adhesion promoter

Adhesion promoters include a wide range of chemical families, which are selected according to application conditions. The fundamental concept, is that different chemical natures imply different compatibility and final properties depending on the substrate and organic polymers chemical natures. These additives share a similar structure: a metallic center (such as silicon, zirconium, titanium, aluminum, or others) that will be responsible for the inorganic substrate bonding, and an organofunctional group, responsible for the inorganic interactions. They can be classified as reactive or non-reactive depending whether they posses a reactive group or not. In addition, they are called compatibilizers when they are used to compatibilize two immiscible organic polymers, they are called coupling agents when they are used to compatibilize a polymeric system and a filler (inorganic).{{Cite web|url=https://polymer-additives.specialchem.com/selection-guide/adhesion-promoters-for-polymers|website=www.specialchem.com|title=Comprehensive Guide on Adhesion Promoters for Polymers|language=en|access-date=2025-04-22}}

Silane coupling agents are denoted by the general monomeric structure X-R-Si-(OR)₃, where R is an aliphatic or aromatic group, X is a reactive organofunctional group, such as an amine, epoxide, isocyanate, thiol and vinyl group to name a few.{{Cite web|url=http://www.usi-chemical.com/category/silane/1|website=www.usi-chemical.com|title=USI Products Catalog|language=en|access-date=2025-04-23}} While OR rapresents a hydrolyzable group, for example, a methoxy, ethoxy or acetoxy group. This kind of promoters has been used extensively as additives and primers for adhesives and sealants to improve adhesion, compounding properties and as crosslinking agent.{{Cite web|url=https://adhesives.specialchem.com/selection-guide/adhesion-promoters-adhesives-sealants|website=www.specialchem.com|title= Adhesion Promoters: Adhesion Basics & Material Selection Tips for Adhesives|language=en|access-date=2025-04-22}} Oligomeric versions of organosilanes are obtained via polycondensation from the monomers and have been regarded as a safer alternative to the classical monomeric versions. As oligomers have a higher molecular weight, their boiling points are higher consequentially reducing their VOC (Volatile Organic Compounds) index, resulting in a safer labelling and logistic advantages.{{Cite web|url=https://patentscope.wipo.int/search/en/WO1998052992|website=www.patentscope.wipo.int|title=ORGANOSILANE OLIGOMERS|language=en|access-date=2025-04-23}}{{Cite web|url=https://www.nasampe.org/store/viewproduct.aspx?id=4391403|website=www.nasampe.org|title= Functional Silane Oligomers—The Way Into a High-Performing, Environmentally...|language=en|access-date=2025-04-23}}

Titanates and Zirconates are organometals compounds with excellent adhesion promoting properties, they are used with critical substrates such as glass, metals and ceramics where adhesion is difficult to obtain.{{Cite web|url=https://polymerinnovationblog.com/organic-coatings-part-four-adhesion-promoters-for-thermoset-coatings/|website=www.polymerinnovationblog.com|title= Organic Coatings Part Four: Adhesion Promoters for Thermoset Coatings|date=4 November 2024 |language=en|access-date=2025-04-24}} The general structure of these organometals can be represented as (RO)_n-Me-(-O-X-R'-Y)_4-n, where Me represents the metallic atom (Zr or Ti). Based on this, we can see that there are some similarities as well as differences compared to organosilanes, as the reaction mechanisms of these two compounds are different: Titanium and Zirconium based adhesion promoters do not need water to react, unlike organosilanes, who need water for the hydrolysis reaction. In fact, these organometals chemically bridge to surface protons through solvolysis. Many fillers have surface protons available, some examples are: carbonates (CaCO3), nitrates, carbon, boron and metal powders, which are typically non-reactive towards organosilanes, placing Titanium and Zirconium based adhesion promoters as a more versatile solution.{{Cite web|url=https://4kenrich.com/technical-information/titanates-and-zirconates-in-thermoplastic-and-elastomer-compounds/|website=|title=Six Functions of the Titanate/Zirconate Molecule Compounds|language=en|access-date=2025-04-24}}{{Cite web|url=https://www.researchgate.net/publication/293357466|website=www.researchgate.net|title=Titanates and Zirconates in thermoplastic and elastomer compounds|language=en|access-date=2025-04-24}}

Chlorinated polypropylene resins (CPO) are a group of polymers obtained by halogenation of polypropylene (PP) with chlorine. These polymers are soluble in

toluene and halogenated hydrocarbons and can be classified as low, medium or high chlorine content, depending on the final application; for example, high content chlorinated polypropylene is widely used in fireproof coating and paints, while lower content resins are mostly used in inks.{{Cite web|url=https://www.schem.net/blog/what-is-chlorinated-polypropylene_b71#:~:text=Chlorinated%20polypropylene%20%28also%20called%20CPP%20resin%29%20is%20a,development%20of%20chlorinated%20polypropylene%20began%20in%20the%201960s.|website=www.schem.net|title=What is Chlorinated Polypropylene|language=en|access-date=2025-04-29}} Their use as adhesion promoters is widely known in the automotive industry, specifically, from the mid 1970s, metallic car bumpers were starting to be replaced by thermolplastic olefins (TPO) thanks to the intrinsic advantages of these materials: recyclability, cost, weight reduction and better mechanical properties. CPOs are usually mixed with other resins and pigments, partially acting as levelling agent. Many studies tried to characterize a model, but the results have shown that the adhesion mechanism is strongly influenced by many factors such as the chemistry of the topcoat, the CPO used and the properties of the polypropylene substrate.{{Cite web|url=https://www.researchgate.net/publication/225593930|website=www.researchgate.net|title=Characterization of adhesion performance of topcoats and adhesion promoters on TPO substrates|language=en|access-date=2025-04-29}}

• Organosilane
• Silicone sealant
• Thermoplastic olefin
• Filler (materials)
• Surface energy
• Adhesion

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Category:Adhesives