c$)$ You are required to design a polymer of intrinsic microporosity $($PIM$)$ with the highest possible surface area for tests as a gas separation membrane by using reagents from the selection below. Explain your design considerations in terms of how you would synthesise the material. Your answer should include the following:

i$.$ An explanation of your selection of the reagents you would use and how these produce a microporous polymer. $1$

ii$.$ An explanation of why the polymer you prepared would be suited to applications in gas separation.

iii. A drawing of the final repeat unit of the polymer:.

iv$.$ Your material is tested for gas separation and its performance is found to deteriorate over time. Explain why this is happening and suggest one approach you could use to reduce this ageing behaviour. :