For basic proportion first you have to calculate the approx no. of NCO:OH ratio. So that you can easily form Polyurethane with good flexible properties.

Considering you are talking about a polyurethane, the NCO:OH ratio is the key parameter. If it is not a polyurethane, it will depend on what kind of resin (or mix o polymers) you are using and which kind of cross lik.

I'm assuming SMP = shape memory polymer, which are viscoelastic in nature.  Assuming that a 1:1 molar ratio of NCO:OH gives you a strong PU rubber (as opposed to a glassy material, which you would get if your crosslinkers are low hydroxyl equiv. weight, say

 First of all I am thankful for your informative response. I made different samples and found the the mixing ratio which gives me a proper SMP showing SME. Now as I mixed it by hand stirring and at room temperature, so I am confused to understand the chemistry. I want to know that when mixing 2 polymers gave us a proper SMP then how can we get to know the chemical reactions between mixed polymers?

Since you say it's a typical polyurethane system, the reaction would then be that between alcohol groups and isocyanate groups to form urethane linkages.  Even though the reaction starts at room temperature, the reaction is exothermic, so unless you're doing this in dilute solution, you'll likely be able to measure the temperature rise (for example with an infrared temperature sensor, or else contacting the polyurethane mixture with a thermocouple).