Silicon poly organosiloxanes

Many investigators have studied dissolved solutions of poly(organosiloxanes) with different side groups at silicon atoms in the macromolecule backbones [32 - 35], These works show results of the studies of the effect of the side groups origin, their disposition and the influence of hydrodynamic and conformation parameters of macromolecules. 

Also compatibilizers can be applied for two-phase systems in order to reduce the phase size and improve the properties. This method has been successfully applied in an EPDM-silicone system using a silane grafted ethylene-propylene rubber (EPR) [5]. However, the combination possibilities of poly(organosiloxane)s with thermoplastics and elastomers are still limited to special systems. 

In contrast, the synthesis of the initiator functionality and the modification of the poIy(siloxane) is only one single step for TMP using an easily available diazonium compound 2 with a yield of about 60-80 %. Structure verification and determination of the initiator group content could be done by h NMR spectroscopy. GPC analysis showed that the modified poly(organosiloxane)s retain their original molecular weights. About 4-8 initiating sites have been attached onto the silicone backbone. Due to the chromophores, AMP and TMP are yellow products. 

Polymeric initiators based on azo or triazene modified poly(organosiloxane)s can be used to synthesize graft copolymers with silicone backbone and thermoplastic side chains. The azo functionality has some advantages such as lower thermal stability, known reaction mechanism, no homopolymer formation and cleaner graft products. However, the synthesis of the triazene polymeric initiators requires fewer synthetic steps. The graft products microseparate but form stable films. 

Modification of thermoplastics or thermosets with precrosslinked poly(organosiloxane) elastic particles should impart impact strength as well as typical silicone properties, i.e., low temperature flexibility, stability against weathering, and improved chemical resistance [4]. 

Precrosslinked poly(organosiloxane) particles are composed of crosslinking trifunctional and linear difunctional siloxane units (T and D units, respectively) [5]. The molar ratios of D and T units can be varied without restrictions thus, hard spheres (fillers) as well as soft, elastic silicone particles are accessible. In this study, the siloxane particles were synthesized in emulsion. The particle size was controlled by emulsifier concentration and crosslink density highly crosslinked particles were obtained with particle diameters ranging from 20-50 nm the size of elastic particles could be varied between 70 and 150 nm. The composition of precrosslinked poly(organosiloxane) particles is summarized in Scheme 1 further, organic radicals R which can be incorporated into the partieles are listed [6,7]. 

Thermal analysis as well as particle morphology and redispersion of precrosslinked poly(organosiloxane) microparticles proved to be promising with regard to an application as potential toughening agents. This caused us to investigate the principal suitability of silicone particles as modifiers for thermoplastic polymers. 

Poly(organosiloxanes) are built up of a combination of the units R3SiO]/2 (monofunctional, abbreviated to M), R2Si02/2 (difunctional, abbreviated to D), RSi03/2 (trifunctional, abbreviated to T) and Si04/2 (tetrafunctional, abbreviated to Q). A combination of these units is chemically possible in the widest sense. In industrial silicone products R is generally a methyl- or a phenyl-group. 

Pure silicone resins are poly(organosiloxanes) with a high proportion of branching, i.e. tri-or tetra-functional siloxy groups together with di- and optionally mono-functional siloxy groups. 

Silicone PSAs are blends or reaction products of the combination of a poly-organosiloxane, such as poly(dimethyl siloxane) or its copolymers with diphenyl-siloxane or methylphenyl siloxane, with a polysiloxane resin, which is largely inorganic. Pendant vinyl groups may also be incorporated into silicone PSAs,... 

The health and environmental aspects of poly(dimethylsiloxane) fluids have been reviewed. Sea water saturated with poly(dimethylsiloxane) fluid shows no toxic activity against phytoplanktons, molluscs, crustaceans, and fish. The toxicity of the pyrolysis gases from organosiloxane polymer fluids, rubbers, and resins has been shown to be the least toxic from those of 300 materials tested. Two excellent texts have been published on the analysis of silicones both in bulk and additive forms. > A comparative study of techniques for the trace analysis of Si—H and Si—Cl groups in poly(organosiloxane)s shows that levels of 0.01 p.p.m. H and 1.0 p.p.m. Cl bonded to silicon may be determined, ... 

When a substituent on the silicon is replaced with organic groups like hydrogen, methyl or phenyl groups, it is called oiganosilane. Polymers that are long, such as i-O-Si-O, are called poly(organosiloxane). 

It may be noted that silicones are more properly referred to as poly-organosiloxanes. (The term silicone was originated by Kipping to describe compounds with empirical formula R2SiO these were originally considered to be analogous to ketones, R2CO.)... 

Silicones are semi-inorganic polymers (poly-organosiloxanes) that may be fluid, elastomeric, or resinous, depending on the types or organic groups on the silicone atoms and the extent of cross-linkage between polymer chains. An example of silicone resin structure is exhibited in Fig. 8.6. 

Poly(organosiloxanes) (slioone polymers) Most silicone polymers are either homopolymers or eopolymers of dimethylsiloxane. They have high flexibility over a wide range of temperatures. They repel water strongly. Membranes are an important application for elastomeric grades. Other applications include stopcock grease, car polishes, and anti-stick formulations. 

Hydrosilylation of unsaturated organosilicon compounds has also found several applications in molecular and polymer organosilicon chemistry. In particular, the addition of polyfunctional silicon hydrides to poly(vinyl)organosiloxane, catalyzed exclusively by Pt compounds and providing an activated cure for silicon rubber [10], has been of great practical importance. Hydrosilylation of the vinyl group at silicon seems to be effective synthetic method for preparation of oligomers and polymers with a linear or cyclolinear stmcture (polyhydrosilylation), and can occur either via the addition of dihydro-carbosilanes and -siloxanes to divinyl-silanes and -siloxanes [25, 26] or by intermolecular hydrosilylation [4] (eq. (1)). 

Hydrosilylation Cure. The addition of polyfunctional silicon hydrides to poly(vinyl)organosiloxane provides cure for silicone rubber. The commonest activated curing method is based on hydrosilylation of polydiorganosiloxanes containing small numbers of vinyl groups and Si—H groups (usually end-blocked by them) (7) (see Scheme 33). 

A number of polymers containing tin and silicon have also been synthe-sized. The poly(organostanno-organosiloxane)s (215, 217) shown in Scheme 54 were found to have improved thermal stability and lubricating properties over polysiloxane lubricating ods. ... 

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