Polymers for contact lenses

A process for preparing a polyurethane xerogel, said process comprising:

• preparing a mixture comprising
• (a) at least one isocyanate;
• (b) at least one silicone containing compound of formula Jii:
• where each R independently represents a hydrocarbyl group or H;
• each R2, R3, and R5 group represents a hydrocarbyl group;
• p represents an integer from 1 to 40;
• q represents an integer from 1 to 40;
• z is an integer from 1 to 50;
• u is an integer from 1 to 100;
• w is an integer from 1 to 40;
• y is an integer from 1 to 40;
• and
• each Q group independently represents a COOH, OH, SH, NH2, NHR or NCO group;
• (c) at least one chain extender comprising one or more of COOH, OH, SH, and NH2 terminal groups;
• (d) optionally one or more PEG compounds;
• and
• (e) a polyfunctional compound having an average functionality greater than 2, comprising COOH, OH, SH, NH2, NHR and/or NCO functional groups where R represents an alkyl group and
• wherein at least 95 wt % of the reactants in the mixture have an average functionality of 2 or less, and
• (ii) reacting the mixture formed in step (i) under substantially anhydrous conditions to form a polyurethane xerogel wherein the polyurethane xerogel has a silicone content of over 25 wt %.

A polyurethane xerogel prepared from a mixture comprising:

• (a) at least one isocyanate;
• (b) at least one silicone containing compound(s) of formula Ji:
• where each R independently represents a hydrocarbyl group or H;
• each R1, R4 and R5 group represents a hydrocarbyl group;
• where p represents an integer from 1 to 40;
• q represents an integer from 1 to 40;
• z is an integer from 1 to 50;
• u is an integer from 1 to 100;
• w is an integer from 1 to 40;
• y is an integer from 1 to 40;
• and
• each Q group independently represents a COOH, OH, SH, NH2, NHR or NCO group;
• (c) optionally at least one chain extender comprising one or more of COOH, OH, SH, and NH2 terminal groups;
• (d) optionally one or more PEG compounds;
• and
• (e) a polyfunctional compound having an average functionality greater than 2, comprising COOH, OH, SH, NH2, NHR and/or NCO functional groups where R represents an alkyl group;
• wherein the reactants are reacted under substantially anhydrous conditions,
• wherein at least 95 wt % of the reactants in the mixture have an average functionality of 2 or less, and
• wherein the polyurethane xerogel has a silicone content of over 25 wt %.