Methylene Bisphenyl Diisocyanate Research Articles

Mechanically strong and resilient shape memory polyurethane with hexamethylene diisocyanate as mixing segment

Mechanical robustness and flexibility of shape memory polyurethane (SMPU) make them a prominent candidate in various field. However, the shape memory characteristics are hampered due to the lower breaking stress and strain originating from the slippage of hard segments during deformation and entropic elasticity of the segments. Herein, SMPU is synthesised by modification of Polycaprolactone diol (PCL) based soft segment by introducing a linear chain diisocyante, that is hexamethylene diisocyanate (HDI) as the mixing segment and rigid MDI (4,4′-methylene bis-phenyl diisocyanate) as the hard segment. The HDI based soft segment is expected to improve the chain flexibility, and MDI will retain the strength factor. The SMPU is characterised by chemical, structural and thermal analysis. The stress relaxation behaviour of the film was analysed w.r.t time and correlated with recovery studies using the Maxwell model. The thermomechanical conditions are optimised to attain higher shape fixity (SF) and shape recovery (SR) and the SMPU shows maximum SF (60.8%) and SR (97%) at 70°C temperature and 50% strain condition. Also, SMPU shows the tensile strength of 23.4 MPa with elongation at break of nearly 1270%. Thus, the combination of both diisocyanate and soft segments imparts strength and ductility to the SMPU.

Adsorption of nitrophenol compounds from aqueous solution by cross-linked starch-based polymers

Two kinds of cross-linked starch polymers were synthesized and used as adsorbent materials for the adsorption of o-nitrophenol (o-NP), p-nitrophenol (p-NP), 2,4-dinitrophenol (2,4-DNP) and 2-s-butyl-4,6-dinitrophenol (DNBP) from aqueous solutions. Results from adsorption experiments showed that the polymer 1 prepared by 4,4′-methylene-bis-phenyldiisocyanate (MDI) as cross-linking agent exhibited higher adsorption behaviors than that of the polymer 2 prepared by hexamethylene diisocyanate (HMDI). Equilibrium and thermodynamic of four nitrophenols on polymer 1 were further studied. Analyzed experimental data showed that the Freundlich model fitted the isotherm data better than the Langmuir model of the four nitrophenols onto polymer 1. The thermodynamics for the adsorption of the nitrophenols on polymer 1 were estimated in the range of 303–333 K. It has been found that the values of Gibbs free energy (ΔG) became more negative with decreasing temperature, which indicated that the adsorption process was more favorable at low temperature.

Quantification of isocyanates and amines in polyurethane foams and coated products by liquid chromatography-tandem mass spectrometry.

An analytical method for the identification and quantification of 10 different isocyanates and 11 different amines in polyurethane (PUR) foam and PUR-coated products was developed and optimized. Isocyanates were extracted and derivatized with di-n-butylamine, while amines were extracted with methanol. Quantification was subsequently performed by liquid chromatography–tandem mass spectrometry. Using this methodology, residual levels of isocyanates and amines in commercial PUR products were quantified. Although the recoveries of certain isocyanates and amines were low, the main compounds used as monomers in the production of PUR products, and their decomposition species, were clearly identified at quantifiable levels. 2,4-and 2,6-toluenediisocyanate were detected in most PUR foam samples and a pastry bag in the range of 0.02–0.92 mg/kg, with their decomposition compounds, 2,4-and 2,6-toluenediamine, detected in all PUR foam samples in the range of 9.5–59 mg/kg. PUR-coated gloves are manufactured using 4,4′-methylenebisphenyl diisocyanate as the main raw material, and a large amount of this compound, in addition to 4,4′-methylenedianiline and dicyclohexylmethane-4,4′-diamine were found in these samples.

A Comparison of Two Sampling Methods for the Detection of Airborne Methylene Bisphenyl Diisocyanate

The purpose of this study was to determine if there was a significant difference between two readily available sampling methodologies for airborne methylene bisphenyl diisocyanate (MDI), which is an essential precursor in the spray-on truck bed lining industry. Seventy-two personal airborne samples of MDI were collected and analyzed from nine spray-on truck bed liner businesses in northern Colorado. Wide ranges of exposure concentrations were encountered during the spray-on application, including concentrations that exceeded the OSHA permissible exposure limit. The highest airborne MDI concentration measured was 690 ppb. A statistically significant difference between field-desorbed and laboratory-desorbed methods was determined. The field-desorbed sampling methodology yielded consistently higher MDI concentrations than the laboratory-desorbed sampling methodology, which suggests that immediate desorption minimizes isocyanate loss and potential underestimations. Results from the analysis of variance also indicated that different facility factors and environmental conditions within each company, such as the use of ventilation or humidity level, affected the MDI concentrations, indicating the potential for better mitigation of exposures using the hierarchy of controls.

Preparation and Properties of Rigid Cross-Linked PVC Foam

High performance rigid cross-linked PVC foam has been prepared by molding process and boiling foam process with the main materials including polyvinyl chloride paste resin (PVC), liquefied methylene bis-phenyl diisocyanate (MDI-L) and methylhexahydrophthalic anhydride (MHHPA). The chemical structure, cellular structure and thermal properties were respectively characterized by fourier transform infrared spectrometer (FTIR), scanning electron microscopy (SEM), thermomechanical analyzer (TMA) and thermogravimetric analyzer (TGA). Results showed that the foam had a uniform cellular structure, and cell size was about 760μm. The glass transition temperature (Tg) was 81°C and 5% weight loss temperature (T5d) was 252°C.

Novel whey protein‐based aqueous polymer‐isocyanate adhesive for glulam

AbstractWhey, a by‐product of cheese making, contains whey proteins, lactose, vitamins, and minerals. Whey and whey proteins are still not fully used. In this study, whey protein‐based aqueous polymer‐isocyanate (API) adhesives were developed and characterized by bond test, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscope (SEM) for bond strength, chemical structures, and morphology. The optimized whey protein‐based API adhesive for Glulam had a 28‐h boiling‐dry‐boiling wet strength of 6.81 MPa and a dry strength of 14.34 MPa. Results indicated that the addition of polyvinyl acetate emulsion can prolong the work life of the API adhesive. Addition of crosslinker polymeric methylene bisphenyl diisocyanate (P‐MDI) not only increased the cohesive strength of the cured adhesive by crosslinking whey proteins but also resulted in strong chemical bonds via urethane linkage in wood bondlines. Addition of polyvinyl alcohol (PVA) further increased the crosslinking density of the cured adhesive due to its capability of crosslinking whey proteins through the reaction with P‐MDI. Nanoscale CaCO3 powder (3.5 wt %) as filler significantly improved bond strength due to its mechanical interlock with the polymers in the adhesive. SEM examinations confirmed that both PVA and nanoscale CaCO3 improved the compatibilities of the components in the optimized whey protein‐based API adhesive. FTIR results revealed that P‐MDI reacts mainly with the residual amino groups rather than the hydroxyl groups of whey proteins. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Removal of direct azo dyes and aromatic amines from aqueous solutions using two β-cyclodextrin-based polymers

Two β-cyclodextrin (β-CD)-based polymers were synthesized using 4,4′-methylene-bis-phenyldiisocyanate (MDI) or hexamethylenediisocyanate (HMDI) as a cross linking agent in dimethylformamide and used as sorbents for the removal of azo dyes (Evans Blue and Chicago Sky Blue), as well as aromatic amines (benzidine, p-chloroaniline and α-naphthalamine) from aqueous solutions. The sorption experiments were carried out by using batch-wise procedure involving the determination of pH effect, sorbate concentration and contact time. Moreover, from the equation isotherms such as Langmuir and Freundlich were successfully applied to model the experimental data. From the results polymer 2 was found to be a better sorbent for both azo dyes and the aromatic amines as compared to polymer 1 as proved by Langmuir isotherm model. The proposed sorption mechanism involved several kinds of interactions: physical adsorption, hydrogen bonding and formation of an inclusion complex due to the β-CD molecules through host–guest interactions.

Effect of glycerol cross-linking and PDI on the shape memory effect and mechanical properties of polyurethane

A series of shape memory polyurethane (PU) copolymers synthesized from 1,4-phenyldiisocyanate (PDI), poly(tetramethyleneglycol) (PTMG), 1,4-butanediol (BD) as a chain extender, and glycerol as a cross-linking agent were tested for the mechanical properties and the shape memory effect at the temperature 20 °C above melting temperature (Tm), and were compared with other PUs synthesized from 4,4′-methylene-bis-phenyldiisocyanate (MDI), PTMG, and BD. Mechanical properties and shape memory effect were improved substantially by adopting both PDI and glycerol. Interestingly, enthalpy of melting and Tm were not affected by the glycerol content. Vibration and shock absorption ability was investigated by measuring both loss tan δ and storage modulus with dynamic mechanical analyzer (DMA).

The interaction between hydrolytic and oxidative pathways in macrophage‐mediated polyurethane degradation

Although relatively resistant to oxidation, polycarbonate-based polyurethanes (PCNUs) are degraded by monocyte-derived macrophages (MDM) by a co-mediated mechanism involving both hydrolytic and oxidative pathways. Since a previous study showed that PCNU pretreatment with H(2)O(2) modulated degradation by esterases, human MDM were used to further elucidate this dual pathway mechanism of degradation for (14)C-radiolabeled PCNUs (synthesized with 1,6-hexane diisocyanate:polycarbonatediol: butanediol with different stoichiometry (HDI431 and HDI321) or another diisocyanate 4,4'-methylene bisphenyl diisocyanate (MDI321)). Scanning electron microscopy of PCNU slips pretreated with 20% H(2)O(2) showed that HDI431 had visible holes with more radiolabel release than from the other PCNUs. When MDM were seeded on H(2)O(2)-treated PCNUs, degradation of HDI321 and MDI321, but not HDI431 was decreased. Esterase activity was inhibited in MDM on all surfaces except MDI321, whereas inhibition of acid phosphatase occurred on all surfaces. The material surface itself, induced H(2)O(2) release from live MDM, with more H(2)O(2) elicited by phorbol myristate acetate treated MDM when cultured on HDI431 but not the other materials. H(2)O(2) pretreatment affected cell function by chemically altering the material surface and MDM-mediated degradation, known to be dependent on surface chemistry. The findings highlight that both oxidative and hydrolytic mechanisms need to be understood in order to tailor material chemistry to produce desired cell responses for in vivo applications.

Use of β-cyclodextrin and starch based polymers for sorption of Congo red from aqueous solutions

Two starch-based and a β-cyclodextrin (β-CD)-based polymers were synthesized using 4,4′-methylene-bis-phenyldiisocyanate (MDI) or hexamethylenediisocyanate (HMDI) as a cross linking agent in dry dimethylformamide and used as a sorbent for the removal of Congo red from aqueous solutions. The cross-linked polymers were characterized by Fourier transform infrared spectroscopy, thermogravimetric and differential scanning calorimetric analysis. The dye adsorption experiments were carried out by using batch and recycling column procedure. The effects of initial pH (pH 0), the contact time and the initial dye concentration were changed to obtain the best experimental conditions. The pH 0 of the dye solution strongly affected the chemistry of both the dye molecules and polymer 3 in an aqueous solution. The effective pH 0 was 7.0 for adsorption on polymer 3. The equilibrium adsorption data were interpreted using Langmuir and Freundlich models. The adsorption of Congo red was better represented by the Freundlich equation.

A Calix[4]arene Oligomer and Two Beta‐cyclodextrin Polymers: Synthesis and Sorption Studies of Azo Dyes

Two insoluble β‐cyclodextrin polymers were synthesized by reacting β‐cyclodextrin with hexamethylene diisocyanate (HMDI) or 4,4′methylene bis phenyldiisocyanate (MPDI) as a crosslinking agent and a calix[4]arene‐based oligomer was prepared by the condensation of p‐tert‐butylcalix[4]arene with HMDI and utilized to remove selected water‐soluble azo dyes from aqueous solution. Oligomer 2 was found to be a poor sorbent for the azo dyes. The influence of several parameters (pH, contact time, and NaCl concentration) on the sorption capacity was evaluated using the batch and recycling column methods. The proposed sorption mechanism involved several kinds of interactions: physical adsorption, hydrogen bonding and formation of an inclusion complex due to the β‐CD molecules through host‐guest interactions.

The human macrophage response during differentiation and biodegradation on polycarbonate-based polyurethanes: Dependence on hard segment chemistry

Human monocytes, isolated from whole blood, were seeded onto tissue culture grade polystyrene (PS) and three polycarbonate-based polyurethanes (PCNUs) (synthesized with either 1,6-hexane diisocyanate (HDI) or 4,4′-methylene bis-phenyl diisocyanate (MDI), poly(1,6-hexyl 1,2-ethyl carbonate) diol (PCN) and 1,4-butanediol (BD) in different stoichiometric ratios (HDI:PCN:BD 4:3:1 or 3:2:1 and MDI:PCN:BD 3:2:1) (referred to as HDI431, HDI321 and MDI321, respectively). Following their differentiation to monocyte-derived macrophages (MDMs) the cells were trypsinized and reseeded onto each of the PCNUs synthesized with either 14C-HDI or 14C-BD and degradation was measured by radiolabel release (RR). When the differentiation surface was MDI321, there was more RR from 14C-HDI431 than from any other surface ( p < 0.0001 ) whereas the amount of esterase (identified by immunoblotting) as well as the esterase activity was the greatest in MDM differentiated on PS, reseeded on 14C-HDI431 ( p < 0.0001 ). The effect of potential degradation products (methylene dianiline (MDA) and BD) from the PCNUs was carried out to determine possible links between products and substrate-induced activation of MDM. MDA was found to inhibit RR 60% from MDM seeded on 14C-MDI321B ( p < 0.0001 ), ∼20% from 14C-HDI431 ( p = 0.002 ) and no effect from 14C-HDI321B. MDA inhibited esterase activity 30% from MDM only on 14C-MDI321B ( p = 0.003 ), but no effect on esterase activity was observed for the other two polymers. BD had no inhibitory effect on RR from any PCNU, but did inhibit esterase activity in MDM on 14C-HDI431 ( p = 0.025 ). This study indicates that the degradation of a specific material is a multi-factorial process, dictated by its susceptibility to hydrolysis, the effect of specific products generated during this course of action, and perhaps not as well appreciated, the material's inherent ability to influence enzyme synthesis and release.

Polycarbonate-urethane hard segment type influences esterase substrate specificity for human-macrophage-mediated biodegradation

Previous studies have shown that esterase activity can degrade a variety of polyurethanes (PUs), including polycarbonate-based PUs (PCNUs). When cultured on PCNUs, differing in their chemistries, monocyte-derived macrophages (MDM) synthesized and secreted different amounts of both cholesterol esterase (CE) and monocyte-specific esterase (MSE). MDM were seeded on PCNUs synthesized with hexane diisocyanate (HDI) or 4,4′-methylene-bis-phenyl diisocyanate (MDI), PCN and [14C]butanediol (BD) in the ratio 3:2:1 (referred to as HDI321 or MDI321). The effect of phenylmethylsulfonyl fluoride (PMSF, a serine esterase and proteinase inhibitor), sodium fluoride (NaF, a MSE inhibitor) and sodium taurocholate (NaT, a CE stimulator) was assessed on degradation (measured by radiolabel release (RR)) and esterase activity in MDM lysate. The results were compared to the effect that these reagents had on commercially available CE and carboxyl esterase (CXE), which has a specificity similar to MSE. NaF inhibited CXE- and MDM-mediated RR to the same extent as for both PCNUs. However, the MDM-mediated RR from MDI321 was 1.8-times higher than HDI321 in the presence of NaT (P = 0.005). This study suggests that the difference in diisocyanate chemistry may dictate the relative contribution of each esterase to a specific material's degradation. This may be related to both the substrate specificity of each esterase, as well as by the relative amount of each esterase that the specific biomaterial substrates induce the cells to synthesize and secrete.

Phospholipase A 2 pathway association with macrophage-mediated polycarbonate-urethane biodegradation

Activation of the phospholipase A 2 (PLA 2) pathway is a key cell signaling event in the inflammatory response. The PLA 2 family consists of a group of enzymes that hydrolyze membrane phospholipids, resulting in the liberation of arachidonic acid (AA), a precursor to pro-inflammatory molecules. Given the well-documented activating role of biomaterials in the inflammatory response to medical implants, the present study investigated the link between PLA 2 and polycarbonate-based polyurethane (PCNU) biodegradation, and the effect that material surface had on PLA 2 activation in the U937 cell line. PCNUs were synthesized with poly(1,6-hexyl 1,2-ethyl carbonate)diol, 1,4-butanediol and one of two diisocyanates (hexane 1,6-diisocyanate or 4,4′-methylene bisphenyl diisocyanate) in varying stoichiometries and incubated with adherent U937 cells. PLA 2 inhibiting agents resulted in significantly decreased PCNU biodegradation ( p < 0.05 ). Moreover, when activation of PLA 2 was assessed ( 3H-AA release), significantly more 3H-AA was released from PCNU-adherent U937 cells than polystyrene-adherent U937 cells ( p < 0.05 ) which was significantly decreased in the presence of PLA 2 inhibitors. The pattern of inhibition of U937 cell-mediated biodegradation and 3H-AA release that was modulated by PCNU surface differences, suggests a role for secretory PLA 2 along with cytosolic PLA 2. Understanding PCNU activation of intracellular pathways, such as PLA 2, will allow the design of materials optimized for their intended use.

Determination of technical grade isocyanates used in the production of polyurethane plastics.

A method for determination of technical grade isocyanates used in the production of polyurethane (PUR) is presented. The isocyanates in technical grade products were characterised as di-n-butylamine (DBA) derivatives using LC-MS and LC-chemiluminescent nitrogen detection (CLND) and the total isocyanate content was compared to a titration assay. For collection of isocyanates in air, an impinger-filter sampling technique with DBA as derivatisation reagent was used. Characterised DBA and nonadeuterium labelled DBA derivatives of isocyanates in technical products were used as calibration standards and internal standards, respectively, in the analysis of air samples. Three workplaces were studied where PUR products were produced either by spraying or by moulding. In both technical products and in air samples, a number of monomeric, oligomeric and prepolymeric isocyanates of e.g. methylenebisphenyl diisocyanate (MDI) and hexamethylene diisocyanate (HDI) were characterised. Several of these have not previously been described in workplace atmospheres. In the technical isocyanate products, between 69 and 102% of the NCO content determined by titration was accounted for by LC-CLND. Quantifications of a wide range of isocyanates in air samples were performed with correlation coefficients in the range 0.988-0.999 (n= 8) and the instrumental detection limits were 0.7-25 pg. At the two workplaces where MDI- and HDI isocyanurate-based products were sprayed, the isocyanate composition in the air reflected the composition in the technical product. At the workplace where a MDI-based product was used in a moulding process, only the monomeric isocyanates were found in the air. The advantage of using characterised technical grade isocyanates as analytical standards was clearly demonstrated and the possibility of using index compounds when monitoring isocyanate exposure is discussed.

Spectroscopic linear dichroism FT‐IR studies of synthetic spider silk

AbstractThis work deals with the analysis of the orientation behavior of different segments of synthetic spider silk samples containing hard and soft segments. Two different types of spider silk were examined, one with an aliphatic hard segment (hexamethylene‐diisocyanate) and an amorphous soft segment (polytetramethylene oxide) (A40) and the other with an aromatic hard segment (4,4′‐methylene bisphenyl diisocyanate) and a semicrystalline soft segment (polyethylene oxide‐polypropylene oxide‐ polyethylene oxide) (A143). In order to observe the orientation behavior of the hard and the soft segments it was necessary to define marker bands. While for both samples the chosen marker bands for the hard segments were the same, the marker bands for the soft segments were different. FT‐IR spectra were recorded while strain was applied to the material at the same time. Two parameters, the dichroic ratio R and the order Parameter f were used to evaluate the behavior of these materials under conditions of strain. It was found that sample A143 broke at a strain level of 37,5 %, while sample A40 showed a high dynamic range up to a strain level of 307 %.

Comparison of thermal/mechanical properties and shape memory effect of polyurethane block-copolymers with planar or bent shape of hard segment

A series of shape memory polyurethane copolymers synthesized from 1,4-phenyldiisocyanate (PDI) and poly(tetramethyleneglycol) (PTMG) plus 1,4-butanediol as chain extender were compared with similar ones from 4,4′-methylene-bis-phenyldiisocyanate (MDI) and PTMG in various shape memory tests at temperature ranges of ±20 °C around glass transition temperature ( T g). Similarity and some differences between two series were found in other characterization methods such as IR spectra, phase transition, and mechanical properties. Especially, T g increased with the content of hard segment (PDI or MDI) and both copolymers generally showed similar T g at the same content of hard segment. In addition, vibration and shock absorption ability was investigated by measuring both loss tan δ and storage modulus with dynamic mechanical analyzer.

Enzyme induced biodegradation of polycarbonate-polyurethanes: dose dependence effect of cholesterol esterase

The current study has investigated the influence of esterase activity (80−400 units/ml) on the biodegradation of polycarbonate-urethanes (PCNUs) by cholesterol esterase (CE), with a particular interest in studying the influence of different hard segment structures and their contribution to sensitizing the polymer towards enzyme catalyzed hydrolysis. Polycarbonate based polyurethanes were synthesized with varying hard segment content as well as hard segment chemistry based on three different diisocyanates, 1,6-hexane diisocyanate (HDI), 4,4′-methylene bisphenyl diisocyanate (MDI) and 4,4-methylene biscyclohexyl diisocyanate (HMDI). The effect of different chemistry on surface contact angle was measured in order to define the relative chemical nature of the surfaces. The enzyme dose response was found to be lower when hard segment content in the polymer was high. There was a very strong dependence on enzyme concentration for polyurethanes with different hard segment chemistry, despite the fact that the nature of the hydrolysable polycarbonate segment remained the same. The PCNU which showed the most dramatic dependence on enzyme concentration was synthesized with HMDI. At low enzyme concentration (80 units/ml) this material was the most stable of the polymers while at elevated CE concentration (400 units/ml) the polymer underwent a catastrophic breakdown. The findings suggested that protein binding on the surfaces was saturated even though enzyme degradation did not achieve saturation on any of the surfaces. The role of protein binding in modulating the hydrolytic action of the enzymes at different activity levels highlights a need for further study in this area.

Influence of surface morphology and chemistry on the enzyme catalyzed biodegradation of polycarbonate-urethanes

—Polycarbonate based polyurethanes were synthesized with varying hard segment content as well as hard segment chemistry based on three different diisocyanates,1,6-hexane diisocyanate (HDI), 4,4′-methylene bisphenyl diisocyanate (MDI) and 4,4-methylene biscyclohexyl diisocyanate (HMDI). The surface chemistry and morphology were characterized using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The polymers were incubated with cholesterol esterase (CE) in a phosphate buffer solution at 37°C over 10 weeks. XPS results showed that the surface chemistry changed as the size and chemistry of the hard segment varied within the materials. AFM images exhibited distinctive surface morphologies for all polymers, and this was particularly apparent with changes in the hard segment chemistry. The results showed that the surface of HDI polymers consisted of relatively stiff rod-like structures, which corresponded to the soft segment domains. Polymers with a higher HDI content exhibited a dense top layer containing a relatively higher hard segment component, covering the sub-surface matrix of rod like structures. The MDI based polyurethane had large aggregates on its top surface, which corresponded to the aggregation of harder components. The HMDI based polycarbonate-urethane presented a relatively homogeneous surface where no phase separation could be detected. The relative differences in hard and soft segment content in their surface structure was supported by XPS findings. The analysis of the biodegradation results, concluded that enzyme catalyzed biodegradation within these materials was initiated in amorphous soft segment regions located in the region of the interface between hard and soft segments. A higher hard segment content at the surface contributed significantly to an increase in biostability. The findings provided an enhanced understanding for the role of surface molecular structure in the enzyme catalyzed biodegradation of polyurethanes.

Fluorescence and IR Characterization of Cure in Polyurea, Polyurethane, and Polyurethane−Urea

Fluorescence and IR spectroscopic techniques have been used to characterize cure in polyurea (PUa), polyurethane (PU), and polyurethane−urea (PUU), based on the study of model compounds. Polyurea cured in a nonreactive diluent by reacting liquid MDI (4,4‘-methylenebisphenyl diisocyanate) with 3,5-diethyltoluene diamine (DETDA) showed fluorescence intensity decrease at 339 nm due to DETDA consumption and an emerging peak near 310 nm from the formation of the urea derivative of MDI. The reaction at room temperature was complete after 50 min with supporting IR evidence of urea carbonyl at 1642 cm-1. When nonfluorescent liquid MDI was reacted with ethylene oxide terminated PPO (EO−PPO) to form polyurethane, the fluorescence intensity at 310 nm increased slowly, taking approximately 1500 min to plateau with an intensity increase of at least 15 times. For PUU, which was cured by reacting MDI, EO−PPO, and DETDA, the fluorescence behavior was more complex: first, a peak at 303 nm showed up immediately following the mixing of the reactants, probably due to urea group formation, while the peak at 333 nm decreased due to DETDA consumption, and second, the peak intensity at 303 nm, after a slight decrease began to increase with a gradual shift to 310 nm. These results were correlated with the overall extent of cure as well as the extent of urea and urethane formation monitored by FTIR spectroscopy. Within certain regions, the fluorescence behavior can be correlated to the extent of urea and urethane reaction.