Silanes for Adhesives

  Nanjing Aocheng Chemical Co.,LTD is a supplier  of silane , let's introduce the silane adhesion promoters are as follows:

Silane adhesion promoters are bifunctional organosilicone compounds which act as molecular bridges between the polymer matrix of an adhesive or sealant and the substrate, either inorganic or organic.

The silane end contains hydrolysable alkoxy groups that are activated by reaction with ambient moisture. The hydrolysable alkoxy groups attached to the silicon end of the silane are typically either methoxy or ethoxy. Once activated (hydrolyzed), the resultant silanol groups will condense with o ther silanols or with reactive groups on the surface of a substrate such as SiOH, AIOH, or other metal oxides or hydroxides.The silane’s ability to bond to a surface will generally be determined by the concentration of such sites on the surface. Selecting the optimal silane for an application requires matching the reactivity of the silane‘s organofunctional group to that of the polymer.

The silanes can be blended into an adhesive formulation or used as primers on substrates. The structure and re activity of the silane will affect the ability of the silane to migrate. The most effective way to promote adhesion is to apply the silane as a primer to the surface, followed by application of the adhesive/sealant.

In this way, the silane will be on the s urface and therefore at the interface where it can enhance adhesion between the polymer and the substrate. Silane primers are usually dilute solutions of 0.5 to 5 percent silane in alcohol or water/alcohol solvent. They are wiped or sprayed on the substrate, after which the solvent is allowed to evaporate. While the concentration needed for a specific application may vary, one percent (1%) based on resin content is recommended as a good starting point.

The organofunctional group of the silane can react, and bond to, the polymer backbone. Residual moisture activates the silane’s alkoxy groups to the active silanol form which react with each other, liberating
moisture, and forming siloxane bonds between the polymers. The resulting Si-O-Si crosslink is extremely durable, offering excellent weather, UV, temperature, chemical and moisture resistance.

The filler may either be treated with silane before it is added to the sealant formulation (pretreatment method), or it can bind with the filler during compounding (additive method).

Alkoxysilanes react very rapidly with water;they are usually used to capture excess moisture in sealants and adhesives.

Vinyltrimethoxysilane is the most common moisture scavenger , due to the electron interactions of the vinyl group it reacts with moisture faster than other alkoxy silanes, enabling it to function as a moisture scavenger in the presence of other silanes incorporated as adhesion promoters, crosslinkers or coupling agents. The amount of silane added will depend on the water content of the formulation constituents.

Methanol is formed as a byproduct, and the vinyl silane crosslinks into an inactive species in the formulation. Other alkoxy silanes, such as methyltrimethoxysilane, are also used as waters.

 
(source:http://www.ac-chem.net/news/silanes-for-adhesives-8e0b.html)

Silanes as Primers and Adhesion Promoters

Organosilanes are "molecular bridges" that are used as primers and adhesion promoters for coatings or adhesives. The addition of a silane at the interface results in high bond strength and corrosion resistance. The chemical link created by the use of a silane contributes various benefits, such as:

• A strong bond between the inorganic surface and the organic polymer to provide enhanced adhesion in both wet and dry environments;
• a barrier to prevent moisture penetration through the interface;
• improved bulk physical properties of the coating or adhesive through enhanced adhesion between the polymer and the filler particles within the formulation and the efficient transfer of stress from the resin to the filler;
• effective dispersion of fillers and reduction in the apparent viscosity of the system.

Silanes are a group of specialty organo functional compounds that possess dual reactivity. The silanes act chemically with both the metal substrate and the organic base polymer in the coating or adhesive.The silane adhesion promotes and protects the metal substrate by forming covalent bonds across the interface that are both strong and durable.

Silanes can be applied directly to the substrate, similar to conventional primers, or they can be mixed into the coating or adhesive formulation as an additive. Optimum results are generally achieved by using the silane as a substrate primer. When applied directly to the substrate, they are very thin coatings only about one monolayer in thickness. When mixed with the coating, the coupling agent is capable of migrating to the interface and reacting with the substrate surface as the coating or adhesive dries.

Over the last 20 years, the silane adhesion promoter marketplace has evolved to include a plethora of materials of which organosilanes have secured a prominent position. The choice of a particular silane will depend on the specific formulation of the coating or adhesive, on the substrate and on the method of application.

Optimizing the potential properties of silane systems offers a challenge.There are many parameters that can effect the performance of silane. Therefore, it is recommended that the silane supplier be contacted to assist in making a selection.

Silanes are multifunctional in that they can be used to promote crosslinking, and they can be incorporated directly into a polymer chain by various reaction mechanisms. In addition to coatings and adhesives, silanes have multiple commercial uses, such as coupling agents for reinforced plastics, crosslinking agents for polyethylene cables, and dispersants for paints and printing inks.

(source:http://www.ac-chem.net/news/silanes-as-primers-and-adhesion-promoters-b75e.html)

Effect of Silane Crosslinker on the Thermal Properties of Rice Straw/HDPE Biocomposite

A formulation was designed to produce silane crosslinkers rice straw/high density polyethylene (RSPE) compound suitable for injection molding process. The formulations consist of high density polyethylene (HDPE) as the base polymer, rice straw as the filler, processing aids and a mixture of crosslink chemicals. Crosslink chemicals consist of vinyltrimethoxysilane (VTMO) as crosslinking agent, dicumyl peroxide (DCP) as the initiator, dibutyltin dilaurate (DBTL) as the condensation catalyst. Lignocellulosic material, rice straw was oven dried at 70°C for 24 h, grinded and sieved. A counter rotating twin shaft high speed mixer was utilized to mix the rice straw, HDPE and the processing aids. Blends were then compounded on co-rotating and intermeshing twin screw extruder. Test specimens were prepared via injection molding process followed by oven curing at 90°C. Fourier Transform Infra Red (FTIR) was used to determine the chemical group involved in the crosslinking reaction. Degree of crosslinking in the silane crosslinked compound was measured by determining their gel content. Thermal properties were analyzed on the Differential Scanning Calorimetry (DSC) for the melt temperature, Tm, whereas Thermogravimetric (TGA) analysis for its thermal stability behavior. The degree of crosslinking in RSPE increases with an increased in VTMO and DCP concentration. The results from FTIR showed the presence of Si-O-Si bond and Si-O-C indicative of crosslinks formation. Thermal behavior of the compound illustrated that the crosslinked RSPE was more stable than the uncrosslinked RSPE and pure HDPE, while the Tm was unchanged.

silane in fiberglass

1. Glass fiber surface treatment Objective and Significance
　　Surface treatment is a processing which use the treating agent to cover the surface of reinforcement.These treating agents include treating compound, some of silane coupling agent and auxiliaries. It helps forming a well bond surface between reinforcement and substrate and also can improve various properties of compound materials.
　　Significance of treatment: We know that function of compound materials are not only related with content and property of resin and fiber, but also greatly depend on the bond of resin and fiber. Surface treatment includes interface processing which is coating a called “surface treatment agent” on the surface of glass fiber. This agent could solidly combined fiber and resin so as to increase the function of glass.
　　
2. Silane coupling agent and their reaction theories.
　　Silane coupling agent is this kind of materials which are usually have two different groups on
themselves ends. One end’s groups have the chemical action or physics action with the surface of
reinforcement, while the other end’s groups can react with base materials, so that well bond the
reinforcement with substrate to get the good bonding between interfaces and improve many respects of functions and effectively resist water.
　　Organic-functional silane is a kind of surface treating agent with many different and effective kinds and it’s normal chemical structure is RnSiX4-n.
There are four steps to treat fiber glass with Organic functional Silane coupling agent:
1. First, there are three unreliable X groups in atom Si to hydrolyze
2. Second, the silane coupling agent condensate Oligomers
3. Third, those oligomers formed hydrogen bond with the “–OH” group of the glass fiber surface
4. Last, In the process of drying and curing, silane creates covalent bonds with glass fiber surface.

3. Glass fiber surface processing method and factors.
　1. The treatment method of silane coupling agents for the surface of fiberglass:
　（1）Post-treatment （2）Pre-treatment （3）Grafting
Most of silanes are used in treating compound of fiberglass. We will mainly introduced pre-treatment.
　　Changing the formula of treating compound appropriately, it is not only meet the requirements of fiber forming, spinning and other process, but also not hinder the infiltrating and adhesion between the resin matrix and fiberglass. And also not hinder resin base material wetting and sticking on glass fiber. In the process of fiber forming, we add the silane coupling agent into the treating compound which make the surface treating agent coated on the surface of fiberglass, and we call this process is pre-treatment, which is weaving fiber cloth with fiber which is covered by reinforced treating compound.
  2. The dosage of silane coupling agent and factors of treatment.
　a. The dosage of silane coupling agent
　　Playing the role in silane coupling agent is the micro-quantity of monolayer of silane coupling agent. And the appropriately dosage of each kind of silane is result from the experiment.
Attention: the dosage of silane coupling agent can calculate:
Computing method: V2/ V1 = M
V1: The minimum coating area of 1g silane coupling agent
V2: The surface area of 100g reinforced materials
M: The required quantity of silane coupling agent to coat a monolayer in 100g treated materials.
b. Factors of treatment:
1) The dosage of silane coupling agent
2) The temperature and time of drying
3) The pH value of treatment compound

5. Requirements on silane coupling in fiberglass industry
a. Silane coupling must be dispersed in water, because the wetting agent of fiberglass adopts water as the carrier;
b. Purity of silane coupling should be higher, such as AC-220 requires the purity is higher than 98%; if the content is low and foreign substance is too much, the strength of the compound materials will change greatly;
C. The hydrolysis rate is required to be within 30 min, affecting the production efficiency of wetting agent.
d. It can improve the strength and electric properties, etc. of fiberglass reinforced resin.

(source:http://www.ac-chem.net/news/Silane-in-Fiberglass-8a3a.html)

Typical Silane Applications

Silane Coupling Agent: Organofunctional alkoxysilanes are used to couple organic polymers to inorganic materials. Typical of this application are reinforcements, such as fiberglass and mineral  fillers, incorporated into plastics and rubbers. They are used with both thermoset and thermoplastic systems. Fiberglass applications include auto bodies, boats, shower stalls, printed circuit boards, satellite dishes, plastic pipes and vessels, and many others. Mineral-filled systems include reinforced polypropylene, silica-filled molding compounds, silicon-carbide grinding wheels, aggregate-filled polymer concrete, sand-filled foundry resins, clay-filled EPDM wire and cable, clay- and silica-filled rubber for automobile tires, shoe soles, mechanical goods and many other applications.

Silane Adhesion Promoter: Silane coupling agents are effective adhesion promoters when used as integral additives or primers for paints, inks, coatings, adhesives and sealants. As integral additives, they must migrate to the interface between the adhered product and the substrate to be effective. By using the right silane coupling agent, a poorly adhering paint, ink, coating, adhesive or sealant can be converted to a material that often will maintain adhesion even if subjected to severe environmental conditions.

 Hydrophobing and Dispersing Agent: Alkoxysilanes with hydrophobic organic groups attached to silicon will impart that same hydrophobic character to a hydrophilic inorganic surface. They are used as durable hydrophobing agents in construction, bridge and deck applications. They are also used to hydrophobe inorganic powders to make them free-flowing and dispersible in organic polymers and liquids.

Silane Crosslinking Agent: Organofunctional alkoxysilanes can react with organic polymers to attach the trialkoxysilyl group onto the polymer backbone. The silane is then available to react with moisture to crosslink the silane into a stable, three-dimensional siloxane structure. Such a mechanism can be used to crosslink plastics, especially polyethylene, and other organic resins, such as acrylics and urethanes, to impart durability, water resistance and heat resistance to paints, coatings and adhesives.

Silane Moisture Scavenger: The three alkoxy groups on silanes will hydrolyze in the presence of moisture to convert water molecules to alcohol molecules. Organotrialkoxysilanes are often used in sealants and other moisture-sensitive formulations as water scavengers.

Polypropylene Catalyst “Donor”: Organoalkoxysilanes are added to Ziegler-Natta catalyzed polymerization of propylene to control the stereochemistry of the resultant polypropylene. The donors are usually mono- or di-organo silanes with corresponding tri- or di-alkoxy substitution on silicon. By using specific organosilanes, the tacticity and properties of the polypropylene are controlled.

Silicate Stabilizer: A siliconate derivative of a phosphonate-functional trialkoxysilane functions as a silicate stabilizer to prevent agglomeration and precipitation of silicates during use. The predominant application is in engine coolant formulations to stabilize the silicate corrosion inhibitors.

(source:http://www.ac-chem.net/news/typical-silane-applications-80ac.html)

Silane coupling agents

Silane coupling agents are silicon-based chemicals that contain two types of reactivity–inorganic and organic–in the same molecule. A typical general structure is (RO)3SiCH2CH2CH2-X,where RO is a hydrolyzable group, such as methoxy, ethoxy, or acetoxy, and X is an organofunctional group, such as amino, methacryloxy, epoxy, etc.
A silane coupling agent will act at an interface between an inorganic substrate (such as glass, metal or mineral) and an organic material (such as an organic polymer, coating or adhesive) to bond, or couple, the two dissimilar materials.
A simplified picture of the coupling mechanism is shown in Figure 1.

(source:http://www.ac-chem.net/news/Silane-Coupling-Agents-9338.html)

resin modifier

The electrolyte may further comprise an opacifying and reflecting material or pigment such as titanium dioxide. The object of this material is optically to isolate the front from the rear electrode in a display electrochromic cell and to reflect ambient light which has passed through the front electrode material. Suitably, the electrolyte contains from 10 to 30 percent of the opacifying material by weight based upon the weight of the electrolyte, e.g. from 15 to 25 percent. The electrolyte preferably also comprises a resin modifier such as ethylacrylate, 2-ethylhexylacrylate copolymer. The purpose of the resin modifier will be described below in connection with the fabrication of the electrolyte.

3-Aminopropyltriethoxysilane

3-Aminopropyltriethoxysilane (APTES) has been tested for acute toxicity by the oral, dermal, and inhalation routes of exposure.  Acute oral LD50s in rats range from 1570 to 3650 mg/kg bw.  The dermal LD50 is 4.29 g/kg bw and the 4-hour inhalation LC50 of the hydrolysate is greater than 7.35 mg/L.  Six hours of exposure to substantially saturated vapor of APTES did not kill any of the 5 male or female rats (LT50 > 6 hours). The kidney is a target organ for toxicity for oral and dermal exposures.

APTES is severely irritating to the skin and eyes. In a Buehler study in guinea pigs, 7/30 animals showed a skin sensitization response.  The hydrolysis products of this material do not elicit a sensitization response in a guinea pig maximization test.  

Repeated inhalation exposure of rats to 147 mg/m3 of APTES hydrolysate respirable aerosol for four weeks produced squamous metaplasia and foci of minimal granulomatous laryngitis. No systemic toxicity was observed in rabbits after 9 repeated dermal doses of 17 or 84 mg/kg bw/day or three repeated dermal doses of 126 mg/kg bw/day of APTES; the site of contact NOAEL is less than 17 mg/kg bw/day. The no-observed-adverse-effect level (NOAEL) of APTES in a 90-day oral (gavage) study with rats was 200 mg/kg bw/day.  

APTES has been tested in several bacterial reverse mutation/Ames assays,  in vitro V79 hamster lung cell and Chinese hamster fibroblast chromosome aberration assays, two Chinese hamster ovary cell HGPRT gene mutation assays, and an  in vivo mouse micronucleus assay.  In vivo and  in vitro screening assays have not revealed any
evidence of genotoxic potential.

At the highest dose-level (600 mg/kg/day) in a 90 day oral gavage study in rats, no effects were seen on parameters of oestrus cycle and spermatogenesis or reproductive organs. The NOAEL for developmental effects has been identified for APTES following exposure via oral (gavage) in rats, with a value of 100 mg/kg bw/day, the NOAEL for maternal toxicity based on deaths and ulceration of the GI tract is <0.5 mL/kg

Silane moisure scavengers

Silane are bifunctional molecules that possess dual reactivity and act as surface resin modifier,silane adhesion promoters,silane crosslinkers and silane moisure scavengers in many different industrial applications.The properties and effects of silanes are defined by their molecular structure:

Y-(CH2)n-Si(OX)3

Y=organofunctional group,OX=silicon-functional group(alkoxy),n=0 or 3.

The organofunctional group Y links with the polymer resin.This group must be chosen carefully to ensure maximum compatibility with the polymer resin of choice.
The silicon-functional groups OX,usually alkoxy groups,must be hydrolyzed to silanols(Si-OH) first before they can bond to the substrate or crosslink.

Adhesion Accelerators

With the advancement of tire technology, radial tires have captured 90-95% of the tire market in most of the advanced countries and steel cord has been established as the best carcass and belt material for radial tires. It has a number of advantages like higher tenacity that leads to higher load carrying capacity, higher modulus, higher fatigue life, low extension and highest durability, etc., over all kinds of presently available commercial tire cords. But due to wide variation of physical as well as chemical properties, a good marriage between rubber and steel cord is not so easy. A number of adhesion accelerators and silane adhesion promoters are available in the market to enhance the bonding, but most of them have failed to retain the bonding substantially after different aging conditions especially at elevated temperatures. This problem is more aggravated e.g., in a country like India due to to overloading, rough road conditions, high humidity and temperature, or in advanced countries where the tires are abused due to higher speeds which leads to higher heat development and gradual separation of steel cord from rubber. The problem is even more severe when cuts develop in the tire through which engress of moisture, water, dirt, etc., takes place and ultimately affects the adhesion between rubber and steel cords. Although cobalt boron acylate alone can take care of good adhesion in normal conditions as well as under salt aging or steam aging conditions even at elevated temperature, to maintain the physicals as well as adhesion properties in anaerobic aging condition, it is essential to have a suitable network structure which can be achieved by using specialty chemicals like post vulcanization stabilizer (PVS) such as hexamethylene-l,6-bisthio sulfate disodium salt dihydrate (HTSNa) and bis-(3-triethoxy silylpropyl) tetrasulfide (TESPT).

3-Aminopropyltriethoxysilane

3-aminopropyltriethoxysilane (APTES) is commonly used to functionalize glass substrates because it can form an amine-reactive film that is tightly attached to the surface. In this study, we investigated the morphology and chemical reactivity of APTES films prepared on glass substrates using common deposition techniques. Films were prepared using concentrated vapor-phase deposition, dilute vapor-phase deposition, anhydrous organic-phase deposition and aqueous-phase deposition. All films were annealed, or cured, at 150 degrees C. The morphology of the films was quantified by fluorescence and by atomic force microscopy (AFM). The optical equivalent of the AFM images was computed and then used to directly compare optical and AFM images. Reactive amine density was determined by a picric acid assay and by a method that employed N-succinimidyl 3-[2-pyridyldithio]-propionamido (SPDP) cross-linked rhodamine. Fluorescence and AFM images showed that silane films prepared from dilute vapor-phase and aqueous-phase deposition were more uniform and had fewer domains than those deposited by the other methods. The ratio of picric acid-accessible amino groups to SPDP cross-linked rhodamine-accessible groups varied with the preparation method, suggesting reactant size-dependent difference in amine accessibility. We found a larger number of accessible amino groups on films prepared by vapor-phase deposition than on those prepared from solution deposition. The dilute vapor-phase deposition technique produced relatively few domains, and it should be a good choice for bioconjugation applications. There were appreciable differences in the films produced by each method. We suggest that these differences originate from differences in film rearrangement during annealing.

amino silane

The surface properties and structure of mono-, di-, and tri-amino silane treated glass surfaces were investigated using surface analytical techniques including X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM), and streaming potential. An optimized dip-coating process was demonstrated to produce roughly silane monolayer coverage on the glass surface. The surface charge measurements indicated that amino silanization converts the glass surface from negative to positive potentials at neutral pH values. Higher positive streaming potential was observed for tri-compared with mono- and di-aminosilane treated glass surfaces. For all  amino silane treated glass samples, the high-resolution N 1s XPS spectra indicated a preferential orientation of the protonated amino-groups towards the glass surface whereas the free amino groups were protruding outward. This study aimed to obtain uniform, reproducibly thin, strongly adhering, internally cross-linked, and high positively charged amino silane -coated glass surfaces for the attachment of DNA fragments used in microarraying experiments.

Silane crosslinking agent

Silane crosslinking agent polyethylenes are a  commercial product for the global wire and cable market. The crosslinking takes place in the presence of trace amounts of water and the reactions can be accelerated by  incorporating a tin-based catalyst. In the first step, the methoxyl groups are hydrolysed to hydroxyl groups during. The crosslinking takes place in the second step where the hydroxyl groups recombine through a condensation step26, as shown in Figure 2. The schematic picture below shows the crosslinking mechanism for vinyltrimethoxy silane grafted onto the polyethylene backbone;  however in the case of copolymerised ethylene-vinyltrimethoxy silane, the silane trimethoxy group is coupled directly to the polyethylene backbone.

Silane coupling agents

Silane coupling agents belong to a class of organosilane compounds having at least two reactive groups of different types bonded to the silicon atom in a molecule. One of the reactive groups of different types (ex. methoxy, ethoxy and silanolic hydroxy groups) is reactive with various inorganic materials such as glass, metals, silica sand and the like to form a chemical bond with the surface of the inorganic material while the other of the reactive groups (ex, vinyl, epoxy, methacryl, amino and mercapto groups) is reactive with various kinds of organic materials or synthetic resins to form a chemical bond.
As a result of possessing these two types of reactive groups,Silane coupling agents are capable of providing chemical bonding between an organic material and an inorganic material.
This unique property of  Silane coupling agents  is utilized widely in the application of the silane Silane coupling agents  for the surface treatment of glass fiber products, performance improvement of fiber-reinforced plastics by the direct admixture to the synthetic resin, improvement of paints and other coating materials and adhesives, modification of surface properties of inorganic fillers, surface priming of various substrate materials, etc.
When a silane coupling agent is used in a thermosetting resin-based fiber-reinforced material, remarkable improvements are obtained in the mechanical and electrical properties of the material and the effect is more remarkable when the material is used in a wet or humid condition.
Application of Silane coupling agents  to thermoplastic resin-based fiber-reinforced materials is also actively performed along with the efforts to develop a silane coupling agent having further enhanced coupling effects.

Effect of EVA copolymer on properties of different polyethylenes in silane crosslinking agent

The effect of molecular structure of polyethylene (PE) [low density PE (LDPE), linear LDPE and high density PE] and silane/peroxide concentration on the grafting level and gel content in silane crosslinking agent has been studied. The effect of incorporation of ethylene vinyl acetate (EVA) copolymer on the rate of crosslinking and thermal properties of PEs has been reported. The order of gel content was LDPE>linear LDPE>high density PE. With the incorporation of EVA, the rate of crosslinking increased. The degree of crystallinity did not change with crosslinking significantly. However, the shape of melting and crystallisation peaks changed, and two regions due to gel and sol parts were formed. In EVA/PE blends, two melting points were observed for both crosslinked and uncrosslinked samples. The SEM images showed the droplet matrix morphology with the EVA as the dispersed phase, especially for EVA/LDPE blend. The EVA/PE blends failed in hot set test, while the origin of PEs passed the hot set test successfully.

Adhesion Promotion on Inorganic and Organic Substrates

An adhesion promoter is a bi-functional compound that can chemically react with both the substrate and the adhesive. Known for increasing an adhesive’s bond strength, it can be applied in two ways by being mixed with the adhesive or applied directly to the substrate. Unlike priming systems, silane adhesion promoters are generally applied at thinner film thicknesses. An adhesion promoter’s effectiveness depends on both the substrate and the adhesive being used. Surface pretreatments, such as solvent cleaning or mechanical etching, can be used with adhesion promoters as part of a pretreatment method.

ADHESION PROMOTERS FOR METAL AND HIGH-SURFACE-ENERGY INORGANIC SUBSTRATES

The most common commercial adhesion promoter is based around silane coupling agents. Silanes are most often used to promote the adhesion between polymeric systems and inorganic substrates.
Silane promoters typically comprise a tetravalent Si core (which has an organo functional tail) and some form of hydrolyzable group, such as a chloro or alkoxy attached. When applied to the substrate surface, the silane is hydrolyzed to form a silanol, which condenses and polymerizes with itself to form an extended network. If the silanol is on a substrate with sufficient oxide functionality, cross coupling can take place, anchoring the polymerized silanol to the surface . The choice of organofunctional tail on the silane is dictated by the adhesive class that is being used (e.g., for an epoxy adhesive system, a tail containing an amino or epoxy moiety would be suitable).
The effectiveness of silanes depends on the substrate being used; smooth, high-surface-energy substrates are better than low-surface-energy or discontinuous substrates .
Titanate and zirconate coupling agents are growing in popularity. They are predominately used to improve filler polymer adhesion in composites. Both titanates and zirconates react similarly to silane coupling agents by way of condensation to surface hydroxyl groups; however, unlike silanes, there is not condensation polymerization to produce a network at the interface.

ADHESION PROMOTERS FOR ORGANIC AND LOW-SURFACE-ENERGY INORGANIC SUBSTRATES

Low-surface-energy and solvent and chemical inertness all make organic materials difficult to bond. The lack of “surface chemistry”(such as hydroxyl) on most organic substrates renders silane adhesion promoters ineffective.

Recently, Oxford Advanced Surfaces developed Onto®, a novel class of adhesion promoters for use on organic and low-surfaceenergy inorganic substrates.
Adhesion promoters conceptually resemble those based around a silane — a functional tail covalently linked to a reactive head. The reactive head in the Onto adhesion promoter is based around a latent reactive intermediate, a class of organic functionality, which, upon application of an external stimulus, converts from a stable state to a highly reactive radical intermediate. This radical intermediate is capable of reacting with C-H, O-H and N-H bonds, as well as C C and C C bonds . This range of reactivity allows the adhesion promoter to react with nearly all organic substrates — from polyolefins to polyimides, as well as polyesters and inorganic materials such as carbon black and diamond .
Onto adhesive promoters are applied as solventborne formulations in MEK or toluene by way of appropriate coating techniques (such as spray, dip, spin or roll-to-roll) then cured by activated heat (approximately 100oC) or UV light (254 nm).
These adhesive promoters have been demonstrated on both Melinex-OD polyester film and Kapton-HN polyimide film, and have been shown to increase the T-peel and lap sheer forces when used in conjunction with cyanoacrylate  or epoxy adhesives