Living radical polymerization by biradical compounds of tetramethylpiperidine-1-oxyl

The polymerization of styrene was performed using two types of biradical co mpounds derived from 2,2,6.6-tetramethylpiperidine-1-oxyl (TEMPO). The bira dical compounds are diesters of 4-hydroxy-TEMPO with phthalic acid (o-TEMPO ) and with terephthalic acid (p-TEMPO). When the polymerization was carried out by o-TEMPO and benzoyl peroxide (BPO) as an initiator, a polymer obtai ned had showed bimodal GPC. This suggests that dimerization by coupling of the polymers occurred during the polymerization. GPC demonstrated that the polymerization in the absence of BPO suppressed the dimerization and gave a polymer with narrow polydispersity. The polymerization was found to procee d in accordance with a living mechanism, because the molecular weight was d irectly proportional to the conversion, and was inversely proportional to t he initial concentration of the biradical compound. A polystyrene obtained by the polymerization with the biradical compound initiated the polymerizat ion of tert-butoxystyrene, giving ABA type of triblock copolymer.