A series of aliphatic acid side-chain copolysiloxanes based on a poly(hydrogenmethyldimethylsiloxane) backbone have been synthesised and evaluated. The length of the aliphatic acid side-chain of each compound has been varied in order to examine the effect on the Langmuir film properties. The surface pressure - area isotherms have indicated that each copolysiloxane forms a stable monomolecular layer on a pure water subphase. Alternate layer structures, in which each siloxane copolymer is co-deposited with a monomeric eicosylamine, have been prepared in order to measure their static pyroelectric coefficients. The magnitude of the coefficient increases as the length of the aliphatic acid side-chain is reduced. The thickness dependence of the coefficient has also been characterised for one of the copolysiloxane derivatives and shows that the pyroelectric effect is greatest for a 25 layer sample (13 layers of copolysiloxane 8/12 layers of eicosylamine).