Presentation by: Sitanshu Kumar

1. Inorganic Polymers Silicones & Phosphazenes Presentation by: Sitanshu Kumar

2. Introduction “Inorganic polymer” Main chain element is organized Ⅲ~Ⅵ group element. Especially, boron, silcon, phosphorous, germanium. and sulfur. Properties • low temperature flexibility • high thermal and oxidative stability • flame retardancy • novel forms of chemical reactivity Structures and Classification Classical main group inorganic polymers Polysiloxanes Polysilanes Polyphosphazene New Polymers Based on Main Group Elements Poly(carbosilane)s Polygermanes & Polystannanes

3. Polysilanes • In the 1920s, first silane polymer by Kipping. • In the late 1970s, soluble and processable polysilane • Synthesis method • Wurtz coupling polymerization Adv. : High molecular weight Disadv. : Low yield Side product

4. Synthesis Dehydrogenative coupling polymerization • Lower MW (Mn.<.8000) than Wurtz - coupling • Slow rate of reaction • Transition metal catalyst Advanced method for high MW • Reduced amount of solvent • Low temp. • Slow addition rate of silane • New catalyst Ultrasonic polymerization Masked disilenes

5. Electrochemical polymerization: • •Unlike the wurtz methods, • Very low temperature • Potential required for reductive • formation(-1.3 to -2.1V) • Polysilane forms initially coating on the • cathode

6. Applications Conductive polysilane 1 2 3 4

7. Polysiloxane or Silicones Polysiloxanes were first developed in the 1930s and 1940s. Silicon (Si) Silica Silanes Siloxanes Silsesquioxanes Synthesis method & Ring Opening Polymerisation or Equillibriation reaction

8. Chemical reactions: Hydrolysis Condensation And / or Net Reaction: Solvent Swollen SiO2 Matrix

9. Properties: • Highly thermally and chemically stable. • Water repellent. • Used for low temp. lubrication. • LMW silicon polymers are soluble in organic solvents. • Good insulators. • Resistant to oxidation. • Have non-sticking and anti-foaming properties. Applications: • Used as greases, varnishes and lubricants. • Used for water proofing in electrical condensers. • Also used for various purposes at low temperatures. • Used in medicinal and cosmetic implants because of low toxicity. • Used for high temp. oil baths, high vaccum pumps, etc.

10. Silicone fluids are linear polysiloxanes of 50-200 units. • Prepared by treating a mixture of tetrakiscyclodimethyl siloxanes and hexamethyldisiloxane with a small quantity of 100% sulphuric acid. • These are used as water repellents, insulating material, hydraulic oils and various lubrication purposes. • Used in processing of cooking oils and fruit juices due to its non-toxicity. • Silicone elastomers are long chain polymers made of 6000-600000 silicone units. • Have high molecular weights. • These can be vulcanised to give rubber. • Vulcanisation is the formation of cross-linked chains. • Silicone resins are solvent solutions of branched chain siloxanes containing residual hydroxyl groups. Silicone fluids & Silicone elastomers

11. Polyphosphazenes The phosphazene backbone possesses a unique range of unusual properties. Poly phosphazenes are also of interest as biomedical materials, bioinert, bioactive, membrane forming, and bioerodable materials. Synthesis method

12. Neilson and Wisian-Neilson method De Janger method N-silyl-P-(trifluoroethoxy)phosphoranimine R=alkyl or aryl Matyjaszewski method Synthesis operates at room temperature and allows molecular weight control. N-silylphosphoranimine R=alkyl or aryl

13. Applications: • Halides of phosphazenes are used as rigid plastics, expanded foam and fibres. • Used as water and fire proof materials. • These are unaffected by oil, petrol and other solvents. • Used as catalysts in manufacturing of silicones. • Used as flexible plastics.

14. Structure and bonding

15. The halide trimers consist of planar six membered rings. • The bond angles are consistent with SP2 hybridization of the nitrogen and approximately SP3 hybridization of the phosphorous. • Two of the SP2 orbital of nitrogen, containing one electron each, are used for 's' bonding and the third contains a lone pair of electron. This leaves one electron for the unhybridised PZ orbital. • The four SP3 hybrid orbital (containing four electrons) of phosphorous are used for 's' bonding leaving a fifth electron to occupy a 'd' orbital. • All phosphazenes are not planar. • The dxz orbital of the phosphorous atom overlaps with the pz orbital of the nitrogen atom adjacent to it. • The dyz orbital which is perpendicular to the dxz, can also overlap with the p z orbital of Nitrogen. • There may be in–plane – P bonding between the sp2 non bonding orbital of nitrogen and the dxy and for dx2 – y2 orbital of the phosphorous. Structure studies

16. Nature of bonding (Orbital form)