Patent Publication Number: US-2022235180-A1

Title: Elastomeric compositions and their applications

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 16/731,019, filed on Dec. 30, 2019, which is a continuation of application Ser. No. 15/546,164, filed on Jul. 25, 2017, now U.S. Pat. No. 10,563,015, which is a 371 of international application No. PCT/EP2016/051573, filed on Jan. 26, 2016, which claims priority to GB application No. 1501430.1, filed on Jan. 28, 2015, and to GB application No. 1514689.7, filed on Aug. 19, 2015, the contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure generally relates to silicone encapsulants and gels cured via a condensation cure chemistry and their applications. 
     BACKGROUND OF THE INVENTION 
     In many instances, gels used as coating, potting, and encapsulating materials must maintain adhesion to substrates and/or other materials. In electronics for example, gels are a special class of encapsulants that cure to form an extremely soft material. They are used to provide high levels of stress relief to sensitive circuitry. Gels perform many important functions in electronics. Their major job is to protect electronic assemblies and components from adverse environments, such as by: functioning as dielectric insulation, protecting the circuit from moisture and other contaminants, and/or relieving mechanical and thermal stress on components. In such situations, the gels are required to adhere to electronic and electrical components and printed circuit boards in addition to the electrical connectors and conductors that pass through the coating or encapsulating material. 
     The materials that form the gels are expensive being based on addition cure chemistry, i.e., they are cured by the reaction of a silicon hydride group and an unsaturated carbon radical with the help of a catalyst, which is typically a platinum based compound. Historically, the industry has preferred addition cure compositions of this type for these applications because they immediately cure throughout the body of the compound resulting in a cured gel material in a matter of minutes, while on the other hand condensation cure systems are significantly slower. For example, titanate cured condensation processes can take up to 7 days curing per 6 mm of depth of the body of the uncured material. Tin cured condensation systems do cure over a shorter period of time, but they are not desired for electronics applications because they undergo reversion (i.e., depolymerisation) at temperatures above 80° C. 
     While from a cure speed standpoint, gels made from these hydrosilylation cure compositions are excellent, there are several potential problems and/or disadvantages with the use of these types of products. First, they are generally cured at elevated temperature, e.g., temperatures significantly above room temperature. The hydrosilylation compositions can be contaminated and rendered uncurable (or incurable) due to inactivation of expensive platinum based cure catalysts. The platinum catalysts are sensitive and may be poisoned by amine containing compounds, sulphur containing compounds, and phosphorus containing compounds. 
     Alkoxy titanium compounds—alkyl titanates—are suitable catalysts for formulating one component moisture curable silicones (References: Noll, W.; Chemistry and Technology of Silicones, Academic Press Inc., New York, 1968, p. 399; and Michael A. Brook, Silicon in Organic, Organometallic, and Polymer Chemistry, John Wiley &amp; Sons, Inc. (2000), p. 285). Titanate catalysts have been widely described for their use to formulate one part curing silicone elastomer. To formulate multi component silicone elastomers, other metal catalysts are used such as tin or zinc catalyst, e.g., dibutyl tin dilaurate, tin octoate, or zinc octoate (Noll, W.; Chemistry and Technology of Silicones, Academic Press Inc., New York, 1968, p. 397). In two component silicones, one part contains a filler which typically will contain the moisture required to activate the condensation cure in the bulk of the product. In the presence of such an amount of moisture, alkyl titanate catalysts are fully hydrolysed to form tetrahydroxy titanate, which is insoluble in silicone and loses its catalytic efficiency. 
     SUMMARY OF THE INVENTION 
     A gel is provided. The gel is the condensation reaction product of (i) at least one condensation curable silyl terminated polymer and (ii) a cross-linker, in the presence of (iii) a condensation catalyst. The at least one condensation curable silyl terminated polymer may also be referred to herein simply as the “polymer (i)” or “polymer”. The condensation catalyst may also be referred to herein simply as the “catalyst (iii)” or “catalyst”. 
     The at least one condensation curable silyl terminated polymer has at least one hydrolysable and/or hydroxyl functional group per molecule. In certain embodiments, the polymer has at least two hydrolysable and/or hydroxyl functional groups per molecule. In specific embodiments, the polymer has one such functional group or has two such functional groups. 
     The cross-linker is selected from the group consisting of a silicone, an organic polymer, a silane, a disilane molecule, and combinations thereof. The silane may also be referred to as a monosilane. In various embodiments, the cross-linker is selected from the group consisting of monosilanes, disilane molecules, and combinations thereof. In certain embodiments, the cross-linker comprises or is a monosilane. In further or alternate embodiments, the cross-linker comprises or is a disilane molecule. In many embodiments, the disilane molecule is selected from the group consisting of silyl functional molecules having as least two silyl groups, where each silyl group contains at least one hydrolysable group. In specific embodiments, the disilane molecule has two such silyl groups. The disilane molecule may also be referred to herein simply as the “disilane”. 
     The cross-linker contains at least two hydrolysable groups per molecule. In various embodiments, the cross-linker contains at least three hydrolysable groups per molecule. 
     The condensation catalyst is selected from the group consisting of titanates, zirconates, tin (II) catalysts, and combinations thereof. The titanates and zirconates comprise M-OR functional groups (or “functions”), where M is titanium or zirconium, respectively, and R is an aliphatic hydrocarbon group. In various embodiments, the condensation catalyst is selected from the group consisting of titanates, zirconates, and combinations thereof. In certain embodiments, the condensation catalyst comprises or is a titanate. In further or alternate embodiments, the condensation catalyst comprises or is a zirconate. 
     In various embodiments, the molar ratio of hydroxyl and/or hydrolysable groups in the polymer to hydrolysable groups from the cross-linker is between 0.5:1 to 1:1 when using a monosilane cross-linker or is between 0.75:1 to 3:1 using a disilane molecule cross-linker. In addition, in instances where a titanate and/or a zirconate is/are utilized as the condensation catalyst, the molar ratio of M-OR functional groups to the hydroxyl and/or hydrolysable groups in the polymer is comprised between 0.01:1 and 0.5:1, where M and R are as defined above. In specific embodiments, the molar ratio of M-OR functional groups to the hydroxyl groups in the polymer is comprised between 0.01:1 and 0.5:1, where M and R are as defined above. In certain embodiments, where a titanate is utilized as the condensation catalyst and the at least one condensation curable silyl terminated polymer has hydroxyl groups, the molar ratio of Ti—OR functional groups to the hydroxyl groups is comprised between 0.01:1 and 0.5:1, where R is an aliphatic hydrocarbon group. In further or alternate embodiments, the condensation catalyst comprises or is a titanate and the composition is free of other condensation catalyst types, e.g., zirconates. In yet further embodiments, the condensation catalyst comprises or is a titanate and the composition is free of other condensation catalyst types, e.g., zirconates and/or tins, and is free of hydrosilylation catalyst, e.g., platinum based catalysts. 
     Thus, in addition to the gel formed from the composition, the present disclosure also provides the condensation curable gel composition itself. As described above, the composition is based on titanate, zirconate, or tin (II) cure catalysts. The composition can be cured in the absence of moisture bearing filler leading to a bulk cure in a few minutes to a few hours depending on the composition. The condensation curable gel composition comprises polymer (i), cross-linker (ii), and condensation catalyst (iii), each being as described above. 
     Applications of the composition and the gel formed from the composition are also provided. The gel may also be referred to as an elastomer. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present disclosure provides a condensation curing silicone elastomer (or gel) exhibiting excellent physical properties. In various embodiments, the elastomer has a hardness below Shore 80 in the type 00 scale according to ASTM D 2240-05(2010). Products having a hardness of Shore below 0 in the type 00 scale, i.e., “soft” gels, can also be obtained using the composition of this disclosure. The hardness of such gels are typically measured with the help of a penetrometer. 
     The composition of this disclosure has a number of advantages. The primary advantages of the composition is to cure at room temperature, and to be more resistant to contaminants relative to platinum cure silicones. Further advantages can be appreciated below, e.g., in the Examples section. 
     Polymer (i) is at least one or alternatively is a moisture/condensation curable silyl terminated polymer. Any suitable moisture/condensation curable silyl terminated polymer may be utilised, including polydialkyl siloxanes, alkylphenyl siloxane, or organic based polymers with silyl terminal groups, e.g., silyl polyethers, silyl acrylates and silyl terminated polyisobutylenes or copolymers of any of the above. In various embodiments, the polymer is a polysiloxane based polymer containing at least two hydroxyl or hydrolysable groups. In certain embodiments, the polymer comprises terminal hydroxyl or hydrolysable groups. Examples of suitable hydroxyl or hydrolysable groups include —Si(OH) 3 , —(R a )Si(OH) 2 , —(R a ) 2 Si(OH), —RaSi(OR b ) 2 , —Si(OR b ) 3 , —R a   2 SiOR b , and —(R a ) 2 Si—R c —SiR d   p (OR b ) 3-p  where each R a  independently represents a monovalent hydrocarbyl group, for example, an alkyl group, in particular having from 1 to 8 carbon atoms (e.g., methyl); each R b  and R d  group is independently an alkyl or alkoxy group in which the alkyl groups suitably have up to 6 carbon atoms; R c  is a divalent hydrocarbon group which may be interrupted by one or more siloxane spacers having up to six silicon atoms; and p has the value 0, 1 or 2. 
     In various embodiments, polymer (i) has the general formula (1): 
       X 3 -A-X 1    (1)
 
     where X 3  and X 1  are independently selected from siloxane groups which terminate in hydroxyl or hydrolysable groups and A is a siloxane containing polymeric chain. 
     Examples of hydroxyl-terminating or hydrolysable groups X 3  or X 1  include —Si(OH) 3 , —(R a )Si(OH) 2 , —(R a ) 2 Si(OH), —(R a )Si(OR b ) 2 , —Si(OR b ) 3 , —(R a ) 2 SiOR b , and —(R a ) 2 Si—R c —Si (R d ) p (OR b ) 3-p  as defined above. In certain embodiments, each R b  group, when present, is a methyl group. In various embodiments, the X 3  and/or X 1  terminal groups are hydroxydialkyl silyl groups, e.g., hydroxydimethyl silyl groups or alkoxydialkyl silyl groups, such as methoxydimethyl silyl or ethoxydimethyl silyl. 
     Examples of suitable siloxane groups in polymeric chain A of general formula (1) are those which comprise a polydiorgano-siloxane chain. Thus, in certain embodiments, polymeric chain A includes siloxane units of the general formula (2): 
       —(R 5   s SiO (4-s)/2 )  (2)
 
     in which each R 5  is independently an organic group, such as a hydrocarbyl group having from 1 to 10 carbon atoms optionally substituted with one or more halogen group (such as chlorine or fluorine); and s is 0, 1 or 2. Particular examples of groups R 5  include methyl, ethyl, propyl, butyl, vinyl, cyclohexyl, phenyl, a tolyl group, a propyl group substituted with chlorine or fluorine such as 3,3,3-trifluoropropyl, chlorophenyl, beta-(perfluorobutyl)ethyl or chlorocyclohexyl group. In specific embodiments, at least some to substantially all of the groups R 5  are methyl. 
     Typically, the polymers of the above type will have a viscosity in the order of 1000 to 300000 mPa·s, alternatively 1000 to 100000 mPa·s, at 25° C. measured by using a Brookfield cone plate viscometer (RV DIII) using a cone plate. In various embodiments, polymer (i) has a viscosity of from 1000 to 100000, optionally of from 1000 to 90000, optionally of from 1000 to 80000, optionally of from 1500 to 75000, optionally of from 2000 to 70000, optionally of from 2000 to 60000, or optionally of from 2000 to 50000, mPa·s at 25° C. Various subranges and more specific viscosities are also possible, including, for example, a viscosity of at least 2000, at least 12500, or at least 50000, mPa·s at 25° C., and including the specific viscosities illustrated in the Examples section. 
     Suitable polysiloxanes containing units of general formula (2) are thus polydiorganosiloxanes having terminal, silicon-bound hydroxyl groups or terminal, silicon-bound organic radicals which can be hydrolysed using moisture. The polydiorganosiloxanes may be homopolymers or copolymers. Mixtures of different polydiorganosiloxanes having terminal condensable groups are also suitable. 
     In accordance with the present disclosure, polymeric chain A may alternatively be organic based polymers with silyl terminal groups, e.g., silyl polyethers, silyl acrylates and silyl terminated polyisobutylenes. In the case of silyl polyethers, the polymeric chain A is based on polyoxyalkylene based units. Such polyoxyalkylene units typically comprise a linear predominantly oxyalkylene polymer comprised of recurring oxyalkylene units, (—C n H 2n —O—) illustrated by the average formula (—C n H 2n —O—) y  wherein n is an integer from 2 to 4 inclusive and y is an integer of at least four. The average molecular weight of each polyoxyalkylene polymer block may range from about 300 to about 10000, but can be higher in molecular weight. Moreover, the oxyalkylene units are not necessarily identical throughout the polyoxyalkylene monomer, but can differ from unit to unit. A polyoxyalkylene block, for example, can be comprised of oxyethylene units, (—C 2 H 4 —O—); oxypropylene units (—C 3 H 6 —O—); or oxybutylene units, (—C 4 H 8 —O—); or mixtures thereof. 
     Other polyoxyalkylene units may include, for example, units of the structure: 
       —[—R—O—(—R f —O—) p —Pn—CR g   2 —Pn—O—(—R f —O—) q —R—]—
 
     in which Pn is a 1,4-phenylene group, each Re is the same or different and is a divalent hydrocarbon group having 2 to 8 carbon atoms, each R f  is the same or different and is, an ethylene group or propylene group, each Rg is the same or different and is, a hydrogen atom or methyl group, and each of the subscripts p and q is a positive integer in the range from 3 to 30. 
     For the purpose of this disclosure “substituted” means one or more hydrogen atoms in a hydrocarbon group has been replaced with another substituent. Examples of such substituents include, but are not limited to, halogen atoms such as chlorine, fluorine, bromine, and iodine; halogen atom containing groups such as chloromethyl, perfluorobutyl, trifluoroethyl, and nonafluorohexyl; oxygen atoms; oxygen atom containing groups such as (meth)acrylic and carboxyl; nitrogen atoms; nitrogen atom containing groups such as amino-functional groups, amido-functional groups, and cyano-functional groups; sulphur atoms; and sulphur atom containing groups such as mercapto groups. 
     The backbone of the polymeric chain A which may contain organic leaving groups within the molecule is not particularly limited and may be any of organic polymers having various backbones. In certain embodiments, the backbone includes at least one selected from a hydrogen atom, a carbon atom, a nitrogen atom, an oxygen atom, and a sulphur atom because the resulting composition has excellent curability and adhesion. 
     Cross-linkers that can be used are generally moisture curing silanes. For the sake of the disclosure herein, a monosilane cross-linker shall generally be understood to mean a molecule containing a single silyl functional group, which contains at least one hydrolysable group. For the sake of the disclosure herein, a disilane generally means a molecule containing two silyl groups, each containing at least one hydrolysable group. Typically, a cross-linker requires a minimum of two hydrolysable groups per molecule and may have three or more hydrolysable groups per molecule. In both case, the molecule can be polymeric. 
     Any suitable cross-linker may be used. Suitable cross-linkers include, for example, alkoxy functional silanes, oximosilanes, acetoxy silanes, acetonoxime silanes, and enoxy silanes. For softer materials, disilanes are generally preferable. In various embodiments, the cross-linker used in the moisture curable composition is a silane compound containing hydrolysable groups. These include one or more silanes or siloxanes which contain silicon bonded hydrolysable groups such as acyloxy groups (e.g., acetoxy, octanoyloxy, and benzoyloxy groups); ketoximino groups (e.g.,dimethyl ketoximo, and isobutylketoximino); alkoxy groups (e.g., methoxy, ethoxy, and propoxy) and alkenyloxy groups (e.g.,isopropenyloxy and 1-ethyl-2-methylvinyloxy). 
     Alternatively, the cross-linker may have a siloxane or an organic polymeric backbone. In the case of such siloxane or organic based cross-linkers, the molecular structure can be straight chained, branched, cyclic or macromolecular. Suitable polymeric cross-linkers may have a similar polymeric backbone chemical structure to polymeric chain A as depicted in general formula (1) above; typically however, any such cross-linker(s) (ii) utilised will be of significantly shorter chain length than polymer (i). 
     The cross-linker may have two but generally has three or four silicon-bonded condensable (typically hydroxyl and/or hydrolysable) groups per molecule which are reactive with the condensable groups in polymer (i). In certain embodiments, the cross-linker used is a disilane having up to six hydroxyl and/or hydrolysable groups per molecule. When the cross-linker is a silane and when the silane has three silicon-bonded hydrolysable groups per molecule, the fourth group is suitably a non-hydrolysable silicon-bonded organic group. These silicon-bonded organic groups are suitably hydrocarbyl groups which are optionally substituted by halogen such as fluorine and chlorine. Examples of such fourth groups include alkyl groups (e.g., methyl, ethyl, propyl, and butyl); cycloalkyl groups (e.g., cyclopentyl and cyclohexyl); alkenyl groups (e.g., vinyl and allyl); aryl groups (e.g., phenyl, and tolyl); aralkyl groups (for example 2-phenylethyl) and groups obtained by replacing all or part of the hydrogen in the preceding organic groups with halogen. In many embodiments, the fourth silicon-bonded organic groups is methyl. 
     Silanes and siloxanes which can be used as cross-linkers include alkyltrialkoxysilanes such as methyltrimethoxysilane (MTM) and methyltriethoxysilane, alkenyltrialkoxy silanes such as vinyltrimethoxysilane, vinyltriethoxysilane, and isobutyltrimethoxysilane (iBTM). Other suitable silanes include ethyltrimethoxysilane, vinyltriethoxysilane, phenyltrimethoxysilane, alkoxytrioximosilane, alkenyltrioximosilane, 3,3,3-trifluoropropyltrimethoxysilane, methyltriacetoxysilane, vinyltriacetoxysilane, ethyl triacetoxysilane, di-butoxy diacetoxysilane, phenyl-tripropionoxysilane, methyltris(methylethylketoximo)silane, vinyl-tris-methylethylketoximo)silane, methyltris(methylethylketoximino)silane, methyltris(isopropenoxy)silane, vinyltris(isopropenoxy)silane, ethylpolysilicate, n-propylorthosilicate, ethylorthosilicate, and dimethyltetraacetoxydisiloxane. The cross-linker used may also comprise any combination of two or more of the above. The cross-linker may be polymeric, with a silicone or organic polymer chain bearing alkoxy functional end groups such as 1,6-bis(trimethoxysilyl)hexane (alternatively known as hexamethoxydisilylhexane). 
     In various embodiments, the molar ratio of hydroxyl and/or hydrolysable groups in polymer (i) to hydrolysable groups from cross-linker (ii) is between 0.5:1 to 1:1 using a monosilane cross-linker. In other embodiments, the molar ratio of hydroxyl and/or hydrolysable groups in polymer (i) to hydrolysable groups from cross-linker (ii) is between 0.75:1 to 3:1, or optionally 0.75:1 to 1.5:1, using a disilane cross-linker. In general, it is believed that having a SiOH/SiOR molar ratio that is &gt;0.3 ensures adequate bulk cure of the gel after reaction/cure of the composition (where R is a hydrolysable group). 
     The composition further comprises a condensation catalyst. This increases the speed at which the composition cures. The catalyst chosen for inclusion in a particular composition depends upon the speed of cure required. Titanate and/or zirconate based catalysts may comprise a compound according to the general formula Ti[OR 22 ] 4  or Zr[OR 22 ] 4  where each R 22  may be the same or different and represents a monovalent, primary, secondary or tertiary aliphatic hydrocarbon group which may be linear or branched containing from 1 to 10 carbon atoms. Optionally, the titanate and/or zirconate may contain partially unsaturated groups. However, preferred examples of R 22  include but are not restricted to methyl, ethyl, propyl, isopropyl, butyl, tertiary butyl and a branched secondary alkyl group such as 2,4-dimethyl-3-pentyl. Preferably, when each R 22  is the same, R 22  is an isopropyl, branched secondary alkyl group or a tertiary alkyl group, in particular, tertiary butyl. 
     Suitable examples include: tetra n-butyl titanate, tetra t-butyl titanate, tetra t-butoxy titanate, tetraisopropoxy titanate and diisopropoxydiethylacetoacetate titanate. Alternatively, the titanate or zirconate may be chelated. The chelation may be with any suitable chelating agent such as an alkyl acetylacetonate such as methyl or ethylacetylacetonate. Alternatively, the titanate may be monoalkoxy titanates bearing three chelating agents such as, for example, 2-propanolato, tris isooctadecanoato titanate. 
     In various embodiments, the molar ratio of M-OR or tin (II) functions to the hydroxyl and/or hydrolysable groups in polymer (i) is comprised between 0.01:1 and 0.5:1, or optionally between 0.02:1 and 0.2:1, where M is titanium or zirconium, and R is an aliphatic hydrocarbon group. In general, it is believed that having a SiOH/M (e.g., SiOH/Ti) molar ratio that is &gt;8 prevents viscosity spike/climb or excessive thickening during reaction/cure of the composition, which can prevent formation of the gel or impart the gel with undesirable properties. 
     The gel is typically made from the condensation curable gel composition which is stored in a two part manner. Thus, the composition of this disclosure may be referred to as a two part composition. The two part composition may be mixed using any appropriate standard two-part mixing equipment with a dynamic or static mixer and is optionally dispensed therefrom for use in the application for which it is intended. In various embodiments, the composition is stored in two parts having polymer (i) and cross-linker (ii) in one part and polymer (i) and catalyst (iii) in the other part. In alternative embodiments, the composition is stored in two parts having cross-linker (ii) in one part and polymer (i) and catalyst (iii) in the other part. In yet other embodiments, the composition is stored in two parts having a first polymer (i) and cross-linker (ii) in one part and a second polymer (i) and catalyst (iii) in the other part. 
     In various embodiments, the catalyst is present in a molar amount which is at least 50% of the molar amount of any moisture (i.e., water) that may be present cumulatively in the composition (or the two-parts thereof) as determined in accordance with ISO 787-2:1981. In general, it is believed that having a M/H 2 O (e.g., Ti/H 2 O) molar ratio that is &gt;0.5 ensures that the catalyst (e.g., titanate) remains active. 
     Optional Ingredients 
     Fillers 
     In many embodiments, the composition does not contain a filler of any sort. In particular, the composition does not contain fillers that brings or imparts a significant amount of moisture in the composition. In general, the total moisture content brought about by the filler should not exceed 0.02% (which can be measured in accordance with ISO 787-2:1981) of the total composition. Suitable anhydrous filler may be utilised if required. 
     Should the need arise, the composition may incorporate anhydrous fillers, for example thermally and/or electrically conductive fillers, e.g., metallic fillers, anhydrous inorganic fillers and anhydrous meltable fillers, or a combination thereof. Metallic fillers include particles of metals and particles of metals having layers on the surfaces of the particles. These layers may be, for example, metal nitride layers or metal oxide layers on the surfaces of the particles. Suitable metallic fillers are exemplified by particles of metals selected from the group consisting of aluminium, copper, gold, nickel, tin, silver, and combinations thereof, and alternatively aluminium. Suitable metallic fillers are further exemplified by particles of the metals listed above having layers on their surfaces selected from the group consisting of aluminium nitride, aluminium oxide, copper oxide, nickel oxide, silver oxide, and combinations thereof. For example, the metallic filler may comprise aluminium particles having aluminium oxide layers on their surfaces. 
     Inorganic fillers which are anhydrous and may be exemplified by onyx; aluminium trihydrate, metal oxides such as aluminium oxide, beryllium oxide, magnesium oxide, and zinc oxide; nitrides such as aluminium nitride and boron nitride; carbides such as silicon carbide and tungsten carbide; and combinations thereof. Further fillers may include barium titanate, carbon fibres, diamond, graphite, magnesium hydroxide, and a combination thereof. 
     Meltable fillers may comprise Bi, Ga, In, Sn, or an alloy thereof. The meltable filler may optionally further comprise Ag, Au, Cd, Cu, Pb, Sb, Zn, or a combination thereof. Examples of suitable meltable fillers include Ga, In—Bi—Sn alloys, Sn—In—Zn alloys, Sn—In—Ag alloys, Sn—Ag—Bi alloys, Sn—Bi—Cu—Ag alloys, Sn—Ag—Cu—Sb alloys, Sn—Ag—Cu alloys, Sn—Ag alloys, Sn—Ag—Cu—Zn alloys, and combinations thereof. The meltable filler may have a melting point ranging from 50° C. to 250° C., alternatively 150° C. to 225° C. The meltable filler may be a eutectic alloy, a non-eutectic alloy, or a pure metal. Meltable fillers are commercially available. 
     The shape of the thermally conductive filler particles is not specifically restricted, however, rounded or spherical particles may prevent viscosity increase to an undesirable level upon high loading of the thermally conductive filler in the composition. The average particle size of the thermally conductive filler will depend on various factors including the type of thermally conductive filler selected and the exact amount added to the curable composition, as well as the bondline thickness of the device in which the cured product of the composition will be used. In some particular instances, the thermally conductive filler may have an average particle size ranging from 0.1 micrometre to 80 micrometres, alternatively 0.1 micrometre to 50 micrometres, and alternatively 0.1 micrometre to 10 micrometres. 
     The thermally conductive filler may be a single thermally conductive filler or a combination of two or more thermally conductive fillers that differ in at least one property such as particle shape, average particle size, particle size distribution, and type of filler. In some embodiments, combinations of metallic and inorganic fillers, such as a combination of aluminium and aluminium oxide fillers; a combination of aluminium and zinc oxide fillers; or a combination of aluminium, aluminium oxide, and zinc oxide fillers may be used. In other embodiments, it may be desirable to combine a first conductive filler having a larger average particle size with a second conductive filler having a smaller average particle size in a proportion meeting the closest packing theory distribution curve. An example would be mixing two aluminium oxide preparations having different average particle sizes. In other embodiments, different thermally conductive filler materials with difference sizes may be used, for example, a combination of an aluminium oxide having a larger average particle size with a zinc oxide having a smaller average particle size. Alternatively, it may be desirable to use combinations of metallic fillers, such as a first aluminium having a larger average particle size and a second aluminium having a smaller average particle size. Use of a first filler having a larger average particle size and a second filler having a smaller average particle size than the first filler may improve packing efficiency, may reduce viscosity, and may enhance heat transfer. 
     Other optional additives include anhydrous reinforcing and/or anhydrous extending fillers, e.g., precipitated and ground silica, precipitated and ground calcium carbonate, treated silicas, glass beads, carbon black, graphite, carbon nanotubes, quartz, talc, chopped fibre such as chopped KEVLAR®, or a combination thereof, filler treating agents, stabilizers (e.g., a hydrosilylation cure stabilizer, a heat stabilizer, or a UV stabilizer), adhesion promoters, a surfactant, a flux agent, an acid acceptor, a hydrosilylation inhibitor and/or an anti-corrosion additives and a combination thereof. The filler can also be a siloxane resin comprising R 3 SiO 1/2  units and SiO 4/2  units, where in this instance R is a hydroxyl or a hydrocarbon radical bound directly or via an oxygen atom to the silicon atom. 
     Filler Treating Agent 
     The thermally conductive filler and/or the anhydrous reinforcing and/or extending filler, if present, may optionally be surface treated with a treating agent. Treating agents and treating methods are known in the art, see for example, U.S. Pat. No. 6,169,142 (col. 4, line 42 to col. 5, line 2). The surface treatment of the filler(s) is typically performed, for example with a fatty acid or a fatty acid ester such as a stearate, or with organosilanes, organosiloxanes, or organosilazanes such as hexaalkyl disilazane or short chain siloxane diols. Generally, the surface treatment renders the filler(s) hydrophobic and therefore easier to handle and obtain a homogeneous mixture with the other components in the composition. 
     Adhesion Promoter 
     Suitable adhesion promoters may comprise alkoxysilanes of the formula R 14   q Si(OR 15 ) (4-q) , where subscript q is 1, 2, or 3, alternatively q is 3. Each R 14  is independently a monovalent organofunctional group. R 14  can be an epoxy functional group such as glycidoxypropyl or (epoxycyclohexyl)ethyl, an amino functional group such as aminoethylaminopropyl or aminopropyl, a methacryloxypropyl, a mercapto functional group such as mercaptopropyl or an unsaturated organic group. Each R 15  is independently an unsubstituted, saturated hydrocarbon group of at least 1 carbon atom. R 15  may have 1 to 4 carbon atoms, alternatively 1 to 2 carbon atoms. R 15  is exemplified by methyl, ethyl, n-propyl, and iso-propyl. 
     Examples of suitable adhesion promoters include glycidoxypropyltrimethoxysilane and a combination of glycidoxypropyltrimethoxysilane with an aluminium chelate or zirconium chelate. Examples of adhesion promoters may be found in U.S. Pat. Nos. 4,087,585 5,194,649. The curable composition may comprise 0.01% to 1% of adhesion promoter based on the weight of the composition. In general, the speed of hydrolysis of the adhesion promoter should be lower than the speed of hydrolysis of the cross-linker in order to favour diffusion of the molecule towards a substrate rather than its incorporation in a product network. 
     Surfactant 
     Suitable surfactants include silicone polyethers, ethylene oxide polymers, propylene oxide polymers, copolymers of ethylene oxide and propylene oxide, other non-ionic surfactants, and combinations thereof. The composition may comprise up to 0.05% of the surfactant based on the weight of the composition. 
     Flux Agent 
     The composition may comprise up to 2% of a flux agent based on the weight of the composition. Molecules containing chemically active functional groups such as carboxylic acid and amines can be used as flux agents. Such flux agents can include aliphatic acids such as succinic acid, abietic acid, oleic acid, and adipic acid; aromatic acids such as benzoic acids; aliphatic amines and their derivatives, such as triethanolamine, hydrochloride salts of amines, and hydrobromide salts of amines. Flux agents are known in the art and are commercially available. 
     Acid Acceptor 
     Suitable acid acceptors include magnesium oxide, calcium oxide, and combinations thereof. The composition may comprise up to 2% of acid acceptor based on the weight of the composition, if appropriate. 
     Anti-Corrosion Additive 
     Anti-corrosion additives, such as nitrogen/sulphur containing heterocyclic compounds containing a triazole structure, a thiadiazole structure, a benzotriazole structure, a mercaptothiozole structure, a mercaptobenzothiazole structure or a benzimidazole structure, may be utilized. The composition can include such in various amounts, e.g., up to 2% based on the weight of the composition. 
     Optional Dual Cure System 
     In some embodiments of the present disclosure, the composition used to form the gel is a mixture of the condensation curable polymer (i), cross-linker (ii), and catalyst (iii) as described above in combination with a hydrosilylation curable polymer together with a suitable cross-linker and catalyst. It should be appreciated that in other embodiments, the composition is just a single cure, moisture/condensation curable composition. In such embodiments, the composition is typically free of hydrosilylation curable components, such as those that are described immediately below. 
     Hydrosilylation Curable Polymer 
     Any suitable polymer curable via a hydrosilylation reaction pathway may be utilized. Typically, the polymer is a polydialkyl siloxane or polyalkylphenyl siloxane having terminal groups containing one or more unsaturated groups (for example alkenyl terminated, e.g. ethenyl terminated, propenyl terminated, allyl terminated (CH 2 ═CHCH 2 —)) or terminated with acrylic or alkylacrylic such as CH 2 ═C(CH 3 )—CH 2 — groups. Representative, non-limiting examples of the alkenyl groups are shown by the following structures; H 2 C═CH—, H 2 C═CHCH 2 —, H 2 C═C(CH 3 )CH 2 —, H 2 C═CHCH 2 CH 2 —, H 2 C═CHCH 2 CH 2 CH 2 —, and H 2 C═CHCH 2 CH 2 CH 2 CH 2 —. Representative, non-limiting examples of alkynyl groups are shown by the following structures; HC≡C—, HC≡CCH 2 —, HC≡CC(CH 3 ) 2 —, and HC≡CC(CH 3 ) 2 CH 2 —. Alternatively, the unsaturated organic group can be an organofunctional hydrocarbon such as an acrylate, methacrylate and the like such as alkenyl and/or alkynyl groups. Alkenyl groups are particularly preferred. The hydrosilylation curable polymer may therefore be further defined as an alkenyldialkylsilyl end-blocked polydialkylsiloxane which may itself be further defined as vinyldimethylsilyl end-blocked polydimethylsiloxane. Alternatively, the polymer may be further defined as a dimethylpolysiloxane capped at one or both molecular terminals with dimethylvinylsiloxy groups; a dimethylpolysiloxane capped at one or both molecular terminals with methylphenylvinylsiloxy groups; a copolymer of a methylphenylsiloxane and a dimethylsiloxane capped at both one or both molecular terminals with dimethylvinylsiloxy groups; a copolymer of diphenylsiloxane and dimethylsiloxane capped at one or both molecular terminals with dimethylvinylsiloxy groups; a copolymer of a methylvinylsiloxane and a dimethylsiloxane capped at one or both molecular terminals with dimethylvinylsiloxy groups; a copolymer of a methylvinylsiloxane and a dimethylsiloxane capped at one or both molecular terminals with dimethylvinylsiloxy groups; a methyl (3,3,3-trifluoropropyl) polysiloxane capped at one or both molecular terminals with dimethylvinylsiloxy groups; a copolymer of a methyl (3,3,3-trifluoropropyl) siloxane and a dimethylsiloxane capped at one or both molecular terminals with dimethylvinylsiloxy groups; a copolymer of a methylvinylsiloxane and a dimethylsiloxane capped at one or both molecular terminals with silanol groups; a copolymer of a methylvinylsiloxane, a methylphenylsiloxane, and a dimethylsiloxane capped at one or both molecular terminals with silanol groups; or an organosiloxane copolymer composed of siloxane units represented by the following formulae: (CH 3 ) 3 SiO 1/2 , (CH 3 ) 2 (CH 2 ═CH)SiO 1/2 , CH 3 SiO 3/2 , (CH 3 ) 2 SiO 2/2 , CH 3 PhSiO 2/2  and Ph 2 SiO 2/2 . 
     Hydrosilylation Cross-Linker 
     The hydrosilylation cross-linker has an average of at least two silicon-bonded hydrogen atoms per molecule and may be further defined as, or include, a silane or a siloxane, such as a polyorganosiloxane. In various embodiments, the hydrosilylation cross-linker may include 2, 3, or even more than 3, silicon-bonded hydrogen atoms per molecule. The hydrosilylation cross-linker may have a linear, a branched, or a partially branched linear, cyclic, dendrite, or resinous molecular structure. The silicon-bonded hydrogen atoms may be terminal or pendant. Alternatively, the hydrosilylation cross-linker may include both terminal and pendant silicon-bonded hydrogen atoms. 
     In addition to the silicon-bonded hydrogen atoms, the hydrosilylation cross-linker may also include monovalent hydrocarbon groups which do not contain unsaturated aliphatic bonds, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, decyl, undecyl, dodecyl, or similar alkyl groups; cyclopentyl, cyclohexyl, or similar cycloalkyl groups; phenyl, tolyl, xylyl, or similar aryl groups; benzyl, phenethyl, or similar aralkyl groups; or 3,3,3-trifluoropropyl, 3-chloropropyl, or similar halogenated alkyl group. Preferable are alkyl and aryl groups, in particular, methyl and phenyl groups. 
     The hydrosilylation cross-linker may also include siloxane units including, but not limited to, HR 3   2 SiO 1/2 , R 3   3 SiO 1/2 , HR 3 SiO 2/2 , R 3   2 SiO 2/2 , R 3 SiO 3/2 , and SiO 4/2  units. In the preceding formulae, each R 3  is independently selected from monovalent organic groups free of aliphatic unsaturation. 
     The hydrosilylation cross-linker may alternatively be further defined as a methylhydrogen polysiloxane capped at both molecular terminals with trimethylsiloxy groups; a copolymer of a methylhydrogensiloxane and a dimethylsiloxane capped at both molecular terminals with trimethylsiloxy groups; a dimethylpolysiloxane capped at both molecular terminals with dimethylhydrogensiloxy groups; a methylhydrogenpolysiloxane capped at one or both molecular terminals with dimethylhydrogensiloxy groups; a copolymer of a methylhydrogensiloxane and a dimethylsiloxane capped at both molecular terminals with dimethylhydrogensiloxy groups; a cyclic methylhydrogenpolysiloxane; and/or an organosiloxane composed of siloxane units represented by the following formulae: (CH 3 ) 3 SiO 1/2 , (CH 3 ) 2 HSiO 1/2 , and SiO 4/2 ; tetra(dimethylhydrogensiloxy) silane, or methyl-tri(dimethylhydrogensiloxy) silane. 
     It is also contemplated that the hydrosilylation cross-linker may be or include a combination of two or more organohydrogenpolysiloxanes that differ in at least one of the following properties: structure, average molecular weight, viscosity, siloxane units, and sequence. The hydrosilylation cross-linker may also include a silane. Dimethylhydrogensiloxy-terminated poly dimethylsiloxanes having relatively low degrees of polymerization (DP) (e.g., DP ranging from 3 to 50) are commonly referred to as chain extenders, and a portion of the hydrosilylation cross-linker may be or include a chain extender. In certain embodiments, the hydrosilylation cross-linker is free of halogen atoms per molecule. In other embodiments, the hydrosilylation cross-linker includes one or more halogen atoms. It is contemplated that the gel, as a whole, may be free of halogen atoms or may include halogen atoms. 
     Hydrosilylation Catalyst 
     The hydrosilylation catalyst is not particularly limited and may be any known in the art. In one embodiment, the hydrosilylation catalyst includes a platinum group metal selected from platinum, rhodium, ruthenium, palladium, osmium or iridium, organometallic compounds thereof, or combinations thereof. In another embodiment, the hydrosilylation catalyst is further defined as a fine platinum metal powder, platinum black, platinum dichloride, platinum tetrachloride; chloroplatinic acid, alcohol-modified chloroplatinic acid, chloroplatinic acid hexahydrate; and complexes of such compounds, such as platinum complexes of olefins, platinum complexes of carbonyls, platinum complexes of alkenylsiloxanes, e.g. 1,3-divinyltetramethyldisiloxane, platinum complexes of low molecular weight organopolysiloxanes, for example 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane, complexes of chloroplatinic acid with β-diketones, complexes of chloroplatinic acid with olefins, and complexes of chloroplatinic acid with 1,3-divinyltetramethyldisiloxane. 
     Alternatively, the hydrosilylation catalyst may be further defined as a rhodium compound, such as those expressed by formulae: RhX 3 [(R 4 ) 2 S] 3 ; (R 5   3 P) 2 Rh(CO)X, (R 5   3 P) 2 Rh(CO)H, Rh 2 X 2 Y 4 , H f Rh g (En) h Cl i , or Rh[O(CO)R] 3-j  (OH) j , wherein each X is independently a hydrogen atom, chlorine atom, bromine atom, or iodine atom, each Y is independently a methyl group, ethyl group, or a similar alkyl group, CO, C 8 H 14 , or 0.5 C 8 H 12 ; each R 4  is independently a methyl, ethyl, propyl, or a similar alkyl group; a cycloheptyl, cyclohexyl, or a similar cycloalkyl group; or a phenyl, xylyl or a similar aryl group; each R 5  is independently a methyl group, ethyl group, or a similar alkyl group; phenyl, tolyl, xylyl, or a similar aryl group; methoxy, ethoxy, or a similar alkoxy group, wherein each “En” is ethylene, propylene, butene, hexene, or a similar olefin; subscript “f” is 0 or 1; subscript “g” is 1 or 2; subscript “h” is an integer from 1 to 4; subscript “i” is 2, 3, or 4; and subscript “j” is 0 or 1. Particularly suitable but non-limiting examples of rhodium compounds are RhCl(Ph 3 P) 3 , RhCl 3 [S(C 4 H 9 ) 2 ] 3 , [Rh(O 2 CCH 3 ) 2 ] 2 , Rh(OCCH 3 ) 3 , Rh 2 (C 8 H 15 O 2 ) 4 , Rh(C 5 H 7 O 2 ) 3 , Rh(C 5 H 7 O 2 )(CO) 2 , and Rh(CO)[Ph 3 P](C 5 H 7 O 2 ). 
     The hydrosilylation catalyst may also be further defined as an iridium group compound represented by the following formulae: Ir(OOCCH 3 ) 3 , Ir(C 5 H 7 O 2 ) 3 , [Ir(Z)(En) 2 ] 2 , or [Ir(Z)(Dien)] 2  wherein each “Z” is chlorine atom, bromine atom, iodine atom, or a methoxy group, ethoxy group, or a similar alkoxy group; each “En” is ethylene, propylene, butene, hexene, or a similar olefin; and “Dien” is (cyclooctadiene)tetrakis(triphenyl). The hydrosilylation catalyst may also be palladium, a mixture of palladium black and triphenylphosphine. The hydrosilylation catalyst and/or any of the aforementioned compounds may be microencapsulated in a resin matrix or coreshell type structure, or may be mixed and embedded in a thermoplastic organic resin powder, e.g. a methylmethacrylate resin, carbonate resin, polystyrene resin, silicone resin, or similar resin. Typically, the hydrosilylation catalyst is present/utilized in an amount of from 0.01 to 1,000 ppm, alternatively 0.1 to 500 ppm alternatively 1 to 500 ppm, alternatively 2 to 200, alternatively 5 to 150 ppm, based on the total weight of the hydrosilylation curable polymer and hydrosilylation cross-linker. 
     Optionally, the dual cure embodiments may require the presence of a hydrosilylation stabilizer to prevent premature curing of the curable composition in which it includes a hydrosilylation cure composition. In order to adjust speed of curing and to improve handling of the composition under industrial conditions, the composition may be further combined with an alkyne alcohol, enyne compound, benzotriazole, amines such as tetramethyl ethylenediamine, dialkyl fumarates, dialkenyl fumarates, dialkoxyalkyl fumarates, maleates such as diallyl maleate, and a combination thereof. Alternatively, the stabilizer may comprise an acetylenic alcohol. The following are specific examples of such compounds: 2-methyl-3-butyn-2-ol, 3-methyl-1-butyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, 2-phenyl-3-butyn-2-ol, 3-phenyl-1-butyn-3-ol, 1-ethynyl-1-cyclohexanol, 1,1-dimethyl-2-propenyl)oxy)trimethylsilane, methyl(tris(1,1-dimethyl-2-propynyloxy))silane, or similar acetylene-type compounds; 3-methyl-3-penten-1-yne, 3,5-dimethyl-3-hexen-1-yne, or similar en-yne compounds. Other additives may comprise hydrazine-based compounds, phosphines-based compounds, mercaptane-based compounds, cycloalkenylsiloxanes such as methylvinylcyclosiloxanes such as 1,3,5,7-tetramethyl-1,3,5,7-tetravinyl cyclotetrasiloxane, 1,3,5,7-tetramethyl-1,3,5,7-tetrahexenyl cyclotetrasiloxane, benzotriazole, or similar triazols. The content of such inhibitors in the hydrosilation curable composition may be within the range of 0.0001 to 5 parts by weight per 100 parts by weight of the hydrosilylation curable polymer. 
     Methods and Applications 
     There is also provided herein a method of making the gel as hereinbefore described whereby the aforementioned two parts of the composition are intermixed and cured. In various embodiments, subsequent to intermixing, the condensation curable gel composition can be applied on to a substrate using a suitable dispenser such as, for example, curtain coaters, spray devices, die coaters, dip coaters, extrusion coaters, knife coaters and screen coaters which upon gel formation, provides a coating on the substrate. 
     Gels in accordance with the above may be utilised in a wide variety of applications, including, for the sake of example, as an encapsulant/pottant in an electronic article. The article may be a power electronic article e.g. an electronic component with gel disposed thereon such that the gel encapsulates, either partially or completely, the electronic component. Alternatively, the electronic article may include the electronic component and a first layer. The first layer is not particularly limited and may be a semiconductor, a dielectric, metal, plastic, carbon fibre mesh, metal foil, a perforated metal foil (mesh), a filled or unfilled plastic film (such as a polyamide sheet, a polyimide sheet, polyethylene naphthalate sheet, a polyethylene terephthalate polyester sheet, a polysulphone sheet, a polyether imide sheet, or a polyphenylene sulphide sheet), or a woven or nonwoven substrate (such as fibreglass cloth, fibreglass mesh, or aramid paper). Alternatively, the first layer may be further defined as a semiconductor and/or dielectric film. The gel may be sandwiched between the electronic component and the first layer, may be disposed on and in direct contact with the first layer, and/or on and in direct contact with the electronic component. If the gel is disposed on and in direct contact with the first layer, the gel may still be disposed on the electronic component but may include one or more layers or structures between the gel and the electronic component. The electronic component may be further defined as a chip, such as a silicon chip or a silicon carbide chip, one or more wires, one or more sensors, one or more electrodes, and the like. The electronic article is not particularly limited and may be, for the sake of example, defined as an insulated gate bipolar transistor (IGBT), a rectifier such as a Schottky diode, a PiN diode, a merged PiN/Schottky (MPS) rectifier and Junction barrier diode, a bipolar junction transistors (BJTs), a thyristor, a metal oxide field effect transistor (MOSFET), a high electron mobility transistor (HEMT), a static induction transistors (SIT), a power transistor, and the like. Alternatively, the electronic article can be a power module, e.g. one of more of the aforementioned devices for power converters, inverters, boosters, traction controls, industrial motor controls, power distribution and transportation systems. The electronic article can alternatively be further defined as including one or more of the aforementioned devices. 
     The disclosure also provides a method of forming aforementioned electronic article. The method may include one or more of the aforementioned steps of forming the gel, the step of providing the gel, and/or the step of providing the electronic component. Typically, the method includes the curable compositions as hereinbefore described onto an electronic component and curing the composition to form a gel on the electronic component under the condition sufficient to form the gel without damaging the component. The gel may be formed on the electronic component. Alternatively, the gel may be formed apart from the electronic component and subsequently be disposed on the electronic component. 
     Alternatively, the silicone gel may be utilised in adhesive compositions for use as the skin-facing layer of a medical device or wound dressing. In addition to the silicone gel adhesive composition, the medical device or wound dressing contains an absorbable or porous substrate. The absorbable substrate may be any material known to those of skill in the art capable of at least partially absorbing the exudate from a wound. Absorbable substrates include, but are not limited to, the following materials: foams (e.g., polyurethane and/or polymer foams), synthetic sponges, natural sponges, silks, keratins (e.g., wool and/or camel hair), cellulosic fibres (e.g., wood pulp fibres, cotton fibres, hemp fibres, jute fibres, and/or flax fibres), rayon, acetates, acrylics, cellulose esters, modacrylics, polymers, super-absorbent polymers (e.g., polymers capable of absorbing approximately 10 times their weight or greater), polyamides, polyesters, polyolefins, polyvinyl alcohols, and/or other materials. Combinations of one or more of the above-listed materials may also be used as the absorbable or porous substrate. 
     The silicone gel as hereinbefore described may be incorporated in adhesive compositions for use as the skin-facing layer in various applications where suitable skin-facing adhesive materials are desired, e.g. in athletic apparel such as biking shorts and feminine hygiene products. 
     Other applications include the manufacturing of silicone adhesive tapes (e.g. polyurethane nonwoven/fabric with silicone gel on it), gel sheeting (e.g. polyurethane film with gel on it), wound dressings (e.g. polyurethane film or polyurethane foam with gel on it), bandages, adhesive strips, surgery drapes (e.g., polyethylene with gel on it), topical or transdermal patches, fragrance/cosmetics patches and the like. As most gels prepared by curing the compositions described in the present disclosure are visually crystal clear, these materials can be used to seal, glue or protect materials in optical devices or for any other purposes linked to its transparency. Still further potential applications include protection for light emitting diodes, gels or elastomers for implants and prosthesis, shoe sole, elastomers for drug release applications, and in tire industry as an anti-puncture material or a self-sealing pneumatic rubber tire. A self-sealing pneumatic rubber tire with a sealing band adheringly attached in the circumferential direction on the inner side of the tire, radially within the tread, with the gel as herein before described applied on a carrier material. The present disclosure also relates to a method for producing a self-sealing tire using a sealing band with a sealant applied on a carrier material, which sealing band is introduced into the tire and applied on the inner wall surface of the tire, running between the shoulder regions. 
     EXAMPLES 
     In a first general embodiment wherein the gel is solely cured via a condensation pathway, a series of gels (examples 1 to 16) as herein described were prepared as a one part composition (to save lab time). It was identified that compositions of the type depicted in Examples 1-16 will in practice have to be sold in multiple part compositions because they were found to cure in the cartridge prior to intended use. Examples 17-19 provide examples of how the compositions need to be stored prior to use with a view to avoid curing in storage. The compositions in Examples 1 to 19 were unexpectedly found to be cured in bulk after only 2 to 3 hours, contrary to expectations. All viscosity values were measured at 23° C. using a Brookfield cone plate viscometer (RV DIII) adapting the cone plate and the speed according to the polymer viscosity. Each prepared composition was evaluated to determine penetration and softness, using the methods described below, in the Tables below: 
     Example 1 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethylsiloxane polymer having a viscosity at 23° C. of 2000 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-52 at 20 rpm) was introduced into a dental container followed by 1 part by weight of methyltrimethoxysilane cross-linker per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. Subsequently, 0.08 parts of tetra n-butyl titanate per 100 parts by weight of the polymer was added and the final mixture was stirred again in the speedmixer for a further 30 seconds at a speed of 2000 rpm. The total weight of the mixture was 70 g. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in a Relative Humidity (RH) of 50%. 
     Example 2 
     The same method of preparation was utilised as described in Example 1 with the exception that 1 part of tetraethoxysilane per 100 parts by weight of the polymer was utilised as the cross-linker. 
     Example 3 
     The same method of preparation was utilised as described in Example 1 with the exception that 0.4 parts of 1,6-bis(trimethoxysilyl)hexane per 100 parts by weight of the polymer was utilised as the cross-linker. 
     Example 4 
     The same method of preparation was utilised as described in Example 1 with the exception that 0.5 parts of 1,6-bis(trimethoxysilyl)hexane per 100 parts by weight of the polymer was utilised as the cross-linker. 
     Example 5 
     The same method of preparation was utilised as described in Example 1 with the exception that 0.7 parts of 1,6-bis(trimethoxysilyl)hexane per 100 parts by weight of the polymer was utilised as the cross-linker. 
     Example 6 
     The same method of preparation was utilised as described in Example 1 with the exception that 1 part of 1,6-bis(trimethoxysilyl)hexane per 100 parts by weight of the polymer was utilised as the cross-linker. 
     Example 7 
     The same method of preparation was utilised as described in Example 1 with the exception that 1 part of methyltrioximino silane per 100 parts by weight of the polymer was utilised as the cross-linker. 
     Example 8 
     The same method of preparation was utilised as described in Example 1 with the exception that 1 part of a 50/50 by weight mixture of methyl triacetoxysilane and ethyl triacetoxysilane per 100 parts by weight of the polymer was utilised as the cross-linker. 
     Example 9 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethyl siloxane polymer having a viscosity at 23° C. of 2000 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-52 at 20 rpm) was introduced into a dental container followed by 0.8 part of methyltrimethoxysilane cross-linker per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. Subsequently, 0.02 parts of tetra n-butyl titanate per 100 parts by weight of the polymer was added and the final mixture was stirred again in the speedmixer for a further 30 seconds at a speed of 2000 rpm. The total weight of the mixture was 184.69 g. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in an RH of 50%. 
     Example 10 
     100 parts per weight (e.g. 150 g) of a hydroxydimethyl silyl terminated polydimethyl siloxane polymer having a viscosity at 23° C. of 2000 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-52 at 20 rpm) was introduced into a dental container followed by 0.77 parts (e.g. 1.15g) of tetraethoxysilane cross-linker per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. Subsequently, 0.02 parts of tetra n-butyl titanate (e.g.0.30 g) per 100 parts by weight of the polymer was added and the final mixture was stirred again in the speedmixer for a further 30 seconds at a speed of 2000 rpm. The total weight of the mixture was 151.45 g. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in an RH of 50%. 
     Example 11 
     The same method of preparation was utilised as described in Example 9 with the exception that 0.6 parts of 1,6-bis(trimethoxysilyl)hexane per 100 parts by weight of the polymer was utilised as the cross-linker and 0.2 parts of tetra t-butyl titanate was added and the weight of the final mixture was 218.3 g 
     Example 12 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethyl siloxane polymer having a viscosity at 23° C. of 4000 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-52 at 20 rpm) was introduced into a dental container followed by 0.71 parts of 1,6-bis(trimethoxysilyl)hexane cross-linker per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. Subsequently, 0.15 parts of tetra n-butyl titanate per 100 parts by weight of the polymer was added and the final mixture was stirred again in the speedmixer for a further 30 seconds at a speed of 2000 rpm. The total weight of the mixture was 100.86 g. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in an RH of 50%. 
     Example 13 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethyl siloxane polymer having a viscosity at 23° C. of 13,500 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-52 at 5 rpm) was introduced into a dental container followed by 0.47 parts of 1,6-bis(trimethoxysilyl)hexane cross-linker per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. Subsequently, 0.10 parts of tetra n-butyl titanate per 100 parts by weight of the polymer was added and the final mixture was stirred again in the speedmixer for a further 30 seconds at a speed of 2000 rpm. The total weight of the mixture was 100.57 g. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in an RH of 50%. 
     Example 14 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethyl siloxane polymer having a viscosity at 23° C. of 50,000 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-51 at 0.5 rpm) was introduced into a dental container followed by 0.33 part of 1,6-bis(trimethoxysilyl)hexane cross-linker per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. Subsequently, 0.07 parts of tetra n-butyl titanate per 100 parts by weight of the polymer was added and the final mixture was stirred again in the speedmixer for a further 30 seconds at a speed of 2000 rpm. The total weight of the mixture was 100.40 g. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in an RH of 50%. 
     Example 15 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethyl siloxane polymer having a viscosity at 23° C. of 2000 mPa·s (Brookfield cone plate viscometer (RV DIII using a cone plate CP-52 at 20 rpm) was introduced into a dental container followed by 0.7 part of 1,6-bis(trimethoxysilyl)hexane cross-linker per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. Subsequently, 0.25 parts of titanium diisopropoxide bis(ethylacetoacetate) per 100 parts by weight of the polymer was added and the final mixture was stirred again in the speedmixer for a further 30 seconds at a speed of 2000 rpm. The total weight of the mixture was 100.95 g. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in an RH of 50%. The cured product is yellowing over time. 
     Example 16 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethylsiloxane polymer partially trimethylsilyl terminated exhibiting viscosity at 23° C. of about 12,500 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-52 at 5 rpm) was introduced into a dental container followed by 0.37 part of 1,6-bis(trimethoxysilyl)hexane cross-linker per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. Subsequently, 0.08 parts of tetra t-butyl titanate per 100 parts by weight of the polymer was added and the final mixture was stirred again in the speedmixer for a further 30 seconds at a speed of 2000 rpm. The total weight of the mixture was 100.45 g. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in an RH of 50%. 
     Example 17 
     Preparation of a Two Part Mixture 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethylsiloxane polymer having a viscosity at 23° C. of 50,000 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-51 at 0.5 rpm) was introduced into a dental container followed by 0.62 parts of 1,6-bis(trimethoxysilyl)hexane cross-linker per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm and filled in a 300 ml cartridge as part A of a two part composition. 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethylsiloxane polymer having a viscosity at 23° C. of 50,000 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-51 at 0.5 rpm) was introduced into a dental container followed by 0.08 parts of tetra n-butyl titanate per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm and filled in a 300 ml cartridge as part B of the two part composition. 
     A mixture 1:1 in weight of part A and Part B were mixed in a speedmixer for 30 seconds at a speed of 2000 rpm. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in an RH of 50%. 
     Example 18 
     Preparation of a Two Part Mixture 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethylsiloxane polymer having a viscosity at 23° C. of 13,500 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-52 at 5 rpm) was introduced into a dental container followed by 0.94 parts of 1,6-bis(trimethoxysilyl)hexane cross-linker per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm and filled in a 300 ml cartridge as part A of a two part composition. 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethylsiloxane polymer having a viscosity at 23° C. of 13,500 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-52 at 5 rpm) was introduced into a dental container followed by 0.16 parts of tetra n-butyl titanate per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm and filled in a 300 ml cartridge as part B of the two part composition. 
     A mixture 1:1 in weight of part A and Part B were mixed in a speedmixer for 30 seconds at a speed of 2000 rpm. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in an RH of 50%. 
     Example 19 
     Preparation of a Two Part Mixture 
     100 parts per weight of a trimethoxysilyl terminated polydimethylsiloxane polymer having a viscosity at 23° C. of 56,000 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-52 at 5 rpm) was introduced into a dental container 0.2 parts of tetra n-butyl titanate per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm and filled in a 300 ml cartridge as part A of a two part composition. The aforementioned trimethoxysilyl terminated polydimethylsiloxane polymer functions in this example as the cross-linker. 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethylsiloxane polymer having a viscosity at 23° C. of 50,000 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-52 at 5 rpm) was introduced in a 300 ml cartridge as part B of the two part composition. 
     A mixture 1:5 in weight of part A and Part B were mixed in a speedmixer for 30 seconds at a speed of 2000 rpm. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in an RH of 50%. 
     A series of comparative compositions were also prepared as described below. 
     Comparative Example 1 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethylsiloxane polymer having a viscosity at 23° C. of 2000 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-52 at 20 rpm) was introduced into a dental container followed by 0.5 part of methyltrimethoxysilane cross-linker per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. Subsequently, 0.08 parts of tetra n-butyl titanate per 100 parts by weight of the polymer was added and the final mixture was stirred again in the speedmixer for a further 30 seconds at a speed of 2000 rpm. The total weight of the mixture was 70 g. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in a Relative Humidity (RH) of 50%. 
     Comparative Example 2 
     The same method of preparation was utilised as described in Comparative Example 1 with the exception that 0.5 part of tetraethoxysilane per 100 parts by weight of the polymer was utilised as the cross-linker. 
     Comparative Example 3 
     The same method of preparation was utilised as described in Comparative Example 1 with the exception that 2.5 part of methyltrimethoxysilane per 100 parts by weight of the polymer was utilised as the cross-linker. 
     Comparative Example 4 
     The same method of preparation was utilised as described in Comparative Example 1 with the exception that 2.5 part of tetraethoxysilane per 100 parts by weight of the polymer was utilised as the cross-linker. 
     Comparative Example 5 
     The same method of preparation was utilised as described in Comparative Example 1 with the exception that 2.5 part of 1,6-bis(trimethoxysilyl)hexane per 100 parts by weight of the polymer was utilised as the cross-linker. 
     Comparative Example 6 
     The same method of preparation was utilised as described in Comparative Example 1 with the exception that 0.5 part of methyltrioximino silane per 100 parts by weight of the polymer was utilised as the cross-linker. 
     Comparative Example 7 
     The same method of preparation was utilised as described in Comparative Example 1 with the exception that 0.5 part of a 50/50 by weight mixture of methyl triacetoxysilane and ethyl triacetoxysilane per 100 parts by weight of the polymer was utilised as the cross-linker. 
     Comparative Example 8 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethylsiloxane polymer having a viscosity at 23° C. of 2000 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-52 at 20 rpm) was introduced into a dental container followed by 0.5 part of 1,6-bis(trimethoxysilyl)hexane cross-linker per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. Subsequently 0.04 parts of tetra n-butyl titanate per 100 parts by weight of the polymer was added and the final mixture was stirred again in the speedmixer for a further 30 seconds at a speed of 2000 rpm. The total weight of the mixture was set to 70 g. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in an RH of 50%. 
     Comparative Example 9 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethylsiloxane polymer having a viscosity at 23° C. of 2000 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-52 at 20 rpm) was introduced into a dental container followed by .5 part of 1,6-bis(trimethoxysilyl)hexane cross-linker per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. Subsequently 0.08 parts of dimethyl tin neodecanoate per 100 parts by weight of the polymer was added and the final mixture was stirred again in the speedmixer for a further 30 seconds at a speed of 2000 rpm. The total weight of the mixture was set to 70 g. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in an RH of 50%. 
     Comparative Example 10 
     100 parts per weight of a hydroxydimethyl silyl terminated polydimethylsiloxane polymer having a viscosity at 23° C. of 2000 mPa·s (Brookfield cone plate viscometer (RV DIII) using a cone plate CP-52 at 20 rpm) was introduced into a dental container followed by 0.5 part of 1,6-bis(trimethoxysilyl)hexane cross-linker per 100 parts by weight of the polymer. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. Subsequently 0.08 parts of stannous octoate per 100 parts by weight of the polymer was added and the final mixture was stirred again in the speedmixer for a further 30 seconds at a speed of 2000 rpm. The total weight of the mixture was set to 70 g. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in an RH of 50%. 
     The level of cure was observed after 4 days (4D) and 7 days (7D) in the Tables below. Each sample cured was tested for Penetration and Hardness as described below: 
     Penetration was measured after 3 days of cure at a temperature 23° C. and 50% relative humidity using a Universal Penetrometer with a total weight of about 19.5 g after 5 seconds of penetration of the head in the material (ASTM D217-10 (2010)). Results are provided in 1/10 mm and were measured a period of 7 days curing at 23° C. in an RH of 50%. 
     Hardness was measured after 7 days (7D) of cure at a temperature 23° C. and 50% relative humidity according to ASTM D2240-05(2010) in the Shore 00 scale. 
     The results of the above are depicted in the following Tables: 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1a 
               
               
                   
               
               
                   
                 Ex. 1 
                 Ex. 2 
                 Ex. 3 
                 Ex. 4 
                 Ex. 5 
                 Ex. 6 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Observation after 4D 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
               
               
                 Observation after 7D 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
               
               
                 Penetration (1/10 
                 25 
                 0 
                 92 
                 61 
                 7 
                 0 
               
               
                 mm) after 7D cure 
                   
                   
                   
                   
                   
                   
               
               
                 Hardness shore 00 
                 0 
                 18 
                 0 
                 0 
                 0 
                 13 
               
               
                 after 7D cure 
                   
                   
                   
                   
                   
                   
               
               
                   
               
               
                 CiD = cure in depth. 
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1b 
               
               
                   
               
               
                   
                 Ex. 7 
                 Ex. 8 
                 Ex. 9 
                 Ex. 10 
                 Ex. 11 
                 Ex. 12 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Observation after 4D 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
               
               
                 Observation after 7D 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
               
               
                 Penetration (1/10 mm) 
                 106 
                 8 
                 37 
                 27 
                 35 
                 50 
               
               
                 after 7D cure 
                   
                   
                   
                   
                   
                   
               
               
                 Hardness shore 00 after 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 7D cure 
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 1c 
               
               
                   
               
               
                   
                 Ex. 13 
                 Ex. 14 
                 Ex. 15 
                 Ex. 16 
                 Ex. 17 
                 Ex. 18 
                 Ex. 19 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Observation after 4D 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
               
               
                 Observation after 7D 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
                 CiD 
               
               
                 Penetration (1/10 
                 50 
                 62 
                 0 
                 107 
                 47 
                 7 
                 31 
               
               
                 mm) after 7D cure 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Hardness shore 00 
                 0 
                 0 
                 9 
                 0 
                 0 
                 0 
                 0 
               
               
                 after 7D cure 
                   
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2a 
               
             
            
               
                   
               
               
                 Comparative Examples 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 C Ex. 1 
                 C Ex. 2 
                 C Ex. 3 
                 C Ex. 4 
                 C Ex. 5 
                 C Ex. 6 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Observation 
                 No cure 
                 No cure 
                 Top skin cure  
                 Top skin cure  
                 Top skin cure  
                 No cure 
               
               
                 after 4D 
                   
                   
                 not in bulk  
                 not in bulk  
                 not in bulk  
                   
               
               
                   
                   
                   
                 Cure like  
                 Cure like  
                 Cure like  
                   
               
               
                   
                   
                   
                 a one part 
                 a one part 
                 a one part 
                   
               
               
                   
                   
                   
                 elastomer 
                 elastomer 
                 elastomer 
                   
               
               
                 Observation 
                 No cure 
                 No cure 
                 Cure in 
                 Cure in 
                 Cure in 
                 No cure 
               
               
                 after 7D 
                   
                   
                 depth 
                 depth 
                 depth 
                   
               
               
                 Hardness 
                 Not 
                 Not 
                 55 
                 45 
                 48 
                 Not 
               
               
                 shore 00 
                 measured 
                 measured 
                   
                   
                   
                 measured 
               
               
                 after 7D 
                   
                   
                   
                   
                   
                   
               
               
                 cure 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2b 
               
             
            
               
                   
               
               
                 Comparative Examples 
               
            
           
           
               
               
               
               
               
            
               
                   
                 C Ex. 7 
                 C Ex. 8 
                 C Ex. 9 
                 C Ex. 10 
               
               
                   
               
               
                 Observation after 
                 No cure 
                 No cure 
                 No cure 
                 Very gelly 
               
               
                 4D 
                   
                   
                   
                   
               
               
                 Observation after 
                 No cure 
                 Cured 
                 Cured like 
                 Cured 
               
               
                 7D 
                   
                   
                 a one part 
                   
               
               
                 Penetration (1/10 
                 Not 
                 116 
                 7 
                 10 
               
               
                 mm) after 7D cure 
                 measured 
               
               
                   
               
            
           
         
       
     
     Comparative examples 1 and 2 may be directly compared to Examples 1 to 2 and it is noticeable that halving the amount of monosilane cross-linker resulted in no cure. Disilane cross-linkers appeared to be more efficient in the curing process than monosilane cross-linkers. 
     Comparative examples 3 to 5 were provided to demonstrate that above a certain level of cross-linker there is no cure in bulk in the system but merely a skin cure that occurs through a moisture diffusion process as might usually be expected in condensation cure systems. Such composition could not be formulated to provide bulk cure like the typical two part moisture curing systems. 
     More specifically, Comparative examples 3, 4, and 5 show that a large amount of alkoxy groups in the formulation is leading to a cure with skin formation such as a one part alkoxy curing silicone. It is believed that this is because these groups have to react with moisture from the air first. After 7 days they have cured in the bulk by moisture diffusion from the top of the cup to the bottom. This is notable relative to the inventive SiOH/SiOR molar ratio and the results, e.g. properties, it provides. 
     Comparative examples 6 and 7 should be compared with examples 7 and 8 and show the lower limit of cross-linker for oxime and acetoxy curing system respectively below which no cure is observed. 
     Comparative example 8 is to be compared to example 4 and provides the lower limit of titanate to be added in the system below which no cure is observed. At this level very slow cure is observed and the material is very soft. Comparative example 9 and 10 is comparable to example 4 and is showing that a tin (IV) catalyst is leading to a skin curing system and not to a bulk cure and the tin (II) is leading to a bulk cure but at a very low curing rate, which highlights that titanate catalyst works better for this system. 
     Many two part condensation curing systems are based on tin (or Sn) catalyst. While some literature suggests that titanium (or Ti) can be used in place of Sn, practical results prove otherwise. Specifically, it has been found that simply attempting to replace Sn by Ti leads to non-curing systems. See, for example, the Example section of U.S. Pat. No. 10,526,453 to Chambard et al., the disclosure of which is incorporated herein by reference in its entirety. 
     In a second general embodiment there is provided a dual cure system in which there is provided a mixture of a condensation curable polymer and a hydrosilylation curable polymer, which are respectively cured using a condensation cross-linker and catalyst and using a hydrosilylation cross-linker and catalyst which results in cured end product being cured partially via a condensation pathway and partially via a hydrosilylation pathway. 
     Example 20 
     Preparation of a Two Part Dual Cure Mixture 
     50 parts per weight of a hydroxydimethyl silyl terminated polydimethylsiloxane polymer having a viscosity at 23° C. of 2000 mPa·s was introduced into a dental container followed by 50 parts per weight of a dimethylvinyl silyl terminated polydimethylsiloxane polymer per 50 parts by weight of hydroxydimethyl silyl terminated polydimethylsiloxane polymer having a viscosity at 23° C. of 450 mPa·s. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. 0.5 parts per weight of 1,6-bis(trimethoxysilyl)hexane cross-linker per 100 parts by weight of the total polymer weight was introduced into the mixture and the resulting mixture was again stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. 0.9 parts per weight of a trimethylsiloxy-terminated polydiorganosiloxane having an average of five methylhydrogensiloxane units and three dimethylsiloxane units per molecule with a silicon-bonded hydrogen atom content of about 0.7 to 0.8 weight percent was then introduced and the resulting mixture was again stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. The final composition was filled in a 300 ml cartridge as part A of a two part composition. 
     50 parts per weight of a silanol terminated polydimethylsiloxane polymer exhibiting a viscosity at 23° C. of about 2,000 mPa·s has been added in a dental container followed by the addition of 50 parts per weight of a vinyl terminated polydimethylsiloxane polymer exhibiting a viscosity at 23° C. of about 450 mPa·s per 50 parts per weight of a silanol terminated polydimethylsiloxane polymer. The mixture was then mixed in a speedmixer for 30 seconds at a speed of 2000 rpm. Then, 0.016 parts per weight of platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane has been added in the mixture and mixed in a speedmixer for 30 seconds at a speed of 2000 rpm. Finally, 0.08 parts per weight of tetra t-butyl titanate was added in the mixture and then mixed in a speedmixer for 30 seconds at a speed of 2000 rpm and filled in a 300 ml cartridge as part B. 
     50 parts per weight of a hydroxydimethyl silyl terminated polydimethylsiloxane polymer having a viscosity at 23° C. of 13,500 mPa·s was introduced into a dental container followed by 50 parts per weight of a dimethylvinyl silyl terminated polydimethylsiloxane polymer per 50 parts, per weight of the hydroxydimethyl silyl terminated polydimethylsiloxane polymer, having a viscosity at 23° C. of 450 mPa·s. The resulting mixture was then stirred in a speedmixer for 30 seconds at a speed of 2000 rpm. 0.016 parts per weight of the total polymer weight in Part B Platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane was added in the mixture with the resulting mixture being mixed in a speedmixer for 30 seconds at a speed of 2000 rpm. Finally, 0.08 parts per weight of tetra t-butyl titanate was added and the final mixture was also mixed in a speedmixer for 30 seconds at a speed of 2000 rpm and subsequently then filled in a 300 ml cartridge as part B of the two part composition. 
     A mixture 1:1 in weight of part A and Part B were mixed in a speedmixer for 30 seconds at a speed of 2000 rpm. The mixture was poured in a 50 ml aluminium cup and cured at 23° C. in an RH of 50%. 
     The resulting cured material was noted to be cured in bulk in about 12 minutes and after 7 days of cure had a hardness of Shore 00 (measured as described above) of 40. 
     ADDITIONAL EMBODIMENTS 
     Embodiment 1 relates to a gel which is the condensation reaction product of the following composition: 
     (i) at least one condensation curable silyl terminated polymer having at least one, typically at least 2 hydrolysable and/or hydroxyl functional groups per molecule;
 
(ii) a cross-linker selected from the group of a silicone, an organic polymer, a silane or a disilane molecule which contains at least two hydrolysable groups per molecule and typically at least three hydrolysable groups per molecule; and
 
(iii) a condensation catalyst selected from the group of titanates, zirconates or tin (II) characterized in that the molar ratio of hydroxyl and/or hydrolysable groups in polymer (i) to hydrolysable groups from (ii) is between 0.5:1 and 1:1 using a monosilane cross-linker or 0.75:1 to 3:1 using disilanes and the molar ratio of M-OR or tin (II) functions to the hydroxyl and/or hydrolysable groups in polymer (i) is comprised between 0.01:1 and 0.5:1, where M is titanium or zirconium, and R is an aliphatic hydrocarbon group.
 
     Embodiment 2 relates to a condensation curable gel composition for making a gel in accordance with Embodiment 1, comprising: 
     (i) at least one condensation curable silyl terminated polymer having at least one, typically at least 2 hydrolysable and/or hydroxyl functional groups per molecule;
 
(ii) a cross-linker selected from the group of a silicone, an organic polymer, a silane or a disilane molecule which contains at least two hydrolysable groups per molecule and typically at least three hydrolysable groups per molecule; and
 
(iii) a condensation catalyst selected from the group of titanates, zirconates or tin (II) characterized in that the molar ratio of hydroxyl and/or hydrolysable groups in polymer (i) to hydrolysable groups from (ii) is between 0.5:1 and 1:1 using a monosilane cross-linker or 0.75:1 to 3:1 using disilanes and the molar ratio of M-OR or tin (II) functions to the hydroxyl and/or hydrolysable groups in polymer (i) is comprised between 0.01:1 and 0.5:1, where M is titanium or zirconium, and R is an aliphatic hydrocarbon group.
 
     Embodiment 3 relates to a gel in accordance with Embodiment 1 or a condensation curable gel composition in accordance with Embodiment 2, wherein the composition is stored in two parts having polymer (i) and cross-linker (ii) in one part and polymer (i) and catalyst (iii) in the other part. 
     Embodiment 4 relates to a gel in accordance with Embodiment 1 or a condensation curable gel composition in accordance with Embodiment 2, wherein the composition is stored in two parts having cross-linker (ii) in one part and polymer (i) and catalyst (iii) in the other part. 
     Embodiment 5 relates to a gel in accordance with Embodiment 1 or a condensation curable gel composition in accordance with Embodiment 2, wherein the composition is stored in two parts having a first polymer (i) and cross-linker (ii) in one part and a second polymer (i) and catalyst (iii) in the other part. 
     Embodiment 6 relates to a gel in accordance with Embodiment 1 or a condensation curable gel composition in accordance with Embodiment 2, wherein the molar ratio of hydroxyl and/or hydrolysable groups in polymer (i) to hydrolysable groups from (ii) is between 0.5:1 and 0.75:1 using a monosilane cross-linker or 0.75:1 to 3:1 using disilanes. 
     Embodiment 7 relates to a gel in accordance with Embodiment 1 or a condensation curable gel composition in accordance with Embodiment 2, wherein the molar ratio of M-OR or tin (II) functions to the hydroxyl and/or hydrolysable groups in polymer (i) is comprised between 0.02:1 and 0.2:1, where M is titanium or zirconium, and R is an aliphatic hydrocarbon group. 
     Embodiment 8 relates to a gel in accordance with Embodiment 1 or a condensation curable gel composition in accordance with Embodiment 2, which additionally contains a polymer curable by hydrosilylation, a hydrosilylation cross-linker and a hydrosilylation catalyst. 
     Embodiment 9 relates to a gel in accordance with Embodiment 1 or any one of Embodiments 3 to 9, exhibiting a hardness below Shore 80 in the type 00 scale according to ASTM D 2240-05(2010). 
     Embodiment 10 relates to a method of making a gel in accordance with Embodiments 3, 4 or 5 or Embodiments 6, 7 or 8, whereby the two parts of the composition are intermixed and cured. 
     Embodiment 11 relates to use of a gel in accordance with any one of Embodiments 1 to 9, as an encapsulant or pottant for electronic devices, solar photovoltaic modules and/or light emitting diodes. 
     Embodiment 12 relates to use of a gel in accordance with any one of Embodiments 1 to 9, in implants, in shoe soles, and/or in tyres as a self-sealing anti-puncture coating. 
     Embodiment 13 relates to use of a gel in accordance with any one of Embodiments 1 to 9, as a pressure sensitive adhesive, or in a vibration or sound dampening application or in the manufacture of laminates, adhesives optically clear coatings, for displays, or wave guides. 
     Embodiment 14 relates to use of a gel in accordance with any one of Embodiments 1 to 9, in a lamination process to laminate substrates together. 
     Embodiment 15 relates to a condensation curable gel composition in accordance with Embodiment 2 or Embodiments 3 to 9, which is applied on to a substrate using a dispenser selected from curtain coaters, spray devices, die coaters, dip coaters, extrusion coaters, knife coaters, and screen coaters which upon gel formation provides a coating on the substrate. 
     Embodiment 16 relates to a gel in accordance with Embodiment 1 or Embodiments 3 to 9, for use in a medical application. 
     Embodiment 17 relates to a gel in accordance with Embodiment 16, wherein the medical application is for drug delivery, wound care, a soft skin adhesive, a transdermal patch and/or in a means for the controlled release of medicaments.