Polymers and Plastics

On the basis of molecular forces, polymers are classified in the following four types-

1. Elastomers: These are rubber – like solids with elastic properties. In these elastomeric polymers, 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. The examples are buna-S, buna-N, neoprene etc.
2. Fibres: Fibres are the thread forming solids which possess high tensile strength and high modulus. These characteristics can be attributed to the strong intermolecular forces like hydrogen bonding. These strong forces also lead to close packing of chains and thus impart crystalline nature. The examples are polyamides (nylon 6, 6), polyesters (terylene), etc.
3. Thermoplastic polymers: 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. Some common thermoplastics are polythene, polystyrene, polyvinyls, etc. 4 Thermosetting polymers: These polymers are cross linked or heavily branched molecules, which on heating undergo extensive cross linking in moulds and again become infusible. These cannot be reused. Some common examples are bakelite, urea-formaldelyde resins (UFR), etc.

The classification based on source is sub categorized in-

1. Natural polymers: These polymers are found in plants and animals. Examples are proteins, cellulose, starch, resins and rubber.
2. Semi-synthetic polymers: Cellulose derivatives as cellulose acetate (rayon) and cellulose nitrate, etc. are the usual examples of this sub category.
3. Synthetic polymers: A variety of synthetic polymers as plastic (polythene), synthetic fibres (nylon 6,6) and synthetic rubbers (Buna - S) are examples of manmade polymers extensively used in daily life as well as in industry.

1. Cellulose is the homopolymer of glucose as monomer unit. Inulin is the homopolymer of fructose as monomer unit.
   1. Nylon 6 is obtained by heating caprolactum with water at a high temperature.
   2. Plexiglass or polymethyl methacrylate is the addition polymer of methyl methacrylate.
   3. Glyptal is the copolymer of ethylene glycol and phthalic acid. Bakelite is the condensation polymer (copolymer) of phenol and formaldehyde.

Polyetherimide (PEI) is an amorphous, amber-to-transparent thermoplastic which is made from the polymerisation of etherimide.

A large number of polymer applications in different fields depend on their unique mechanical properties like tensile strength, elasticity, toughness, etc. These mechanical properties are governed by intermolecular forces, e.g., van der Waals forces and hydrogen bonds, present in the polymer. These forces also bind the polymer chains. Under this category, the polymers are classified into the following four sub groups on the basis of magnitude of intermolecular forces present in them- elastomers, fibers, thermoplastic and thermosetting. Elastomers are rubber – like solids with elastic properties. In these elastomeric polymers, 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. Examples are buna-S, buna-N, neoprene, Bromo Isobutylene Isoprene (bromobutyl), Viton (a brand of synthetic rubber and fluoropolymer elastomer commonly used in O-rings and other molded or extruded goods) etc.

Melamine is a fire proof plastic.

Teflon  is used for non-stick coating on cookware.

Polyvinyl chloride  is not a thermosetting plastic.

A blowing agent is a substance which is capable of producing a cellular structure via a foaming process in a variety of materials that undergo hardening or phase transition, such as polymers, plastics and metals. Chemical blowing agents are isocyanate and water (for PUs), azo-, hydrazine and other nitrogen-based materials (for thermoplastic and elastomeric foams), sodium bicarbonate (aka baking soda, used in thermoplastic foams). Titanium hydride is used as a foaming agent in the production of metal foams, as it decomposes to form titanium and hydrogen gas at elevated temperatures.

The glass transition temperature is the reversible transition in amorphous materials or in amorphous regions within semicrystalline materials from a hard and relatively brittle state into a molten or rubber-like state. The glass transition temperature of polymethyl methacrylate is 105 ^oC. The glass transition temperature of polyvinyl alcohol is 85 ^oC. The glass transition temperature of polyvinyl chloride is 80 ^oC. The glass transition temperature of polyethylene terephthalate is 70 ^oC. The glass transition temperature of poly carbonate is 145 ^oC. Hence, poly carbonate has the highest Tg.

Thermosetting polymers: These polymers are cross-linked or heavily branched molecules which, on heating, undergo extensive cross linking in moulds and again become infusible. These cannot be reused. Some common examples are bakelite, urea-formaldelyde resins (UFR), etc. Melamine resin is an example of thermosetting polymers and used in the making of worktop surfaces. Duroplast is a thermosetting polymer that is light in weight. It is used for making car parts.  Hence, melamine resin and duroplast are the examples of thermosetting polymers.   

Polynucleotides such as DNA are composed of a variety of nucleotide subunits as monomer units.

Polyacrylonitrile (PAN) is made from the addition polymerisation of acrylonitrile and is manufactured under the brand name of Orlon.

The examples of non-biodegradable polymers are- PMMA (poly methyl methacrylate), PVC (polyvinyl chloride), PVAc (polyvinyl acetate), PFR (phenol formaldehyde resin), PP (polypropylene) etc.

P. PVC (polyvinyl chloride) has glass transition temperature of 80 ^oC. The glass transition temperature of nylon-6,6 is 70 ^oC. Q. Polyetherimide (PEI) is an amorphous, amber-to-transparent thermoplastic. Ultem is a family of PEI products manufactured by SABIC as a result of acquiring the General Electric Plastics Division in 2007. Ultem resins are used in medical and chemical instrumentation due to their heat, solvent and flame resistance properties. R. Polyethylene terephthalate (PET), or polyethylene terephthalic ester (PETE), is a condensation polymer produced from the monomers ethylene glycol, (a dialcohol) and dimethyl terephthalate (a diester). PET fibers are manufactured under the trade name of Dacron. Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. The best known brand name of PTFE is Teflon by DuPont Co. Hence, the statement R is false.