Conclusive chemical deciphering of the consistently occurring double‐peak carbonyl‐stretching FTIR absorbance in polyurethanes

Polyurethanes include an extremely vast and varied family of polymers, exhibiting a vast range of properties and applications. Although the urethane chemical structure consists of a single carbonyl group, the vast majority of polyurethane Fourier transform infrared spectroscopy (FTIR) spectra exhibit two distinct adjacent carbonyl‐stretching absorbances. It was the purpose of the present research to investigate and determine the reason of occurrence of this consistently observed phenomenon. A polyurethane, designed and synthesized here as linear and containing only urethane and methylene groups, strongly exhibited two very distinct carbonyl‐stretching FTIR absorbances. A new polyurethane, exhibiting an extremely high degree of trifunctional crosslinking, was hereby designed and synthesized to sterically inhibit diisocyanate access to already established urethanes and thus inhibit the allophanate and further tertiary oligo‐uret forming side‐reactions. The resulting polymer dramatically exhibited only a single, strong and sharp, carbonyl‐stretching FTIR absorbance belonging only to the urethane group. Synthesis of a polymer exhibiting a lower degree of crosslinking led to the reappearance of the split double carbonyl‐stretching FTIR absorbance. Solid‐state ¹³C NMR measurement results of the same polymers were highly consistent with the FTIR spectroscopy results. The experimental results of the present research conclusively prove and determine the exclusive side‐reaction‐related double carbonyl‐stretching absorbance in the FTIR analysis of polyurethanes. These research results conclusively reveal that, in fact, the so‐called linear polyurethanes synthesized from diisocyanates and diols are branched or even loosely crosslinked.     

Catalysis of poly(urethane imidine) copolymer formation from amine‐blocked isocyanate and bisphthalide

The catalysis of imidine formation between an amine‐blocked polyurethane prepolymer and bisphthalide was studied with a series of metal alkoxides, phenoxides, and organotin compounds and tertiary amines. The carbon dioxide released during the reaction was followed for monitoring of the reaction. The metal alkoxides and phenoxides catalyzed the imidine formation reaction but did not catalyze the deblocking reaction, whereas the organotin compounds and tertiary amines showed no catalytic activity in the reaction between isocyanate and phthalide. With tin catalysts, the imidine formation reaction depended on the deblocking of the blocked prepolymer, but it was independent of deblocking with amine catalysts. The resultant poly(urethane imidine) copolymers were characterized with Fourier transform infrared, ¹H NMR, ¹³C NMR, gel permeation chromatography, and thermogravimetric analysis techniques. The thermal stability of polyurethane increased significantly with the incorporation of imidine groups. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4236–4242, 2001     

Synthesis and characterization of polyurethane–urea nanoparticles containing methylenedi‐p‐phenyl diisocyanate and isophorone diisocyanate

Water‐based polyurethane–urea (WPUU) nanoparticles containing 4,4′‐methylenedi‐p‐phenyl diisocyanate (MDI) and isophorone diisocyanate (IPDI) were synthesized by a stepwise prepolymer mixing process, that is, the consecutive formation of hydroxyl‐terminated and isocyanate‐terminated polyurethane prepolymers. The reaction behavior, chemical structure, and consequent morphology of the polyurethane prepolymers and WPUU were investigated with Fourier transform infrared (FTIR), gel permeation chromatography, and NMR techniques with MDI concentrations ranging from 0 (pure IPDI) to 50% with respect to the total moles of isocyanate. Wide‐angle X‐ray diffraction and differential scanning calorimetry patterns showed that the crystallinity of WPUU, which mostly originated from crystallizable poly(tetramethylene adipate) polyol, was significantly affected by the MDI content. Both the crystallinity and melting temperature of WPUU decreased as the MDI content increased. Deconvoluted relative peak areas of the carbonyl region in the FTIR spectrum revealed that the effect of hydrogen bonding among the hard segments became favorable as the MDI content increased, whereas the hydrogen bonding of the soft segments significantly decreased. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4353–4369, 2004     

Synthesis of NIPU by the carbonation of canola oil using highly efficient 5,10,15‐tris(pentafluorophenyl)corrolato‐manganese(III) complex as novel catalyst

For the green synthesis of polyurethane (PU), non‐isocyanate routes are worthy alternatives. In the present work, we have explored 5,10,15‐tris(pentafluorophenyl)corrolato‐manganese(III) complex as novel catalyst for coupling reaction between epoxidized canola oil and CO₂ (gaseous) to introduce cyclic carbonate moieties in the oil and further used it to obtain non‐isocyanate PU, generally abbreviated as NIPU, by curing with different diamines. The results obtained indicated a 1/4th of the reduction in reaction time with the use of 5,10,15‐tris(pentafluorophenyl)corrolato‐manganese(III) complex as catalyst as compared to the previously reported literature data. As per the reported studies, the corrole metal complex has not been used for this reaction earlier. The structure of products and intermediates were confirmed by using different characterization techniques like ¹H NMR and FTIR spectroscopies. The thermal and mechanical behavior of final product was analyzed by TGA and universal testing machine, respectively. The non‐isocyanate PU obtained showed a good thermal stability up to 200°C and a tensile strength of up to 8 MPa. The effect of structure of diamines on the properties of non‐isocyanate PU was also extensively studied.     

REACTIONS IN SOLID STATE WITHIN POLYURETHANES. KINETICS AND POSTCURE REACTION MECHANISM IN CASTING POLYURETHANE ELASTOMERS

The solid state postcure reaction mechanism of polyurethane elastomers (PU) synthesized using a relatively small excess (up to 10%) of isocyanate was studied. The postcure process succeeds especially with the assistance of atmospheric humidity and, its process velocity depends on PU sample thickness. The polymer network is consolidated mainly by the formation of a new urea group. The formation of allophanate, uretidinedione, and isocyanurate groups and possible reticulations by the intermediary amine groups formed, play only a secondary role in the studied conditions. Kinetic equations regarding the postcure evolution were followed by means of the changes in mechanical properties. The evolution of the process was correlated to different kinetic measurements regarding the elementary processes involved like the consumption of NCO groups, absorption of water from the atmospheric humidity, and desorption of CO₂ resulted during the formation of urea group. The CO₂ desorption appears to be the slowest dynamic process.     

An expedient ‘click’ approach for the synthetic evaluation of ester‐triazole‐tethered organosilica conjugates

The present work articulates the synthesis of a new series of organo‐functionalized triethoxysilanes derived from versatile carboxylic acids and 3‐azidopropyltriethoxysilane in excellent yields. A proficient and convenient route implicating the Cu(I)‐catalysed 1,3‐cycloaddition of organic azide with terminal alkynes, labelled as click silylation, has been developed for the generation of ester‐triazole‐linked alkoxysilanyl scaffolds ( 4a – f ). All the synthesized compounds have been thoroughly characterized using elemental analysis and Fourier transform infrared, ¹H NMR and ¹³C NMR spectroscopic techniques. Importantly, the fabricated alkoxysilanes are potentially amenable for an in situ sol–gel condensation reaction with silica nanospheres leading to the incorporation of organic functionality via covalent grafting onto the nanostructured particle system. As a proof of concept, a one‐pot preparation of organic–inorganic hybrid nanoparticles is presented using bis‐silane 4 f . The efficiency and selectivity of the prepared nanocomposite towards metal ions is highlighted using adsorption experiments, and the immobilized nanoparticles present a high sensing efficiency towards Cu²⁺ and Pb²⁺ ions while demonstrating better response than that of the bulk material.     

Thiol‐isocyanate‐acrylate ternary networks by selective thiol‐click chemistry

Thiol‐isocyanate‐acrylate ternary networks were formed by the combination of thiol‐isocyanate coupling, thiol‐acrylate Michael addition, and acrylate homopolymerization. This hybrid polymerization reaction sequence was preferentially controlled by using phosphine catalyst systems in combination with photolysis. The reaction kinetics of the phosphine/acrylate thiol‐isocyanate coupling reactions were systematically investigated by evaluating model, small molecule reactions. The thiol‐isocyanate reaction was completed within 1 min while the thiol‐acrylate Michael addition reaction required ～10 min. Both thiol‐isocyanate coupling and thiol‐acrylate Michael addition reactions involving two‐step anionic processes were found to be both quantitative and efficient. However, the thiol‐isocyanate coupling reaction was much more rapid than the thiol‐acrylate Michael addition, promoting initial selectivity of the thiol‐isocyanate reaction in a medium containing thiol, isocyanate, and acrylate functional groups. Films were prepared from thiol‐isocyanate‐acrylate ternary mixtures using 2‐acryloyloxyethylisocyanate and di‐, tri‐, and tetra‐functional thiols. The sequential thiol‐isocyanate, thiol‐acrylate, and acrylate homopolymerization reactions were monitored by infrared spectroscopy during film formation, whereas thermal and mechanical properties of the films were evaluated as a function of the chemical composition following polymerization. The results indicate that the network structures and material properties are tunable over a wide range of properties (T_g ～ 14–100 °C, FWHM ～ 8–46 °C), while maintaining nearly quantitative reactions, simply by controlling the component compositions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3255–3264, 2010     

Synthesis and characterization of novel fluorinated polyurethane elastomers based on 2,2‐bis[4‐(4‐amino‐2‐trifluoromehyloxyphenyl) phenyl]propane

2,2‐Bis[4‐(4‐amino‐2‐trifluoromehyloxyphenyl) phenyl]propane (BAFPP) was synthesized based on 2‐chlorobenzotrifluoride and bisphenol A and characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance. BAFPP was used as a chain extender to prepare a series of fluorine‐containing polyurethane elastomers (FPUEs) with different fluorine contents by changing the soft segments and isocyanate index (R). The FPUEs were investigated by water absorption, contact angle, X‐ray photoelectron spectroscopy, thermogravimetric analysis, and microscale combustion calorimetry. The results show that the FPUEs prepared from BAFPP were elastomers that have low surface tension, low water absorption, and good thermal stability. Furthermore, FPUEs also exhibit good flame resistance, and the peak heat release rate of FPUE based on BAFPP (282.9 W/g) is much lower than that of polyurethane elastomer without the F element (537.2 W/g). Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of head‐to‐tail polyurethanes from nonsymmetric diisocyanate and ethylene glycol with organotin catalysts

An ordered head‐to‐tail (HT) polyurethane was successfully prepared by the polyaddition reaction of p‐isocyanatobenzyl isocyanate with ethylene glycol with dibutyltin dilaurate as a catalyst. Furthermore, the HT regularity of polyurethane was improved to 83% with 1,1,3,3‐tetraphenyl‐1,3‐dichlorodistannoxane. The polymerization was conducted in N,N‐dimethylformamide at 30 °C with both monomers mixed at once. The microstructure of the polymer was investigated by ¹H and ¹³C NMR spectroscopy, and the polymer obtained by the polyaddition reaction had the expected HT linkages. The constitutional regularity of the polymers influenced the thermal properties and crystallinity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 416–429, 2001     

Photolysis and Thermolysis of Pyridyl Carbonyl Azide Monolayers on Single‐Crystal Platinum

The photochemical and thermal reactivity of a number of acyl azide‐substituted pyridine compounds, namely nicotinyl azide, isonicotinyl azide, picolinyl azide and dinicotinyl azide with investigated as saturated monolayers on a single‐crystal Pt(111) surface in an ultrahigh vacuum chamber. Multilayers of the substrates exhibited a maximum rate of desorption at 270 K, above which, stable saturated monolayers formed as characterized by reflection‐absorption infrared spectroscopy by observation of C=O and N₃ bands at 1700 cm^?1, and 2100 and 1300 cm^?1 respectively. The monolayers were stable up to 400 K. Photolysis of the monolayer (or heating above 400 K) results in the formation of the respective isocyanate intermediate after loss of nitrogen as evidenced by the appearance of a new infrared band at 2260 cm^?1 with concomitant loss of the azide bands. The resulting isocyanate saturated monolayer is stable in absence of nucleophiles, but can be quenched with appropriate nucleophiles.     

Cyclic poly(ε‐caprolactone) synthesized by combination of ring‐opening polymerization with ring‐closing metathesis,ring closing enyne metathesis,or “click” reaction

This article described the synthesis of cyclic poly(ε‐caprolactone) (PCL) via ring‐closing metathesis (RCM), ring closing enyne metathesis (RCEM), and “click” reaction of different difunctional linear PCL. Linear PCL precursors were prepared by ring‐opening polymerization (ROP) of ε‐caprolactone in bulk using 10‐undecen‐1‐ol or propargyl alcohol as the initiator, followed by reacting with corresponding acyl chloride containing vinyl or azido end group. The subsequent end‐to‐end intramolecular coupling reactions were performed under high dilution conditions. The successful transformation of linear PCL precursor to cyclic PCL was confirmed by Gel permeation chromatography, ¹H NMR, and Fourier transform infrared measurements. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3022–3033, 2009     

Fluoropolyethers end‐capped by polar functional groups. III. Kinetics of the reactions of hydroxy‐terminated fluoropolyethers and model fluorinated alcohols with cyclohexyl isocyanate catalyzed by organotin compounds

The kinetics of the dibutyltin dilaurate (DBTDL)‐catalyzed urethane formation reactions of cyclohexyl isocyanate (CHI) with model monofunctional fluorinated alcohols and fluoropolyether diol Z‐DOL H‐1000 of various molecular weights (100–1084 g mol^?1) in different solvents were studied. IR spectroscopy and chemical titration methods were used for measuring the rate of the total NCO disappearance at 30–60 °C. The effects of the reagents and DBTDL catalyst concentrations, the solvent and hydroxyl‐containing compound nature, and the temperature on the reaction rate and mechanism were investigated. Depending on the initial reagent concentration and solvent, the reactions could be well described by zero‐order, first‐order, second‐order, or more complex equations. The reaction mechanism, including the formation of intermediate ternary or binary complexes of reagents with the tin catalyst, could vary with the concentration and solvent and even during the reaction. The results were treated with a rate expression analogous to those used for enzymatic reactions. Under the explored conditions, the rate of the uncatalyzed reaction of fluorinated alcohols with CHI was negligible. Moreover, there was no allophanate formation, nor were there other side reactions, catalysis by urethane in the absence of DBTDL, or a synergetic effect in the presence of the tin catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3771–3795, 2002     

Side Reactions in the Formation of Polyurethanes: Model Reactions Between Phenylisocyanate and 1-Butanol

The following side reactions occurring in the formation of polyurethanes were modeled: a reaction of excess phenyl isocyanate either with 1-butanol in 1, 4-dioxane and in bulk, or with n-butylphenyl urethane or water in dioxane catalyzed with dibutyltin dilaurate that leads to the formation of n-butyl-α, γ-diphenyl allophanate N, N-diphenylurea, and 1, 3, 5-triphenylbiuret. The reaction products were determined quantitatively by means of liquid chromatography. The rate and equilibrium constants were calculated at various temperatures and various initial ratios of functional groups. Biuret is formed from N, N'-diphenylurea much more quickly than allophanate from urethane, and the equilibrium constant of its formation is also higher.     

Reaction of diisocyanates with alcohols. II. Catalyzed reactions

In a previous work we reported a procedure to calculate rate constants for the primary and secondary reactions (urethane and allophanate formation, respectively) between isocyanate and alcohols. In the present paper the same procedure is applied to the catalyzed reaction, thus defining the selectivity for a series of catalysts.     

Ionic liquid‐functionalized mesoporous silica nanoparticles ([pmim]FeCl4/MSNs): Efficient nanocatalyst for solvent‐free synthesis of N,N′‐diaryl‐substituted formamidines

We report the synthesis of ionic liquid‐functionalized mesoporous silica nanoparticles ([pmim]FeCl₄/MSNs) via a method of post‐grafting on parent MSNs. This hybrid material was characterized using scanning and transmission electron microscopies, energy‐dispersive X‐ray spectroscopy, nitrogen adsorption–desorption analysis, Fourier transform infrared spectroscopy, powder X‐ray diffraction and thermal analyses. The material was utilized as an efficient heterogeneous catalyst for the synthesis of N ,N ′‐diaryl‐substituted formamidines through the reaction of triethyl orthoformate with arylamines under solvent‐free conditions. The catalyst was recovered easily and reused several times without significant loss of its catalytic activity.     

Design,Synthesis, and Characterization of Some New bis‐thiazoles

The essential idea of the work in this article is mainly dependent on the use of bis‐hydrazonoyl halides for heterocyclic synthesis. The present work describes preparation and characterization of new bis‐thiazoles from reaction of bis‐hydrazonoyl chlorides with thiosemicarbazones. The synthetic Schemes for the final compounds are proposed and discussed. Structures of the final products were elucidated by elemental analyses and Fourier transform infrared, mass spectrometry, ¹H, and ¹³C‐NMR spectra.     

Hybrid inorganic–organic poly(carborane‐siloxane‐arylacetylene) structural isomers with in‐chain aromatics: Synthesis and properties

Structural isomers of thermo‐oxidatively stable poly(carborane‐siloxane‐arylacetylene) (PCSAA), namely, m‐PCSAA and p‐PCSAA, were synthesized by the reaction of the dimagnesium salts of m‐diethynylbenzene or p‐diethynylbenzene with 1,7‐bis(chlorotetramethyldisiloxyl)‐m‐carborane. The developed polymers have exceptional thermo‐oxidative properties similar to their diacetylene counterpart poly(carborane‐siloxane‐acetylene), PCSA. Thermal treatment of either of the PCSAAs results in a fully crosslinked thermoset by 500 °C resulting from the cycloaddition reactions involving the acetylene and aryl functionalities and subsequent formation of bridging disilylmethylene entities as discerned from Fourier transform infrared, ¹³C and ²⁹Si solid‐state NMR, and XPS studies. X‐ray diffraction analysis revealed that the thermosets obtained from p‐PCSAA possess enhanced crystallinity when compared to that obtained from m‐PCSAA possibly due to more efficient packing interactions of the p‐diethynylbenzene groups during thermoset formation. The presence of the aryl groups in the backbone of the PCSAAs' chains appeared to have enhanced the storage and bulk moduli of their thermosets when compared to the thermoset of PCSA. Dielectric studies of m‐PCSAA and p‐PCSAA revealed segmental relaxation peaks, α, above their glass transition temperatures with p‐PCSAA exhibiting a broader peak with a slower relaxation rate than m‐PCSAA. © 2013 Wiley Periodicals, Inc.^? J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2638–2650     

Synthesis of Derivatives of the Optically Active β‐Amino Acids from (+)‐Car‐2‐ene

The reaction of (+)‐car‐2‐ene ( 4 ) with chlorosulfonyl isocyanate (=sulfuryl chloride isocyanate; ClSO₂NCO) led to the tricyclic lactams 6 and 8 corresponding to the initial formation both of the tertiary carbenium and α‐cyclopropylcarbenium ions (Scheme 2). A number of optically active derivatives of β‐amino acids which are promising compounds for further use in asymmetric synthesis were synthesized from the lactams (see 16, 17 , and 19 – 21 in Scheme 3).     

Conducting core‐sheath nanofibers for electroactive shape‐memory applications

Conducting nanofibers coated with polypyrrole (PPy) and poly(3‐hexylthiophene) (P3HT) exhibiting core‐sheath structures were prepared by vapor‐phase polymerization of the conducting polymers on electrospun polyurethane nanofibers. The synthesis of the conducting polymers was confirmed by Fourier transform infrared spectroscopy and energy‐disperse X‐ray spectroscopy. The surfaces of the PPy‐coated nanofibers were slightly rough, while very smooth and regular surfaces were observed in the case of the P3HT‐coated nanofibers. The initial polymerization rate of PPy was higher than that of P3HT. In addition, the electrical conductivities of the core‐sheath structured nanofiber webs of both types increased with polymerization time. The maximum sheet conductivity of the PPy and P3HT‐coated nanofiber webs was 5 × 10^?3 S/cm and 1 × 10^?2 S/cm, respectively. The webs of the conducting core‐sheath structured nanofibers were effective in generating sufficient electrical heating necessary for harnessing these materials for electroactive shape‐memory‐based applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of thiophene/phenylene co‐oligomers. II [1]. Block and alternating co‐oligomers

We report the synthesis of block and alternating thiophene/phenylene co‐oligomers that is based either on the Suzuki coupling reaction or on the Grignard reaction. These reaction schemes enable us to obtain the target compounds at reasonably high yields. The resulting materials have been fully characterized through the solid‐state ¹³C nmr and Fourier‐transform ir as well as the ¹H nmr. Of these, the solid‐state ¹³C nmr and ir are particularly useful in characterizing the materials of higher molecular weight, since those materials are difficult to dissolve in organic solvents.