Keith E. Polmanteer

Silicone rubber, its development and technological progress

Abstract This paper has described silicone rubber, its first commercial development in 1944, and its technological progress since then. Pioneering research on silicon opened the door to the development of silicone polymers and silicone rubber. The substitution of two methyl groups on silicon was present in the first examples of silicone rubber and still is the predominant organic group in commercial silicone rubber today. Silicone rubbers have filled a need in the marketplace because of their combination of unusual properties not found in other rubbers. The alternating inorganic main-chain atoms of silicon and oxygen, and the two pendant organic groups, primarily methyl, provide strong chain bonds, backbone flexibility, ease of side-group rotation, and low “inter” and “intra” molecular forces. This molecular makeup and properties thereof are primarily responsible for the observed performance of silicone rubbers. Many significant advances in silicone rubber have been discussed in chronological sequence to ...

Novel Wet-Process Silica Prepared from Alkyl Silicates. Part I: Synthesis

Abstract A simple procedure for preparing a silica filler possessing both the necessary structure and surface character to be useful as a reinforcing filler for silicone elastomers has been developed. The novel, one-step process involves hydrolysis and condensation of alkyl silicates in the presence of a silica surface treatment agent exemplified as follows: (see PDF for diagram) Only easily recycled by-products are generated during the synthesis of the new WPH silica. Performance of the resultant WPH silica filler in reinforcing silicone elastomers will be discussed in detail in Part II of this series, while their use in silicone elastomers for optical applications will be described in Part III.

Novel Wet Process Silica Prepared from Alkyl Silicates. Part III: Use in Silicone Elastomers for Optical Applications

Abstract The first two papers of this three-part series of papers dealing with a novel wet-process hydrophobic (WPH) silica technology covered the silica synthesis (Part I) and reinforcement performance (Part II) respectively. The WPH silica was highly reinforcing and provided optically clear compositions as well. The first optically clear, high consistency silicone elastomer was developed in the midnineteen fifties by Polmanteer et al., using different technology from that described in this paper. Optical clarity was accomplished in the earlier work by matching the refractive indices of the filler and polymer at 25°C, making them isorefractive at this specific temperature. This paper will discuss the unique features of this new silica technology as it relates to optically clear silicone elastomers. The term, optically clear, in the context of this paper refers to an elastomeric material, 2.54 mm in thickness, that exhibits less than 4% haze, and more than 85% transmission. It will be shown that, when usi...

Novel Wet-Process Silica Prepared from Alkyl Silicates. Part II: Performance in Reinforcing Silicone Elastomers

Abstract The wet-process hydrophobic (WPH) silica process provides a technology which allows control of surface area, structure, and surface treatment. These are the primary factors which determine the extent to which a silica can reinforce silicone elastomers. Thus, it is possible to tailor the silica to achieve specific desirable elastomer property profiles. Reinforcing capability of WPH silica is greater than that of pyrogenic silica. The unique method of passivating the silica by introducing the treating agent prior to formation of the silica eliminates the need for separate processing steps to passivate the silica and produces well treated silica, as evidenced by the exceptional shelf stability of silicone bases containing WPH silica. The optical properties of silicone elastomers reinforced with WPH silica is described in Part III of this series of papers.

The effect of humidity on the dissipation factor of polydimethylsiloxane

Residual silanol was shown to be the determining factor in the dissipation factor-relative humidity response curve for polydimethyl-siloxanes. In a PDMS gum, 60 ppm metal ion impurities had a minimal effect on the 100 Hz dissipation factor at 50% relative humidity. However, their presence resulted in a two-fold decrease in volume resistivity.