“Controlled” Synthesis and Characterization of High Molecular Weight Methyl Methacrylate/tert-Butyl Methacrylate Diblock Copolymers via ATRP

Abstract

Atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) using CuCl/ N,N,N′,N′′,N′′′,N′′′-hexamethyltriethylenetetramine (HMTETA) as a catalyst system with 2,2,2-trichloroethanol (TCE) as initiator was investigated. Poly(methyl methacrylate) (PMMA) macroinitiators with defined molecular weight, low polydispersity index (PDI), and a high end-group functionality were obtained. These PMMA macroinitiators successfully initiate block copolymerization of tert-butyl methacrylate (tBMA), resulting in poly(MMA-b-tBMA) diblock copolymers with low PDI for a range of tBMA block lengths. Gradient polymer elution chromatography (GPEC) was used to confirm the block copolymer structure. Furthermore, the effect of molecular weight of the macroinitiator, nature of catalyst system (heterogeneous/homogeneous), and the amount of solvent on the degree of control achieved in the block copolymerization was studied. The GPEC technique was successfully used to demonstrate the effect of the aforementioned parameters on the block copolymer structure. In particular, the use of a homogeneous catalyst system, CuBr/4,4′-di-5-nonyl-2,2′-bipyridine (dNbpy), and a large ratio of methyl ethyl ketone (MEK) to PMMA macroinitiator led to the synthesis of well-controlled high molecular weight diblock copolymers. This can be explained by the complete solubility of the Cu(II) complex, the deactivating species in the ATRP mechanism. The use of the dNbpy ligand and the polar solvent (MEK) promotes the homogeneous catalyst conditions. The homogeneous condition leads to efficient activation/deactivation exchange reactions between the growing polymer chains and the dormant polymer chains, resulting in well-controlled block copolymers.

Band broadening in size-exclusion chromatography of polydisperse samples

“…Calculations also allow M w and the PDI to be derived from the spectrum. The latter two parameters tend to be less accurate [39]. Large ions are more likely to be obscured by noise and baseline problems are aggravated.…”

Photochromic Block Copolymer Poly(styrene‐b‐azo monomer) by ATRP

“…To solve this problem, Lutz diminishes the initial amount of initiator in his experiments; however, the ratio between the concentration of the initiator and monomer has to be adjusted according to the desired molecular weight. An alternative, proposed by Klumperman, [8] is the addition of Cu (II) salts in order to increase the dormant species during the propagation of the polymerization.…”

Chemoenzymatic synthesis of an AB‐type diblock copolymer combining enzymatic self‐condensation polymerization and atom transfer radical polymerization

“…It was paramount that the self-condensation of 1 resulted in polyester 2 (Scheme 1) end-functionalized with an active À ÀCCl 3 group, an effective ATRP-initiating group. 17,18 This avoided an intermediate transformation step for the subsequent ATRP. Enzymatic SCP of linear aliphatic x-hydroxyester TCE-10-HD was performed with 5% (w/w; with respect to monomer) Novozyme 435 in toluene (1:1 v/v of the monomer) at 70 8C.…”

“…The small leaving molecules of TCE during enzymatic SCP have been proved to be effective ATRP initiators in previous reports; 17 thus, the resulting crude polyester 2 (see Table 1) must be precipitated with methanol/chloroform to remove TCE before ATRP. Otherwise, unwanted TCE-initiated polystyrene homopolymer will appear with the subsequent ATRP of styrene.…”