Polymethylacrylate

Comparison of the photochemical behaviour of polymethylacrylate with that of polymethylmethacrylate provides an example of application of the empirical rule predicting that polymers of structure I (where and R2 are not hydrogen) undergo chain scission almost exclusively, whereas polymers of structure II (where R may be H) usually become 

One important exception to this rule is vinylketone polymers in which the Norrish type II reaction is responsible for the decrease of the molecular weight of irradiated polymers (see section 4). In contrast to polymethylmethacrylate, polymethylacrylate becomes insoluble on irradiation with 253.7 nm in vacuo [82]. In air, no visible insoluble material is formed and an apparent quantum yield of chain scission of 1.3 x 10-2 has been determined by viscosity measurements [82]. However, a qualitative comparison of sedimentation patterns of initial and irradiated samples indicates that crosslinking also occurs in the presence of air even if gelation is retarded by oxygen. This makes the above-mentioned value meaningless. Photolysis of thin polymethylacrylate films at 253.7 nm in vacuo has also been studied by measuring the insoluble fraction as a function of dose as described in section 2. Quantum yields of 1.9 x 10-3 have been estimated for both the chain scission and the crosslinking processes [83]. 

Quantum yields of formation have been measured for formaldehyde (2 x 10-2), methanol (1.9 x 10-3) and methyl formate (8 x 10-3) [82]. A modification of the absorption spectrum of polymethylacrylate during irradiation has also been observed (Fig. 14). [82]. The change is similar to that observed with polymethylmethacrylate in the same experimental conditions (Fig. 13) and is probably to be ascribed to the same origin. The photodegradation of polymethylacrylate can be visualized as 

The propagating radical formed in the last step as a consequence of chain breaking has been detected by ESR spectroscopy [28]. 

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Note that polymethylacrylate and polyethylacrylate have glass transition temperatures, which are close to room temperature. These polymers also have fairly... 

Standard-grade PSAs are usually made from styrene-butadiene rubber (SBR), natural rubber, or blends thereof in solution. In addition to rubbers, polyacrylates, polymethylacrylates, polyfvinyl ethers), polychloroprene, and polyisobutenes are often components of the system ([198], pp. 25-39). These are often modified with phenolic resins, or resins based on rosin esters, coumarones, or hydrocarbons. Phenolic resins improve temperature resistance, solvent resistance, and cohesive strength of PSA ([196], pp. 276-278). Antioxidants and tackifiers are also essential components. Sometimes the tackifier will be a lower molecular weight component of the high polymer system. The phenolic resins may be standard resoles, alkyl phenolics, or terpene-phenolic systems ([198], pp. 25-39 and 80-81). Pressure-sensitive dispersions are normally comprised of special acrylic ester copolymers with resin modifiers. The high polymer base used determines adhesive and cohesive properties of the PSA. 

Weakly acidic cation exchangers (e.g. polymethylacrylic acid resins). These resins (Zerolit 226, Amberlite 50, etc.) are usually supplied in the hydrogen form. They are readily changed into the sodium form by treatment with 1M sodium hydroxide an increase in volume of 80-100 per cent may be expected. The swelling is reversible and does not appear to cause any damage to the bead structure. Below a pH of about 3.5, the hydrogen form exists almost entirely in the little ionised carboxylic acid form. Exchange with metal ions will occur in solution only when these are associated in solution with anions of weak acids, i.e. pH values above about 4. 

Encapsulation within an enteric coat (resistant to low pH values) protects the product during stomach transit. Microcapsules/spheres utilized have been made from various polymeric substances, including cellulose, polyvinyl alcohol, polymethylacrylates and polystyrene. Delivery systems based upon the use of liposomes and cyclodextrin-protective coats have also been developed. Included in some such systems also are protease inhibitors, such as aprotinin and ovomucoids. Permeation enhancers employed are usually detergent-based substances, which can enhance absorption through the gastrointestinal lining. 

The reactions were carried out in dilute homogeneous solution in dipolar aprotic solvents ([ester]g=0.2-0.4 mole.l- ) using stereoregular (pure I or S) or predominantly syndiotactic radical (R) PMMA, polymethylacrylate (PMA) and radical azeotropic styrene-MMA copolymer (PSMMA, MMA mole.fraction = 0.47) as well as model monomeric (methylpivalate) and dimeric (dimethylglutarate) compounds. The overall reaction is outlined in the simplified scheme ... 

Polyelectrolytes such as Na polyacrylate, polymethylacrylate and polystyrene sul-phonate which form multiple site, surface complexes, strongly retarded dissolution and this effect was attributed to blocking of the surface sites by adsorption of these compounds (Baumgartner, 1985). 

RhCI3 Cross-linked polystyrene-substituted with —CH2PPh2 and —CH2NMe2 polymethylacrylate with —0(CH2)2NMe2 and —0(CH2)2CN n-Heptene 23... 

Dynamit-Nobel AG, NethP, Appl 6411854 (1966) CA 65, 6992(1966) (Liquid esters of nitric acid and aromatic nitro compds can be gelatinized with polymers of unsatd acids or unsatd alcohols and their derivs. The advantages of these polymers include increased safety of manipulation and increased rate of gelatinizacioii. Thus a 60/40—NG/ NGc soin was mixed with 3 wt %-of finely powd polymethylacrylates and, after 1.5 hrs, had a viscosity of 4250 cp at 20° under shearing gradient of 15 sec )... 

I 2 Ito, H., S. Shimizu and S. Suzuki Dependence of the viscosity of solutions of polymethylacrylate and polysodiumacrylate on molecular weight. K6gy6 Kagakn Zasshi 59, 930 (1956). 

Estimate the LA-value for a Polystyrene/Polymethylacrylate 33/67 statistical copolymer (cross-linked). 

The acrylic plastics use the term acryl such as polymethyl methacrylate (PMMA), polyacrylic acid, polymethacrytic acid, poly-R acrylate, poly-R methacrylate, polymethylacrylate, polyethylmethacrylate, and cyanoacrylate plastics. PMMA is the major and most important homopolymer in the series of acrylics with a sufficient high glass transition temperature to form useful products. Repeat units of the other types are used. Ethylacrylate repeat units form the major component in acrylate rubbers. PMMAs have high optical clarity, excellent weatherability, very broad color range, and hardest surface of any untreated thermoplastic. Chemical, thermal and impact properties are good to fair. Acrylics will fail in a brittle manner, independent of the temperature. They will suffer crazing when loaded at stress about halfway to the failure level. This effect is enhanced by the presence of solvents. 

We have demonstxated that the coverage of particles by the anion-active emulsifier (sodium alkyl sul-phonate) in the polymethylacrylate latex does not exceed 30%, and reaches 4 in the polybutylacrylate latex (10). 

The use of ultrasound radiation for polymerizing various monomers was reviewed in [la]. Here we will discuss how ultrasound waves have been used successfully been to embed ultrafine metallic partides in a polymeric matrix. The first report was by Wizel and coworkers [57]. They used ultrasound radiation to prepare a composite material made of polymethylacrylate and amorphous iron nanopartides. 

This product is an ultraviolet light absorber for use in polystyrene, unsaturated polyesters, coatings, varnishes, lacquers, and coatings based on epoxy or phenolic alkyds. It is also used in pressure sensitive adhesives, polymethylacrylate (fdm or sheeting), thermoplastic rubbers, polyisoprene latex and alcohol based cosmetics. 

The composition of the PAA-g-PS graft copolymer reaction product and its purification, especially as far as the removal of unreacted PS-MA macromonomer by silica column chromatography is concerned, and the successful selective cleavage of the ferf-butyl ester under acidic conditions to render the graft copolyelectrolyte PAA-g-PS were analyzed by XH NMR spectroscopy and SEC. Figure 8a shows the SEC curves of the polystyrene macromonomer (PS-MA), the crude poly (ferf-butyl acrylate-gra/f-styrene) (PTBA-g-PS) and the PTBA-g-PS the polymethylacrylate (PMA) originates from esterification of the poly (acrylic acid) (PAA) obtained after complete saponification of the graft copolymer and represents the backbone. The XH NMR spectra of PSMA, PTBA-g-PS and of the final reaction product PAA-g-PS are shown in Fig. 8b. 

Fig. 8 (a) SEC curves of the PS macromonomer (PS-MA curve 1), the crude (curve 2) and the purified (curve 3) poly( ter t-butyl acrylate-gra/f-styrene) (PTBA-g-PS), and the esterified polymethylacrylate (PMA curve 4) backbone, (b) H NMR spectra of the macromonomer PSMA, the graft copolymer PTBA-g-PS and the final purified reaction product poly(acrylic acid-gra/f-styrene) (PAA-g-PS)... 

Viscosity Modifiers, as polymethylacrylates, affecting low-temperature viscometrics and shear stability. 

All these data can be interpreted by a free radical mechanism including random initiation and inter- and intramolecular transfer [111]. The shape of the curve of rate of volatilization plotted as a function of percentage volatilization is in agreement with this kinetic scheme. Theoretical calculations (section 3) have in fact shown that, for polymers undergoing random degradation, the maximum rate of weight loss has to correspond to 26% conversion and not to the 10—20% observed for polymethylacrylate. The position of the maximum is, however, sensitive to chain transfer. 

The mechanism proposed by Cameron and Kane [111] for the thermal degradation of polymethylacrylate is... 

Polybenzylacrylate [112] appears to pyrolyse according to a mechanism similar to that of polymethylacrylate. The main chain polymer backbone decomposes in a random manner. The main products of degradation are carbon dioxide, benzylalcohol and low polymers. 

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