Rank these structural features of a quenched high molecular

Rank these structural features of a quenched high molecular weight semi-crystalline polymer in order of their size, smallest first (based on average values - there will be some overlap in ranges): Features A. Chain length B. Lamellar thickness C. Spherulite radius D. Root-mean-squared end-to-end distance of chains

Ranking, smallest to largest:

a) B, D, C, A

b) A, C, B, D

c) D, C, A, B

d) C, B, D, A

Solution

a) B<D<C<A

REASON:

Provided the sample is quenched, the lamellar thickness should be smaller than the r.m.s. end-to-end distance. This is because the lamellae are much wider and broader than they are thick, and there is some memory of the random coil configuration in the melt, with each chain participating in several different lamellae. The spherulite radius is typically 1-10 microns, depending on the polymer and crystallisation conditions, whereas the chain length could be much larger than this for a high molecular weight polymer.