The character of the backbone, i.e. its flexibility, determines the thermal properties of the polymer (such as the glass transition temperature), e.g. in polisiloxanes the backbone chain is very flexible, resultin in very low glass transition temperature of -123 °C. The polymers with a rigid backbone are prone to crystallization (e.g. polythiophenes) in thin films and in solution. Crystallization in its turn affects the optical properties of the polymers, its optical band gap and electronic levels.
The flexibility of the peptide backbone determines its ability to stretch which is important for proteins under mechanical stress.
^Brabec, C.J.; Winder, C.; Scharber, M.C; Sariciftci, S.N.; Hummelen, J.C.; Svensson, M.; Andersson, M.R. (2001). "Influence of disorder on the photoinduced excitations in phenyl substituted polythiophenes". J. Chem. Phys.115: 7235.