Polyether-based Polyurethane Research Articles

Water diffusion in a crosslinked polyether-based polyurethane adhesive

Crosslinked polyurethanes (PU) are employed as structural adhesives. Research has been done extensively on the interaction of water with thermoplastic PU but is still largely unexplored in the case of PU networks. A chemically simple but well-defined PU is utilized here as a starting point to understand the influence of water in this kind of polymer. For up to 15 days of immersion in water, no changes in the chemical composition of the PU were observed in the IR spectra. Depending on temperature, water saturates the PU samples much earlier. Plasticization is the result as a significant decrease of the mechanical modulus and a glass transition shift to lower temperature is observed in the polymer. Interestingly, only some 70% of the water saturation is sufficient for maximum plasticization. It is concluded from the IR spectra that water debilitates the interactions between polymer chains within the network. The bridging of at least a part of the originally hydrogen-bonded urethane groups is substituted by hydrogen bonds between water and the urethane moieties.

The effects of organic template and thickening agent on structure and mechanical properties of titanium foam fabricated by replica impregnation method

Several organic components are involved in the fabrication of titanium foam using the replica impregnation method, for example polyurethane (PU) foam is used as sacrificial template and PVA as a thickening agent in titanium slurry. Such organic ingredients if not properly selected and subsequently efficiently removed during debinding can be detrimental to the mechanical properties of the titanium foam produced. In this study, polyester- and polyether-based PU foams, as well as degraded polyester-based PU foam, have been used to study the effects of template material on titanium foam quality. In addition, the effects of three different weight percentages of PVA in slurry formulation on coating uniformity have been investigated. The results showed that new (non-degraded) polyester-based PU foam is suitable as the template material for titanium foam production providing foam with a low level of contamination and acceptable compressibility behaviour. Although increasing PVA content increased the viscosity of titanium slurry and improved the coating coverage ability of slurry on the PU foam template, too high PVA content tended to cause pore blockage. The optimum PVA content was found to be 1.5wt%.

Modelling and Analysis of pH Responsive Hydrogels for the Development of Biomimetic Photo-Actuating Structures

ABSTRACTPhoto-actuating structures inspired by the chemical sensing and signal transmission observed in sun-tracking leaves have recently been proposed by Dicker et al. The proposed light tracking structures are complex, multicomponent material systems, principally composed of a reversible photoacid or base, combined with a pH responsive hydrogel actuator. New modelling and characterization approaches for pH responsive hydrogels are presented in order to facilitate the development of the proposed structures. The model employs Donnan equilibrium for the prediction of hydrogel swelling in systems where the pH change is a variable resulting from the equilibrium interaction of all free and fixed (hydrogel) species. The model allows for the fast analysis of a variety of combinations of material parameters, allowing for the design space for the proposed photo-actuating structures to be quickly established. In addition, experimental examination of the swelling of a polyether-based polyurethane and poly(acrylic acid) interpenetrating network hydrogel is presented. The experiment involves simultaneously performing a titration of the hydrogel, and undertaking digital image correlation (DIC) to determine the hydrogel’s state of swelling. DIC allows for the recording of the hydrogel’s state of swelling with previously unattained levels of resolution. Experimental results provide both model material properties, and a means for model validation.

Synthesis of highly elastic biocompatible polyurethanes based on bio-based isosorbide and poly(tetramethylene glycol) and their properties.

Bio-based high elastic polyurethanes were prepared from hexamethylene diisocyanate and various ratios of isosorbide to poly(tetramethylene glycol) as a diol by a simple one-shot bulk polymerization without a catalyst. Successful synthesis of the polyurethanes was confirmed by Fourier transform-infrared spectroscopy and 1H nuclear magnetic resonance. Thermal properties were determined by differential scanning calorimetry and thermogravimetric analysis. The glass transition temperature was −47.8℃. The test results showed that the poly(tetramethylene glycol)/isosorbide-based elastomer exhibited not only excellent stress–strain properties but also superior resilience to the existing polyether-based polyurethane elastomers. The static and dynamic properties of the polyether/isosorbide-based thermoplastic elastomer were more suitable for dynamic applications. Moreover, such rigid diols impart biocompatible and bioactive properties to thermoplastic polyurethane elastomers. Degradation tests performed at 37℃ in phosphate buffer solution showed a mass loss of 4–9% after 8 weeks, except for the polyurethane with the lowest isosorbide content, which showed an initial rapid weight loss. These polyurethanes offer significant promise due to soft, flexible and biocompatible properties for soft tissue augmentation and regeneration.

Fixation of ionic liquids into polyether-based polyurethane films to maintain long-term antistatic properties

Ionic liquids (ILs) were fixed into polyether-based polyurethane (PU) films for sustainable antistatic properties. Preliminarily, ILs were screened in terms of efficiency of antistatic effect. Surface resistivity (ρs) for IL-doped PU films changed depending the anion species, and the smallest ρs was found for the PU films containing bis(trifluoromethanesulfonyl)imide ([Tf2N])-type ILs. Then, [Tf2N]-type ILs composed of ammonium cations having hydroxyl groups were fixed into the PUs through urethane bonds. The fixation of 1000 ppm of the ILs reduced the ρs of the PU films from 2.1 × 1012 to 2.1 × 109 Ω sq−1. These IL-fixed PU films were revealed to possess high washing durability confirmed by negligible change of ρs before and after ultra-sonication treatment in methanol.

Thin, Tough, pH-Sensitive Hydrogel Films with Rapid Load Recovery

Stimuli-responsive hydrogels are used as the building blocks of actuators and sensors. Their application has been limited, however, by their lack of mechanical strength and recovery from loading. Here, we report the preparation of pH-sensitive hydrogels as thin as 20 μm. The hydrogels are made of a polyether-based polyurethane and poly(acrylic acid). A simple method was employed to create hydrogels with thicknesses in the range of 20-570 μm. The hydrogel films volume changed by a factor of ∼2 when the pH was switched around the transition point (pH 4). Tensile extensibilities of up to ∼350% were maintained at each pH, and the average Young's modulus and tensile strength were in the range of 580-910 and 715-1320 kPa, respectively, depending on the pH. Repeated tensile loading and unloading to 100% extension showed little permanent damage, unlike analogous double-network hydrogels, and with immediate recovery (up to 75-85% of the first loading cycle), unlike hybrid ionic-covalent interpenetrating network hydrogels.

Polyurethane-Silica Nanocomposite Membranes for Separation of Propane/Methane and Ethane/Methane

This study examines the role that silica nanoparticles play on the permeation of methane, ethane, and propane gases through two types of polyurethane (PU) membranes: one based on polyether and the other based on polyester. These PU membranes are synthesized from polycaprolactone (PCL225) polyester and polypropylene glycol (PPG) polyether in a 1–3–2 mol ratio of polyol/hexamethylenediisocyanate/1,4-butane diol. The prepared PU-silica membranes are characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and wide-angle X-ray diffraction (WAXD) analyses. The characterization analyses confirmed the nanoscale distribution of silica particles within the polymer matrix. Permeation experiments reveal that in polyether-based PU, permeability first increases by increasing silica content up to 2.5%, and then decreases. The permeability of gases in polyester-based PU constantly decreases by increa...

Sorption of food dyes on polyurethane foam and aluminum oxide

The sorption of food dyes Sunset Yellow (E-110), Tartrazine (E 102), Ponceau 4R (E-124), Fast Green FCF (E-143) on polyether-based polyurethane foam, and α-Al2O3 from water solutions has been studied. It has been found that the maximum sorption is observed in the range of 0.2 M HCl-pH 2 on polyurethane foam and at pH 2–4 on aluminum oxide. Under the optimal conditions the recoveries on polyurethane foam and α-Al2O3 are 20–30% and 70–80%, respectively. It has been shown by diffuse reflectance spectroscopy that, for all dyes except for Fast Green FCF, only one form of the dye that dominates under these conditions in the aqueous solution is extracted on the sorbents in the range of 0.5 M HCl, pH 8.0. Possible models of the interaction between the dyes and the sorbent surface are proposed.

Gas separation properties of poly(ethylene glycol)/poly(tetramethylene glycol) based polyurethane membranes

In this study, the effect of the structure of polyether-based polyurethane (PU) membranes on their gas separation properties has been investigated. In this regard, a series of polyurethanes based on hexamethylene diisocyanate (HDI) and 1,4-butanediol as hard segments and different soft segments such as poly(tetramethylene glycol) (PTMG, 2000 g/mol), poly(ethylene glycol) (PEG, 2000 g/mol) and PTMG/PEG mixture were synthesized. PU membranes were prepared by thermal phase inversion method and their physical properties were analyzed by FT-IR, XRD and DSC analyses. The obtained results from FT-IR and DSC analyses indicated that the phase separation of hard and soft segments decreased and chain mobility was restricted, resulting in the increase in glass-transition temperature of the soft segment, by content of the PEG in the PU structure. The permeability of pure N 2 , O 2 , CH 4 and CO 2 gases were determined using constant pressure method at different feed pressures and temperatures. The results of gas permeation experiments showed that by increasing the ether group content in the polymer structure, permeability of the pure gases decreased, while CO 2 /N 2 ideal selectivity increased. The obtained results also indicated that the permeability of CO 2 decrease from 132.52 barrer in PU0 (PU containing 100 wt% of PTMG in soft segment) to 20 barrer in PU100 (the PU containing 100 wt% of PEG in soft segment), respectively. CO 2 /N 2 selectivity increased from 28 to 90. Trade-off evaluation also showed that the potential of studied membranes for commercialization in CO 2 /N 2 and even CO 2 /CH 4 separations increase by PEG content in polymer and the PU membrane which contains 75/25 wt% ratio of PEG/PTMG had the highest. ▸ The effect of soft segment on gas separation properties of PU membrane investigated. ▸ By increasing the amount of PEG in PU, the phase separation decreases. ▸ The solubility domination of gas transport in studied PU membranes investigated. ▸ Low permeability of CO 2 , but high selectivity of CO 2 /N 2, observed for PEG based PU. ▸ The studied PU membranes show high performance in CO 2 /N 2 gas separation.

전기분사를 이용한 양성담관 협착 치료용 약물방출 스텐트 개발

최근에 내시경 관련기술의 진보에 따라서 시술 편리성, 회복시간 단축, 환자 고통 경감 등의 장점으로 인해 스텐트 삽입술이 빠르게 진보하였다. 본 연구에서 양성담관 협착 치료를 목적으로 파클리탁셀을 이용한 약물방출 스텐트를 전기분사 방법에 의해 제조하였으며, 이 때 사용된 고분자는 polyether-based polyurethane(상표명 : PELLETHANE 2363-80AE<TEX>$^{(R)}$</TEX>)과 첨가제로서 Pluronic F127, 약물로서 파클리탁셀을 사용하여 금속스텐트 표면에 코팅하였다. 그 결과로서, 약물이 코팅된 고분자 필름의 물리적 특성은 SEM, FTIR, 접촉각 측정기, XRD에 의해 확인하였으며, 약물방출속도는 약물함량이 높을수록 감소하였음을 알 수 있었다. Recently, along with technology development of endoscopic equipment, the stent technology has been developed for the convenience of operation, shortening of recovery times, and reduction of patient's pain. In this study, paclitaxel-eluting metal stents for treatment of biliary benign stenosis were developed through an electrospray-coating method. Polyether-based polyurethane (PELLETHANE 2363-80AE<TEX>$^{(R)}$</TEX>)) and paclitaxel were coated onto the surface of a metallic stent and Pluronic F127 was used as an additive. As a result, physicochemical characterization of paclitaxel via SEM, FTIR, contact angle and XRD techniques revealed the information of solid state of paclitaxel-loaded PU film. The in vitro release profile showed a slower release rate with a higher content of paclitaxel.

Surface characterisation of oxygen plasma treated electrospun polyurethane fibres and their interaction with red blood cells

In this work, the effects of oxygen plasma surface modification have been studied on electrospun polyether-based polyurethane in order to investigate the imposed limitations and possibilities to improve surface characteristics on fibrous assemblies. The evolution of induced changes in surface morphology, chemistry and wettability by the plasma treatment has been characterised for increasing plasma exposure time using scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Significant reduction in fibre diameter concomitant with progressing rough surface textures are found on the fibres in surface layers during early treatment phases while extended exposure eventually causes the fibre structure to deteriorate. Surface oxygen content and functionalities such as carbonyl and carboxyl increase slightly with longer treatments until loss of material integrity occurs. The results have also shown that oxygen plasma rapidly alters the initially strong hydrophobic character of the non-woven fibres to hydrophilic behaviour, allowing water penetration into the network, but without significant changes for increased exposure time. In addition, the response of red blood cell shape to pristine and oxygen plasma treated fibres were found to be similar. In both cases, a population of cells having fibre contact displayed protrusions while measurements showed that the cell function remain intact and indicated that the adhesion was non-specific. The reported findings yield useful process knowledge that can support the formation of well-defined fibre architectures and are valuable in the designs of electrospun polyurethane material systems utilising oxygen plasma surface modification.

Assessment of the degradation of polyurethane foams after artificial and natural ageing by using pyrolysis-gas chromatography/mass spectrometry and headspace-solid phase microextraction-gas chromatography/mass spectrometry

Polyurethane foams are widely present in museum collections either as part of the artefacts, or as a material for their conservation. Unfortunately many of PU foam artefacts are in poor condition and often exhibit specific conservation issues. Their fast thermal and photochemical degradations have been the aim of previous researches. It is now accepted that hydrolysis predominates for polyester-based polyurethane PU(ES) whereas oxidation is the principal cause of degradation for polyether-based polyurethane PU(ET) variety. Only a few studies have been devoted to volatile organic compounds (VOCs) emitted by polyurethanes and, to our knowledge, none were performed on polyurethane foams by using headspace-solid phase microextraction (HS-SPME). The objective of the work described here is to assess the impact of some environmental factors (humidity, temperature and daylight) on the degradation of PU foams by evaluating their volatile fractions. We investigated morphological changes, polymerized fractions and volatile fractions of (i) one modern produced PU(ES) foam and one modern PU(ET) foam artificially aged in different conditions as well as (ii) four naturally aged foams collected from various daily life objects and selected for the representativeness of their analytical data. Characterization procedure used was based on attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and non-invasive headspace solid-phase microextraction coupled with gas chromatography and mass spectrometry (HS-SPME-GC/MS). In this paper, the formation of alcohol and acid raw products for PU(ES) and glycol derivatives for PU(ET) during natural and artificial ageing is confirmed. These main products can be considered as degradation markers for PU foams. Results show that artificial and natural ageing provide similar analytical results, and confirm that the dominant degradation paths for PU(ES) and for PU(ET) are hydrolysis and photo-oxidation, respectively. Lastly, we highlight that non-invasive HS-SPME-GC/MS analysis allows to distinguish between PU(ES) and PU(ET) at any point of their degradations.

Gas separation properties of polyether-based polyurethane–silica nanocomposite membranes

In this study, the effect of silica nanoparticles on the gas permeation properties of polyether-based polyurethane membrane was investigated. Polyether-based polyurethane was synthesized by bulk two-step polymerization of polypropylene glycol/hexamethylenediisocyanate (HMDI)/1,4-butanediol (BDO) in mole ratios of 1:3:2. Silica nanoparticles were prepared through the sol–gel method by hydrolysis of tetraethoxysilane (TEOS). Polyurethane and polyurethane–silica nanocomposite membranes were prepared by solution blending and casting method. The prepared polyurethane–silica membranes were characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), thermal gravimetery analysis (TGA) and differential scanning calorimetry (DSC) analyses. These methods confirmed the homogenous and nano scale distribution of silica nanoparticles in prepared polymers. Gas permeation properties of polyurethane–silica nanocomposite membranes with silica content of 2.5, 5, 10 and 20 wt.% was studied for pure CO 2, CH 4, N 2 and O 2 gases. The obtained results indicated the reduction in permeability of all gases, but enhancement in CO 2/N 2, CO 2/CH 4 and O 2/N 2 selectivities was observed by increasing the content of non-permeable silica nanoparticles in polyurethane–silica membranes. In the case of polyurethane–silica (20 wt.%) nanocomposite membrane, the obtained CO 2/N 2 selectivity was 1.65 times of pure polyurethane, while the CO 2 permeability reduction of polyurethane–silica membranes was 35.6% in comparison with pure polyurethane. Finally, the modified Higuchi model was applied to predict the permeability of polyurethane–silica membranes and fairly good agreement was observed between experimental and predicted gas permeabilities of these membranes.

Improvement of electrostrictive properties of a polyether-based polyurethane elastomer filled with conductive carbon black

The electrostrictive properties of a polyether-based polyurethane elastomer and its corresponding composites filled with conductive carbon black (CB) were studied by measuring the thickness strain S Z induced by external electric fields E. For films with thicknesses of approximately 50 μm, the apparent electrostrictive coefficient M was measured at low electric fields, E ⩽ 4 V/μm, and different CB contents (up to a volume fraction of 2%). Dielectric measurements in AC mode were performed in order to determine the percolation threshold f c , which was 1.25 v%. This optimal volume fraction yielded a remarkable threefold increase in M, associated with an increase of the dielectric constant by a factor 7, in comparison with pure PU. This enhancement of the electric field-induced strain and apparent electrostriction was mainly triggered by an increase of the dielectric constant, even if the intrinsic electrostriction coefficient Q was decreased. The nanocomposites thus seem to be very attractive for low-frequency electromechanical applications. Above f c , their conductivity was raised and their electrostrictive activity lost. Finally, there is a good agreement between the experimentally determined dependence on the CB content of the M coefficient and the theoretical estimation calculated from dielectric and mechanical measurements.

Synthesis, Characterization and Mechanical Properties of Hydroxyl-Terminated Hyperbranched Polymer Graft Polyether-Based Aliphatic Polyurethane Elastomer

Hydroxyl-terminated hyperbranched polyurethane elastomer (HBPU) was synthesized by graft copolymerization of hyperbranched poly (amine-ester) polyols(HPAE) and polyether-based aliphatic polyurethane prepolymer(PPU), and the PPU was synthesized by step polymerization of isophorone diisocyanate(IPDI) with polyethylene glycol(PEG) and dibutyltin dilaurate(DBTDL) as catalyst. The FT-IR spectroscopy, TGA and XRD were used to characterize the structure, thermal properties and crystallinity of HBPU. The mechanical properties of the elastomers were conducted on a testing machine. Microphase separation of HBPU film surface was studied by atomic force microscopy (AFM). The experimental results showed that the HBPU took on excellent hydrogen bonding and mechanical properties. The tensile strength of HBPU elastomer reached to 20.6MPa, which increased by 41.2 times than that of PPU elastomer. And the elongation at break was as high as 251.3%.

Hydrogen bonding and mechanical properties of thin films of polyether-based polyurethane–silica nanocomposites

Two series of thin films of polyether-based polyurethane–silica nanocomposites having hard segment content of 51% and 34% and different concentrations of SiO 2 nanoparticles (0, 0.5, 1.0 and 3.0 vol.%) have been prepared. Infrared linear dichroic (LDIR) ratio, mechanical and differential scanning calorimetry (DSC) measurements were performed in order to determine the influence of hydrogen bonding on their mechanical and thermal properties. The degree of phase separation (DPS) and orientational functions in dependence on strain were calculated from the polarized IR spectra. The presence of silica nanoparticles gives rise to significant differences in the mechanical (stress–strain) properties of the nanocomposites with regard to the pure polymer. The nanocomposite thin films with lower hard segment content (HSC) displayed decreased stiffness and tensile and increased elongation at break in comparison to the nanocomposites with higher HSC. There was no distinctive influence of nanoparticles on the glass transition temperatures of soft segments. Nanosilica significantly affected the melting behavior of the hard phase only in samples with higher HSC.

SYNTHESIS, CHARACTERIZATION AND MECHANICAL PROPERTIES OF POLYETHER-BASED ALIPHATIC POLYURETHANE ELASTOMERS COMPOSED OF HYPERBRANCHED POLYESTER SEGMENTS

Aliphatic polyether-based polyurethane(PU) elastomers with hyperbranched polyester segments were synthesized by prepolymer process from polytetramethylene ether glycol,hydroxyl-terminated hyperbranched polyester(HB-20),IPDI and 1,4-butanediol.The crosslinking density of the PU elastomer was calculated by using the Flory-Rehner equation.The degree of hydrogen bonding,the microstructure and the morphologies of these PU materials were characterized by means of FTIR,WAXD and DSC,respectively.The experimental results indicated that the PU elastomers containing small amount of HB-20 exhibited the enhanced hydrogen bonding and the micro-phase separated morphologies as well as the mechanical properties.As compared with the comparable PU specimen,the tensile strength of the polyether-based aliphatic PU containing 6 wt% HB-20 increased by 2.1 times,up to 37.9 MPa,and the elongation at break was still as high as 414%,resulting from the dual effects of the hydrogen bonding and the crosslinking density in the PU system.

In vitro interaction of human fibroblasts and platelets with a shape‐memory polyurethane

Physicochemical and mechanical properties, in vitro cytotoxicity, cytocompatibility, and platelet adhesion were investigated on a shape-memory polyether-based polyurethane (MM-5520 SMPu) using the polyether-based Pellethane 2363-80AE (Pell-2363 SPU) as reference. MM-5520 SMPu and Pell-2363 SPU showed similar average molecular weights and different surface properties, with a higher hydrophilicity and roughness for the SMPu. By tensile tests and dynamic mechanical analysis, the peculiar characteristics of the MM-5520 SMPu were evidenced: strong temperature-dependent behavior for SMPu compared with SPU, and a high shape recovery. MM-5520 SMPu did not show any cytotoxic effect on the adhesion and proliferation of human skin fibroblasts and gingival fibroblasts, and a good cytocompatibility was observed with both cell types, as demonstrated by cell counting and scanning electron microscopy observations. SMPu compared with SPU showed higher adsorption of extracellular matrix proteins such as fibronectin, fibrinogen, and collagens. Proteins adsorbed onto SMPu significantly enhanced the adhesion and proliferation of human fibroblasts. The interaction of SMPu with platelets was studied with platelet rich plasma. Fewer platelets adhered to the SMPu, with minor morphological variations than onto the SPU. The cytocompatibility and hemocompatibility of MM-5520 SMPu combined with its unique properties such as change in shape or in stiffness, depending on practical requirements, make this shape-memory material potentially advantageous for biomedical applications.

Studies on indium sorption from iodide medium by polyurethane foam

The sorption behavior of indium iodide onto polyether-based polyurethane (PUF) foam was investigated. The system shows rapid kinetics and maximum sorption from a meaningful range of either acidic or basic media and achieves distribution ratios above 10(4) L kg-1 ([KI] > 0.6 mol kg-1). Sorption equilibrium analysis indicates tetraiodo-indate (MInI4) as the main species sorbed on the foam matrix. A Langmuir isotherm was successfully fitted and values of (1.55±0.02) x 10-1 mol kg-1 and (7.0±1.3) x 10(4) L g-1 were obtained for the saturation capacity Ks and adsorption coefficient b, respectively. The temperature effect was evaluated and the thermodynamic parameters calculated. The values of the equilibrium constant, Kc, decreased with increasing temperature. The negative values of deltaG, deltaH and deltaS indicate a spontaneous and exothermic chemisorption process favored at low temperatures.

Low-temperature pyrolysis products from a polyether-based urethane

The pyrolysis products from a polyether-based polyurethane were analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), direct probe chemical ionization mass spectrometry (CI-MS), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Pyrolysis of the urethane was found to ensue about 250°C in inert atmosphere. The initial degradation products (∼250–275°C) may be explained by three decomposition pathways. Dissociation to isocyanate and alcohol yields as pyrolyzates diphenylmethane diisocyanate, an ‘amine–isocyanate’, 1,4-butanediol, and hydroxyl-terminated polyurethane and polyether oligomers. Dissociation to amine, olefin, and carbon dioxide is less prevalent initially; this produces an amine-isocyanate, methylene dianiline, and butenyl-terminated polyurethane and polyether oligomers. ‘Intramolecular exchange’ produces cyclic urethane oligomers. At about 300°C, more oligomeric pyrolyzates are observed with aromatic amine and/or butenyl end groups. These indicate that contributions from dissociation to amine, olefin, and carbon dioxide increase with increasing degradation temperature. Also at about 300°C, some oligomeric pyrolyzates are observed that have alkyl and/or aldehyde end groups. These are formed via free radical processes. By 325°C, all nitrogen-containing oligomeric pyrolyzates have decomposed. The remaining nitrogen is in the form of methylene dianiline (MDA) or methylated MDA.