polymers Flashcards
mass of polymer range
103 to 107
natural polymers
found in plants and animals
e.g. proteins, cellulose, starch, resins, rubber
semi-synthetic polymers
cellulose derivatives like cellulose acetate (rayon) and cellulose nitrate etc
synthetic polymers
plastic (polythene), synthetic fibres (nylon 6.6), synthetic rubbers (Buna-S)
free radical mechanism- what is formed
alkenes, dienes and their derivatives
free radical mechanism- how does it take place + catalysts
alkenes, dienes, derivatives as polymerised in the presence of a free radical generating initiator (catalyst) like benzoyl peroxide, acetyl peroxide, tert-butyl peroxide
what is the intermediate formed in free radical mechanism, chain initiation step from benzoyl peroxide
phenyl radical
homopolymer
addition polymers formed by polymerisation of a single monomeric species are known as homopolymers. e.g. polythene
copolymers
polymer formed from addition product of two different monomers are called copolymers
e.g. Buna-S
under what conditions is a low density polythene obtained
- obtained by polymerisation of ethene
- under high pressure of 1000 to 2000 atm
- at a temperature of 350 K to 570 K
- in the presence of dioxygen or a peroxide initiator (catalyst)
structure of low density polythenes
highly branched
straight chain structure with some branches
Low density polythene properties
- Chemically inert
- tough but flexible
- poor conductor of electricity
use of low density polymers
- insulation of electricity carrying wires
- manufacture of squeeze bottles, toys, flexible pipes
high density polyhene formation how
- addition polymerisation of ethene takes place in a hydrocarbon solvent
- in the presence of a catalyst such as triethylaluminium and titanium tetrachloride (Ziegler-Natta catalyst)
- at a temp of 333 to 343 K
- under a pressure of 6-7 atm
HDP structure
linear molecules and has high density due to close packing
HDP properties
inert and more tough and hard
used for manufacturing buckets, dustbins, bottles, pipes, etc
Teflon
polytetrafluoroethene
how is teflon manufactured
by heating tetraflurorethene with a free radical or persulphate catalyst at high pressures
uses of teflon
chemically inert and resistant to attack by corrosive reagents so used in making oil seals and gaskets and non stick sruface
Polyacrylonitrile
The addition polymerisation of acrylonitrile in presence of a peroxide catalyst leads to its formation
use of polyacrylonitrile
substitute for wool in making artificial fibres as orlon or acrilan
addition polymerisation also called
chain growth polymerisation
condensation polymerisation also called
step growth polymerisation
what happens in condensation polymerisation
result in loss of simple molecules like water, alcohol, hydrogen chloride etc
what is the product of each step in condensation polymerisation
a bi-functional species
terylene other name
dacron
monomer of terylene
ethylene glycol and terephthalic acid
polyamides
polymers possessing amide linkages are examples of synethetic fibres and are termed as nylons
Nylon 6,6 preparation how?
type of polymerisation
monomers
condensation polymers
monomers;
hexamethylenediamine with adipic acid under high pressure, temp
why does nilon 6,6 have high tensile strength
- strong intermolecular forces like hydrogen bonding
- these strong forces lead to close packing of chains and thus impart crystalline nature
nylon 6 formation
obtained by heating caprolactam w water at high temp
polyesters formation
polycondensation products of dicarboxylic acids and diols
e.g. dacron/terylene
dacron/terylene formed in the presence of what catalyst
zinc acetate-antimony trioxide catalyst
dacron fibre
crease resistant used in blending w cotton and wool fibres
also as glass reinforcing materials
phenol formaldehyde polymer formed how
condensation rxn of phenol with formaldehyde in the presence of either acid or base catalyst
initial product ontained in formation of phenol-formaldehyde polyer
Novolac as used in paints
novolac on heating with formaldehyde undergoes cross linking to form an infusible solid mass called ___
bakelite
it is a termosetting polymer which cant be reused or remoulded
melamine formation how
formaldehyde polymer formed by condensation of melamine and formaldehyde
Buna-S formed from
1,3-butadiene and styrene
elastomeric polymer
natural rubber
natural rubber structure
linear polymer of isoprene (2-methyl-1,3-butadiene) also called cis-1,4-polyisoprene
temp at which natural rubber becomes soft
greater tahn 335K
temp at which natural rubber becomes brittle
less than 283K
what is natural rubber soluble in
non-polar solvents and non resistant to attack by oxidising agents
vulcanisation of rubber
heating raw rubber with sulphur
on vulcanisation sulphur forms cross links at the reactive sites of double bonds and thus rubber gets stiffened
neoprene
synthetic rubber
neoprene or polychloroprene formed by free redical polymerisation of chloroprene
