Making nylon experiment - Questions
Nylon reaction:

$\ce{nH2N(CH2)6NH2 + nClOC(CH2)8COCl → H2N[(CH2)6NHCO(CH2)8]_{n}COCl + nHCl}$

Looking at the reagents, 1,6-hexanediamine is dissolved in water as it can form hydrogen bonds with the water molecules. Meanwhile the sebacoyl chloride is non-polar and thus dissolves best in non-polar solvents. The two solvents (polar and non-polar) cannot dissolve each other, just like oil and water.

The hexane is poured so it floats on top to minimize mixing -- the reaction only happens at the boundary between layers. Then we pull the thread causing more of the reagents to mix and react at the boundary. If we poured the hexane solution in quickly, we'd end up with a large lump of nylon instead of a thread.

To help with your other questions, some questions...


I've given some details about the solvents above. What kind of solvents would you choose to replace the hexane and water with?
Looking at the densities of hexane (0.659 g / mL) and water (1 g / mL), and looking at the procedure, why was the hexane poured? Why not pour the water onto the hexane?
Following on, do some research into the density of dichloromethane. That will give you your answer to (a)
You've mentioned "not enviromentally friendly" for dichloromethane. Are there any other issues? A good starting point are the CLEAPSS student safety sheets.