Free Isocyanate Research Articles

Development and Applications of an Amide Linchpin Reagent.

Linchpin reagents are building blocks that can be chemoselectively functionalized to afford products with a common, useful functional group. In this work, we describe the development and validation of the first amide linchpin reagent and demonstrate its use as a doubly electrophilic building block for the synthesis of a variety of amides, including challenging classes. The linchpin reagent was first functionalized via rhodium-catalyzed electrophilic amination. Selected masked C-isocyanate products were then further derivatized with Grignard reagents to produce secondary amides, or tertiary amides if an alkylating agent was added subsequently. The success of this sequence relies on fully controlled reactivity at each electrophilic site, first exploiting the weak N-O bond and then, the ability to form the free isocyanate intermediate in situ. The overall transformation proceeds with high chemoselectivity, demonstrating the ability of this new linchpin reagent to form amides through atypical bond construction. Finally, the potential of this reagent as a more broadly applicable NCO linchpin is demonstrated by the formation of lactams and unsymmetrical ureas.

Extrudable Covalently Cross‐Linked Thio‐Urethane Liquid Crystalline Elastomers

AbstractLiquid crystalline elastomer networks cross‐linked by dynamic covalent bonds (xLCEs) possess the remarkable capability of being (re)processed during plastic flow at high temperatures, while also allowing for the (re)programming of their local alignment. However, the current generation of xLCEs cannot be extruded directly into filaments or injection‐molded into shapes capable of actuation. Here, a novel poly(thio‐urethane) (PTU) LCE thermoset is presented. The inclusion of dibutyltin dilaurate as a catalyst enables the manipulation of the elastic–plastic transition through two distinct pathways. The dissociative equilibrium exchange between the thio‐urethane linkage to form separate thiol and isocyanate competes with the associative exchange of thio‐urethane and a free isocyanate or thiol groups. The temperature of fast plastic flow onset is ≈160 ˚C, and the associated bond‐exchange activation energy is ≈54 kJ mol−1. The hydrogen bonding below the elastic‐plastic transition makes the elastomer robust and extremely ductile with a failure strain exceeding 600% and a Shore hardness A of 72, preventing any creep during cyclic thermal actuation. The versatility of this dynamically cross‐linked elastomer is successfully demonstrated by extruding it using a commercial twin‐screw extruder, injection molding it into required shapes, and hot‐pressing it into flat films or shapes.

Synthesis and Characterization of Hydrophobic and Low Surface Tension Polyurethane

Polyurethane is a common polymeric coating, providing abrasion resistance, chemical durability, and flexibility to surfaces in the biomedical, marine, and food processing industries with great promise for future materials due to its tunable chemistry. There exists a large body of research focused on modifying polyurethane with additional functionalities, such as antimicrobial, non-fouling, anticorrosive action, or high heat resistance. However, there remains a need for the characterization and surface analysis of fluoro-modified polyurethanes synthesized with commercially available fluorinated polyol. In this work, we have synthesized traditional solvent-borne polyurethane, conventionally found in food processing facilities, boat hulls, and floor coatings, with polyurethane containing 1%, 2%, and 3% perfluoropolyether (PFPE). Polyurethane formation was confirmed by attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy, with the urethane band forming at 1730 cm−1 and the absence of free isocyanate stretching from 2275–2250 cm−1. X-ray photoelectron spectroscopy (XPS) was used to confirm perfluoropolyether polymerization with an increase in the atomic percentage of fluorine. Wettability and hydrophobicity were determined using a dynamic water contact angle with significant differences in advancing the water contact angle with the inclusion of perfluoropolyether blocks (PU–co–1PFPE 131.5° ± 8.0, PU–co–2PFPE 130.9° ± 5.8, and PU–co–3PFPE 128.8° ± 5.2) compared to the control polyurethane (93.6° ± 3.6). The surface orientation of fluorine supported the reduced critical surface tensions of polyurethane modified with PFPE (12.54 mN m−1 for PU–co–3PFPE compared to 17.19 mN m−1 for unmodified polyurethane). This work has demonstrated the tunable chemical qualities of polyurethane by presenting its ability to incorporate fluoropolymer surface characteristics, including low critical surface tension and high hydrophobicity.

Polyaspartic polyurea/graphene nanocomposites for multifunctionality: Self-healing, mechanical resilience, electrical and thermal conductivities, and resistance to corrosion and impact

Polyurea elastomers have attracted increasingly more attention due to excellent mechanical performance, and their wide industrial applications are in need of multifunctionality such as thermal conductivity. We herein prepared polyaspartic polyurea elastomers with optimal tensile strength and fracture strain by adjusting the isocyanate index and free isocyanate content. As a class of nanofiller, isocyanate-modified graphene nanoplatelets (IP-GNPs) were developed and they formed a stable, robust interface with the polyurea matrix, resulting in mechanical reinforcement and multifunctionality. The nanocomposite at 0.05 vol% of IP-GNPs revealed a tensile strength of 15.72 ± 0.67 MPa, representing an increment of 108.21% over pure polyurea, with excellent resistance to acidic and alkali corrosion. After 9 h of post-maintenance at 60 °C, the nanocomposite reached a healing efficiency up to 80.10% as driven by hydrogen bonds. An electrical percolation threshold was observed at 3.61 vol% of IP-GNP for the nanocomposites. The thermal conductivity reached 38.49 W/m K at 7.00 vol% due to the formation of the IP-GNP network in polyurea, where the electron thermal conductivity plays a dominant role. In comparison with those high thermal conductivity values obtained by back-filling polymers into a network established beforehand, this facile approach would be highly favored in industry for the development of elastomer nanocomposites with multifunctionality for many applications, e.g. smart sensors, protective coatings, energy harvesting, etc.

Synthesis and characterization of isocyanic bonding agents by the reaction of TDI and 5,5‐dimethylhydantoin for use in composite propellants

AbstractThis paper aims to present the study of obtaining a potential isocyanic bonding agent. The process is based on introducing free isocyanate groups into hydantoin ring. In addition to acting as bonding agents, they can act as curing agents, promoting the formation of cross‐links with the binder so that the propellant cures. The synthesis process consisted of the reaction between toluene diisocyanate (TDI) and 5,5‐dimethylhydantoin (DMH) under different parameters (time, temperature, reaction atmosphere, solvent, and product purification). The reactions were monitored by Fourier transform infrared spectroscopy in the mid‐infrared region (FT‐IR). Furthermore, the product obtained was characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), elemental analysis (CHN), and volumetric chemistry (determination of the isocyanate‐NCO index). Changes in physical characteristics and the results of the determination of index NCO, FT‐IR, TGA, DSC, and CHN analysis indicate that the proposed reactions occurred. It is concluded that, among the parameters studied, those most suitable for the reaction system between isocyanic reagents TDI and DMH are a temperature of 90 °C, coupling of a nitrogen cylinder, and use of toluene solvent in the reaction system.

Preparation and characterization of hybrid resin from used urea-formaldehyde and isocyanate resin

Hybrid resins composed of polymeric 4-4 diphenyl methane diisocyanate (pMDI) and used urea-formaldehyde (UUF) resins were prepared and studied. In these hybrid resins, high ratios of pMDI (e.g., 20%) were evenly dispersed in UUF resins by using acetone as a solvent for pMDI. The viscosity of the hybrid resin containing 15% of pMDI only changed from 216 to 424 mPa s with 30 h of storage. Chemical composition analysis showed that the free isocyanate groups were reacted with hydroxyl groups in the hybrid resins within 2 h. From a curing kinetics analysis, even without obvious active isocyanate groups, these hybrid resins still showed lower curing peak temperatures and Kissinger activation energies than the UUF resin. Moreover, the hybrid resins presented significantly higher dry and wet tensile shear strengths than the UUF resin. The effective use time of the hybrid resin with 15% pMDI reached up to 12 h. This study provided a new method for modifying UF resin with pMDI. These results also proved the feasibility of applying the hybrid resins in wood-based composites manufacturing.

Preparation process and performance of thermoplastic polyurethane/amorphous poly alpha olefin compound modified bitumen

As a bitumen modifier, waste thermoplastic polyurethane (TPU) could effectively improve the intermediate and low temperature pavement performance of bitumen and increase the recycling rate of waste. However, the high temperature performance of TPU modified bitumen is insufficient, which limits the application of TPU modified bitumen in pavement engineering. The objective of this study is to improve the high temperature performance of TPU-modified bitumen by compounding amorphous poly alpha olefin (APAO). The orthogonal test of TPU/APAO modified bitumen was conducted to determine the preparation process parameters. The physical and rheological properties of TPU/APAO modified bitumen were investigated by penetration, softening point, ductility, elastic recovery, viscosity, dynamic shear rheometer (DSR, including temperature sweep and multiple stress creep recovery), and bending beam rheometer (BBR) tests. The compatibility and modification mechanism of TPU/APAO modified bitumen were studied by storage stability, fluorescence microscopy (FM), and Fourier transform infrared spectroscopy (FTIR) tests. The test results show that the optimum preparation process of TPU/APAO compound modified bitumen is 5000 rpm for 60 min at 190 °C. The addition of APAO reduces penetration and ductility, increases softening point and viscosity of TPU modified bitumen. The low temperature performance is not sacrificed with the improvement of the high temperature PG grade. Besides, the anti-aging properties and creep recovery rate of compound modified bitumen are optimal at 2% TPU and 6% APAO. The proper content of APAO can improve the compatibility between TPU and bitumen. APAO is physically mixed with bitumen, but the free isocyanate in TPU can react with the polar carboxyl group (asphaltene) and their product is closely related to the PU bond.

Reactivity and Curing Efficiency of Isocyanate Cross-Linkers with Imidazole-Based Blocking Agents for Low-Temperature Curing of Automotive Clearcoats

For the application of low-temperature curing on automotive clearcoats, isocyanate cross-linkers blocked with imidazole derivatives were newly synthesized. The effect of the alkyl groups in the imidazole derivatives on the deblocking behavior and curing kinetics was investigated. The free isocyanate groups exposed by the deblocking of imidazole-based blocking agents were monitored by real-time Fourier-transform infrared spectroscopy. The bond dissociation energy, activation energy of deblocking, and H–N distance were interpreted through density functional theory simulation of various imidazole-based blocked isocyanates. To evaluate their applicability to automotive clearcoats, the synthesized imidazole-based blocked isocyanates were mixed with a polyol binder containing hydroxyl groups, and the clearcoat samples were cured at relatively low curing temperatures (100, 110, and 120 °C). The real-time storage modulus was measured using a rotational rheometer to elucidate the thermal curing dynamics by the blocking agents. In addition, the surface hardness of the cured clearcoat layers, which is affected by the chemical structure of the imidazole derivatives, was evaluated by nanoindentation test. In-depth analyses of the deblocking behaviors and thermal curing properties of clearcoats using imidazole-based blocked isocyanates demonstrated that the newly developed coating system could be suitably applied for the development of low-temperature curing technology.

Supramolecular thermogels from branched PCL-containing polyurethanes.

Thermogels are temperature-responsive hydrogels which are most commonly formed by supramolecular self-assembly of polymer amphiphiles comprising of both hydrophobic and hydrophilic segments. Although polyurethane thermogels have shown great promise as biomaterials, their synthesis by step-growth polymerisation of diols and diisocyanates can also result in formation of allophanate branches, which arise from the reaction between free isocyanate groups and urethane linkages along the polymer backbone. In this paper, we investigate the effects of different synthetic conditions on the degree of allophanate branching on polyurethane amphiphiles, and explore the influences of these branches on the polymers' critical micelle concentration (CMC), thermodynamics of micellization and subsequent thermogel properties. Our findings offer new insights into the relationship between polymer structure, micelle and gel properties. These results highlight the importance of taking polymer branching into account for understanding the hierarchical self-assembly of polymer amphiphiles and the resulting thermogel properties and behaviour.

Synthesis and characterization of lignin-polyurethane based wood adhesive

The present work aims to evaluate the influence of addition of kraft lignin in moisture curing polyurethane (PU) based wood adhesives. The mechanical, thermal properties and chemical structure of the adhesive were studied. The lignin-PU adhesives were obtained by replacing 1%, 3% and 5% of polypropylene glycol (PPG) by Kraft lignin and further reacted with monomeric diphenylmethanediisocyanate (MDI). The aliphatic hydroxyl level of lignin was not taken into consideration in the stoichiometry, in order to find out effect on % free NCO of the final product. The chemical structure of the synthesized lignin-PU adhesives were analyzed by Fourier transform infrared spectroscopy (FTIR). The lap shear strength of the adhesives was tested by bonding canarium wood substrates. The results illustrated that by increasing the weight % of lignin in such lignin-PU adhesives, a decrease in the free isocyanate content, leading to slower setting time but higher shear strength values, were observed. Similarly, the thermal properties of lignin-PU adhesive were also studied, showing an increase in glass transition temperature (Tg) with increase in lignin content.

Synthesis and mechanical properties of bio-sourced polyurethane adhesives obtained from castor oil and MDI-modified cellulose acetate: Influence of cellulose acetate modification

In this study, cellulose acetate and castor oil have been used to synthesize new eco-friendly alternatives to traditional polyurethane adhesives. First, cellulose acetate (CA) was modified with diphenylmethane-4,4′-diisocyanate (MDI) at different NCO:OH molar ratios, ranging from 2 to 4.53, and then the resulting biopolymers were mixed with castor oil (CO) at 1:1 wt ratio. The fully cured bio-sourced adhesives were rheologically characterized by applying dynamic oscillatory torsional tests at different temperatures (from −30 up to 200 °C). Furthermore, their adhesion performance on stainless steel and poplar wood substrates was analyzed, by conducting standardized mechanical tests, namely single-lap shear and 180° peel strengths, at room temperature and 100 °C. Fourier transform infrared spectroscopy-attenuated total reflectance along with differential scanning calorimetry and thermogravimetric analysis were also performed. Above a critical NCO:OH ratio, a thermo-rheological simplicity was found within the whole temperature range considered, being able to apply the t-T superposition principle. However, an increase in the temperature led to a depletion in their mechanical performance, thus reducing their temperature range of application. Thermal and spectroscopic analysis corroborated the complete disappearance of free isocyanate during the first few days of curing, and a segmented structure, typical of polyurethanes. Optimum thermo-rheological behaviour and adhesion performance on wood and stainless steel of the bio-sourced polyurethanes studied were found for NCO:OH molar ratios higher than 3.5, which was related to the higher compatibility between hard and soft microdomains.

A Simple Method for the Quantification of Free Isocyanates on the Surface of Cellulose Nanocrystals upon Carbamation using Toluene Diisocyanate

In many reports, cellulose and nanocellulose have been carbamated using 2,4-toluene diisocyanate (2,4-TDI) to allow the grafting of molecules or polymers onto their surfaces. Such a process usually involves the reaction of the more reactive isocyanate group of TDI (para-NCO) selectively with a hydroxyl group from the cellulose surface, followed by the reaction of the free isocyanate (ortho-NCO) with a desired molecule. After the first step, it is not possible, using elemental analysis, to determine the amount of ortho-NCO on the cellulosic surface, as an ideal para/ortho selectivity is difficult to obtain. This paper presents a simple method for the quantification of ortho-NCOs on the surface of cellulose nanocrystals upon TDI-based carbamation. It relies on the pH increase upon a complete hydrolysis of ortho-NCOs to amine groups using acidified dimethylsulfoxide. The method was found to be accurate and valid for a degree of substitution of up to 20%.

Preparation of five‐membered bis(cyclic carbonate)s at atmospheric pressure for polyhydroxyurethane coatings

ABSTRACTCyclic carbonates reacted with diamines or polyamines have been proposed as a greener and safer method to prepare free isocyanate polyurethane coatings. Here, five kinds of bis(cyclic carbonate)s (TDC: toluene bis(cyclic carbonate), MDC: 4,4′‐diphenylmethane bis(cyclic carbonate), IPDC: isophorone bis(cyclic carbonate), HMDC: 4,4′‐methylenebis(cyclohexyl cyclic carbonate), HDC: hexamethylene bis(cyclic carbonate)) were prepared by reacting glycerol carbonate with diisocyanate under atmospheric pressure. Their structures were verified by 1H‐NMR and 13C‐NMR. These difunctional cyclic carbonates were then reacted with several amines to prepare new polyhydroxyurethane (PHU) coatings, and the film properties were tested. It was found that PHUs based on aromatic and alicyclic structures including TDC, MDC, IPDC, and HMDC displayed high hardness but had poor flexibility and impact resistance, whereas PHUs based on aliphatic structures such as HDC exhibited good flexibility and impact resistance and low hardness. When the length of the alkyl groups in the amine curing agents increased, the impact resistance and flexibility of the PHUs increased, but their pencil hardness decreased. PHUs from TDC, MDC, and IPDC had excellent chemical resistance, but the PHUs from HMDC and HDC had less chemical resistance. Some films displayed excellent properties including 4H pencil hardness, 100 cm kg impact resistance, and excellent flexibility. Some PHUs exhibited good thermal stability, with T5% values all above 242°C. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47957.

Designed Polyurethanes for Potential Biomedical and Pharmaceutical Applications: Novel Synthetic Strategy for Preparing Sucrose Containing Biocompatible and Biodegradable Polyurethane Networks

In this paper the preparation and detailed characterization of designed polyurethanes (SPURs) are reported for potential biological, biomedical and/or pharmaceutical applications. Importantly, in order to fulfill these goals all reactants and solvents used were selected according to the proposal of EUR-8 Pharmacopoeia. For the synthesis, a novel strategy was introduced and elaborated. A series of SPUR samples was prepared from poly(ε-caprolactone)-diol, 1,6-hexamethylene diisocyanate and sucrose as a chain extender/crosslinking agent to obtain sucrose containing polyurethanes. In addition, the mol ratios of the sucrose were varied within an order of magnitude. The prepolymers and the products of the syntheses were investigated by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and infrared spectroscopy (IR), respectively. It was found that the reactivity of the eight free hydroxyl groups of sucrose are different, and after curing the SPUR samples at 60 °C no free isocyanate groups can be observed. Furthermore, swelling experiments performed with various solvents of different polarities revealed that the highest degree of swelling took place in dimethyl-sulfoxide. However, low degrees of swelling were recognized in water and hexane. It is important to note that the gel contents were around 90% in all cases, which demonstrate that the crosslinking was almost complete. In addition, the kinetics of swelling were also evaluated and successfully modeled. The crosslink densities were calculated from the data of the swelling experiments by means of the Flory-Rehner equation. Unexpectedly, it was found that the crosslink density decreased with the increasing sucrose content also in line with the results obtained by relaxation modulus experiments and dynamic mechanical analysis (DMA). The Tg and Tm of SPUR samples, determined from DSC and DMA measurements, were around −57 °C and 27 °C, respectively. According to the mechanical tests the SPUR samples showed high elongation at break values, i.e., high flexibilities. Furthermore, the stress-strain curves were also modeled and discussed.

The interfacial interaction between isocyanate and stainless steel

The interfacial interactions between methylene diphenyl di-isocyanate (MDI) and polymeric MDI (PMDI) with 316L stainless steel have been studied in order to understand the adhesion properties of polyurethane based adhesives (containing free isocyanate groups) on metal surfaces. A thin (<5 nm) layer of MDI and PMDI was deposited on the surface of clean 316L stainless steel and then analysed by X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). By using density functional theory (DFT) methods for the interpretation of XPS data, the presence of specific interactions between the adsorbate and the substrate was established. The reaction between isocyanate and metal hydroxyl groups with the formation of urethane-like bonding with the metal was observed. The formation of hydrogen bonds between the isocyanate nitrogen and the hydroxyl groups and the formation of a nitrogen-metal double bond, as a consequence of the cycloaddition reaction between isocyanate and metal oxide, are also proposed.

Peptide-Functionalized Polyurethane Coatings Prepared via Grafting-To Strategy to Selectively Promote Endothelialization.

Endothelialization, formation of endothelial cells (ECs) layer on cardiovascular implant surface, is considered an ideal approach to prevent restenosis (renarrowing of blood vessel mainly due to the accumulation of proliferated vascular smooth muscle cells, SMCs) and thrombosis. In this study, the possibility of using polyurethane (PU) as a coating platform for functionalization with peptide to enhance endothelialization on implants is explored. PUs are synthesized through metal-free organocatalytic polymerization followed by chemical conjugation with an EC-specific REDV peptide through thiol-ene reaction. Meanwhile, the free isocyanate groups of PU allow for covalent grafting of REDV-functionalized PU (PU/REDV) to silanize implant materials (nitinol and PET). PU/REDV coating with peptide grafting density of ≈2 nmol cm-2 selectively accommodates primary human umbilical vein ECs (HUVECs) and retards spreading of primary human umbilical artery SMCs (HUASMCs). In addition, a layer of HUVECs is formed within 3 d on PU/REDV-coated surfaces, while proliferation of HUASMCs is inhibited. The selectivity is further confirmed by coculture of HUVECs and HUASMCs. Moreover, the PU/REDV-coated surfaces are less thrombogenic as evidenced by reduced number and activity of adhered platelets. Therefore, PU/REDV can be potentially used as a coating of cardiovascular implants to prevent restenosis and thrombosis by promoting endothelialization.

Kinetics of Uncatalyzed Reactions of 2,4′- and 4,4′-Diphenylmethane-Diisocyanate with Primary and Secondary Alcohols

The kinetics of the uncatalyzed reaction of an industrially important 50/50 blend of isomers of 4,4′-diphenylmethane-diisocyanate (4,4-MDI) and 2,4′-diphenylmethane-diisocyanate (2,4′-MDI) with primary and secondary alcohols was studied using high-performance liquid chromatography coupled with photodiode array detector. The alcohols such as 1-propanol, 2-propanol, 1-hexanol, 2-hexanol, 3-hexanol, 1-methoxy-2-propanol, and 3-methoxy-1-propanol were used in high molar excess to diisocyanate in toluene at 80°C, and pseudo–first-order dependences on the concentrations of 4,4′-MDI and 2,4′-MDI were found. Appropriate treatments of the kinetic data allowed us to determine the corresponding pseudo–first-order rate constants. According to the kinetic results, the reactivity of the isocyanate group in the para-position is about four to six times higher than that of the ortho-positioned isocyanate group, depending on the reacting alcohol. Furthermore, the substitution effect, i.e., change in the reactivity of the free isocyanate group after the other has been reacted, was found for both 4,4′-MDI and 2,4′-MDI isomers. The differences in the reactivities of the isocyanate groups of 2,4′-MDI and 4,4′-MDI isomers before and after one of two isocyanate groups has been reacted are explained in terms of partial positive charges on the corresponding carbonyl carbon atom calculated by high-level quantum chemical calculations. In addition, the UV-spectral properties of the products obtained by quenching the reaction mixture with methanol are also discussed in light of practical implications.

Polyurethane-based microcapsules containing reactive isocyanate compounds: Study on preparation procedure and solvent replacement

In this study, preparation and characterization of isophorone diisocyanate (IPDI) filled polyurethane (PU) microcapsules were studied. At first, a pre-polymer was synthesized through reaction of toluene 2, 4- diisocyanate (TDI) with 1, 4-butanediol using either cyclohexanone or n-butyl acetate solvent. The synthesized pre-polymer was characterized using Fourier transform infrared spectroscopy, gel permeation chromatography, and free isocyanate content. Polyurethane-based microcapsules containing reactive isocyanates were synthesized using TDI-based pre-polymer and IPDI as the shell and core materials, respectively. Shape and morphology of prepared microcapsules were studied using optical microscopy and scanning electron microscopy (SEM).The spherical microcapsules prepared in this study had a diameter of 50–200μm and shell thickness of 2–20μm. The synthesis procedure developed in this work, replaces toxic solvents commonly used in the preparation of PU microcapsules, namely cyclohexanone and chlorobenzene, with a more benign solvent, namely n-butyl acetate. SEM microscopy of the scratched epoxy specimens showed appropriate healing performance using both type of microcapsules.

Mechanical and Thermal Properties of Polyurethane Foams from Liquefied Sugar Beet Pulp

Abstract Polyurethane (PU) foams were prepared from microwave liquefied sugar beet pulp (LSBP) and polymethylene polyphenyl isocyanate (PAPI) by using a one-step method. The [NCO]/[OH] ratio was increased from 0.6 to 1.2, and the effect of this ratio on the mechanical, thermal and microstructural properties of the LSBP–PU foams was studied. The allophanate, isocyanurate and free isocyanate were detected in all the foams. The thermal degradation of these foams in air occurred in two main stages; the first one occurred at 200–350 °C and the second one occurred at 300–400 °C. The Tg of the foams increased when the [NCO]/[OH] ratio increased up to 0.9 above which it decreased. As the [NCO]/[OH] ratio increased, the less regular structure and broken cell shape (observed through SEM) indicated that severe damage in structural stability and mechanical properties of LSBP–PU foams occurred. The cellular structure of the foams could be controlled by controlling the gelling and blowing reactions through the control of NCO]/[OH] ratio.

Synthesis of thermally and mechanically improved polyurethane-urea elastomers by using novel diamines as chain extenders

AbstractThis article reports the synthesis of novel diamines as chain extenders for the improvement of thermal and mechanical properties of polyurethane (PU). Three novel diamine, 1,2-di(p-aminophenoxy)ethane (BAE), 1,2-di(p-aminophenoxy)propane (BAP) and 2,2-bis(p-(p-aminophenoxy)phenyl)propane (BAPP) were synthesized as chain extenders. Formation of diamines and their reaction with PU prepolymer was analyzed by using Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy. The conversion of the free isocyanate group (NCO) into a urethane-urea group was confirmed through the disappearance of the isocyanate peak at 2244 cm-1. The thermogravimetric analysis (TGA) reveals the thermal stabilization effect of urethane-urea hard segments of the polyurethane system. From the SAXS investigations, the hard segment inter-domain spacing (d) was calculated, which was 24 nm for the reference sample, and 25, 26, and 28.5 nm for the synthesized PU systems. Mechanical test shows an increase in the Young’s modulus and yield strength with BAE and BAP diamines, while BAPP diamine based systems reveal lower modulus values as compared to the reference sample.