spiro chain

in a polymer
A double-strand chain consisting of an uninterrupted sequence of rings, with adjacent rings having only one atom in common. Alternatively, a spiro chain is a double-strand chain with adjacent constitutional units joined to each other through three atoms, two on one side and one on the other side of each constitutional units.
PAC, 1996, 68, 2287. 'Glossary of basic terms in polymer science (IUPAC Recommendations 1996)' on page 2295 (https://doi.org/10.1351/pac199668122287)