Which polymer has 'chiral' monomer(s)?

A chiral carbon is an $$sp^3$$ hybridised carbon atom bonded to four different groups. We need to check whether the monomer(s) of each given polymer contain any chiral carbon.

Option A: Neoprene

Neoprene is a polymer of chloroprene (2-chloro-1,3-butadiene). The structure of chloroprene is:

$$CH_2 = CCl - CH = CH_2$$

All the carbon atoms in chloroprene are either $$sp^2$$ (doubly bonded) or part of $$=CH_2$$ groups. None of them is bonded to four different groups. So the monomer is not chiral.

Option B: Buna-N

Buna-N is a copolymer of 1,3-butadiene ($$CH_2=CH-CH=CH_2$$) and acrylonitrile ($$CH_2=CH-CN$$). In 1,3-butadiene, all carbons are $$sp^2$$. In acrylonitrile, $$CH_2=CH-CN$$, the carbons are also $$sp^2$$ or bonded to only three different groups. Neither monomer has a chiral centre.

Option C: Nylon 6,6

Nylon 6,6 is a copolymer of hexamethylenediamine ($$H_2N-(CH_2)_6-NH_2$$) and adipic acid ($$HOOC-(CH_2)_4-COOH$$). In hexamethylenediamine, the internal $$-CH_2-$$ carbons each carry two identical H atoms, so they are not chiral. Similarly in adipic acid, the internal carbons carry two H atoms each. Neither monomer is chiral.

Option D: PHBV

PHBV stands for poly(3-hydroxybutyrate-co-3-hydroxyvalerate). It is a copolymer of two monomers:

(i) 3-Hydroxybutanoic acid ($$\beta$$-hydroxybutyric acid): $$CH_3-CH(OH)-CH_2-COOH$$

Look at the carbon bearing $$-OH$$: it is bonded to (1) $$-CH_3$$, (2) $$-OH$$, (3) $$-H$$, and (4) $$-CH_2COOH$$. All four groups are different. This carbon is chiral.

(ii) 3-Hydroxypentanoic acid ($$\beta$$-hydroxyvaleric acid): $$CH_3CH_2-CH(OH)-CH_2-COOH$$

The carbon bearing $$-OH$$ is bonded to (1) $$-C_2H_5$$, (2) $$-OH$$, (3) $$-H$$, and (4) $$-CH_2COOH$$. All four are different. This carbon is also chiral.

Therefore, PHBV is the polymer whose monomers contain chiral centres.

The correct answer is Option D.