1. Inorganic polymers Inorganic polymers are macromolecules composed of atoms other than carbon in main or back chain linked together by single or double covalent bonds.
Source: Research Gate Polyphosphazines
General properties of inorganic polymers Following are the properties of inorganic polymers. i.Inoranic polymers are stronger, harder and brittle than organic polymers. ii. At high temperature they become soft ie. Melt but do not burn (expect polymers containing sulphurs). iii. Due to stiffness and shortness of chain segment of cross linked polymer insertion of solvent molecules doesn’t take place and are less elastic than organic polymers. iv. High density of covalent bonds are present in them. v. They are mostly pure amorphous or pure crystalline in nature. vi. Most of inorganic polymers have polar units so they dissolve in polar solvents.
Classification of inorganic polymers a. Phosphorus based polymers : Polyphosphazines The inorganic polymers in which nitrogen and phosphorous catenate together resulting in the very extensive chemistry of polymeric compounds known as polyphosphazines. Source: Research Gate Where, R = -Cl in polyphosphonitrile chlorides
R = -OCH3 in polydimethoxy phosphazines
R = -OC2H5 in polydiethoxy phosphazines
i. Polyphosphonitrilic chlorides They are prepared by reaction between phosphorus pentachloride and ammonium chloride in o o presence of C6H5Cl at 120-150 C followed by heating cyclic tetramer in vacuum at 250 C forming chain polymer.
Fig : Preparation of chain polymer of polyphosphonitrilic chlorides Source : Wikipedia Fig- Trimer (Cyclic phosphonitrillic chlorides)
ii. Polydimethoxy phosphazines and polydiethoxy phosphazines They are prepared by the reaction of phosphonitrile chloride with sodium methoxide and sodium ethoxide respectively.
Properties i. Polyphosphonitrilic chlorides has high elasticity (also called inorganic rubbers), soluble in chloroform, becomes brittle when stored in moist air. ii. Polydimethoxy phosphazines and polydiethoxy phosphazines are colorless , transparent , film thermoplastics and form cyclic polymers on heating above 100oC.
Uses i. They are used as plastics necessary for making fuel hoses and baskets. ii. They are used as water proof thermoplasts as they have water repelling capacity. iii. They form foams and fibers and have lower electrical conductivity.
a. Sulphur based polymers They are inorganic polymer containing Sulphur due to its catenation property.It has two catagories. i. Linear chain polymers Polymeric Sulphur(PS)
o It is prepared by melting rombic Sulphur (S8) at 165-168 C followed by pouring of molten Sulphur into ice water. S8 is coverted to free radical which on combination with S8 produces long chains.The solid product is washes with carbon disulphide to remove S8 which if present converts polymeric Sulphur to S8.
Properties It is unstable below boiling point of Sulphur ie.114oC and gets converted to rombic Sulphur. Uses i. It is used as flame proofing fabrics known as plasticizers. ii. It is as catalyst in silicones manufacturing process.
Polymeric Sulphur nitride (SN)n
Polythiazyl also known as polymeric sulfur nitride (SN)n is an electrically conductive gold coloured polymer with metallic luster. S4N4 is source for preparation of (SN)n. At first disulphur dinitride is formed when S4N4 is vaporized at reduced pressure and passed through silver wool followed by its slow polymerization resulting polythiazyl (SN)n.
6S2Cl2 + 16NH3 S4N4 + 12NH4Cl + 8S
S4N4 + 4Ag S2N2 + 2Ag2S + N2
Source:Engineering polymers pdf KEC Properties i. It is soft, malleable and golden bronze in colour. ii. It gets moisturized slowly when left open. iii. It shows metallic conductivity and becomes super conductor at 0.26K so called as non metallic super conductor. Uses It is used for construction of digital circuit, digital computer, transformer, electric motor etc. b. Chalcogenide glass or Network polymers They are cross-linked amorphous polymers formed by reacting polyvalent elements like As,Ge, In, P, Sb etc with chalcogens (S,Se,Te). It is prepared under condition for minimizing oxidation and loss of volatization. For eg- (SiS2)n , (As2S3)n (best known chacogenide) etc.
Properties i. They are stable to acid but not to concentrated alkalies. ii. They possesses lower softening points and tensile strength. iii. They can be distilled without decomposition in vacuum. iv. They are coloured. v. Switching is observed on them which is reversible change of conductivity from lower to higher state under applied voltage. Uses i. They are used in ultra sonic delay lines, high energy particle dectector , memory device, electroluminent displays. ii. Infrared transmitting windows are made from them.