Past exam of the chemistry course of the year 3 of the natural sciences course of the University of Cambridge / 2022 / Paper 3 / 50 / c / Solution

B contains both $-\mathrm{C}{\mathrm{H}}_2-\mathrm{CH}(\mathrm{Cl})-$ and $-\mathrm{C}{\mathrm{H}}_2-\mathrm{CH}(\mathrm{OCOC}{\mathrm{H}}_3)-$ monomeric units distributed along the same carbon backbone: a vinyl chloride-vinyl acetate copolymer. One possible local segment isThe ester is attached through oxygen to the backbone carbon. A random copolymer should not be drawn as two long homopolymer blocks. The stated $75:25$ monomer feed is not enough to prove an incorporated $75:25$ unit ratio: monomer reactivity ratios and conversion affect composition and sequence statistics. Under an explicitly ideal equal-incorporation assumption that ratio could be used as a schematic average, not a periodic repeat.