Sound absorption properties of polyurethane/nano‐silica nanocomposite foams

In this study, polyurethane (PU)/nano‐silica nancomposite foams were prepared. The effects of isocyanate index, cell size, density, and molecular weight of polyols on the sound absorption ratio of PU/nano‐silica foams were investigated. With increasing nano‐silica content, the sound absorption ratio of PU/nano‐silica foams increases over the entire frequency range investigated in this study. Decrease of isocyanate index, cell size, and increase of density leads to the increase of sound absorption ratio of PU/nano‐silica foams. PU/nano‐silica foams have a broad T_g centered around room temperature by decreasing molecular weight of polyol resulting in good sound absorbing ability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Highly flame‐retardant polyurethane foam based on reactive phosphorus polyol and limonene‐based polyol

Polyurethane foams are in general flammable and their flammability can be controlled by adding flame‐retardant (FR) materials. Reactive FR have the advantage of making strong bond within the polyurethane chains to provide excellent FR over time without compromising physico‐mechanical properties. Here, phenyl phosphonic acid and propylene oxide‐based reactive FR polyol was synthesized and used along with limonene based polyol for preparation of FR polyurethanes. All the obtained foams showed higher closed cell content (above 96%). By the addition of FR–polyol, the compressive strength of the foams showed 160% increment which could be due to reactive nature of FR–polyol. Moreover, 1.5 wt % of phosphorus (P) content reduced the self‐extinguishing time of the foam from 81 (28% weight loss) to 11.2 s (weight loss of 9.8%). Cone test showed 68.6% reduction in peak heat release rate along with 23.4% reduction in thermal heat release. The change in char structure of carbon after burning was analyzed using Raman spectra which, suggests increment in the graphitic phase of the carbon over increased concentration of phosphorus. It can be concluded from this study that phosphorous based polyol could be blended with bio‐based polyols to prepare highly FR and superior physico‐mechanical rigid polyurethane foams. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46224.     

A simple one‐step synthesis and polymerization of plant oil triglyceride iodo isocyanates

In this study, a novel and simple route for the synthesis of the iodine isocyanate (INCO) adduct of soybean oil triglycerides is described. Soybean oil iodo isocyanate (ISONCO) was synthesized by the reaction of iodine isocyanate and soybean oil at room temperature. ISONCO was then polymerized with polyols, such as, castor oil, pentamethylene glycol, and glycerol to give the corresponding polyurethanes and with polyamines, such as, ethylene diamine, hexamethylene diamine, and triethylene tetramine to give corresponding polyureas. The structures of the monomer and the polymers were determined by FTIR and ¹H‐NMR analyses. Thermal properties of the polymers were determined by DSC and TGA. Thermal degradation of the polyurethanes started at 150°C. Stability of the polyureas was higher than polyurethanes. Almost all polymers showed a T_g around ?50°C. The mechanical properties of the polymers were determined by tensile tests. Among the polymers synthesized, castor oil polyurethane showed the highest elongation at break and the lowest tensile strength of 140 KPa. The highest tensile strength of 900 KPa was observed in the pentamethylene glycol polyurethanes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Development of polyurethanes with azo‐type chromophores for second‐order nonlinear optical applications

Active nonlinear optical nitro‐substituted thiazole, benzothiazole, and thiadiazole chromophores were prepared and condensed with tolylene‐2,4‐diisocyanate (TDI) and 4,4′‐methylenedi(phenyl isocyanate) (MDI) to yield a series of polyurethanes. The resulting polyurethanes were characterized with Fourier transform infrared, proton nuclear magnetic resonance, and ultraviolet–visible spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and gel permeation chromatography. The weight‐average molecular weights of the polyurethanes ranged between 19,500 and 28,000 (weight‐average molecular weight/number‐average molecular weight = 1.71–2.15). All the polyurethanes exhibited excellent solubility in most common organic solvents, and this indicated that these polyurethanes offered good processability. The glass‐transition temperatures (T_g's) of the polyurethanes were in the range of 166–204°C. Among the polyurethanes, chromophores containing the nitrothiazole moiety exhibited lower T_g values in comparison with those of chromophores containing nitrobenzothiazole and nitrothiadiazole moieties. This was attributed to the small size of the nitrothiazole moiety in the polyurethane matrix. The polyurethanes containing a TDI backbone demonstrated relatively high T_g values in comparison with those of the polyurethanes containing an MDI backbone. This was a result of an enhancement of the rigidity caused by the incorporation of a toluene ring into the polyurethane backbone. The second harmonic generation (SHG) coefficients of the poled polyurethane films ranged from 67.29 to 105.45 pm/V at 1064 nm. High thermal endurance of the poled dipoles was observed for all the polyurethanes. This was attributed to the formation of extensive hydrogen bonds between urethane linkages. Furthermore, none of the developed polyurethanes showed SHG decay below 150°C, and this signified their acceptability for nonlinear optical devices. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Biobased hyperbranched shape‐memory polyurethanes: Effect of different vegetable oils

Hyperbranched polyurethanes were synthesized from poly(ε‐caprolactone) diol as a macroglycol, butanediol as a chain extender, a monoglyceride of a vegetable oil (Mesua ferrea, castor, and sunflower oils separately) as a biobased chain extender, triethanolamine as a multifunctional moiety, and toluene diisocyanate by a prepolymerization technique with the A₂ + B₃ approach. The structure of the synthesized hyperbranched polyurethanes was characterized by ¹H‐NMR and X‐ray diffraction studies. M. ferrea L. seed‐oil‐based polyurethane showed the highest thermal stability, whereas the castor‐oil‐based one showed the lowest. However, the castor‐oil‐based polyurethane exhibited the highest tensile strength compared to the other vegetable‐oil‐based polyurethanes. All of the vegetable‐oil‐based polyurethanes showed good shape fixity, although the castor‐oil‐based polyurethane showed the highest shape recovery. Thus, the characteristics of the vegetable oil had a prominent role in the control of the ultimate properties, including the shape‐memory behaviors, of the hyperbranched polyurethanes. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39579.     

Antibacterial oil‐based polyurethane films for wound dressing applications

As an alternative to petroleum‐based polyol, hydroxyl containing material was prepared from linseed oil for polyurethane synthesis. Hexamethylene di‐isocyanate (HMDI) and/or 4, 4′‐methylene diphenyl di‐isocyanate (MDI) were used as isocyanate source. The polymerization reaction was carried out without catalyst. Polymer films were prepared by casting‐evaporation technique. The MDI/HMDI‐based polyurethane and its films had higher T_g and better thermal property than that of the HMDI‐based one because of the existence of benzene ring in the polymer chain. Static water contact angle was determined to be 74° and 77.5° for HMDI and MDI/HMDI‐based films, respectively. Water adsorption was found to be around 2.6–3.6% for both films. In vitro degradation of polyurethanes in phosphate buffered saline at 37°C was investigated by gravimetric method. Fourier transform infrared spectroscopy and scanning electron microscopy were used for confirmation of degradation on the polymer surface. The degradation rate of the HMDI‐based polyurethane film was found higher than that of the MDI/HMDI‐based film. Both the direct contact method and the MMT test were applied for determination of cytotoxicity of polymer films, and the polyurethane films investigated here was not cytotoxic. Silver‐containing films were prepared using Biocera A® as filler and were screened for their antibacterial performance against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and/or Bacillus subtilis. The films prepared with and without Biocera A® exhibited antibacterial activity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Performance of novel hyperbranched poly(aryl‐ether‐urea)s doped with N3‐dye in nanocrystalline DSSC

An amine‐terminated hyperbranched poly(aryl‐ether‐urea) (HBPEU) was prepared from an AB₂‐type blocked isocyanate monomer and then its end groups were modified into urea (M‐HBPEU) by reaction with phenyl isocyanate. Both of the polymers were doped with N3‐dye along with KI/I₂ to work as efficient polymer electrolytes in nanocrystalline dye sensitized solar cell. The increment in the conductivity of doped HBPEU and doped M‐HBPEU was very significant and reached its value at 8.2 × 10⁻³ and 4.1 × 10⁻² S/cm, respectively. The current–voltage (I–V) characteristics of these two doped polymers measured under simulated sunlight with AM 1.5 at 60 mW/cm² generate photocurrent of 2.5 and 3.6 mA/cm², together with a photo voltage of 690 and 750 mV, and fill factor of 0.55 and 0.61 yielding a overall energy conversion efficiency of 2.4% and 4.1%, respectively. These results suggest that M‐HBPEU show better cell performance and conductance properties than the HBPEU. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40408.     

Biobased polyisocyanates from plant oil triglycerides: Synthesis,polymerization, and characterization

In this study, an easy and efficient synthesis of unsaturated plant oil triglycerides having isocyanate groups is reported. In the first step of the synthesis, the triglyceride was brominated at the allylic positions by a reaction with N‐bromosuccinimide, and in the second step, these brominated species were reacted with AgNCO to convert them to isocyanate‐containing triglycerides. At the end of the reaction, approximately 60–70% of the bromine was replaced by NCO groups, and the double bonds of the triglyceride were not consumed. When the amount of AgNCO was increased, the yield also increased. The final products were characterized with IR and ¹H‐NMR, and polyurethanes and polyureas were obtained from these fatty isocyanates with alcohols and amines, respectively. The polymers were characterized by differential scanning calorimetry and thermogravimetric analysis. Differential scanning calorimetry curves showed that glycerin polyurethane showed a glass‐transition temperature at 19°C, castor oil polyurethane showed two glass‐transition temperatures at ?43 and 36°C, and triethylene tetraamine polyurea showed a glass‐transition temperature at 31°C. Some properties of the polymers, such as the tensile strength and swelling ratios, were also determined. The swelling rate of glycerin polyurethane was higher than that of castor oil polyurethane in dichloromethane. The equilibrium swelling ratio was highest for the castor oil polyurethane. The polyurethanes synthesized in this study had a Young's modulus around 50 kPa and a tensile strength around 0.01 N/mm² (100 kPa). The tensile strength of glycerin polyurethane was higher than that of castor oil polyurethane. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Physical properties of water‐blown rigid polyurethane foams containing epoxidized soybean oil in different isocyanate indices

To explore the potential of isocyanate usage reduction, water‐blown rigid polyurethane foams were made by replacing 0, 20, and 50% of Voranoll® 490 in the B‐side of the foam formulation by epoxidized soybean oil (ESBO) with an isocyanate index ranging from 50 to 110. The compressive strength, density, and thermal conductivity of foams were measured. The foam surface temperature was monitored before and throughout the foaming reaction as an indirect indication of the foaming temperature. Increasing ESBO replacement and/or decreasing isocyanate index decreased the foam's compressive strength. The density of the foam decreased while decreasing the isocyanate index to 60. Further decrease in isocyanate index resulted in foam shrinkage causing a sharp increase in the foam density. The thermal conductivity of foams increased while decreasing the isocyanate index and increasing the ESBO replacement. Mathematical models for predicting rigid polyurethane foam density, compressive strength, and thermal conductivity were established and validated. Similar to compressive strength, the foaming temperature decreased while decreasing the isocyanate index and increasing the ESBO replacement. Because of the lower reactivity of ESBO with isocyanate, the rate of foaming temperature decrease with decreasing isocyanate index was in the order of 0% > 20% > 50% ESBO replacement. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Physical properties of water‐blown rigid polyurethane foams from vegetable oil‐based polyols

Fifty vegetable oil‐based polyols were characterized in terms of their hydroxyl number and their potential of replacing up to 50% of the petroleum‐based polyol in waterborne rigid polyurethane foam applications was evaluated. Polyurethane foams were prepared by reacting isocyanates with polyols containing 50% of vegetable oil‐based polyols and 50% of petroleum‐based polyol and their thermal conductivity, density, and compressive strength were determined. The vegetable oil‐based polyols included epoxidized soybean oil reacted with acetol, commercial soybean oil polyols (soyoils), polyols derived from epoxidized soybean oil and diglycerides, etc. Most of the foams made with polyols containing 50% of vegetable oil‐based polyols were inferior to foams made from 100% petroleum‐based polyol. However, foams made with polyols containing 50% hydroxy soybean oil, epoxidized soybean oil reacted with acetol, and oxidized epoxidized diglyceride of soybean oil not only had superior thermal conductivity, but also better density and compressive strength properties than had foams made from 100% petroleum polyol. Although the epoxidized soybean oil did not have any hydroxyl functional group to react with isocyanate, when used in 50 : 50 blend with the petroleum‐based polyol the resulting polyurethane foams had density versus compressive properties similar to polyurethane foams made from 100% petroleum‐based polyol. The density and compressive strength of foams were affected by the hydroxyl number of polyols, but the thermal conductivity of foams was not. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis and characterization of bis‐triethoxysilane endcapped polyurethane/urea

A type of bistriethoxysilane endcapped polyurethane/ureas (SPU) with well‐defined structure was synthesized from bis(triethoxysiylpropyl) amine and purified prepolymers, which were obtained from the reaction of 2,4‐toluene diisocyanate (TDI) and polyoxyethylene glycol (PEG) with different molecular weight. Then, fourier transform infrared spectroscopy (FTIR), hydrogen nuclearmagnetic resonance (¹H‐NMR) and standard dibutylamine back‐titration method were used to confirm the structures of prepolymers and SPUs. Moreover, the properties of SPU were investigated by wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), and percentage of water uptake. Results indicated that these polyurethanes were amorphous, and the percentage of water uptake and thermal stability of these polyurethanes went up with the increase of M _n of SPU, accompanying with the glass transition temperature (T_g) values decreased with the increase of M _n. This study provides us with a method to synthesize well‐defined end‐functionalized polyurethane. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Highly flame‐retardant bio‐based polyurethanes using novel reactive polyols

Poor flame retardancy of polyurethanes (PU) is a global issue as it limits their applications particularly in construction, automobile, and household appliances industries. The global challenge of high flammability of PU can be addressed by incorporating flame‐retardant materials. However, additive flame‐retardants are non‐compatible and depreciate the properties of PU. Hence, reactive flame‐retardants (RFR) based on aliphatic (Ali‐1 and Ali‐2) and aromatic (Ar‐1 and Ar‐2) structured bromine compounds were synthesized and used to prepare bio‐based PU using limonene dimercaptan. The aromatic bromine containing foams showed higher close cell content (average 97 and 100%) and compressive strength (230 and 325 kPa) to that of aliphatic bromine containing foams. Similar behavior was observed for a horizontal burning test where with a low concentration of bromine (5 wt %) in the foams for Ar‐1 and Ar‐2 displayed a burning time of 12.5 and 11.8 s while, Ali‐1 and Ali‐2 displayed burning time of 25.7 and 37 s, respectively. Neat foam showed a burning time of 74 s. The percentage weight loss for neat PU foam was 26.5%, while foams containing 5 wt % bromine in Ali‐1, Ali‐2, Ar‐1, and Ar‐2 foams displayed weight loss of 11.3, 14, 7.9, and 14%, respectively. Our results suggest that flame retardant PU foams could be prepared effectively by using RFR materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46027.     

Synthesis and characterization of chlorine‐containing flame‐retardant polyurethane nanocomposites via in situ polymerization

We have developed flame‐retardant polyurethanes (FRPUs) and polyurethane (PU) nanocomposites via in situ polymerization. Three series of thermoplastic elastomeric PUs were synthesized to investigate the effect of incorporating 3‐chloro‐1,2‐propanediol (CPD) and nanoclay on mechanical, thermal properties, and also resistance to burning. PU soft segments were based on poly(propylene glycol). Hard segments were based on either CPD or 1,4‐buthane diol (BDO) in combination with methyl phenyl di‐isocyanate named PU or FRPU, respectively. In the third series, CPD was used as chain extender also nanoclay (1% wt) and incorporated and named as flame‐retardant polyurethane nanocomposites (FRPUN). Mechanical properties and LOI of PUs and nanocomposites have been evaluated. Results showed that increasing the hard segment (chlorine content) leads to the increase in flame retardancy and burning time. Addition of nanoclay to CPD‐containing PUs leads to obtain self‐extinguish PUs using lower CPD contents, higher Young's modulus, and strength without any noticeable decrease in elongation at break. Investigation of the TGA results showed that copresence of nanoclay and chlorine structure in the PU backbone can change thermal degradation pattern and improve nanocomposite thermal stability. X‐ray diffraction and transmission electron microscopy studies confirmed that exfoliation and intercalation have been well done. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Electrospinning of plant oil‐based,non‐isocyanate polyurethanes for biomedical applications

Non‐isocyanate polyurethanes (NIPU) have rapidly emerged as a sustainable, less toxic, and environmentally friendly alternative to traditional isocyanate‐based thermoplastic polyurethane (TPU) synthesis. TPU is widely used in the medical industry due to its excellent mechanical properties and elasticity. However, little work has been done to synthesize and electrospin NIPU into fibrous mats for biomedical applications. In this work, melt polymerization of a plant oil‐based cyclic carbonate monomer with polyether soft segments and various diamines yielded isocyanate‐free, segmented poly(amide hydroxyurethane)s (PAHUs). Electrospinning of segmented PAHUs afforded ductile, free‐standing fibrous mats with Young's modulus values between 7 and 8 MPa, suitable for tissue scaffold applications. PAHU fiber mats exhibited 3–4 times greater water uptake than the electrospun TPU control, demonstrating potential utility in drug delivery. Fibroblasts adhered to electrospun PAHU fibrous mats with viability values over 90% after 72‐h, validating its biocompatibility. The results highlight the high performance and potential of electrospun isocyanate‐free polyurethanes mats for biomedical application. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46464.     

Polyphenolic extracts of Pinus radiata bark and networking mechanisms of additive‐accelerated polycondensates

The use of various chemicals for extracting polyphenolic fractions (tannins) from Pinus radiata bark was examined with the aim of obtaining high yields of high‐quality tannins to be used as wood adhesives. Extractions carried out under very highly alkaline conditions (pH > 10.5) gave relatively high yields but also excessive viscosity values even in 30% (w/w) solutions, and this demonstrated their inability to function as wood adhesives. Solutions (30% w/w) of mildly extracted (pH < 8.3) fractions gave workable viscosity values and were used in a subsequent study. A rapid acceleration effect was observed in these fractions when ammonia was used as a catalyst. Solid‐state, cross‐polarization/magic‐angle‐spinning ¹³C‐NMR of the cured samples showed evidence proving the existence of benzyl amine bridging networks in their hardened state. Simultaneously accelerated copolymerization could be observed in phenol–resorcinol–formaldehyde/P. radiata bark tannin mixtures with the addition of ammonia, as indicated by viscosity measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2487–2493, 2007     

Fabrication of isocyanate‐based polyimide foam by a postgrafting method

Density and flame retardancy controlled isocyanate‐based polyimide foam was prepared by a postgrafting method. The first solution containing prepolymer that was synthesized by dianhydride and overdose isocyanates was added into the second solution containing dianhydride derivatives, water, catalysts, and surfactants. The possible reactions during preparation are discussed. The obtained Fourier transform infrared spectra indicate that an increased amount of imide rings was generated with increasing molar ratio of the anhydride/isocyanate groups. The size and walls of the cells became smaller and thinner with less carbon dioxide (CO₂) escaping into the air during the first solution preparation process, as shown in scanning electron microscopy images. The thermogravimetric analysis curves demonstrated that the 5% weight loss temperature (T_5%) was greater than 289 °C, and the residual weight retention at 800 °C was more than 45%. In addition, differential thermogravimetry curves demonstrated that the thermal stability decreased with more byproducts in polyimide foams. The limiting oxygen index increased gradually from 30.63% ± 0.56 to 48% ± 0.50 with increasing molar ratio of the anhydride/isocyanate groups. Meanwhile, the density of obtained polyimide foams ranged from 38.31 kg/m³ ± 0.90 to 99.53 kg/m³ ± 10.85. When the molar ratio of anhydride/isocyanate groups ranged from 0.4 to 0.8, the prepared isocyanate‐based polyimide foams all exhibit both great flame retardancy and lower density. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44240.     

Thermal and mechanical behavior of flexible polyurethane‐molded plastic films and water‐blown foams with epoxidized soybean oil

Water‐blown flexible polyurethane foams and molded plastic films were made by replacing 0 to 50% of Voranol® 4701 in the B‐side of foam and plastic film formulation by epoxidized soybean oil (ESBO). Physical properties of foams including density, 50% compression force deflection (CFD), 50% constant deflection compression (CDC), and resilience were determined. A dynamic mechanical spectrometer (DMS) and a differential scanning calorimeter (DSC) were used to characterize the hard segment (HS) and soft segment (SS) ratio and thermal properties of plastic. Various functional groups in both flexible polyurethane foam and plastic film were characterized using Fourier transform‐infrared spectroscopy with attenuated total reflectance (FTIR‐ATR). When increasing the ESBO content, both density and 50% CFD of water‐blown polyurethane foams decreased first, then increased. On the other hand, the 50% CDC and resilience of foams showed a sharp increase and decrease, respectively. When increasing the ESBO content, the peak of tan δ in DMS analysis and Δc_p in DSC analysis of plastic films both decreased indicating the hard segment increased and the soft segment decreased in plastic film, respectively. The FTIR‐ATR results also show the hydrogen‐bonded urethane group increased in plastic films with increasing ESBO content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and cell morphology of ethylene‐vinyl acetate copolymer (EVA)/wood‐flour foams with low density

The main objective of this study is to obtain ethylene‐vinyl acetate copolymer (EVA)/wood‐flour foams with low density (< 0.2 g/cm³) using chemical blowing agent. Stearic acid was used as a compatibilizer to improve not only the compatibility between wood‐flour and EVA but also the compatibility between moisture and EVA in this study. The effects of wood‐flour content on the density and mechanical properties of EVA/wood‐flour foams were studied. Also, the effects of content of stearic acid on the cell morphology of EVA/wood‐flour foams were investigated. The shape of EVA/wood‐flour foams with 20% wood‐flour content becomes more uniform with increasing content of stearic acid. The most stabilized shape of the foams is obtained with 5 wt % stearic acid content. The density of EVA/wood‐flour foams with 20% wood‐flour and 5 wt % stearic acid is 0.11 g/cm³. With increasing content of stearic acid, more gas remains in the EVA matrix and consequently, average cell size and density increase. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40894.     

Synthesis of Carbon‐Rich Hybrid Foam from GAP‐Modified Polyurethane

4,4′‐Diisocyanato diphenylmethane (MDI)‐based polyurethanes melt and start to burn at 150–200 °C. Mainly H₂O, CO₂, CO, HCN, and N₂ are formed. The new modified polyurethane shows a different pyrolysis behavior. GAP‐diol (glycidyl azide polymer), which was used as a modifying agent, is a well‐known energetic binder with a high burning velocity and a very low adiabatic flame temperature. The modified polyurethane starts to burn at approximately 190 °C because of the emitted burnable gases, but it does not melt. The PU foam shrinks slightly and a black, solid, carbon‐rich hybrid foam remains. TGA and EGA‐FTIR revealed a three‐step decomposition mechanism of pure GAP‐diol, the isocyanate‐GAP‐diol, and PU‐GAP‐diol formulations. The first decomposition step is caused by an exothermic reaction of the azido group of the GAP‐diol. This decomposition reaction is independent of the oxygen content in the atmosphere. In the range of 190–240 °C the azido group spontaneously decomposes to nitrogen and ammonia. This decomposition is assumed to take place partly via the intermediate hydrogen azide that decomposes spontaneously to nitrogen and ammonia in the range of 190–240 °C. The second decomposition step was attributed to the depolymerization of the urethane and bisubstituted urea groups. The third decomposition step in the range of 500–750 °C was attributed to the carbonization process of the polymer backbone, which yielded solid, carbon‐rich hybrid foams at 900 °C. In air, the second and the third decomposition step shifted to lower temperatures while no solid carbon hybrid foam was left. Samples of PU‐GAP‐diol, which were not heated by a temperature program but ignited by a bunsen burner, formed a similar carbon‐rich hybrid foam. It was therefore concluded that the decomposition products of the hydrogen azide, ammonia and mainly nitrogen act as an inert atmosphere. FTIR, solid‐state ¹³C‐NMR, XRD, and heat conductivity measurements revealed a high content of sp²‐hybridized, aromatic structures in the hybrid foam. The carbon‐rich foam shows a considerable hardness coupled with high temperature resistance and large specific surface area of 2.1 m²⋅g⁻¹.     

Effects of 4,4′‐diaminodiphenyl ether on the structures and properties of isocyanate‐based polyimide foams

A series of thermal insulation, acoustic absorption isocyanate‐based lightweight polyimide (PI) foams with 4,4′‐diaminodiphenyl ether (ODA) units were prepared from polyaryl polymethylene isocyanate (PAPI) and the esterification solution derived from pyromellitic dianhydride (PMDA) and ODA. The structures and properties of the PI foams prepared with different molar ratio of ODA/PMDA were investigated in detail. The results show that the ODA units have great influence on the foam properties. With the increase of the ODA units, the density decreases firstly and then increases. When the molar ratio of ODA/PMDA is 3/10, the foam reaches the minimum density (13.7 kg/m³). Moreover, with increasing the ODA units, the acoustic absorption properties increase firstly and then decrease owing to the variation of the average cell diameter of the PI foams. All PI foams show excellent thermal stability, and the 5% and 10% weight loss temperature are in the range of 250–270 °C and 295–310 °C, respectively. In addition, the PI foams present low thermal conductivity and thermal diffusivity. Furthermore, the mechanical property was also evaluated and the compressive strength of the PI foams is in the range of 33.0–45.7 kPa. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46029.