Schiff bases of types 1, 2, and 3, easily prepared by the condensation of primary amines with pyridine-2-carboxaldehyde, glyoxal, or 2-acetylpyridine, respectively, are described as ligands for a copper(I) catalyst in the atom transfer polymerization of a range of methacrylates in toluene and xylene solution. Increasing the length of the alkyl group on ligands of type 1 increases the solubility of the catalyst in nonpolar solvents. The rate of polymerization increases on going from R = ethyl to propyl; however, on increasing the length of R further, we see no effect on the rate. The molecular weight distribution is narrow for all ligands where R = n-alkyl, and the number-average molecular weight (M n) increases linearly with conversion. A decrease in rate and a loss of control are observed when branching is introduced in the α-position of the side chain. The polymerization is approximately first order in initiator, 0.90 ± 0.22, CuBr, 0.90 ± 0.13, and methyl methacrylate, 0.93 ± 0.01. Polymerization with CuBr in conjunction with diazabutadiene ligands does not proceed very effectively, due to the high stability of the copper(I) complexes with regard to oxidation. The mechanism of the reaction is complex and may differ on subtle changes in ligand, metal, solvent, etc. The ligand systems presented in this paper offer a wide range of versatility when choosing the most effective system for a particular application. The Schiff base ligands, when used as described, provide an excellent method for achieving the controlled polymerization of a wide range of methacrylates at relatively mild temperatures in hydrocarbon, noncoordinating, solvents.

This paper demonstrates that atom transfer polymerization of methyl methacrylate mediated by CuBr/N-alkyl-2-pyridylmethanimine complexes in toluene proceeds effectively at temperatures as low as 15°C, while maintaining control over molecular weights and yielding narrow polydispersity indexes. The reaction can even be performed at -15°C with a number average molecular weight, M n, of 6980 and a polydispersity, PDI, of 1.28 being achieved in 116 h; however, the molecular weight control is less effective. The polymerizations were performed at 90, 60, 40, and 15°C with the first-order rate plots, molecular weight vs conversion plots, and final polydispersity indexes consistent with little or no terminationsliving/controlled polymerization. Methyl hydroquinone (MeHQ) has been demonstrated to accelerate the polymerization by a factor of 3-4 at temperatures below 40°C. An activation energy, Ea, for polymerization in the absence of phenol was determined to be 60.3 kJ‚mol -1 and is significantly reduced to 44.9 kJ‚mol -1 in the presence of MeHQ. These results suggest that coordinating phenols modify the active polymerization center. The stereochemistry of the polymers produced are consistent with that observed for conventional free-radical polymerization in that the fraction of syndiotactic arrangements increases as the reaction temperature is lowered. At 90°C, 59.1% rr triads are obtained with a persistence ratio of 0.924 and at -15°C, 71.5% rr triads are obtained.

Atom transfer polymerisation of methyl methacrylate can be effected using solid supported copper(i) pyridylmethanimine catalysts which facilitate easy removal and reuse of the catalyst.Controlled polymerisation of vinyl monomers, such as methacrylates, acrylates and styrene, is of continuing interest for the synthesis of polymers of specific composition and structure. 1 Controlled, or living, free-radical systems are attracting increasing attention as processes which are tolerant to protic species in the medium, e.g. from solvents, monomers, impurities, etc. Transition metal mediated living radical polymerisation, or atom transfer polymerisation, has been developed by Matyjaszewski 2-4 and Sawamoto, 5,6 utilising Cu(i)X/bipyiridines (X = Cl, Br) and Ru 2 Cl 2 (PPh 3 ) 3 , respectively. 7 In our laboratories we have been developing catalysts based on Cu(i)X and alkylpyridylmethanimine Schiff base ligands. [8][9][10][11][12] The attraction of these catalysts is that the Schiff base ligands are simple to synthesise and allow scope to vary the catalyst properties (e.g. redox potential, solubility) by varying the appropriate substituent groups.Typical [monomer] : [catalyst] ratios are 100 : 1 with stoichiometric amounts of initiator and catalyst, in order for acceptable rates of polymerisation. A potential solution to this problem is the use of supported catalysts. Inorganic supported catalysts, e.g. silica, have found widespread use in the polymerisation of olefins. 13 The extension of this approach to the use of functionalised inert poly(styrene) as supports for vanadium ethylene polymerisation catalysts has also been recently described. 14 This recent work prompts us to report our own work where we have been utilising supported catalysts for living radical polymerisation reactions; to the best of our knowledge this is the first example of the use of inert poly(styrene) supports for a non-co-ordination type polymerisation.We describe herein polymerisation of MMA mediated by Cu(i)Br supported Schiff base complexes (prepared from both primary amine functionalised silica gel and cross-linked poly(styrene) resins) via an atom transfer polymerisation process. In order to evaluate the potential of supported catalysts for atom transfer polymerisation, four different solid supports were tried in combination with CuBr. In the first two examples, the ligand was covalently attached to the solid support, either primary amino-functionalised silica gel (SiO 2 ) or aminofunctional cross-linked poly(styrene) beads (PS), Scheme 1. In the second and third examples, free ligand was used in conjunction with primary amine-functionalised and non-functionalised silica gel. The reactions were performed with 33 vol. % MMA in toluene solution with ethyl-2-bromoisobutyrate as the initiator.Addition of CuBr to ligated silica produces a dark brownorange free flowing powder, Scheme 1. † Atom transfer polymerisation of methyl methacrylate proceeds effectively at 90°C, reaching 70.4% conversion with a number average molecular mass, M n , of 15 500...

Copolymerizations of styrene and methyl methacrylate have been performed using different monomer feed compositions in the presence of a catalytic chain transfer agent at 40 °C. Average chain transfer constants as a function of monomer feed composition were determined with the conventional Mayo procedure using both number (M n) and weight (M w) average molecular weights, and with the chain length distribution procedure using both high (ΛH) and peak (ΛP) molecular weight slopes. It is found that the average chain transfer constants determined from M w and ΛP are generally very similar, with those obtained from M n and ΛH being larger and smaller, respectively. The average chain transfer constants obtained from M w and ΛP are compared with model predictions based upon both the terminal and penultimate unit models of free-radical copolymerization and are in satisfactory agreement. These two models are used to predict the fraction of propagating radicals with a terminal styrene unit, and it is found, similar to earlier studies reported in the literature, that this parameter is very sensitive to the penultimate model s values (in contrast to the average propagation rate coefficient), and a satisfactory agreement between model and experiment is obtained for s M = 2. This finding possibly suggests a complimentary route to measuring average propagation rate coefficients, for the determination of penultimate model s values.