POLYMERS Flashcards
Polymer
Long molecule formed by the joining togethor of thousands of small molecular units by chemical bonds.
Macromolecules
Due to their large size polymers are also sometimes called macromolecules
Polymer
Any substance made up of many repeating units building blocks called mers
Resins
when in form ready for further working polymers are called resins
polymerisation
chemical process leading to the formation of polymers is called polymerisation
degree of polymerisation
number of monomeric units contained in the polymer is known as degree of polymerisation
monomers
small molecules which combine with each other to form polymer molecules are known as monomers
greek translation of poly and mers
poly : many
mers : units or parts
Functionality
number of bonding sites in a monomer
significance of functionality
1) when the functionality of monomer is two, linear or straight chain polymer molecule is formed. Ex : All vinyl monomers, ethylene glycol, amino-acid
2) when functionality is three, 3-D network polymer is formed. Ex: phenol, melamine, etc
3) when a trifunctional monomer is mixed in small amounts with a bifunctional monomer, a branched chain polymer is formed
4) when a bifunctional monomer is mixed in small amounts with a trifunctional monomer, a 3-D network polymer is formed
functionality of monomer
number of bonding sited in a given molecule. The number of reactive functional groups per molecule of compound defines its functionality
why all single organic compounds cannot act as monomer during polymerisation process
because for a substance to act as a monomer it must be at least bi-functional. thus organic compounds like acetic acid and benzoic acid cannot act as monomer since they are monofunctional
Explain characteristics of polymers
1) they are macromolecules
2) they have both amorphous and crystalline regions
3) intermolecular forces in polymers can be van der waals, dipole-dipole or or hydrogen bonding.
4)they show time-dependent properties
5)they are combustible
6) they have low densities and excellence resistance to corrosion
7) they are thermal and electrical insulators
Advantages of polymers
low density
low absolute strength and stiffness but favourable specific strength and specific stiffness
resistant to corrosion
great electrical and thermal insulators
some polymers are inherently flexible
easily mouldable
ability to take various colours and shades
they are tailor made
crystallites
polymers have regions of crystallinity called crystallites embedded in amorphous regions.
crystallites provide strength and hardness
amorphous regions provide flexibility
Drawbacks of polymers
lower strength and stiffness, easily deformed under load
temperature limitations
time-dependent properties
combustible nature
classification of polymers based on structure or shape
linear
branched
cross linked
linear polymers
monomeric units that are joined in the form of long straight chains
high MP density and tensile strength
Branched polymers
polymers which are mainly linear in nature but also possess some branches along the main chain
low MP, density and tensile strength
Cross-linked polymers
3-D network polymers which contain cross-links in the form of strong covalent bonds btw polymer chains
Hard, rigid, do not melt on heating
PVC is soft and flexible as compared to bakelite
PVC is a linear polymer so it is soft and flexible. Bakelite is cross-linked polymer in which polymeric chains are bonded togethor by strong covalent bonds. thus no deformation can take place in its molecule as cross-links restricts the motion of polymer chains
classification of polymers based on physical state
amorphous
semi-crystalline
Amorphous polymers
polymer chains tend to be flexible and easily entangled or folded; tend to be disordered and are hard to crystallize.
Ex: LDPE, Rubbers
Crystalline polymers
Polymer chains that exhibit ordered structures. Degree of crystallinity depends upon amount of ordering in a polymer
Ex: HDPE, Nylon
classification of polymers based on number of monomers
Homopolymers
copolymers
homopolymers
polymers which are obtained by the repeated combination of only one type of monomer molecules
Ex: PE,PP,PVC
copolymers
polymers which are obtained by repeated combination of two or more types of monomers
Ex: styrene acrylonitrine copolymer, SAN
classification of polymers based on end use
Fibers
elastomers
adhesive
membranes
plastics
films
paints
Fibers
polyester Nylon
Plastics
thermoplastics and thermosets
elastomers
Rubber, Buna-S, Polyurethane
Films
PP, LDPE, PET, HDPE
Adhesives
PVA, Epoxy resin
Paints
epoxy
Membranes
polyacetylene, Polyaniline
classification of polymers based on tacticity or configuration
isotactic
syndiotactic
atactic
Tacticity
orientation of side groups around the main backbone chain in three-dimensional structure of a polymer
Isotactic polymers
side groups are all on the same side
Syndiotactic polymers
Arrangement of side groups is in alternating fashion
Atactic polymers
arrangements of side groups is random around the main chain
classification of polymers based on origin
Natural
Synthetic
Synthetic polymers
polymers which are synthesised in the laboratory are called synthetic polymers
Ex: rubber, fibers
Natural polymers
Polymers which can be found in nature
Ex: Carbohydrate and proteins
Conductance polymers
insulating polymers
conducting polymers
conducting polymers
polymers which conduct heat
Ex: polyaniline , Polypyrrole
classification of polymers based on environment friendly nature
durable
Biodegradable
biodegradable polymer example
Starch based PE
classification of polymers based on based on polarity of monomers
polar
non-polar
Polar monomers
PET, Nylon
non-polar monomers
PE, PP
classification of polymers based on their behavior when heated to processing temperature
thermoplastics
thermosets
Difference btw thermoplastics and thermosets
Book pg. 170
Polymerization
synthesis of large molecular weight polymers is termed as polymerization
Different ways for doing polymerization
by opening double bond
by opening a ring
by using molecules having 2 functional groups
addition polymerization
polymer synthesized by addition polymerization has the same empirical formula as that of monomer . No molecule is evolved during polymerization and the polymer is an exact multiple of original monomeric molecule
substituent groups:
-H
-CH3
-Cl
-C6H5
Polymer
Polyethene
polypropylene
polyvinyl chloride
Polystyrene
condensation polymerization
It takes place by condensation of two different bi- or poly functional monomers having functional groups which have affinity for each other.
Difference btw condensation and addition polymerization
Book pg 172
Copolymerization
polymerization of two or more monomeric species together
resultant polymer possesses some advantageous properties from both monomers Ex: styrene-butadiene rubber (SBR)
Different types of copolymers
Alternate
Block
Random
Graft
Alternate copolymers
monomers are arranged in regular alternate fashion
Block copolymers
A block of repeating unit of one kind of monomer is followed by block of another kind of monomer
Random copolymers
monomers are randomly distributed along the polymer chain
Graft copolymers
they have branched structures in which the monomer segments on the backbone and branches differ
Reaction mechanism of free-radical polymerization
monomer is activated by its transformation into radical by the action of light, heat, ionizing radiation, or by adding chemicals
Initiators
compounds which readily decompose into free-radical so that monomer molecules can interact with these free-radicals for their activation
Ex: benzoyl peroxide, AIBN
Initiation by oxygen
Oxygen is known to initiate some free radical ethylene polymerization reactions It occurs at higher temperatures by the thermal decomposition of peroxides and hydroperoxides formed from the monomer
Mechanism of free radical polymerization
1) Chain initiation- it involves 2 steps decomposition of initiator and the addition of first vinyl monomer molecule to free radical leading to the formation of intermediate
2)Chain propagation- addition of monomer molecules to leading to the formation of macro-radicals.
3)Chain termination- Growing polymer chain can be terminated by :
(I)Recombination
(II)Disproportionation
(III)Reaction with polymerization inhibitors
(IV)Reaction with Solvent Molecules
Chain propagation helps determine:
1) rate of polymerization
2) molecular weight of polymer
3) structure of polymer chain
4)mode of monomer addition
Head-to-tail placement of monomer units
in final polymer monomer units are linked together in such a manner that they have substituents on alternate carbon atoms. This H-T placement is favored on both steric and resonance grounds
Chain transfer reactions
in these reactions the original growing free radical chain is terminated by reaction with the monomer molecule and a new chain is initiated
how do chain transfer reactions decrease molecular weight of polymer
there will be no change in the overall rate of polymerization but the avg molecular weight of polymer will decrease
Explain branching and cross-linking during the free-radical addition polymerization
once a macroradical is formed by the propogation of free-radical polymerisation reaction, back-biting can take place, leading to the abstraction of hydrogen atom from the growing end of the polymer chain to the middle of the chain. Now propogation of reaction from middle centres will create branches .
There will also be the possibility of reaction between 2 molecules of type II leading to the formation of cross-linkages
PG 176-177
Monomers which can be polymerized by free radical polymerization
ethylene and other vinyl derivatives
Acrylic acid derivatives
Butadiene , isoprene and chloroprene
Cationic polymerization
Monomers with electron releasing substituents undergo cationic polymerization in the presence of lewis acids and friedel-craft catalysts. They add on to the monomer forming a carbonium ion. Electron releasing substituents such as alkyl , alkyloxy and phenyl increase the e- density at C-C double bond and facilitate its bonding to cationic species
The mechanism can be explained by polymerization of styrene
polymerization of styrene
PG NO 178
Anionic polymerization
Monomers with electron attracting substituents undergo anionic polymerization in the presence of sodium or potassium amide and grignard reagent as catalysts.
In anionic polymerization catalysts interact with monomer to generate a carbanion as the active centre for chain growth . As the intermediate carbanion is stabilized by electron withdrawing substituens hence anionic polymerization is favourable with the monomers having such substituents.
The mechanism can be explained by formation of PMMA
Formation of PMMA
Book pg 179
Conclusions from generalized anionic mechanism for the formation of PMMA
(1) in Anionic polymerization end group posseses high activity and good stability. Polymerization process continues till available monomers are consumed.
(2) Its possible to produce very high molecular weight polymers by anionic polymerization
(3) block copolymers can also be made by anionic polymerization by carefully adding alternatively the required monomers with pre-determined concentration
Killed polymers
polymers which are produced by stopping the polymerization process at predetermined stage with the help of a sutaible terminating agent like water
Difference btw radical and ionic polymerization
Pg 180
Types of PVC
rigid PVC
Plasticized PVC
Manufacturing of PVC
PVC can be made from vinyl chloride by emulsion polymerisation. Vinyl chloride is mixed with water in equal parts, small amount of catalyst and an emulsifier. Mixture is vigorously stirred and then senf to autoclave at temp. of 40-45°C. The polymer is then coagulated by acid and dried. The desired properties in PVC can be achieved by using plasticizers , stabilizers , lubricants and fillers.
Equation: PG187
Properties of PVC
1) stronger and tougher than polyethylene
2)colourless, odourless, and non-inflammable
3)it has superior chemical resistance but dissolves in ethyl chloride and hydro furan
4)excellent oil resistance
Applications of PVC
In acid recovery plants to handle hydrocarbons
in pipes for drainage and guttering
making bottles
PVC is tougher and stronger than polyethylene
presence of chlorine atom on alternate carbon atoms of pvc with C-C dipole causes an increase in interchain attraction. These strong dipole-dipole attractive forces make PVC tougher and stronger than polyethylene which has weak van der waals forces of attraction between different PE chains
Prepartion of Plasticized PVC
it is obtained by adding plasticizers such as DOP, dibutyl phthalate to rigid PVC
Properties of plasticized PVC
It is good insulator for direct current and low frequency AC current
Uses of Plasticized PVC
car applications
kitchen upholstery
ladies handbags
plastic rainwear
baby pants
garden hose
Polymethyl Methacrylate (PMMA) preparation
polymerization of methyl methacrylate in the presence of acetyle peroxide or hydrogen peroxide as catalyst
Polymethyl Methacrylate (PMMA) aka
plexiglass or lucite
properties of PMMA
1)amorphous, colourless, transparent thermoplastic
2)hard
3)polar polymer hence no electrical insulation properties
4)high softening point due to intermolecular dipole forces
5)critical angle for polymer air boundary is 42 degree. A wide light beam mat be transmitted through long lengths of solid polymer
Applications of PMMA
Display signs
light fittings
motorcycle windscreen
wash basins
optical fibres
Preparation of Nylon 6
pg no 192-193
properties of Nylon-6
fibres are tough, they own high tensile strength elasticity and lustre
they are wrinkleproof
highly resistant to abrasion and chemicals
they can absorb upto 2.4% of water
easily dyeable
applications of Nylon-6
as thread in bristles for toothbrushes, surgical sutures and strings for musical instruments
used in hosiery and knitted garments
glass fibre reinforced Nylon-6 is used in gears, bearings and fittings
preparation of Nylon-66
pg no 194-195
properties of Nylon-66
high crystallinity which imparts high strength, high melting point, elasticity and toughness
they are sterilisable
good hydrocarbon resistance
Applications of Nylon-66
used in fibres
in gears, bearings, bushes etc. they can run without much lubrication
for jacketing electrical ware
Preparation of Polytetrafluoroethylene (PTFE)
It is prepared by polymerisation of tetrafluoroethylene under pressure in the presence of benzoyl peroxide as catalyst
PTFE is aka
Teflon
Properties of Teflon
High density
excellent electrical insulation properties
chemical inertness over wide temperature range
non-adhesive characteristics
excellent toughness and heat resistance
Application of Teflon
Wire and cable insulation
laminates for printed circuitry
coating of frying pans
non-lubricating bearings
insulators for motors, generators, etc
Structure of Teflon
it has a twisted zig-zag structure with fluorine atoms packing tightly in a spiral around the C-C skeleton. Due to presence of highly electronegative fluorine atoms there are very strong attractive forces between different chains
Polyacrylonitrile preparation
it is prepared by polymerization of vinyl cyanide (Acrylonitrile)
Polyacrylonitrile is aka
Orlon
properties of polyacrylonitrile
does not dissolve in its monomer
it dissolves in dimethylformamide and tetramethylenesulphone
resistant to water and quick drying
more resistant to acid and gases than nylon
Applications of polyacrylonitrile
in manufacturing window shades
as wool-like fibre in suits, sweaters etc
Polyvinyl acetate (PVA) preparation
Catalyst used is either benzoyl peroxide or acetyl chloride. A solution of vinyl acetate and catalyst is prepared in benzene.
Properties of Polyvinyl acetate
It is clear, colourless and transparent material
amorphous polymer
they become gum-like when masticated
fairly soluble in organic solvents
applications of polyvinyl acetate
production of water-based emulsion paints
chewing gums
making records
bonding of paper
Phenol formaldehyde resin preparation
Book pg 196-197
Phenol formaldehyde resin aka
bakelite
Phenol formaldehyde resin properties
they are hard rigid and strong materials
they have excellent heat and moisture resistance
good chemical resistance
good abrasion resistance
good electrical insulation characteristics
usually dark coloured, pinkish brown
Applications of Phenol formaldehyde resin
domestic plugs and switches
distributor heads of cars
adhesive
impregnating word,paper and other fillers for producing decorative laminates
electrical insulation and protective coating
Urea formaldehyde resins preparation
book pg no 198
Urea formaldehyde resins properties
clear and colourless
better hardness and tensile strength
good solvent , grease and moisture resistance
good adhesive characteristics
Urea formaldehyde resins applications
as adhesives for plywood etc
for finishing of cotton textiles
for making buttons, vacuum flask cups etc
for bottle caps
for coloured toilet seats
Biopolymerization
a polymerization process for the production of biopolymers
Types of biopolymerization
using microbes
using fermentation
Biopolymers using microbes
biopolymers made using microbes. they are produced by a range of micro-organisms cultivated under various nutrient and growth conditions
Production of biopolymers
biopolymers are made from a compound called poly-hydroxy-alkanoate (PHA). bacteria accumulate PHA in the presence of excess carbon source.
Example of bacteria useful for bio-polymerization:
archaebacteria, bacillus megaterium, ralstonia eutropha , bacillus mycoides
fermentation
it is the use of micro-organisms to break down organic substances usually in the absence of oxygen
Bacterial polyester fermentation
ralstonia eutropha bacteria use the sugar of harvested plants to fuel their cellular processes. The by-product of this cellular process is polyester which is then separated from the bacterial cells
Lactic acid fermentation
Lactic acid is fermented from sugar using bacteria. After the lactic acid is produced by fermentation process it is converted to polylactic acid using traditional polymerization processes
polymer formed is called PLA
Growing plants using plants
A genetically engineered plant ( Arabidopsis thaliana) contains enzymes used by bacteria. bacteria create plastic through the conversion of sunlight. Through transfer of gene codes for this enzyme production into the plant we are able to produce the plastic through the cellular processes of plant. Plant is harvested and plastic is extracted from it using a solvent. Subsequently using distillation plastic is separated from the solvent
Advantages of biopolymerization
1) eco friendly synthetic process
2)bio-polymers are biodegradable
3) biopolymer is derived from renewable resources and possesses good mechanical properties
Shortcoming of biopolymerization
1) prone to thermal degradation
2) brittle
3) reactive groups and not present in biopolymers so they interact poorly with additives
4) processing is difficult
Biodegradation
process carried out by biological systems wherein a polymer chain is cleaved via enzymatic activity
Biodegradable polymers
those polymers which get decomposed by the process of biodegradation
Requirements of biodegradation
Micro-organisms
Environment
Substrate
Microorganisms in biodegradation
they must exist with the appropriate biochemical machinery to synthesize enzymes specific for the target polymer to initiate the depolymerization process
Environmental factor in biodegradation
following enviornmental factors must be tuned in a given enviornment within the window of acceptibility for the organisms producing the appropriate enzymes to degrade the target polymer:
1) temperature
2) pressure
3) moisture
4) oxygen
5) type and concenteration of salts
6) light
etc
substrate factor in biodegradation
polymer must have following essential features for biodegradation process to be successful
1) suitable functional groups (like ester)
2) hydrophilicity (should be greater)
3) low molecular weight
4) less crystallinity
Types of biodegradable polymers
Natural- natural rubber, collagen, lignin,
Synthetic - polyvinyl alcohol, polyanhydrides, PHBV
Need for biodegradable polymers
solid waste problem
Litter problem
Entrapment
Applications of biopolymers
PHB is used in shampoo bottles
HB-HV is used as matrices for controlled release of drugs
PLA is used in sutures, drug-delivery-systems and wound clips
Limitations of biopolymers
Not easily recyclable
expensive
not easily available
Drawbacks of raw rubber
1)soft & sticky in hot summer and hard & brittle in cold winter
2)low tensile strength
3)attacked by oxidising agents
4)in organic solvents it undergoes swelling and disintegration
5)oxidises in air
Compounding
incorporation of suitable substances in the polymer so as to impart the desired properties in it
Compounding of rubber includes
vulcanizers
accelerators
antioxidants
reinforcing agents
plasticizers
colouring agents
inert fillers
Vulcanization of rubber
Book pg 203
Advantages of vulcanization
1) increase in tensile strength
2) excellent resilience
3) broader temperature range
4) better resistance to moisture, oxidation and abrasion
5) resistance to organic solvents
6) slight tackiness
7) low elasticity
Styrene rubber
Book pg 204
Properties of styrene rubber
high abrasion resistance
high load bearing capacity
resilience
swells in oil
low oxidation resistance
applications of styrene rubber
motor tyres
shoe soles
insulation of wires
carpet backing
gaskets
adhesives
tank-lining
nitrile rubber
Book pg 205
properties of nitrile rubber
less resistant to alkalis
increased resistance to oils,salts, solvents and acids
more heat resistant
good abrasion resistance
applications of nitrile rubber
conveyor belts
lining of tanks
gaskets
printing rollers
oil-resistant foams
automobile parts
hoses
adhesives
Monomers of all thermoplastic polymers
Book pg 207
