Question

Controlled Degradation Question We've discussed how controlled degradation can be an important component of drug delivery systems. Name another, non- medical application where controlled degradation could be important and the mechanism by which this degradation could happen

Answer 1

Controlled degradation of polymers

REASON:  The production of functionalized or modified polymers by conventional synthetic routes is expensive and time-consuming. However, advances in degradation technology have become an enabling factor in the production of modified polymers and their functionalization.

Mild irradiation, ozonization, and enzymatic routes are among the processes that have been explored for polymer modification. Biopolymers, such as chitosan, hyaluronic acids, and polyhydroxyalkanoates, are known to be suitable for a diverse number of applications, ranging from biomedical to organic?electronics.

Controlled degradation processes can be used to prepare these types of polymers with reasonably low molecular weights and to generate radical species that help to stabilize these polymers or to initiate further beneficial reactions.

Degradation can be useful for recycling/reusing the polymer waste to prevent or reduce environmental pollution. Degradation can also be induced deliberately to assist structure determination.

MECHANISMS :
1.Solvolysis

Step-growth polymers like polyesters, polyamides, and polycarbonates can be degraded by solvolysis and mainly hydrolysis to give lower molecular weight molecules. The hydrolysis takes place in the presence of water containing an acid or a base as catalyst. Polyamide is sensitive to degradation by acids and polyamide moldings will crack when attacked by strong acids. For example, the fracture surface of a fuel connector showed the progressive growth of the crack from acid attack (Ch) to the final cusp (C) of a polymer. The problem is known as stress corrosion cracking, and in this case, was caused by hydrolysis of the polymer. It was the reverse reaction of the synthesis of the polymer:

HO OH

2.Oxidation:

Oxidation is usually relatively easy to detect owing to the strong absorption by the carbonyl group in the spectrum of polyolefins. Polypropylenehas a relatively simple spectrum with few peaks at the carbonyl position (like polyethylene). Oxidation tends to start at tertiary carbon atoms because the free radicals formed here are more stable and longer lasting, making them more susceptible to attack by oxygen. The carbonyl group can be further oxidised to break the chain, this weakens the material by lowering its molecular weight, and cracks start to grow in the regions affected.

3.Biological degradation:

Biodegradable plastics can be biologically degraded by microorganisms to give lower molecular weight molecules. To degrade properly biodegradable polymers need to be treated like compost and not just left in a landfill site where degradation is very difficult due to the lack of oxygen and moisture .