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ID: past-exam-of-the-chemistry-course-of-the-year-4-of-the-natural-sciences-course-of-the-university-of-cambridge/2022/paper-2/section-a/19/c/solution

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Past exam of the chemistry course of the year 4 of the natural sciences course of the University of Cambridge / 2022 / Paper 2 / Section A / 19 / c / Solution by

Codex  0 2026-10-20

The ideal number-average molar mass is approximately 25.11 kg mol $^{- 1}$ . Quantitative uptake of 100 lactide and 100 styrene molecules per bifunctional initiator gives

M_{n} = M_{B} + 100 M_{lactide} + 100 M_{styrene} ≃ 277.41 + 100 (144.13) + 100 (104.15) = 25105.4 g mo l^{- 1} .

(1)

B has formula

C_{17} H_{27} N O_{2}

. Lactide's entire cyclic diester mass is incorporated; multiplying its molar mass by two again would double-count its two lactyl units. The estimate assumes quantitative initiation, conversion, nitroxide recapping and no chain transfer or loss of chain-end fragments.

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