Acrylamide Hydrogels Preparation via Free Radical Crosslinking Copolymerization: Kinetic Study and Morphological Investigation (original) (raw)
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Polymer Bulletin, 1999
In situ fluorescence and light scattering techniques were used to study the formation of heterogeneities during the free-radical crosslinking polymerization of sodium acrylate (NaAc) in the presence of N,N'-methylene(bisacrylamide) (BAAm) as a crosslinker. Pyranine was used as a fluorescence probe in the experiments. The reactions were carried out at room temperature and at a monomer concentration of 20.6 w/v% in water. It was found that the gel forming system became turbid at the start of the reaction; continuing polymerization and crosslinking reactions turned the opaque gels into slightly opaque and finally transparent gels. Two peaks were observed both in the scattered and emitted light intensities versus the reaction time plots. The first peak corresponds to the formation and growth of the phase separated domains whereas the second peak reflects the macrogelation point in the reaction system.
Macromolecules, 2014
This article presents the implementation of the Chiu, Carratt, and Soong (CCS) gel/glass model in an analytical solution (AS) derived for the free radical polymerization under isothermal condition. This implantation allows AS to be applicable for the whole range of conversion thus making it more useful for practical applications. The results were compared with numerical solution (NS) as well as with experimental data for two different monomers: styrene (St) and methyl methacrylate (MMA). MMA with chain transfer agent was also used for this purpose. The results were found to be in good agreement with both NS and experimental data. NS with and without quasi-steady state assumption were also found to be in good agreement with each other for the entire range of conversion. As constant time step was used, the effect of stiffness on AS during gel effect was visible at low temperature compared to higher temperature. A dx.doi.org/10.1021/ma501251j | Macromolecules XXXX, XXX, XXX−XXX AS has been shown to be successfully integrated with CCS model for gel/glass effect. It was found to work well for different monomers, with variations in temperature, initiator, and its concentration and chain transfer agent. The results match quite well Macromolecules Article dx.doi.org/10.1021/ma501251j | Macromolecules XXXX, XXX, XXX−XXX J
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e-Polymers, 2008
A hydrogel from acrylic acid and hydroxypropyl cellulose was made. The percentages of raw materials and crosslinkers were varied and its swelling behavior was evaluated. Some of the gels obtained absorbed more than 300% wt. The gels with higher swelling percentages were characterized by means of IR spectroscopy, differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), and scanning electron microscopy (SEM). The FTIR showed the presence of the main reactants in the gel, while the DSC showed a phase separation in the gel. This gel is partly biodegradable because of the content of hydroxypropyl cellulose and has the viscoelastic properties of poly(acrylic acid).
Critical properties for gelation in free-radical crosslinking copolymerization
Macromolecular Theory and Simulations, 1995
A kinetic model was used to predict the molecular weight developments and the critical properties in free-radical crosslinking copolymerization. The predictions of the model were compared to the experimental data reported previously. Agreement of the kinetic model with experiments is satisfactory for both low and high crosslinker contents. The model parameters indicate increasing extent of shielding of pendant vinyl groups as the reaction proceeds due to the increasing number of multiple crosslinkages. The calculation results indicate that the real critical exponents can only be observed in the region E < 10-2-10-3 where experimental studies are very difficult. Outside of this region, the apparent critical exponent y describing the divergence of the weight-average molecular weight was found to deviate from the classical value due to the conversion dependent kinetics of free-radical crosslinking copolymerization.
A series of hydrogels were prepared from acrylamide and 2-acrylamido-2methylpropanesulfonic acid (AMPS) monomers with 0 -80 mol % AMPS and using N,NЈ-methylenebis(acrylamide) as the crosslinker. The swelling capacities of hydrogels were measured in water and in aqueous NaCl solutions. The volume swelling ratio q v of hydrogels in water increases sharply when the mole fraction f c of AMPS increases from 0 to 0.06. At higher values of f c from 0.06 up to 0.18, no change in the swelling capacities of hydrogels was observed; in this range of f c , q v becomes nearly constant at 750. However, as f c further increases, q v starts to increase again monotonically over the entire range of f c . At a fixed value of f c , the swelling ratio of hydrogels decreases with increasing salt concentration in the external solution. The results of the swelling measurements in aqueous salt solutions were compared with the predictions of the Flory-Rehner theory of swelling equilibrium. It was shown that the theory correctly predicts the swelling behavior of hydrogels up to 80 mol % charge densities. The method of estimation of the network parameters was found to be unimportant in the prediction of the experimental swelling data. The network parameters used in the simulation only correct the deficiency of the swelling theory.
Reducing the gel effect in free radical polymerization
2001
The gel e!ect is a phenomenon that often takes place during a free radical polymerization at intermediate or high degrees of conversion. It consists of the autoacceleration of the rate of the polymerization and it is due to di!usion limitations that slow down the termination reaction leaving the propagation and the initiation reactions una!ected. This phenomenon is highly undesired in industrial application because it causes a fast and dramatic increase of the temperature of the reacting medium, often leading to scale-up problems, instabilities, hot spots, and erratic behavior. In this paper, we present the results of kinetic experiments performed in a cone and plate rheometer with two common monomers: styrene and n-butylmethacrylate. We show that the gel e!ect can be signi"cantly reduced, if not eliminated, performing the polymerization at high shear rate. A new experimental device, the helical barrel rheometer, has been used and some preliminary results are presented.
e-polymers 026 2011 Lárez-Velásquez
Swelling studies of an acrylamide/maleic acid/methylene-bis-acrylamidebased hydrogel prepared by free radical polymerization (weight ratio of 90/10/3) are presented. Water penetration mechanism was studied by using two classical definitions, i.e., Crank (F C = w t /w eq ) and Karadag (F K = (w t -w o )/w o ), of the water fraction into the hydrogel (F). An anomalous water penetration mechanism (0.5<n<1.0) was obtained by employing both definitions and Buckley equation (F = kt n ); however, using the combined Peppas and Sahlin equation (F = k 1 t 1/2 + k 2 t) pointing out that swelling occurs in two stages: at first controlled by diffusion and relaxation contributions and then defined mainly by the diffusion contribution. Hydrogel was also studied as a system for the adsorption of cationic dye Safranin. Results show that this system perfectly fit to a Langmuir isotherm and the dye adsorption process stops when coverage of all active sites on the hydrogel has been achieved. Interestingly, adsorption process does not seem to be affected even though the hydrogel concurrently suffers the well known collapse phenomenon.