Abstract
Low molecular weight, highly crosslinked silicone resins are widely used as reinforcing agents for highly transparent elastomers and adhesion/tack promoters in gels. The resins are complex mixtures and their structure / property relationships are ill defined. We report the synthesis of a library of 2, 3 and 4-fold hyperbranched polymeric oils that are comprised of linear, lightly branched or highly branched dendronic structures. Rheological examination of the fluids and tack measurements of gels filled with 10, 25 or 50% dendronic oils were made. Viscosity of the hyperbranched oils themselves was related to molecular weight, but more significantly to branch density. The properties are driven by chain entanglement. When cured into a silicone gel, less densely branched materials were more effective in improving tack than either linear oils or Me3SiO-rich, very highly branched oils of comparable molecular weight, because the latter oils underwent phase separation.
Highlights
Silicone resins are highly reticulated materials comprised primarily of tri- and/or tetrafunctionalSiO monomers and can be considered to be 3-dimensional hyperbranched copolymers
MQ resins are of particular interest [1]
MQ resins are highly reticulated silica-like cores capped with hydrophobic Me3 Si groups
Summary
Silicone resins are highly reticulated materials comprised primarily of tri- and/or tetrafunctionalSiO monomers and can be considered to be 3-dimensional hyperbranched copolymers. MQ resins are highly reticulated silica-like cores capped with hydrophobic Me3 Si groups. As a consequence of their small silica particle-like structure, they are widely used as reinforcing fillers to impart an improvement of the mechanical properties of highly transparent silicone elastomers [2], and may be used as viscosity modifiers, adhesion/tack additives, and passivating layers in electronics [2,3]. MQ resins are an important class of commercial silicone resins. They can be prepared in a sol-gel process by acidification of sodium silicate followed by capping [4], or hydrolysis and condensation [5]; recently, a transesterification approach to their synthesis using Si(OEt4 ) was described (Figure 1A–C) [6]
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