Crosslinked-PMMA

FATIGUE CRACK PROPAGATION. As shown in Figures 7 and 8, the SINs from both the one-shot and the prepolymer procedure were significantly superior in FCP behavior to the crosslinked-PMMA control. The FCP resistance was improved with increasing PU content. Unfortunately, when the amount of PU was larger than 50... 

There are several interesting polymerization schemes intermediate between a sequential IPN and an SIN. For example, in in situ prepared sequential IPNs, both monomers are polymerized via free radical reaction [He et ai, 1993 Rouf et ai, 1994]. The two monomers must have quite different reactivities towards the free radicals. This situation arises with vinyl or acrylic double bonds and aUylic double bonds. The allylic double bonds react about 100 times slower than acrylic or methacrylic bonds. Often, two initiators are used, one reacting at a lower temperature, and the other at a higher temperature. In one of the systems studied, based on methyl methacrylate and diallyl carbonate of bisphenol-A (DACBA), first, crosslinked PMMA was formed at moderate temperatures. Then, by just increasing the temperature after completion of the first polymerization, the synthesis of the allylic network followed. 

Chem. Descrip. Spherical fine polymer powd. with crosslinked PMMA base material... 

Crosslinked PMMA is used in food contact films, and silicone antiblocks have been developed to compete with silica. 

Food contact packaging film can also contain antiblocks. The additives must not only achieve regulatory approval, but must minimise taint and odour and maximise colour stability. Nippon Shokubai developed crosslinked PMMA particles called Epostar MA about five years ago, as a food contact antiblock for polyethylene. The company was claimed at the time to have been the first to have an antiblocking agent approved by the EU for food contact applications with polyethylene. 

Seeded soapless emulsion polymerisation is carried out with linear or crosslinked PMMA as seeds, styrene (ST)... 

Polyherbicide derivatives based on PMMA resins were prepared by the reactions of crosslinked PMMA (2 % DVB) with hydrazine, ethylene- and hexamethylene diamine followed by modification with the acid chlorides of 2,4-D and CMPA (Scheme 3.8). The effect of the polymer stracture and pH of the aqueous environment on hydrolysis rates were investigated [133],... 

L. N. Johnson, Composite Resins as a Dental Restorative Material, /. Biomed. Mater. Res. Symp. 1, 207 (1971). History of use of polymers in tooth fillings. Description of composite materials for tooth fillings. Description of linear PMMA/crosslinked PMMA semi-II IPNs. 

Blumstein [a.295] showed that free-radical-polymerised PMMA inserted between the lamellae of montmorillonite clay ( f-spacing increase of 0.76 nm) resisted thermal degradation under conditions that would otherwise completely degrade pure PMMA (refluxing decane, 215 °C, N2,48 h). TG revealed that both linear PMMA and crosslinked PMMA intercalated into Na+ montmorillonite have a 40-50 °C higher decomposition temperature. Improvements in thermal stability similar to that reported by Blumstein for... 

Commercial interpenetrating polymer networks (not including thermoplastic compositions) include artificial teeth (Dentsply) made Ifom crosslinked PMMA mixed with MMA monomer and polymerized (sequential IPN), sound and vibration damping compositions (e.g., vinyl-phenolic Hitachi) and sheet molding compositions (acryhc/urethane/polystyrene Ferro Chemical) [164]. Water-borne acrylic methane semi-IPNs are commercial Ifom several sources where acrylate monomers are polymerized in the presence of a polymethane water dispersion. A silicone/polytetrafluoroethylene composition described as an IPN is offered by Biomed Sciences under the Silon tradename. The fluoropolymer provides the mechanical strength and the silicone rubber offers the softness and oxygen and moisture permeability for applications in the wound care area. 

These crosslinked PMMA samples were heated above Tg in an environmental chamber on an Instron test apparatus. They were stretched (behaving like a rubber) to the desired extent and rapidly cooled to 80 C by direct injection of CO2 gas. (See Figure 1, treatment of uncrosslinked... 

PMMA, and Figure 2, crosslinked PMMA.) The energy that had been applied to the sample was determined from the energy under the stress-strain curve. Table I describes the internal energies of the various irradiated PMMA samples prepared. The method of preparing samples and calculating the values has been well described. 

The possibility raised by the work of Taylor and Layman that a polymeric matrix can raise the hardness of a composite material above that of its ceramic microphase has important potential in the design of such materials. Therefore, despite the unfavorable findings described above for abalone nacre, experiments were made to explore this possibility further. In the experiment in which the matrix of a specimen of nacre was replaced with crosslinked PMMA the hardness was little changed, from 149 + 9 to 144 + 12. However, this experiment was inconclusive because the replacement of the matrix was confined to a surface layer and results may have been influenced by... 

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