The query is a bit obscure to me.
Do you want a chemical reaction to provide the heat? I suppose you need an accurate and adjustable temperature to tinker and stabilize your process, and no side products. A reaction uses to have side products and a badly defined temperature.
Or do you want to heat to 240°C the polymer you deposit? Then a heated nozzle looks more adequate, espeically if you regulate locally its temperature against the variations in polymer throughput.