A series of three-arm star densely grafted molecular brushes with poly(n-butyl acrylate)
side chains were prepared by atom transfer radical polymerization (ATRP). The three-arm macroinitiators
of poly(2-bromopropionyloxyethyl methacrylate) were prepared by ATRP of 2-trimethylsilyloxyethyl
methacrylate using trifunctional initiators 1,1,1-tris(4-(2-bromoisobutyryloxy)phenyl)ethane and different
catalytic systems, i.e., a CuIX/dNbpy complex (X = Br, Cl) with and without CuIIX2 (X = Br, Cl) as
deactivators, followed by the subsequent esterification with 2-bromopropionyl bromide. The kinetics
exhibited first-order reaction with respect to the monomer concentration in all systems. Polymerization
rates decreased with the catalyst in the order of CuBr > CuBr/CuBr2 > CuCl > CuCl/CuCl2. The different
initiation conditions also affect the polydispersities of the final brushes, although in all cases the number-average molecular weight (M
n) increases with the increasing monomer conversion. AFM measurements
of multiarm brushes enabled quantitative analysis of the length distribution. Because of visualization of
individual starlike molecules, one could separately analyze the brush arms and the whole molecule. The
polydispersities of the arm length decreased in the order of CuBr > CuBr/CuBr2 > CuCl > CuCl/CuCl2.
The CuCl/CuCl2 system seems to be the best catalyst for the star synthesis yielding brushes with narrow
length distribution. CuBr is a relative “worst” catalyst system in which several coupled molecular brushes
were observed, while some arms were missing. These led to the broadest distribution of arm length.
Similar analysis for four-arm molecular brushes was performed. The polydispersity of the total length
was significantly lower than those of the arm length. Here, the total length polydispersity displayed
amazing agreement with Schulz−Flory theory for chain coupling.
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