Polymethylmethacrylate, solvent

Common examples of the high Tg macromers are based on polystyrene or polymethylmethacrylate (PMMA) polymers of sufficiently high molecular weight to have a high T (typically on the order of 70-100°C as measured by differential scanning calorimetry) and also to make them immiscible with the acrylic polymer backbone once the solvent or heat has been removed. Typical molecular weight of the polystyrene or PMMA macromers is on the order of 5000-10,000 Da. Their generic structure can be pictured as in Fig. 13 (shown there for polystyrene). 

Smaller diameter columns are especially useful when expensive solvents are used. Figure 11.3 shows the analysis of poly (1,4-butylene terephthalate) using a Waters Alliance narrow-bore GPC system, quantitated against narrow polymethylmethacrylate standards. In this case, the solvent used is hexaflu-oro-2-isopropanol with 0.05 M sodium trifluoroacetic acid at a flow rate of... 

Organic solvents are most commonly used, and encapsulating polymers include ethylcellu-lose, NC, polvvinylidene chloride, polystyrene, polycarbonate, polymethylmethacrylate, polyvinyl acetate and others. Inter facial polymerization produces a polymer such as nylon at the interface between layered solns of two precursor materials such as (in the case of a nylon) a diamine and a diacid (Refs 3 11). If the particle or drop-... 

For instance, one of the various crystalline forms of polyoxacyclobutane is a hydrate [62], Syndiotactic polymethylmethacrylate also forms nonstoichiometric inclusion compounds with a variety of solvents [63,64]. 

Transport Properties Although the densities of SCFs can approach those of conventional liquids, transport properties are more favorable because viscosities remain lower and diffusion coefficients remain higher. Furthermore, CO2 diffuses through condensed-liquid phases (e.g., adsorbents and polymers) faster than do typical solvents which have larger molecular sizes. For example, at 35°C the estimated pyrene diffusion coefficient in polymethylmethacrylate increases by 4 orders of magnitude when the CO2 content is increased from 8 to 17 wt % with pressure [Cao, Johnston, and Webber, Macromolecules, 38(4), 1335-1340 (2005)]. 

Preparation of nanoparticles can be by a variety of different ways. The most important and frequently used is emulsion polymerization others include interfacial polymerization, solvent evaporation, and desolvation of natural proteins. The materials used to prepare nanoparticles are also numerous, but most commonly they are polymers such as poly-alklcyanoacrylate, polymethylmethacrylate, poly-butylcyanoacrylate, or are albumin or gelatin. Distribution patterns of the particles in the body can vary depending on their size, composition, and surface charge [83-85]. In particular, nanoparticles of polycyanoacrylate have been found to accumulate in certain tumors [86,87]. 

A detailed study of the mechanism of the insertion reaction of monomer between the metal-carbon bond requires quantitative information on the kinetics of the process. For this information to be meaningful, studies should be carried out on a homogeneous system. Whereas olefins and compounds such as Zr(benzyl)4 and Cr(2-Me-allyl)3, etc. are very soluble in hydrocarbon solvents, the polymers formed are crystalline and therefore insoluble below the melting temperature of the polyolefine formed. It is therefore not possible to use olefins for kinetic studies. Two completely homogeneous systems have been identified that can be used to study the polymerization quantitatively. These are the polymerization of styrene by Zr(benzyl)4 in toluene (16, 25) and the polymerization of methyl methacrylate by Cr(allyl)3 and Cr(2-Me-allyl)3 (12)- The latter system is unusual since esters normally react with transition metal allyl compounds (10) but a-methyl esters such as methyl methacrylate do not (p. 270) and the only product of reaction is polymethylmethacrylate. Also it has been shown with both systems that polymerization occurs without a change in the oxidation state of the metal. 

A novel approach to determine the solvent concentration profile in a photoresist undergoing dissolution via fluorescence quenching and laser interferometry is introduced. Fluorescence arising from phenanthrene dye labels in a l-/im-thick polymethylmethacrylate)... 

Polymers, for example, polypropylene or polymethylmethacrylate (PMMA, Plexiglas transparent) and many others, may be interesting materials of easy machinability. But their chemical stability, especially against organic solvents, has to be tested individually. 

The problem of high pressure drops with gel entrapped materials has been overcome by entrapping the enzymes in plastic materials snch as polystyrene and polymethylmethacrylate (Wang et al, 1997). The method involves chemical acryloylation of the enzyme to provide a polymerizable functionality, formation of non-covalent ion pairs between the enzymes and a snrfactant, solntion of these ion pairs in an organic solvent followed by addition of vii rl monomers, a crosshnker, and an initiator to give the desired vinyl polymer with the entrapped enzymes. 

Acrylates. Polymethylmethacrylate (Lucite, Plexiglas, Perspex) is easily machined and is widely used with dilute aqueous solutions. Acrylates are resistant to nonoxidizing acids and weak alkalies, but are attacked by concentrated oxidizing acids and strong alkalies. They will withstand petroleum oils and most alcohols, but are generally unsuitable for use in contact with organic solvents. They are dissolved by ketones, esters, and aromatic and chlorinated hydrocarbons. They are thermoplastic and cannot be used continuously above 75 °C. The acrylates are perfectly clear and transparent and often are used to make shields or inert atmosphere enclosures. The materials bum slowly when ignited. 

In comparison to bulk plastics, thermoplastic polymethylmethacrylate (PMMA) is much more expensive. Its particular characteristics are clarity, hardness, low absorbance and resistance to aqueous solutions, acids, alkalis, carbon dioxide and fat. It is attacked or dissolved by polar organic solvents. The world-wide use of PMMA in 1997 was ca. 1.2 x 106 t, principaly for optical articles in cars and buildings and glazing material in aircraft. Typical food contact articles are dishes, cups and silverware. In addition it has orthopedic and denture uses. 

There are several ways of isolating molecules, in addition to dilution in appropriate solvents. For instance, extremely long PDA chains can be diluted in their monomer single crystal by exploiting the peculiar polymerization mechanism [91] of this class of polymers. In the case of CPs blended with non-conjugated macromolecules (polyethylene, polymethylmethacrylate, etc.) or inclusion crystalline compounds [92], the interaction between molecule and environment is usually strongly suppressed, but at the expense of the sample optical density, in a way that may easily challenge the common sensitivity of time-resolved techniques. 

Polymethylmethacrylate (acrylic) Acetone, methyl ethyl ketone, detergent, methanol, trichloroethylene, isopropanol Abrasion. Grit or vapor blast or 100-grit emery cloth followed by solvent degreasing. For maximum strength, relieve stresses by annealing plastic for 5 h at 100°C... 

The other kind of systems largely studied, consists of polymethylmethacrylate (PMMA) or silica spherical particles, suspended in organic solvents [23,24]. In these solvents Q 0 and uy(r) 0. The particles are coated by a layer of polymer adsorbed on their surface. This layer of polymer, usually of the order of 10-50 A, provides an entropic bumper that keeps the particles far from the van der Waals minimum, and therefore, from aggregating. Thus, for practical purposes uw(r) can be ignored. In this case the systems are said to be sterically stabilized and they are properly considered as suspensions of colloidal particles with hard-sphere interaction [the pair potential is of the form given by Eq. (5)]. 

Table 8. Unperturbed dimensions of polymethylmethacrylate in various solvents...

The solution was diluted with cyclohexane, a solvent for polystyrene and a nonsolvent for polymethylmethacrylate, and the product thereafter precipitated by addition to methanol THF/cyclohexane/methanol = 1 2 10 (by volume). The product was finally dried to constant weight. 

Many transparent crystalline materials can incorporate chro-mophores, either substitutionally or interstitially. If sufficiently soluble, a chromophore may also be dissolved in a polymer film such as polyvinyl alcohol or polymethylmethacrylate. Incorporation of a chromophore can be achieved by dissolving the chromophore and polymer in a solvent. A suitable film is then quite simply created by evaporation of the solvent. Other types of supporting media are sol-gels. When a chromophore is present in the reaction medium, a rigid sol-gel embedded with the chromophore can be created. 

Brendle described a process which he called polymer grafting, in which particles of molybdenum disulphide or other solid lubricants were coated with various polymers, including polystyrene, polymethylmethacrylate and poly-isobutylvinyl ether. The process was most conveniently carried out by grinding coarse molybdenum disulphide powder in a 20% - 30% solution of the appropriate monomer in a solvent. The quantity of polymer added to the molybdenum disulphide particles was very small, and could not be detected by scanning electron microscopy or infrared spectroscopy. The carbon content (1-4%) indicated a polymer content up to 6% maximum. Brendle considered that the polymer was preferentially grafted onto surface freshly exposed by grinding. This may be partly true, but in view of later... 

Polystyrene Although polystyrene is usually bonded by solvent cementing, it can be bonded with vinyl acetate/vinyl chloride solution adhesives, acrylics, polyurethanes, unsaturated polyesters, epoxies, urea-formaldehyde, rubber-base adhesives, polyamide (Versamid-base), polymethylmethacrylate, and cyanoacrylates. The adhesives should be medium-to-heavy viscosity and room-temperature and contact-pressure curing. An excellent source is a Monsanto Company technical information bulletin which recommends particular commercial adhesives for bonding polystyrene to a number of different surfaces. Adhesives are recommended in the fast-, medium-, and slow-setting ranges (10). 

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