Excess NCO Research Articles

Novel moisture-cured hyperbranched urethane alkyd resin for coating application

A hyperbranched polyol (HBP) was synthesized using dipentaerythritol as a core material and 2,2-bis(methylol) propionic acid as a chain extender. This was reacted with varying concentrations of soya fatty acid to make hyperbranched alkyd (HBA) resins. The HBA resins containing unreacted hydroxyl groups were reacted with isophorone diisocyanate at NCO/OH ratio of 1.6:1 to make high solid hyperbranched urethane alkyd (HBUA) resins. The excess NCO content in the HBUA resins was used to cure with atmospheric moisture, and thus moisture-cured HBUA coatings were formed. The resins were characterized by FTIR, and 13C NMR spectroscopic analysis. A series of such resins were made using different fatty acid/isocyanate ratios with respect to the hydroxyl groups present in the HBP. The effect of compositions on the mechanical and weathering properties of the cured resins was investigated. It was observed that there was an optimum fatty acid–isocyanate ratio in terms of the requirements of solvent, mechanical and weathering properties of the resin. The requirement of solvents for formulating HBUA coatings is much lower compared to linear alkyd-based coatings. The present study reveals that the moisture-cured HBUA resins can be used as a binder material in the field of low-pollution weather-resistance coatings.

Synthesis of triazole ring‐containing pentol chain extender and its effect on the properties of hyperbranched polyurethane‐urea coatings

AbstractThis article describes the synthesis and property evaluation of different hyperbranched polyurethane‐urea (HBPUU) coatings based on a newly synthesized triazole ring‐based pentol chain extender. For this initially, the chain extender was synthesized using acetylene azide click reaction and the structure of the intermediate compounds were confirmed by 1H‐, 13C‐NMR, FTIR, and ESI‐mass spectrometry. In the further steps, the required HBPUU coatings were prepared by a systematic three‐step reaction process. In the first step, a isocyanate terminated prepolymer resin was synthesized at NCO/OH ratio of 1.2 : 1, while the second and third step involves the partially chain extension followed by moisture curing. The excess NCO content in the prepolymer was calculated by standard dibutylamine titration method and partially (10, 20, 30, 50, and 70% of the excess NCO content) chain extended with the pentol chain extender and remaining was moisture cured. The structure property relation of different HBPUU coating films were analyzed by FTIR peak deconvulation technique using Gaussian curve fitting procedure while, their viscoelastic and thermo‐mechanical properties were measured by dynamic mechanical thermal analysis, thermo gravimetric analysis, differential scanning calorimetric, and universal testing machine instruments. These results showed that thermal stability, glass transition temperature (Tg), elongation at break increases but the storage and tensile modulus decreases with increasing the percent loading of the triazole chain extender. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Hyperbranched polyurethane (HBPU)-urea and HBPU-imide coatings: Effect of chain extender and NCO/OH ratio on their properties

Effect of chain extender and NCO/OH ratio on the properties of hyperbranched polyurethane (HBPU)-urea and HBPU-imide coatings were examined. The NCO terminated pre-polymers were prepared by reacting the first (G1) and the second (G2) generation hyperbranched polyester polyols (HBP-G1 and HBP-G2) with excess diisocyanate. The excess NCO content of the prepolymer was reacted with different chain extenders viz., 3-aminopropyl triethoxysilane (APTES), pyromellitic dianhydride (PMDA) and N-hydroxyphthalimide (NHTM) to obtain HBPU-urea or HBPU-imide coatings. The structure–property relationships of the different coatings were investigated by FTIR peak deconvolution, and these data suggests the highest extent of hydrogen bonding interaction for PMDA-based coatings, which increases with increasing NCO/OH ratio. Film properties were evaluated by TGA, DMTA, UTM and contact angle measurements; these results were supported by FTIR deconvolution results. As per contact angle measurements, hydrophobicity of coatings increased by increasing NCO/OH ratio. The adhesive strength, abrasion resistance, alkali resistance, and gel content of the coatings were also evaluated.

Properties of isocyanate‐reactive waterborne polyurethane adhesives: Effect of cure reaction with various polyol and chain extender content

AbstractThree series of isocyanate‐reactive waterborne polyurethane adhesives were prepared with various contents of chain extender (4.25/8.25/12.50 mol %) and polyol (20.75/16.75/12.50 mol %). Each series had a fixed amount of excess (residual) NCO group (0.50–2.00 mol %). FTIR and 1H‐NMR spectroscopy identified the formation of urea crosslink structure mainly above 80°C of various cure temperatures (20–120°C) with excess diisocyanate. The molecular weight, tensile strength, Young's modulus, and adhesive strength depend on excess NCO content and cure temperature and also varied with polyol and chain extender content. The optimum cure temperature was 100°C for all the samples. The tensile strength, Young's modulus, and adhesive strength increased with increasing cure temperature above 60°C up to the optimum temperature) (100°C) and then almost leveled off. Among all the samples, the maximum values of tensile strength, Young's modulus, and adhesive strength were found with 63.22 wt % polyol, 0.93 wt % chain extender, and 1.50 mol % excess (residual) NCO content at 100°C optimum cure temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Thermal and thermomechanical properties of hyperbranched polyurethane‐urea/cenosphere hybrids

AbstractHyperbranched polyurethane (HBPU)‐urea/cenosphere hybrid coatings were synthesized by incorporating various concentrations of cenosphere into HB polyester matrix by ultrasonication technique, and this polyester was further used for the preparation of isocyanate terminated HBPU prepolymers by reacting with excess isophorone diisocyanate (IPDI) in a NCO/OH ratio of 1.6 : 1. The desired hybrid coating is obtained by moisture curing the excess NCO present in the prepolymer through film casting. The structure of the hyperbranched polyester (HBPE) was conformed by 1H, 13C NMR and FTIR spectroscopy and the degree of branching (DB) was calculated using Frechet and Frey equations. These hybrid films were characterized by powder XRD, FTIR, SEM, DMTA, and TGA. The structure property correlation, intermolecular/intramolecular hydrogen bonding, the surface morphology, and viscoelastic properties were studied. These results showed an increase in Tg and thermal stability of the hybrid coatings than the base polymer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The effects of NCO/OH ratio on propylene oxide‐modified oil palm empty fruit bunch‐based polyurethane composites

AbstractIn this study, the effects of NCO/OH ratio on polyurethane composites prepared from propylene oxide‐modified oil palm empty fruit bunch (EFB‐PO) properties were studied. From the results obtained, the diffusion of solvents in the composites produced was classified as Fickian type. The molecular weight between crosslink points and degree of crosslinking were affected as the NCO/OH was increased. This phenomenon was attributed to the interaction between excess NCO and accessible OH groups from EFB‐PO to form a three‐dimensional network. From the mechanical testing results, it was found that the NCO/OH ratio had a significant effect on tensile and flexural test. However, no significant influence was observed on impact strength of the composites produced. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Synthesis and Characterization of Hyperbranched Polyurethane−Urea/Silica Based Hybrid Coatings

A series of organic−inorganic hybrid coatings from hyperbranched polyurethanes (HBPU) were prepared using hyperbranched polyester and 3-aminopropyltriethoxysilane. Initially, isocyanate terminated HBPU prepolymers were synthesized from hyperbranched polyesters [prepared by the reaction of 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) with pentaerythritol, TMP, or glycerol as core moiety] with isophorone diisocyanate at NCO/OH ratio of 1.6:1 for 5 h at 70−80 °C. The partial excess NCO content of this prepolymer was reacted with 3-aminopropyltriethoxysilane in different concentrations. The remaining excess NCO completely reacted with atmospheric moisture. Fourier transform infrared (FTIR) spectroscopy was used for the structural analysis of HBPU hybrid coatings. Deconvolution of the FTIR spectra using Origin 6.0 software through Gaussian curve-fitting method was used to find out the changes and types of intermolecular H-bonding interactions in the hybrid films with the variation in concentration of sol−gel...

Organically modified montmorillonite hyperbranched polyurethane–urea hybrid composites

The synthesis and characterization of hyperbranched polyurethane/clay (HBPu/o-clay) hybrid coatings prepared from HB aliphatic polyester polyols (HPs) and isophorone diisocyanate (IPDI) is reported. The HPs are prepared by reacting adipic acid (AA) separately with pentaerythritol (PE), trimethylol propane (TMP) and glycerol (Gly) in different mole ratios of 0.6:1.0, 0.8:1.0 and 1.0:1.0, respectively. K +-montmorillonite (K10) modified with cetyltrimethyl ammonium bromide (CTAB) is used to increase the compatibility between the clay and polymer matrix. The clay is well-dispersed into the polyester matrix by ultrasonication method. Later on, NCO capped HBPU prepolymer (NCO–HBPu) is synthesized from the clay-dispersed polyester by reacting with IPDI at NCO/OH ratio of 1.6:1.0. In the next step, excess NCO content in the binder is cured with moisture. The properties of different HBPu/o-clay hybrid coatings were studied by FTIR, TGA and DMTA instruments and a structure to property correlation is drawn. The deconvolution technique is used to identify the amount of hydrogen bonding present in the hybrid coatings. The TGA and DMTA result showed an enhancement of the thermal stability, room temperature modulus ( E′) and glass transition value ( T g) for the clay modified hybrid coatings, and increases with increasing clay content. TGA results also suggest that the PE-based HBPu/o-clay hybrid coatings have higher thermal stability than TMP or Gly-based systems, which are in close agreement to the FTIR analysis.

Synthesis and characterization of hyperbranched polyesters and polyurethane coatings

AbstractPolyurethane (PU) coatings are widely used for variety of high‐performance applications in today's coating technology. The emerging hyperbranched polymers having three‐dimensional morphology have opened a new avenue to tailor the architecture of PU coatings. The methodology followed here is based on preparation of PU coatings from hyperbranched polyester. Initially, different hyperbranched polyester polyols (HPs) were synthesized by varying the hydroxyl‐terminated precursors that is, pentaerythritol, trimethylol propane or glycerol and keeping the diacid that is, adipic acid quantity constant at various mole ratios of 1:0.6, 1:0.8, 1:0.9, and 1:1, respectively. The obtained HPs were characterized by nuclear magnetic resonance (NMR) spectroscopy, matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF)‐mass spectrometry, and Fourier transform‐infrared (FTIR) spectroscopy. The degree of branching and the quantity of different structural units present in the various HPs were calculated by integrating the quaternary carbon and carbonyl zone in 13C NMR spectroscopy. The extent of condensation in different HPs was also calculated from 1H NMR spectra. Later on, NCO‐terminated PU prepolymers (NCO‐PU) were synthesized by reacting HPs with isophorone diisocyanate (IPDI) at NCO/OH ratio of 1.6:1. In the third step, the excess NCO content in the NCO‐capped PU prepolymers were reacted with atmospheric moisture and hyperbranched polyurethane (HPU) coatings were formed. The coating films were analyzed by FTIR and dynamic mechanical thermal analysis instruments. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2673–2688, 2007

Synthesis and characterization of hyperbranched polyurethane–urea coatings

A series of hyperbranched polyurethane (HBPU)–urea coatings were synthesized by a systematic two-step reaction process. Initially, isocyanate terminated PU prepolymers were prepared from a hyperbranched polyester polyols with isophorone diisocyanate at NCO/OH ratio of 1.6:1 for 5 h at 70–80 °C. The excess NCO content after the synthesis of NCO terminated HBPU prepolymer was completely reacted with atmospheric moisture. The obtained HBPU–urea networks were characterized with Fourier transform-infrared (FT-IR) spectroscopy for the quantitative evolution of the extent of urethane and urea bonds as well as to study the structure-property relationship. In order to find out the changes and types of intermolecular H-bonding interaction in the HBPU–urea films with the variation in polyester structure, the deconvolution of FT-IR spectra were carried out using Origin 6.0 software through Gaussian curve-fitting method. The viscoelastic properties and thermal stability of the synthesized coatings were determined by dynamic mechanical and thermal analyzer and thermogravimetric analyzer, respectively. For HBPU–urea samples glass transition temperature and thermal stability increased with the generation number from the first to the third. Polyester samples showed single step decomposition profile and HBPU–urea samples showed two-steps decomposition with good thermal stability.

Thermal and viscoelastic properties of polyurethane-imide/clay hybrid coatings

This paper reports the synthesis and characterization of polyurethane (PU)-imide/clay hybrid coatings based on two types of polyester (PE) polyols (PE-1 and PE-2). PE-1 was prepared from neopentyl glycol (NPG), adipic acid (AA) and isophathalic acid (IPA), whereas PE-2 contains NPG, AA, IPA and TMP (trimethylol propane) with the same hydroxyl value 280 as PE-1. Cetyl trimethyl ammonium bromide (CTAB) modified montmorillonite (K10) was used as the organoclay for the synthesis of the hybrid coatings. The organoclay particles (3 wt%) were well-dispersed into the PE matrix by ultrasonication method. Then the isocyanate terminated PU prepolymers were synthesized by the reaction of polyester polyols with hard segments such as 2,4-toluene diisocyanate (TDI) or isophorone diisocyanate (IPDI) in different NCO/OH ratios e.g., 1.6:1, 2:1 and 3:1, respectively. Finally the thermally stable imide rings were incorporated into the PU backbone by complete reaction of excess NCO content present in the PU prepolymer with pyromellitic dianhydride (PMDA). The thermogravimetric analysis (TGA) shows a higher thermal stability for the PU-imide hybrid coatings with respect to the corresponding PU-imide films. A higher NCO/OH ratio has resulted in higher thermal stability. The activation energies of degradation were calculated by the Broido and Coats–Redfern methods, respectively. The dynamic mechanical thermal analysis (DMTA) results show an enhancement in the glass transition temperature value ( T g) for the clay containing hybrid coatings. The surface analysis by angle resolved X-ray photoelectron spectroscopy (AR-XPS) showed an enrichment of the soft segment towards the surface, and an enhancement in the hard segment composition in the hybrid coatings, resulted in phase mixing.

FT-IR and XPS studies of polyurethane-urea-imide coatings

A series of polyurethane (PU)-urea-imide coatings were synthesized by a systematic three-step reaction process. Initially isocyanate terminated PU prepolymers were prepared by reacting soft segments such as polyester polyols (prepared from neopentyl glycol, adipic acid, isophathalic acid and trimethylol propane) or polyether polyols (polypropylene glycol-1000) with hard segments such as 2,4-toluene diisocyanate or isophorone diisocyanate with NCO/OH ratio of 2:1. Heterocyclic imide ring into the PU backbone was incorporated by co-polymerization with pyromellitic dianhydride (PMDA) from the excess NCO groups in the PU prepolymer with an NCO/anhydride ratio of 1:0.5 and the surplus NCO content after imidization was moisture cured. PU-urea-imide coatings were also obtained by partial chain extension of the excess NCO groups in the NCO terminated PU-imide copolymers, and the remaining excess NCO groups were completely reacted with atmospheric moisture. The obtained polymers were analyzed with Fourier transform-infrared (FT-IR) and angle resolved X-ray photoelectron spectroscopy (AR-XPS). The type and change in intermolecular H-bonding interaction in the PU-urea-imide films with structural variables was identified by deconvolution of the FT-IR spectra using Origin 6.0 software through Gaussian curve-fitting method. The FT-IR analyses of the PU-urea-imide coating films show dependence of phase separation on the nature of chain extender. Surface characterization data from AR-XPS suggests the dependence of phase segregation behaviour on the nature of the chain extender, which also supports the FT-IR observations.

Extent of side reactions and gelation of polyether polyurethanes

Gelation and gel build-up due to a side reaction in poly-(oxypropylene) diol — 4,4′-diisocyanatodiphenylmethane systems, catalyzed by dibutyltin dilaurate and containing excess NCO groups was studied at 60 to 140°C. Formation of allophanate groups from urethane and urea and biuret from traces of water were the main side reactions. The extent of these reactions was monitored by the determination of isocyanate reacted in excess to that consumed for the formation of urethane and urea groups. Two gel point were observed: one corresponding to the sol→gel transition at a low excess of NCO groups and the other one corresponding to the gel→sol transition at a high excess of NCO groups. The width of the gel and the maximum amount of gel decrease with increasing temperature.

Isocyanurate Crosslinking as a Means of Producing Thermally Stable Polyurethane Elastomers

Castable polyurethane solid elastomers (PUS) based on the poly-caprolactone ( CAPA 225) and the cycloaliphatic diisocyanate trans 1,4–cyclohexane diisocyanate (CHDI) were synthesised to form two series of PUS: in one series the initially prepared prepolymer was chain extended with 1,4–butane diol (BDO) whilst in the second series a mixed chain extender system was used. The first PU elastomer series synthesised had the following composition CAPA 225/CHDI/BDO and covered the molar ratio range 1/2/1 to 1/3/1; the second series CAPA 225/CHDI/BDO + CHDM covered the molar range 1/3/2 to 1/4·5/2. In each series a controlled excess of diisocyanate was allowed to remain in the initially formed PUS: within a particular series each polymer differed from its immediate analogue by 5% excess NCO and the series covered the range 0–50% of excess NCO in a series of 5% steps. It was discovered that elastomers containing a molar excess of iso-cyanate which had been cast and initially cured at 120°C for 16 h were apparently free from reactive NCO groups and did not emit hazardous fumes when subjected to post-curing or rearrangement by heating to 130°C. When, after conditioning for I week, these PUS are post-cured at a higher temperature (16 h at 130°C) then a second crosslinking system is formed in situ in the PU which considerably enhances its thermal deformation and heat resistance properties. The conventional PU system possessing typically 0–0·2% of free NCO has a maximum service temperature of approximately 120°C; this is raised to 210–240°C by the use of this excess isocyanate technique. It is considered that the second in situ crosslinking system consists of isocyanurate type crosslinks. Tensile properties at elevated temperatures and dynamic mechanical thermal analysis (DMTA) were used to measure thermal stability and strength retention. An important feature of these CHDI based PUS is the remarkable independence of storage modulus to temperature changes. For example, over the temperature range 23–180°C for the BDO series and 23–200°C for the BDO + CHDM series no change is observed. Storage modulus E is defined as dynamic storage modulus with units Nm-2 measured at 10% tensile strain.