Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
  • C08G77/60—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule in which all the silicon atoms are connected by linkages other than oxygen atoms
  • C08G77/62—Nitrogen atoms

Definitions

• This invention relates to processes for preparing curable polysilazane-containing compositions and, in another aspect, to compositions prepared thereby.
• Ceramic materials are well-known and widely used for different applications due to some of their exceptional properties, such as relatively high modulus, hardness, high temperature stability, and/or chemical resistance. Ceramic materials can also be, however, relatively heavy, brittle, and/or difficult to process. Alternatively, organic polymers can be relatively tough, flexible, light, and/or easy to fabricate and process, but their relatively low moduli and relatively low decomposition temperatures prevent their use in some applications. Pre-ceramic polymer technology is emerging as a promising approach for producing materials that share the advantages of both polymers and ceramics, while minimizing the disadvantages.
• Mixed organic/inorganic polymer compositions have been prepared (for example, by the hydrolysis of tetraalkoxysilanes containing polymerizable organic groups) to circumvent the insolubility of many important engineering polymers within sol-gel solutions.
• Curing of such sol-gel processed monomers has provided mixed systems exhibiting some of the properties of the organic components, as well as some of the properties of the inorganic components.
• Such mixed systems have typically comprised semi-interpenetrating networks composed of linear organic polymers and a three- dimensional silicon dioxide network.
• Polysilazanes and modified polysilazanes have been prepared and used for pyrolytic conversion to a ceramic material (for example, silicon nitride).
• Polysilazanes have also been used to modify materials such as epoxy resins, phenolic resins, and polyamines.
• Hybrid organic/inorganic polymers or ceramers have been prepared by the reaction of organic electrophiles with metal-containing polymers.
• the hybrid polymers are said to comprise organic segments derived from the organic electrophiles and inorganic fractions derived from segments of the metal-containing polymers.
• Such hybrid polymers have been proposed for use as coatings on substrate materials, for molding applications (with or without fillers), and for other polymer applications in which their hybrid properties (for example, a combination of relatively high mechanical strength and high temperature stability) can be advantageous.
• polyorganosilazanes (homopolymers or copolymers composed of organo-modified silazane units) have been prepared by ammonolysis of various dihalosilanes and organodihalosilanes, respectively.
• a curable copolysilazane hybrid organic/inorganic copolymer, with only a portion of its silazane units being organo-modified silazane units
• curable polysilazanes can have main chains or backbones that comprise structural units having the following general formula:
• each R a , each R b , and each R c is independently hydrogen, an organic group, a heteroorganic group, or a combination thereof.
• all of R a , R b , and R c in Formula I above are hydrogen, and, in the other polysilazanes, at least one of R a and R b is a group other than hydrogen for a portion (copolysilazane) or all
• perhydropolysilazane and the copolysilazane typically have involved the use of relatively large excess amounts of pyridine (for example, at least about 12 times the stoichiometric amount of silicon-halogen bonds in the starting silanes). These large excesses have been used to form pyridine adducts of apparently all starting silanes in situ, and the resulting pyridine adducts have then been co-ammonolyzed in the presence of the remainder of the large excess of base.
• Such processes will preferably be capable of flexibly and controllably producing polymers having tailored structures and physical properties.
• this invention provides a process for preparing curable oligomeric and/or polymeric polysilazanes comprising
• the base (1) is used for the dihalosilane-base adduct formation in a limited amount that is less than or equal to twice the stoichiometric amount of silicon- halogen bonds in the dihalosilane or (2) is used for the dihalosilane-base adduct formation in excess of (more than) this limited amount and, prior to the ammonolysis, the total amount of the resulting reacted and unreacted base is reduced to no more than this limited amount (for example, by removal of base by evaporation).
• the base is preferably used for the dihalosilane-base adduct formation in an amount that is at least equal to the stoichiometric amount of silicon-halogen bonds in the dihalosilane but less than or equal to twice this amount.
• the dihalosilane is dichlorosilane
• the base is pyridine
• the ammonolysis is carried out by reaction with ammonia.
• the organodihalosilane can be selected from monoorganodihalosilanes, diorganodihalosilanes, and combinations thereof.
• Optional step (b) of the process is preferably carried out, so as to prepare curable copolysilazane (more preferably, both this step and the ammonolysis step are carried out in the presence of no more than the above-defined limited amount of base).
• the process can optionally further comprise the use of aprotic (preferably, nonpolar aprotic) solvent (preferably, hexane) and/or the purification, isolation, coating (for example, after optional solvent addition or change), and/or curing of the resulting curable polysilazane.
• curable oligomeric and/or polymeric polysilazanes having relatively low initial viscosities (and, accordingly, relatively long shelf lives even in the absence of solvent (that is, in neat or 100 percent solids form)) can be prepared.
• the curable polysilazanes surprisingly exhibit significantly improved shelf stability, relative to corresponding polysilazanes prepared by the prior art method that uses much larger amounts of base.
• curable polysilazanes (perhydropolysilazane and copolysilazanes) prepared by the process of the invention generally can be stable for periods of about 1 to about 3 days in the absence of solvent (100 percent solids form) or at high concentration in solvent before dilution to avoid gellation can become necessary. Such time periods can be sufficient to enable purification and/or work-up in an industrial setting without the loss of a batch or a kettle due to gellation.
• the process of the invention can provide curable polysilazanes that exhibit greater industrial compatibility (relative to corresponding polysilazanes prepared by the typical prior art method described above) and that can be more easily stored and then cured on demand.
• copolysilazanes prepared by the process of the invention provide a versatile class of hybrid organic/inorganic polymers or ceramers that can be cured to form crosslinked networks.
• the properties of the crosslinked networks can be tailored to the requirements of various different applications by varying the relative amounts of the starting dihalosilane (which determines the degree of inorganic content of the curable polysilazane, affects the curing agents that can be effective, and increases the hardness of the cured polysilazane) and the starting organodihalosilane (which determines the degree of organic content of the curable polysilazane, also affects the curing agents that can be effective, and increases the flexibility of the cured polysilazane).
• the copolysilazanes do not exhibit phase separation and can be cured to provide homogeneous, optically clear coatings.
• the incorporation of only a relatively small portion of organo-modified silazane units can provide copolysilazanes that can retain the excellent curability and hardness characteristics of perhydropolysilazane, while gaining the benefit of improved flexibility (and therefore reduced crack formation in the cured coating).
• the process of the invention can be carried out with less pyridine (a relatively expensive base) than the prior art method and therefore can be relatively more cost- effective.
• the process also can be relatively more efficient, as the use of less pyridine (which is relatively hydrophilic and boils at a relatively high temperature) can result in less moisture absorption and gellation during polysilazane preparation and can facilitate purification during work-up.
• the resulting curable polysilazanes can be used in a number of applications including, for example, use in forming coatings or surface treatments, use in molding applications (optionally in combination with at least one filler) to form various shaped articles, use in forming ceramic coatings, and so forth.
• At least some embodiments of the process of the invention can meet the above-described, ongoing need for hybrid organic/inorganic polymers or ceramers (and, in particular, hybrid polysilazane polymers or ceramers) that can fulfill the performance requirements of a variety of different applications, as well as the need for efficient and cost-effective preparation processes that can flexibly and controllably produce polymers having tailored structures and physical properties.
• this invention also provides a curable polysilazane prepared by the process of the invention, and the curable polysilazane in cured form.
• catenated heteroatom means an atom other than carbon (for example, oxygen, nitrogen, or sulfur) that replaces one or more carbon atoms in a carbon chain (for example, so as to form a carbon-heteroatom-carbon chain or a carbon-heteroatom-heteroatom- carbon chain);
• cure means conversion to a crosslinked polymer network (for example, through irradiation or catalysis);
• fluoro- for example, in reference to a group or moiety, such as in the case of
• fluoroalkylene or “fluoroalkyl” or “fluorocarbon) or “fluorinated” means only partially fluorinated such that there is at least one carbon-bonded hydrogen atom;
• fluorochemical means fluorinated or perfluorinated;
• heteroorganic means an organic group or moiety (for example, an alkyl or alkylene group) containing at least one heteroatom (preferably, at least one catenated heteroatom);
• oligomer means a molecule that comprises at least two repeat units and that has a molecular weight less than its entanglement molecular weight; such a molecule, unlike a polymer, exhibits a significant change in properties upon the removal or addition of a single repeat unit;
• perfluoro- (for example, in reference to a group or moiety, such as in the case of "perfluoroalkylene” or “perfluoroalkyl” or “perfluorocarbon") or “perfluorinated” means completely fluorinated such that, except as may be otherwise indicated, there are no carbon-bonded hydrogen atoms replaceable with fluorine;
• perfluoroether means a group or moiety having two saturated or unsaturated perfluorocarbon groups (linear, branched, cyclic (preferably, alicyclic), or a combination thereof) linked with an oxygen atom (that is, there is one catenated oxygen atom);
• perfluoropolyether group or segment or moiety
• perfluoropolyether group means a group or moiety having three or more saturated or unsaturated perfluorocarbon groups (linear, branched, cyclic (preferably, alicyclic), or a combination thereof) linked with oxygen atoms (that is, there are at least two catenated oxygen atoms);
• polysilazane refers to compounds having at least one of a linear, branched, or cyclic main chain or backbone comprising a plurality of Si— linkages
• polysiloxazane refers to compounds having at least one of a linear, branched, or cyclic main chain or backbone comprising both Si— and Si— O linkages; for simplicity, in this patent application, “polysilazane” also includes “polysiloxazane” and
• polyureasilazane refers to compounds having at least one of a linear, branched, or cyclic main chain or backbone comprising a plurality of Si— N linkages and having at least one carbonyl group bonded to each of two nitrogen atoms;
• substituted aryl means an aryl group substituted by non-interfering (with cure) atoms such as one or more of halogens, alkyl groups, and heteroalkyl groups.
• Dihalosilanes that are suitable for use in carrying out the process of the invention include those that can be represented by the general formula S1H2X2, wherein each X is independently a halogen atom (selected from fluorine, chlorine, bromine, iodine, and combinations thereof; preferably, selected from chlorine, bromine, iodine, and
• Dichlorosilane is most preferred.
• Organodihalosilanes that are suitable for use in carrying out the process of the invention include those that can be represented by the general formula R a R b SiX2, wherein R a and R b are independently hydrogen, an organic group, a heteroorganic group, or a combination thereof, with the proviso that at least one of R a and R b is an organic or heteroorganic group; and X is as defined above.
• Suitable organic and heteroorganic groups include alkyl, alkenyl, cycloalkyl, aryl, aralkyl, alkylsilyl, arylsilyl, alkylamino, arylamino, alkoxy, aryloxy, aralkyloxy, and the like, and combinations thereof (preferably, alkyl, alkenyl, cycloalkyl, aryl, aralkyl, alkoxy, aryloxy, aralkyloxy, and combinations thereof); the groups preferably having from 1 to about 18 carbon atoms (more preferably, 1 to about 12 carbon atoms; even more preferably, 1 to about 8 carbon atoms; most preferably, 1 to about 2 carbon atoms (for example, methyl or vinyl)).
• the groups can be further substituted with one or more substituent groups such as halogen, alkoxy, amino, carboxyl, hydroxyl, alkoxycarbonyl, nitro, and the like, and combinations thereof.
• useful organodihalosilanes include those wherein R a and R b are independently hydrogen, a linear, branched, or cyclic alkyl group having fewer than about 9 carbon atoms, a linear, branched, or cyclic heteroalkyl group having fewer than about 7 carbon atoms, a substituted or unsubstituted aryl group having fewer than about 13 carbon atoms, an ethylenically unsaturated group, a ring structure formed from R a and R b , taken together, having fewer than about 8 carbon atoms, or a combination thereof, with the proviso that at least one of R a and R b is a group other than hydrogen; and X is as defined above.
• R a and R b are independently selected from hydrogen, alkyl (more preferably, methyl), aryl (more preferably, phenyl), alkenyl (more preferably, vinyl), and combinations thereof, with the proviso that at least one of R a and R b is a group other than hydrogen; and/or each X is preferably chlorine.
• Bases are independently selected from hydrogen, alkyl (more preferably, methyl), aryl (more preferably, phenyl), alkenyl (more preferably, vinyl), and combinations thereof, with the proviso that at least one of R a and R b is a group other than hydrogen; and/or each X is preferably chlorine.
• Bases that are suitable for use in carrying out the process of the invention include those that can form a base adduct with a halosilane.
• Useful bases include tertiary amines (for example, trialkylamines such as trimethylamine, triethylamine,
• pyridine substituted (for example, with one or more substituents such as methyl or ethyl groups) pyridines (for example, picolines), sterically-hindered secondary amines, phosphines (for example, trimethyl phosphine, dimethylethyl phosphine, methyldiethyl phosphine, and
• arsines for example, trimethyl arsine
• arsines for example, trimethyl arsine
• Preferred bases include tertiary amines, pyridine, substituted pyridines, and combinations thereof. More preferred bases include tertiary amines, pyridine, picolines, and combinations thereof (even more preferably, tertiary amines, pyridine, and combinations thereof; still more preferably, trimethylamine, pyridine, and combinations thereof). Most preferred is pyridine.
• the dihalosilane-base adduct can be prepared by combining at least one of the above-described dihalosilanes with at least one of the above-described bases.
• the dihalosilanes can react with the base to form an adduct, the rate of formation and stability of which can depend on the acidity of the dihalosilane and the basicity of the base.
• the dihalosilane and the base can be selected so as to produce an adduct that is sufficiently stable to function as a reaction intermediate that is capable of reacting with ammonia or a primary amine.
• one mole of dichlorosilane is known to react with two moles of pyridine to form a 1 : 2 (halide : base) adduct or with one mole of
• At least one dihalosilane for example, dichlorosilane
• at least one base for example, pyridine
• at least one aprotic solvent for example, hexane
• any suitable reactor for example, a round bottom flask equipped with a magnetic stir bar, a reflux condenser, and a gas inlet
• a desired reaction temperature for example, about 23 °C to about 100°C
• a dry (for example, nitrogen) atmosphere for example, nitrogen
• the base in forming the dihalosilane-base adduct, can be used in an amount that is less than or equal to about twice the stoichiometric amount of silicon-halogen bonds in the dihalosilane.
• a monobasic compound such as pyridine (for which the stoichiometric amount of base is 2 moles of base for every mole of dihalosilane) less than or equal to about 4 moles of base can be used per mole of dihalosilane.
• a dibasic compound such as tetramethylethylenediamine (for which the stoichiometric amount of base is 1 mole of base for every mole of dihalosilane), less than or equal to about 2 moles of base can be used per mole of dihalosilane.
• the base is preferably used for the dihalosilane-base adduct formation in an amount that is at least equal to the stoichiometric amount of silicon-halogen bonds in the dihalosilane but less than or equal to twice this amount.
• the amount of base is less than or equal to about 1.5 times the stoichiometric amount of silicon-halogen bonds in the dihalosilane (more preferably, less than or equal to about 1.25 times the stoichiometric amount; most preferably, about equal to the stoichiometric amount).
• Suitable solvents for use in the process of the invention include aprotic solvents such as aromatic solvents (for example, xylene, benzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, and the like, and mixtures thereof), alkanes (for example, hexane, heptane, isoparaffinic hydrocarbons, and the like, and mixtures thereof), and the like, and mixtures thereof.
• Preferred solvents include xylene, hexane, heptane, and mixtures thereof, with xylene, hexane, and mixtures thereof being more preferred and hexane being most preferred.
• the resulting product (preferably, solvent has been used for the adduct formation step or has been subsequently added to form a slurry) can optionally be stirred (for example, at room temperature for about one hour) prior to addition of a stoichiometric excess of ammonia (for example, by bubbling through the slurry at room temperature), a primary amine, or a combination thereof (preferably, ammonia).
• the temperature of the resulting reaction mixture generally rises as ammonolysis proceeds, and ammonia (or amine) can generally be added to the reaction mixture until the temperature of the reaction mixture begins to drop (which can indicate that sufficient ammonia has been added to enable the reaction to run to completion).
• the ammonolysis reaction is preferably carried out in an inert gas atmosphere (for example, under nitrogen or argon).
• Base can be present during the ammonolysis in only a limited amount, wherein the total amount of reacted and unreacted base resulting from adduct formation is less than or equal to about twice the stoichiometric amount of silicon-halogen bonds in the dihalosilane (a "limited amount of base"). This can be achieved either by using only this limited amount of base to form the dihalosilane-base adduct, or by subsequently removing a sufficient amount of unreacted base prior to ammonolysis to reduce the total amount of reacted and unreacted base to this limited amount (for example, by evaporation of a relatively volatile base such as trimethylamine (boiling point of about 3°C)).
• a relatively volatile base such as trimethylamine (boiling point of about 3°C)
• Ammonolysis of the dihalosilane-base adduct can provide curable
• At least one dihalosilane- base adduct and at least one of the above-described organodihalosilanes can be combined prior to ammonolysis.
• Such combining (and the subsequent ammonolysis) preferably can be carried out in the presence of no more than the above-defined limited amount of base.
• excess (as defined above) base preferably can be removed prior to addition of the organodihalosilane.
• the reactor can be cooled and vented, and the reactor contents can be removed and optionally further purified.
• salt by-products can be removed by filtration, and solvent can be removed by evaporation.
• the curable polysilazanes prepared by the process of the invention are generally viscous liquids (for example, having initial viscosities of about 1 X 10 ⁇ 3 Pa- s to about 500 X 10 ⁇ 3 Pa - s).
• the curable polysilazanes include those having linear, branched, or cyclic structures, or a combination thereof.
• the copolysilazanes can have random, alternating, or block polymer structures, or a combination thereof.
• modified polysilazanes for example, polymetallosilazanes, polysiloxazanes, polyureasilazanes, and the like, and combinations thereof) can be prepared by using known methods.
• the curable polysilazanes can be converted to curable organo fluorine- modified polysilazanes by reaction with one or more fluorochemical compounds including those that comprise (a) at least one organofluorine or heteroorganofluorine moiety and (b) at least one functional group that is capable of reacting with an above-described curable oligomeric or polymeric polysilazane through at least one of its chemically reactive sites (selected from silicon-nitrogen bonds, silicon-hydrogen bonds, carbon-carbon double bonds, nitrogen-hydrogen bonds, and combinations thereof).
• the curable organofluorine- modified polysilazanes by reaction with one or more fluorochemical compounds including those that comprise (a) at least one organofluorine or heteroorganofluorine moiety and (b) at least one functional group that is capable of reacting with an above-described curable oligomeric or polymeric polysilazane through at least one of its chemically reactive sites (selected from silicon-nitrogen bonds, silicon-hydrogen bonds, carbon
• organofluorine or heteroorganofluorine moiety of the fluorochemical compound is a perfluorinated moiety (more preferably, a perfluoroalkyl, perfluoroalkylene,
• a class of useful fluorochemical compounds includes those that can be represented by the following general formula:
• R f is a monovalent or multivalent (preferably, monovalent or divalent) linear, branched, alicyclic, or aromatic, fluorinated or perfluorinated, organic or heteroorganic group or a combination thereof (preferably, a perfluorinated organic or heteroorganic group or a combination thereof; more preferably, a perfluoroalkyl, perfluoroalkylene, perfluoroether, or perfluoropolyether group or a combination thereof; even more preferably, a perfluoroalkyl, perfluoroalkylene, or perfluoropolyether group or a combination thereof; most preferably, a perfluoropolyether group); each Y is a monovalent or multivalent (preferably, monovalent or divalent) linear, branched, alicyclic, or aromatic, fluorinated or perfluorinated, organic or heteroorganic group or a combination thereof (preferably, a perfluorinated organic or heteroorganic group or a combination thereof; more
• each X is independently an electrophilic or nucleophilic group (preferably, selected from isocyanato, isothiocyanato, epoxide, amino, oxazolino, hydroxyl, mercapto, vinyl, and hydrolyzable silyl groups (for example, silyl groups comprising at least one hydrolyzable moiety such as alkoxy or acyloxy), and combinations thereof; more preferably, selected from isocyanato, epoxide, amino, oxazolino, hydroxyl, and hydrolyzable silyl groups,
• Rf which can be saturated or unsaturated; preferably, saturated
• Y which can be saturated or unsaturated; preferably, saturated
• Such preferred curable polysilazanes include perhydropolysilazane
• Me-H Me-Vinyl Me-Me H-H Me-Ph wherein Me is methyl and Ph is phenyl, as well as Vinyl-H units (that is, Me-H units wherein methyl is replaced with vinyl).
• Some of the units of the perhydropolysilazane or the copolysilazane can become modified (for example, by replacement of the nitrogen- hydrogen bond with a nitrogen-silicon bond) as the reaction advances, so as to introduce a degree of branching into the resulting curable polysilazane.
• preferred copolysilazanes can comprise Me-H and H-H units (for example, in a mole ratio of about 30 parts of Me-H to about 70 parts of H-H or about 50 parts of Me-H to about 50 parts of H-H); Me-H, Me-Vinyl, and H-H units (for example, in a mole ratio of about 50 parts of Me-H to about 20 parts of Me-Vinyl to about 30 parts of H-H); or Me-Me and H-H units (for example, in a mole ratio of about 10 parts of Me-H to about 90 parts of H-H).
• Me-H and H-H units for example, in a mole ratio of about 30 parts of Me-H to about 70 parts of H-H or about 50 parts of Me-H to about 50 parts of H-H
• Me-H, Me-Vinyl, and H-H units for example, in a mole ratio of about 50 parts of Me-H to about 20 parts of Me-Vinyl to about 30 parts of
• the curable polysilazanes prepared by the process of the invention can have relatively long shelf lives, even when stored in neat (or 100 percent solids) form.
• the curable polysilazanes can be in the form of relatively viscous liquids that can be used alone or that can be used in admixture with each other, with one or more other types of polymers, and/or with commonly-used solvents (for example, alkyl esters, ketones, ethers, alkanes, aromatics, and the like, and mixtures thereof).
• Useful compositions can comprise conventional additives such as, for example, catalysts, initiators, surfactants, stabilizers, anti-oxidants, flame retardants, and the like, and mixtures thereof.
• the curable polysilazanes (or a composition comprising, consisting, or consisting essentially thereof) can be used in various applications.
• the curable polysilazanes can be used in molding applications (optionally in combination with at least one filler) to form various shaped articles, as ceramic precursors, and in coating applications (for example, to form hardcoats).
• the curable polysilazanes can serve as fluorinated surface treatments to impart a degree of hydrophobicity and/or oleophobicity to a variety of substrates (for example, for surface protection or to enhance ease of cleaning).
• the curable polysilazanes (or a composition comprising, consisting, or consisting essentially thereof) can be cured by exposure to moisture (for example, through their H-H content, as described above), by the use of free radical initiators (for example, through their Me-Vinyl, Me-H, or H-H content, as described above), by the use of hydrosilation catalysts such as platinum catalysts (for example, through their Me-Vinyl, Me-H, or H-H content, as described above), or the like.
• the preferred curing method will vary, depending upon the particular application and its accompanying requirements and conditions.
• Moisture cure can be effected at temperatures ranging from room temperature (for example, about 23°C) up to about 80°C or more, depending upon the degree of H-H content. Moisture curing times can range from a few minutes (for example, at the higher temperatures) to hours (for example, at the lower temperatures).
• Useful moisture curing catalysts are well-known in the art and include ammonia, N-heterocyclic compounds (for example, 1 -methylpiperazine, 1 -methylpiperidine, 4,4'- trimethylenedipiperidine, 4,4' -trimethylene-bis( 1 -methylpiperidine),
• mono-, di-, and trialkylamines for example, methylamine, dimethylamine, trimethylamine, phenylamine, diphenylamine, triphenylamine, DBU (that is, 1,8- diazabicyclo[5.4.0]-7-undecene), DBN (that is, l,5-diazabicyclo[4.3.0]-5-nonene), 1,5,9- triazacyclododecane, 1,4,7-triazacyclononane, and the like, and combinations thereof), organic or inorganic acids (for example, acetic acid, propionic acid, butyric acid, valeric acid, maleic acid, stearic acid, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, chloric acid, hypochlorous acid, and the like, and combinations thereof), metal carb
• the moisture curing catalysts can be present in amounts ranging from about 0.1 to about 10 weight percent (preferably, from about 0.1 to about 5 weight percent; more preferably, from about 0.1 to about 2 weight percent), based upon the total weight of catalyst and curable polysilazane.
• the catalysts can be added before, during, or after shelf storage (preferably, after) and can be activated at low temperatures (for example, to enable room temperature curing, as described above).
• Suitable free radical initiators include organic and inorganic peroxides; alkali metal persulfates; ammonium persulfate; redox systems; aliphatic azo compounds; organic and inorganic peroxides in combination with metal or amine compounds as activators; and the like, and combinations thereof.
• Preferred free radical initiators include organic and inorganic peroxides (for example, hydrogen peroxide and acyl or aryl peroxides such as p- menthane hydroperoxide, ethyl ketone peroxide, benzoyl peroxide, lauroyl peroxide, tert- butyl peroxybenzoate, acetyl benzyl peroxide, p-chlorobenzoyl peroxide, alkoxy benzoyl peroxide, dicaproyl peroxide, crotonyl peroxide, di-tert-alkyl peroxide, di-tertbutyl diphosphate peroxide, peracetic acid, cyclohexyl hydroperoxide, dicumyl peroxide, and the like, and combinations thereof); and combinations thereof.
• organic and inorganic peroxides for example, hydrogen peroxide and acyl or aryl peroxides such as p- menthane hydroperoxide
• the free radical initiators can be present in amounts ranging from about 0.1 to about 10 weight percent (preferably, from about 1 to about 5 weight percent), based upon the total weight of initiator and curable polysilazane.
• the free radical initiators can be added before, during, or after shelf storage (preferably, after) and can be activated by the heat of their reaction (in some cases) or by radiation or thermal energy from an external source (for example, convection heating, induction heating, or electron beam or microwave irradiation).
• free radically-initiated curing can be effected by heating to a temperature of about 150°C for a period of minutes to hours (for example, about 18 hours).
• Suitable hydrosilation catalysts include thermal catalysts (for example, platinum catalysts) and photocatalysts that can be effective for catalyzing a hydrosilation reaction between silicon-bonded hydrogen groups and silicon-bonded ethylenic groups.
• thermal catalysts for example, platinum catalysts
• photocatalysts that can be effective for catalyzing a hydrosilation reaction between silicon-bonded hydrogen groups and silicon-bonded ethylenic groups.
• Useful thermal hydrosilation catalysts include those described, for example, in U. S. Patent Nos.
• hydrosilation catalysts and techniques also include those described in U.S. Patent No. 5,520,978 (Boardman et al.); the hydrosilation catalyst and technique descriptions of which are incorporated herein by reference. Combinations of thermal catalysts and photocatalysts can be used.
• the hydrosilation catalyst can typically be present in an amount that is effective to catalyze the hydrosilation reaction (for example, in amounts ranging from about 1 to about 1000 parts per million (ppm); preferably, from about 10 to about 500 ppm; more preferably, from about 50 to about 250 ppm), based upon the total weight of catalyst and curable polysilazane.
• the catalyst can be added before, during, or after shelf storage (preferably, after) and can be activated by the heat of their reaction (in some cases) or by radiation (for example, ultraviolet- visible light, gamma irradiation, e-beam, or the like) or thermal energy from an external source (for example, convection heating, induction heating, irradiation, or the like).
• platinum catalyzed curing can be effected by heating to a temperature of about 120°C for a period of about seconds to minutes.
• the curable polysilazanes can be cured to form crosslinked hardcoats.
• the hardcoats can exhibit hybrid properties that can be tailored by varying the degree of crosslinking and by varying the natures and relative amounts of the starting silane(s).
• Methyldichlorosilane was obtained from Aldrich Chemical Company, Milwaukee, WI. Methyl vinyl dichlorosilane was obtained from Aldrich Chemical Company,
• Ammonia was obtained from Aldrich Chemical Company, Milwaukee, WI.
• Xylene was aobtained fom Alfa Aesar, Ward Hill, MA,
• Me 3 N was obtained from Aldrich Chemical Company, Milwaukee, WI.
• Heptane was obtained from Aldrich Chemical Company, Milwaukee, WI.
• Example 1 Preparation of For Example 1, a 1 -liter, three-necked flask equipped with a mechanical stirrer, a dry ice/acetone condenser, and an ammonia inlet tube was charged with hexane (300 mL) and dichlorosilane (25 weight percent in xylene, 0.16 mole, 64.6 g). Anhydrous pyridine (0.32 mole, 99.5 percent purity, 25.4 g, equal to the stoichiometric amount of silicon- chlorine bonds in the dichlorosilane) was added dropwise to the flask. White solid pyridine adduct was produced. The resulting slurry was stirred at room temperature for one hour.
• Methyldichlorosilane (0.16 mole, 18.4 g) was then added to the slurry, and ammonia was then slowly bubbled into the flask. The temperature of the resulting reaction mixture increased. The reaction continued until 56 g of ammonia had been added. The resulting byproduct salt was filtered off. Evaporation of solvent from the resulting filtrate (using an oil bath set at 55°C and 668.7 Pa (0.0066 atmosphere) vacuum) gave 10.0 g of viscous copolysilazane (yield of 68.7 percent).
• the viscosity (measured using a Brookfield Model DV-III programmable rheometer obtained from Brookfield Engineering Laboratories, Inc., Middleboro, MA) of the copolysilazane was 61.9 X 10 ⁇ 3 Pa- s (61.9 cP) at 25°C. After one month of aging under ambient conditions, the viscosity increased to 103.6 X 10 ⁇ 3 Pa- s (103.6 cP) at 25°C.
• Example 2 Preparation of For Example 2, a 3 -liter, three-necked flask equipped with a mechanical stirrer, a dry ice/acetone condenser, and an ammonia inlet tube was charged with hexane (1500 mL) and anhydrous pyridine (1.98 mole, 156.6 g, equal to the stoichiometric amount of silicon- chlorine bonds in the dichlorosilane).
• Dichlorosilane 25 weight percent in xylene, 0.99 mole, 400 g
• White solid pyridine adduct was produced and precipitated out. The resulting slurry was stirred at room temperature for one hour.
• Methyldichlorosilane 0.5 mole, 57.5 g
• methyl vinyl dichlorosilane 0.2 mole, 28.2 g
• ammonia was slowly bubbled into the flask.
• the temperature of the resulting reaction mixture increased.
• the reaction continued until 65 g of ammonia had been added.
• the resulting byproduct salt was filtered off. Evaporation of solvent from the resulting filtrate gave 63 g of viscous copolysilazane.
• Example 5 For Example 5, a 1 -liter, three-necked flask equipped with a mechanical stirrer, a dry ice/acetone condenser, and an ammonia inlet tube was charged with dichlorosilane (25 weight percent in xylene, 0.35 mole, 141.4 g) and 500 mL hexane. Anhydrous pyridine (0.7 mole, 55.4 g, equal to the stoichiometric amount of silicon-chlorine bonds in the dichlorosilane) was added dropwise to the flask over a period of 1 hour. White solid pyridine adduct was produced. The resulting slurry was stirred at room temperature for one hour. Ammonia was then slowly bubbled into the flask.
• dichlorosilane 25 weight percent in xylene, 0.35 mole, 141.4 g
• Anhydrous pyridine 0.7 mole, 55.4 g, equal to the stoichiometric amount of silicon-chlorine bonds
• Example 6 For Example 6, a 1 -liter, three-necked flask equipped with a mechanical stirrer, a dry ice/acetone condenser, and an ammonia inlet tube was charged with dichlorosilane (25 weight percent in xylene, 0.35 mole, 141.4 g) and 500 mL hexane. Anhydrous pyridine (1.4 moles, 110.8 g, equal to twice the stoichiometric amount of silicon-chlorine bonds in the dichlorosilane) was added dropwise to the flask over a period of 1 hour. White solid pyridine adduct was produced. The resulting slurry was stirred at room temperature for one hour. Ammonia was then slowly bubbled into the flask.
• dichlorosilane 25 weight percent in xylene, 0.35 mole, 141.4 g
• Anhydrous pyridine 1. moles, 110.8 g, equal to twice the stoichiometric amount of silicon-chlorine
• trimethylamine was allowed to evaporate over a period of two hours.
• the viscosity of the copolysilazane was 78.46 X 10 Pa- s (78.46 cP) at 25°C.
• the copolysilazane did not gel upon aging for two weeks under ambient conditions.
• Table 1 Summary of Examples 1-7 and Comparative Examples A-D.
• Cured coatings were prepared from the copolysilazanes of Examples 2 and 3 (as Examples 8 and 9, respectively). Coating solutions of copolysilazane in heptane (and containing 4,4'-trimethylenebis(l-methylpiperidine) as a curing catalyst) were prepared and coated on polycarbonate substrates using a #12 wire. The actual amounts of the copolysilazane, heptane, and 4,4'-trimethylenebis(l-methylpiperidine) were adjusted as indicated below in Table 2, to obtain coating solutions of similar viscosities and thus similar thicknesses. The resulting coatings were then dried and cured at 60°C at a relative humidity of 95 percent for 12 hours.
• the hardnesses of the resulting cured coatings (as well as the hardness of an uncoated polycarbonate substrate, as Comparative Example E) were measured using a nanoindenter (Nanoindenter XP with a Dynamic Contact Module, obtained from MTS Nano Instruments, Oak Ridge, TN).
• the hardness (H) of each coating was determined using nanoindentations at depth regimes of 100-150 nm to minimize substrate effects.
• the resulting data is shown in Table 2 below.

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