TITLE:
Synthesis and Characterization of Poly Styrene-Co-Poly 2-Hydroxyethylmethacrylate (HEMA) Copolymer and an Investigation of Free-Radical Copolymerization Propagation Kinetics by Solvent Effects
AUTHORS:
Anaif M. Alhewaitey, Ishrat Khan, Naif M. Alhawiti
KEYWORDS:
2-Hydroxyethyl Methacrylate, Polymerization
JOURNAL NAME:
Open Journal of Polymer Chemistry,
Vol.14 No.1,
February
29,
2024
ABSTRACT: A
series of homo and copolymers of styrene (ST) and 2-hydroxyethyl methacrylate
(HEMA) in three different media (bulk, tetrahydrofuran, and benzene) have been
investigated by free radical polymerization method. The samples obtained from
the synthesis were characterized by Fourier Transform-Infrared spectroscopy
(FT-IR), proton nuclear magnetic resonance spectroscopy (1H NMR),
atomic force microscopy (AFM), and differential scanning calorimetry (DSC). The
results show that the synthesis of the polymers is more feasible under neat
conditions rather than solvent directed reaction.
Moreover, the DSC data shows that the polystyrene obtained is amorphous
in nature and therefore displayed only a glass transition signal rather than
crystallization and melting peaks. In addition, this study indicates that
homolopolymerization of styrene via free radical polymerization tends to be
preferable in less polar solvents like
THF than in non-polar solvents like
benzene. Benzene might destabilize the formation of the reactive radicals
leading to the formation of the products. In summary, the homolpolymerization of styrene is more feasible than the homopolymerization 2-hydroxyethyl methacrylate under the experimental
setup used. Styrene is more reactive than 2-hydroxyethyl methacrylate than free
radical polymerization reaction due in part of the generation of the benzylic radical intermediate which is more
stable leading to the formation of products than
alkyl radical which are less stable. Furthermore, polymerization of styrene
under neat conditions is preferable in solvent-assisted environments. The
choice of solvent for the synthesis of these polymers is
crucial and therefore the selection of solvent that leads to the formation of a
more stable reaction intermediate is more favorable. It is worth noting that
the structure of the proposed copolymer consists of a highly
polar and hydrophilic monomer, 2-hydroxyethyl methacrylate and a highly
non-polar and hydrophobic monomer, styrene. These functionalities constitute an
amphiphilic copolymer with diverse characteristics. A plausible explanation
underlying our observations is that the reaction conditions employed in the
synthesis of these copolymers might not be the right route required under free
radical polymerization.