1. Classification of Polymers:
I. Classification Based on Origin: Polymers are classified into three categories based on their origin. These are discussed below:
- Natural Polymer: The polymers which are obtained from nature (plant and animal) are called natural polymer.
Example - Natural rubber, starch, cellulose etc.
- Synthetic Polymer: The polymers which are made artificially in laboratory by using chemicals are called synthetic polymer.
Example - Polyvinyl chloride (PVC), Dacron, Glyptal etc.
- Semi-synthetic Polymer: These are obtained after the chemical modification of polymers which are naturally origin.
Example - Cellulose nitrate, Cellulose acetate etc.
II. Classification Based on Polymerization:
- Chain or, Addition Polymers: Polymers which are formed due to chemical reaction of monomers through chain pathway are called Chain or, Addition polymer. Example - Polyethene, Polyvinyl chloride etc.
- Condensation Polymers: Polymers which are formed due to chemical reaction of two or, more functional groups containing monomers through condensation pathway are called Condensation polymer.
Example - Dacron, Glyptal etc.
III. Classification Based on Effect of Heat:
- Thermoplastic Polymer: Polymers which soften on heating and harden on removal of heat and if this can be done repeatedly by keeping intact the properties of polymer then the polymer is called thermoplastic polymer.
Example - PVC, Polyethene etc.
- Thermosetting Polymer: Polymer which soften on heating and harden on removal of heat and if on again heating it soften but removal of heat does not hardened it then such polymers are called thermosetting polymer. Example - Phenol-formaldehyde resin.
IV. Classification Based on Structure:
- Linear Polymer: If monomeric units are joined linearly to generate long chain polymer molecule then those polymers are called linear polymers.
Example - PVC, Polystyrene etc.
- Branched Polymer: Polymers which has long polymeric chain along with branched chain are called branched polymer.
Example - Low density polyethene.
- Network Polymer: These are formed when the branched chains of branched polymers reacting each other to generate network.
Example - Phenol-formaldehyde resin.
V. Classification Based on Mode of, Arrangement of Monomer:
- Homopolymer: The polymers whose polymeric chain contains only one type of monomeric unit.
Example - Polyethene, PVC etc.
- Copolymer: The polymers whose polymeric chain contains two or, more different types of monomeric unit. Example - Nylon 6,6, Bakelite etc. .
VI. Classification Base on Inter-molecular Force Present in Polymer:
- Elastomer: The polymers which has lowest inter- molecular force are called elastomer. Weakest van der Waals' force is present in these polymers.
Example - Natural rubber, Styrene-Butadiene rubber etc.
- Plastic: The polymers which ha moderate inter- molecular force are called plastic.
Example - Polyethene, Polystyrene etc.
- Fibre: The polymers which has highest inter-molecular force are called fibre. Strong H-bonding is present in these polymers.
Example - Cotton, Silk etc.
2. Characteristics of Polymers: Some general characteristics of polymers are given below:
- Polymers have high molecular weights.
- Polymers are generally colourless.
- These may be transparent or, opaque.
- These are non-conductors of heat and electricity.
- These are highly viscous.
- These does not have any sharp melting point.
- These are generally insoluble in water and commonly soluble in organic solvent.
3. Polymerization Reactions: Polymerization reactions are classified into two types - 1. Addition polymerization and II. Condensation polymerization.
I. Addition Polymerization: Here, simply monomeric units are combined together to generate polymers without removal of stable buy small molecules. Addition polymerization can occur in three different pathways.
- Chain pathway: Polymerization will follow this pathway when radical initiator like AIBN, Benzoyl peroxide etc. are present. This process consist of three steps. - Chain initiation, Chain propagation and Chain termination.
- Cationic pathway: Polymerization will follow this pathway when monomer contains one or, more EWG like alkyl which can stabilize cation. This pathway also consists of three steps similar to Chin pathway.
- Anionic pathway: Polymerization will follow this pathway when monomer contains one or, more EWG like -CN which can stabilize anion. It also consists of three steps.
II. Condensation Polymerization: Here, the monomers must contains at least two active functional groups. The polymerization process involves the removal of small but stable molecules like water, carbon dioxide, methanol etc.
4. List of Some Polymers Alongwith Their Monomeric Units:
7. Ozone Layer:
- Formation: In stratosphere O2 absorb UV light to decompose into atomic oxygen which combines with molecular oxygen to produce ozone.
- Role: It absorbs most of the harmful UV light radiated by sun.
- Depletion: Due to emission of some foreign substance into atmosphere , the ozone layer become thin to thinner. The phenomenon of thinning of ozone layer at stratosphere is known as depletion.
- Cause: CFCs i.e. chlorofluorocarbons produce Cl radical which destroys millions of ozone molecules in chain pathway.
- Effect: 1. The temperature of earth surface will increase,
2. Causes skin cancer, eye cataract,
3. Production of crop will decrease.
8. Greenhouse and Greenhouse Effect: Greenhouse gases such as CH4, CFCs, CO2, O3 etc. absorb the radiation emitted by the earth's surface and keep the surface of earth and the adjacent atmosphere warm and create an environment suitable for the existence of livings is called greenhouse effect.
9. Global Warming: Due to the various activities of humans, the amount of greenhouse gases are increased. Hence, the temperature of atmosphere is gradually increases. This progressive increase of temperature due to greenhouse gases all over the world is called global warming.
10. London smog vs. Los Angeles Smog: