Polymerization thermal gelation

Thermal gelation The polymeric solution is cast hot. Cooling causes precipitation... 

Other synthetic approaches to the kinetic problem have been taken. Variations in catalyst concentration for the formation of each component network from linear polyurethanes and acrylic copolymers have been used along with a rough measure of gelation time (5) to confirm the earlier (2-3.) results. Kim and coworkers have investigated IPNs formed from a polyurethane and poly(methyl methacrylate) (6) or polystyrene (7) by simultaneous thermal polymerization under varied pressure increasing pressure resulted in greater interpenetration and changes in phase continuity. In a polyurethane-polystyrene system in which the polyurethane was thermally polymerized followed by photopolymerization of the polystyrene at temperatures from 0 to 40 C, it was found (8.) that as the temperature decreased, the phase-... 

The adhesive properties of epoxy resins coupled with their dielectric behavior have made them attractive to the electronic industry. The evaluation of thermally cured rubber modified epoxy thermosets has been the subject of recent studies (1, 2), which dealt with the dependence of morphology on the curing parameters, e.g., catalyst, cure schedule, time of gelation, etc. This work utilizes one of the new series of photocationic initiators (PCI) developed by Crivello, et al (3) which are presently commercially available. These onium salts initiate the reaction by absorbing the actinic radiation, generating radicals and producing a protonic acid. The radicals can lead to polymerization of olefinic moieties (4) while the acid initiates the polymerization of the epoxy groups (3). 

The pH responsive gel used in the project is based on the monomer methacrylic acid (MAA) The gels are synthesised via a free-radical mechanism. The synthesis was carried out in an aqueous environment using 2,2 -azobis (2-methylpropionamidine) dihydrochloride (AMPA) and N,N -methylene bisacrylamide (MBA) which are water-soluble free radical initiator and crosslink agent respectively (Scheme 1). The polymerizations were carried out in water (20%w/v MAA 0.03%w/v MBA 0.06%w/v AMPA) under a nitrogen atmosphere. The polymerization was initiated thermally at 70°C, and gelation occurred in less than one hour. Residual monomer was removed from the gels by alternate soaking in water and methanol. 

In chemical gels the network connection (crosslink) is usually a covalent bond, which leads to a thermally irreversible gel. When the crosslinking is purely physical in nature, a physical gel is formed which is thermally reversible. There have been at least two excellent works published in the last few years. Reversible Polymeric Gels and Related Systems by Russo [2] and Thermoreversible Gelation of Polymers and... 

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