Abstract: A polysiloxane prepolymer that is useful for forming biomedical devices has the formula: M(*Dii*PS)x*Dii*M??(I) wherein: each M is independently a polymerizable ethylenically unsaturated radical; each Dii is independently a diradical residue of a diisocyanate; each PS is independently a diradical residue of a polysiloxane-diol or a polysiloxane-diamine; each * is independently —NH—CO—NH—, —NH—COO— or —OCO—NH—; and x is at least 2.

Abstract: A polysiloxane prepolymer that is useful for forming biomedical devices comprises blocks (I) and (II) and is terminated at each end with an ethylenically unsaturated radical: (*Dii*Diol*Dii*PS)x??(I) (*Dii*PS)y??(II) wherein: each Dii is independently a diradical residue of a diisocyanate; each Diol is independently a diradical residue of a diol having 1 to 10 carbon atoms; each PS is independently a diradical residue of a polysiloxane-containing diol or diamine; each * is independently —NH—CO—NH—, —NH—COO— or —OCO—NH—: x represents the number of blocks (I) and is at least 2, and y represents the number of blocks (II) and is at least 1.