Polylactic acid (PLA) has the repeat unit $- [O - CH (CH X_{3}) - C (= O)] X^{-}$ . A PLA sample has molar mass 108500 g/mol. Taking C 12, H 1, O 16 and ignoring end groups, calculate the degree of polymerisation, to the nearest integer.

Numerical answer type, tolerance 0.5.

Answer: 1507

The repeat unit is

C X_{3} H X_{4} O X_{2}

, mass 36 + 4 + 32 = 72. Degree of polymerisation = 108500/72 = 1506.94, i.e. 1507 to the nearest integer.