Polyether‐based main‐chain‐type polytriazole elastomer with benzoxazine via a 1,3‐dipolar cycloaddition reaction

A novel functional polyether‐based elastomer with a benzoxazine structure in its main chain was successfully synthesized via a 1,3‐dipolar cycloaddition reaction. Benefitting from a facile one‐pot synthesis strategy, the elastomer was prepared at low temperature (80°C) and was characterized clearly afterward. The azide‐terminated polyether and acetylene‐terminated benzoxazine were used as the soft and hard segments, respectively, in the polymer chain. Because the triazole rings served as stable linkage between the soft and hard segments, the elastomer possessed good thermal stability (the 5% weight loss temperature could exceed 350°C) compared to traditional elastomers, such as polyurethane. The rigid benzoxazine rings provided the product with good mechanical properties (the tensile strength of the elastomer could exceed 30 MPa). Furthermore, the ring‐opening polymerization of oxazine rings in the structure gifted the elastomer with possibility of thermally induced structural transformation. The thermally induced structural transformation could conveniently realize the conversion of the elastomer to a thermosetting resin. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42820.     

Influence of the cross‐linking density on the main dielectric relaxation of poly(methyl acrylate) networks

A series of polymer networks of varying cross‐linking density was prepared by copolymerization of methyl acrylate and ethyleneglycol dimethacrylate. The aim of this work is to study the influence of cross‐linking on the conformational mobility of the polymer chains using dielectric relaxation spectroscopy (DRS) in the temperature range of the main dielectric relaxation. As expected, the temperature range in which glass transition takes place became wider with increasing crosslinking density. DRS results were analyzed using the Havriliak‐Negami equation. Master Cole‐Cole arcs could be drawn for all the networks. The arcs become more symmetric as cross‐linking density increases, as a consequence of the different effect of cross‐links on large and small scale mobility. The conformational mobility that produces the main relaxation is drastically reduced when the cross‐linking density increases what reduces the relaxation strength, but it also gives a qualitative change of behavior, as shown by the temperature dependence of the relaxation strength. In the loosely cross‐linked networks the relaxation strength decreases monotonously as temperature increases, as in the main dielectric relaxation of linear polymers. Nevertheless, in highly cross‐linked networks the curve of relaxation strength against temperature presents a maximum. POLYM. ENG. SCI., 45:1336–1342, 2005. © 2005 Society of Plastics Engineers     

Synthesis and characterization of polyesters based on 1,1,1‐[bis(4‐hydroxyphenyl)‐4′‐pentadecylphenyl]ethane

Aromatic polyesters are of considerable interest because of their excellent mechanical properties, chemical resistance and thermal stability. However, most aromatic polyesters are difficult to process due to their high glass transition temperatures coupled with their insolubility in common organic solvents. The present article describes a series of organosoluble polyesters and copolyesters based on 1,1,1‐[bis(4‐hydroxyphenyl)‐4′‐pentadecylphenyl]ethane. A series of new aromatic polyesters containing pendant pentadecyl chains was synthesized by interfacial polycondensation of 1,1,1‐[bis(4‐hydroxyphenyl)‐4′‐pentadecylphenyl]ethane with terephthalic acid chloride (TPC), isophthalic acid chloride (IPC) and a mixture of TPC and IPC. A series of copolyesters was synthesized from 4,4′‐isopropylidenediphenol with TPC by incorporating 1,1,1‐[bis(4‐hydroxyphenyl)‐4′‐pentadecylphenyl]ethane as a comonomer. Inherent viscosities of the polyesters and copolyesters were in the range 0.72–1.65 dL g^?1 and number‐average molecular weights were in the range 18 170–87 220. The polyesters and copolyesters containing pendant pentadecyl chains dissolved readily in organic solvents such as chloroform, dichloromethane, pyridine and m‐cresol and could be cast into transparent, flexible and apparently tough films. Wide‐angle X‐ray diffraction data revealed the amorphous nature of the polyesters and copolyesters. The formation of loosely developed layered structure was observed due to the packing of pendant pentadecyl chains. The temperature at 10% weight loss, determined using thermogravimetric analysis in nitrogen atmosphere, of the polyesters and copolyesters containing pendant pentadecyl chains was in the range 400–460 °C. The polyesters and copolyesters exhibited glass transition temperatures in the range 63–82 °C and 177–183 °C, respectively. Copyright © 2010 Society of Chemical Industry     

Preparation of All Polyester‐Based Semi‐IPN Elastomers Containing Self‐Associative or Non‐Associative Guest Chains via Post‐Blending Cross‐Linking

Mechanical properties of semi‐interpenetrating polymer network (semi‐IPN) elastomers consisting of chemical networks and self‐associative/non‐associative guest chains are demonstrated. Amorphous low T_g polyesters with thiol side groups (PE‐SH) are first synthesized by melt polycondensation. PE‐SH are then converted to polyesters containing COOH side groups (PE‐COOH) and amide side groups (PE‐amide) through Michael addition reaction of thiol groups with acrylic acid and acrylamide, respectively. Homogeneous semi‐IPN elastomers are obtained by thermal cross‐linking for bulk mixtures of PE‐COOH and PE‐amide in the presence of diepoxy cross‐linkers, where COOH and epoxy groups are reacted to form chemical cross‐links while the amide units form self‐complementary hydrogen bonds. Another sample containing non‐associative chains is also prepared by using polyester with N,N‐dimethylamide units, instead of PE‐amide. Dynamic mechanical analysis reveals that guest chain incorporation systematically brings plateau modulus reduction and a unique relaxation with higher tan δ value depending on the fraction and nature of guest chains. Tensile properties are also affected by the fraction and nature of guest chains; the incorporation of hydrogen bonded chains are beneficial to enhance breaking elongation and toughness without the sacrifice of maximum stress. The knowledge found in this work will be thus beneficial for creating tough soft materials with damping applications.     

Preparation of supramolecular thermally repairable elastomer by crosslinking of maleated polyethylene‐octene elastomer with 3‐amino‐1,2,4‐triazole

A supramolecular thermally repairable elastomer was prepared by crosslinking of semicrystalline maleated polyethylene‐octene elastomer (mPOE) with 3‐amino‐1,2,4‐triazole (ATA) via melt mixing method. Crosslinking of mPOE with ATA induced supramolecular hydrogen bonding networks; the nature of the networks was affected by the amount of ATA, which was confirmed by Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy. In addition, at 3 phr ATA content or above, a small number of ionic domains were observed in the tan δ curves of dynamic mechanical analysis. Dynamic mechanical analysis also showed that the storage modulus increased with increasing ATA content along with increase in the relaxation transition temperature which revealed strengthening of the network structures. Differential scanning calorimetry showed a reduction in melting temperature and degree of crystallinity of the mPOE with increasing ATA content which is attributed to hydrogen bonding networks. The shape memory property of the mPOE matrix imparted a thermal healing capability which was greatly enhanced in the presence of hydrogen bonding networks. The scratch marked on the polymer surface healed within 20 s after being heated at around 80 °C. © 2014 Society of Chemical Industry     

Thermo‐Responsive Membranes with Cross‐linked Poly(N‐Isopropyl‐acrylamide) Hydrogels inside Porous Substrates

Thermo‐responsive membranes were prepared by fabricating cross‐linked poly(N‐isopropylacrylamide) (PNIPAM) hydrogels inside the pores of porous Nylon‐6 (N6) membranes by the free radical polymerization method. SEM micrographs of the prepared membranes showed that PNIPAM hydrogels were filled uniformly throughout the entire thickness of the porous N6 membranes. Both PNIPAM‐filled N6 membranes prepared at 60 °C and at 25 °C exhibited significant reversible and reproducible thermo‐responsive diffusional permeability. When the environmental temperature remained constant, the diffusional coefficient of vitamin B₁₂ (VB₁₂) across the PNIPAM‐filled N6 membrane prepared at 25 °C was ca. twice the value of that prepared at 60 °C due to different filling yields. The thermo‐response factor of the membrane prepared at 25 °C was higher than that prepared at 60 °C. The 3‐dimensional interpenetrating network structure of the cross‐linked PNIPAM hydrogels inside the N6 porous substrates could effectively ensure a repeatable thermo‐responsive permeation performance.     

Phenolic‐epoxy matrix curable by click chemistry—synthesis,curing, and syntactic foam composite properties

Alkyne functional phenolic resin was cured by azide functional epoxy resins making use of alkyne‐azide click reaction. For this, propargylated novolac (PN) was reacted with bisphenol A bisazide (BABA) and azido hydroxy propyloxy novolac (AHPN) leading to triazole‐linked phenolic‐epoxy networks. The click cure reaction was initiated at 40–65°C in presence of Cu₂I₂. Glass transition temperature (Tg) of the cured networks varied from 70°C to 75°C in the case of BABA‐PN and 75°C to 80°C in the case of AHPN‐PN. DSC and rheological studies revealed a single stage curing pattern for both the systems. The cured BABA‐PN and AHPN‐PN blends showed mass loss above 300°C because of decomposition of the triazole rings and the novolac backbone. Silica fiber‐reinforced syntactic foam composites derived from these resins possessed comparable mechanical properties and superior impact resistance vis‐a‐vis their phenolic resin analogues. The mechanical properties could be tuned by regulating the reactant stoichiometry. These low temperature addition curable resins are suited for light weight polymer composite for related applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41254.     

A Composite Thermo‐Responsive Membrane System for Improved Controlled‐Release

A novel composite thermo‐responsive membrane system for improved controlled‐release is successfully developed. The membrane is composed of a porous membrane with grafted poly(N‐isopropylacrylamide) (PNIPAM) gates acting as functional valves, and a cross‐linked PNIPAM hydrogel inside the reservoir acting as the solute carrier. The thermo‐responsive controlled‐release characteristics of the proposed system are studied when the ambient temperature is continuously increased from 20 to 45 °C (across the LCST of PNIPAM) at a constant rate of 1.5 °C/min. The experimental results show that the prepared system exhibits significantly better performance for thermo‐responsive controlled‐release than single‐functional systems currently in existence, due to the cooperative action of the gating membrane and the inner cross‐linked hydrogel. Furthermore, due to the distinctive composite architecture, the proposed system can overcome some inherent disadvantages of current systems, such as the drug security problem of the reservoir‐type systems and the mechanical strength problem of the hydrogel matrix‐type systems. The system proposed in this study provides a new mode for thermo‐responsive controlled‐release.     

The influence of cross‐linking reaction on the mechanical and thermal properties of polyarylene ether nitrile

The processing of cross‐linked polyarylene ether nitrile (PEN), which has a triazine rings structure, has been investigated under different reaction times and temperatures. In this study, the PEN films prepared by the tape‐casting formed the thermally stable triazine rings by catalytic cross‐linking reaction gradually, which was characterized by Fourier transform infrared spectroscopy. The chemical cross‐linking reaction occurred as the CN group absorption of PEN at 2221 cm⁻¹ decreased and a new absorption peak, at 1682 cm⁻¹, was observed, and the absorption peak intensity would be progressively larger, with the extension of the processing time. After the formation of cross‐linking networks, the cross‐linking degree and thermal and mechanical properties of the processed films were improved substantially, compared with the untreated films. The film with added ZnCl₂ as the catalyst was more rapidly cross‐linked, and its properties were better than that without catalyst at the same treatment conditions. The glass‐transition temperature (T_g) of PEN films processed at 350°C for 4 h (213.65°C) was higher than that of PEN films before the treatment (161°C), and the tensile strength was also improved significantly. The PEN was processed at 350°C for 2 h, whose initial decomposition temperature increases by about 10°C, compared with that of untreated film, at one time. The rheology behavior of the cross‐linked films was processed on dynamic rheometer to monitor and track the process of polymer cross‐linking reaction. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Novel polymethoxylsiloxane‐based crosslinking reagent and its in‐situ improvement for thermal and mechanical properties of siloxane elastomer

Polymethoxylsiloxane (PMOS) with dense pendant silicone‐methoxy groups was synthesized from cyclosiloxane monomers by ring‐opening polymerization and dehydrocoupling reaction. Synthesis reactions were followed by IR spectroscopy and ²⁹Si NMR analyses. PMOS was used as crosslinking reagent for room temperature vulcanized polydimethylsiloxane (PDMS), and the apparent activation energy for crosslink reaction was 3.92 kJ/mol. TEM study shows that many dispersed high crosslink density PMOS phases were formed in siloxane elastomer as well as the PDMS networks, and the crosslink density increased from PDMS networks to PMOS phases gradually, without a clear interface. It was detected that these PMOS phases improved the thermal and mechanical properties of siloxane elastomer significantly because of their in‐situ microscale improvement effect. TG analysis demonstrated that thermal decomposition process of PMOS crosslinked siloxane elastomer was divided into three stages, the second one corresponding to a possible loss of some new structures, and the residual mass at 500°C was 66 wt %. The crosslink density went up as the loading of PMOS increased. Tensile stress and elastic module increased twice and three times, respectively, when the PMOS content increased from 15.1 to 41.6 wt %. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

High‐temperature‐resistant polymer gel system with metal–organic mixed cross‐linking agents

A high‐temperature (200°C)‐resistant polymer gel system was developed from partially hydrolyzed polyacrylamide (HPAM), chromium lactate (CrL), and water‐soluble phenol/formaldehyde resin (WPF) mixed cross‐linkers. Rheological measurements indicated that the gelation process of the gel system could be divided into four successive steps: induction, first cross‐linking with metal cross‐linker, secondary cross‐linking with organic cross‐linker, and stabilization. Effects of various parameters that affect the gelation time and gel strength including polymer concentration, cross‐linker concentration, salinity, pH, and the gelation temperature were evaluated. Gelant formulated with 0.5 wt % HPAM, 0.1 wt % CrL, and 0.9 wt % WPF and treated at 80°C for 48 h showed sufficient gelation time, high rigidity, and good thermal stability. Morphology observation by scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that the gel had compact network microstructure. A cross‐linking mechanism for the gel system was proposed based on the gelation process and experimental results. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42261.     

The use of acrylated fatty acid methyl esters as styrene replacements in triglyceride‐based thermosetting polymers

Resins containing plant oil‐based cross‐linkers were studied with two reactive diluents: a styrene and an acrylated fatty acid methyl ester‐based (AFAME) monomer. Acrylated epoxidized soybean oil and maleinated castor oil monoglyceride were bio‐based cross‐linkers used. The viscosity and mechanical properties of the resulting polymers were measured and analyzed. Both bio‐based cross‐linkers prepared using the modified AFAME as diluent had a fairly high viscosity, so blends of AFAME and styrene were needed to meet the viscosity requirements established by the composite industry (<1000 cP at room temperature). In addition, the glass transition temperature (T_g) and stiffness of bio‐based cross‐linker/AFAME polymers were significantly lower than the resin/styrene polymers. Ternary blends of maleinated castor oil monoglyceride with AFAME and styrene improved the mechanical properties to acceptable comparable values (storage modulus at 30°C ～ 1200 MPa and T_g ～ 100°C). The addition of 5 wt% of chemically modified lignin led to an improvement in the mechanical properties of the polymeric matrix but caused an increase in the viscosity. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Cross‐linking of polybutadiene: correlation between solid‐state 1H NMR spectroscopy,thermoporosimetry, densimetry and crystallinity measurements

T₂ proton NMR relaxation times were used to follow the changes in the macromolecular chain mobility of a chemically (by dicumyl peroxide) cross‐linked polybutadiene matrix. The same phenomenon was also studied by an investigation of the ability of the polymer to crystallize using DSC measurements. The solubility of the elastomer depends on the size of its macromolecular chains. Cross‐linking, leading to an increase in the size of macromolecules, provokes an insolubility of the elastomer. By densimetry measurements, it was possible to follow the changes in the solubility of the polymer up to its gel‐point. Beyond the gel‐point, the swelling solvent, cyclohexane, was used as a textural probe. Using the shift of its solid‐solid thermal transition points, it was possible to calculate the distribution of the distances between the cross‐links as a function of the curing times by thermoporosimetry analysis. Copyright © 2003 Society of Chemical Industry     

Epoxy‐toughened,unsaturated polyester interpenetrating networks

A series of translucent interpenetrating polymer networks (IPNs) made of a reactive elastomer [linear (D) and branched (T) with varying molecular weights] (Jeffamine?), a commercially available epoxy (D.E.R. 331), and an unsaturated polyester (15:85 wt %) were prepared. DSC data indicated complete cure after 8 h at 90°C. DMTA data showed a single glass‐transition temperature (T_g) for all elastomer‐containing IPNs, an indication of homogeneity. As expected, all IPNs showed a decrease in T_g with incorporation of elastomer, from 16 to 114°C or lower, the largest decrease being with T‐5000. Izod impact strengths were increased by 28–44%, but with no apparent pattern among structure and molecular weight variations. In several cases the standard deviation of impact data increased significantly. Flexural data were measured using a three‐point bend test. The highest flexural modulus obtained was that which incorporated linear D‐2000 with a decrease of only 22% upon incorporation of the elastomer, whereas other compositions dropped up to 55% in flexural modulus. The strongest material obtained was that using D‐2000 with a flexural strength increase of 65% upon incorporation of the elastomer. Two of the three branched elastomer components showed flexural strength increases of about 53%, but one was only equal to the base polyester resin. TGA data were recorded for all IPNs and values compared well to that of the pure polyester resin, with the exception of T‐403, which showed a 20°C decrease, and D‐2000 with a 10°C decrease. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2283–2286, 2002     

Cross‐Linking of Polyesters Based on Fatty Acids

This study aims at obtaining cross‐linked polymeric materials of biomass origin. For this purpose, one‐pot polyesterification of methyl ricinoleate and methyl 12‐hydroxystearate using titanium isopropoxide as a catalyst is performed leading to polyesters known as estolides. The obtained estolides are successfully cross‐linked using dicumyl peroxide or a sulfur vulcanization system. The so‐formed bio‐based elastomers appear to exhibit promising properties. The latter are analyzed by mechanical tensile tests and thermal techniques (TGA, DSC, DMA) and show high thermal stability (T_5% = 205–318 °C), tailored physico‐mechanical properties (low glass transition temperature in the range from ?69 to ?54 °C), and good tensile strength (0.11–0.40 MPa). Networks prepared from high molecular weight estolides appear to be promising bio‐based elastomers. Practical Applications: The vegetable oil‐based estolides described in this contribution are new fully bio‐based precursors for further elastomers synthesis. The resulting estolide networks (obtained by peroxide or sulfur cross‐linking) exhibit tailored thermo‐mechanical properties.     

Polyethylene battery separator with auto‐shutdown ability,thermal stability of 220°C,and hydrophilic surface via solid‐state ultraviolet irradiation

To assure the safety of the lithium‐ion battery, the separator is required to have good thermal stability. Because the single‐layer polyethylene (PE) separator can only tolerate a temperature of 130°C, it is seldom employed currently by lithium‐ion battery manufacturers although its cost is low. In this article, we modified PE separator chain structure through solid‐state ultraviolet (UV) irradiation method to achieve a separator with composite structure of ～40% crystallized PE and ～70% gel content. Approximately 40% crystallized PE chains fulfill the task of auto‐shutdown at 130°C through melting and filling the pores. At the same time, the PE separator can maintain integrity till 220°C because of its highly cross‐linked chain structure. Besides, the modified PE separator is hydrophilic with a water contact angle of 33° after UV treatment and is able to absorb more electrolyte. However, the tensile strength and elongation at the break decreased because the cross‐linking network increased the rigidity. Nevertheless, these values still meet the requirements as the separator for lithium‐ion battery. Considering the low cost and easy preparation, current cross‐linked PE separator has potential to be used in lithium‐ion batteries for various applications, including electric vehicles and energy storage purpose. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42169.     

Cross‐Linked Fluorinated Poly(Aryl Ether) (C‐FPAE) Films: Preparation Strategy,Performance Study,and Low Dielectric Applications

The production of low dielectric materials that can be used in high temperature environments is the primary aim of this work. A cross‐linked structure is introduced into fluorinated poly(aryl ether) (named as FPAE) with high molecular weight (M_w, 140 000 g mol^?1) and linear molecular structure using nucleophilic substitution reaction at the ortho‐position of decafluorobiphenyl monomer units in the FPAE molecular chain. The curing temperature and curing time are optimized and the final conditions for the cross‐linking reaction in this study are determined to be 300 °C for 1 h. Moreover, the dielectric constant and dielectric loss of the C‐FPAE film respectively are 2.67 and 0.006 at 1000 Hz when 1 wt% of crosslinking agent is added, and the cross‐linked fluorinated poly(aryl ether) film shows excellent thermal stability (T_d(5%), 495 °C), dimensional stability, hydrophobic properties, and high storage modulus in high temperature environments. Such novel low dielectric material with excellent performances has important application value in the aerospace and the integrated electronics field.     

Fabrication of Cross‐Linked Anion Exchange Membranes Using a Pillar[5]arene Bearing Multiple Alkyl Bromide Head Groups as Cross‐Linker

A pillararene‐based macrocycle with up to 10 flexible chains bearing alkyl bromide head groups is synthesized and investigated for the first time as a multiarm cross‐linker for tertiary‐amine functionalized polyethersulfone. Different from any previously reported cross‐linker, this has a unique pillar‐shaped structure and abundant reactive sites to form multifunctional clusters in the conductive domain. This advantage enables cross‐linking to occur smoothly at the membrane‐casting stage and endows the cross‐linked membranes with improved performance. The cross‐linked anion exchange membranes are found to possess high conductivities and excellent alkaline stability. With a controllable swelling ratio of 19.5%, the maximum conductivity of a membrane can reach 155 mS cm^–1 at 80 °C. Due to its local high‐density cross‐linked structure, a delay in degradation kinetics under alkaline condition can be observed, and the loss of conductivity is <10% after 400 h of alkaline stability test at 80 °C.     

Preparation and characterization of di‐hexadecanol maleic/triallyl isocyanurate cross‐linked copolymer as solid–solid phase change materials

Di‐hexadecanol maleic/Triallyl isocyanurate cross‐linked copolymers as a novel solid–solid phase change materials were successfully synthesized through bulk polymerization. TAIC is the skeleton and DM is a functional side chain that stores and releases heat during its phase transition process. Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, polarizing optical microscopy, differential scanning calorimetry, and thermogravimetry were employed to study the composition, chemical structure, crystalline properties, phase transition behaviors, and the thermal stability of the cross‐linked copolymers, respectively. The test results indicate that DM/TAIC cross‐linked copolymers have good thermal reliability and heat storage durability after 500 thermal cycles. The phase change temperatures of DM/TAIC cross‐linked copolymers were approximately 28.24–37.02°C, and it has high latent heat storage capacity of more than 83 J/g. At the same time, DM/TAIC cross‐linked copolymers have good thermal stability, and they can be processed or used in high temperature environments. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44065.     

Studies on damping properties of P(MMA‐AN)/P(EA‐nBA) LIPNs

Using a two‐stage emulsion polymerization method, a series of poly(methyl methacrylate‐acrylonitrile)/poly(ethyl acrylate‐n‐butyl acrylate) [P(MMA‐AN)/P(EA‐nBA)] latex interpenetrating polymer networks (LIPNs) were synthesized by varying AN content, ratio of network I/network II, crosslinker content, and introducing chain transfer agent. The damping properties of the LIPNs were investigated using a Rheovibron Viscoelastometer. The results indicates that a suitable content of AN can improve the damping properties of the LIPNs. Three kinds of fillers were incorporated into the LPINs, respectively, to measure the change in the damping properties. Mica and TiO₂ both increased the damping properties of the LIPNs over the wide temperature range. For TiO₂‐filled LIPNs, it was observed that the tan δ values exceeded 0.4 over 112.6°C temperature range from −50 to 72.6°C. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 722–727, 2000