Thermal degradation of film cast from aqueous polyurethane dispersions

In this paper, water‐dispersible polyurethanes based on isophorone diisocyanate and polytetramethylene glycol were synthesized, and their thermal degradation behavior under nitrogen and air was studied by thermogravimetric (TG) analysis. The influence of NCO/OH ratio and functional group concentration was discussed. The thermal decomposition kinetics under nonisothermal conditions was analyzed using Ozawa method. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2552–2558, 2002     

Thermal degradation of poly(dimethylsilylene) and poly(tetramethyldisilylene‐co‐styrene)

Thermal degradation of poly(dimethylsilylene) homopolymer (PDMS) and poly(tetramethyldisilylene‐co‐styrene) copolymer (PTMDSS) was investigated by pyrolysis‐gas chromatography and thermogravimetry (TG). PDMS decomposes by depolymerization, producing linear and cyclic oligomeric products, whereas PTMDSS decomposes by random degradation along the chain resulting in each monomeric product and various other combination products. The homopolymer was found to be much less stable than the copolymer. The decomposition mechanisms leading to the formation of various products are shown. The kinetic parameters of thermal degradation were evaluated by different integral methods using TG data. The activation energies of decomposition (E) for the homopolymer and the copolymer are found to be 122 and 181 kJ/mol, respectively, and the corresponding values of order of reaction are 1 and 1.5. The observed difference in the thermal stability and the values of the kinetic parameters for decomposition of these polymers are explained in relation with the mechanism of decomposition. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Synthesis and characterization of polyurethane anionomers

Un‐ionized polyurethane was obtained by the reaction of an isocyanate‐terminated urethane prepolymer, which was synthesized from 4,4′‐diphenylmethane diisocyanate and poly(oxytetramethylene)‐α,ω‐glycol, with 2,2‐bis(hydroxymethyl)propionic acid. A carboxylate‐based polyurethane anionomer was then derived from the polyurethane by the use of the sodium, potassium, or magnesium salt of acetic acid as a neutralizer. The ionomerization resulted in the following changes in the characteristics of the polyurethane: (1) an increase in the tensile strength, (2) a decrease in the glass‐transition temperature, (3) an increase in the wettability and hygroscopicity with respect to water, and (4) susceptibility to thermal decomposition. A sulfonate‐based polyurethane was also synthesized for comparison with the carboxylate‐based polyurethane. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2144–2148, 2005     

Halogen‐free flame‐retardant waterborne polyurethane with a novel cyclic structure of phosphorus−nitrogen synergistic flame retardant

A novel phosphorus?nitrogen flame retardant, octahydro‐2,7‐di(N,N‐dimethylamino)‐1,6,3,8,2,7‐dioxadiazadiphosphecine (ODDP), with bi‐phosphonyl in a cyclic compound, was synthesized by the reaction of POCl₃, NH(CH₃)₂·HCl with OHCH₂CH₂NH₂ in CH₂Cl₂ solution, and characterized by Fourier transform infrared spectrometer, nuclear magnetic resonance, and mass spectrum. ODDP has been successfully reacted with polyurethane (PU) as a chain extender to prepare phosphorus–nitrogen synergistic halogen‐free flame‐retardant waterborne PU (DPWPU). Limiting oxygen index (LOI), UL‐94, thermogravimetric analysis and scanning electron microscopy suggest the excellent flame retardancy of the DPWPU polymer. When the content of ODDP was 15 wt %, the LOI of DPWPU was 30.6% and UL‐94 achieved a V‐0 classification. Compared with the unmodified WPU, the thermodecomposition temperature of the DPWPU was reduced and the amount of carbon residue was increased to 18.18%. The surface of carbon residue was shown to be compact and smooth without holes, which would be favorable for resisting oxygen and heat. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41288.     

Crystallinity evolution of soft segments during the synthesis of polyester‐based waterborne polyurethane

Polyester‐based waterborne polyurethane (WPU) dispersions having poly(ethylene glycol) adipate diol, isophorone diisocyanate, and hexamethylene diisocyanate as the main raw materials were synthesized by an acetone process. In each step of the synthesis process, the intermediate products were collected, and the crystallization morphologies and relative crystallinity (X) of the soft segments (SSs) in their films were investigated by means of polarizing optical microscopy, differential scanning calorimetry, and X‐ray diffraction. The fracture surfaces and thermostability of the intermediate films were also investigated by scanning electron microscopy (SEM) and TGA, respectively. The results show that the crystalline dimensions of the SSs decreased substantially during the synthesis process of WPU. X of the SSs decreased after the prepolymerization reaction and increased after the hydrophilic chain‐extending reaction, then decreased after emulsification, and finally increased after the secondary chain‐extending reaction. Moreover, The SEM photos indicate that with decreasing crystalline dimensions, the fracture mechanisms of the intermediate films varied gradually from brittle failure to ductile fracture. The thermostability of the intermediates obtained in each step of the synthesis process was in accordance with the variation tendency of the X of the SSs. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40270.     

Strategy for kinetic parameter estimation—Thermal degradation of polyurethane elastomers

The kinetics of the thermal degradation of polyurethane (PU) elastomers based on poly(ether polyol) soft segments and an aromatic type of diisocyanate were investigated by thermogravimetric analysis (TGA) under a nitrogen atmosphere employing four heating rates. The corresponding kinetic parameters of the two degradation stages were estimated by minimizing the output error functional and by the Kissinger method. In evaluating the kinetic parameters of the two‐step PU thermal decomposition, a differential thermogravimetry curve was applied as an objective functional in a regression procedure. Parameter estimation was obtained by minimizing the weighted quadratic output error functional with the modified Nelder–Mead simplex search algorithm. The confidence regions in the preexponential factor‐activation energy space were established for both the first and second stages of degradation. The effect of the molecular weight of the soft segment and the content of the hard segment on the activation energy of the degradation process was constructed by response surface methodology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 764–772, 2007     

Phase structure and thermal stability of crosslinked polyurethane elastomers based on well‐defined prepolymers

Taking advantage of the DSC method, general procedures were presented for qualitative and quantitative evaluation of the phase separation degree and the crystalline phase content in polyurethane elastomers with well‐defined structures. Those elastomers were obtained not only in a typical one‐step method but also in the prepolymer method with the use of urethane oligomers with controlled molecular weight distribution (MWD). Prepolymers with well defined chain structures and narrow distributions of their molecular weights (MWD) M _w/M _n = 1.1–1.3 were produced in a multistage method, i.e., in step‐by‐step polyaddition of 2,4‐ and 2,6‐TDI with polyoxyethylenediols or with polycaprolactonediols of varied molecular weights. Isocyanate oligomers obtained at individual stages were then crosslinked with triethanolamine, whereas hydroxyl‐terminated oligomers were crosslinked with 4,4′,4″‐triphenylmethane triisocyanate (Desmodur RE). The obtained polyurethane elastomers were found to be characterized by the presence of five phases: soft phase consisted of flexible polyol‐type segments, crystalline phase made of soft segments, crystalline and amorphous hard phase made of hard segments, and intermediate phase, which was a composition of the soft and hard segments. The polyurethanes obtained out of prepolymers with defined MWD were characterized by better phase separation of the soft segments and increased structural order inside the hard phase as well as by better thermal stability than polyurethanes obtained from the typical one‐step method. The structural effects were also discussed on the thermal properties of the synthesized elastomers as analyzed by the TG and DTA methods. © 2007 Wiley Periodicals, Inc. J Appl PolymSci 104: 1464–1474, 2007     

Thermal decomposition kinetics of rigid polyurethane foam and ignition risk by a hot particle

Rigid polyurethane foam, one kind of building insulation material used in China, is prone to being ignited by hot particles from fireworks or welding processes and has been the fuel for some catastrophic fire accidents. Thermal decomposition has long been recognized to play an important role in the ignition and fire‐spreading processes of materials, and thus, it is important to understand the behavior and kinetics of material decomposition. In this study, the characteristics of the thermal decomposition of polyurethane foam were investigated in an air atmosphere with nonisothermal thermogravimetry and differential scanning calorimetry (DSC). Model‐free (isoconversional) methods and model‐fitting methods were used to study the decomposition kinetics. The results reveal that the decomposition process of polyurethane foam in air presented three main stages: the loss of low‐stability organic compounds (bond fission of the weakest link in the chain), oxidative degradation of organic components, and oxidative degradation of residue material. A scheme containing three consecutive reactions was proposed to describe the decomposition process, and good agreement was found between the experimental and simulated curves. The heat during decomposition was calculated from DSC measurement. On the basis of the kinetics and heat of decomposition, the critical conditions for a hot particle to ignite polyurethane foam was evaluated, and this was helpful for the understanding the ignition risk of polyurethane foam. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39359.     

Halogen‐free flame‐retardant rigid polyurethane foams: Effect of alumina trihydrate and triphenylphosphate on the properties of polyurethane foams

Rigid polyurethane foam (PUF) filled with mixture of alumina trihydrate (ATH) and triphenyl phosphate (TPP) as fire retardant additive was prepared with water as a blowing agent. In this study, the ATH content was varied from 10 to 100 parts per hundred polyol by weight (php), and TPP was used at a higher loading of ATH (75 and 100 php) in a ratio of 1 : 5 to enhance the processing during PUF preparation. The effects of ATH on properties such as density, compressive strength, morphological, thermal conductivity, thermal stability, flame‐retardant (FR) behavior, and smoke characteristics were studied. The density and compressive strength of the ATH‐filled PUF decreased initially and then increased with further increase in ATH content. There was no significant change in the thermal stability with increasing ATH loading. We determined the FR properties of these foam samples by measuring the limiting oxygen index (LOI), smoke density, rate of burning, and char yield. The addition of ATH with TPP to PUF significantly decreased the flame‐spread rate and increased LOI. The addition of TPP resulted in easy processing and also improved FR characteristics of the foam. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

N,N‐diethyl dithiocarbamato group induced photografting of methyl methacrylate onto polyurethane

The N,N‐diethyl dithiocarbamato group present in a variety of compounds acts as an initiator in the photopolymerization processes. The photolability of this group is due to the cleavage of the C S bond by UV irradiation. N,N‐Diethyl dithiocarbamato‐(1,2)‐propane diol with a pendent N,N‐diethyl dithiocarbamato group was prepared from 3‐chloro‐(1,2)‐propane diol and sodium diethyl dithiocarbamate. A polyurethane macrophotoinitiator was then synthesized by a two‐step process, where N,N‐diethyl dithiocarbamato‐(1,2)‐propane diol was used as the chain extender. Other components used included 4,4′‐diphenylmethane diisocyanate and poly(propylene glycol) (molecular weight = 1000). The polyurethane thus synthesized had pendent N,N‐diethyl dithiocarbamato groups. This polyurethane macrophotoinitiator was then used to polymerize methyl methacrylate in a photochemical reactor (Compact‐LP‐MP 88) at 254 nm. The resulting graft copolymer, polyurethane‐g‐poly(methyl methacrylate), was freed from the homopolymer by a standard procedure. The graft copolymer was characterized by Fourier transform infrared spectroscopy, ¹H‐NMR spectroscopy, thermogravimetric analysis, differential scanning calorimetry, solution viscometry, and scanning electron microscopy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal degradation kinetics of rigid polyurethane foams blown with water

The thermal decomposition behavior of rigid polyurethane foams blown with water was studied by dynamic thermogravimetric analysis (TGA) in both nitrogen and air atmosphere at several heating rates ranging from room temperature to 800°C. The kinetic parameters, such as activation energy (E), degradation order (n), and pre‐exponential factor (A) were calculated by three single heating rate techniques of Friedman, Chang, and Coats–Redfern, respectively. Compared with the decomposition process in nitrogen, the decomposition of foams in air exhibits two distinct weight loss stages. The decomposition in nitrogen has the same mechanism as the first stage weight loss in air, but the second decomposition stage in air appears to be dominated by the thermo‐oxidative degradation. The heating rates have insignificant effect on the kinetic parameters except that the kinetic parameters at 5°C/min have higher values in nitrogen and lower values in air, indicating different degradation kinetics in nitrogen and air. The kinetic parameters of foam samples blown with different water level in formulation decline firstly and then increase when water level increases from 3.0 to 7.0 pph. According to the prediction for lifetime and half‐life time of foams, water‐blown rigid foams have excellent thermostability, when used as insulation materials below 100°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4149–4156, 2006     

Thermal stability and molecular interaction of polyurethane nanocomposites prepared by in situ polymerization with functionalized multiwalled carbon nanotubes

Polyurethane (PU) nanocomposites were prepared through conventional and in situ methods with multiwalled carbon nanotubes (MWNTs) functionalized with poly(ϵ-caprolactone). The thermal degradation and stability of PU–MWNT nanocomposites were investigated with nonisothermal thermogravimetry and were explained in terms of the interaction between MWNTs and PU molecules with Fourier transform infrared spectroscopy. The difference in thermal stability between the conventional and in situ nanocomposites was also compared. The thermal degradation of all the nanocomposite samples took place in two stages and followed a first-order reaction. The degradation temperature of the in situ nanocomposites was higher than that of the conventional nanocomposites with the same loading of MWNTs. The activation energy at 10% degradation and the half-life period were also higher in the in situ nanocomposites compared to the conventional nanocomposites. Such higher thermal stability of the in situ nanocomposites was ascribed to covalent bond formation between MWNTs and PU chains, which could result in better dispersion of MWNTs in the PU matrix for the in situ nanocomposites than for the conventional nanocomposites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of hydroxypropyl terminated polydimethylsiloxane‐polyurethane copolymers

Polyurethane (PU) block copolymers were synthesized using prepared hydroxypropyl terminated polydimethylsiloxane (HTPDMS MW 990) and polyether diols (N‐210) as soft segment with 4,4′‐diphenylmethane diisocyanate (MDI) and 1,4‐butanediol. This low molecular weight polydimethylsiloxanes (PDMS) containing hydroxypropyl end‐groups displayed better compatibility with PU than common PDMS. In this article, we illustrate its synthesis routes and confirmed the proposed molecular structures using NMR and infrared radiation (IR). We varied the contents of HTPDMS and N‐210 in soft segments (HTPDMS—N‐210: 0 : 100, 20 : 80, 40 : 60, 60 : 40, 80 : 20, and 100 : 0) to synthesize a series of PDMS‐PU copolymer. IR spectroscopy showed the assignment characteristic groups of each peak in copolymers and confirmed that the desired HTPDMS‐PU copolymers have been prepared. The different thermal, dynamic mechanical and surface properties of the copolymers were compared by thermogravimetry, DMA, contact angle and solvent resistance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal degradation and pyrolysis study of phosphorus‐containing polysulfones

This article deals with the thermal decomposition behavior of a polysulfone containing 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide versus the initial chloromethylated polysulfone under an inert atmosphere and in air. Thermogravimetric characteristics from thermogravimetry and differential thermogravimetry data revealed important differences related to the employed atmosphere, the types of substituted functional groups, or the degree of substitution. The introduction of the 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide pendent group into polysulfone enhanced the thermal stability of the initial chloromethylated polysulfone in both an inert atmosphere and air. Thermal degradation in nitrogen consisted of one degradation step, whereas thermooxidative degradation in air involved more steps. In air, the degradation mechanism was more complex. The volatile products and solid residues that resulted after pyrolysis in an inert atmosphere and in air were analyzed with Fourier transform infrared and mass spectrometry. Environmental scanning electron microscopy showed that the char residues had different morphologies, which suggested that a more compact structure led to better resistance to heat and oxygen. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci 000: 000–000, 2011     

Synthesis and characterization of calcium‐containing poly(urethane‐urea)s

A calcium salt of mono(hydroxyethoxyethyl)phthalate [Ca(HEEP)2] was synthesized by the reaction of diethylene glycol, phthalic anhydride, and calcium acetate. Four different bisureas like hexamethylene bis(ω,N‐hydroxyethylurea), tolylene 2,4‐bis(ω,N‐hydroxyethylurea), hexamethylene bis(ω,N‐hydroxypropylurea), and tolylene 2,4‐bis(ω,N‐hydroxypropylurea) were prepared by reacting ethanolamine or propanolamine with hexamethylene diisocyanate (HMDI) or tolylene 2,4‐diisocyanate (TDI). Calcium‐containing poly(urethane‐urea)s (PUUs) were synthesized by reacting HMDI or TDI with 1:1 mixtures of Ca(HEEP)2 and each of the bisureas using di‐n‐butyltin dilaurate as a catalyst. The PUUs were well characterized by Fourier transform infrared, 1H‐ and 13C‐NMR (nuclear magnetic resonance), solid‐state 13C cross‐polarization–magic angle spinning NMR, viscosity, solubility, elemental, and X‐ray diffraction studies. Thermal properties of the polymers were also studied by using thermogravimetric analysis and differential scanning calorimetry. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3488–3496, 2003     

Synthesis and electro‐optic properties of novel polyurethane containing the nitrophenylazoresorcinoxy group

A novel Y‐type polyurethane (polyurethane 3) containing 4‐(4‐nitrophenylazo)resorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute part of the polymer backbone, was prepared and characterized. Polyurethane 3 is soluble in common organic solvents such as acetone and N,N‐dimethylformamide. It shows thermal stability up to 270 °C from thermogravimetric analysis with a glass transition temperature obtained from differential scanning calorimetry of 102 °C. The second harmonic generation (SHG) coefficient (d₃₃) of the poled polymer film at 1064 nm fundamental wavelength is 2.06 pm V^?1. Polymer 3 exhibits thermal stability up to T_g, and no significant SHG decay is observed below 100 °C, which is acceptable for nonlinear optical device applications. Copyright © 2012 Society of Chemical Industry     

Bamboo tar‐based polyurethane wood coatings

Bamboo tar is a natural resource of aromatic polyol obtained from a residue of by setting or distilling crude bamboo vinegar. In this study, the two‐packed polyurethane (PU) coatings were prepared by blending bamboo tar and castor oil varying with different weight ratios and polymeric toluene diisocyanate (PTDI) was used as a hardener at the NCO/OH molar ratio of 1.0. Six kinds of PU coatings were formulated and the viscosity, pot‐life, drying time, mechanical properties (hardness, tensile strength, impact resistance, adhesion, and abrasion resistance), gel content, durability, lightfastness, FTIR, thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA) were characterized. The results indicated that the bamboo tar containing PU film appearance is semitransparent yellow‐brown color and the wood texture could be kept after finishing. All PU films possessed excellent adhesion as well as durability. The increase in bamboo tar content led to shorten drying time of coatings and to increase in hardness, tensile strength, lightfastness, and thermal stability of films. From these results and due to a light smell flavor, it is suggested that the bamboo tar‐based PU coatings is suitable to be used as an exterior wood coatings. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polyurethanes derived from carbohydrates and cystine‐based monomers

Linear [m,n]‐type polyurethanes (PUs) fully based on renewable materials are synthesized by interfacial polycondensation reaction of diamines derived from the amino‐acid cystine with (bis)chloroformates derived from alditols having L‐arabino or xylo configuration. The degradability of the new PUs has been enhanced by the introduction of disulfide linkages into the polymer backbone leading to a new group of stimulus‐responsive sugar‐based polyurethanes able to be degraded by glutathione under physiological conditions. All these polyurethanes are stable up to around 245°C, decomposing at higher temperatures through a one‐stage mechanism. The new materials display high chemical homogeneity and degradability in both hydrolytic and reductive environments, with reductions of above 90% in M_w. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41304.     

Thermal degradation kinetics of poly(N‐adamantyl‐exo‐nadimide) synthesized by addition polymerization

The thermal decomposition behavior and degradation kinetics of poly(N‐adamantyl‐exo‐nadimide) were investigated with thermogravimetric analysis under dynamic conditions at five different heating rates: 10, 15, 20, 25, and 30°C/min. The derivative thermogravimetry curves of poly(N‐adamantyl‐exo‐nadimide) showed that its thermal degradation process had one weight‐loss step. The apparent activation energy of poly(N‐adamantyl‐exo‐nadimide) was estimated to be about 214.4 kJ/mol with the Ozawa–Flynn–Wall method. The most likely decomposition process was an F1 deceleration type in terms of the Coats–Redfern and Phadnis–Deshpande results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3003–3009, 2007     

Thermal stability of chemically crosslinked moisture‐cured polyurethane coatings

Polyurethane prepolymers are widely used in reactive hot melt adhesives and moisture‐cured coatings. The segmented moisture‐cured formulations, based on polytetramethylene glycol (PTMG‐1000)/trimethylol propane (TMP)/isophorone diisocyanate (IPDI) and PTMG/TMP/toluene diisocyanate (TDI), were prepared with NCO/OH ratio of 1.6 : 1.0. The excess isocyanate groups of the prepolymers were chain extended in the ratio of 2 : 1 (NCO/OH) with different aliphatic diols and 4 : 1 with different aromatic diamines. The surplus isocyanate groups of the formulations were completely reacted with atmospheric moisture, and the thermal stability of the postcured materials obtained as cast films were evaluated by thermogravimetric (TG) analysis. It was observed that initial degradation temperatures were above 270°C, with two‐ or three‐step degradation profiles. The degradation parameters were evaluated using the Broido and Coats–Redfern methods. The thermal resistance of moisture‐cured formulations using diisocyanates with the cycloaliphatic structures (IPDI) and the aromatic TDI, at the same NCO/OH ratio (1.6), and TMP content were compared from the isothermal TG experiments at different temperatures and dynamic TG experiments at different heating rates in nitrogen and oxygen environments. The observation suggests that polyurethane‐containing sulfone groups and straight‐chain diol chain extenders were more stable. It was also observed that at lower temperature polyurethane, prepared from aliphatic diisocyanates (IPDI), was more stable than the aromatic diisocyanate (TDI) containing polyurethanes. At high temperature, the stability order follows the reverse trend. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1509–1518, 2005