If London Dispersion Forces are only $1-2$kca$\frac{l}{m}ol,$ why are polyethylene,

polypropylene, and polystyrene such good plastics?

Why is polyvinyl chloride fairly compatible with polymethyl methacrylate and nitrile

rubber?

With increasing polarity, what is the effect on modulus, strength, Tg$,$ Tm$,$ oxygen

permeability, surface tension?

Why are nylons useful at lower molecular weights than polyolefins?

Why is Tm of polyureas $>$ nylons $>$ polyurethanes $>$ polyethylene?