Chemistry 2 Marks Questions

A thermoplastic polymers are the linear or slightly branched long chain molecules capable of repeatedly softening on heating and hardening on cooling. These polymers posses intermolecular forces of attraction intermediate between elastomers and fibres. For example polythene, polystyrene, polyvinyls, etc.
A thermosetting polymer are cross linked or heavily branched molecules, which on heating undergo extensive cross linking in moulds and again become infusible. These cannont be reused. For example are bakelite, urea- formaldehyde resin etc.

Polymers are high molecular mass substances consisting of a very large number of simple repeating structural units joined together through covalent bonds in a regular fashion. Polymers are also called macromolecules. Some examples are polythene, nylon-66, bakelite, rubber, etc. Monomers are the. simple and reactive molecules from which the polymers are prepared either by addition or condensation polymerisation. Some examples are ethene, vinyl chloride, acrylonitrile, phenol and formaldehyde etc.

There are three different types based on the structure of the polymers.

1. Linear polymer: These polymers consist of long and straight chains. Such as polythene, polyvinyl chloride etc.
2. Branched chain polymers: These polymers contain linear chains having some branches. Such as low density polythene.
3. Cross-linked polymers: These are formed from bi- functional and tri- functional monomers. Such as bakelite, malamin etc.

When two or more different monomers are allowed to polymerise together the product formed is called a copolymer, and the process in called copolymerisation. Example, Buna-S and Buna-N. Buna- Sis a copolymer of 1, 3- butadiene and styrene while Buna-N is a copolyrner of 1, 3-butadiene and acrylonitrile.

1. Chain initiation step:

2. Chain propagating step:

3. Chain termination steps:

1. By combination of free radicals (II):

2. By disproportionation of free radicals:

1. Elastomers.
2. Fibres.
3. Thermoplastics.
4. Thermosetting plastics.

Natural polymers: Polymers which are found in nature,i.e., in animals and plants are called natural polymers, e.g., proteins, starch, cellulose, nucleic acids, resins and natural Sol. rubber.
Synthetic polymers: Man-made polymers are called synthetic polymers, e.g., plastics (polythene, PVC), synthetic fibres (polyester, 15.8 nylon-66) and synthetic rubber (neoprene, Buna-S).

1. Tetrafluoroethene.
2. 1, 3–butadiene and acrylonitrile.

1. Ethylene glycol (Ethane–1,2–diol) and terephthalic acid. (Benzene–1,4–dicarboxylic acid)
2. Hexamethylenediamine & adipic acid.

1. Phenol & Formaldehyde.
2. 2–Chloro–1,3–butadiene.

Alternate Answer

Chloroprene.

Thermoplastics: These polymers are easily softened on heating, moulded and then hardened on cooling.
Examples: polythene, polypropylene, polystyrene, polyvinyl chloride, teflon, polyvinyl acetate, etc.
Thermosetting polymers: These polymers on heating become infusible and form an insoluble hard mass thus, cannot be remoulded.
Examples: Bakelite, urea-formaldelyde resins, etc.

The polymers which can be degraded by the micro organism.
Example: PHBV.

S. No.	Thermoplastic	Thermosetting Plastics
i)	Soften and melt on heating and can be remoulded.	Do not soften on heating and cannot be remoulded.
ii)	It is linear.	It has cross-links .
iii)	e.g polythene/PVC.	e.g Bakelite/Terylene.

Polymers which can be remoulded again and again are called thermoplastic polymers.
Ex. Polythene, PVC etc.
Polymers which cannot be remoulded again and again are called thermosetting polymers.
Ex. Bakelite, Melamine etc.

1. Bakelite: For making combs, electrical switches, handles of utensils, computer discs.
2. Nylon-6: For making tyre cords, fabrics, ropes.

Low density polythene: It is obtained by the polymerisation of ethane under high pressure of 1000 to 2000 atmospheres at a temperature of 350K to 570K in the presence of traces of dioxygen or a peroxide initiator (catalyst). The low-density polythene (LDP) obtained through the free radical addition and H-atom abstraction has highly branched structure.
High density polythene: It is formed when addition polymerisation of ethane takes place in a hydrocarbon solvent in the presence of a catalyst such as triethylaluminium and titanium tetrachloride (Ziegler-Natta catalyst) at a temperature of 333K to 343K and under a pressure of 6-7 atmospheres. High density polythene (HDP) thus produced, consists of linear molecules and has a high density due to close packing. It is also chemically inert and more tougher and harder. It is used for manufacturing buckets, dustbins, bottles, pipes.

Synthetic polymers are quite resistant to environmental degradation process and are responsible for accumulation of polymer solid waste material. New biodegradable synthetic polymers have been designed and developed. These polymers contain similar functional groups as present in biopolymers, e.g., aliphatic polyesters Biopolymers are polymers of amino acids or carbohydrates which are linked to each other by peptide or glycosidic linkages as shown below:

Polymer of amino acid Biopolymer can or cannot be biodegradable. e.g., protein, starch etc., are biodegradable but keratin are non-biodegradable. Biodegradable polymer are polymers which can be degradable always, e.g., DHBV nylon-2, nylon-6.

To improve upon physical properties of natural rubber, a process of vulcanisation is carried out. This process consists of heating a mixture of raw rubber with sulphur and an appropriate additive at temperature range between373K to 415k. On vulcanization, sulphur forms cross links at the reactive sites of double bonds and thus the rubber gets stiffened.

Polyamides: The polymers having large number of amide linkage the chain are called polyamides, for example, nylon-6, 6 and nylon-6.

	LDP		HDP
1.	It is obtained the polymerisation of ethene under high pressure of 1000 to 2000 atmospheres at a temperature of 350K to 570K in the presence of traces of dioxygen or a peroxide initiator (catalyst).	1.	It is formed when 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 temperature of 333K to 343K and under a pressure of 6-7 atmospheres.
2.	(LDP) obtained through the free radical addition and H-atom abstraction has highly branched structure.	2.	(HDP) consists of linear molecules and has a high density due to close packing.
3.	Low density polythene is chemically inert and tough but flexible and a poor conductor of electricity.	3.	It is also chemically inert and more tough and hard.

Vulcanized rubber:

When it is heated withs at 373-415K, it results into -S-S-links forming.

Buna-S is an elastomer having weak van der Waals intermolecular forces whereas terylene is a fibre having strong intermolecular hydrogen bonding.

Benzoquinone traps the radical intermediate to form a non-reactive radical, which is highly stabilised by resonance. Due to the lack of reactivity of this intermediate, further progress of the chain reaction is interrupted and the reaction stops.

Polyesters: These are the polycondensation products of dicarboxylic acids and diols. Dacron or terylene is the best known example of polyesters.

In nylon-6, 6, two sixes stand for hexamethylene diamine (a monomer with 6C-atoms) and adipic acid (another monomer with 6C-atoms).
In nylon-6, six stands for the only monomer caprolactam (6C-atoms).

Yes, step growth polymers (nucleic acids, proteins and starch) are conden¬sation polymers and they can be formed by the loss of simple molecule like water leading to the formation of high molecular mass polymers.

Vulcanisation is a process of heating natural rubber with sulphur. This is done so as to make it more elastic, hard, more abrasion resistant by sulphur cross-linking. Diphenyl amine is added to rubber so as to prevent its oxidation.

Polyolefins: These are polymers derived from unsaturated hydrocarbons, for example, polypropene.

Polymer ‘A’ is Novalac and ‘B’ is Bakelite. The reactions involved in the formation of these two polymers are given below:



Novalac on heating with HCHO undergo cross-linkage to form an infusible solid called Bakelite. Novolac is linear chain polymer while Bakelite is cross linked polymer.

1. LDPE (Low Density Polyethylene): LDPE is obtained by the polymerisation of ethene under high pressure of 1000-2000 atm at 350-570K in the presence of an initiator.
2. HDPE (High Density Polyethylene): It is obtained when polymerisation is done in the presence of Ziegler-Natta catalyst at 333-343K under 6-7 atm pressure.

Rubbers: In rubber, the polymer chains are held together by the weakest intermolecular forces. These weak binding forces permit the polymer to be stretched. A few ‘crosslinks’ are introduced in between the chains, which help the polymer to retract to its original position after the force is released as in vulcanised rubber.
Plastics: These are the linear or slightly branched long chain molecules capable of repeatedly softening on heating and hardening on cooling. These polymers possess intermolecular forces of attraction intermediate between elastomers and fibres.