Environmentally-Friendly Acrylates-Based Polymer Latices - Advanced Materials for Agriculture, Food and Environmental Safety - page 162

distribution of particles during i lm formation could present dissimilar
features compared to traditional monomodal thermoplastic latexes.
In some thermosetting latex dispersions, crosslinking reactions are
benei tted by the presence of strong or weak acid groups. For instance,
crosslinking reactions of hydroxyl and/or carboxyl groups in acrylic latex
dispersions with melamine-formaldehyde-based resins or cycloaliphatic
epoxide resins are usually enhanced by the addition of strong acid catalysts
such as sulfonic acids. h e presence of such strong acids along with weak
acids (as reactive groups) on the surface of latex particles gives an acidic
character to the dispersion. In this way, weak bases are typically used for
pH control, further stabilization of particles, and additionally as blocking
agents for reactive and catalyst acid sites. In this way, acid-base interac-
tions between catalysts, blocking agents and reacting groups are expected
to af ect i lm forming processes and crosslinking reactions.
During the last decade, polymers with hydrophilic crosslinking agents
have received much attention [103]. h e hydrophilicity and l exibility
imparted by the crosslinking agents improved the salvation characteris-
tics and enhanced the reactivity of the polymer-bound functional groups
[104]. Ethylene glycol dimethacrylate (EGDMA) has been widely used as a
crosslinking agent in the synthesis of hydrophilic or hydrophobic copoly-
mer networks [105]. Some aspects of the copolymerization of MMA with
EGDM have been investigated since 1945 [106-116]. Some authors esti-
mated the ei ciency of crosslinking [108, 114] and determined the Tg of
the copolymers [109]. h e fast transient l uorescence technique was used to
study the sol-gel phase transition in free-radical crosslinking monomers.
Since the 1970s several scientists [117-123] have investigated the behav-
iors of crosslinked PMMA. Crosslinked PMMA is used in a variety of com-
mercial materials such as membranes [124], dental i llings [125], dentures,
latex coatings [126], computer-to-sensor data transmission links [127],
composites [128], optically clear sheeting, limb prostheses, bathtubs, bath-
room sinks and shower surrounds, etc., where crosslinking plays a vital
role in both processing and ultimate properties.
Crosslinked copolymers can be synthesized by various polymeriza-
tion techniques such as bulk, solution, suspension and emulsion. A num-
ber of scientists studied the crosslinked copolymers synthesized by bulk
technique. Huang et al. [123] used DSC to determine monomer conver-
sion, rate of polymerization, reaction rate constants, and reaction order
during the copolymerization of EGDMA and HEMA. h is detailed
research revealed trends in reaction parameters that were dependent on
both EGDMA concentration and temperature. Copolymers of MMA with
dif erent glycol dimethacrylates were synthesized by Loshack and Fox