View
14
Download
0
Category
Preview:
Citation preview
Polymer�Polymer: Maromolecule built-up by the linking together of a large no. of small molecules
Ex. Nucleic acid, paper, bakelite,PVC
�Monomer: The small molecule which combine with each other
� Mer: The repeat unit
�Degree of polymerisation (DP): The no. of repeating unit(n)Degree of polymerisation=Molecular wt of the polymeric network/molecular wt of the repeating unit
�Depends on degree of polymerisation polymers are two types
�Oligo polymers:Polymer with low mol.wt
�High ploymer: Polymer with high mol. wt
Polypropylene
mer
Monomer
Nomenclature of PolymerI. Based on the chemical structure of monomer
i)Homo polymer and ii)copolymer
II. Based on the arrangement of monomer in the structure
Homo Polymer:
i)Linear, ii)branched and iii)Cross linked or 3-D polymer
Co polymer:
Linear:i) Regular, ii)Alternating, iii) block and iv)random
copolymer
Branched: Graft copolymer
Cross-linked copolymer
III. Based on atoms in the main chain
i)Homochain polymer and ii)heterochain polymer
Nomenclature-contdI)Based on the chemical nature of the monomer units
� Homopolymer : Identical monomers Homopolymer : Identical monomers (Polyethylene)(Polyethylene)
� Copolymer : Monomers with different chemical Copolymer : Monomers with different chemical structure (Buna-S: butadiene and styrene)structure (Buna-S: butadiene and styrene)
II) Based on structure of polymer chains II) Based on structure of polymer chains (Homopolymer &Copolymer)(Homopolymer &Copolymer)
i. Linear homopolymer : - A – A – A – A – i. Linear homopolymer : - A – A – A – A – ii. Branched homopolymer : - A – A – A – A -
A
iii. Cross – linked polymer :
- A – A – A – A – A – A – A – A -
- A – A – A – A – A – A – A –
Linear polymer
Branched chain polymer
Cross linked or 3-D polymer-Bakelite
Copolymers� Regular Polymer : Regular
arrangement of monomer units A&B
� Alternating copolymers with regular alternating A and B units
� Random copolymers with random sequences of monomer A and B
� Block copolymers comprised of two or more homo polymer subunits in long sequences linked by covalent bonds
� Graft Copolymers are a special type of branched copolymer in which the side chains are structurally distinct from the main chain.
A-A-A-B-A-A-A-B-A-A-A-B
Regular Copolymer
Nomenclature-contd
III)III. Based on atoms in the main chain
� Homochain polymer: Main chain is made up of same species of atoms
Ex., PVC
� ii)heterochain polymer: Main chain is made up of different atoms
ex.,Nylon 6:6 (mer),
Copolymer ( Buna-S or SBR)
mer
Tacticity (Difference in Configuration)Affect their physical properties
Isotactic: Functional gpsor side
gps are all on the same
side:ex., Polypropylene
synthesised using Zielgar Natta
catalyst
Syndiotactic Arrangement of
functional groups or side gps in
alternating fashion: Gutta
percha-Natural rubber
Atactic: Arrangement of
functional gps or side gpsare
at random around the main
chain ex., Polypropylene
Functionality� Number of bonding sites in a monomer
� It determines the structure of the polymer.
Three Typee
� Bifunctional, trifunctional and polyfunctional1
1)Bifunctional monomer:Two reactive sites or bonding sites.
� Reactive gp attach side by side to each other forming linear or straight chain molecule
� Monomer units linked by covalent bonds but different chains are held by van der Waals force
� Chain movement in one direction is possible
� Compound with double bond, amino acid, di-ol etc.,
� ex., ethylene glycol, ethylene.
Functionality -contd
2)Trifunctional monomer: Contains three active sites
� Result in branched chain molecule even if it presents in small amount with bifunctional monomer ex.,dimethylol phenol
� Movement of chain molecules are restricted due to presence of side chain
3) Containing more than three functional gps.ex., trimetylol phenol
Monomers are connected to each other by covalent bonds which results in the formation of 3D network ex., bakelite
� The movement of individual molecules are prevented by strong cross-links
Types of Polymerisation• Addition or Chain polymerisation : Polymer is formed by an
addition reaction, where many monomers bond together via rearrangement of bonds without the loss of any atom or molecule
• Monomers contains one or more double bonds which by intermolecular rearrangement make the polymer which is an exact multiple of monomer
• Reaction is instigated by the application of heat, light, pressure or a catalyst -break the double bond.
• The polymerisation once initated cannot continue indefinitely as it becomes difficult to sustain long chain.
• Growth reaction adds repeating units one at a time to the chain
• Ex for Homo polymerisation ; PVC
Addition or Chain polymerisation • Ex. Homo polymerisation :,Nylon-6: Involves an intramolecular
rearrangement of bonds by opening of cyclic monomer
• Ex. Copolymerization of two different monomer:Polybutadiene-co-styrene
mer
Condensation or Step Polymerisation
• Reaction between simple polar gp containing monomers
• Formation of polymer takes place by elimination of small molecules like water, HCl, CH3OH, NH3 etc.,
• An intermolecular combination of monomer.
• When monomers contain three functional gps it may give cross-linked structure molecule.
• Ex.,(Nylon 6,6)
+ 2n H2O
n n
n
Chain and condensation polymerisation•Chain polymerisation
•Monomer must have two bonding
sites
•Inter molecular or intramolecular
Rearrangement
•Mostly results in homo chain
polymer
•Only growth reaction adds repeating
units one at a time to the chain
•Number of units decreases steadily
throughout the reaction
•Reaction mixture contains only
monomer and polymer- no other pdts
•Linear polymer and Thermoplastics
•Mol. Wt of polymer is exact multiple
of mol.wt of monomer
•longer reaction time has little effect
on the molecular wt but gives higher
yields
Condensation polymerisation
•Monomer must contain polar group
• Intermolecular combination of
monomers
•Mostly results in hetero chain polymer
•All types of molecular species present
can react
•Monomer disappears early in the
reaction
• All types of molecular species and by
products are present at any stage
•Branched and cross-linked polymer-
thermosetting plastics
•Molecular wt is not an exact multiple of
mol.wt of monomer
•Moecular mass (DP)rises steadily
throughout the reaction and hence
reaction time is essential
ClassificationClassification� Based on origin:Based on origin:
Natural (Cellulose, Protein, silicone) and synthetic Natural (Cellulose, Protein, silicone) and synthetic
(Bakelite)(Bakelite)
Based on Structure Based on Structure
Linear, Branched, 3-dimensional or cross linkedLinear, Branched, 3-dimensional or cross linked
Based on main chain (back bone/ skeleton)Based on main chain (back bone/ skeleton)
i) Homo chain: made up of single type of atom (ex) PEi) Homo chain: made up of single type of atom (ex) PE
ii) Hetero chain: made up of different types of atoms ii) Hetero chain: made up of different types of atoms
(ex)nylons(ex)nylons
Based on molecular forces (Thermal behaviour) Based on molecular forces (Thermal behaviour)
Thermoplastics, Thermosetting plastics, Fibres, ElastomersThermoplastics, Thermosetting plastics, Fibres, Elastomers
� Based on method of synthesis Based on method of synthesis
Addition polymer (eg) PE, PP, PS, nylon 6. Addition polymer (eg) PE, PP, PS, nylon 6.
Condensation polymer (eg)Polyesters , nylon 6,6 Condensation polymer (eg)Polyesters , nylon 6,6
Thermo plastics and Thermosetting plasticsThermo plastics and Thermosetting plasticsThermosetting Plastics�Do not soften; they burn on heating
�3-D cross-linked structure with co-valent bond
�Condensation polymer
�Can not be reshaped
�Hard, strong and brittle
�Cannot be reclaimed
�Due to strong bonds and cross links they are insoluble in almost all org. solvents Ex.,Bakelite
Thermo plastics�Soften on heating and harden on cooling reversibly
�Long-chain macromolecule
�Addition polymerisation
�Reshaped, reused
�Soft, weak and less brittle
�Reclaimed from waste
�Soluble in some org. solvents
�Ex., PVC
Elastomers and Fibers
Elastomer: Rubber
• High elastic properties
• Can be stretched to 4 to 10 times its original length
• Unstressed condition they are not in straigth chain but in the form of coil
Fibers
• Held by strong intermolecular forces like
H-bonding
• Continuous filament ex. Cellulose
Plastics
Org .materials of high mol.wt, which can be moulded
into any desired form, when subject to pressure and
heat in presence of the catalyst
Resin
� Basic binding material, a macro molecule (polymer),
major parts of the plastics
� Undergoes polymerization and condensation
�during preparation (Thermosetting plastics).
�Mixed with 4-10 ingredients-Compounding
�of plastics
• Classification Plastics
1) Based on usage
Commodity plastics
� PE, PS , PP, PVC,
Engineering Plastics
� Teflon (PTFE) ,PC (Lexan), Polyesters and
Polyamides (Nylon, PET)
2) Based on thermal behaviour
Thermoplsatics
Thermosetting plastics
Engineering PlasticsEngineering Plastics� Used to replace conventional materials like metal, wood, glass, Used to replace conventional materials like metal, wood, glass,
ceramics etc.ceramics etc.� Used to develop composite articlesUsed to develop composite articles
CharacteristicsCharacteristics� Resistant to corrosionResistant to corrosion� cast into any desired shapecast into any desired shape� light-weightlight-weight� low thermal coefficient of expansionlow thermal coefficient of expansion� chemical inertnesschemical inertness� low melt.pt.low melt.pt.� decorative finishdecorative finish� impermeable to waterimpermeable to water� low heat resistancelow heat resistance� deformation under load,deformation under load,� High abrasion resistanceHigh abrasion resistance� Dimensional stabilityDimensional stability
ApplicationsIn automobile
In defense
Electrical and electronics
Telecommunication
Textile
Satellite
Computer components (table top, screen)
Robots
In aeronautical engineering
Chemical industry
Paper Industry
Adhesives
Lubricants
Recommended