Synthesis and Characterization of Fluorinated Acrylic Polymer and the Properties of Epoxy Thermosets Modified With It

A novel fluorinated acrylic polymer poly(2,2,3,4,4,4-hexafluorobutyl methacrylate)-r-poly(glycidyl methacrylate) (PHFMA-r-PGMA) was synthesized and used to modify the general performances of epoxy resin. Fourier transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance spectroscopy (¹H-NMR) successfully verified the synthesis of PHFMA-r-PGMA. In order to study the effect of epoxy groups in PHFMA-r-PGMA on the properties of modified epoxy resin, corresponding fluoropolymer without epoxy group (PHFMA) was also prepared, and the properties of epoxy thermosets modified by two kinds of fluoropolymers were comparatively studied. The contact angle measurements indicated that the PHFMA-r-PGMA and PHFMA modified thermosets both showed considerable hydrophobicity and lipophobicity. For further comparison, it was also found that the thermosets modified by PHFMA-r-PGMA had a little worse hydrophobicity and lipophobicity but better surface stability than which modified by PHFMA because the epoxy groups in PHFMA-r-PGMA “locked” more fluoropolymers in the bulk matrix of the thermosets, but PHFMA was more freely able to migrate to the surface of the thermosets. SEM images of the fracture surface of PHFMA-r-PGMA and PHFMA modified epoxy thermosets displayed “irregular ripples” or “protuberant island” structures, which suggesting both of these two copolymers could significantly toughen epoxy resin. The results of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the thermosets modified by PHFMA-r-PGMA had better thermal stability than which modified by PHFMA due to the higher crosslinking density between PHFMA-r-PGMA and epoxy resin because of the epoxy groups in PHFMA-r-PGMA. The mechanical properties were investigated by tensile testing and impact testing. Although the tensile strength of the PHFMA-r-PGMA and PHFMA modified epoxy thermosets both declined slightly with growing the content of fluoropolymers, the elongation at break and impact strength both increased first and then decreased in the meantime, which indicated that the two kinds of modified thermosets had better toughness than pure epoxy resin. It may be because the macro-phase separation between the long fluorine carbon chain segments and epoxy resin during curing could absorb the impact energy effectively.     

Insertion of Supramolecular Segments into Covalently Crosslinked Polyurethane Networks towards the Fabrication of Recyclable Elastomers

Thermoset plastics have become one of the most important chemical products in the world. The consequent problem is that although the thermosets possess excellent performance in mechanical strength, they cannot be reprocessed because of the internal permanent network structures. Optimizing the molecular design of thermosets is one of the most feasible ways to improve their recyclability. Here we present a facile and robust strategy to engineer the reprocessability of thermoset polyurethanes without compromising their mechanical toughness and chemical resistance via adding supramolecular additives during the polymer synthesis process. By using a multiple hydrogen bonding moiety as the model supramolecular additive, we demonstrate that the mechanical properties, recyclability, and chemical resistance of the crosslinked polyurethanes can be precisely controlled by adjusting the contents of the supramolecular additive. Systematic studies on the relations between molecular design and material properties are performed, and the optimized polyurethane network with a moderate amount of the supramolecular additive achieves the right balance between the robustness and recyclability. This work provides a cost-effective and practical way to chemically engineer thermoset plastics, aiming to enable the recycling of mechanically tough and chemically stable polymer materials.     

The synthesis and characterization of nadimidized aromatic bisaspartimides and their polymerization to high-temperature-resistant laminating resins

4,4′-Bis(N²)-{4-[4-(2,3-bicyclo-[2.2.1]hept-5-ene-dicarboximido)phenoxy]-phenyl(-aspartimido)-di-phenyl ether (2NAD/1020) and various similar polymer percursors were synthesized from bismaleimides by the Michael addition of two moles of aromatic diamine followed by end capping of the resultant amino-terminated bisaspartimide groups with nadic anhydride. These precursors were characterized by using Fourier-transform infrared (FT-IR), proton, and carbon-13 nuclear magnetic resonance spectroscopies (¹H- and ¹³C-NMR). Thermal polymerization of 2NAD/1020 by heating it above its melting point gave a reddish brown thermoset polymer. The curing behavior and thermal stability of these nadimides were evaluated by differential scanning calorimetry and thermogravimetric analysis studies. Graphite fiber laminates were prepared from these polymer precursors and their mechanical properties evaluated. Gas Chromatography/Mass Spectra of the precursors and thermosets have given an understanding of their decomposition behavior. The structures of the thermosets were examined by FT-IR spectroscopy.     

Highly Recyclable and Tough Elastic Vitrimers from a Defined Polydimethylsiloxane Network

Despite intensive research on sustainable elastomers, achieving elastic vitrimers with significantly improved mechanical properties and recyclability remains a scientific challenge. Herein, inspired by the classical elasticity theory, we present a design principle for ultra-tough and highly recyclable elastic vitrimers with a defined network constructed by chemically crosslinking the pre-synthesized disulfide-containing polydimethylsiloxane (PDMS) chains with tetra-arm polyethylene glycol (PEG). The defined network is achieved by the reduced dangling short chains and the relatively uniform molecular weight of network strands. Such elastic vitrimers with the defined network, i.e., PDMS-disulfide-D, exhibit significantly improved mechanical performance than random analogous, previously reported PDMS vitrimers, and even commercial silicone-based thermosets. Moreover, unlike the vitrimers with random network that show obvious loss in mechanical properties after recycling, those with the defined network enable excellent thermal recyclability. The PDMS-disulfide-D also deliver comparable electrochemical signals if utilized as substrates for electromyography sensors after the recycling. The multiple relaxation processes are revealed via a unique physical approach. Multiple techniques are also applied to unravel the microscopic mechanism of the excellent mechanical performance and recyclability of such defined network.     

Molecular Structures and Mechanical Properties of Microbe Rapid Coagulation Natural Rubber

In this work,molecular structures,dynamic mechanical properties and glass transition temperatures of microbe coagulated natural rubber(NR) samples were analyzed by using pyrolysis gas chromatography-mass spectrometry(py-GC/MS),rubber process analyzer(RPA) and dynamic mechanical thermal analysis(DMA).And the cross-linked network structures and mechanical properties of the corresponding NR vulcanizates were further determined by using nuclear magnetic resonance(NMR) crosslink density spectrometer(XLDS-15) and universal testing machines.The results show that NR raw rubber produced by rapidly coagulated with microorganism exhibits a simple molecular structure composition and good dynamic mechanical properties,and the corresponding NR vulcanizates possess the aggregation structure of high cross-linked density,a high glass transition temperature of-61.5 ℃ and high mechanical properties(tensile strength reaches 25.2 MPa),as compared with that coagulated with acetic acid.     

Synthesis and characterization of bismaleimides derived from polyurethanes

A series of novel bismaleimides (BMIs) were prepared from maleic anhydride and polyurethane prepolymers based on MDI (4,4′-diphenylmethane diisocyanate) and polyether and polyester diols with various chain lengths. All the BMIs were characterized by IR, ¹H-NMR, and elemental analysis. DSC studies indicated that the thermal polymerization of the BMIs could be carried out in the temperature range of 102–245°C, and that curing behavior was significantly affected by the molecular weight of the BMIs. The crosslinked BMI elastomers showed good mechanical properties and much better thermal stability than that of the traditional polyurethane elastomers. The glass transition temperatures, mechanical, and dynamic mechanical properties were dependent on the types of polyols used and the resultant crosslink densities due to various chain lengths of the BMIs. © 1994 John Wiley & Sons, Inc.     

双马来酰亚胺增韧研究Ⅱ.链扩展双马来酰亚胺及其树脂的合成及表征

合成了一系列结构不同和链长短不一的双马来酰亚胺，并对其结构和性能作了表征，同时研究了它们的固化反应和固化产物的性能。用双马来酰亚胺和二烯丙基化合物反应制造了增韧树脂，研究了该树脂的固化和热稳定性。     

含二苯甲烷结构四元共缩聚杂萘聚芳酰胺的合成与性能

采用自制二胺1,2-二氢-2-(4-氨基苯基)-4-[4-(4-氨基苯氧基)-苯基]-二氮杂萘-1-酮、商品二胺4,4′-二氨基二苯甲烷和对苯二胺与对苯二甲酰氯进行低温溶液缩聚反应,改变三种二胺的比例,得到了一系列共聚酰胺树脂,其特性粘数为1·24~2·32dL/g,用FT-IR、1H-NMR手段研究了聚合物的结构;利用DSC和TGA研究了聚合物的耐热性能,结果表明,该类聚合物具有较高玻璃转化温度(301℃以上);氮气气氛中5%热失重温度在438℃以上;用一定比例的二胺制得的聚合物分别能溶于N-甲基吡咯烷酮、N,N-二甲基乙酰胺等非质子极性溶剂中并浇注得到韧性薄膜.     

Side-chain engineering of supramonomers enables tailorable cross-linked supramolecular polyureas

The integration of tailorable mechanical properties, dimensional stability, and reprocessability is of significance in the design of sustainable polymer materials. Herein, side-chain engineering is employed to fabricate cross-linked supramolecular polymers with customizable mechanical properties. Three kinds of side chains, including methyl, 1-ethyl pentyl, and 1-hexyl nonyl, are used to modify the supramonomers. Through the copolymerization of low-content supramonomers and covalent monomers, cross-linked supramolecular polyureas with a wide range of mechanical properties spanning from rigid plastics to elastic materials are successfully constructed. Specifically, the Young's modulus can be adjusted from 525 to 128 MPa by tuning the side chain of supramonomers from methyl to 1-hexyl nonyl. Meanwhile, the materials still retain exceptional recyclability and solvent resistance. Even after seven generations of recycling processes, the reprocessed cross-linked supramolecular polyureas maintain over 95% of their original mechanical properties. It is anticipated that side-chain engineering is a facile method for designing customized polymer materials to achieve both tailored mechanical properties and desirable functions.     

Flexible Self-healing Cross-linked Polyamides Synthesized Through Bulk Michael Addition,Polycondensation, and Diels-Alder Reaction

Three new thermally responsive self-healing cross-linked polyamides(cPA-FU-DAs) with good tensile strength and toughness were synthesized through bulk Michael addition, polycondensation, and Diels-Alder reaction. Unlike common stable polymers, cPA-FU-DAs can seal cracks by mere heating. First, the Michael addition of methyl acrylate and furfurylamine was conducted, and a furfurylamine-diester(FU-DE) was prepared. FU-DE was transformed into polyamide prepolymers that contained furfuryl pendant groups(PA-FUs) through bulk polycondensation with a poly(propylene glycol)(PPG) diamine and a PPG triamine. PA-FUs were crosslinked by bismaleimide, and cPA-FU-DAs were prepared. The Michael addition was monitored by Fourier transform infrared spectroscopy and electrospray ionization mass spectroscopy. The reverse DA reaction of the cPA-FU-DAs was demonstrated by differential scanning calorimetry and dissolution property. Their thermally self-healing properties were verified by polarizing optical microscopy and tensile test. The cPA-FU-DAs exhibited good mechanical properties and high self-healing efficiency. They self-healed at 130℃. The tensile strength after repairing was up to 19 MPa with self-healing efficiency reaching 92%.     

New Structures of Bismaleimides and Polyaspartimides with Ether Units

New bismaleimide monomers with various structures, synthesized by the reaction of maleic anhydride and new diamines, were used in the reaction with diamines to yield polyaspartimides. The structure of these monomers was confirmed by Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance (¹H-NMR) spectroscopy, and polymer structure was evidenced by FT-IR spectroscopy. The resulting new compounds were characterized by differential scanning calorimetry (DSC) and thermogravimetry (TGA). The polymers exhibited film-forming ability. The quality of these films was studied by atomic force microscopy (AFM), and their mechanical properties (tensile strength, tensile modulus) were investigated.     

Highly Soluble Phenylethynyl-terminated Imide Oligomers and Thermosetting Polyimides Based on 2,2′3,3′-Biphenyltetracarboxylic Dianhydride

The properties of a series of imide oligomers were characterized according to their molecular weights, solubility, and thermal and rheological properties. This series of imide oligomers was synthesized via a two-step method using 2,2′,3,3′-biphenyltetracarboxylic dianhydride(3,3′-BPDA) and aromatic diamines as the monomers, and 4-phenylethynyl phtlialic anhydride(PEPA) as the end-capping agent. The imide oligomers based on 3,3′-BPDA showed excellent solubility in low boiling point solvents and low melt viscosity, which were attributed to their unique bent architectures. High-performance thermosetting polyimides were produced from these oligomers via thermal crosslinking of the phenylethynyl groups. The mechanical and thermal properties of the thermosets were studied using tensile testing, dynamic mechanical thermal analysis(DMTA), and thermogravimetric analysis(TGA). The 3,3′EPDA-based thermosets exhibited excellent thermal properties, with glass transition temperatures of up to 455℃, and 5% mass loss temperatures of up to 569℃ in air. The thermosets based on 3,3-BPDA showed superior thermal properties compared to those derived from TriA-X series oligomers.     

环氧丁羟型聚氨酯弹性体的制备与性能

以间氯过氧苯甲酸(mCPBA)为氧化剂对降解法制备的端羟基聚丁二烯(DHTPB)中的部分双键进行环氧化改性,通过控制mCPBA和双键的比例制得具有不同环氧率的环氧化端羟基聚丁二烯(EHTPB),经1H-NMR分析测试表明EHTPB的环氧率分别为5%、10%和15%,与设计值基本一致.进一步以EHTPB为多元醇、4,4'-二苯基甲烷二异氰酸酯(MDI)为异氰酸酯、1,4-丁二醇为扩链剂制备了环氧丁羟型聚氨酯弹性体(EPU),并对其性能进行了测试,研究结果表明:丁羟胶的环氧化改性对聚氨酯弹性体的力学性有着一定的提升作用,其杨氏模量和拉伸强度随环氧率的上升而提高,而断裂伸长率则随环氧率的上升有所下降;环氧丁羟型聚氨酯弹性具有优异的弹性恢复能力;环氧化改性后,聚氨酯弹性体的热稳定性有一定程度的提高;聚氨酯弹性体的玻璃化转变温度随环氧率的上升而升高.     

Synthesis of a novel phosphorus‐containing curing agent and its effects on the flame retardancy,thermal degradation and moisture resistance of epoxy resins

A novel phosphorus‐containing compound diphenyl‐(1, 2‐dicarboxylethyl)‐phosphine oxide defined as DPDCEPO was synthesized and used as a flame retardant curing agent for epoxy resins (EP). The chemical structure of the prepared DPDCEPO was well characterized by Fourier transform infrared spectroscopy, and ¹H, ¹³C and ³¹P nuclear magnetic resonance. The DPDCEPO was mixed with curing agent of phthalic anhydride (PA) with various weight ratios into epoxy resins to prepare flame retardant EP thermosets. The flame retardant properties, combustion behavior and thermal analysis of the EP thermosets were respectively investigated by limiting oxygen index (LOI), vertical burning tests (UL‐94), cone calorimeter measurement, dynamic mechanical thermal analysis and thermogravimetric analysis (TGA) tests. The surface morphologies and chemical compositions of the char residues for EP thermosets were respectively investigated by scanning electron microscopy and X‐ray photoelectron spectroscopy (XPS). The water resistant properties of the cured EP were evaluated by putting the samples into distilled water at 70°C for 168 hr. The results revealed that the EP/20 wt% DPDCEPO/80 wt% PA thermosets successfully passed UL‐94 V‐0 flammability rating and the LOI value was as high as 33.2%. The cone test results revealed that the incorporation of DPDCEPO effectively reduced the combustion parameters of the epoxy resin thermosets, such as heat release rate and total heat release. The dynamic mechanical thermal analysis test demonstrated that the glass transition temperature (Tg) decreased with the increase of DPDCEPO content. The TGA results indicated that the incorporation of DPDCEPO promoted the decomposition of epoxy resin matrix ahead of time and led to a higher char yield and thermal stability at high temperatures. The surface morphological structures and analysis of the XPS of the char residues of EP thermosets revealed that the introduction of DPDCEPO benefited the formation of a sufficient, compact and homogeneous char layer with rich flame retardant elements on the epoxy resin material surface during combustion. The mechanical properties and water resistance of the cured epoxy resins were also measured. After water resistance tests, the EP/20 wt% DPDCEPO/80 wt% PA thermosets retained excellent flame retardancy, and the moisture adsorption of the EP thermosets decreased with the increase of DPDCEPO content in EP thermosets because of the existence of the P–C bonds and the rigid aromatic hydrophobic structure in DPDCEPO. Copyright © 2015 John Wiley & Sons, Ltd.     

Facile fabrication of fast recyclable and multiple self‐healing epoxy materials through diels‐alder adduct cross‐linker

A reversibly cross‐linked epoxy resin with efficient reprocessing and intrinsic self‐healing was prepared from a diamine Diels‐Alder (DA) adduct cross‐linker and a commercial epoxy oligomer. The newly synthesized diamine cross‐linker, comprising a DA adduct of furan and maleimide moieties, can cure epoxy monomer/oligomer with thermal reversibility. The reversible transition between cross‐linked state and linear architecture endows the cured epoxy with rapid recyclability and repeated healability. The reversibly cross‐linked epoxy fundamentally behaves as typical thermosets at ambient conditions yet can be fast reprocessed at elevated temperature like thermoplastics. As a potential reversible adhesive, the epoxy polymer with adhesive strength values about 3 MPa showed full recovery after repeated fracture‐thermal healing processes. The methodology explored in this contribution provides new insights in modification of conventional engineering plastics as functional materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2094–2103     

Synthesis and Properties of Novel Thermoplastic Poly(ester-ether-imide) Elastomers Derived from 4,4′-bis(N-trimellitimide)-diphenylether Unit with Excellent Thermal Stability

The novel poly(ester-ether-imide)s (PEEIs) were synthesized by 1, 6-hexanediol (HD), poly(tetramethylene glycol) (PTMG1000) and imide dicarboxylic acid was prepared from 1,2,4-trimellitic anhydride (TMA) and 4,4′-oxydianiline (ODA) by the traditional chemical two-step method. The structures of synthesized imide dicarboxylic acid and poly(ester-ether-imide)s were confirmed by FT-IR and ¹H-NMR spectroscopy, respectively. The intrinsic viscosities, thermal properties, dynamic mechanical properties, mechanical properties and solubility of these polymers were characterized. The results indicate that these polymers have good solubility, exhibit excellent thermal stability owing to the introduction of imide units, and the tensile strength of PEEIs increases with increasing the number of imide groups while maintaining the good elasticity of the polymers.     

A Review on the Potential and Limitations of Recyclable Thermosets for Structural Applications

Abstract

The outstanding performance of conventional thermosets arising from their covalently cross-linked networks directly results in a limited recyclability. The available commercial or close-to-commercial techniques facing this challenge can be divided into mechanical, thermal, and chemical processing. However, these methods typically require a high energy input and do not take the recycling of the thermoset matrix itself into account. Rather, they focus on retrieving the more valuable fibers, fillers, or substrates. To increase the circularity of thermoset products, many academic studies report potential solutions which require a reduced energy input by using degradable linkages or dynamic covalent bonds. However, the majority of these studies have limited potential for industrial implementation. This review aims to bridge the gap between the industrial and academic developments by focusing on those which are most relevant from a technological, sustainable and economic point of view. An overview is given of currently used approaches for the recycling of thermoset materials, the development of novel inherently recyclable thermosets and examples of possible applications that could reach the market in the near future.     

Structure–property relationships of anionic poly(urethane–urea) dispersion cross-linked with partially methylated melamine formaldehyde

An anionic poly(urethane–urea) dispersion (PUD) was cross-linked with different amount of partially methylated melamine formaldehyde (PMMF). The isothermal curing behavior was observed by a rigid-body pendulum rheometer. The test results showed that cure response of PUD cross-linked with PMMF was a function of the concentration of PMMF. Also, PMMF self-condensation could take place during the curing process. In this experiment, the anionic poly(urethane–urea) dispersion has a large number of >N–H cross-linking or branching sites in urethane and urea groups per molecule that allow a large number of PMMF to couple into elastic PUD backbone to form branched structure with partial cross-linking. The dynamic mechanical properties of PUD cross-linked with PMMF were affected by the concentration of PMMF. It was further shown that the tensile properties were strongly influenced by the concentration of PMMF and curing temperature.     

Plant Oil‐Derived Epoxy Polymers toward Sustainable Biobased Thermosets

Epoxy polymers (EPs) derived from soybean oil with varied chemical structures are synthesized. These polymers are then cured with anhydrides to yield soybean‐oil‐derived epoxy thermosets. The curing kinetic, thermal, and mechanical properties are well characterized. Due to the high epoxide functionality per epoxy polymer chain, these thermosets exhibit tensile strength over an order of magnitude higher than a control formulation with epoxidized soybean oil. More importantly, thermosetting materials ranging from soft elastomers to tough thermosets can be obtained simply by using different EPs and/or by controlling feed ratios of EPs to anhydrides.

     

The effect of electrophoretic deposition p-aminobenzenesulfonamide grafted CNT on mechanical properties of carbon fiber filled polyamide 6 composite

The surface treatment of carbon fiber is carried out by electrophoretic deposition of p-aminobenzenesulfonamide grafted carbon nanotube (CNT), and it is used as a reinforcement of polyamide 6. The monofilament tensile test and XPS were used to study the effect of p-aminobenzenesulfonamide concentration on the tensile strength and surface functional groups of carbon fiber monofilaments. The results show that the higher the p-aminobenzenesulfonamide concentration, the greater the decrease in the mechanical properties of carbon fibers, and the greater the content of oxygen-containing functional groups on the surface. It is preferred that carbon fiber and thermoplastic polyamide 6 with higher retention rate of monofilament tensile strength and rich oxygen-containing functional group content are made into composite materials, and the interlaminar shear strength (ILSS) is evaluated.