Mid-Sem Assignmrnt
The word polymer is derived from greek words, poly= many and mers=
parts or units.
Polymers are giant molecules of high molecular weight, called macromolecules, which are build up by linking together of a large number of small molecules, called monomers.
The reaction by which the monomers combine to form polymer is known as polymerization
The number of repeating units in chain formed in a polymer is known as the "degree of polymerization(DP).
Definition of Polymer
Homopolymers – Synthesized from a single type of monomer.
Example : polyethylene and polypropylene.
These may be represented as : -[A-A-A-A-A-A]-
Copolymers – formed from two or more different types of monomers are called copolymers. These may be represented as : -[A-B-A-B-A-B]-
Orientation of monomeric units in polymer takes place in orderly/disorderly fashion with respect to main chain. The difference in configuration affects their physical properties.
Isotactic: Head-to-tail configuration Functional groups are all on the same side of the main chain, Functional group(FG)= Y
Tacticity
Syndiotactic: Functional groups occupy alternating position. Eg: gutta percha
Atactic: Functional groups arranged in random manner For example:polypropylene
CLASSIFICATION OF POLYMERS
Polymer can have different chemical structure, physical properties, mechanical behavior, thermal characteristics, etc., and on the basis of these properties polymer can be classified in different ways,
1. Natural polymers
These polymers are found in plants and animals.
Examples:
proteins, cellulose, starch, some resins and rubber.
Teflon 2. Synthetic polymers
Manmade polymers extensively used in daily life as well as in industry
Examples:
plastic (polythene), synthetic fibres (nylon 6,6) and synthetic rubbers (Buna - S)
On the Basis of Origin
Basis of THERMAL RESPONSE
a) Thermoplastic polymers:
Linear long chain polymers which can be softened on heating and hardened on cooling
Hardness is temporary property Can be processed again and again
Examples: PE, PP, PVC, PS, Teflon, Nylon
b) Thermosetting polymers (thermosets):
Permanent setting polymers
Three dimensional cross linked structure with strong covalent bonds
Cannot be reprocessed
Examples: Polyester, bakelite, epoxy resins, urea formaldehyde resin
Thermoplastics vs. Thermosetting plastics
Thermoplastics
1. Soften on heating 2. Long chain linear
3. By addition polymerisation
4. Can be reshaped and reused 5. Soft weak and less brittle 6. Soluble in organic solvents 7. Reclaimed for wastes
Thermosetting polymers
1. Do not soften on heating 2. 3-D structure
3. By condensation polymerisation
4. Can not be reshaped 5. Hard and strong
6. Insoluble in organic solvents.
7. Can not be reclaimed
On the basis of structure
1. Linear polymers
Monomeric units are joined in the form of long straight chain
Posess high m.p, density and tensile strength due to close packing of polymer chain Examples: High density polythene (HDPE), Nylons, polyester
2. Branched chain polymers
Mainly linear in nature with some branching along the main chain.
Posess low m.p, density, and tensile strength due to poor packing of polymer chain in the presence of branches.
Examples: low density polyethene (IDPE), glycogen, amylopectin 3. Three dimensional network polymers (cross-linked)
Gaint molecules in which contain strong covalent bonds (cross link) between various linear polymer chains
Hard, rigid, brittle, do not melt but burn on strong heating due to the presence of cross links
Example: bakelite, urea-formaldehyde , melamine-formaldehyde
Types of Polymerisation
A. Addition polymers:-
The polymers which are formed by an addition reaction, where many monomers bond together via rearrangement of bonds without the loss of any atom or molecule. Their empirical formulae is same that of their monomers.
Examples of such polymers are polyethylene, polypropylene, polystyrene.
Types of Addition Reaction
Homopolymers
Copolymers
addition polymers which involve the reaction of unsaturated monomers
1. However, the addition polymers formed by the polymerisation of a single monomeric species are known as homopolymers, e.g., polythene.
2. The polymers made by addition polymerisation from two different monomers are termed as copolymers, e.g., Buna-S, Buna-N, etc.
B. Condensation polymers:
In condensation reaction—where molecules join together—losing small molecules as by-products such as water or methanol.
Examples are nylon-66, bakelite and polyester etc.
Difference Between Addition and Condensation Polymers
Addition Polymers Condensation Polymers
Formed by addition reaction. Formed by condensation process with elimination of small molecules like H
2O.
Molecular mass is a whole number multiple of the monomer.
Molecular mass is not whole number multiple of the monomer units.
Generally involve one monomer unit. Generally involve more than one monomer unit.
Monomers are unsaturated molecules. Monomer units must have two active functional groups.
They are generally chain growth polymers. They are generally step growth polymers.
Mechanism of Polymerisation
1. Free radical mechanism of polymerization
2. Cationic mechanism of polymerization
3. Anionic mechanism of polymerization
FREE RADICAL Polymerization
Free radical polymerization of vinyl chloride involves the following steps:
1. Chain initiating step 2. Chain propagating step 3. Chain Termination Step
Introduction:
A variety of alkenes or dienes and their derivatives are polymerized in the presence of a free radical generating initiator (catalyst) like benzoyl peroxide, acetyl peroxide, tert-butyl peroxide, etc.
1. Initiation step
The polymerisation of vinyl chloride to polvinyl chloride (PVC) consists of heating or exposing to light a mixture of vinyl chloride with a small amount of benzoyl peroxide initiator. The process starts with the addition of phenyl free radical formed by the peroxide to the vinyl chloride double bond thus generating a new and larger free radical. This step is called chain initiating step.
As this radical reacts with another molecule of vinyl chloride , another bigger sized radical is formed. The repetition of this sequence with new and bigger radicals carries the reaction forward and the step is termed as chain propagating step.
2. Propagating step
Ultimately, at some stage the product radical thus formed reacts with another radical to form the polymerized product. This step is called the chain terminating step.
3. Terminating step
Termination can occur by two different mechanism which are given below:
(a). By coupling or combination
(b). By disproportionation in which hydrogen atom of one radical center is transferred to another radical center. This results in the formation of two polymer molecules, one saturated and one unsaturated, e.g.,
Cationic Mechanism
Chain Initiation Step
Chain Propagation Step
Chain Termination Step
Anionic Mechanism
Chain Initiation Step
Chain Propagation Step
Chain Termination Step
Plastics
It is an organic material of high molecular weight, which can be moulded into any desired shape, when subjected to heat and pressure in the presence of a catalyst.
Properties of plastic
Low density
To make low weight with high strength
Anti friction & self lubrication sometimes achieved
Corrosion resistance, water proofing & noise less operation of moving path
Low in cost
Insulation of heat & electricity
Chemically stable
Less brittle
Good toughness
Easily moulded
Colour ability
Advantages and Disadvantages of Plastic
Some of the Advantages of Plastic are:
1.Plastic is available at low cost.
2.Plastic is strong and water and chemical resistant.
3.Plastic is light in weight.
4.Various products of plastic are available for household and other purposes.
5.Plastic is also more flexible than glass.
6.Plastic consumes very less energy for recycle compared to glass.
7.Plastic is usually used for packaging of various products.
8.Plastic is odourless and unbreakable.
9.Plastics are durable.
Some of the Disadvantages of Plastic are:
1.Plastics are non renewable.
2.Plastic causes water and land pollution.
3.Some plastics causes highly toxic fumes when they are allowed to burn.
4.Plastics are non biodegradable.
5.Plastic bags or its products present in water or land are harmful for marine animals or animals on land respectively.
Thermoplastics: Preparation, properties
and applications: Cellulose acetate, PS,
PVC, Nylons and PTFE
Thermoplastics
No cross links between chains.
Weak attractive forces between chains broken by warming.
Change shape - can be remoulded.
Weak forces reform in new shape when cold.
Polystyrene (PS) is obtained by the polymerization of styrene (dissolved in ethyl benzene) in presence of benzoyl peroxide catalyst.
Polystyrene (PS)
Properties:
Transparent, light in weight, light-stable and excellent moisture resistant.
Good electric insulation, high resistant to acids and other chemicals.
USES
Toys, combs, buttons, buckles, radio and television parts, refrigerator parts, battery cases, lenses, indoor lightening –panels etc,.
Disadvantages:
Low softening temperature (90-100 oC) and brittle.
Transmitting light through curved surfaces
Poly Vinyl Chloride (PVC)
It is obtained by heating a water emulsion of Vinyl chloride in presence of small amounts of benzyl peroxide or hydrogen peroxide in an auto clave under pressure.
Properties
PVC is a colourless, odourless, inflammable chemically inert, resistant to light, atmospheric oxygen, inorganic acids, alkalies but soluble in hot chlorinated hydrocarbons such as ethyl chloride
Greater stiffness and rigidity compared to PE but is brittle
Most widely used synthetic plastic
Pure resin possesses a high softening point (148 ⁰C) and a greater stiffness.
USES
Rigid PVC has superior chemical resistance and high rigidity but is brittle
Used for making sheets which are employed for tank lining
Light fittings, safety helmets
Refrigerator components
Tyres
Cycle and motor cycle mudguards
Plasticized PVC is used for making continuous sheets which are employed in packing rain-coats, table cloths and curtains etc.
It is obtained by the polymerization of water-emulsion of tetrafluoroethylene, under pressure in presence of benzoyl peroxide as a catalyst.
Polytetrafluoroethylene (PTFE) or TEFLON
Properties:
Due to the presence of highly electronegative fluorine atoms and the regular configuration of the polytetrafluoro ethylene molecules results in a very strong attractive forces between the different chains.
These strong attractive forces give the material extreme toughness, high softening point (about 350 ⁰C), high density (2.1 to 2.3 g/cm3), waxy touch, good electrical and mechanical properties.
Uses:
As insulating material (for motors, transformer, cables )
making gaskets, packaging, pump parts and non-sticking non–stick surface coated utensils.
Nylon
These polymers possessing amide linkages are important examples of synthetic fibres and are termed as nylons. The general method of preparation consists of the condensation polymerisation of diamines with dicarboxylic acids and also of amino acids and their lactams.
Preparation of nylons (i) Nylon 6,6:
It is prepared by the condensation polymerization of hexamethylenediamine with adipic acid under high pressure and at high temperature.
Uses: Nylon 6, 6 is used in making sheets, bristles for brushes and in textile industry.
(ii) Nylon 6:
It is obtained by heating caprolactum (Ɛ-aminocaproic acid )with water at high temperature.
Uses: Nylon-6 is primarily used for moulding purposes for gears, bearing and tyre-cords, fabrics and ropes.
Properties of nylons:
They are translucent, whitish, horny, high melting (160 to 264 oC) polymers.
They possess high temperature stability and good abrasion- resistance.
They are insoluble in common organic solvents and soluble in phenol and formic acid.
CELLULOSE ACETATE
It is made by reacting natural cellulose with acetic anhydride or glacial acetic acid in the presence of a catalyst (H2SO4).
Properties
Toughness, high tensile strength, high dielectric properties
Resistance towards some mineral acids
Spun into fibers
Uses
Radio appliances, Automobile steering wheel, handles, windows, goggles, combs, musical instruments etc.
Thermosetting: Preparation, Properties
and applications of Bakelite, Polyester
and Epoxy Resins
Thermosetting: Bakelite and Polyester
Thermosetting
Extensive cross-linking formed by covalent bonds.
Bonds prevent chains moving relative to each other.
What will the properties of this type of plastic be like?
It is manufactured by heating a mixture of ethylene glycol and terephthalic acid at 420 to 460 K in the presence of zinc acetate antimony trioxide catalyst.
Dacron or terylene is the best known example of polyesters.
Polyester
Characteristics of Polyester
Polyester fabrics and fibers are extremely strong.
Polyester is very durable: resistant to most chemicals, stretching and shrinking, wrinkle resistant, mildew and abrasion resistant.
Polyester is hydrophobic in nature and quick drying. It can be used for insulation by manufacturing hollow fibers.
Polyester retains its shape and hence is good for making outdoor clothing for harsh climates.
It is easily washed and dried
Uses of Polyester
The most popular and one of the earliest uses of polyester was to make polyester suits – all the rage in the 70s. Polyester clothes were very popular.
Due to its strength and tenacity polyester was also used to make ropes in industries.
PET bottles are today one of the most popular uses of polyester.
Dacron fibre (terylene) is crease resistant and is used in blending with cotton and wool fibres and also as glass reinforcing materials in safety helmets, etc.
Bakelite OR
Phenol - formaldehyde polymer
It is a thermosetting phenol formaldehyde resin, formed from a condensation reaction of phenol with formaldehyde in the presence of a catalyst such as hydrochloric acid, zinc chloride, or the base ammonia.
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Uses:
Bakelite was used for its electrical non-conductivity and heat- resistant properties in electrical insulators, radio and telephone casings, and such diverse products as kitchenware, jewelry, pipe stems, children's toys, and firearms.
Epoxy Resins
The reactive epoxide and hydroxyl groups give 3-D cross-linked structure.
Properties: Due to presence of ether-linkage: chemical resistance to water, various solvents, acids, alkali etc,.excellent adhesive in nature.
Uses: General purpose adhesives, as the binder in cement and mortars, rigid foams, non-skid coatings, solidifying sandy surfaces in oil drilling, industrial coatings, potting and encapsulating media, fiber reinforced plastics
Molecular Mass(weight) of a polymer
The properties of polymers are largely dependent on their size, molecular mass and structure. There are different methods to find out the molecular mass of polymers. Polymers are polydisperse and quite heterogeneous in molecular mass. In other words-polymers are mixtures of molecules of different molecular masses.
Classification of polymers masses:
1. Number-average molecular mass: Defined as total mass (w) of all the molecules in polymer sample divided by the total number of molecules present.
It is good index of impact and tensile strength.
Determined by: Cryoscopy, ebullimetry, osmatic pressure, lowering of vapour pressure.
It can be defined as:
1. Weight-average molecular mass:
It measures molecular size.
It can be obtained by light-scattering and ultracentrifugation.
It is always greater than number-average molecular mass.
It is defined as:
2
33.
Elastomers:
Natural rubber, structure of natural rubber, Extraction and
processing of natural rubber from rubber plant, Limitations
of natural raw rubber, vulcanization and its advantages,
Synthetic rubber: properties and uses of BUNA Rubbers,
Neoprene and thiocol rubbers and compounding of rubbers.
Assignment Questions
1. Describe the Extraction and processing of natural rubber from rubber plant.
2. What is the molecular weight of polymer ? Discuss various methods for the determination of molecular weight.
3. Write short notes on the following (a) Compounding of rubbers (b) Vulcanization
Limits: Not more than 4-5 pages
Deadline for submission: 24/04/2019
Elastomer
An elastomer is any vulcanisable man-made rubber-like polymer, which can be stretched to at least thrice its length, but it returns to its original shape and dimensions as soon as stretching force is removed.
An elastomer is a polymer with visco-elasticity, generally having low Young’s modulus and high failure strain compared with other materials.
Types of Elastomers
• Thermosets
• Thermoplastic
Elastomers are usually Thermosets (requiring vulcanizaton) but may also be Thermoplastic.
Common characteristics;
Large elastic elongation (i.e.200%)
Can be stretched and then immediately return to their original length when the load was released
Elastomers are sometimes called rubber or rubbery materials
The term elastomer is often used interchangeably with the term rubber
No stress
Stressed in Tension
Natural rubber (NR)
Rubber is a natural polymer and possesses elastic properties.
It is manufactured from rubber latex which is a colloidal dispersion of rubber in water.
This latex is obtained from the bark of rubber tree and is found in India, Srilanka, Indonesia, Malaysia and South America.
Natural rubber may be considered as a linear polymer of isoprene (2- methyl-1, 3-butadiene) and is also called as cis - 1, 4 -polyisoprene.
The cis-polyisoprene molecule consists of various chains held together by weak van der Waals interactions and has a coiled structure. Thus, it can be stretched like a spring and exhibits elastic properties.
Vulcanisation of rubber
Natural rubber becomes soft at high temperature (>335 K) and brittle at low temperatures (<283 K) and shows high water absorption capacity. It is soluble in non-polar solvents and is non-resistant to attack by oxidising agents.
Natural rubber
High Temperature
Solubility
Absorption
Non-resistivity
Low Temperature
Soft
Non-polar solvents
Water absorption
Oxidising agents
Brittle
How to improve these physical properties ie., Vulcanization
This process consists of heating a mixture of raw rubber with sulphur and an appropriate additive at a temperature range between 373 K to 415 K. On vulcanisation, sulphur forms cross links at the reactive sites of double bonds and thus the rubber gets stiffened.
In the manufacture of tyre rubber, 5% of sulphur is used as a crosslinking agent. The probable structures of vulcanised rubber molecules are depicted below:
Synthetic Rubber
1. Styrene rubber (GR-S or Buna-S) 2. Nitrile rubber (GR-A or Buna-N) 3. Neoprene
4. Thicol Rubber
5. Compounding of Rubber
Synthetic rubber is any vulcanisable rubber like polymer, which is capable of getting stretched to twice its length. However, it returns to its original shape and size as soon as the external stretching force is released. Thus, synthetic rubbers are either homopolymers of 1, 3 - butadiene derivatives or copolymers of 1, 3 - butadiene or its derivatives with another unsaturated monomer.
Nitrile rubber (GR-A or Buna-N)
Properties:
It possesses excellent resistance to heat, oils, sunlight, acid and salts but is less resistance to alkali than natural rubber, because of the presence of cyano group (-CN).
Vulcanized nitrile rubber is more resistant to heat and ageing than natural rubber and may be exposed to high temperatures.
Copolymer of butadiene and acrylonitrile.
Uses:
For making conveyer belts, high altitude aircraft components, hoses, gaskets, printing rollers, adhesives and automobile parts.
Styrene rubber (GR-S or Buna-S)
The most important type of rubber, which is produced by copolymerization of butadiene CH2=CH-CH=CH2 (about 75% by weight) and styrene C6H5CH=CH2 (25% by weight)
Properties:
Styrene rubber resembles natural rubber in processing characteristics as well as the quality of the finished products. It possesses high- abrasion resistance, high load-bearing capacity. However, it gets readily oxidized, especially in the presence of ozone present in the atmosphere.
It can vulcanized by sulphur or sulphur monochloride (S2Cl2).
Uses:
In the manufacture of tyres, floor tiles, shoe sole, cable insulations and gaskets etc.
Thanks
Next Lecture
Neoprene and thiokol rubbers
Neoprene
Also known as polychloroprene
Also known as polychloroprene
Developed during the 1930s
Extremely versatile synthetic rubber
Originally developed as an oil-resistant substitute for natural rubber
Also found in liquid state
Good mechanical strength
High ozone and weather resistance
Good aging resistance
Low flammability
Good resistance toward chemicals
Moderate oil and fuel resistance
Applications
Protective covers
Gloves
Wetsuits
Belts
Insulation Others
Gaskets
Medicine Use
• Neoprene Suit May Save Women's Lives with Obstetrical hemorrhage ( refers to heavy bleeding during pregnancy)
How?
• provides compression to the abdominal cavity
• The compression realized by the suit moves blood
from the inferior extremities and abdominal area to
the vital organs
Wetsuit
• Neoprene suit traps water between the suit and the person's skin
• Body heat warms the water against the skin which helps to reduce heat loss from the body
• For this matter a person can stay longer in cold water
• Neoprene is also buoyant which helps the diver to
float in the water
Interrogate
What property does
chlorine give to the overall polymer?
• Lower flammability!!!
Thiokol Rubber
Thiokol rubber is a polymer of ethylene polysulphide. Thiokol rubber can be prepared by the condensation of 1,2-dichloroethane with sodiumpolysulphide
Some of the important properties are:
i) Thiokol is resistant to the action of oxygen and ozone.
ii) It is also resistant to the action of petrol lubricants and organic solvents.
iii) Thiokols outstanding resistance to swelling by organic solvents but benzene and its derivatives cause some swelling.
iv) Thiokol films are impermeable to gases to a large extent.
Uses
It is used in hoses and tank linings for the handling and storage of oils and solvents.
It is used in lining of vessels used in the manufacture of chemicals.
It can be applied to engine gaskets and other such products that come into contact with oil.
Thiokol mixed with oxidizing agents can be used as a fuel in rocket engines.
Assignment Questions
1. Describe the Extraction and processing of natural rubber from rubber plant and discuss the limitation of natural rubber.
2. Write short notes on the following (a) Compounding of rubbers (b) Advantages of Vulcanization
Limits: Not more than 5-6 pages
Deadline for submission: 26/11/2019