Description
Temperature/pH stimuli-responsive hydrogel particles were synthesized using
inverse-suspension polymerization in batch stirred reactor. Different water soluble comonomers
were present in the initial mixture (namely N-isopropylacrylamide and
acrylic acid) as well as crosslinkers with different functionalities (bi-, tri- and tetrafunctional) so that their effect on the network crosslinking density could be seen.
Different operating conditions such as polymerization temperature (in the range 20 to
70 °C), monomers dilution, neutralization and the inilial ratios 01 co-monomers and
monomers/crosslinker were also tried. Classical Iree-radical polymerization (FRP)
and RAFT polymerization (e.g. using 4-cyano-4-phenylcarbonothioylthio-pentanoic
acid) were compared in order to put into evidence the impact of the polymerization
mechanism on the hydrogel molecular architecture. Sampling at different
polymerization limes allowed the study of the kinetics of gel formalin through the
analysis by SEC of the soluble phase. RI, LALLS, Intrinsic Viscosity and UV signals
were simultaneously measured using a tetra-detector array, thus yielding absolute
molecular weight, branching factors, hydrodynamic radius and radius 01 gyration. The
performance 01 hydrogel beads was assessed through drug delivery tests triggered
by changes in the environmental temperature/pH. Aiming at the development of tools hopefully useful for the design of such advanced materials, a general kinetic approach (Chem. Eng. Sci. 2005, 60, 423) was used to carry out modeling studies
including consideration of finite loop formation reactions.
; Pinto, Virgínia 
