"Controlled" synthesis and characterization of high molecular weight methyl methacrylate/tert-butyl methacrylate diblock copolymers via ATRP

Atom transfer radical polymn. (ATRP) of Me 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(Me methacrylate) (PMMA) macroinitiators with defined mol. wt., low polydispersity index (PDI), and a high end-group functionality were obtained. These PMMA macroinitiators successfully initiate block copolymn. of tert-Bu methacrylate (tBMA), resulting in poly(MMA-b-tBMA) diblock copolymers with low PDI for a range of tBMA block lengths. Gradient polymer elution chromatog. (GPEC) was used to confirm the block copolymer structure. Furthermore, the effect of mol. wt. of the macroinitiator, nature of catalyst system (heterogeneous/homogeneous), and the amt. of solvent on the degree of control achieved in the block copolymn. 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 Me Et ketone (MEK) to PMMA macroinitiator led to the synthesis of well-controlled high mol. wt. diblock copolymers. This can be explained by the complete soly. 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. [on SciFinder (R)]