Lanthanide ion complexes anchored in a polymeric matrix have several applications such as biomarkers and chemosensors. In this work several polydimethylsiloxane were synthetised in order to use in lanthanide-based optical sensors. It was observed in general that higher the concentration of the crosslinking agent lower the flexibility of the membrane and apart from that, for the same polymer, a bulkier crosslinker provides higher flexibility than a less bulky crosslinker.