An aromatic–aliphatic polyamide and methanol are formed. Let . The polymer repeat unit isEach amide linkage comes from nucleophilic acyl substitution: an amine attacks an ester carbonyl, the tetrahedral intermediate expels methoxide, and proton transfer produces methanol. There are approximately molecules of methanol for complete repeat units in a long chain; the precise finite-chain count depends on its end groups. Removal of methanol drives this step-growth polymerization.
Syndiotactic polypropylene is the expected principal product:The bridged cyclopentadienyl–fluorenyl metallocene has approximately site symmetry. Activation by methylaluminoxane gives a cationic zirconium–alkyl polymerization-active site. Repeated coordination chemistry and migratory insertion of propene extend the chain. The two environments encountered during successive insertions favor alternating stereochemistry, giving syndiotactic tacticity. There is no stoichiometric small molecule eliminated in the propagation step; initiator fragments and chain-transfer products belong to the end groups.
Predominantly head-to-tail poly(3-hexylthiophene) is formed, with thiophene rings connected through their 2 and 5 positions. The hexyl groups occupy equivalent 3 positions along the conjugated polymer.
Selective iodine–magnesium exchange first generates an organomagnesium monomer while retaining the carbon–bromine bond. Nickel-catalyzed Kumada coupling then joins the organomagnesium end of one ring to the brominated end of another. Transfer of the nickel center to the new chain end permits catalyst-transfer polymerization and favors head-to-tail regioregularity. Organic side products of the activation include isopropyl iodide; magnesium halides accompany the coupling. The repeat unit itself contains neither iodine nor bromine.
An approximately alternating styrene–maleic anhydride copolymer is produced. Its backbone alternates a segment with the two former alkene carbons of a maleic anhydride unit; those latter carbons remain connected to the intact five-membered cyclic anhydride ring.
Homolysis of benzoyl peroxide supplies initiating free radicals. Cross-propagation between electron-rich styrene and electron-poor maleic anhydride is favored over successive additions of the same monomer. Both carbon–carbon double bonds become backbone sigma bonds, without loss of a small molecule from each monomer. Initiator-derived benzoyloxy or phenyl fragments can occur at chain ends, with carbon dioxide formed when benzoyloxy free radicals decarboxylate.
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