A simple easily scalable one-pot route to new phosphonic acid polysilsesquioxanes, PAPSQ, [(O3/2SiCH2R)(x)(O3/2SiCHR(CH2)(2)SiO3/2)(y)](n) where R = CH2PO3H2, is described in this paper. Nuclear magnetic resonance (NMR), electron microscopy (SEM), thermogravimetric analysis, nitrogen sorption porosimetry, phosphorus and available acid analysis were used to characterise the new PAPSQ materials. The materials were shown to be very efficient and recyclable mild solid acid catalysts for organic transformations including those relevant to biomass conversion such as esterification, transesterification and dehydration of fructose to the important intermediate 5-hydroxymethylfurfural. (C) 2013 Elsevier B.V. All rights reserved.