Faquan Zeng

Supported atom transfer radical polymerization of methyl methacrylate mediated by CuBr–tetraethyldiethylenetriamine grafted onto silica gel

Silica-gel particles grafted with tetraethyldiethylenetriamine were synthesized as support for CuBr for the heterogeneous atom transfer radical polymerization of methyl methacrylate (MMA). The immobilized CuBr mediated a living polymerization of MMA, demonstrated by an increase in molecular weight with conversion and low polydispersity. An excessive amount of catalyst (typically, CuBr/initiator = 1.5) was required to achieve a living process because of the limited mobility of the supported catalyst. The silica-gel concentration had a strong effect on the polymerization. The recycled catalyst still mediated a living process but showed a reduced catalytic activity due to the presence of Cu(II). After being regenerated by a reaction with Cu(0), the catalyst regained its activity.

Synthesis of methacrylate macromonomers using silica gel supported atom transfer radical polymerization

A silical gel supported CuBr-hexamethyltriethylenetetramine (HMTETA) (SG-CuBr/HMTETA) catalyst system was developed for the synthesis of poly(methyl methacrylate) (PMMA) and poly(dimethylaminoethyl methacrylate) (polyDMAEMA) macromonomers with terminal vinyl or allyl group by atom transfer radical polymerization (ATRP). Catalysed by SG-CuBr/HMTETA and with vinyloxyethyl 2-bromoisobutyrate (VBIB) or allyl 2-bromoisobutyrate (ABIB) as initiator, the MMA polymerization showed first order kinetics up to a 60% monomer conversion. The polymerization rate slowed down at higher conversions due to a reduction in radical concentration. Gel permeation chromatography (GPC) results showed that the decrease in radical concentration was caused by the reaction of radicals with the initiators vinyl or ally group moieties. In contrast, the DMAEMA polymerization was first order kinetics throughout the polymerization. The molecular weights of the resulting PMMA and polyDMAEMA increased linearly with conversion with low polydispersities. After the first run polymerization, the catalysts were recycled for second and thrid runs. The recycled catalysts still mediated a living polymerization of MMA or DMAEMA, producing polymers with controlled molecular weight and narrow polydispersity, but their catalytic activities decreased significantly. The reactivity reduction of the recycled catalyst was due to radical side reactions that yielded an extra amount of CuBr 2 as well as the catalyst loss during recycling.

Atom transfer radical polymerization of alkyl methacrylates using T-triazine as ligand

A new multidentate amine ligand, 1,3,5-tris[(3-dimethylamino)propyl]-hexahydro-1,3,5-triazine (T-triazine) was developed for the atom transfer radical polymerization of methacrylates (dimethylaminoethyl methacrylate (DMAEMA) and methyl methacrylate (MMA)). It was found that with T-triazine as ligand, CuBr mediated a living polymerization of DMAEMA and MMA, producing polymers with controlled molecular weight and narrow polydispersity. The DMAEMA bulk polymerization and MMA solution polymerization in THF and γ-butyrolactone (γBL) followed first order kinetics with respect to the monomer. At lower temperature, both polymerizations had an induction period and the induction time decreased with increasing temperature. The measured apparent active energy was 67.8 kJ/mol for DMAEMA polymerization. The NMR spectra confirmed that the polymerizations proceeded via an atom transfer radical process.

Synthesis of Styrenic‐Terminated Methacrylate Macromonomers by Nitroanion‐Initiated Living Anionic Polymerization

N-Isopropyl-4-vinylbenzylamine (PVBA) was synthesized and used as an initiator for the polymerization of methacrylates to synthesize macromonomers with terminal styrenic moieties. LiPVBA initiated a living polymerization and block copolymerization of methyl methacrylate, 2-(N,N-dimethylamino)ethyl methacrylate and tert-butyl methacrylate and produced polymers having well-controlled molecular weights and very low polydispersities (Mw/Mn < 1.1) in quantitative yield. 1H NMR analysis revealed that the polymers contained terminal 4-vinylbenzyl groups. The macromonomers were reactive in the copolymerization with styrene.