text: this is difficult without using structures, but it is a free-radical mechanism.  I've added a link below which gives the mechanism about 2/3rds down the page.\n\nA peroxide initiator is thermally cleaved to generate two oxygen radicals.  These then add in a radical mechanism to the alkenic bond of styrene, to generate another carbon centred radical.  This carbon centred radical then adds to another double bond of another styrene molecule...etc  etc.  The reaction between a carbon centred radical and another radical terminates the polymerisation process.\n\nCommonly 1 - 2% of divinylbenzene is added to the polymer mix to allow cross-linking and strengthening of the formed polymer.\n\nHope this helps.