A PLA sample has weight-average molar mass M_w=2.40x10^5 g/mol and PDI =M_w/M_n=2.0. With the repeat unit -[O-CH(CH3)-CO]- of 72 g/mol and ignoring end groups, the number-average degree of polymerisation is closest to

JEE Advanced levelSingle correct optionDifficulty 3 of 3pl176

A PLA sample has weight-average molar mass $M_{w} = 2.40 \times 1 0^{5}$ g/mol and PDI $= M_{w} / M_{n} = 2.0$ . With the repeat unit $- [O - CH (CH X_{3}) - CO] X^{-}$ of 72 g/mol and ignoring end groups, the number-average degree of polymerisation is closest to

M_{n} = M_{w} / PDI = 2.40 \times 1 0^{5} /2.0 = 120000

g/mol.

DP_{n} = M_{n} /72 = 1666.7 \approx 1667

. Using

M_{w}

directly gives 3333.