Complex sentence: That said there are alternative precursors to arrive at the parylene polymers that possess leaving groups as opposed to the cyclophane precursor, the most popular using bromine to yield the parylene AF-4 polymer.
Split into simpler sentences: That said there are alternative precursors to arrive at the parylene polymers that possess leaving groups as opposed to the cyclophane precursor. The most popular using bromine to yield the parylene AF-4 polymer.