The ratio of the mean-square end-to-end distance,

, of a
linear polymer chain in a theta state to

, where

is the number of rigid sections in the main chain, each of length

; if all of the rigid sections are not of equal length, the mean-square value of

is used, i.e.
In simple single-strand chains, the bonds are taken as the rigid sections. The recommended
symbol is:
(
when

).
Source:
Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
https://doi.org/10.1351/goldbook.