Ambient Temperature RAFT Polymerization Of Methacrylate Under Visible Light Radiation

The reversible addition fragmentation chain transfer (RAFT) polymerization is a highly versatile living radical polymerization. It can be applied to most monomers that can be polymerized under conventional free radical polymerization conditions, able to finely control the molecular weight, afford polymers with low molecular weight distributions, and allow for the synthesis of polymers with complex architectures. This technique has also been successfully utilized for the facile fabrication of functional materials, In addition, ambient temperature RAFT polymerization facilitates some particular industrial applications. In this paper , a range of well-defined methacrylate polymers and methacrylate -based block copolymers were synthesized via a highly efficient and well controlled 2-cyanoprop-2-yl(4-fluoro) dithiobenzoate or CPFDB-mediated RAFT polymerization of methacrylate monomer under environment-friendly visible light radiation (λ= 405-577 nm) at 30 oC, using (2,4,6-trimethylbenzoyl) diphenylphosphine oxide (TPO) as a photo-initiator. For comparison, the CPFDB-mediated ambient temperature RAFT polymerizations of methacrylate monomer under both full-wave radiation (λ= 254-577 nm) and long-wave radiation (λ= 365-577 nm) were also studied.The results indicate that the functionalities of CTA and its corresponding growing chain derivatives are strongly sensitive to the UV radiation around their characteristic maximum absorption wavelength, unavoidably leading to significant photolysis of the CTA moieties in the duration of RAFT polymerization. Cutting off the CTA-sensitive short-wave radiation significantly suppresses this photolysis, thus remarkably improving the living behavior of these polymerizations. under either full-wave radiation or long-wave radiation, the CPFDB compound and its corresponding growing chain derivatives in the methacrylate polymerizing solution have been significantly photolyzed, thus undermining the controlled behavior of this RAFT process. Whereas this photolysis is significantly suppressed under visible light radiation, thus the CPFDB functionalities exert well control over the RAFT process, leading to a remarkably living behavior of this polymerization up to 90% glycidyl methacrylate(GMA) monomer conversion.UV-vis spectrophotometry has been used to follow the initialization period where the initial CTA was consumed, and the UV-induced decomposition of the CTA moiety in (2,4,6-trimethylbenzoyl) diphenylphosphine oxide (TPO)-initiated RAFT polymerization. Addition of TPO photoinitiator remarkably suppress retardation effect in RAFT process, thus shorten initialization period and accelerate overall RAFT process. The CTA moiety decomposed much faster under full wave radiation than long wave and visible radiation; Moreover, under visible light radiation, a relatively low concentration of CTA leads to both effects of shortening initialization period of this RAFT process and accelerating the overall polymerization rate. Different monomers have different reactive rate, under environment-friendly visible light radiation,GMA monomer can receive up to 90% monomer conversions in reasonably short reaction time, e.g. 4 h, While n-Butyl methacrylate (nBMA) monomer can receive only 40% monomer conversions in 6 h.RAFT polymerization of GMA or nBMA using CPFDB as a CTA, TPO as a photoinitiator in benzene under visible radiation at 30 oC, yields PGMA or PnBMA , which shows the characteristics of controlled/"living"polymerization. The living polymerization characteristics was evidenced by: narrow molecular weight distribution, linear increase of molecular weight with increasing conversion, well-controlled molecular weight, and first-order polymerization kinetics. The PnBMA-based macro-CTA and the PGMA-based macro-CTA is sufficiently chain-extended with addition of GMA and TPO.