Polymers and omposite Materials Shibu G. Pillai hemical Engineering Department shibu.pillai@nirmauni.ac.in
ontents lassification of Polymers Types of polymerization Elastomers/ Rubber Advanced Polymeric Material Biopolymers omposite Materials
POLYMERS (the whole train) are made out of MONOMERS (individual cars of the train) joined together.
Polymers: Introduction Polymer: igh molecular weight molecule made up of a small repeat unit (monomer). A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A- Monomer: Low molecular weight compound that can be connected together to give a polymer Oligomer: Short polymer chain (unit 6-12)
lassification of Polymers I. On the basis of SOURE or ORIGIN (onventional lassification) (a) Natural/Biopolymers (found in nature) examples: cellulose, rubber, RNA, DNA, protein (b) Semi-synthetic polymers (main source is nature but with some modification as per our need) examples: cellulose-nitrate,-acetate, vulcanized rubber etc. (c) Synthetic Polymers (which are prepared in the lab/industries) examples: polyethene, PV, nylon, polyester etc.
II. Depending upon the mode of synthesis a) Addition Polymer b) ondensation polymer ADDITION POLYMER When the monomer units are repeatedly added to form long chains without the elimination of any by-product molecules, the product formed is called addition polymers Examples: polyethene, PV, Teflon, polyurethane, SBR etc.
ONDENSATION POLYMER When the monomer units are react together, with the elimination of by-product molecules such as water, carbon dioxide, l, ammonia alcohol etc., the product formed is called condensation polymers Examples: nylon-6, nylon-6,6, epoxy resins, UF resins, Kevlar (polyamide) etc.
III. Depending upon the nature of the repeating structural units a) omo-polymer b) o-polymer OMO-POLYMER The polymer formed from one kind of monomers, called homo-polymer. Examples: Polyethene, PV, Teflon, etc.
Types of omo-polymer a) Linear b) Branched c) ross-linked Linear polymers These polymers consist of long and straight chains. Examples are high density polythene, PV, etc.
Branched Polymers These polymers contain linear chains having some branches, e.g., Examples are low density polythene, amylopectine etc.
ross-linked Polymers Monomeric units are linked together to constitute a 3-dimensional network structure ard and rigid Example: vulcanized rubber etc.
O-POLYMER The polymer formed from more than one kind of monomers, called co-polymer. Examples: Terylene, Nylon-6,6, SBR, Saran, Kevlar etc.
Types of o-polymer
IV. Based on molecular forces/applications polymer applications in different fields depend on their unique mechanical properties like tensile strength, elasticity, toughness, etc. These mechanical properties are governed by intermolecular forces, e.g., van der Waals forces and hydrogen bonds, present in the polymer. the polymers are classified on the basis of magnitude of intermolecular forces present in them. a) Elastomers (b) Fibers (c) Plastic
Elastomers These are rubber like solids with elastic properties. the polymer chains are held together by the weakest intermolecular forces. These weak binding forces permit the polymer to be stretched. A few crosslinks are introduced in between the chains, which help the polymer to retract to its original position after the force is released as in vulcanised rubber. The examples are buna-s, buna-n, neoprene
Fibers Fibres are the thread forming solids which possess high tensile These characteristics can be attributed to the strong intermolecular forces like hydrogen bonding. These strong forces also lead to close packing of chains and thus impart crystalline nature. Examples are polyamides (nylon 6, 6), polyesters (terylene)
Thermoplastic Polymers These are the linear or slightly branched long chain molecules capable of repeatedly softening on heating and hardening on cooling. These polymers possess intermolecular forces of attraction intermediate between elastomers and fibres. Some common thermoplastics are polythene, polystyrene, polyvinyls, etc
Thermosetting Polymers These polymers are cross linked or heavily branched molecules, which on heating undergo extensive cross linking. chain motion is greatly restricted by a high degree of crosslinking. These cannot be reused. Some common examples are bakelite, urea-formaldelyde resins, epoxy resins etc.
Types of Polymerization I. Addition Polymerization II. ondensation Polymerization
Addition polymerization the molecules of the same monomer or different monomers add together on a large scale to form a polymer. The monomers used are unsaturated compounds, e.g., alkenes, alkadienes and their derivatives. This mode of polymerisation leading to an increase in chain length or chain growth can take place through the formation of either free radicals or ionic species. owever, the free radical governed addition or chain growth polymerisation is the most common mode.
Examples of Addition polymerization
ondensation polymerization Polymerization generally involves a repetitive condensation reaction between two bi-functional monomers. These poly-condensation reactions may result in the loss of some simple molecules as water, alcohol, etc., and lead to the formation of high molecular mass polymers. In these reactions, the product of each step is again a bi-functional species and the sequence of condensation goes on. Since, each step produces a distinct functionalised species and is independent of each other, this process is also called as step growth polymerisation
Examples of condensation polymerization
Examples of condensation polymerization
Rubber
Tacticity Tacticity stereoregularity or spatial arrangement of R units along chain R R R R isotactic all R groups on same side of chain R R R R syndiotactic R groups alternate sides
Tacticity (cont.) atactic R groups randomly positioned R R R R
Biopolymer I. Starch II. ellulose
Glucose Structural formula. Straight chain glucose 1 -=O 2 --O 3 O-- 4 --O 5 --O 6 2 O bends Glucose glucose bending Glucose bends itself into 4 different shapes millions of times a second flips either way Used in making starch Used in making cellulose Glucose Two ring-shape versions alpha-glucose beta-glucose
4 1 4 1 Glucose Glucose (a) and glucose ring structures
1 4 (b) Starch: 1 4 linkage of glucose monomers 1 4 (c) ellulose: 1 4 linkage of glucose monomers