Coupling agents with 2,4,6,8-tetramethylcyclotetrasiloxane core – synthesis and application in styrene–butadiene rubber production

Abstract

A facile one-pot procedure for the functionalization of 2,4,6,8-tetramethylcyclotetrasiloxane DH₄ to branched organosilicon compounds DSP₃ or DS₃P bearing various, but clearly defined, numbers of silyl groups with an affinity to silica (S) and organic groups (alkyl, alkenyl, perfluoroaryl, epoxy, ether and ester) capable of bonding with polymers (P) has been demonstrated. Sequential hydrosilylation of allyltrimethoxysilane in the first step and olefin or alkyne in the second (and reverse order of reagents) has been applied in the presence of Karstedt's catalyst, which is commercially available and commonly used in industry. The developed procedure permitted the synthesis of 13 new, branched organosilicon compounds DSP₃ and DS₃P with excellent yields and precise distribution of functional groups. All products were easily isolated by simple filtration followed by drying under reduced pressure and fully characterized by spectroscopic methods (¹H, ¹³C, ²⁹Si NMR, IR) and mass spectrometry (ESI or MALDI). The obtained compounds, because of the presence of two different functional groups with an affinity to inorganic filler and polymer matrix, are regarded as versatile silica modifiers, silane coupling agents for various applications, and starting materials in the preparation of polymer networks and vapor-deposited coatings. The vulcanizates prepared using cyclosiloxane-functionalized rubber showed enhanced rolling resistance and wet skid resistance, proving the compound's potential in producing novel “Green Tire” treads.