In the past few years, a series of papers has examined the shock response of common engineering polymers as their microstructure changes. In this latest work, the behaviour of two polymers, polyoxymethylene and polyethylene, is investigated under conditions of shock loading in one-dimensional strain. The two are semi-crystalline thermoplastics differing only in the components of the chain. Equation of state data are investigated for the low pressure (u p <1 km s-1) regime. Further, measurements of the lateral component of stress and knowledge of the impact conditions allow calculation of the shear strength. Variations both with impact stress amplitude and pulse duration are discussed in terms of the polymer chain structure. © 2007 IOP Publishing Ltd.