SUBMITTED BY-

•Arun Kotnala(2007UMT131)

•Abhishek Soni (2007UMT107)

•Ankur Tripathi (2007UMT151)

•Anurag Satpathy (2007UMT143)

MOLECULAR CONFIGURATION• Configuration refers to the order that is

determined by chemical bonds. The configuration of a polymer cannot be altered unless chemical bonds are broken and reformed.

MOLECULAR CONFIGURATION In polymers, configuration can be roughly

classified into 3 types- Based on Molecular chain- Head-to-Head Head-to-Tail Tail-to-Tail Based on Stereo configuration-Isotactic Atactic Syndiotactic Based on Geometric configuration-Cis Trans

CONFIGURATION BASED ON MOLECULAR CHAIN

Monomers can react as head-to-head,head-to-tail or tail-to-tail.

The free radical can be added to monomers in 2 ways-

+ CH2=CHX R-CHX-CH2 . -(I)

R-CH2-CHX. -(II)

• If the substituent X occurs on alternate C-atoms ,form (II) would lead to formation of Head-to-Tail arrangement.

• A combination of form (I) and (II) may also lead to Tail- to-Tail or Head-to-Head configuration.

CONFIGURATION BASED ON MOLECULAR CHAINHead-to-Tail arrangement is thermodynamically more

predominant.In general, a mixture of all the above configurations may

occur.In most polymers Head-to-Tail configuration is preferred as

there is often a polar repulsion that occurs between substituent groups for Head-to-Head or Tail-to-Tail configuration.

In Head-to-Head or Tail-to-Tail, although the chain units are fully chemically bonded together, it represents a weak link in the chain because less energy is needed to break the chain here than elsewhere. So in failure problems, such as thermal degradation, breakage will start here rather than in the normal chain. The occurrence of head-to-head joints or tail-to-tail joints is less than 1 per cent in normal polymers.

CIS & TRANS CONFIGURATION

CIS CONFIGURATIONThe cis configuration arises when substituent

groups are on the same side of a carbon-carbon double bond.

Soft rubber generally contains ‘cis’ type structure.

Cis configuration imparts flexibility to polymers.

TRANS CONFIGURATIONThe trans configuration arises when

substituent groups are on the opposite side of a carbon-carbon double bond.

Polymers of the ‘trans’ isomer called “Gutta-percha” has a bond angle pattern different from ‘cis’ type i.e the unsaturated position balance each other across the double bond.

In ‘trans’ type bond, the chain is almost straight ,therefore as the stress is applied, straightening will be very less.

Trans imparts hardness and stiffness.

STEREO CONFIGURATIONBased on stereoisomerism, configuration is of

3 types-ISOTACTICSYNDIOTACTICATACTIC

STEREO CONFIGURATION

ISOTACTIC-Isotactic polymers are composed of isotactic macromolecules . In isotactic macromolecules all the substituents are located on the same side of the macromolecular backbone. Polypropylene formed by Ziegler-Natta catalysis is an isotactic polymer. Isotactic polymers are usually semi crystalline and often form a helix configuration.

SYNDIOTACTIC-Syndiotactic polymers are composed of syndiotactic macromolecules . In syndiotactic or syntactic macromolecules the substituents have alternate positions along the chain. Syndiotactic polystyrene, made by metallocene catalysis polymerization, is crystalline with a melting point of 161 °C.Syndiotactic forms are stronger than isotactic.

ATACTIC-In atactic macromolecules the substituents are placed randomly along the chain.Atactic form is universally amorphous except for PVA.

REFERENCESEngineering Materials-Polymer,Ceramic &

Composites-Dr. A.K.BhargavaTextbook of Polymer science-Fred W.

Billimeyerhttp://en.wikipedia.org/wiki/Tacticityhttp://openlearn.open.ac.uk/mod/

resource/view.php?id=196631 Class Notes

Copolymer is a polymer derived from 2 or more monomeric species.

Copolymerization refers to methods used to chemically synthesize a copolymer.

Commercially relevant copolymers include ABS plastic,SBR,Nitrile rubber, styrene acrylonitrile,ethylene vinyl acetate etc.

• Alternating Copolymers –Regular alternating A and B units.(2)

• Random Copolymers –Sequence of monomers is not fixed and monomer appears in a random manner.(3)

• Block Copolymers-Comprises 2 or more homopolymer subunits linked by covalent bonds.(4)

• Graft Copolymers-Special type of branched copolymer in which the side chains are structurally distinct from the main chain.

• Different monomers are organized into distinct segments or blocks.

• Further classified by the number of blocks each molecule contains ,and how they are arranged.

• Made by various techniques like atom transfer free radical polymerization, reversible addition fragmentation chain transfer, ring-opening metathesis polymerization.

• 2 blocks-Diblocks• 3 blocks-Triblocks• More blocks-Multiblocks• Linear arrangement-Connected end-to-end• Star arrangement-Connected to a single

junction

Copolymer made by polymerizing styrene (40-60%) & acrylonitrile (15-35%) in the presence of polybutadiene.

Common thermoplastic used to make light,rigid,molded products such as piping,musical instruments,golf club heads,automotive body parts,wheel covers,enclosures,protective headgear etc,colorant in tattoo inks.

Nitrile group makes ABS stronger than pure polystyrene.

Impact value of ABS can be increased by raising the proportion of Butadiene but at the cost of Tensile strength and HDT.

ABS can be injection moulded to produce telephones,steering wheels and small appliance cases.

It can be electroplated to make metallised door knobs and handles.

Copolymer consisting of styrene and butadiene.

It has good abrasion resistance and good aging stability when protected by additives.

It can be produced from solution. The reaction is via free radical polymerization.

High styrene-content rubbers are hard, since the Tg of Butadiene is extremely low.

It is widely used in car tires, where it is blended with natural rubber.

SAN is a random ,amorphous copolymer of styrene and acrylonitrile.

It is optically transparent and brittle in mechanical behaviour.

Improved weatherability,stress crack resistance and barrier properties.

Polar nature of AN increases the resistance of the copolymer to non polar solvents such as oils and greases.

Polarity increases H-bond attractive forces between polymer chains leading SAN exhibit higher tensile strength,hardness,stiffness and HDT,better chemical resistance,toughness than PS alone.

Uses include food containers,kitchenware,computer products,packaging materials ,battery cases and plastic optical fibres.

It is a random copolymer of styrene and maleic anhydride monomer.

Formed by a radical polymerization using an organic peroxide as the initiator.

Its main characteristics are its transparent appearance, high heat resistance, high dimensional stability, and the specific reactivity of the anhydride groups.

SMA copolymers with a high molecular weight are widely used in engineering plastic applications, normally in the impact modified and optically glass fibre filled variants.

The solubility of SMA in alkaline solutions makes it suitable for various applications in the field of paper, binders and coatings.

•A gradient copolymer has gradient in repeat units arranged from mostly monomer A to mostly monomer B along much or all of the copolymer chain. •Developments of controlled radical polymerization led to the study of concepts and properties of gradient copolymers because the synthesis of this group is more straightforward.

PROPERTIES-• By controlling the molecular weight ,composition

and the shape of the gradient along the polymer backbone,phase transitions in a gradient copolymer can be manipulated.

• Changing the gradient along the polymer backbone can alter the volume fraction.

APPLICATIONS-• Reinforcing agents• Impact Modifiers & sound or Vibration dampers• Pressure Sensitive Adhesives• Wetting or Levelling Additives for coatings or

Inks

Engineering Materials-Polymers,Ceramics & Composites-Dr.A.K.Bhargava

Textbook of Polymer science-Fred W. Billimeyer

http://en.wikipedia.org/wiki/Copolymers

http://en.wikipedia.org/wiki/Gradient_copolymers

Class Notes

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