Synthesis and characterization of new phosphorus and other heteroatom containing aryl cyanate ester monomers and networks

Several aromatic dicyanate monomers have been synthesized bearing para-linked strong electron withdrawing groups, such as phenylphosphine oxide, sulfone, and carbonyl. These groups increased the reactivity of the cyanate functional groups and eliminated the need for curing catalysts. However, an undesirable decrease in the processing window between the monomer melting point and the onset of cure was also generally observed. An arylene ether phenyl phosphine oxide system was designed that displayed several attractive characteristics such as a low softening point, a wide processing window, cure with no catalyst, high T_g and high char yield in air, suggesting that these new thermosets might show good fire resistance. The dicyanate ester monomers were synthesized in high yield by reacting various bisphenols with cyanogen bromide in the presence of triethylamine. The high reactivity of the cyanate functional groups required that the cyanation reaction be conducted at temperature below 0°C in order to prevent imidocarbonate side reactions. Proton NMR and FT-IR were used to characterize these monomers. The cyclotrimerization curing process was monitored by the disappearance of the carbon-nitrogen triple bond stretch (2270 cm⁻¹). An optimal cure schedule was determined and the cured polycyanurate networks were characterized by DSC, DMTA, and TGA. Tg values were typically > 250°C and 5% weight loss values were observed by TGA in air above 400°C. Several of the dicyanate monomers with sufficiently large processing windows were cured into single lap shear adhesive bonds onto titanium 6/4 and the measurements are reported herein. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 977–987, 1997     

Interpenetrating polymer networks based on diisocyanates and polar monomers

Compatible interpenetrating polymer networks systems (IPS) have been obtained by two-stage polymerization of a mixture of diisocyanates (M₁) with various different polar monomers (M₂) initiated by catalytic systems based on tertiary amines. In the first stage, a polyisocyanate network (P₁) is formed and then M₂ is polymerized on a regenerated active centre with the formation of a linear polymer (L₂) specially arranged in P₁. The essential features of the formation of IPS of this type are considered. Some physico-mechanical and thermal characteristics are reported.     

Three-fold polyfluoroalkylated amines and isocyanates based on tris(hydroxymethyl)aminomethane (TRIS)

Three-fold polyfluoroalkylated amines were prepared from tris(hydroxymethyl)aminomethane (TRIS) in five steps including perfluoroalkyl iodide addition to the corresponding allyl derivative, reduction of C-I bond and deprotection of the amino group. They can be easily converted to the corresponding isocyanates.     

Novel carbamoyl phosphonate monomers and polymers from unsaturated isocyanates

Carbamoyl phosphonate derivatives of methacrylic acid and α-methyl styrene were synthesized in good yield by reacting dimethyl and diethylphosphite with isocyanato ethylmethacrylate (IEM) or with meta-isopropenyl-α,α-dimethylbenzylisocyanate (m-TMI). The IEM derivatives yield soluble homopolymers with common radical initiators. The m-TMI carbamoyl phosphonates were copolymerized with styrene and with acrylates yielding soluble materials with better than 50 mol % incorporation of the phosphonate monomer. The side chain carbamoyl phosphonate group drastically lowers the T_g relative to those of the parent polymers. Thermogravimetric studies suggest the NHC(O)? P(O)(OR)₂ bond to be stable to about 225°C. The radiopacifying salt UO₂(NO₃)₂6 H₂O yields transparent films with the phosphonate-containing polymers. The T_g increases with uranyl content. © 1993 John Wiley & Sons, Inc.     

Condensation of acyl chloride on sodium cyanate : preparation of acyl isocyanates

The catalytic effects of various metal halides and solvents on the reaction of benzoyl chloride with sodium cyanate were studied. It has been found that SnCl₄, and ZnCl₂. catalyze the reaction to give the corresponding acyl isocyanates in good yields. The scope of the reaction was studied and a number of aroyl isocyanates and their derivatives were prepared. A few non aromatic isocyanates and their derivatives were also prepared.     

Shape memory polymers based on cyanate ester-epoxy-poly (tetramethyleneoxide) co-reacted system

Thermoset polymers showing shape memory properties were synthesized by reacting bisphenol A dicyanate (BADC) with diglycidyl ether of bisphenol A (DGEBA) and phenol telechelic poly(tetramethyleneoxide) (PTOH). The cure characteristics of the blend were evaluated by DSC, FTIR and rheometry. Blends with varying proportion of DGEBA/PTOH/BADC were studied for their flexural, dynamic mechanical and thermal properties. The flexural strength and thermal stability increased with increase in cyanate ester concentration, while these properties decreased with increase of PTOH concentration for a given composition. The storage modulus showed a similar trend. The transition temperature (T_trans) of the system increased with increase in cyanate ester content. The polymers showed good shape memory properties wherein the shape recovery increased with increase in PTOH content with a concomitant decrease in the shape recovery time. While the shape recovery increased proportional to the modulus ratio (E_g/E_r), the recovery time showed an inverse relationship with it. The transition temperature could be tuned by the reactant composition and the speed of shape recovery increased with increase in actuation temperature. These epoxy-cyanate ester systems possesses good thermal, mechanical and shape memory characteristics for potential use in smart actuator development.     

Preparation and characterization of carbon foams derived from cyanate esters and cyanate/epoxy copolymers

Journal of Thermal Analysis and Calorimetry - The aim of this study was to obtain carbon foams (CFs) of various pore structure and high mechanical strength using a simple and efficient method to...     

Block polymers of isocyanates and vinyl monomers by homogeneous anionic polymerization

The “living” polymer method was used to prepare block polymers of vinyl monomers and isocyanates at low temperatures in toluene–tetrahydrofuran mixtures. Vinyl monomers and diisocyanates, which have one hindered isocyanate group, as in 2,4-toluene diisocyanate, form block polymers which contain pendant reactive isocyanate groups. These block polymers can be crosslinked with water, diols, diamines, etc. The polymerization is apparently limited to block polymer formation, since the polyisocyanate anion is incapable of initiating the polymerization of common vinyl monomers.     

Functionalized monomers based on N-(4-hydroxy phenyl)maleimide

N-(4-Hydroxy phenyl)maleimide (HPMI) is functionalized with acryloyl, methacryloyl, allyl, propargyl and cyanate groups and the structures of the materials are characterized by FTIR, ¹H NMR and ¹³C NMR. Thermal curing behaviours of the monomers and thermal stabilities of the polymers are studied using thermal analysis. Introduction of polymerizable groups shifts the curing exotherm to low temperatures, and the curing behaviour is dictated by the polymerizable substituent present in the aromatic ring. Polymer from acryloyl-functionalized monomer shows the highest thermal stability (402 °C), whereas the highest char value (49 % at 700 °C) is noted for the polymer obtained from propargyl-functionalized monomer. Polymers derived from functionalization of HPMI with acryloyl and methacryloyl showed better thermal stabilities. Thermosets formed by the thermal polymerization of HPMI functionalized with propargyl and cyanate groups showed higher char values at 700 °C in nitrogen atmosphere.     

Organosilicon synthesis of isocyanates: IV. Synthesis of isocyanates from aliphatic and alkylaromatic amino acid esters

Treatment of an alcoholic suspension of amino acids with trimethylchlorosilane yielded phenylglycine, valine, β-phenylalanine, and homovaline ester hydrochlorides. Their saccharin-catalyzed silylation with hexamethyldisilazane proceeds quantitatively and involves only one proton of the amino group. The best conversion of the amino acid esters to the corresponding isocyanates was achieved by phosgene treatment of their monosilyl urethanes, rather than of the silylated amino esters. Monosilyl urethanes are formed quantitatively by treatment of the amino acid ester hydrochlorides with the hexamethyldisilazane-CO₂ system. The ¹H NMR spectra show that monosilyl urethanes derived from α-and β-amino acid esters are characterized by intramolecular interaction of the silicon atom and the oxygen atom of the carboxy group.     

Preparation and reactivity of metal-containing monomers. 12. Metallochelate monomers based on N-(2-pyridyl)methylacrylamide

Metallochelate monomers have been synthesized on the basis of N-(2-pyridyl)methylacrylamide. On the basis of data obtained by IR and UV spectroscopy and magnetochemistry, it is concluded that the metal ion has an octahedral configuration in the compounds obtained. The diffuse reflection spectra indicate that the metal-ligand bond in the chromium(III) complex is covalent in character, with a 0.375 degree of covalency.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2474–2477, November, 1989.     

Intelligent networks based on poly(oxyethylene)

Films of PEO and PEO blends were efficiently crosslinked by exposure to ultraviolet radiation with high-pressure mercury lamp. Photochemical crosslinking proceeded in the presence of photoinitiator such as benzophenone or pentaerythritol triacrylate. PEO networks obtained by UV irradiation in the presence of potassium salts (thiocyanate, perchlorate and triflate) as templates showed enhanced cation binding ability for Li⁺ and Na⁺ cations. Cationic networks were prepared from crosslinked PEO modified with ethyl methacrylate dimethyl dodecyl ammonium bromide. Stimuli-sensitive hydrogels (pH and temperature) were prepared from combinations of PEO and poly-N-isopropyl acryl amide, polyvinyl methyl ether, polyvinyl acetate and poly-2-vinyl pyridine subjected to UV irradiation.     

Synthesis and characterization of novel low‐dielectric cyanate esters

For the purpose of increasing the mobility of residual bisphenol A dicyanate ester (BADCY) during the final stage of curing and achieving a complete reaction of cyanate groups, a small quantity of monofunctional phenol was added to BADCY to form an imidocarbonate, or a small quantity of monofunctional cyanate esters was added to form cyanate ester copolymers. The proposed structures were confirmed with Fourier transform infrared, elemental analysis, mass spectrometry, and NMR spectroscopy. The thermal properties of the cured cyanate esters were measured with dynamic mechanical analysis, thermogravimetric analysis, and dielectric analysis. These data were compared with those for the cured BADCY resin. The cured modified cyanate esters exhibited a lower dielectric constant, a lower dissipation factor, and lower moisture absorption than the cured BADCY system. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2589–2600, 2004     

Interpenetrating polymer networks based on poly(chloroprene) and poly(carbonate-urethane)

Simultaneous interpenetrating polymer networks (SIN's) of poly(chloroprene) (CR) and poly(carbonate-urethane) (PCU) were prepared and characterized. The effect of composition on the phase morphology of full IPN's of CR/PCU has been studied by DSC and SEM. A single phase morphology of IPN's has achieved when the content of CR component is below 50 wt %. The microphase separation of the component networks in the IPN's occurred in samples whose weight percentage of the CR component was 50% and higher. © 1993 John Wiley & Sons, Inc.     

Anisotropic networks, elastomers and gels

Anisotropic networks, elastomers and gels exhibit piezoelectric, pyroelectric, ferroelectric and NLO properties of potential interest for use communication and processing technologies. The formation, properties and applications of such anisotropic, mainly liquid crystalline, networks are described. If some of the molecules in a liquid mixture contain at least two reactive groups which can be either photochemically or thermally polymerized, then crosslinked, anisotropic networks, elastomers and gels can be produced. Solid macroscopically aligned elastomers or networks can be formed as required beforehand or simultaneously by orientation of the sample. Anisotropic gels consist of a solid anisotropic network and non-covalently bonded, but strongly oriented domains of low molar mass liquid crystals. Anisotropic networks, elastomers preformed amorphous or liquid crystalline polymers incorporating additional reactive groups, which can be macroscopically oriented in the additional crosslinking reactions. Reversible networks, elastomers and gels can be prepared either non-covalently or covalently by thermally side group polymers and low molar mass molecules, liquid crystalline properties in the pure state. in many electro-optic devices for optical and gels can be prepared from liquid crystalline state and then fixed by reversible linkages between, for example, neither of which necessarily exhibit     

Synthesis,characterization, and properties of novel epoxy resins and cyanate esters

We synthesized a novel epoxy (dopotep) and cyanate ester (dopotcy) based on a phosphorus‐containing triphenol (dopotriol). The proposed structures were confirmed by IR, mass spectra, NMR spectra, and epoxy‐equivalent‐weight titration. The synthesized dopotep or dopotcy was copolymerized with diglycidyl ether of bisphenol A (DGEBA), 6′,6‐bis(3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazineyl)methane (F‐a), or dicyanate ester of bisphenol A (BADCY). Thus, copolymers based on DGEBA/dopotep/diphenylmethane (ddm), F‐a/dopotep, BADCY/dopotcy, and DGEBA/dopotcy were developed. The thermal properties, dielectric properties, and flame retardancy of these copolymers were investigated. The curing kinetics of dopotep/ddm and dopotep/diamino diphenylsulfone were studied with differential scanning calorimetry. The microstructure of DGEBA/dopotcy was studied with IR. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3487–3502, 2006     

Polymer blends based on an epoxy-amine thermoset and a thermoplastic

The effect of thermoplastic modification of an epoxy-amine system on the cure reaction, miscibility and thermal stability of the system was investigated. The cure kinetics showed an autocatalytic behavior. Modifier did not affect either the total reaction heat or the achieved maximum conversion but delayed the kinetics. The model of Horie-Kamal corrected by diffusion factor was used to adjust kinetics in the whole range of conversions. The modified systems showed two glass transitions indicating two separated phases, whose compositions were estimated using the Fox and Couchman equations. Modifier did not affect the thermal and thermooxidative stability of the system.     

Fluoroacrylic esters and related monomers: Preparation and use as synthons

Preparations of acrylic compounds substituted by fluorine atoms or trifluoromethyl groups at the a or β positions are reviewed. Their use in Michael additions, annelation reactions and Diels-Alder condensations leads to more complex molecules, such as fluorinated analogues of natural products.     

Reaction of acyl(aroyl) isocyanates with dimedon

Conclusions The benzoyl and trichloroacetyl isocyanates react with dimedon to give the [4 + 2]-cycloadducts and the O- and C-addition products, whereas trifluoroacetyl isocyanate reacts to give the acid azomethine.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2788–2790, December, 1981.