Abstract
Atom transfer radical polymerization (ATRP) of methyl acrylate (MA) was carried out by continuous feeding of Cu(I) activators. Typically, the solvent, the monomer, the initiator, and the CuBr2/Me6TREN deactivator are placed in a Schlenk flask (Me6TREN: tris[2-(dimethylamino)ethyl]amine), while the CuBr/Me6TREN activator is placed in a gas-tight syringe and added to the reaction mixture at a constant addition rate by using a syringe pump. As expected, the polymerization started when Cu(I) was added and stopped when the addition was completed, and polymers with a narrow molecular weight distribution were obtained. The polymerization rate could be easily adjusted by changing the activator feeding rate. More importantly, the loss of chain end-groups could be precisely predicted since each loss of Br from the chain end resulted in the irreversible oxidation of one Cu(I) to Cu(II). The Cu(I) added to the reaction system may undergo many oxidation/reduction cycles in ATRP equilibrium, but would finally be oxidized to Cu(II) irreversibly. Thus, the loss of chain end-groups simply equals the total amount of Cu(I) added. This technique provides a neat way to synthesize functional polymers with known end-group fidelity.
Highlights
Atom transfer radical polymerization (ATRP) [1,2,3,4] is a widely-used technique in preparing polymeric materials with various architectures, e.g., block copolymers, star polymers, polymer brushes, and gradient copolymers, for applications in thermoplastic elastomers, nanostructured carbons, surfactants, dispersants, functionalized surfaces, bio-medical materials, etc. [5,6,7]
In ATRP, as well as in any other reversible-deactivation radical polymerization (RDRP) [8], the growth of polymer chains is always accompanied by radical termination
The molecular weights and the molecular weight distributions of the obtained polymers were characterized by gel permeation chromatography (GPC) using poly(methyl methacrylate) (PMMA)
Summary
Atom transfer radical polymerization (ATRP) [1,2,3,4] is a widely-used technique in preparing polymeric materials with various architectures, e.g., block copolymers, star polymers, polymer brushes, and gradient copolymers, for applications in thermoplastic elastomers, nanostructured carbons, surfactants, dispersants, functionalized surfaces, bio-medical materials, etc. [5,6,7]. The loss of chain end-groups is not desirable, but cannot be completely avoided [9]. The retention of polymer end-groups is a critical tool for successful chain extension, post polymerization reactions, and controlling material properties [10,11,12,13,14]. In the synthesis of block copolymers, the lower chain end-group fidelity of the macroinitiators resulted in less regular self-assembled nano-structures [15]. Since the end-group fidelity varies greatly depending on the reaction conditions, the batch-to-batch difference may hinder industrial applications. In the synthesis of cyclic polymers, both α and ω chain end-groups are important [16]. In many cases, the extent of chain end-group preservation is difficult to predict, and hard to determine. Gel permeation chromatography (GPC) can give a hint about the chain end preservation by comparing
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