Polymers Notes PDF

# Polymer The compound formed by a large number of small molecules (monomer) linked together are known as POLYMER. The molecule that forms the basic unit for structure. ## Classification of Polymer ### On the Basis of: - Nature of monomer - Structure - Synthesis - Origin/Source - Intermolecular fo...

# Polymer The compound formed by a large number of small molecules (monomer) linked together are known as POLYMER. The molecule that forms the basic unit for structure. ## Classification of Polymer ### On the Basis of: - Nature of monomer - Structure - Synthesis - Origin/Source - Intermolecular forces ### On the Basis of Origin #### Natural - Found in nature - Examples: Cellulose, Starch, Silk, Protein #### Synthetic - Man-made Polymer - Examples: Nylon, PVC, Polythene #### Semi-synthetic - It is obtained from naturally occurring polymer by chemical treatment. Most of semisynthetic polymer are prepared - Examples: Cellulose acetate, from cellulose. Cellulose nitrate. ### On the Basis of Structure #### Linear - Examples: HDPE - Polymer comprising of long and straight chain. - The various linear polymer change are stacked over one another to give a well-packed structure, having high density, high melting point, high tensile strength. #### Branched - Polymer in which monomeric unit constitute a branched chain. - Branched chain polymers have low MP, low density, low tensile strength. - Examples: LDPE, Amylopectin etc. #### Cross-linked - When linear polymer chain are joined together to form a three dimensional network structure. - This polymer has hard, brittle, rigid. - Examples: Bakelite, Resin - Condensation polymerization. ### On the Basis of Nature of Monomer #### Homopolymer - Comprising of only one type of monomeric unit. - Examples: Polyethylene, PVC etc #### Heteropolymer - comprising of more than one type of monomeric unit. - Examples: Nylon 6,6 ### On the Basis of Tacticity (Arrangement) - Isotactic - Regular arrangement. - Atactic - Random Arrangement - Syndiotactic - Alternate arrangement ### On the Basis of Intermolecular force #### Elastomers - Intermolecular force of attraction is low. - Examples: Rubber (Buna-s), Buna-N etc #### Fibers - Intermolecular force of attraction are strong. - These polymers are held together by H-bonding. - Examples: Nylon-6,6, Kevlar #### Thermo Plastic - Intermolecular force of attraction are in between those of elastomers & fibers. - Become soft & viscous on heating. - Examples: Polythene, Nylon #### Thermo setting - Is semi-fluid & viscous on heating. - Substance is hard and infusible. ## On the Basis of Polymerisation ### Addition Polymerisation / Chain Growth Polymer - Is a chain rxn which on initiated propagate itself till the change is not terminating. - Formed by addition oxy. - For addition poly. to take place, the monomer must be unsaturated. - If monomer is ethylene, then addition polymerisation may be either linear polymer or branched polymer. - Examples: - CH₂=CH-CH=CH₂ Monomer - [-CH₂-CH=CH-CH₂-] Branched polymer ### Types of Addition Polymerisation #### Free-Radical Polymerisation - Take place in presence of Radical initiator such as dioxygen, benzoyl peroxide, acetyl peroxide etc. ### Mechanism 1. **Chain-initiating step** : - [C₆H₅-C-0-0-C-C₆H₅] Benzoyl peroxide (Homolytic cleavage) - [C₆H₅-C-0] Benzoyl radical *+ 2 C₆H₅ -(phenyl free radical) 2. **Chain-propagating step** : - C₆H₅ + H₂C=CH₂ -> C₆H₅-CH₂-CH₂ + CH₂=CH₂ 3. **Chain-terminating step** : - **By combination of 2 free radical:** - C₆H₅-(CH₂-CH₂)n-CH₂ + CH₂-CH₂-(CH₂-CH₂)n-C₆H₅ -> C₆H₅-(CH₂-CH₂)2n-CH₂-CH₂-(CH₂-CH₂)n-C₆H₅ - **By disproportionation of free radical:** - C₆H₅-(CH₂-CH₂)n-CH₂ + CH₂-CH₂-(CH₂-CH₂)n-C₆H₅ -> C₆H₅-(CH₂-CH₂)n-CH₃ + CH₂=CH-(CH₂-CH₂)n-C₆H₅ ### Anionic Polymerisation - It takes place in the presence of strong bases such as KNH₂, NaOH, KOH. - Some organometallic compound. ### Cationic Polymerisation - It takes place in the presence of strong protonic acid such as H₂SO₄, AlCl₃, BF₃ etc. ### Condensation Polymerization - Also known as step-growth polymerisation. - Formed due to condensation rxn - Monomers should have at least 2 FG (same or diff) - During condensation, elimination of small molecules eq. ammonia, alcohol, water, HCl take place. - Example: - nH₂N-R-NH₂ + n/HO-C-R-C-OH -> [-HN-R-NH-C-R-C-OH]n + nH₂O (Polyamide) ### Types Of Condensation Polymerization - **Monomer with 2 FG:** Always give linear polymer - **Monomer with ≥3 FG:** Always give cross-lined polymer ### Comparison of Addition and Condensation Polymerization - **Addition:** - Monomer must have either = or ≡ - Result in no by-product. - Addition of monomer result in formation of polymer. - Lewis acid Juni Base. - LA, LB, radical initiators are catalyst in addition polymerisation. - Thermoplastic are produced. - No elimination of by-product. - Homo-chain polymer is obtained - Example: Polyethylene, PVC etc. - **Condensation:** - Monomer must have 2 similar or diff FG - Result in by-product such as NH₃, H₂O, HCl. - Condensation rxn blw monomers result in formation of polymer. - diff molecules are used as catalyst in condensation polymerisation - Thermosetting plastics are produced. - Elimination of by-product. - Heterochain polymer is obtained. - Example: Bakelite, Urea-formaldehyde. ### Anionic Polymerisation - Polymerization: - H-C=C-CN | H Acrylonitrile - [H-C=C-CN]n | H Polyacrylonitrile /Acrilan. 1. **Chain Initiator:** (Anion initiator add to è deficient site of monomer resulting in formation of carbanions initiating poly). - Bu - Li + CH₂=CH - CN -> Bu – CH₂ - CH - CN (Stable anion) 2. **Chain propagation:** (Carbanion adds to double bond of another monomer generating) - Bu-CH₂-CH-CN + CH₂=CH-CN -> [Bu-CH₂-CH-CH₂-CH-CN]n 3. **Chain termination:** Polymerize anionic chain is quite stable & continues to grow until terminated by addition of an acid. ### Cationic Polymerisation 1. **Initiation:** add" of cation to double bond of monomer leads to formation of carbonium ion initiating rxn. - H+ + CH₂=CH-R -> CH₃-CH-R 2. **Propogation:** carbonium ions adds to double bond of another monomer generating a bigger carbonium ion. - CH₃-CH-R + CH₂=CH-R -> CH₃-CH-CH₂-CH-R 3. **Termination:** by removal of H+ - CH₃-CH-CH₂-CH-R + CH₂=CH-R -> [CH₃-CH-CH₂-CH]n-CH-CH₂-R ## Specific Polymer ### **1. Nylon 6,6** - **Obtained** by condensation polymerisation of diamine with 6C atoms (hexamethylenediamine) and dibasic acid having 6C atom. (Adipic acid) - n HOOC (CH₂)₄COOH + H₂N (CH₂)₆ NH₂ -> [OC(CH₂)₄CONH(CH₂)₆]n (nylon 6,6) - **Properties:** - White, translucent with high MP. - Insoluble in organic solvent. - Have good mechanical strength, elasticity to abrasion resistance. - Good electrical insulator. - **Application:** - Used as fibers to make carpet, socke, shoes etc. - Used as tapes, toothbrush brietts. - Used for electrical insulator & as ball bearing. ### **2. PVC (Polyvinyl Chloride)** - **Obtained** by addition polymerisation. - n (CH₂=CH-Cl) -> [-CH₂-CH-Cl]n (polyvinylchloride (PVC)) - **Properties:** - Colourless, odourless, non-inflammable. - Resistance to weathering. - **Application:** - used for making pipes for drainage. - Making window, frames & bottles. - Making rain wear. ### 3. Teflon (PTFE) polytetrafluoroethylene - **Manufactured** by heating tetrafluroethylene in presence of peroxide or ammonium persillphate catalyst at high pressure. - n F₂C = CF₂ -> [-F₂C - CF₂]n (Polytetrafluroethene (PTFE) or teflon) - **Properties:** - Excellent resistant to heat. - Great resistance to chemical & oil. - Anti-rusting properties. - **Application:** - Used for making non-stick utensils. - Used as wire & cable in insulation. ### 4. Kevlar - **Formed** by condensation polymerisation - n [C=C -Terephthalaydide ] + nH₂N - p-phenylene diamine [NH₂] -> [-C-O-C-NH-C-O-NH]n - Poly- (p-phenylene diamine) Kevlar - **Properties:** - Extra-ordinary mechanical prop. - High tensile strength due to extensive H-bonding. - Extreme chemical. - Known for its ability to be spun into fibers that have 5-time more tensile strength to steel. - **Application:** - In fabrication of protective wear including bullet proof vest. - Extensively used as in aerospace & aero craft industries. ### 5. Polyester - **Synthetic fiber.** - Ethylene glycol + terephthalic acid -> Polyethylene terephthalate (PET) (recyclable) - **Uses:** - Used in clothing fabrics - In manufacture of many home furnishing material such as bedsheet, blanket. - Manufacture in mouse pad, seatbelt. - Highly resistant to staining, use as tablecloth. - LCD are manufactured. - **Properties:** - Strong, durable. - Resistant to shrinking, streching. - Dries quickly. - Can be recycled. - Retain heat set pleads ### Biodegradable Polymer - Defined as polymer comprised of monomers linked to one another through F-G & have unstable link in backbone. - They are broken down into biologically acceptable molecules that are degraded by microorganism such as bacteria, fungi, algae. - **Mechanism:** Enzyme Degradation, Hydrolysis, Combination - **Biodegradable Polymers:** - **Natural B-P:** - Produced in nature - Example: PHA - **Synthetic B.P:** - Produced by mankind - Example: PLA - **Application:** - Food packaging - Electrical appliances & electronics. - Adhesive, paint & coating. - Hygiene product. - Agriculture & soil stabilization. ### 1. PHBV (poly B hydroxy butyrate co- B hydroxy v) - **Obtained** by co-polymerization of: - CH₃-CH-CH₂-COOH + CH₂-CH₂-COOH -> - [-O-CO-CH₂-CH-S-O-CH₂-CH₂-C-O-CH₂-CH₂-]n - (PHBV) - **Used** in: - Packaging - Orthopedic devices - Controlled release of drugs. - PHBV undergo bacterias degradation in environment. ### PCA (polyglycolic acid) - 1 mol % TiFor, DCM - 800 psi CO, 170°, 3 days -> [O]n poly glycolic acid ### Coordination Polymerisation - In coordination addition polymerisation an organometallic active intermediate act as initiator. - This involves use of zieglar - nalla catalyst. 1. **Chain initiation:** - Transition metal serves as active site. - R-Al-R + Till₄ -> R-Al-R + Till₄ -> R-Al-R + Till₄ 2. **Propogation:** Migration of alkene monomer b/w metal & altyl group inhata polymerisation by formation of 7 metal complex & continue. 3. **Termination:** Occur when monomer migrate & forms an inactive site - stop rxn. ## Structure Properties Relationship of Polymer - Depends on size (of polymer chain, shape) - Chemical nature of monomer, affect physical & mechanical propesties of polymer. 1. **STRENGTH** - Melt viscosity, impact, tensile strength are few mechanical prop. of polymer, - Good polymer - low melt viscosity, high tensile & impact strength. 2. **Crystallinity** - Polymer consist of crystalline & amorphous parts. - Imp as crystalline is regularity of molecular structure with greater symmetry, s.t polymer chain can pack up closed in an order structure. - Linear polymer has high crystallinity, bcoz atoms along chain permit closer approach. - Depend on stereo regular arrangement. - Isotactic & syndiotactic polymer are highly crystalline 3. **Elasticity** - Due to uncoiling & reveiling of molecular chain on application of force. - For a polymer to show elasticity, individual starts chain should not break on prolonged streching. - To avoid: Introduce cross-linking - Avoid bulky side group - To avoid elastomeric material, any factor that introduce crystallinity should be avoided. 4. **Plastic Deformation:** - Studied by applying heat & pressure. - Thermoplastic D: Become soft, flexible & undergo deformation. This prop is called plastic deformation. Back to original on cooling. This is called moulding operation. - Thermosetting plastic: - On strong treating, degradation occur instead of plastic deformation due to breaking of covalent bond. - Not exhibit plastic deformation. 5. **Tensile strength** - Quantities how much stress the polymer will endure before failing. - Change with change in polymer structure. - Branched < lineas < cross-linked. 6. **Solubility** - Ability of polymer to dissolve in a solvent. - ↑ with short branch - ↓ with long branch & cross linking 7. **Glass transition temperature (Tg)** - Temp at which a polymer transition from a hard, glassy material to soft, rubbery material. - Tg depends on ability of a chain to undergo internal rotation. 0 Higher the freedom of rotation, more flexible the chain is. - Big bulky group lower the Tg. ## Commerical Thermoplastics ### 1. Polyethylene - Homopolymers of ethylene. - Commercial Thermoplastics of ethylene produced by add polymerization. - LDPE - Low density polyethylene - HDPE - High density polyethylene #### LDPE (low density polyethylene) - Linear polymer with branching. - n(H₂=CH₂) + benzoyl peroxide -> [-CH₂-CH₂]n (Polyethylene) - Initiators used : benzoyl peroxide & oxygen - Properties: - White waxy & translucent material which floats in water. - Flexible & tough. - Inert & good resistance to acid & alkali. - High impact strength, less brittle. - Insulation prop. - Application: - Manufacturing of transparent films for food, etc. - Products of squeeze bottle, sheets. - Cable & wire insulate. #### HDPE (high density polyethylene) - Linear polymer with little or no branching. - n (CH₂=CH₂) -> [- CH₂-CH₂]n (Polyethylene) - Propesties: - Higher density than LDPE. - Higher rigidity than LDPE. - Better Chemical resistance than LDPE. - Better stiffness, toughness & heat resistance. - Opaque. - Application: - Manufacture of dustbin, cans, drum. - Manufacture of wire & cable insulate. - Manufacture of full tank. ## Commerical Thermosetting Resin ### A) Phenol formaldehyde Resins - Condensation b/w phenol & formaldehyde using acid/base as catalyst. - Novolac - Whereas cross linking of novolac can be done by adding excess of formaldehyde & heating - Res ol -> final product - Both resins give highly cross-linked product. ### Bakelite - Bakelite is rigid, hard, scratch resistance material. - It shows good electrical insulat prop. - It has thermal stability. - Resistant of water. ### Rice Applications - Making electrical equipment part such as switches, plug, switchboard. - Making goy ball. - Used as hot setting adhesive. ### Elastomers - Polymers which undergo high degree of elongation when subjected to external force. This property is called elasticity. ### Elastomers - Natural & Synthetic - **Natural rubber:** is obtained from milk (latex) obtained from trees. - **Rubber** is polymer of isoprene hence also called polyisoprene. In linear polyisoprene - n (CH₂=C=CH-CH₂ ) -> [(CH₂-C=CH-CH₂)]n (Polyisoprene) - **Isoprene** - isoprene (Cis-1,4 polyisoprens (CH₂)n -> [CH₂ = C - CH -CH₂]n (from trees) - Natural rubber is cis-1,4 polyisoprens. - Trans isomer of polyisoprene, hard & brittle. - [CH₂=C= CH₂- CH₂]n (From gutta-percha (CH₂)n) ### Drawbacks of Natural Rubber - Becomes hard & brittle at low temp & soft & sticky at high temp. - High water absorbent capacity - Weak tensile strength - Poor abrasion resistance - To overcome, it is subjected to processes such as vulcanization. ### Vulcanization - Process of heating of mixing rubber with sulphur to a definite temp. It modifies it to become more durable with better mechanical prop. - The extent of stiffness of vulcanized rubber depend on amount of sulphur added. - A rubber tyse contain 3-5%. Sulphur. ### Properties - Good Tensile strength - Excellent resistance - Low water alsospth capacity - Good exelectrical insulation prop. ### Synthetic Rubber - Advantage: - More economical than natural rubber. - Low temp flexibility & high temp stability. - Produced using monomer derived from petrochemical saw material. Example: neoprene, Buna sublars