NVQ Practice Test & Exam Prep | United Kingdom

To start polymerisation you need something to create reactive centers that can kick off the chain reaction. An initiator provides exactly that: it decomposes (often under heat or light) to form reactive species such as free radicals or ions that attack a monomer’s double bond and generate the first growing polymer chain end. Once this active end exists, monomers can add one by one in the propagation steps, building the polymer. A solvent simply dissolves reactants and can influence rate but isn’t what starts the reaction. A catalyst can speed up certain types of polymerisations, but it isn’t universally required to initiate; and heat alone may not reliably produce the necessary reactive species in many systems unless the design specifically relies on thermal initiation with an initiator.