Silyl-modified polymers (SMP; also ''silane-modified polymers'', ''modified-silane polymers'', ''MS polymers'', ''silane-terminated polymers'', etc.) are

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

s terminating with a

silyl Silylation is the introduction of one or more (usually) substituted silyl groups (R3Si) to a molecule. Silylations are core methods for production of organosilicon chemistry. Silanization, while similar to silylation, usually refers to attachmen ...

group. SMPs are the main components in

solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...

-free and

isocyanate In organic chemistry, isocyanate is the functional group with the formula . Organic compounds that contain an isocyanate group are referred to as isocyanates. An organic compound with two isocyanate groups is known as a diisocyanate. Diisocyan ...

-free

sealant Sealant is a substance used to block the passage of fluids through openings in materials, a type of Seal (mechanical), mechanical seal. In building construction ''sealant'' is sometimes synonymous with ''caulk'' (especially if acrylic latex or ...

and

adhesive Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advantage ...

products.Jeffrey D. Umpleby "Polymer composition
U.S. patent 4574133
1986. Sealant products manufactured with silyl-modified polymers generally have most of the desirable properties of acrylic- or polyurethane-based products, including high opacity, short drying time, and good paint adhesion, as well as some key properties of silicone-based products, including adhesion to a wider range of substrate materials, higher temperature and UV resistance, higher elasticity, and greater resistance to bacteria and fungi. MS polymers consist of a polyether backbone with dimethoxy-silyl or trimethoxy-silyl ends, with trimethoxy-silyl groups being more reactive. Backbones can be linear with single or double ends, or branched for an increased amount of cross linking. Precursors can also be varied in the molecular weight and reactive silyl group concentration, resulting in variable cure times, strength, density, and hardness.

Curing process

The products cure from a liquid or gel state to a solid

elastomer An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus (E) and high failure strain compared with other materials. The term, a portmanteau of ''ela ...

. Curing entails crosslinking by the hydrolysis of

silyl ether Silyl ethers are a group of chemical compounds which contain a silicon atom covalently bonded to an alkoxy group. The general structure is R1R2R3Si−O−R4 where R4 is an alkyl group or an aryl group. Silyl ethers are usually used as protectin ...

s: : 2 RSi(OCH₃)₂R' + H₂O → Si(OCH₃)R'sub>2O + 2 CH₃OH In a hydrolysis reaction, a

catalyst Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...

and

moisture Moisture is the presence of a liquid, especially water, often in trace amounts. Moisture is defined as water in the adsorbed or absorbed phase. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some comme ...

is required to form an intermediate silanol, which then reacts to form

siloxane In organosilicon chemistry, a siloxane is an organic compound containing a functional group of two silicon atoms bound to an oxygen atom: . The parent siloxanes include the oligomeric and polymeric hydrides with the formulae and . Siloxanes ...

linkages in a condensation process.

References

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