3-Aminopropyl Silica Supported Living Radical Polymerization of Methyl Methacrylate: Dichlorotris(triphenylphosphine)ruthenium(II) Mediated Atom Transfer Polymerization

Abstract

3-Aminopropyl-functionalized silica support (APSS) has been used as a solid support for the heterogeneous atom transfer polymerization of methyl methacrylate (MMA), to poly(methyl methacrylate) (PMMA), mediated by adsorbed RuCl2(PPh3)3 as catalyst. This system displays characteristics of a living radical polymerization as indicated by (i) an increase in the number-average molecular weight (Mn) with conversion, (ii) relatively low polydispersity indexes (PDI), and (iii) linear first-order rate plots. When PMMA of Mn = 20 000 g mol-1 was targeted, the reaction reached 91% conversion after 4 h with a measured Mn = 21 500 g mol-1 and PDI = 1.49. It was found that polymerization of MMA mediated by RuCl2(PPh3)3 in the presence of APSS does not require the addition of an aluminum alkoxide (e.g., Al(OiPr)3) as an activating reagent. The rate of reaction is higher than for similar homogeneous reactions; however, the polydispersity indexes are also higher. The ruthenium content of polymers thus produced is typically approximately 0.1% w/w, corresponding to about 90% of the metal remaining adsorbed onto the surface of the support. This is thus an effective method of minimizing the metal content of the final polymer without postreaction purification. It is also shown that the supported catalyst can be reused for subsequent polymerization reactions. The polymers produced via this heterogeneous process can be subsequently used as macroinitiators to synthesize block copolymers and hence contain active halogen end groups.