Hai Ni

Preparation and characterization of alkoxysilane functionalized isocyanurates

Alkoxysilane functionalized isocyanurates were prepared from hexamethylene diisocyanate (HDI) isocyanurate and 3-aminopropyltriethoxysilane. The reactants and functionalized isocyanurate were characterized by 1H, 13C and 29Si NMR, IR and electrospray ionization-mass spectrometry. Two-dimensional NMR was necessary to accurately assign the proton and carbon spectra for both the reactants and functionalized products. The composition of the HDI isocyanurate was a mixture of oligomers ranging from two to three HDI monomers. The functionalization reaction was performed neat, and as a function of dilution. As expected, substitution on the isocyanurate becomes more uniform with increasing solvent content.

Acid-catalyzed moisture-curing polyurea/polysiloxane ceramer coatings

The para-toluene sulfonic acid (p-TSA) was used to catalyze the moisture curing of an organic/inorganic hybrid coating system. The organic phase was based on the isocyanurate of 1,6-hexamethylene of diisocyanate (HDI). The inorganic phase was based on the prepolymerized oligomers of tetraethyl orthosilicate (TEOS). An alkoxysilane-functionalized HDI isocyanate was added into the coating formulation to aid in phase miscibility. The general coating and tensile properties were evaluated as a function of the acid catalyst concentration. In addition, the films were analyzed using differential scanning calorimetry (DSC) and dynamical mechanical thermal analysis (DMTA). The results indicated that the acid catalyst enhanced the adhesive properties of the hybrid coatings. The addition of the acid catalyst increased the changed crosslink density of films and decreased the crystallinity of the organic phase.

Moisture-curing alkoxysilane-functionalized isocyanurate coatings

An amilnosilane functionalzed isocyanurate of 1,6-hexamethylene diisocyanate (HDI isocyanurate) was used to formulate coatings. The coatings were formulated using a mixture of the silane-functionalized isocyanurate and the unfunctionalized HDI isocyanurate. The general coating properties and tensile properties were evaluated as a function of alkoxysilane modified isocyanurate. In addition, the thermo-machanical and rheological properties of the films were also investigated. The moisture-curing process was investigated using FT-IR and NMR. The results indicates that alkoxysilane-functionalized isocyanurate dramatically enhances the adhesion and increases the crosslink density.

Polyurethane/polysiloxane ceramer coatings: Evaluation of corrosion protection

A series of polyurea and polyurethane ceramer coatings were formulated using hexamethylene diisocyanate (HDI) isocyanurate, alkoxysilane-functionalized HDI isocyanurate, tetraethyl orthosilicate (TEOS) oligomers and cycloaliphatic polyesters. The coatings were prepared as a function of alkoxysilane-functionalized HDI isocyanurate and TEOS oligomers concentration. Also, the effect of acid catalyst was investigated. The corrosion resistance of polyurea or polyurethane ceramer coating systems were evaluated using a prohesion chamber on aluminium alloy 2024-T3 substrate. The polyurethane ceramer coatings were compared with the chromate pretreatment and the epoxy-polyamide primer containing the chromate pigment. In addition to prohesion, the interface between the coating and substrate was characterized using X-ray photoelectron spectroscopy (XPS). The prohesion data showed that the corrosion was inhibited by the TEOS oligomers. However, high concentrations of TEOS oligomers and acid catalyst produced blistering in the polyurea/polysiloxane ceramer coatings. The prohesion data alsoi showed that the corrosion protection of ceramer coatings performed as well as the chromate pretreatment and competitively with the epoxy primer. From the XPS and prohesion data, a self assembling silicon oxide layer at the metal-coating interface was proposed.

Cycloaliphatic polyester based high solids polyurethane coatings: I. The effect of difunctional alcohols

High-solids polyesters were synthesized with two cycloaliphatic diacids, 1,4- cyclohexanedicarboxylic acid (1,4-CHDA) and 1,3-cyclohexanedicarboxylic acid (1,3-CHDA); and with five diols, 1,4-cyclohexanedimethanol (CHDM), neopentyl glycol (NPG), hydroxypivalyl hydroxypivalate (HPHP), 2-butyl-2-ethyl-1, 3-propanediol (BEPD), and 1,6-hexanediol (HD). The viscosity of the polyesters was dependent on the structures of diols. The viscosity of polyesters is lower with the diol HD, intermediate with BEPD and HPHP, and higher with the diols CHDM and NPG. The polyesters were crosslinked with hexamethylene diisocyanate isocyanurate (HDI isocyanurate) affording polyurethane coatings. The mechanical properties, tensile properties, fracture toughness, and viscoelastic properties were investigated for the polyurethane films with five different diols. The cyclohexyl structure of the CHDM provides the polyurethane with rigidity which is manifested in high tensile modulus, hardness, and fracture toughness. In contrast, the linear diol, 1,6-hexanediol provides polyurethane with very high flexibility, but these coatings suffer with respect to low hardness and tensile modulus.

Nanostructured polyurethane ceramer coatings for aircraft

A new low VOC (volatile organic compounds) polyurethane/oligosiloxane coating was formulated using 1,6-hexamethylene diisocyanate (HDI) isocyanurate, alkoxysilane-functionalized HDI isocyanurate, tetraethyl orthosilicate (TEOS) oligomers, and three cycloaliphatic polyesters. One series of polyesters was synthesized using 1,4-cyclohexanedimethanol (CHDM) with 1,4-cyclohexanedicarboxylic acid (1,4-CHDA) and 1,3-cyclohexanedicarboxylic acid (1,3-CHDA). A second series of polyesters was synthesized using 2-butyl-2-ethyl-1,3-propanediol (BEPD) with 1,4-CHDA or 1,4-CHDA, and 1,3-CHDA, respectively. The polyurethane provided the general mechanical properties and the polysiloxane functioned as an adhesion promoter and corrosion inhibitor. The continuous organic polyurethane phase was coupled with the inorganic polysiloxane phase via the alkoxysilane-functionalized HDI isocyanurate. The general coatings, tensile, and viscoelastic properties were evaluated for the ceramer coatings as functions of the polyester and concentration of TEOS oligomers. Damage tolerance was evaluated via fracture toughness and development of the film deformation zone prior to crack propagation. The coatings’ properties were dominated by the organic phase. The film morphology was investigated using the combination of SEM (scanning electron microscope) and X-ray analysis. Phase separation was observed for ceramer coatings resulting in SiO2 particles. The size of the preceramic silicon-oxo-particles was controlled by the Tg of the organic phase and the concentration of TEOS oligomers.