Reverse atom transfer radical polymerisation (RATRP) of methacrylates using copper(I)/pyridinimine catalysts in conjunction with AIBN

Abstract

N- n-Propyl-2-pyridylmethanimine, 1, N- n-octyl-2-pyridylmethanimine, 2, N- n-lauryl-2-pyridylmethanimine, 3, and N- n-octadecyl-2-pyridylmethanimine, 4 have been used in conjunction with copper(II) bromide and azo initiators for the reverse atom transfer radical polymerisation of a range of methacrylates. AIBN to Cu IIBr 2 ratios of 0.5:1, 0.75:1 and 1:1 give PMMA with M n 11 500 g mol −1 (PDi = 1.24) (at 22% conversion), 12 500 g mol −1 (PDi = 1.06) (at 83% conversion) and 10 900 g mol −1 (PDi = 1.11) (at 84% conversion), respectively. A Cu IIBr 2 complex is demonstrated to be needed at the start of the reaction for good control over molecular weight and polydispersity as reactions using Cu(I)Br as catalyst yielded PMMA of M n 31 000 g mol −1 (PDi = 2.90), reactions with no copper yield PMMA of M n 33 000 g mol −1 (PDi = 2.95). The RATRP of styrene was carried out using Cu IIBr 2 as catalyst. AIBN to Cu IIBr 2 ratio of 0.5:1, 0.75:1 and 1:1 gave PS with M n = 12 400 g mol −1 (PDi = 1.27) at low conversion, M n = 15 500 g mol −1 (PDi = 1.11) and 12 400 g mol −1 (PDi = 1.38), respectively at ∼85% conversion. A series of block copolymers of MMA with BMA, BzMA and DMEAMA (15 600 g mol −1 (PDi = 1.18), 13 300 g mol −1 (PDi = 1.14) 15 300 g mol −1 (PDi) = 1.16), using a PMMA macroinitiator were prepared. Emulsion polymerisation of MMA using [initiator]:[Cu (II)Br 2] ratio = 0.5:1 with Brij surfactant gave a linear increase of M n with respect to conversion, final M n = 112 800 g mol −1 (PDi = 1.42). Further reactions were carried out with [initiator]:[Cu (II)Br 2] ratio = 0.75:1 and 1:1. Both giving PMMA with M n ∼ 32 000 g mol −1 (PDi ∼ 2.4). These reactions exhibit no control, this is because the azo initiator is present in excess and all of the monomer is consumed by a free radical polymerisation as opposed to a controlled reaction. Particle size analysis (DLS) showed the particle size between 160 and170 nm in all cases.