--- title: "Cross linked polymer; inorganic polymer; chalcogenide" subject: "Engineering Chemistry" chapter: 4 key: "semester_2/engineering_chemistry:crosslinked-inorganic-chalcogenide" source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/crosslinked-inorganic-chalcogenide site: BCT Engineering --- # Cross linked polymer; inorganic polymer; chalcogenide Engineering Chemistry · Chapter 4: Engineering Polymers - Asked in: 2072 Asoj, 1+2+2 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/crosslinked-inorganic-chalcogenide - Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-4 ## Question What do you mean by cross linked polymer? What are the general characteristics of inorganic polymer? What are the engineering application of chalcogenide polymer? ## Short answer Cross-linked polymers have covalent bridges between chains forming a 3D network, e.g., Bakelite, infusible. Inorganic polymer traits: high thermal stability, non-flamability, oxidation resistance, flexibility, good insulation. Calcogenide glass engineering uses: IR lenses, phase-change memory, photocopier drums. ## Answer #### Cross-linked polymer A **cross-linked polymer** has its linear chains joined together by covalent bonds (cross-links) to form a three-dimensional network. It is hard, rigid, insoluble, infusible and does not melt on heating. Examples: Bakelite, vulcanised rubber, epoxy resin, melamine–formaldehyde. #### 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. #### Engineering applications of chalcogenide glasses - Infrared lenses, windows and fibres for thermal imaging, night vision and sensing. - Phase-change memory and rewritable optical discs (Ge–Sb–Te). - Photoreceptors in photocopiers (amorphous Se, As₂Se₃). - Switching devices, solar cells and chemical sensors. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How does a cross-linked polymer behave on heating? A. Melts easily B. Does not melt; it is hard, rigid and insoluble C. Dissolves in water D. Becomes liquid Answer: B. Covalent cross-links form a 3-D network that is infusible and insoluble. (Key point: Cross-linked polymer) 2. Why do inorganic polymers like silicones have high thermal stability? A. Weak backbone bonds B. Strong backbone bonds such as Si-O (452 kJ/mol) C. Presence of C=C D. Low molecular mass Answer: B. Strong Si-O bonds resist heat and make them non-flammable. (Key point: Thermal stability) 3. Why do many inorganic polymers stay flexible at low temperature? A. Rotation about Si-O or P-N bonds is easy, giving low glass transition temperature B. They are cross-linked C. They are ionic D. They are crystalline Answer: A. Easy rotation about the backbone gives a low Tg. (Key point: Low-temperature flexibility) 4. Which is a chalcogenide glass application? A. Photocopier photoreceptors using amorphous Se or As2Se3 B. Cooking pots C. Tyre cord D. Mattresses Answer: A. Amorphous Se and As2Se3 are used in photoreceptors, along with IR optics and phase-change memory. 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