Ring Formation Also called the intramolecular reaction A chain containing two mutually reactive groups can react with it self and a ring structure forms. Ring formation depends strongly on the number of atoms linked together in the ring.

Example Preparation of a polyester. O HO-----C-OH C-O O 5,6 and to some extent 7 members rings are stable and have tendency to for ring.

Example 3, 4, 8, 9, 10 and 11 rings are un stable due to bond angle strain and steric repulsion’s between atoms. (Rowded into the center of the ring respectively and usually not formed). 12 members and larger rings are more stable and can be formed. Their probability of formation decreases as the ring size increases. This is because the probability of the two ends of a single chain meeting decreases as the chain length increases. Self condensation of w-hydroxyl carboxylic acids HO - (CH 2 ) 3 - COOH CH 2 -CH 2 + H 2 O CH 2 O C O

Non Linear Step Polymerization The presence of a reactivity monomer with functionality > 2, causes branching initially and crosslinking structure ultimately. This has a great effect on the structure and molar mass of the polymer. Normally the resulting polymer are rigid. The point at which the first net work molecules is formed is known as the gel-point (gelation) i.e. change of the Reaction mixture from a viscous liquid to solid gel which shows no tendency to flow.

Example The reaction of dicarboylic acid with a triol. HOOC-R 1 -COOH + HO-R 2 -OH OH O O O O O O ----O-R 2 -O-C-R 1 -C-O-R 2 -O-C-R 1 -C-O-R 2 O O C = O R 1 C = O O O O -----O-C-R 1 -C-O-R 2 O C = O R 1 -C-O-R 2 -O----- O

Thank You See You Next Lecture