Acrylic AB and ABA Block
Copolymers Based on Poly(2-ethylhexyl
acrylate) (PEHA) and Poly(methyl methacrylate) (PMMA) via ATRP
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Abstract
Acrylic block copolymers have several advantages over
conventional
styrenic block copolymers, because of the presence of a saturated
backbone and polar pendant groups. This investigation reports the
preparation and characterization of di- and triblock copolymers (AB
and ABA types) of 2-ethylhexyl acrylate (EHA) and methyl methacrylate
(MMA) via atom transfer radical polymerization (ATRP). A series of
block copolymers, PEHA-<i>block</i>-PMMA(AB diblock) and
PMMA-<i>block</i>-PEHA-<i>block</i>-PMMA(ABA triblock)
were prepared via ATRP at 90 °C using CuBr as catalyst in combination
with N,N,N′,N″,N″-pentamethyl diethylenetriamine
(PMDETA) as ligand and acetone as additive. The chemical structure
of the macroinitiators and molar composition of block copolymers were
characterized by <sup>1</sup>H NMR analysis, and molecular weights
of the polymers were analyzed by GPC analysis. DSC analysis showed
two glass transition temperatures (<i>T</i><sub>g</sub>),
indicating formation of two domains, which was corroborated by AFM
analysis. Small-angle X-ray scattering (SAXS) analysis of AB and ABA
block copolymers showed scattering behavior inside the measuring limits
indicating nanophase separation. However, SAXS pattern of AB diblock
copolymers indicated general phase separation only, whereas for ABA
triblock copolymer an ordered or mixed morphology could be deduced,
which is assumed to be the reason for the better mechanical properties
achieved with ABA block copolymers than with the AB analogues