--- title: "Inorganic polymer characteristics; polyphosphazines" subject: "Engineering Chemistry" chapter: 4 key: "semester_2/engineering_chemistry:inorganic-polymer-polyphosphazines" source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/inorganic-polymer-polyphosphazines site: BCT Engineering --- # Inorganic polymer characteristics; polyphosphazines Engineering Chemistry · Chapter 4: Engineering Polymers - Asked in: 2070 Magh, 2+3 marks - Video: [Introduction To Inorganic Polymer And Polyphosphazines | M.Sc 1st Semester | @hellochemistry](https://www.youtube.com/watch?v=u6Y0bIemu4Q) — Hello Chemistry - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/inorganic-polymer-polyphosphazines - Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-4 ## Question What are the general characteristics of inorganic polymer? Describe the preparation and uses of polyphosphazines. ## Short answer Inorganic polymers have backbones of non-carbon atoms (e.g., Si–O, P–N), offering high thermal stability, non-flammability, chemical resistance, and flexibility at low temperatures. Polyphosphazines are prepared by heating PCl5 and NH4Cl to (NPCl2)n, then ring-opening polymerization; uses: flame-resistant coatings, elastomers, biomedical implants, and battery electrolytes. ## Answer #### General characteristics of inorganic polymers An **inorganic polymer** is a polymer whose backbone is made of atoms other than carbon (e.g. Si–O, P–N, S–N, B–N). Examples: silicones, polyphosphazenes, polythiazyl, plastic sulphur. General characteristics: - High thermal stability (strong backbone bonds such as Si–O, 452 kJ/mol) and non-flammability. - High chemical and oxidation resistance, and weather resistance. - Flexibility at low temperature (low glass transition temperature) because of easy rotation about Si–O or P–N bonds; many are elastomers. - Good electrical insulation (some, like (SN)ₓ, conduct). - Usually higher cost, and some are sensitive to hydrolysis. #### Polyphosphazines **Phosphonitrilic compounds (phosphazenes)** contain the –N=PX₂– unit (X = Cl, F, Br, OR, NR₂) and are formed as cyclic oligomers (NPX₂)₃, (NPX₂)₄ and long chain polymers (NPX₂)ₙ. **Preparation of phosphonitrilic chloride** 1. Phosphorus pentachloride is heated with ammonium chloride at about 120–150 °C in a solvent (chlorobenzene or sym-tetrachloroethane): n PCl₅ + n NH₄Cl → (NPCl₂)ₙ + 4n HCl The main product is the cyclic trimer (NPCl₂)₃ with some tetramer. 2. On heating the trimer at about 250 °C in a vacuum (or sealed tube), ring-opening polymerisation gives the high polymer, polydichlorophosphazene (NPCl₂)ₙ, a rubber-like substance called "inorganic rubber". ```text N / \ Cl₂P PCl₂ (NPCl₂)₃ trimer: | | six-membered ring of N N alternating N and P \ / PCl₂ ``` The P–Cl bonds are very reactive. Replacing Cl by organic groups gives stable polyorganophosphazenes: (NPCl₂)ₙ + 2n NaOCH₃ → [NP(OCH₃)₂]ₙ + 2n NaCl (polydimethoxyphosphazene) (NPCl₂)ₙ + 2n NaOC₂H₅ → [NP(OC₂H₅)₂]ₙ + 2n NaCl (polydiethoxyphosphazene) The repeating units (monomers) are therefore N=P(OCH₃)₂ and N=P(OC₂H₅)₂. **Uses:** - Flame-resistant and non-burning materials and coatings. - Elastomers (fluoroalkoxy phosphazene rubber) that stay flexible from –60 °C to 180 °C: seals, O-rings, fuel hoses and gaskets in aircraft and the oil industry. - Biomedical uses: biodegradable implants, drug delivery, artificial skin, dental materials. - Solid polymer electrolytes for lithium batteries; membranes for gas separation. - Water-repellent coatings, lubricants, hydraulic fluids and low-temperature insulation. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What defines an inorganic polymer? A. Its backbone is made of atoms other than carbon, e.g. Si–O or P–N B. It contains no organic groups at all C. Its backbone is only C–C bonds D. It is made only from minerals by melting Answer: A. An inorganic polymer has a non-carbon backbone such as Si–O, P–N, S–N or B–N. (Key point: Definition) 2. Why are many inorganic polymers flexible at low temperature? A. They are heavily cross-linked B. Easy rotation about Si–O or P–N bonds gives a low glass transition temperature C. They contain many C=C double bonds D. They are ionic crystals Answer: B. Free rotation about the backbone bonds keeps chains mobile, so they remain elastomeric when cold. (Key point: Low temperature flexibility) 3. What is the correct sequence to make polyorganophosphazenes? A. NaOR + NH3, then heat with PCl5 B. Heat (NPCl2)3 with NaOR first, then polymerise at 25 °C C. PCl5 + NH4Cl gives (NPCl2)3; heat at 250 °C gives (NPCl2)n; then replace Cl with OR or amines D. PCl3 + H2O, then polymerise Answer: C. The reactive P–Cl polymer is made first and the Cl atoms are then substituted to give stable polymers. (Key point: Preparation of polyphosphazene) 4. Which property of polyphosphazenes makes them suitable for aircraft seals and O-rings? A. They are brittle and very hard B. They conduct electricity like metals C. They dissolve in fuel D. They stay flexible from about –60 °C to 180 °C and resist flame Answer: D. Fluoroalkoxy phosphazene rubber retains flexibility over a wide temperature range and resists burning. (Key point: Uses) ## Related in Engineering Chemistry - [Inorganic polymer; network polymer of sulphur; silicones](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Ainorganic-polymer-sulphur) — Engineering Chemistry, chapter 4 - [Linear chain polymer; sulphur-based inorganic polymers](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Alinear-polymer-sulphur-inorganic) — Engineering Chemistry, chapter 4 - [Cross linked polymer; inorganic polymer; chalcogenide](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Acrosslinked-inorganic-chalcogenide) — Engineering Chemistry, chapter 4 - [Explosive characteristics; TNT preparation and uses](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aexplosive-characteristics-tnt) — Engineering Chemistry, chapter 7 - [Thermosetting polymer; uses of epoxy resin](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Athermosetting-epoxy-uses) — Engineering Chemistry, chapter 4 - [Explosive characteristics; TNT preparation](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Atnt-characteristics) — Engineering Chemistry, chapter 7 ## Related in other subjects - [Contour characteristics and uses of contour map](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Acontour-characteristics-uses) — Surveying II, chapter 4 - [Importance, uses and characteristics of DW](https://www.bctengineer.com/question.md?key=semester_7%2Fdata_mining%3Adw-importance-uses-characteristics) — Data Mining, chapter 1 - [AASHTO classification of inorganic soil](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aaashto-classify-inorganic-soil) — Soil Mechanics, chapter 3