CYF102A_32 Polymers and Polymerization PDF

Lecture No. 32 Polymers At the end of this lecture, students will be able to: Explain the various types of classification of polymers Identify a polymer on the basis of its physical properties and...

Lecture No. 32 Polymers At the end of this lecture, students will be able to: Explain the various types of classification of polymers Identify a polymer on the basis of its physical properties and structural characteristics Explain the different types of isomerism occurring in polymers Differentiate between homopolymers and copolymers 1 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Polymers - Introduction Polymer: A polymer is defined as a macromolecule formed by the repeated combination of several simple molecules (Monomers) through covalent bonds” Molecular weight(104 to 107) Example- Polyethylene, nylon, PVC, Teflon, polyester, bakelite, etc. http://www.e13.physik.tu- 2 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Polymers - Introduction What is a Monomer ? Small molecules of low molecular weight, which combine to give a polymer, are called monomers Polymerization: Polymerization defined as “the chemical reaction in which monomer is converted into polymer” Note: Monomer can’t undergo polymerization but requires the presence of a chemical called Initiator(Per oxides) or a reactive functional group (-0H, -NH, -COOH, -SH) Oligomer: Short polymer chain 3 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Polymers - Introduction Functionality of polymer: The total number of functional groups or bonding sites present in a monomer molecule is called the functionality of the monomer Degree of polymerization: The number of monomers used in the process is called degree of polymerization. 4 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Polymers 5 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Classification Polymer Basis of Classification Polymer Type Origin - Natural, Semi synthetic, Synthetic Thermal Response - Thermoplastic, Thermosetting Mode of formation - Addition, Condensation Line structure - Linear, Branched, Cross-linked Application and Physical Properties - Rubber, Plastic, Fibers Tacticity - Isotactic, Syndiotactic, Atactic Crystallinity - Non crystalline(amorphous), Semi-crystalline, Crystalline Polarity - Polar, Non polar Chain - Hetero, Homo-chain 6 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Classification of polymers Based on their origin polymer can be classified into -Natural and Synthetic polymers Natural polymers-are those which obtained from natural sources such as plants and animal Example-Cellulose, Starch, Protein, Cotton, Silk, Wool, Glycogen, etc. Synthetic polymers- are those which are synthesized from simple molecule Example-Polyethylene, polyester, Teflon, PVC, Nylon, etc. 7 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Natural Polymers Cellulose: Polymer of β-D-glucose Starch: Polymer of α-D-glucose oregonstate.edu www.rsc.org 8 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Synthetic polymers In the late 1830s, Charles Goodyear succeeded in producing a useful form of natural rubber through a process known as "vulcanization" Some 40 years later, Celluloid (a hard plastic formed from nitrocellulose) was successfully commercialized Progress in polymer science was slow until the 1930s, when nylon was developed, and was followed by materials such as vinyl, neoprene and polystyrene http://www.e13.physik.tu- 9 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Physical Properties Thermoplastic polymer: Polymer that softens when heated and hardens when cooled. Can be shaped or moulded. Usually linear or branched. Partly crystalline and partly amorphous. Thermosetting polymer: Very strong and rigid network polymer obtained due to extensive cross-linking. Cannot be reshaped once it sets. Elastomers: Polymers that can stretch and then revert to its original shape. Amorphous in nature. Have twisted, flexible chains that can straighten out on applying tension. Have a low glass transition temperature. 10 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Classification of polymers Based on their thermal behavior, they can be classified into –Thermoplastics and Thermo settings Thermoplastics: The polymer which becomes soft on heating and hard on cooling are called Thermoplatsics Examples: Polyethylene, Teflon, Plexiglas, PVC, etc. 11 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Classification of polymers Thermosettings: The polymers which undergo chemical changes and cross likings on heating and become permanently hard, rigid and infusible on cooling are called Thermo settings Examples: Phenol-formaldehyde resins, Urea-formaldehyde resin, epoxy resin,etc. 12 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Classification of polymers Based on their methods of polymerization, they can be classifieds into –Addition and condensation polymers. Addition polymers(Chain growth polymerization): – Polymers which are formed by addition of monomers (same or different )to each other without elimination of by products are called addition polymers Examples: PVC, polystyrene, Teflon, polyethylene, etc. 13 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Classification of polymers Condensation polymers(step growth polymerization): – The polymers which are formed by intermolecular condensation reaction through functional groups of monomers with continuous elimination of by products are called condensation polymers Examples: Nylons, polyesters, phenol-formaldehyde resin, etc. 14 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences Ra Ra Mechanism of addition polymerization of ethylene Free radical addition polymerization takes place in three distinct steps i)Initiation ii) Propagation iii) Termination 15 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Mechanism of addition polymerization Termination through disproportionation: | | | | | | | | | | | | R-O-C-C-C-C-C-C + C-C-C-C-C-C-O-R | | | | | | | | | | | | | | || | | | | || | | R-O-C-C-C-C-C=C- + -C-C-C-C-C-C-O-R |||| ||||| | 16 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Condensation polymers -H2O 17 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Method of Synthesis www.mn-net.com 18 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Method of Synthesis 19 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Difference between Addition polymerization and Condensation polymerization Addition polymerization Condensation polymerization Presence of double bond Reactive functional group No by product Elimination of small molecule Usually thermoplastic usually thermosetting polymer Chain growth is at one active Chain growth will be on both sides centre Initiator required No initiator required Chains not active after Ends remain active (no termination termination) PVC, Polyethylene, etc Bakelite, nylon, etc 20 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Quiz Identify the polymer, A) (C2H4), B) (C2H4)5, C) (C2H4)10, D) (C2H4)2000 Identify the degree of polymerization, A) (C2H4)500, B) (C2H4)2000 Rubber can be classified as ----------- type of polymer. Which type of polymers can be reshaped by heating repeatedly? Why the chain ends remain active (no termination) in condensation polymerization? 21 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences  Summary Polymers and their classification Origin - Natural, Semi synthetic, Synthetic Thermal Response - Thermoplastic, Thermosetting Mode of formation - Addition, Condensation Polymers which are formed by addition of monomers to each other without elimination of by products are called addition polymers Polymers which are formed by intermolecular condensation reaction through functional groups of monomers with continuous elimination of by products are called condensation polymers 22 Faculty of Mathematical and Physical Sciences © Ramaiah University of Applied Sciences