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-block-PMMA(AB diblock) and PMMA-block-PEHA-block-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 (1)H NMR analysis, and molecular weights of the polymers were analyzed by GPC analysis. DSC analysis showed two glass transition temperatures (T(g)), 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.
Surface initiated polymerization (SIP) is an emerging
powerful
tool to modify and tailor the surface properties of nanoparticles.
Among different methods of SIP, surface initiated atom transfer radical
polymerization (SI-ATRP) has several strategic advantages over other
methods of polymerizations. This investigation reports the preparation
and characterization of poly(2-ethylhexyl acrylate) (PEHA)/clay nanocomposite
from nanoclay surface via SI-ATRP and poly(2-ethylhexyl acrylate)-block-poly(methyl methacrylate) (PEHA-b-PMMA)/clay nanocomposite via conventional ATRP. To carry out SI-ATRP,
the nanoclay (Cloisite Na+) surface was first modified
by incorporating an ATRP initiator (2-bromopropionyl bromide) to nanoclay
surface via a grafting reaction. The prepared bromo-functionalized
nanoclay (Clay–Br) was then used to carry out SI-ATRP of 2-ethylhexyl
acrylate (EHA) at 90 °C using CuBr as catalyst in combination
with N, N, N′, N″, N″- pentamethyl diethylenetriamine
(PMDETA) as the ligand. The macroinitiator (clay-PEHA-Br) was used
to prepare PEHA-b-PMMA/clay nanocomposites via conventional
ATRP using the same reaction conditions as SI-ATRP of EHA. A series
of PEHA-b-PMMA/clay nanocomposites were prepared
via ATRP. The prepared PEHA/clay nanocomposites and PEHA-b-PMMA/clay nanocomposites were characterized by WAXD and TEM analyses.
DSC analysis of PEHA-b-PMMA/clay nanocomposites showed
two T
g values corresponding to two blocks
present in the block copolymers. TGA analysis was also carried out
to study the thermal stability of PEHA/clay nanocomposites and PEHA-b-PMMA/clay nanocomposites at different nanoclay loading.
The chemical structure and molecular weights of the prepared polymers
were analyzed by Fourier transform infrared (FT-IR), 1H
NMR, and gel permeation chromatography (GPC) analyses.
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