Polimérisasi: Béda antarrépisi

Polimérisasi adisi majeujeutkeun pegatna beungkeut ganda atawa rangkep tilu, nu dipaké pikeun nyambungkeun monomér-monomér kana ranté. Dina polimérisasi éténa (gbr. 1), beungkeut pi-na pegat nu salajengna dua éléktronna disusun ulang pikeun nyiptakeun a new propagating center like the one that attacked it. The form this propagating center takes depends on the specific type of addition mechanism. Aya sababaraha mékanisme cara naratasna (inisiasi). Mékanisme [[radikal bébas]] ngarupakeun métode nu pangmunggaranna dipaké. Radikal bébas ngarupakeun atom/molekul nu réaktif pisan nu mibanda éléktron nyorangan (teu boga pasangan). Misalna dina polimérisasi éténa, mékanisme radikal bébas bisa dibagi kana tilu hambalan: inisiasi, propagasi, jeung terminasi.

 

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Inisiasi nyaéta prosés nyipta radikal bébas nu dipikabutuh pikeun propagasi. Radikal bisa dijieun tina molekul péroksida organik, molekul nu mibanda beungkeut tunggal O-O, ku ngaréaksikeun [[oxigén]] jeung [[éténa]]. Hasilna mangrupa molekul nu teu stabil nu gampang pisan dibeulah jadi dua radikal. In an ethene monomer, one electron pair is held securely between the two carbons in a sigma bond. The other is more loosely held in a pi bond. The free radical uses one electron from the pi bond to form a more stable bond with the carbon atom. The other electron returns to the second carbon atom, turning the whole molecule in to another radical.

Other forms of addition polymerization include cationic and anionic polymerization. While not used to a large extent in industry yet due to stringent reaction conditions such as lack of water and oxygen, these methods provide ways to polymerize some monomers that cannot be polymerized by free radical methods such as polypropylene. Cationic and anionic mechanisms are also more ideally suited for living polymerizations, although free radical living polymerizations have also been developed.

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== Polimérisasi kondensasi ==