Nylon 6,6 has the repeat unit $- [NH - (CH X_{2}) X_{6} - NH - CO - (CH X_{2}) X_{4} - CO] X^{-}$ , molecular formula $C X_{12} H X_{22} N X_{2} O X_{2}$ . Taking C = 12, H = 1, N = 14, O = 16, calculate the number-average degree of polymerisation (number of repeat units per chain) of a nylon 6,6 sample with $M_{n} = 30000 g mo l^{- 1}$ . Give the answer to the nearest integer.

Numerical answer type, tolerance 0.5.

Answer: 133

Repeat unit mass

= 12 \times 12 + 22 \times 1 + 2 \times 14 + 2 \times 16 = 226 g mo l^{- 1}

D P_{n} = 30000/226 = 132.74

, which is 133 to the nearest integer.