I think if you  make polyurethane from:

1.     polyols (soft segment) based on polyether or polyester based compounds of molecular weight 4oo- 500, high polyols weigh have good tensil properties

2.    With Isocyanate (hard segment) such as TDI, MDI , MDI is prefer due to its physical properties

3.    Chain extender to extend the length of the hard segment,

this way is better and easy to controlled

Remember two important things in making polyurethane:-

-Start with any reagent (hard segment for example HDI, HHDI, TMDI etc) having NCO-groups.

-Use polyols or polyamines can also react faster with NCO groups even at room temperature.

-Finally as you are talking about hydrogels, but according to my previous experience with this reagent, it is highly hydrobhobic with a water contact angle of 98-106 degree range.

-But during the reaction of NCO with polyols or amine, always use dry conditions (dry solvent), because you will not get the desired product even with moisture.

Good luck!!!

M. Khan

I will suggest following ways to convert your polyurethanes into hydrogels at room temperature.

1. Use aromatic diisocyanate to carry your reaction at room temperature.

2. Use DBTDL catalyst to speed up the reaction.

3. Use very high hydroxyl equivalent than isocyanate equivalent.

4. You may prefer hyperbranched polymer as one of the ingredient.

Rest of the things depends on molecular weight of polyol, tuning of experiment or optimization of parameters.

I hope this will serve your purpose. 

There are several ways to use polyurethanes in water systems. Polyurethane primers are water based systems. Use of ionic chain extenders to create water borne systems can help you to get water dispersible PU systems. End capped with HEMA like monomers will help you to give good UV cross-linked systems that can be combined with hydrophilic monomer and UV cross-linked to give hydrogels. Tuning up of SS/HS ratios over PU/monomers ratios with help you to design final physical properties of PU based hydrogels. Google PU/acrylate hybrid systems for more details..

You may try to produce a polyurethane of a polyether diol with a very high content of ethylene oxide (>50%) as provided by BASF SE or Bayer Materials Science and react this with a trimerized aliphatic diisocyanate such as Desmodur N 3600 or the like with an index lower than 65 in the presence of either tin dioctoate or potassium octoate catalyst. The material will swell at least 400 % in water, if you optimize the formulation you may go up to 1000%.

thanksfor ur comments i am trying these different things hope this will help me