Polyurethanes from Alcell lignin fractions obtained by sequential solvent extraction

Lignin-derived polyurethane films were synthesized by solution casting using three fractions of distinct molecular weight and chemical functionality from Alcell^® lignin. A three-component system of lignin fraction, polyethylene glycol (PEG) of MW = 400 g mol⁻¹ and polymeric methyl-diisocyanate (MDI) was used. For each lignin fraction, the effects of varying the

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ratio and lignin content on the crosslink density, ultimate tensile properties and dielectric strength of the polyurethanes were studied. The crosslink density was found to increase with molecular weight of lignin. Strong polyurethanes were produced with the high molecular weight fraction of Alcell^® lignin, but the polyurethanes from the medium molecular weight fraction appeared to be tougher and more flexible. For both the medium and high molecular weight fractions of Alcell^® lignin used, polyurethanes produced with lignin contents above 35 wt% were found to be too brittle and glassy to be tested. A maximum of 18 wt% of the low molecular weight lignin fraction could be used to prepare polyurethanes. Any higher compositions attempted produced polyurethanes which were too brittle to be tested. For all three fractions, the dielectric constant of the polyurethanes, decreased with increasing lignin content or

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ratio.     

Organic–inorganic hybrid coatings prepared from glycidyl carbamate resins and amino-functional silanes

Organic–inorganic hybrid coatings were prepared from glycidyl carbamate (GC) functional oligomers and different amino-functional trimethoxysilanes via a systematic three-step reaction process. Initially, glycidyl carbamate functional oligomers isocyanurate glycidyl carbamate (IGC) and biuret glycidyl carbamate (BGC) were synthesized from the reaction of the polyisocyanurate of hexamethylene diisocyanate (HDT) with glycidol and the biuret adduct of hexamethylene diisocyanate (HDB) with glycidol, respectively. Then, the GC resins were mixed with 3-aminopropyl trimethoxysilane (APTMES), N-(2-aminoethyl) 3-aminopropyl trimethoxysilane (AEAPTMES) and p-aminocyclohexyl methane (PACM) at different stoichiometric ratios. In order to form the hybrid organic–inorganic networks, the materials were cured either at room temperature and humidity for more than 20 days or with an additional heat treatment at 80 °C for 1 h and then keeping the coatings at room temperature and humidity for more than 10 days. The observable change in the structure during network formation was monitored by FTIR spectroscopy. The cured coatings were characterized by thermogravimetric (TGA) and differential scanning calorimetry (DSC). Atomic force microscopy (AFM) was used to characterize the surface properties of the hybrid systems. AFM observation suggests the phase separation behavior. Coating properties such as König pendulum hardness, crosshatch adhesion, MEK double rub resistance and water contact angle of the coatings were also evaluated. Finally, structure–property relationships are given based on the variable parameters used.     

2,2,6,6-四甲基哌啶-1-氧自由基对低温等离子辐射聚氨酯膜表面过氧自由基的研究

采用2,2,6,6-四甲基哌啶-1-氧自由基(2,2,6,6-Tetramethyl-1-piperidinyloxyl radical,TEMPO)法,测定了经氧气低温等离子体处理后聚氨酯膜表面过氧自由基的浓度,探讨了等离子轰击时间、等离子放电功率、在空气中放置时间等因素对等离子体处理后自由基浓度的影响.在经测定获得的自由基浓度较高的条件下,引发聚氨酯与丙烯酸的接枝聚合,验证了TEMPO法的可行性,讨论了聚合时间对接枝率的影响.丙烯酸在聚氨酯膜表面的接枝共聚由扫描电子显微镜得到确认.在等离子放电功率为600W,放电时间为180s时所测定的自由基浓度最高,相应的接枝率较高.实验结果表明,TEMPO法是一种有效的测定自由基浓度的方法.     

Permeable domains of segmented polyurethanes studied with paramagnetic spin probe

Studies on the permeable regions of the dense polyurethane-based membranes were performed by electron spin resonance spectroscopy (ESR) using TEMPO spin probe incorporated into the membrane via diffusion from the vapour phase. The ESR spectra were measured as a function of temperature and microwave power for polyurethanes (PU) varying in the molecular structure and morphology. It was found that the TEMPO spin probe exhibited anisotropic rotation whose anisotropy increased as temperature decreased and was more pronounced for PU with shorter soft segments. The simplified method was used to obtain apparent correlation time τ_c enabling the comparison of the polyurethanes studied. This approach was based on the Arrhenius relation of τ_c vs. 1/T determined from motionally narrowed ESR spectra and on the assumption that this behaviour prevails over a broader temperature range at temperatures generally greater than T_g of a given polymer.     

Silicone-acrylic hybrid aqueous dispersions of core–shell particle structure and corresponding silicone-acrylic nanopowders designed for modification of powder coatings and plastics. Part III: Effect of modification with selected silicone-acrylic nanopowders on properties of polyurethane powder coatings

Polyurethane powder coating systems consisting of polyester resin, blocked polyisocyanate and two types of “nanopowders” containing core–shell nanoparticles where the core was silicone resin of very low glass transition temperature and the shell was poly(methyl methacrylate) were examined. The blocked polyisocyanate was synthesized using biuretpolyisocyanate obtained from ureapolyisocyanate as starting material capable for blocking and ɛ-caprolactam as blocking agent. The surface properties of cured powder coatings were investigated using scanning electron microscopy (SEM) combined with energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The surface structure was correlated with the chemical structure of the coatings and macroscopic surface behavior: contact angle, surface free energy, gloss, abrasion resistance, hardness and adhesion to the steel surface.     

PREPARATION AND CHARACTERIZATION OF WATERBORNE POLYURETHANES MODIFIED WITH BIS(3-(1-METHOXY-2-HYDROXY-PROPOXY)PROPYL) TERMINATED POLYSILOXANES

Polyurethanes (PU) were prepared using toluene diisocyanate, polypropylene glycol, ethylene glycol,dimethylolpropionic acid and triethylamine, and a siloxane modified PU (PSU) was obtained through reaction of the PU prepolymers with bis(3-(1-methoxy-2-hydroxypropoxy)propyl) terminated polysiloxanes (PMTS) of different molecular weight, specifically designed for this purpose. Results showed that, with increases in molecular weight of PMTS and its content, viscosity of the final PSU latexes decreased; phase separation of the incorporated PMTS in PSU films increased; the average particle sizes of the latexes varied between 110 nm and 330 nm, and the surface tension in the final latexes was relatively constant regardless of PMTS amount and its molecular weight. It was likely that copolymerized polysiloxanes had trend to enrich on top of the film when PMTS molecular weight was around 2000 and its content above 5 wt%. In general,PMTS modified polyurethane films showed higher performance than those from unmodified waterborne polyurethane latexes.     

Temperature dependence of molecular motions in the polyurethane-based membranes studied with paramagnetic spin probe

This third paper in this series regarding structure and dynamics of the polyurethane-based membranes studied with TEMPO spin probe presents the results of the ESR measurements performed to characterise mobility of segments in the permeable regions of the membranes. The variations of the spin probe motions with temperature have been analysed for the series of polyurethanes (PU) differing in molecular structure and compared with the results of the DSC studies. Along with T_50 G, the other temperatures, T_n, T_i, T_τ, at which the significant change in dynamics occurs have been determined and correlated with the length of the PU soft and hard segments, and then discussed with regard to the respective relationships of T_g. The results have demonstrated the sensitivity of the ESR method to the segmental motions, which have not been detected by the DSC technique. From the DSC and ESR data the size of the motional chain segment in various PUs has been estimated, which has been found to follow the trend that polymers with higher T_g have bulkier segments. Two unusual observations have been made, concerning the deviation from the Arrhenius relation at high temperature for some PUs, and the increased mobility of the TEMPO molecules in some poly(urethane-urea)s after their thermal treatment. These results have been interpreted so far either in terms of the possible translational diffusion of the TEMPO molecules for those PUs showing lesser amount of the hard segments, or in terms of the increased free volume resulting from the temperature induced structural changes within the permeable regions of poly(urethane-urea)s.     

Electrochemical properties and characterisation of novel polyurethane/polyindene,poly(ethylene terephthalate)/polyindene and poly(vinyl chloride)/polyindene conducting composites

Abstract

This study covers the synthesis of conducting polyindene (PIn) homopolymer, polyurethane/polyindene (PU/PIn), poly(ethylene terephthalate)/polyindene (PET/PIn) and poly(vinyl chloride)/polyindene (PVC/PIn) composites. Polyindene and composites were synthesised electrochemically by cationic mechanism using LiClO₄ as an initiator. From Fourier transform infrared spectroscopy spectra of polymers, it was revealed that the polymerisation reaction occurred by one to two mechanisms. The conductivities of polymers were also measured by four-probe technique, and it was found that PIn had the highest conductivity with 7·86×10^?4 S cm^?1 among the homopolymer and composites;the conductivity values of PU/PIn, PET/PIn and PVC/PIn composites were 4·23×10^?5, 4·34×10^?5 and 3·87×10^?5 S cm^?1 respectively. Magnetic properties of the polymers were analysed by Gouy scale measurements, and it was found that their conducting mechanisms are of polaron and bipolaron natures. Thermal stability of polymers was investigated by thermogravimetric analysis, and the initial degradation temperatures were found to be 271, 420, 390 and 465°C for PIn, PU/PIn, PET/PIn and PVC/PIn respectively. Scanning electron microscopy was used for microstructural analysis, and when the morphologies of PET/PIn, PVC/PIn composites and PIn, PU/PIn were compared, it was observed that PET/PIn and PVC/PIn composites have smoother layers and are more compact than PIn and PU/PIn composite. X-ray diffraction spectra showed that the crystallisation degree of PET and PVC increased after polymerisation of PIn; degrees of crystallinity of PIn, PU/PIn, PET/PIn and PVC/PIn were obtained as 14·6, 18·8, 19·3 and 20·2% respectively.     

UV curable glycidyl carbamate based resins

The synthesis and characterization of UV curable resins based on glycidyl carbamate chemistry have been explored. Glycidyl carbamate (GC) functional resins have been used to obtain crosslinked coatings with a wide range of properties using several crosslinking techniques such as epoxy-amine, self-crosslinking, and sol-gel. GC resin technology was further expanded to UV curable coatings by reacting polyfunctional GC resins with acrylic acid to yield acrylated glycidyl carbamate (AGC) resins. Alcohol-modified UV curable GC resins were also prepared to obtain lower viscosity. Commonly used reactive diluents were used to prepare a UV curable GC coating formulations. The coatings were cured in air using a Fusion LC6B Benchtop Conveyer with an F300 UV lamp. The degree of conversion of acrylic double bonds during UV curing was determined using real time FTIR and showed that the resins had fast cure rates and high extents of conversion of acrylate groups. Coating properties such as hardness, impact strength, methyl ethyl ketone double rubs, flexibility, and adhesion were studied. Dynamic mechanical analysis was used to determine crosslink density of the coatings. Differential scanning calorimetry and thermogravimetric analysis were used to study the thermal properties of the coatings. The type of polyisocyanates and the extent of modification in GC resins influenced the degree of conversion, crosslink density, and coating performance.     

Microstructural organization of polydimethylsiloxane soft segment polyurethanes derived from a single macrodiol

Segmented polyurethane (PU) block copolymers were synthesized using 4,4′-methylenediphenyl diisocyanate and 1,4-butanediol as hard segments and oligomeric ethoxypropyl polydimethylsiloxane (PDMS) as the soft segments, with hard segment contents ranging from 26 to 52 wt%. The microphase separated morphology, phase transitions, and degrees of phase separation of these novel copolymers were investigated using a variety of experimental methods. Like similar copolymers with mixed ethoxypropyl PDMS/poly(hexamethylene oxide) soft segments, PU copolymers containing only ethoxypropyl PDMS soft segments were found to consist of three microphases: a PDMS matrix phase, hard domains, and a mixed phase containing ethoxypropyl end group segments and dissolved short hard segments. Analysis of unlike segment demixing using small-angle X-ray scattering demonstrates that degrees of phase separation increase significantly as copolymer hard segment content increases, in keeping with findings from Fourier transform infrared spectroscopy measurements.