A
double-strand chain, consisting of an uninterrupted
sequence of rings, with adjacent rings having two or more atoms in common. Alternatively,
a ladder chain is a double-strand chain with adjacent
constitutional units joined to each other through four atoms, two on one side and two on the other side
of each
constitutional unit.
Source:
PAC, 1996, 68, 2287
(Glossary of basic terms in polymer science (IUPAC Recommendations 1996))
on page 2295