Chemistry in Everyday Life (Commercially Important Condensation Polymers)

Polyesters
Polymers with ester linkage are called polyesters.
Terylene or Dacron
Terylene or Dacron is manufactured from ethylene glycol and terephthalic acid. The reaction is carried out at 420 - 460 K in the presence of catalyst zinc acetate and antimony trioxide.
Properties
Terylene forms strong fibers. It is crease resistant, has high moisture absorption and has a high tensile strength.
Uses
(i) Making wash and wear garments.
(ii) In seat belts and sails.
Property
It is a thermoplastic. It dissolves in suitable solvent and the solution on evaporation leaves a tough but non flexible film.
Uses
It is used in the manufacture of paints and lacquers.
Polyamides
Polyamides are polymers with amide linkage (-NH-CO-).
Nylon - 66
In Nylon - 66 both monomers have 6 carbon atoms each and hence the name.
Preparation of Nylon - 66
Here the polymide Nylon-66 is formed by heating the reactant mixture under pressure and the process has been developed so that the molecular mass of the polymer is controlled in the range of 12,000 to 20,000 amu.
Properties of Nylon-66
High tensile strength, tough, abrasion resistant and elastic.
Uses of Nylon-66
It is fabricated into sheets, bristles for brushes and in textiles as crinkled nylon fibers that are used for making elastic hosiery.
Nylon-6 or (perlon)
Preparation
Nylon-6 is prepared form the monomer caprolactum which is obtained from cyclohexane (petrochemical). Since caprolactum is more easily available, it is used for polymerization which is carried out in the presence of water that first hydrolyses the caprolactum to amino acid. Subsequently the amino group of the amino acid can react with caprolactum to form the polyamide polymer. Filaments of Nylon-6 are obtained by melt-spinning of the polymer. The fibers are cooled by a stream of air.
Uses of Nylon-6
(i) Nylons are insoluble in common solvents, have good strength and absorb little moisture.
(ii) It is used for tyre cords, fabrics, ropes, carpets and manufacture of garments.
Formaldehyde Resins
Bakelite (Phenol Formaldehyde Resin)
Bakelite is made from phenol and formaldehyde in the presence of a base catalyst. It involves formation of methylene bridges at the ortho and para positions. The reaction starts with the initial formation of orth6 and/or para-hydroxymethyl phenol derivatives which further react with phenol to form compounds where the rings are formed to each other with -CH2 groups.
Thus linear and cross linked material can be prepared. Cross linked bakelite is a thermosetting polymer.
On further heating with HCHO, novalac undergoes cross-linking to an infusible solid called bakelite. It is hard scratch and water resistant.
Soft bakelite (Low degree of polymerization)
Used as bonding for laminated wooden planks and in varnish and paint.
Hard bakelite (High degree of polymerization)
It possesses excellent electrical insulating character and hence its major use in making electrical goods.
Used to make combs, fountain pen barrels, gramophone records, electric goods, formica table tops. Sulphonated bakelites are used as ion exchange resins.
Melamine Formaldehyde Resins
Uses
Hard and unbreakable - so used to make non-breakable plastic crockery i.e., cups and plates that do not break on being dropped.