Effect of NCO/OH ratio and Ce‐Zr nanoparticles on the thermo‐mechanical properties of hyperbranched polyurethane urea coatings

The present study describes the effect of NCO/OH ratio and addition of Cerium (Ce)‐Zirconium (Zr) mixed oxide nanoparticles on the properties of Hyperbranched Polyurethane Urea (HBPUU) Coatings. Initially a hydroxyl terminated hyperbranched polymer (HTBP) was synthesized through A₃ + CB₂ approach. The HTBP and Ce‐Zr nanopowder dispersed HTBP, both were reacted with hexamethylene diisocyanate (HDI) separately; at various NCO/OH eq. ratios to get different NCO terminated HBPU and HBPU/Ce‐Zr hybrid prepolymers. These prepolymers were used for the preparation of HBPUU and HBPUU/Ce‐Zr hybrid coating films through moisture curing. The techniques such as ¹H NMR, ¹³C NMR, FT‐IR, and XRD have been used for structural information while Dynamic mechanical and thermal analyzer (DMTA), Thermogravimetric analysis (TGA) and Universal testing machine (UTM) have been used for evaluation of thermo‐mechanical properties. The combined spectroscopic investigations results indicate the formation of HBPUU network with a degree of branching of 76% while FT‐IR deconvolution results indicates the formation of more hydrogen bonded structure with increasing NCO/OH ratio. The XRD and FT‐IR studies confirm the presence of Ce‐Zr mixed nanoparticles in the HBPUU hybrids. As per TGA and DMTA analysis the thermal stability, char residue, storage modulus (E', material stiffness) and glass transition temperature (T_g), increases with increasing NCO/OH ratio and Ce‐Zr nanoparticle loading in HBPUU coatings. In general, UTM data suggest that the tensile strength increases and per cent elongation at break decreases with increasing the NCO/OH ratio and addition level of nanoparticles in HBPUU coatings. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and characterization of hyperbranched polyesters and polyurethane coatings

Polyurethane (PU) coatings are widely used for variety of high‐performance applications in today's coating technology. The emerging hyperbranched polymers having three‐dimensional morphology have opened a new avenue to tailor the architecture of PU coatings. The methodology followed here is based on preparation of PU coatings from hyperbranched polyester. Initially, different hyperbranched polyester polyols (HPs) were synthesized by varying the hydroxyl‐terminated precursors that is, pentaerythritol, trimethylol propane or glycerol and keeping the diacid that is, adipic acid quantity constant at various mole ratios of 1:0.6, 1:0.8, 1:0.9, and 1:1, respectively. The obtained HPs were characterized by nuclear magnetic resonance (NMR) spectroscopy, matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF)‐mass spectrometry, and Fourier transform‐infrared (FTIR) spectroscopy. The degree of branching and the quantity of different structural units present in the various HPs were calculated by integrating the quaternary carbon and carbonyl zone in ¹³C NMR spectroscopy. The extent of condensation in different HPs was also calculated from ¹H NMR spectra. Later on, NCO‐terminated PU prepolymers (NCO‐PU) were synthesized by reacting HPs with isophorone diisocyanate (IPDI) at NCO/OH ratio of 1.6:1. In the third step, the excess NCO content in the NCO‐capped PU prepolymers were reacted with atmospheric moisture and hyperbranched polyurethane (HPU) coatings were formed. The coating films were analyzed by FTIR and dynamic mechanical thermal analysis instruments. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2673–2688, 2007     

Thermal degradation of aliphatic hyperbranched polyesters and their derivatives

In this study results of thermal degradation of aliphatic hyperbranched polyesters, AHBP, and their derivatives, determined by non-isothermal thermogravimetric analysis in inert atmosphere (N₂) are presented. The thermal stability of linear polyester PHPA (polyhydroxypivalic acid), additionally synthesized from hydroxypivalic acid, was also studied. AHBP samples, from second to tenth pseudo-generation, were synthesized starting from 2,2-bis(hydroxymethyl)propionic acid and di-trimethylolpropane. Modification of some selected AHBP samples was accomplished with the propionyl and benzoyl chloride, as well as with stearic acid. Thermal degradation of AHBP samples starts in the region between 250 °C and 275 °C and it ends around 430 °C. The thermal stability of AHBP samples increases with the number of end groups in the macromolecule, as well as with the modification of end groups with stearic acid and propionyl chloride. An AHBP sample of the fourth pseudo-generation, where all -OH end groups are modified with benzoyl chloride, shows lower thermal stability than the corresponding unmodified sample. The thermal stability of the linear polyester PHPA is lower than the thermal stability of the AHBP samples of the similar molar mass. The activation energies of thermal degradation for all synthesized AHBP samples were also calculated.     

Thermal and viscoelastic properties of polyurethane-imide/clay hybrid coatings

This paper reports the synthesis and characterization of polyurethane (PU)-imide/clay hybrid coatings based on two types of polyester (PE) polyols (PE-1 and PE-2). PE-1 was prepared from neopentyl glycol (NPG), adipic acid (AA) and isophathalic acid (IPA), whereas PE-2 contains NPG, AA, IPA and TMP (trimethylol propane) with the same hydroxyl value 280 as PE-1. Cetyl trimethyl ammonium bromide (CTAB) modified montmorillonite (K10) was used as the organoclay for the synthesis of the hybrid coatings. The organoclay particles (3 wt%) were well-dispersed into the PE matrix by ultrasonication method. Then the isocyanate terminated PU prepolymers were synthesized by the reaction of polyester polyols with hard segments such as 2,4-toluene diisocyanate (TDI) or isophorone diisocyanate (IPDI) in different NCO/OH ratios e.g., 1.6:1, 2:1 and 3:1, respectively. Finally the thermally stable imide rings were incorporated into the PU backbone by complete reaction of excess NCO content present in the PU prepolymer with pyromellitic dianhydride (PMDA). The thermogravimetric analysis (TGA) shows a higher thermal stability for the PU-imide hybrid coatings with respect to the corresponding PU-imide films. A higher NCO/OH ratio has resulted in higher thermal stability. The activation energies of degradation were calculated by the Broido and Coats-Redfern methods, respectively. The dynamic mechanical thermal analysis (DMTA) results show an enhancement in the glass transition temperature value (T_g) for the clay containing hybrid coatings. The surface analysis by angle resolved X-ray photoelectron spectroscopy (AR-XPS) showed an enrichment of the soft segment towards the surface, and an enhancement in the hard segment composition in the hybrid coatings, resulted in phase mixing.     

A novel hyperbranched copolymer constituted of triphenylamine and divinyl bipyridyl units

A hyperbranched copolymer (HTP) containing triphenylamine and divinyl bipyridyl units has been synthesized via Heck coupling reaction from 5,5′-divinyl-2,2′-bipyridyl and tris(4-bromophenyl)amine. The polymer had a number-average molecular weight of 1895 and a weight-average molecular weight of 2315, and was readily soluble in common organic solvents, such as THF, DMF and chloroform. The chemical structure of HTP was confirmed by FT-IR, ¹H NMR. Its thermal, electrochemical and optical properties have been investigated. The thermal analysis revealed that the polymer had a good thermal stability with the onset decomposition temperature at ca. 267 °C. The Uv-vis absorption and photoluminescence (PL) spectra exhibited that the Stokes shift between the absorption and emission of HTP was relatively large: 103 for HTP solution and 135 nm for HTP film. The electrochemical analysis showed that the electrochemical band gap of HTP was 0.92 eV. The fluorescence of the polymer in solution can be quenched by various transition metal ions and HTP showed different sensitivity in transition metal ions sensing.     

Synthesis and characterization of novel polyamides from new aromatic phosphonate diamine monomer

New aliphatic-aromatic and fully aromatic phosphonate polyamides were prepared by polycondensation reaction of our synthesized aromatic diamine: tetraethyl[(2,5-diamino-3,6-dimethylbenzene-1,4-diyl)dimethanediyl]bis(phosphonate) with the specific di-acylchloride (adipoyl chloride, isophthaloyl chloride and terephthaloyl chloride). The chemical structure of all samples were characterized by (¹H and ³¹P) NMR, MALDI-TOF MS, FT-IR tools, whereas their thermal properties were determined by DSC and TGA techniques. The phosponate polyadipamide (referred as PAP) is a semi-crystalline sample with a melting temperature at about 261 °C and glass transition (T_g) of 71 °C. All polymers show two thermal degradation steps in the temperature range 270-550 °C. Each polymer, independently its structure, shows the first maximum rate of thermal decomposition temperature (PDT) around 300-310 °C, which may be due to thermal degradation of phoshonate groups. MALDI-TOF spectra, beside the linear oligomers terminated with the specific groups expected in accord to the synthesis procedure, reveals the presence of cyclic oligomers in the polyadipamide and polyisophthalamide samples.     

Synthesis, characterization and mechanical properties of polyester-based aliphatic polyurethane elastomers containing hyperbranched polyester segments

Aliphatic polyester-based polyurethane (PU) elastomers with hyperbranched polyester segments were synthesized from polyester diol, hydroxyl-terminated hyperbranched polyester (HB-20), isophorone diisocyanate (PDI) and 1,4-butanediol. The crosslinking density of the PU elastomer was calculated by using Flory-Rehner equation. The degree of hydrogen bonding, the microstructure and the morphologies of these PU materials were characterized by means of FT-IR, WAXD and DSC, respectively. The experimental results showed that the PU elastomers containing small amount of HB-20 exhibited the enhanced hydrogen bonding and mechanical properties. As compared with the comparable PU specimen, the tensile strength of the polyester-based aliphatic PU containing 6 wt% HB-20 increased by 71.2 times, up to 36.1 MPa, and the elongation at break was still as high as 333.1%, resulting from the dual effects of the hydrogen bonding and the crosslinking density in the PU system.     

Synthesis of novel low-viscosity liquid epoxidized aromatic hyperbranched polymers

Low-viscosity liquid epoxidized aromatic hyperbranched polymers are synthesized by the reaction between epichlorohydrin (ECH) and carboxy-end hyperbranched polymers prepared from low-cost products trimellitic anhydride (B₃ TMA) and dihydroxy alcohols (A₂). The low-viscosity property, especially the lowest viscosity of epoxidized aromatic hyperbranched polymers is only 350 cp which has not reported among epoxidized aromatic hyperbranched polymers before, make them can be used to coatings and adhesion fields without organic solvent hopefully. The properties of the epoxidized aromatic hyperbranched polymers are measured by GPC, FT-IR and viscometer.     

Synthesis, characterization and biodegradable studies of 1,3-propanediol based polyesters

A series of biodegradable polyesters were synthesized from dicarboxylic acids and 1,3-propanediol catalyzed by transestrification polycondensation reaction in the bulk. The structure, average molecular weights and physical properties of the resulting aliphatic polyesters were characterized by ¹H NMR, FT-IR, solution viscosity, GPC, DSC and TGA. Homopolyesters show higher degree of crystallinity, melting and thermal stability in comparison to copolyesters. The biodegradability of the polyesters was determined by monitoring the normalized weight loss of polyester films with time in phosphate buffer (pH 7.2) without and with Rhizopus delemar lipase at 37 °C. The rate of enzymatic degradation of homopolyesters follows the path PPSu > PPAd > PPSe. PPSe did not show significant weight loss in presence of enzyme which may be due to its highest degree of crystallinity and melting point compared to the PPSu, PPAd and copolyesters. In the soil burial degradation polyester sample showed severe surface degradation by the attack of microorganism.     

s-Triazine containing flame retardant hyperbranched polyamines: Synthesis, characterization and properties evaluation

A s-triazine containing hyperbranched polyamine (HBPA) has been synthesized from cyanuric chloride and aromatic diamine, 4,4′-(1,4-phenylenediisopropylidene) bis-aniline by nucleophilic displacement polymerization technique using an A₂ + B₃ approach with high yield (>80%). The synthesized polymer has been characterized by ¹H NMR, ¹³C NMR, FT-IR spectroscopic studies, elemental analysis, solubility and measurement of solution viscosity. The thermogravimetric (TG) analysis and differential scanning calorimetric (DSC) studies indicate that the polymer is thermostable upto 290 °C without any decomposition and has glass transition temperature of 243 °C. The flame retardancy of the pure powder polymer and the blends with linear commercial polymers such as plasticized PVC and LDPE with this hyperbranched polymer were investigated by the measurement of limiting oxygen index (LOI) value. The results show that the polymer has self-extinguishing characteristic (LOI = 38) and acts as an effective flame retardant additive for the above linear base polymers. The synergistic effect of this hyperbranched flame retardant was observed with triphenyl phosphine oxide in the same base polymers. The flammability efficiency of the hyperbranched polyamine is also evaluated by help of thermogravimetric (TG) analysis. The heat aging and leaching in different chemical media did not influence the flame retardancy of the blends.     

Novel blue light-emitting hyperbranched polyfluorenes incorporating carbazole kinked structure

A novel series of soluble hyperbranched polyfluorenes P1−P6 with various branching degrees and contents of kinked carbazole units were successfully synthesized with good yields and high molecular weight via a facile “A2 + B2 + C3 + D2” approach. The thermal, optical, and electrochemical properties as well as thermal spectral stability of the resulting hypberbranched polymers were investigated. All polymers exhibited good thermal stabilities and bright blue emission in both solutions and solid-states. Hyperbranched polyfluorenes (P3 and P6) exhibited improved spectral stability upon annealing at 200 °C in air, in sharp contrast to the linear poly(9,9-dihexylfluorene) (PDHF) that showed significant additional green emission at ca. 530 nm within minutes. In particular, outstanding spectral stability was observed with carbazole-incorporating hyperbranched polyfluorene P6. Electrochemical characterization indicated that the presence of carbazole also effectively raised the HOMO level with respect to that of polyfluorene homopolymer, suggesting better hole-injection properties. Hence, the incorporation of kinked carbazole unit into hyperbranched polyfluorenes could provide a new methodology for preparing blue light-emitting polymers with improved optoelectronic characteristics.     

Second-order nonlinear optical hyperbranched polymers via facile ring-opening addition reaction of azetidine-2,4-dione

A new hyperbranched polymeric structure was chosen as a nonlinear optical material. First, a difunctional chromophore, 4-(4′-nitrophenyl-diazenyl) phenyl-1,3-diamine (NDPD) was synthesized, which was then reacted with 4-isocyanato-4′(3,3-dimethyl-2,4-dioxo-azetidino)diphenylmethane (MIA) to form NDPDMIA (A₂ type monomer). The azetidin-2,4-dione functional groups exhibit selective reactivity, which can react only with primary amines under mild conditions. The hyperbranched polymers were synthesized via ring-opening addition reaction between azetidine-2,4-dione (A₂ type monomer) and primary amine (B₃ type monomer). This synthetic scheme comes with easy purification, high yield and rapid synthesis. Chemical structures of the hyperbranched polymers were characterized by FT-IR, ¹H NMR, and elemental analysis. The inherent viscosity of hyperbranched polymers in DMSO ranged from 0.15 to 0.22 dLg⁻¹. All of the obtained polymers were soluble in DMF, DMAc, and DMSO. Using in situ contact poling, r₃₃ coefficients of 6-16 pm/V and their temporal stability at 60 °C were obtained. Optical loss measurement was also achieved by a prism coupling setup.     

Preparation of PbO nanocrystals via decomposition of lead oxalate

The present study reports the preparation and characterization of PbO nanocrystals obtained via a thermal decomposition route. The PbO nanocrystals were synthesized using lead oxalate powder as a precursor. Nanostructured products were investigated by means of XRD, TEM, FT-IR and XPS. The XRD results indicate that tetragonal phase β-PbO with a particle size of about 30–45 nm was obtained when the intermediate precipitate was calcined at 500 °C.     

Synthesis and characterization of new cardo poly(bisbenzothiazole)s containing cyclohexylidene units

A new diaminobenzenethiol 1,1-bis(4-amino-3-mercaptophenyl) cyclohexane dihydrochloride (BAMPCH · 2HCl) containing the bulky pendant cyclohexylidene group was synthesized from cyclohexanone in three steps. Its chemical structure was characterized by ¹H NMR, ¹³C NMR, MS, FT-IR and EA. Aromatic poly(bisbenzothiazole)s (PBTs) were prepared from the new monomer and five aromatic dicarboxylic acids by direct polycondensation. The inherent viscosities were in the range of 0.78-2.04 dL/g. These polymers exhibited good solubility and thermal stability. Most of the prepared PBTs were soluble in various polar solvents. The decomposition temperatures at 10% weight loss were in the range of 482-518 °C in nitrogen. X-ray diffractograms of PBTs showed that all polymers were amorphous.     

Investigations on anticorrosive,thermal, and mechanical properties of conducting polyurethanes with tetraaniline pendent groups

This article describes the synthesis of conducting hybrid polyurethanes from novel tetraaniline‐diol as Gly‐TAni (glycidol with TAni). A new diol Gly‐TAni has been synthesized in a simple process using tetraaniline (TAni) and glycidol via SN2 reaction in a single‐step process. The asymmetric diol (Gly‐TAni) and polyols (PTMEG and TMP) were reacted with isophorone diisocyanate at OH:NCO ratio of 1:1.2 to obtain ―NCO terminated hybrid conducting polyurethanes. These were subjected for curing under atmospheric moisture to obtain conducting polyurethane‐urea coatings. The conducting coatings showed considerable enhancement in thermal and mechanical stabilities. All these conducting coatings films showed excellent corrosion resistance (on mild steel electrode) with an increase in the percentage of Gly‐TANi (5 to 15 wt%). The films of these hybrid polyurethanes containing pendent tetraanilines showed good surface conductivity in the range of 3.69 × 10⁻⁴ to 2.21 × 10⁻³ S/cm. The electrochemical investigation showed 2 single electron oxidation and 2 single reductions reversibly, centred around tetraaniline segments present in the polymer.     

Microwave-treated layered double hydroxides containing Ni and Al: The effect of added Zn

Ni containing layered double hydroxides (LDHs) have been prepared by precipitation and hydrothermally treated under microwave irradiation for different periods of time. The solids have been calcined at three temperatures corresponding to stable phases formed during thermal decomposition of LDHs. The properties of the irradiated samples and of the calcined products were studied in order to ascertain whether the ageing treatment under microwave irradiation modifies not only the properties of the layered materials, but also the properties of the calcined products. A structural and textural study was carried out by PXRD, FT-IR and Vis-UV spectroscopy, thermal analyses (DTA and TG), N₂ adsorption/desorption at −196 °C and TEM microscopy; the reducibility of the nickel species was studied as well by TPR. The results show that the microwave treatment leads to better crystallized LDHs with modified thermal stability and reducibility. In addition, the degree of crystallinity of the layered precursors and their textural properties determine the properties of their thermal decomposition products.     

Investigation of thermal,mechanical, and electrical properties of novel polyurethanes/high molecular weight polybenzoxazine blends

In order to prepare tough polyurethane (PU) electrical insulator with improved thermal stability and electrical insulating properties, high molecular weight polybenzoxazine precursor was mixed and co‐cured with crosslinkable urethane prepolymers. Polybenzoxazine precursor (Bmda) was synthesized from reaction of bisphenol‐A, methylenedianiline, and paraformaldehyde. Epoxy‐terminated polyurethanes (EPU1‐4) were prepared by the reaction of glycidol with NCO‐terminated urethane oligomers. The oligomers were prepared from different molecular weight versions of polycaprolactone polyol (CAPA) and hexamethylene diisocyanate. Blends were prepared through thermal treatment of equal weights of two precursors dissolved in chloroform. Optimum curing condition was determined by DSC and DMTA analysis and measurement of the gel content for cured samples. Viscoelastic, thermal, mechanical, and electrical properties of cured samples were investigated and structure–property relationship was established. Copyright © 2008 John Wiley & Sons, Ltd.     

Poly(ε-caprolactone) + unsaturated isophtalic polyester blends: Thermal properties and morphology

Miscibility of blends composed by a linear unsaturated polyester (LUP) with poly(ε-caprolactone) (PCL) of different molecular weights (M_w = 50 × 10³, 18 × 10³ and 2 × 10³) has been studied. The blends were subjected to different thermal treatments and have been studied by FT-IR spectroscopy, differential scanning calorimetry (DSC) and scanning electronic microscopy (ESEM). FT-IR results allow proving the miscibility of the blends at temperatures above the melting temperature of neat PCL. DSC measurements confirm the existence of a crystalline phase corresponding to neat PCL. The crystallization of PCL is observed in a wide range of blends composition, being detected in all the blend compositions when the crystallization time increases. Thermograms show clearly the glass transition temperatures of samples that have been rapidly quenched from the melt. However, the change in the heat flow corresponding to the glass transition temperatures is difficult to detect in samples with high PCL crystallization degree. The analysis of the results indicates that the morphology of the amorphous phase is heterogeneous for LUP + PCL blends and changes depending on the thermal treatment. The ESEM measurements, confirm the heterogeneity of the amorphous phase. The decrease of the molecular weight of the PCL favours the miscibility of the blends.     

Characterization of CoMCM-41 mesoporous molecular sieves obtained by the microwave irradiation method

CoMCM-41 mesoporous molecular sieves with different amounts of cobalt were synthesized via the microwave irradiation method. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), temperature programmed reduction (TPR), transmission electron microscopy (TEM) and N₂ adsorption-desorption technique, and thermal and hydrothermal stabilities of synthesized CoMCM-41 samples were also investigated. Results show that these synthesized materials have typical mesoporous structure of MCM-41. Also, specific surface area and pore volume of synthesized CoMCM-41 decrease with increasing amount of cobalt added, and mesoporous ordering also decreases. When the molar ratio of SiO₂:CoO in the starting material is 1.0:0.05, mesoporous ordering of synthesized CoMCM-41 is the best among the four doping contents. On the other hand, results of thermal and hydrothermal tests show that CoMCM-41 after calcination at 750 °C for 3 h or hydrothermal treatment at 100 °C for 5 days still retains mesostructure. However, mesoporous framework is entirely damaged after calcination at 850 °C for 3 h.     

Thermal behaviour of mechanochemically synthesized nanocrystalline CuS

Thermal behaviour of mechanochemically synthesized nanocrystalline CuS particles by high-energy milling in an industrial mill has been studied. Structure properties were characterized by X-ray powder diffraction that reveals the formation of copper sulphide CuS as well as of copper sulphate CuSO₄·5H₂O. Thermal properties of the as-prepared products were studied by the differential scanning calorimetry together with X-ray inspection for detection by pass products formed. The decomposition of the as-prepared sample has been studied too. Thermal stability of the anhydrous CuSO₄ formed by the thermal decomposition is lower than the thermal stability of non-milled samples. The final product of the thermal decomposition is metallic copper instead of Cu₂O, which is stable up to 1100 °C. Differential scanning calorimetry (DSC) analysis proved that the percentage of chalcantite in the covellite mechanochemically synthesized by high-energy milling is 48-51%.