This document discusses methods for modifying polymers to facilitate biodegradation. Specifically, it discusses two main types of polymer modifications: [1] inserting functional groups like ester groups into the main chain that can be cleaved by chemical hydrolysis, and [2] inserting functional groups like carbonyl groups into the main chain that can be cleaved by photochemical reactions. Common methods to introduce these groups include copolymerizing vinyl monomers with monomers containing ester or carbonyl groups. The modified polymers can then undergo hydrolysis or photodegradation to form lower molecular weight oligomers that microorganisms can biodegrade.

1. Polymer Modification
To Facilitate Biodegradation
Presented by
Devansh Gupta
M.Sc. Polymer Science
Semester 4

2. Introduction
• Biodegradable polymers are a specific type
of polymer that breaks down after its intended purpose to result
in natural by products such as gases, water, biomass, and
inorganic salts.
• Polymers with main chains containing only carbon–carbon bonds
(except for those with large numbers of polar groups on the main
chain) show little or no susceptibility to enzyme catalysed
degradation reactions.
• Several approaches have been used to modify the polymers by
inserting ‘weak links’ within the back bones of such polymers to
permit the controlled degradation of an initially high molecular
weight polymer into a lower molecular weight oligomer, which
can then be utilized and consumed by microorganisms through
biodegradation processes.

3. • In this approach to create useful biodegradable polymers from
synthetic polymers two types of polymer modifications are there.
a) Insertion of functional groups in the main chain which can be
cleaved by chemical hydrolysis (especially ester groups)
b) Insertion of functional groups in the main chain which can be
cleaved by photochemical reactions (especially carbonyl
groups)
Types Of Modifications

4. • A widely used method for inserting main chain ester groups into vinyl-
type polymers is to carry out a free radical copolymerization reaction
on the appropriate vinyl monomer with a special monomer that
undergoes free radical, ring opening reaction to generate a main chain
ester group.
• These polymers after hydrolysis to their lower molecular weight
carboxy- and hydroxyl-terminated oligomers can be degraded by
fungal & bacterial attack.
Insertion Of Ester Groups
2-methyleneoxepane
Ester Linkage

5. • A widely used method for inserting main chain carbonyl groups
into vinyl-type polymers is to carry out a free radical
copolymerization reaction on the appropriate vinyl monomer with
a special monomer which will generate a main chain carbonyl
group.
Insertion Of Carbonyl Groups

6. • Both carbon monoxide and vinyl ketones will form such
carbonyl linkages, and both of these comonomers have been
used effectively in small amounts to prepare useful copolymers
with a variety of vinyl-type monomers.
Cont

7. • On irradiation with ultraviolet light, the activated carbonyl
groups present can take part in two different types of free
radical bond-breaking reactions.
• In organic photochemistry, these two reactions are referred to as
Norrish I and Norrish II reactions.
Photodegradation Of Carbonyl Linkages

8. • The Norrish I reaction fragments the polymer to generate both
carbonyl and alkyl radicals and in the presence of oxygen these
reactive fragments form carboxylic acid-terminated and
hydroxyl-terminated lower molecular weight chains.
• The Norrish II reaction creates fragments with vinyl and methyl
ketone end groups, and the latter can undergo further
photochemical and oxidative reactions to form carboxylic acid
end groups.

9. That’s All From Me..