polymerisation reaction Aufbau reaction "Aufbau" reaction 'Aufbau' reaction Aufbau process RXNO RXNO:0000276 The insertion of alkenes (usually ethene) into the Al-C bond of an aluminium alkyl, to give a long-chain aluminium alkyl that can go on to react again, or can decompose into the corresponding terminal alkene. The addition of transition metals results in reliable production of high molecular weight polymers.