004 Society of Plastics Engineers.     

Molecular composites via in situ polymerization: Poly(phenylene terephthalamide)–nylon 3

All-polyamide molecular level composites composed of rigid rod and flexible coil polymers were prepared using an in situ polymerization process in which the anion of the rigid rod poly-(phenylene terephthalamide) (PPTA) was used as the initiator for the anionic polymerization of acrvlamide to form the nylon 3 matrix. The rigid aramid component then serves as the reinforcing agent. This polymerization resulted in both graft and homo-nylon 3 formation. Composite films prepared using in situ processing showed greatly improved strength and modulus over unmodified nylon 3 with no loss of flexibility. The composites showed aggregation and phase separation of PPTA fibrils at PPTA weight fractions of > 30% as indicated by wide angle X-ray scattering and electron microscopic analysis. The structure of the PPTA formed is that produced from swelled liquid crystalline solutions, indicating that the in situ process involves polymerization in the liquid crystalline state.