Effects of various Cu(0), Fe(0), and proanthocyanidin reducing agents on Fe(III)-catalysed ATRP for the synthesis of PMMA block copolymers and their self-assembly behaviours

Authors：Huang, Yi-Shen; Hsueh, Han-Yu; Aimi, Junko; Chou, Li-Chieh; Lu, Yu-Chi; Kuo, Shiao-Wei; Wang, Chung-Chi; Chen, Kuo-Yu; Huang, Chih-Feng

Source：Polymer Chemistry, 2020, 11(32): 5147-5155.

DOI：10.1039/d0py00658k

• TRANSFER RADICAL POLYMERIZATION
• AGET ATRP
• ELECTRON-TRANSFER
• PPM AMOUNTS
• ICAR ATRP
• STYRENE

We applied environmentally friendly ferric complexes (i.e., FeCl3/PPh3) to one of the most widely-used controlled/living polymerizations (CRP), atom transfer radical polymerisation (ATRP), for the preparation of well-defined poly(methyl methacrylate) (PMMA) homo- and block (co)polymers. Iron-catalysed supplemental activator and reducing agent (SARA) and activators regenerated by electron transfer (ARGET) ATRPs were investigated using cost-effective Cu(0), Fe(0), and the natural antioxidant proanthocyanidins (PC) as reducing agents. With different ratios of Fe(III)/Cu(0) and Fe(III)/Fe(0) for ATRPs of MMA, the former exhibited fast apparent reaction rates (k(app)s >3 x 10(-5) s(-1)), but showed large PDI values (>1.6); the latter exhibited moderate kapps ( = ca. 7 x 10(-6)- 3 x 10(-5) s(-1)) with low PDI values (<1.45), indicating that moderate reactions could avoid the occurrence of undesired side reactions. In the case of Fe(III)/PC, interestingly, moderate k(app)s ( = ca. 3 x 10(-6)-8 x 10(-6) s(-1)) with low PDI values (<1.30) were obtained. Through UV-Vis measurements and additional chain extension of MMA, the effective reduction of PC on Fe(III) was obviously observed and resulted in high chain functionality of the PMMA-Br macroinitiator. Subsequently, two more chain extensions of PMMA-Br with n-butyl methacrylate (BMA) and benzyl methacrylate (BzMA) were conducted to obtain well-defined PMMA(100)-b-PBMA(537) (M-n,M- NMR = 86 300; PDI = 1.25) and PMMA(100)-b-PBzMA649 (M-n,M- NMR = 124 200; PDI = 1.35) block copolymers (BCPs). Their thermal properties were characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The segmental segregation was characterized by small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). Interestingly, microphase separation was observed only in the PMMA(100)-b-PBMA(537) BCP with an upper critical ordering temperature (UCOT) behaviour and acquired spherical nanostructure (d = ca. 25 nm). We thus demonstrate a "green" ATRP method mainly using the natural product PC to reduce the FeCl3/PPh3 complex for the preparation of well-defined polymethacrylate-based BCPs.

• Institution
  2; 中山大学; 1