Biodegradable Polymers
1. Identifying Biodegradable Polymers
Kevlar.
Kevlar is a polyamide. Condensation polymers like polyamides contain polar amide linkages (-CONH-) which can be hydrolysed by water, acids, alkalis, or enzymes. While Poly(ethenol) is water soluble, it has a continuous carbon backbone (C-C) which is generally resistant to hydrolysis.
Nylon-6,6.
Nylon-6,6 is a polyamide with hydrolysable amide linkages. Poly(phenylethene) is an addition polymer with a chemically inert carbon-carbon backbone.
Poly(ester).
Polyesters contain ester linkages (-COO-) which are susceptible to hydrolysis. Poly(alkenes) possess strong, non-polar C-C and C-H bonds that are difficult to break biologically.
2. Medical Implants
Answer:
Polylactic acid (PLA) will decompose quickly, whereas polyethene does not.
PLA is a polyester containing a polar C=O group. The carbon atom in this bond is electron deficient (δ+) and can be attacked by nucleophiles (such as water or enzymes), making the polymer biodegradable via hydrolysis.
Poly(ethene) consists only of non-polar C-C and C-H bonds, which are chemically inert and cannot be attacked by nucleophiles.
They are decomposed by hydrolysis which requires warm aqueous alkali or warm aqueous acid.
3. Hydrolysis of Poly(aminoethanoic acid)
Answer:
Answer:
In alkaline conditions (e.g., NaOH), the carboxylic acid group forms a salt ($COO^-Na^+$), while the amine group ($NH_2$) remains unchanged.
Answer:
In acidic conditions (e.g., HCl), the amine group accepts a proton to form an ammonium salt ($NH_3^+$), while the carboxylic acid group ($COOH$) remains unchanged.
4. Hydrolysis Mechanism
Poly(hydroxyethanoic acid) can be hydrolysed by a base. Complete the mechanism by adding curly arrows and lone pairs.
Completed Mechanism:
The hydroxide ion acts as a nucleophile, attacking the $\delta+$ carbon of the carbonyl group. The C=O bond breaks and reforms, expelling the leaving group.
