the rubber composition utilised in rubber bonding according to the present invention may further include known additives common to rubber compositions . these include reinforcing carbon blacks ; inactive fillers such as calcium carbonates , chalks , talcs , or metal oxides ; accelerator systems ; vulcanization retarders ; promoters such as zinc oxide or stearic acid ; plasticizers such as aromatic , paraffinic , naphthenic and synthetic mineral oils ; ageing , light - protecting ozone - protecting , fatigue , coloration , and processing auxiliaries ; and sulfur . commonly these additives may be present at a quantity of about 0 . 1 parts to about 80 parts per 100 parts by weight of the rubber composition . prior to application of the silane solution , the surface to be coated may be cleaned to allow better adhesion . for example , cleaning with solvent or alkaline material . additionally and or alternatively , the substrate may be grit blasted . application can then be conducted by a variety of methods , including dipping , spraying , brushing or wiping the solution onto the metal . it has been suggested that for improving rubber adhesion the coating remain partially cross - linked prior to vulcanisation . for this reason , the coating is usually air dried at room temperature as heat drying can cause a higher degree of cross - linking that will result in poorer adhesion between the rubber and the metal surface . compounds utilised in the compositions of the present invention were made as set out below : compounds a , b , c and d ( above ) were synthesised according to the following experimental procedure and as illustrated in the reaction scheme above . reaction ( 1 ) ( vide supra ) was carried out as outlined in j . j d &# 39 ; amico , c . c . tung and l . a . walker , j . am . chem . soc ., 5957 ( 1959 ). reaction ( 2 ): γ - isocyantopropyltriethoxysilane ( ge bayer silicones a - 1310 ) ( 2 . 35 g , 9 . 5 mmol ) was solvated in 10 ml of anhydrous thf in a 50 ml round bottom flask . the reaction flask was flushed with nitrogen and charged with n , n - bis -( 2 - hydroxyethyl )- 4 - nitroso - aniline ( 2 g , 9 . 5 mmol ), followed by a catalytic quantity of dibutyltin dilaurate ( 1 . 5 μmol ). the reaction was refluxed for an additional 2 hours under nitrogen . consumption of the isocyanate ( 2275 cm − 1 ) was monitored using infrared spectroscopy . the solvents were removed under reduced pressure to give the product in a quantitative yield . reaction ( 3 ): γ - isocyantopropyltrimethoxysilane ( abcr gmbh ) ( 1 . 5 g , 7 . 3 mmol ) was solvated in 8 ml of anhydrous thf in a 50 ml round bottom flask . the reaction flask was flushed with nitrogen and charged with n , n - bis -( 2 - hydroxyethyl )- 4 - nitroso - aniline ( 1 . 53 g , 7 . 3 mmol ), followed by a catalytic quantity of dibutyltin dilaurate ( 1 μmol ). the reaction was refluxed for an additional 2 hours under nitrogen . consumption of the isocyanate ( 2275 cm − 1 ) was monitored using infrared spectroscopy . the solvents were removed under reduced pressure to give the product in a quantitative yield . reaction ( 4 ): γ - isocyantopropyltriethoxysilane ( ge bayer silicones a - 1310 ) ( 2 . 35 g , 9 . 5 mmol ) was solvated in 10 ml of anhydrous thf in a 50 ml round bottom flask . the reaction flask was flushed with nitrogen and charged with n , n - bis -( 2 - hydroxyethyl )- 4 - nitroso - aniline ( 1 g , 4 . 75 mmol ), followed by a catalytic quantity of dibutyltin dilaurate ( 1 . 5 μmol ). the reaction was refluxed for an additional 5 hours under nitrogen . consumption of the isocyanate ( 2275 cm − 1 ) was monitored using infrared spectroscopy . the solvents were removed under reduced pressure to give the product in a quantitative yield . reaction ( 5 ): γ - isocyantopropyltriethoxysilane ( ge bayer silicones a - 1310 ) ( 10 . 68 g , 43 . 18 mmol ) was solvated in 30 ml of anhydrous thf in a 100 ml round bottom flask . the reaction flask was flushed with nitrogen and charged with p - benzoquinone dioxime ( sigma - aldrich ) ( 3 g , 21 . 72 mmol ), followed by a catalytic quantity of dibutyltin dilaurate ( 1 . 5 μmol ). the reaction was refluxed for an additional 5 hours under nitrogen . consumption of the isocyanate ( 2275 cm − 1 ) was monitored using infrared spectroscopy . the solvents were removed under reduced pressure to give the product in a quantitative yield . reaction ( 6 ): γ - isocyantopropyltriethoxysilane ( ge bayer silicones a - 1310 ) ( 2 . 35 g , 9 . 5 mmol ) was solvated in 10 ml of anhydrous thf in a 50 ml round bottom flask . the reaction flask was flushed with nitrogen and charged with 2 -( n - ethylanilino ) ethanol ( 0 . 78 g , 4 . 75 mmol ), followed by a catalytic quantity of dibutyltin dilaurate ( 1 . 5 μmol ). the reaction was refluxed for an additional 5 hours under nitrogen . consumption of the isocyanate ( 2275 cm − 1 ) was monitored using infrared spectroscopy . the solvents were removed under reduced pressure to give the product in a quantitative yield . formulations comprising the compounds of the invention were prepared as set out below . tests were carried out using natural rubber of the following composition : the following nitrososilane was utilised in each of formulations 1 to 7 : to assess the efficacy of the adhesive systems of the present invention in bonding rubbers to metal surfaces , a series of tests were performed according to the astm 429 - b standard adjusted to a 45 ° angle . grit - blasted steel laps ( 2 . 54 cm ( 1 inch ) wide , 10 . 16 cm ( 4 inch ) long panels or coupons ) were coated with the adhesive composition and adhered to natural rubber in a vulcanisation process . the adhesive was applied to the steel laps without any cooling . alternatively , the adhesive may be applied to the steel laps having been cooled to room temperature . the natural rubber compositions were sulfur - cured compositions as set out in the formulation tables . before application of the adhesive , 2 . 54 cm ( 1 inch ) of length and 2 . 54 cm wide ( 1 inch ) on both ends of the grit - blasted steel lap were masked to prevent that region being available for bonding to the rubber , leaving a central area of 2 . 54 cm ( 1 inch ) in width and 5 . 08 cm ( 2 inches ) in length available to bond to the rubber . a layer of uncured rubber was then placed on each coupon and cured in a standard hydraulic vulcanisation press for a period of time specified by the rubber &# 39 ; s cure profile . in the case of the natural rubber used in the bonding process in the present invention , the rubber was cured for 20 minutes at 150 ° c . under a pressure of 20 - 30 tonnes , to ensure intimate contact of the surfaces being bonded and the adhesive . after curing the bonded samples were aged for 24 hours at room temperature before being subjected to testing and the tear pattern noted . each sample was tested by the 45 ° angle modified astm 429 - b standard using instron equipment ( instron tester , model no . 5500r ) at a load rate of 50 mm per minute until separation is complete . “ rubber coverage ” is the percentage of rubber remaining on the bonded metal substrate after peel testing . 100 % rubber failure means that the rubber completely failed with no portion of the rubber peeling away from the surface of the metal ( and equates to 100 % rubber failure ). generally it is desirable that the rubber substrate fails before the substrate to rubber bond fails . the results achieved with formulations according to present invention are set out below . pre - bake represents heating at the temperature at time indicated prior to vulcanisation . nitrososilane was dissolved in an ethanol / water ( 1 : 1 ) mixture and stirred into solution . to this bis ( triethoxysilylpropyl ) amine and acetic acid were added and heated to 50 ° c . for 2 hours . bond strength after pre - bake ( 5 min @ 160 ° c .) = 9 . 1 n / mm ( 85 % r ) nitrososilane was dissolved in an ethanol / water ( 95 : 5 ) mixture and stirred into solution . to this ( 3 - aminopropyl ) triethoxysilane , ck3 carbon black , n990 carbon black and aerosil 200 were added and heated to 50 ° c . for 2 hours . bond strength after pre - bake ( 5 min @ 160 ° c .) = 10 . 2 n / mm ( 80 % r ) nitroso silane , ( 3 - aminopropyl ) triethoxysilane , aerosil 200 and ethanol / water ( 95 : 5 ) solution were stirred together and heated at 50 ° c . for 2 hours . after which time a butvar b - 72a in ethanol / water ( 95 : 5 ) solution was added and stirred at room temperature for 30 min . n990 was then added and stirred for 10 min before application to grit - blasted steel laps . bond strength after pre - bake ( 5 min @ 160 ° c .) = 9 . 9 n / mm ( 70 % r ) nitroso silane , ( 3 - aminopropyl ) triethoxysilane , aerosil 200 and ethanol / water ( 95 : 5 ) solution were stirred together and heated at 50 ° c . for 2 hours . after which time a butvar b - 76 in ethanol / water ( 95 : 5 ) solution was added and stirred at room temperature for 30 min . n990 was then added and stirred for a further 10 min before application to grit - blasted steel laps . bond strength after pre - bake ( 5 min @ 160 ° c .) = 11 . 7 n / mm ( 85 % r ) nitroso silane , ( 3 - aminopropyl ) triethoxysilane , aerosil 200 and ethanol / water ( 95 : 5 ) solution were stirred together and heated at 50 ° c . for 2 hours . after which time a butvar b - 72a in ethanol / water ( 95 : 5 ) solution was added and stirred at room temperature for 30 min . csx - 691 was then added and stirred vigorously for a further 10 min before application to grit - blasted steel laps . bond strength after pre - bake ( 5 min @ 160 ° c .) = 7 . 9 n / mm ( 60 % r ) nitroso silane , ( 3 - aminopropyl ) triethoxysilane , aerosil 200 and ethanol / water ( 95 : 5 ) solution were stirred together and heated at 50 ° c . for 2 hours . after which time a butvar b - 72a in ethanol / water ( 95 : 5 ) solution was added and stirred at room temperature for 30 min . csx - 691 was then added and stirred vigorously for a further 10 min before application to grit - blasted steel laps . bond strength after pre - bake ( 5 min @ 160 ° c .) = 10 . 0 n / mm ( 60 % r ) nitroso silane , ( 3 - aminopropyl ) triethoxysilane , aerosil 200 and ethanol / water ( 95 : 5 ) solution were stirred together and heated at 50 ° c . for 2 hours . after which time a butvar b - 72a in ethanol / water ( 95 : 5 ) solution was added and stirred at room temperature for 30 min . special black 4 was then added and stirred vigorously for a further 10 min before application to grit - blasted steel laps . in this example the rubber was bonded to a glass lap / slide available from ideal glass ltd . bond strength after pre - bake ( 5 min @ 160 ° c .) = 8 . 8 n / mm ( 80 % r ) nitrososilane was dissolved in an ethanol / water ( 95 : 5 ) mixture and stirred into solution . to this ( 3 - aminopropyl ) triethoxysilane , ck3 carbon black , n990 carbon black and aerosil 200 were added and heated to 50 ° c . for 2 hours . d . butvar b - 72a is a polyvinyl butyral resin from solutia inc . e . butvar b - 76 is a polyvinyl butyral resin from solutia inc . of lower viscosity than butvar b - 72a . g . special black 4 is an acidic carbon black from evonik . it is appreciated that certain features of the invention , which are , for clarity , described in the context of separate embodiments , may also be provided in combination in a single embodiment . conversely , various features of the invention which are , for brevity , described in the context of a single embodiment , may also be provided separately or in any suitable sub - combination .