Ring Formation
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Transcript Ring Formation
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
Self
condensation of w-hydroxyl carboxylic acids
HO - (CH2)3 - COOH
CH2-CH2 + H2O
CH2 O
C
O
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
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-R1-COOH + HO-R2-OH
OH
O O
O
O
O
----O-R2-O-C-R1-C-O-R2-O-C-R1-C-O-R2
O
O
O
C=O
R1
C=O
O
O O
-----O-C-R1-C-O-R2
O
C=O
R1-C-O-R2-O----O O
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