Polymers

Question 1

What is a Polymer?

Answer 1

Polymer is high molecular weight substance formed by joining a large number of small repeating units called as Monomers.

Question 2

What are the three types of polymers?

Answer 2

Isotactic, Atactic, and Syndiotactic

Question 3

Elaborate on the three types of Polymers

Answer 3

Isotactic polymers: Functional groups are arranged on the same side.

Atactic polymers: No regular arrangement of functional groups on the back bone of the polymer chain.

Syndiotactic Polymers: Alternate arrangement of functional groups .

Question 4

Condensation Polymers

Answer 4

Step Growth Polymers.
Takes place in monomers having reactive functional groups.
Elimination of simple molecules.
Repeat units are different.
Large change in molecular mass of polymer.
Polymer formed in gradual steps
Product can be thermoplastic or setting.
Eg : Polyester, Bakelite

Question 5

Addition Polymers

Answer 5

Chain Growth Polymers
No Elimination of simple molecules
Takes place in monomers having multiple bonds
Little change in the mass of the polymer
Repeating unit is the same
Polymer formed instantly, fast reaction
Thermoplastic
Eg : PVC and Polyethylene

Question 6

Thermoplastic Polymers

Answer 6

Addition Polymerization
Long chains with weak Vander Waals forces
Soften on heating and harden on cooling and no chemical change
Can be remoulded
Scrap can be reused
Soft, weak and less brittle
No cross linkage
Can be dissolved in organic substances
Eg : PVC and polyethylene

Question 7

Thermosetting Polymers

Answer 7

Condensation Polymerization
3D network structure and connected bonds
Harden on heating, no change on cooling and chemical alteration
Cant be remoulded
Hard, stiff and very brittle
Scrap cant be reused
Cant be dissolved in organic substances
Eg : Nylon, Bakelite

Question 8

Significance of Molecular Mass of Polymers

Answer 8

Molecular Mass influences a lot of properties of a polymer, the higher the mass more resilient and strong the polymer is, its viscosity and softening temperature is also higher and that’s why they have specific applications.
The molecular mass of a polymer is not fixed as it depends on the polymerization reaction, which further depends on the availability of functional groups, charge carrier and life time of carrier.
Hence polymers are poly disperse mixture of various molecular mass polymers.

Question 9

Classification of Polymers based on source

Answer 9

• Naturally occurring Polymers: These occur in plants and animals and are very essential for life e.g. starch, cellulose, amino
  acids, etc.
• Synthetic polymers: These polymers are prepared in laboratory they are man made polymers e.g. plastics, synthetic rubbers, etc.
• Semi synthetic polymers: These are derived from naturally occurring polymers by chemical modification. e.g. vulcanized
  rubber, Cuprammonium silk and Cuprammonium rayon, etc.

Question 10

Classification of polymers based on Molecular forces

Answer 10

• Elastomers: In these polymers, chain are held by weakest intermolecular forces which permits the polymers to be stretched. The polymer regains its original position when forces are released.
• Fibers: In these polymers the inter molecular forces are strong due to hydrogen bonding, cross linking, cyclic structure
• Thermoplastics: These are polymers for which inter molecular forces between elastomers and fibers. Due to this they can be easily molded by heating.
• Thermosetting polymers: Thermosetting polymers undergo chemical changes and cross linking on heating and become permanently hard and infusible.

Question 11

Plastics

Answer 11

• Low fabrication cost, low thermal & electrical conductivities, high resistance to corrosion, Plastics are resistant to chemicals & solvents
• Plastics reduce noise & vibrations in machines
• Plastics are bad conductors of heat are useful for making handles used for hot objects, most plastics are inflammable.
• Plastics are electrical insulators & find large scale use in the electrical industry.
• Plastics are clear & transparent so they can be given beautiful colors.

Question 12

Compounding of Plastics

Answer 12

The process of mechanical mixing of various additives with
polymers (resin) to impart some special properties to the plastics.
The additives gets incorporated with resins to give homogeneous mixture.

• Resin or Binder
• Fillers or extenders
• Plasticizers
• Pigments or Dyes
• Activators, catalysts or accelerators
• Lubricants
• Stabilizers

Question 13

Compression Molding

Answer 13

Raw materials or softened resinous mass compressed under heat and pressure.

Done in a mold, molten mass fills the cavities in this.

This is then cured by heating(Thermosetting) or cooling(Thermoplastic)

Question 14

Injection Molding

Answer 14

Used for thermoplastics

Granular or powdered resin melted and poured into mold using a nozzle and piston, after cooling mold removed to obtain final product.

Disadvantage is that air bubbles can form inside the finished product.

Question 15

Transfer Molding

Answer 15

Used for thermosets.

Granular or powder form of resin heated at low temp and introduced into mold using an orifice.

Once in mold, the material is cured at high temps for certain amt of time, after cooling article is removed.

Intricate and detailed shapes can be achieved, no blistering, small wires or glass fibers can be introduced in the mold.

Question 16

Extrusion Molding

Answer 16

Used for thermoplastics

Used to form long continuous objects.

Granular/powder form introduced through hopper using a screw by heating, into a vertical/horizontal mold.

Mold surrounded by water for cooling of mold.

Proper temperature control of heating chamber, and speed of screw are important.

Question 17

Conducting Polymers

Answer 17

• Generally polymers are insulators because of the absence of free electrons.
• But they can be made conductive in certain cases by the process called doping.
• Two conditions for the polymer to become conducting are:
  1. Polymers should possess conjugated double bonds
  2. Polymer structure has to be disturbed either by adding or removing electrons by the process of doping.

Question 18

Intrinsically conducting polymers

Answer 18

Consist Conjugated pi-electrons in the backbone of their macromolecules, which are responsible for high electric conductivity

Conjugated pi-electrons get excited in presence of electric field and can be transported through the solid polymer.

Overlapping of orbitals of conjugated pi-electrons over the entire backbone of the polymer results in the formation of valence bands and conduction bands. This induces conductivity in the presence of electric field.

Poor mechanical properties, environmental
sensitivity, moderate stability of electrical properties with temperature significantly limit the industrial applicability of ICPs.

Question 19

Doped conducting polymer

Answer 19

Step one is formation of a cation or anion, called a soliton or a polaron.

Because it is not until an electron is removed from the valence band (p-doping) or added to the conducting band (n-doping) does a polymer become highly conductive.

Doping generates charge carriers which move in an electric field. Positive charges and negative charges move to the opposite electrodes and this movement is responsible for electrical conductivity.

Question 20

Elaborate on p-doping

Answer 20

Involves treating intrinsically conducting polymer with a Lewis acid, oxidation takes place and positive charges on the polymer backbone are created.

Question 21

Elaborate on n-doping

Answer 21

Involves treating intrinsically conducting polymers with a Lewis Acid, reduction takes place and negative charges on the polymer backbone are created.

Question 22

Extrinsically Conducting Polymer

Answer 22

2 types
1. Conductive element filled polymer - Non conductive polymer as binder, holding conductive substance like carbon black, metals, metal oxides etc. Cheap, good conductivity, light weight.
2. Blended conducting polymer: Obtained by
blending conventional polymers with conducting polymers
either through physical or chemical process.

Question 23

Applications of conducting polymers

Answer 23

• In rechargeable light weight batteries
• In optical display devices
• In aircrafts and aerospace components
• In diodes and transistors
• In solar cells

Question 24

Biodegradable polymers

Answer 24

Polymers in which monomers are joined to one another by functional group linkage and has unstable link in backbone.

They are broken down to biologically accepted
molecules that are metabolized and removed from
the body via normal metabolic pathway.

Question 25

Biodegradation of Polymers

Answer 25

An object undergoes biodegradation in 3 steps,

Bio deterioration - Mechanical weakening of structure

Bio fragmentation - Breakdown of elements by microorganisms

Bio assimilation - Incorporation of the old material into new cells.

Question 26

Advantages of Biodegradable Polymers

Answer 26

Produces less emissions
Less Waste
Biodegradable polymers and Renewable energy the way to go
Decompose quickly and don’t leave behind toxic pollutants like methane or bisphenol.
Bio polymers can be used as absorbable surgical implants, controlled release of drugs, absorbable skin grafts etc.

Question 27

Biodegradable PLAs

Answer 27

Polylactic acid, also known as poly(lactic acid) or polylactide
(abbreviation PLA) is a thermoplastic polyester with backbone formula
(C3H4O2)n or [–C(CH3)HC(=O)O–]n.

Obtained by condensation of lactic acid C(CH3)(OH)HCOOH with loss of water.

It can also be prepared by ring-opening polymerization of lactide [-C(CH3)HC(=O)O–]2, the cyclic dimer of the basic repeating unit.

Look into chemical notation and structural formula

Question 28

Properties of PLA

Answer 28

• PLA polymers range from amorphous glassy polymer to semi-crystalline and highly
  crystalline polymer with a glass transition 60–65 °C, a melting temperature 130-180 °C,
  and a Young’s modulus 2.7–16 GPa.
• Heat-resistant PLA can withstand temperatures of 110 °C. The basic mechanical properties
  of PLA are between those of polystyrene and PET.
• The melting temperature of PLLA can be increased by 40–50 °C and its heat deflection
  temperature can be increased from approximately 60 °C to up to 190 °C by physically
  blending the polymer with PDLA (poly-D-lactide).
• PDLA and PLLA form a highly regular stereocomplex with increased crystallinity. The
  temperature stability is maximised when a 1:1 blend is used, but even at lower
  concentrations of 3–10% of PDLA, there is still a substantial improvement.
• Biodegradation of PDLA is slower than for PLA due to the higher crystallinity of PDLA.
• Racemic PLA and pure PLLA have low glass transition temperatures, making them
  undesirable because of low strength and melting point. A stereocomplex of PDLA and
  PLLA has a higher glass transition temperature, lending it more mechanical strength.

Question 29

Uses of PLA

Answer 29

*Automotive parts such as floor mats, panels, and covers.

• In the form of fibers, used for monofilament fishing line and nettingfor vegetation and weed prevention. It is used for sandbags, planting pots, binding tape and ropes .
• PLA can degrade into innocuous lactic acid, so it is used as medical implants in the form of anchors, screws, plates, pins, rods, and mesh. Depending on
  the exact type used, it breaks down inside the body within 6 months to 2 years. This gradual degradation is desirable for a support structure, because
  it gradually transfers the load to the body (e.g. to the bone) as that area heals. The strength characteristics of PLA and PLLA implants are well documented.
• Variety of consumer products such as disposable tableware, cutlery, housings for kitchen appliances and electronics such as laptops and handheld devices, and microwavable trays.
• It is used for compost bags, food packaging and loose-fill packaging material that is cast, injection molded, or spun.
• PLA has applications in engineering plastics, where the stereo complex is blended with a rubber-like polymer such as ABS. Such blends have good form
  stability and visual transparency, making them useful in low-end packaging applications.