Isocyanate-terminated Polyurethane Prepolymer Research Articles

Solvent-free synthesis of pendant crosslinked polyurethane hot melt adhesive via dynamic Diels-Alder reaction

Pendant cross-linked polyurethane hot melt adhesive was synthesized without any solvents via Diels-Alder reaction (DA reaction) and was coded as DAPU. Firstly, a chain extender containing furan ring was synthesized via Michale addition reaction between hydroxyethyl acrylate (HEA) and furfuryl amine (FA). Secondly, the polyurethane prepolymer with pendant furan rings was synthesized from the reaction between the chain extender and isocyanate-terminated polyurethane prepolymer. Finally, the hot melt adhesive was cross-linked via DA reaction between furan rings and bismaleimide (BMI) without organic solvents due to the viscosity inhibition at higher temperature. DAPU exhibited a higher bonding performance (11.2 MPa) than the commercial reactive polyurethane hot melt adhesive (PUR-Ausbond 3550) and can reach 10.2 MPa after three times break as thermoplastic polyurethane hot melt adhesive (TPU-XJU83), due to the higher cross-linked density and the thermal reversibility of DA adducts. This confirmed that DAPU combined the merits of the two kinds of polyurethane hot melt adhesives successfully without involving solvents.

Self-Healing and shape memory reconfigurable Poly(urethane-urea-amide) elastomers containing multiple dynamic bonds for improving performance of 4D printout

As smart polymer material, 4D printed shape memory polymers (SMPs) can fix a temporary shape under a certain external stimulus and recover to the permanent shape under the same type of stimulus, which has attracted tremendous attention because of its potential applications in flexible electronics, biomedicine and other emerging fields. However, the traditional 4D printable polymer products in the practical multifunctional application usually have poor self-healing, shape memory, recyclability. Herein, a series of poly(urethane-urea-amide) elastomers (sPUUA) containing thiocarbamate, disulfide and carbamate dynamic bonds are successfully prepared by the copolymerization of isocyanate-terminated polyurethane prepolymer (OPU), polyetheramine and amino-terminated oligomeric polyamide-1212 (PA1212) in twin-screw extruder via reactive extrusion. Notably, sPUUA elastomers have self-healing, one-way/two-way and multiple shape memory functions. Damaged sPUUA-TU3 and sPUUA-TU3-H10 films with 0.9 wt% DBTDL can be healed by thermal treatment at 150 °C for 30 min and they also exhibit excellent micro-scratch elimination ability. Furthermore, sPUUA-TU3-H10 demonstrates a tensile stress of 9.6 MPa and an elongation at break of 402.3 % with a healing efficiency of 69 %, and exhibits the outstanding shape memory behavior based on supramolecular interactions and dynamic covalent bonds. Then the sPUUA elastomers were granulated, dried, extruded by single screw extruder, and then hot-stretched by pulling rollers into 1.75 ± 0.05 mm diameter wires for FDM 4D printing. The self-healing, macroscopic shape memory and reconfigurability of the as-printed objects were also demonstrated. Accordingly, sPUUA elastomers based on 4D printing will enable vast potential applications in the fields of multifunctional shape shifting devices, biomedicine, robotics and additive manufacturing.

Lignin-Based Phenolic Foam Reinforced by Poplar Fiber and Isocyanate-Terminated Polyurethane Prepolymer.

Phenolic foams (PFs) are lightweight (<200 kg/m3), high-quality, and inexpensive thermal insulation materials whose heat and fire resistance are much better than those of foam plastics such as polyurethane and polystyrene. They are especially suitable for use as insulation in chemical, petroleum, construction, and other fields that are prone to fires. However, PFs have poor mechanical properties, poor abrasion resistance, and easy pulverization. In this paper, a polyurethane prepolymer was treated with an isocyanate, and then the isocyanate-terminated polyurethane prepolymer and poplar powder were used to prepare modified lignin-based phenolic foams (PUPFs), which improved the abrasion resistance and decreased the pulverization of the foam. The foam composites were comprehensively evaluated by characterizing their chemical structures, surface morphologies, mechanical properties, thermal conductivities, and flame-retardant properties. The pulverization ratio was reduced by 43.5%, and the thermal insulation performance and flame-retardancy (LOI) were improved. Compared with other methods to obtain lignin-based phenolic foam composites with anti-pulverization and flame-retardant properties, the hybrid reinforcement of foam composites with an isocyanate-terminated polyurethane prepolymer and poplar powder offers a novel strategy for an environmentally friendly alternative to the use of woody fibers.

Thermo-expandable microcapsules with polyurethane as the shell

Thermo-expandable microcapsules (TEMs) with polyurethane as the shell and n-hexane as the blowing agent were synthesized by interfacial reaction between isocyanate-terminated polyurethane prepolymer aqueous dispersion and polyamine chain extender. The synthetic process for the thermo-expandable PU-shelled microcapsules was established. The factors which affected the efficiency for blowing agent encapsulation were investigated by fourier transform infrared spectroscopy (FT-IR), laser particle size analyzer and thermo-gravimetric analysis (TGA). The foaming performances of the microcapsules were characterized by polarizing optical microscope with hot platform (POM) and thermo-mechanical analyzer (TMA). The results showed that PU-shelled thermo-expandable microcapsules were successfully synthesized and had good foaming performance. The NCO/OH ratio was found to have a significant effect on the encapsulation of n-hexane and the appropriate ratio was found to be 3:1. Diethylenetriamine (DETA), which is a polyamine chain extender, was found to be a more suitable chain-extender than other polyamine chain extenders in encapsulation the hexane. PU-shelled thermo-expandable microcapsules containing 25.8% blowing agent was fabricated. The onset expand temperature of TEMs was found to be 206 °C, and the maximum foaming temperature was at 235 °C, according to thermo-mechanical analysis. The volume expansion ratio of TEMs reached 27 times according to the measurement by polarizing optical microscope. The PU shelled TEMs showed good foaming performance in vinyl acetate-ethylene copolymer matrix.

Covalently introducing amino-functionalized nanodiamond into waterborne polyurethane via in situ polymerization: Enhanced thermal conductivity and excellent electrical insulation

Polymer-based thermal management nanocomposites with favorable electrical insulation have received increasing attention in the microelectronics industry. How to effectively disperse nanofillers and improve interfacial compatibility with polymer matrix is crucial to enhance comprehensive performance of nanocomposites. In this work, nanodiamond (ND) was first oxidized by hydrogen peroxide and then amino groups generated on its surface via hydrothermal reaction in the presence of ethylenediamine. Amino-functionalized ND particles (ND-NH2) were covalently incorporated into isocyanate-terminated polyurethane prepolymer chains via in situ polymerization, and a series of waterborne polyurethane (WPU)/ND-NH2 (WPN) nanocomposites with low loading levels (0.5, 1 and 2 wt%) were successfully prepared. ND functionalized with amino groups achieved excellent compatibility with the WPU matrix, improving the interfacial interactions between filler and matrix, and reducing the interface thermal resistances and phonon scatterings, further favoring the formation of thermal conductive paths. The highest thermal conductivity of the WPN nanocomposite with a lower ND-NH2 loading of 2 wt% was 0.369 W m−1 K−1, which is about 82% higher than that of the pure WPU film (0.203 W m−1 K−1). The excellent electrical insulation was also found at 2 wt% nanofiller content and the volume electrical resistivity reaches 2.525 × 1015 Ω·cm. Moreover, the incorporating and good dispersion state of ND particles in the WPU-based nanocomposites could increase the thermal stability and mechanical performance of the nanocomposite films. This method provides an effective and promising way to prepare environmentally friendly polyurethane nanocomposites reinforced with reactive surface of functionalized ND.

Synthesis and characterization of castor oil-based branched polyols from renewable resources and their polyurethane-urea coatings

The chemical modifications of castor oil (CO) to develop branched polyols and their polyurethane-urea coatings have been investigated. For this purpose, castor oil-based branched polyols (COBPs) were synthesized from CO by modifying with succinic anhydride followed by reaction with hydroxyl group moieties like petrochemical-based pentaerythritol, trimethylolpropane and bio-based glycerol. The COBPs were characterized by using Fourier transform infrared, 1H and 13C nuclear magnetic resonance spectroscopies, gel permeation chromatography and differential scanning calorimetry. These COBPs were further urethanized with isophorone diisocyanate at OH/NCO ratio of 1:1.6 to get the isocyanate-terminated polyurethane prepolymers. The surplus isocyanate groups of the prepolymer were cured with atmospheric moisture at ambient temperature condition to form uniform film with fast surface drying. The thermo-mechanical, viscoelastic and swelling properties were evaluated for the cured coating films. Properties have been discussed from the viewpoint of branched network and also the urethane segment present in the structure. The glass transition temperatures of the coating films were found to be in the range of 32–64°C. The modified castor oil coating films show better thermo-mechanical and viscoelastic properties in comparison with control (unmodified castor oil) coating films. This work delivers an effective and promising way to synthesize branched moieties in plant oil-based high performance coatings.

Preparation of novel marine antifouling polyurethane coating materials

Polyurethane coating materials with different compositions of low surface energy polydimethylsiloxane and degradable poly(l-lactic acid) were synthesized by three major steps. Initially, the hydroxylation-terminated poly(l-lactide)-functionalized graphene (G-g-PLLA) was prepared by ring-opening polymerization of l-lactic acid using the phenol-functionalized graphene (G-f-OH), which was prepared by 1,3-dipolar cycloaddition reaction of graphene and 3,4-dihydroxybenzaldehyde when N-methylglycine and tin octoate were used as initiator and catalyst, respectively. Subsequently, isocyanate-terminated polyurethane prepolymer with polydimethylsiloxane was obtained by condensation polymerization of polydimethylsiloxane and isocyanate-terminated polyurethane prepolymer that was obtained by the condensation polymerization of 4,4′-diphenylmethane diisocyanate and 1,4-butane diol. Finally, the novel polyurethane coating materials were prepared by the condensation polymerization of G-g-PLLA and isocyanate-terminated polyurethane prepolymer with polydimethylsiloxane. These synthesized materials were carefully analyzed with Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectra (1H NMR), field-emission scanning electron microscopy (SEM), and high-resolution transmission (TEM). In addition, the water contact angles were measured. It was found that the surface free energy of the polyurethane coating materials decreased from 52.19 to 11.74 N/m2 with the increase of polydimethylsiloxane content from 0 to 20% and the water contact angle of the polyurethane coating materials increased from 71° to 108°. Moreover, the mechanical property was investigated. The studies also demonstrated that functionalized polyurethane was able to hydrolyze in seawater and the hydrolysis rate decreased as the PDMS content increased. At the same time, simulative ocean hanging plate experiment confirmed that the novel polyurethane coating materials exhibited a good antifouling performance, which indicated that the functionalized polyurethane has a potentiality in marine antifouling coating application.

Effect of Monomers in Vinyl Urethane Macromonomers on Dispersion Polymerization of Polystyrene

The four different vinyl monomers in the reaction of isocyanate-terminated polyurethane prepolymer were used for the preparation of macromonomers and successfully employed in the dispersion polymerization of styrene. The chemical structures of vinyl monomer in macromonomers influenced on the polystyrene particle characteristics, such as the conversion, weight average molecular weights (Mw), polydispersity index (PDI), weight average diameter (Dw), and uniformity. The conversion of polystyrene increased with amounts of methyl group in vinyl monomer. Also the uniformity of polystyrene particles increased with amounts of methyl group in vinyl monomer.

EFFECT OF INCREASING NCO/OH MOLAR RATIO ON THE CHEMICAL AND MECHANICAL PROPERTIES OF ISOCYANATE TERMINATED POLYURETHANE PREPOLYMER DERIVED FROM BIO-MASS

The study deals the effect of increasing NCO/OH molar ratio on the physico-mechanical properties of isocyanate terminated polyurethane prepolymer. The prepolymer was prepared using castor oil and toluene-2,4-diisocyanate. The NCO/OH molar ratio has been varied from 1.6 to 2.0. The formation of the prepolymer was confirmed by UV and FTIR spectroscopy. The results reveal that the curing time of the prepolymer decreased with increase in NCO/OH molar ratio. When NCO/OH molar ratio increased, the tensile strength of the polyurethane film increased, while percent elongation decreased due to increase in hard segment content.

Polyurethane encapsulated carbon black particles and enhanced properties of water polyurethane composite films

Abstract Polyurethane-encapsulated carbon black (ECB) particles were synthesized successfully through a facile method by encapsulating carbon black (CB) particles in the presence of an amphiphilic isocyanate-terminated polyurethane pre-polymer. Fourier transform infrared spectroscopy demonstrated the existence of a polyurethane layer on the surface of encapsulated CB, and thermo-gravimetric analysis indicated the encapsulation percentage reached 15.77 wt.%. The results of dynamic light scattering, transmission electron microscopy, and UV–vis spectroscopy analyses revealed that the ECBs exhibited better dispersibility and stability in water in comparison with the dispersant-dispersed carbon black (DCB) prepared by simply dispersing CB particles using a polymer super-dispersant. In particular, scanning electron microscope observation of PUB/ECB composite films obtained by blending ECB particles with a waterborne polyurethane binder (PUB), showed enhanced dispersibility and compatibility of the ECBs in the PUB matrix. Therefore, as test results demonstrated, PUB/ECB composite films showed better mechanical, water resistance, and color properties compared with those of PUB/DCB composite film. It is expected that this effective encapsulation method for preparing functional CB dispersions will be used to make waterborne coatings in the leather and textile finishing fields.

Microcapsules containing multi-functional reactive isocyanate-terminated polyurethane prepolymer as a healing agent. Part 1: synthesis and optimization of reaction conditions

Smart self-healing coatings have been attracting tremendous interest due to their capability for preventing crack propagation in the protective coatings by releasing active agents like isocyanate molecules from micro/nanocapsules. The quality of healed area and subsequent use of the healed coated module are directly related to the chemical composition of healing agent. Faster curing rate and more appropriate physical properties were anticipated for moisture curing of bulky isocyanate molecules than the low molecular weight monomeric analogous. For practical utilization of these advantages, encapsulation of such bulky isocyanate molecules was considered in this work. To this end, optimized preparation and characterization of novel single-layer polyurethane-type microcapsules, richly and efficiently loaded with bulky isocyanate molecules is described. This healing agent was prepared through the reaction of excess amount of isophorone diisocyanate (IPDI) with 2-ethyl-2-hydroxymethyl-1,3-propanediol (TMP). The healing agent was then encapsulated with a polyurethane shell via an oil-in-water (O/W) emulsion polymerization technique. The mixing rate and surfactant concentration were altered to optimize the size and shell thickness of the microcapsules. The prepared microcapsules were very stable after 10 months, and they just lost less than 7 wt% of their loaded isocyanate molecules. The microcapsules were loaded into an epoxy-based coating and the crack healing efficiency of incorporated healing agent was clearly recorded. Microcapsules containing monomeric IPDI were also prepared and crack healing efficiency of these two healing agents regarding crack healing was compared.

Polyurethane Dispersions with Peptide Corona: Facile Synthesis of Stimuli-Responsive Dispersions and Films.

Peptide-polymer hybrid particles of submicron size yielding stimuli-responsive macroscopic films are presented. A thermoplastic polyurethane (PU) carrying polysiloxane and polyester soft segments serves as core material to obtain flexible, yet semicrystalline films with temperature-sensitivity. The synthesis is based on the high-sheer emulsification of isocyanate-terminated PU prepolymers, which in our model system purposefully lack any ability of colloidal self-stabilization. While emulsification in water leads to immediate coagulation, stable dispersions of polyurethane nanoparticles were formed in aqueous solutions of a hydrolyzed protein from wool. A comparison of dispersion and film properties to nonreactive, otherwise identical dispersions suggests covalent attachment of the peptide to the PU backbone. We show that the colloidal stability of the hybrid particles is completely governed by the peptide corona, and hence pH-triggered coagulation can be employed to induce particle deposition and film formation. Differential scanning calorimetry confirms partial crystallinity in the film and reveals strongly modified crystallization behavior due to the peptide.

Synthesis and Thermal Curing of Benzoxazine Functionalized Polyurethanes

Benzoxazine (BOX) functionalized polyurethanes (PU) are introduced to provide a conceptually new thermal curing mechanism for polyurethanes. 3,4-Dihydro-3-methyl-2H-1,3-benzoxazine (P-m) was carefully oligomerized through thermal treatment. In a straightforward synthesis the newly formed hydroxyl groups are used for end-capping reactions with isocyanate-terminated polyurethane prepolymers. The isocyanate reactive hydroxyl content (IRH) of the benzoxazine oligomer was investigated in detail via 1H NMR spectroscopy, HPLC-MS, indirect potentiometric titration in various solvents, and comparison with model substances and found to be strongly influenced by hydrogen bonding. The corresponding polyurethane/benzoxazine hybrid materials (PU/BOX) can cross-link at elevated temperatures and do not suffer from shelf-life issues or outgassing of blocked isocyanates. The thermally activated curing reaction was investigated via rheology and DSC. Significant improvements over state-of-the-art systems based on phenol-capp...

Preparation and properties of amine-functionalized reduced graphene oxide/waterborne polyurethane nanocomposites

Amine-functionalized reduced graphene oxide (NH2-RGO), with primary amine (—NH2) groups linked onto surfaces by toluene-2,4-diisocynate), was successfully synthesized. Subsequently, the as-prepared NH2-RGO nanoplatelets were covalently incorporated into a waterborne polyurethane (WPU) matrix to fabricate NH2-RGO/WPU nanocomposites by the reaction of —NH2 groups with the isocyanate-terminated polyurethane prepolymer. Electron microscopic observations confirmed that the NH2-RGO nanoplatelets were homogenously dispersed in the WPU matrix. The NH2-RGO/WPU nanocomposites exhibited a significant improvement in their mechanical and thermal properties. The tensile strength and storage modulus of the nanocomposites increased by 73% and 973%, respectively, with the addition of 1.0 wt% NH2-RGO. The thermal degradation temperature was enhanced by about 40°C compared with the neat WPU. Meanwhile, the thermal conductivity increased by about 258%.

A mathematical model of rheological behavior of novel bio-based isocyanate-terminated polyurethane prepolymers

In this paper, the results of rheological study on isocyanate-terminated polyurethane prepolymers, containing modified soybean oil residues incorporated into the chemical structure are described. Isocyanate-terminated prepolymers were synthesized from 4,4′-diphenylmethane diisocyanate and the mixture of hydroxylated soybean oil and commercial polyether. The measurements were performed by using rotary rheometer R/S-CPS+ (Brookfield, USA), while the rheological parameters were calculated by using Rheo3000 program. Based on rheological measurements, the viscosity curves and flow curves for prepolymers in the temperature range from 50 to 70°C were plotted. Prepolymer samples were tested with controlled shear rate (CSR). It was found that a viscosity of bio-based isocyanate-terminated prepolymers decreases with increasing content of hydroxylated soybean oil in the polyol mixture. The rheological data for bio-based polyurethane prepolymers were also mathematically modeled. It was found that the synthesized prepolymers are non-Newtonian fluids that can be described by Ostwald-de Waele and Herschel Bulkley functions as optimal individual models. The conducted investigations showed that the dynamic viscosity and rheological behavior of bioprepolymers samples could depend on the amount of hydroxylated soybean oil used in the polyol mixture.

New Polyurethane Elastomers with Enhanced Thermal Stability

A series of polyurethane elastomers with enhanced thermal stability was prepared and their physical and thermal properties were studied. For this purpose in the first step, an excess amount of methylene diphenyl diisocyanate was reacted with poly(tetramethylene ether) glycol to produce isocyanate-terminated polyurethane pre-polymer. In the second step, a new imide-based diol chain extender was synthesized via reaction of benzophenonetetracarboxylic dianhydride with 5-amino-1-naphthol. Finally, reaction of the pre-polymer with chain extender resulted in preparation of polyurethane elastomers. Presence of imide unit in the polymer backbone improved their properties and enhanced thermal stability of polyurethane.

Effect of increasing NCO/OH molar ratio on the physicomechanical and thermal properties of isocyanate terminated polyurethane prepolymer

The study investigates the effect of increasing NCO/OH molar ratio on the physico-mechanical and thermal properties of isocyanate terminated polyurethane prepolymer. The prepolymer was prepared using methylene diphenyl diisocyanate and difunctional polypropylene glycol. The NCO/OH molar ratio has been varied from 1.2:1 to 3:1. The formation of the prepolymer was confirmed by FTIR spectroscopy. The results reveal that the viscosity, weight average molecular weight and curing time of the prepolymer decreased with increase in NCO/OH molar ratio. When NCO/OH molar ratio increased, the tensile strength of the polyurethane film increased, while percent elongation decreased due to increase in hard segment content. The glass transition temperature of the prepolymer decreased with increase in NCO/ OH molar ratio of the prepolymer. Keywords : Polyurethane Prepolymer, Viscosity, Molecular Weight, Curing Time, Glass Transition Temperature.

EFFECT OF SOFT SEGMENT CHAIN LENGTH ON TAILORING THE PROPERTIES OF ISOCYANATE TERMINATED POLYURETHANE PREPOLYMER, A BASE MATERIAL FOR POLYURETHANE BANDAGE”

Isocyanate terminated polyurethane prepolymer, a ba se material for water curable polyurethane bandage was prepared from diphenylmethane diisocyanate and poly (propylene ox ide) glycol. In polyurethanes, the diisocyanate ac t as hard segment and provides dimensional stability, whereas the polyol which forms the soft segment gives elastomeric char acter. Due to its segmented structure, polyurethane’s with a wide range of phys ico-mechanical properties can be obtained by varyin g its monomers types and content. In this paper, the effect of different soft segment length on influencing the structure prop erty relationship of polyurethane prepolymer was studied. The soft segment length was varied by using poly (propylene oxide) glycol havi ng different molecular weight and also by blending two polyols having similar che mical composition but of different molecular weight . The formation of the prepolymer was investigated by Fourier transform in frared spectroscopy (FTIR). The results reveal that with increasing soft segment length, the weight average molecular weight and sto rage time of the prepolymer increases, whereas the Brookfield viscosity decreases due to higher content of soft segment. The curing time was found higher in prepolymer having longer s oft segments due to lower isocyanate content. With increasing molecular weigh t of the soft segment, the phase separation between the hard and soft segment increases due to which the prepolymer produce low T g. The tensile strength of the polyurethane film dec reases whereas percent elongation increases with increase in soft segment length. The findings of the study will be beneficia l for understanding the role played by soft segment length on tailoring the stru cture and ultimately the properties of isocyanate t erminated polyurethane prepolymer.

Synthesis and characterization of triazole rich polyether polyols using click chemistry for highly branched polyurethanes

The present work describes development of moisture cured polyurethane–urea coatings based on 1,2,3-triazole rich polyether polyols. In this paper, two polyether polyols were synthesized by using 1,3-dipolar azide–alkyne cycloaddition reaction and they were named as PL-1 and PL-2 where PL-1 is 9 terminal hydroxyl groups and PL-2 is 6 terminal hydroxyl groups. These polyols were reacted with 4, 4′-diisocyanatodicyclohexylmethane (H12MDI) at OH:NCO ratio of 1:1.2 in order to obtain isocyanate terminated polyurethane prepolymers. The resulted prepolymers were casted on tin foil and cured under atmospheric moisture in order to get completely cured polyurethane–urea free films. The free films were characterized by using Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA) techniques. The TGA and DMTA results showed that these films have good thermal and mechanical stability. Anti-microbial studies proved that these polyurethane films show good resistance towards different bacterial and fungal attacks. These polymers were also coated on mild steel panels in order to evaluate corrosion resistance properties by using salt spray and electro chemical polarization studies.

Preparation and Application Properties Analysis of Hyperbranched Polyurethane Leather Finishing Agent

A novel hyperbranched polyurethane (HBPU) finishing agent was prepared by graft copolymerization of hyperbranched poly (amine-ester) polyols (HPAE) and the isocyanate-terminated polyurethane prepolymer(PPU). 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 was used for the structural characterization. The thermal properties of HBPU were characterized by TGA. Microphase separation of HBPU film surface was studied by tapping-mode atomic force microscopy (AFM). Moreover, in contrast to 200-UT, the physical and mechanical properties of HBPU as finishing agent were investigated: curing time was decreased by 26.15% and the water vapor permeability was increased by 9.04%.