Multimodal polymer networks: design and characterisation of nanoheterogeneous PU elastomers

Nanoheterogeneous polymer networks based on polyurethanes (PU) were synthesised by utilisation of the competition between reactivity, dynamics and phase separation processes. Oligomeric α,ω‐dihydroxyoxolanes (PTHF), 4,4′‐methylene‐bisphenylisocyanate (MDI), and trimethylolpropane (TMP) were chosen as reaction components. In dependence of the mole ratio of these components up to four phases concerning their crosslinking density were formed. By a partly substitution of incompatible oligomers for PTHF the network structure was specifically changed including the formation of additional phases. The characterisation of the nanophases was carried out by investigation of the dynamics as reflected by mechanical relaxation spectroscopy. Selected mechanical properties of the samples were measured and discussed using the deduced morphological model.     

UV curable EA-Si hybrid coatings prepared by combination of radical and cationic photopolymerization

A series of UV curable EA-Si hybrid coatings were prepared by a simple approach combining radical and cationic photopolymerization, with epoxy acrylate (EA) as monomer, γ-glycidoxypropyltrimethoxysilane (GPTMS) as inorganic precursor, benzophenone (BP) as free radical photo initiator and a diaryliodonium salt DPIHFP as cationic photo initiator. The chemical structures of EA-Si hybrid coatings were characterized by Fourier transform infrared (FTIR), Raman spectroscopy and X-ray diffraction (XRD). The thermal and optical properties of hybrid coatings were investigated by thermal gravimetric analysis (TGA) and UV–vis transmission spectroscopy, respectively. The results indicated that cross-linked network structure of SiOSi formed in the hybrid coatings, which led to the decrease in crystallinity and of EA-Si hybrid coating. The final conversion of CC bonds was also decreased because of the addition of GPTMS. The thermal stability of EA-Si hybrid coatings was enhanced in the second decomposition stage (300–400 °C) because of the existence of organic–inorganic cross-linked network structures. The transparency of coatings at around 346 nm tended to increase with increasing concentration of inorganic precursor GPTMS.     

FT-IR and 29Si-NMR Studies on UV-Curable DDS-MPTMS/SiO2 Hybrid Coating

Ultraviolet (UV)-curable DDS-MPTMS/SiO₂ hybrid coating was prepared by sol-gel process from tetraethylorthosilicate (TEOS), dimethyl diethylorthosilicate (DDS), and methacrylate propyl trimethoxysilicate (MPTMS). The formation of inorganic–organic hybrid network was studied by FT-IR and ²⁹Si-NMR during UV curing. It was found that the three-dimensional (3D) inorganic networks were formed mainly by condensation of TEOS, and the linear Si-O-Si bonds were also formed by condensation of DDS. The organic networks were formed by the polymerization of C[dbnd]C bonds in methacrylate units and the silanol groups were further condensed when the hybrid coating was cured by UV light. The steric hindrance of organic–inorganic hybrid networks resulted in incomplete polymerization and condensation. When the UV curing time was 240 s, the conversion degree of C[dbnd]C bonds was 81.0% and the condensation degree of silanol groups in TEOS and MPTMS was 81.8% and 91.5%, respectively.     

Formation of nanostructured epoxy networks containing polyhedral oligomeric silsesquioxane (POSS) blocks

Nanostructured epoxy networks, based on DGEBA and poly(oxypropylene)diamine (Jeffamine D), containing nano-sized inorganic blocks, polyhedral oligomeric silsesquioxanes (POSS), were investigated. The POSS were incorporated in the network as crosslinks or as pendant units by using octa- or monoepoxy-POSS monomers, respectively, as well as diepoxides with pendant POSS. The authors focused on investigating the relationship between the network formation process and the final product properties. The reactivity of the epoxy-functional POSS monomers, the hybrid systems' time of gelation, the gel fractions and the phase structure of the networks were determined using ¹H or ¹³C NMR spectroscopy, chemorheology experiments, sol-gel analysis and transmission electron microscopy (TEM).All the POSS epoxides tested show a reduced reactivity if compared to their respective model compounds due to sterical crowding in the neighborhood of their functional groups and due to reduced epoxy group mobility. The incorporation of pendant POSS into networks of the type DGEBA-Jeffamine D-monoepoxy-POSS hence took place only in the late reaction stage. Together with the high tendency of these POSS to aggregation, the kinetics favors the formation of small nano-phase-separated POSS domains, which act as physical crosslinks due to their covalent bonds to the organic matrix. At POSS loadings higher than 70%, topological constraint by POSS leads to a strongly reduced elastic chain mobility, thus additionally strongly reinforcing the networks. The network build-up and gelation of the octaepoxy-POSS-Jeffamine D system were slow compared to the reference DGEBA-Jeffamine D network due to a low octaepoxy-POSS reactivity and due to its strong tendency to cyclization reactions with primary amines. The topology of the amino groups is shown to be very important. In contrast to monoepoxy-POSS, the octaepoxy-POSS becomes dispersed as oligomeric junctions (purely chemical crosslinks) of the network in the cured product. The octaepoxide's reinforcing effect is small and is given only by its high functionality and not by its inorganic nature. The functionality effect is reduced by the mentioned cyclizations.     

Organic/inorganic hybrid materials from polypeptide-based block copolymers

Novel organic/inorganic hybrid material was synthesized from poly(acrylazapropyl-trimethoxysilane)-b-poly(N_ε-trifluoroacetyl-l-lysine) (P(AAPTMS)-b-P(TLL)) block copolymer using the sol–gel process. The treatment with ammonia solution permitted the hydrolysis of both trifluoro acetyl and trimethoxysilyl groups of the hydride copolymer followed by the condensation of the silanol groups, leading to cross-linked copolymers. The resulting cross-linked hybrid material was characterized using FT-IR, ²⁹Si NMR, DSC, TGA, and environmental scanning electron microscopy. These techniques evidenced that a siloxane network was obtained. Amphiphilic polypeptide/inorganic hybrid copolymers were achieved and self-organized as particles in water.     

Thermal and dynamic-mechanical properties of new chiral smectic networks

Summary The thermal and dynamic-mechanical behavior of two chiral liquid-crystalline networks are described. Both polymer networks formed a smectic mesophase whose isotropization temperature and enthalpy decreased with increasing crosslinking degree. The dynamic-mechanical behavior was studied in the linear viscoelasticity range. Three main relaxation regions were assigned to the relaxation, the network relaxation and the isotropization. Thus, it was possible to monitor the dynamic-mechanical response of the networks in both the anisotropic and isotropic states. Values of the storage and loss dynamic moduli in the range 10⁶–10⁷ Pa were detected in the isotropic state. Above the relaxation temperature, either an elasticity or viscosity dominant state was observed depending upon the crosslink density of the network.     

Synthesis of modified SiO2 networks: Polydimethylsiloxane-SiO2 organic-inorganic hybrids via sol-gel chemistry

Poly(dimethylsiloxane)-SiO₂ organic-inorganic hybrid networks were synthesized by a two-step, catalyst-free sol-gel process. Reactive PSX (polydimethylsiloxane) oligomers with methoxysilyl end-groups were used as the organic component, and tetramethylorthosilicate (TMOS) as the inorganic component of the hybrid. Our studies show that uncatalyzed sol-gel reactions based on TMOS can reach gelation in 7.5 h when reacted at room temperature, with a stoichiometric amount of water necessary for complete hydrolysis in the initial stages, and at a high concentration of reacting species. The relatively neutral reaction environment of this catalyst-free process is important in the synthesis of PSX-SiO₂ hybrid networks because it prevents redistribution reactions of PSX modifiers, especially when higher temperatures are used for the drying of the gels. The PSX-SiO₂ hybrid networks have reduced polarity, increased water resistance, and improved toughness compared to inorganic SiO₂ networks produced under similar conditions.     

Synthesis of modified SiO2 networks: Polydimethylsiloxane-SiO2 organic-inorganic hybrids via sol-gel chemistry

Poly(dimethylsiloxane)-SiO₂ organic-inorganic hybrid networks were synthesized by a two-step, catalyst-free sol-gel process. Reactive PSX (polydimethylsiloxane) oligomers with methoxysilyl end-groups were used as the organic component, and tetramethylorthosilicate (TMOS) as the inorganic component of the hybrid. Our studies show that uncatalyzed sol-gel reactions based on TMOS can reach gelation in 7.5 h when reacted at room temperature, with a stoichiometric amount of water necessary for complete hydrolysis in the initial stages, and at a high concentration of reacting species. The relatively neutral reaction environment of this catalyst-free process is important in the synthesis of PSX-SiO₂ hybrid networks because it prevents redistribution reactions of PSX modifiers, especially when higher temperatures are used for the drying of the gels. The PSX-SiO₂ hybrid networks have reduced polarity, increased water resistance, and improved toughness compared to inorganic SiO₂ networks produced under similar conditions.     

Novel Polysilsesquioxane Hybrid Membranes for Proton Exchange Membrane Fuel Cell (PEMFC) Applications

Abstract

Novel polysilsesquioxane (R–Si–(O)_1.5) PEMs with highly cross-linked Si–O backbones and pendant organic side chains comprising propylsulfonic or ethylphosphonic acid groups, were prepared via sol-gel polymerization. The inorganic component provides thermal/mechanical/chemical stability while the organic component gives flexibility and proton-conducting properties. The propylsulfonic acid membranes exhibited proton conductivities (σ) up to 10^?2 S/cm at high relative humidities and temperatures, while the ethylphosphonic acid membranes showed lower proton conductivities but higher thermal stabilities. Preliminary results for the propylsulfonic acid membranes in direct methanol fuel cell (DMFC) performance are reported.     

Organic–inorganic hybrid nanocomposites involving novolac resin and polyhedral oligomeric silsesquioxane

Octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane (OpePOSS) was employed as a nanocrosslinker of novolac resin to prepare the organic–inorganic networks. The crosslinking reaction was investigated by means of Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy via model reaction. Thermal analyses indicate that the glass transition temperatures (T_g’s) and thermal stability of the organic–inorganic networks increased with increasing the content of POSS. Contact angle measurements show that the organic–inorganic nanocomposites displayed a significant enhancement in surface hydrophobicity as well as reduction in surface free energy. The improvement in surface properties was ascribed to the presence of POSS moiety in place of polar component of phenolic thermosets.     

Mechanical properties of crosslinked polyurethanes

Stress–strain and stress–relaxation behavior of polyurethane elastomers based on poly(ethylene adipate), poly(ethylene maleate), polyethylene glycol, and 4,4′-diphenylmethane diisocyanate (MDI) have been studied. The elastomers were crosslinked by an excess of MDI and by dicumyl peroxide (DiCup); the latter was supposed to form additional crosslinks on the unsaturated bonds. The determined values of Young's modulus, Mooney-Rivlin elastic parameters C₁ and C₂, relaxation moduli E(10 sec) and E(100 sec), as well as relaxation speed were used to estimate the effect of MDI- and DiCup-formed crosslinks on the mechanical behavior of polyurethanes. It was found that while the elastomers crosslinked by MDI only apparently displayed viscoelastic properties, the polyurethanes additionally crosslinked by DiCup exhibited more elastic behavior. The results obtained were explained on the basis of changes in the amount of secondary bonding due to the additional network junctions formed by DiCup at nonpolar groups.     

基于聚合物的一维光子晶体研究进展

从一维光子晶体组装材料角度出发,总结分析了基于聚合物的有机/有机型和有机/无机杂化型一维光子晶体的结构特点、组装原理和方法、性能及应用。在有机/有机型一维光子晶体中,主要介绍了含有不同亲疏水链段的嵌段共聚物和含有可聚合双键的表面活性剂自组装形成的一维光子晶体。在有机/无机杂化型一维光子晶体中,既论述了基于聚合物、无机材料直接交替组装形成的多层膜,也讨论了基于两种无机材料组装,然后再填充柔性聚合物的一维光子晶体。通过对以上两类光子晶体材料的总结分析可知,基于聚合物材料制备的一维光子晶体可以实现多种功能,在柔性传感器、柔性光电器件、光子晶体纸、电子皮肤、3D打印等方面具有良好的应用前景。但目前基于聚合物的一维光子晶体存在组装均匀性有待提高、组装面积较小等问题,如何大规模制备均匀的功能性一维光子晶体是重要的研究方向,也是影响其实际应用的关键。     

Thermally stable crosslinked NLO materials based on maleimides

A series of thermally stable second-order nonlinear optical (NLO) polymeric materials based on bismaleimide chemistry have been developed. Two maleimide containing chromophores with excellent thermal stability were incorporated into the bismaleimide polymer matrices to form interpolymer networks. Moreover, a full interpenetrating polymer network (IPN) was formed through simultaneous addition reaction of the bismaleimide, and sol-gel process of alkoxysilane dyes (ASD). Atomic force microscopy results indicate that the inorganic networks are distributed throughout the polymer matrices on the molecular scale. The silica particle sizes are well under 200 nm. Second harmonic coefficients, d₃₃ of 6.9-57.0 pm/V have been obtained for the organic and organic/inorganic materials. Excellent temporal stability was obtained for these NLO materials at 100 °C. The dynamic thermal and temporal stabilities of the IPN system were much better than those of the crosslinked organic systems.     

Chemorheology of crosslinked polyisoprene/poly(butadiene co-styrene) blends

Physical and chemical properties of IR/SBR blend systems crosslinked by dicumyl peroxide were investigated in detail. In order to study physical structure of cross-linked rubber blends, measurement of birefringence of extended samples and observation by scanning electron microscope (SEM) of ones ruptured in liquid nitrogen were also carried out. In the vicinity of IR/SBR = 30/70 (weight ratio) the phase structure of blends was reversed. The size of domain was in about 0.2 to 0.7 μm dependent on the blend ratio. In preparing the cross-linked rubber blends, cross-linking reaction seemed to occur independently in each rubber phase. The birefringence linearly increased with the blend ratio in the range of IR/SBR = 100/0 to 40/60 and then largely increased in IR/SBR < 30/70. Stress relaxation of rubber blends was observed at 373 K in both air and nitrogen. Chemical stress relaxation of these systems could be represented by a combination of rate constant of stress relaxation and volume fraction of each cross-linked rubber, that is, the degradation of the networks of cross-linked rubber blends occurred independently in each rubber phase.     

Role of pyrite in formation of hydroxyl radicals in coal: possible implications for human health

Background  

The harmful effects from inhalation of coal dust are well-documented. The prevalence of lung disease varies by mining region and may, in part, be related to regional differences in the bioavailable iron content of the coal. Pyrite (FeS₂), a common inorganic component in coal, has been shown to spontaneously form reactive oxygen species (ROS) (i.e., hydrogen peroxide and hydroxyl radicals) and degrade nucleic acids. This raises the question regarding the potential for similar reactivity from coal that contains pyrite. Experiments were performed to specifically evaluate the role of pyrite in coal dust reactivity. Coal samples containing various amounts of FeS₂ were compared for differences in their generation of ROS and degradation of RNA.     

Characterization of UV curable hybrid hard coating materials prepared by sol-gel method

Using sol-gel method, UV-curable urethane acrylate resin system was hybridized with inorganic silicate network to produce hybrid coating materials with high anti-abrasive property. In preparation of acrylate/SiO₂ hybrid materials, various acrylic reactants with multi-functional groups in addition to urethane acrylate oligomer as the main network former were employed to obtain more densified organic network structure with a high degree of cross-linking. As a silane coupling agent, 3-methacryloxypropyl-trimethoxysilane (MPTMS) was used to promote interfacial attraction between UV-cured organic acrylate resin and inorganic silicate component in the hybrid. The addition of MPTMS offered significant effect on the improvement of phase compatibility between organic and inorganic phases, which resulted in stable and homogeneous morphology with a dispersion of nano-sized fine silica particles. The results of morphological observation, glass transition behavior, and optical transparency for the hybrid gels provided an evidence for the increased interfacial attraction between two phases. From the Taber abrasion test for the hybrid coating films, it was revealed that there existed optimal ranges of inorganic silicate precursor TEOS and silane coupling agent MPTMS contents for the preparation of UV cured acrylate/SiO₂ hybrid with high abrasion resistant property.     

Coating water-swellable polymer latexes by interfacial polymerization

Two techniques of coating water-swellable polymer latexes (hydrogels) with an inorganic or organic layer were developed, based on interfacial polymerization. The hydrogel latexes were prepared by inverse suspension polymerization. The first kind of interfacial polymerization is hydrolysis and polycondensation of tetraethyl orthosilicate (TEOS) or 3-(trimethoxysilyl) propylmethacrylate (TMS-PMA) on the surface of hydrogel latexes. The hydrochloric acid, which is the catalyst for this reaction, was previously loaded into the hydrogel latexes. The HCL-containing hydrogel latexes were then suspended in an organic solution of TEOS or TMS-PMA. The hydrolysis and condensation occur only at the surface of each hydrogel particle and the generated SiO₂ or SiO(PMA) network covers the hydrogel latexes. The second interfacial polymerization is polymerization of methylenedi-p-phenyl diisocyanate (MDI) and triethylene glycol (TEG) on the surface of hydrogel latexes. TEG was deposited on the hydrogel by suspending the hydrogel powder in a tetrahydrofuran (THF) solution of TEG and evaporating the THF. The TEG-deposited hydrogel powder was then suspended in an organic solution containing both MDI and the catalyst dibutyltin dilaurate (DBTL). The MDI and DBTL molecules react with the TEG molecules only at the surface of the hydrogel particles, and the polyurethane P(MDI-TEG) thus formed wraps the particles. Based on these two coating procedures, three kinds of materials were obtained: SiO₂ coated hydrogels, SiO-(PMA) coated hydrogels and P(MDI-TEG) coated hydrogels. Soft polyether brushes were grafted to the SiO-(PAM) coated latexes. The P(MDI-TEG) coated hydrogels were used as reservoirs for β-hydroethyltheophylline (β-HETP), and the release of the latter molecules from the coated hydrogels was investigated. © 1995 John Wiley & Sons, Inc.     

聚乙烯醇/二氧化硅互穿网络膜的研究

采用溶胶凝胶法制备了聚乙烯醇/二氧化硅有机/无机互穿网络结构。扫描电子显微镜(SEM)观察到样品表面光滑,均匀;原子力显微镜(AFM)观察到样品中无机相与有机相呈互穿网络结构,且随无机物的增多两相分布更均匀;元素分析结果为纯PVA中w(O)为38%,随着无机物的增多w(O)逐渐降低为24.9%,是硅羟基与醇羟基之间脱去水,两相之间进行交联的结果;29SiNMR表明随无机物的增多,化学位移Q3的强度有所降低而化学位移Q4值却略有上升,说明硅羟基含量逐渐减少,两相交联程度逐渐增大,与元素分析结果相印证;热重曲线(TG)表明,无机物的加入使PVA的热降解温度由400℃提高到420℃,进一步证明两相之间已形成网状结构。     

Scratch resistance and oxygen barrier properties of acrylate-based hybrid coatings on polycarbonate substrate

Organic/inorganic hybrid coating materials were synthesized using acrylate end-capped polyester, 1,6-hexanediolacrylate, tetraethoxysilane (TEOS), and 3-trimethoxysilylpropylmethacrylate (TMSPM). The hybrid materials were cast onto a polycarbonate (PC) substrate and cured by UV irradiation to give a hybrid film with covalent linkage between the inorganic and the organic networks. The coating layer was characterized by FT-IR and ²⁹Si-NMR, and pencil hardness and oxygen permeation rate of coated films were investigated. The pencil hardness of all samples examined in this study was higher than 1H, whereas that of uncoated PC substrate was 6B. The hardness enhancement after coating may due to incorporation of organic acrylate resin. The oxygen permeability coefficient of the film coated with hybrid material on 3-aminopropyltriethoxysilane (APTEOS) pretreated polycarbonate substrate was 1.67×10⁻³ GPU, the lowest value in this work, whereas that of uncoated PC substrate was 8.07×10⁻³ GPU. The lower oxygen permeation rates of these films are attributed to the good adhesion between organic/inorganic hybrid coating layer and PC substrate and a dense structure induced by an increase of network density.     

Synthesis and characterization of organically modified attapulgite/polyurethane nanocomposites

Polyurethane (PU) nanocomposites filled with attapulgite (ATT) nanorods were synthesized and characterized with thermal analysis, dynamic mechanical analysis (DMA), and mechanical testing. The formulations were based on 4,4′‐methylene bis(phenyl isocyanate) (MDI), polytetrahydrofuran, 1,4‐butanediol, and inorganic ATT premodified with MDI. The original and premodified ATT (ATT–OH and ATT–MDI) nanorods were characterized with thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The analysis revealed that 17 wt % MDI was grafted/adsorbed onto the surface of ATT as a result of the modification. Pristine PU and ATT–MDI/PU nanocomposites were characterized with scanning electron microscopy, differential scanning calorimetry, and TGA. The mechanical tests and DMA showed an increase in the storage modulus and Young's modulus with increasing ATT–MDI content. The crystallinity of the hard and soft segments and thermal stability showed enhancements over those of the neat resin. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008