Letter pubs.acs.org/macroletters
Temporal Control in Mechanically Controlled Atom Transfer Radical Polymerization Using Low ppm of Cu Catalyst Zhenhua Wang,†,‡,§ Xiangcheng Pan,‡,§ Jiajun Yan,‡ Sajjad Dadashi-Silab,‡ Guojun Xie,‡ Jianan Zhang,‡ Zhanhua Wang,† Hesheng Xia,*,† and Krzysztof Matyjaszewski*,‡ †
The State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute, Sichuan University, Chengdu 610065, China ‡ Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States S Supporting Information *
ABSTRACT: A mechanically controlled atom transfer radical polymerization (mechanoATRP) was successfully carried out in an ultrasound bath with low ppm of copper catalyst. The polymerization of methyl acrylate in the presence of CuBr2/tris(2pyridylmethyl)amine catalyst using ultrasound as an external stimulus was temporally controlled by switching on−off ultrasound agitation. The first order kinetics was observed during ultrasonication. The experimental molecular weights agreed well with the theoretical values and displayed narrow molecular weight distribution. The effects of various types of piezoelectric BaTiO3 nanoparticles, loadings of nanoparticles, and targeted degrees of polymerization were studied.
P
nanoparticles (BaTiO3 NPs).13 High-intensity ultrasound and relatively high catalyst loading (10000 ppm with respect to monomer) were used to prepare relatively low molecular weight (Mn < 3000) poly(n-butyl acrylate). Herein, we report a successful expansion of mechanoATRP to temporal control systems using a low intensity ultrasound bath, low concentration (75 ppm) of Cu/tris(2-pyridylmethyl)amine (TPMA) catalyst to prepare well-defined poly(methyl acrylate), PMA, with excellent control over molecular weight (up to Mn = 20000) and dispersity (1.05 < Đ < 1.18) with various barium titanate nanoparticle. MechanoATRP of methyl acrylate was conducted using BaTiO3 NPs as the mechano-electric transducers, ethyl αbromoisobutyrate (EBiB) as the initiator, and CuBr2 with tris(2-pyridylmethyl)amine (TPMA) ligand in DMSO under ultrasound agitation with a frequency of 40 kHz. Since ultrasound was demonstrated to disrupt metal−ligand interactions,14 TPMA was selected as the ligand to form stable Cu complexes. The effects of size and shapes of BaTiO3 NPs on the polymerization were investigated, and results are summarized in Table 1 (entries 1−3). Polymerization using cubic 50 nm BaTiO3 NPs reached 67% conversion after 8 h ultrasound agitation, affording polymer with Mn = 10820 and Đ = 1.06 (entry 1, Table 1). The polymerization with 200 nm tetragonal BaTiO3 gave similar kinetics (entry 3, Table 1). However, with 100 nm cubic BaTiO3 NPs, the polymerization
recise macromolecular architecture in terms of composition, topology and functionality can now be achieved with temporal and spatial control.1 Thus, various switchable controlled radical polymerization (CRP) techniques have been developed. Photoinduced electron transfer−reversible addition−fragmentation polymerization (PET-RAFT) in the presence of photoredox catalysts can be switched on or off upon the light irradiation.2 Atom transfer radical polymerization (ATRP), regulated by a redox-based transition metal catalyzed activation and deactivation equilibrium,3 can also be tuned by external stimuli. For example, ATRP can be activated by the addition of chemical agents such as reducing agents in activators regenerated by electron transfer (ARGET) ATRP4 and initiators for continuous activator regeneration (ICAR) ATRP.5 Electricity1a,6 and light7 have also been used to control the activation/deactivation process and mediate the polymerization with excellent temporal/spatial control. Additionally, high pressure can accelerate the rate of polymerization while reducing the rate of termination.8 To overcome the limited absorption of monomer or solvent, several methods have been proposed including using NIR light9 and storing light energy in a form of chemical energy.10 An interesting opportunity is offered by mechanical forces, for example, ultrasound has deeper penetration than light and is not affected by light-scattering in heterogeneous systems or gels.11 Ultrasound has already been used to study the polymer mechanochemistry and prepare some functional polymers by breaking chemical bonds.12 Interestingly, ultrasound was recently applied to mechanically controlled ATRP (mechanoATRP) in the presence of piezoelectric barium titanate © XXXX American Chemical Society
Received: February 27, 2017 Accepted: April 24, 2017
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DOI: 10.1021/acsmacrolett.7b00152 ACS Macro Lett. 2017, 6, 546−549
Letter
ACS Macro Letters Table 1. Results of MechanoATRP of MA under Various Conditions entrya
BaTiO3b (4.5 wt %)
DPT
time (h)
conv.g (%)
Mn,thh
Mn,GPCi
Mw/Mni
1 2 3 4 5 6 7 8 9 10 11
50 nm cubic 100 nm cubic 200 nm tetragonal 200 nm tetragonalc 200 nm tetragonald 200 nm tetragonale 200 nm tetragonalf without BaTiO3 200 nm tetragonal 200 nm tetragonal 200 nm tetragonal
200 200 200 200 200 200 200 200 50 100 400
8 8 8 8 8 8 8 8 8 8 8
67 22 61 71
