We simulate, analyse and compare the mechanical properties of a number of molecular sheet‐like systems based on fully substituted, penta‐substituted, tetra‐substituted and tri‐substituted poly(phenylacetylene) using static force‐field based methods. The networks are modeled in a 3D environment with and without inter‐layer interactions in analogy to graphite and graphene respectively. It is shown that by varying the type of substitution and the length of the acetylene chain, one may control the mechanical properties of such systems. In particular, it is shown that poly(phenylacetylene) systems can be specifically designed to exhibit negative Poisson's ratio, and that the stiffness can be controlled in an independent manner from the Poisson's ratios. This is significant as it highlights the fact that such systems can be tailored to exhibit a particular set of mechanical properties.

Molecular mechanics simulations were used to analyse the onaxis mechanical properties of a series of nanonetworks. These consisted of naphthacene-like units linked together through acetylene chains, and designed to mimic the geometry of a winerack-like structure in one of the major planes, a geometry which is closely associated with negative linear compressibility. It was found that these networks have a potential to exhibit a negative linear compressibility in one of the major axis. An analysis of the deformation mechanism as well as the magnitudes of the compressibility in the major directions suggest that this effect arises from relative rotations of the rigid polyphenyl chains and is comparable to that predicted by an idealised winerack model deforming through hinging. This confirms that there is a very strong link between negative linear compressibility and geometry, as is the case with auxetic materials.

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Poly(phenylacetylene) sheets that mimic the geometry of a wine-rack-like structure have been predicted to exhibit negative Poisson's ratios off-axis. However, their potential to exhibit negative linear compressibility (NLC) has remained largely unexplored. In this work, the compressibility and other mechanical properties of wine-rack-like poly(phenylacetylene) networks with 1,2,4,5 tetra-substituted phenyls as well as their equivalent with allene or cyclobutadiene centres are simulated to assess their ability to exhibit negative linear compressibility on-axis and off-axis. It is shown that some of these systems can indeed exhibit negative linear compressibility whilst others exhibit a near-zero compressibility. The results are compared to the compressibility properties of other poly(phenylacetylene) networks reported in literature as well as with those predicted from the analytical model for an idealised wine-rack structure deforming through hinging. Results suggest that these mechanical properties are arising from a wine-rack-like mechanism, and there is a good agreement with the theoretical model, especially for systems with longer acetylene chains whose geometry is closer to that of the idealised wine-rack.