Polymethyl methacrylate yield

Polymerization of t-butyl methacrylate initiated by lithium compounds in toluene yields 100% isotactic polymers 64,65), and significantly, of a nearly uniform molecular-weight, while the isotactic polymethyl methacrylate formed under these conditions has a bimodal distribution. Significantly, the propagation of the lithium pairs of the t-Bu ester carbanion, is faster in toluene than in THF. In hydrocarbon solvents the monomers seem to interact strongly with the Li+ cations in the transition state of the addition, while the conventional direct monomer interaction with carbanions, that requires partial dissociation of ion-pair in the transition state of propagation, governs the addition in ethereal solvents. 

Radical copolymerization of diaryl nitrones, such as a-(2-hydroxyphenyl)-A-(2,6-dimethylphenyl) nitrone (HDN), a-(2-hydroxy-4-methacryloyloxyphenyl)-N -(2,6-dimethylphenyl) nitrone (HMDN), and a-(2-hydroxy-4-methacryloyloxy-phenyl)-A-phenylnitrone (HMPN) (Fig. 2.30), with methyl methacrylate leads to copolymers in good yields with considerable quantities of hydroxy substituted diaryl nitrone pendants. The presence of photoactive nitrone pendants in these copolymers allows one to control photochemically the refractive index of polymethyl methacrylate films (468, 700, 701). 

Fig. 55. Dependence of square root of excess LS for solutions of (a) polyethyleneglycol methacrylate and (b) polymethyl methacrylate in mixed solvents comprising 2,2,3,3-tetrafIuoropro-panol (volume fraction ) and benzyl alcohol. (T = 25 °C, 0 = 546 nm). Broken lines indicate composition of mixed solvent yielding no excess scattering from the polymer in each case1 S2 ...

They are atactic amorphous polymers which have good light transparency (92%) and yield transparent moldings and films. As was noted for polyalkyl acrylates, the solubility parameters decrease as the size of the alkyl groups increases. The flexibility also increases as one goes from polymethyl methacrylate (PMMA) to polyaryl methacrylate and then decreases as the size of the alkyl group is further increased. 

The mechanical degradation and production of macroradicals can also be performed by mastication of polymers brought into a rubbery state by admixture with monomer several monomer-polymer systems were examined (10, 11). This technique was for instance studied for the cold mastication of natural rubber or butadiene copolymers in the presence of a vinyl monomer (13, 31, 52). The polymerization of methyl methacrylate or styrene during the mastication of natural rubber has yielded copolymers which remain soluble up to complete polymerization vinyl acetate, which could not produce graft copolymers by the chain transfer technique, failed also in this mastication procedure. Block and graft copolymers were also prepared by cross-addition of the macroradicals generated by the cold milling and mastication of mixtures of various elastomers and polymers, such as natural rubber/polymethyl methacrylate (74), natural rubber/butadiene-styrene rubbers (76) and even phenol-formaldehyde resin/nitrile rubber (125). 

Silica is less efficient than soda lime glass in initiating the grafting of polymethyl methacrylate in presence of sodium bisulfite (9). The results achieved with semichemical pulp show very high rate and yield of graftings (Figure 8). 

For comparison with this material, a mixture of the homopolymers was examined. Portions of an anionically polymerized polymethyl methacrylate (Mn = 39,200) and a polydimethylsiloxane (Mn = 29,000) were combined to yield a mixture containing 42.2 wt % siloxane the mixture was spread to form a monolayer. Figure 7 shows the tt—A curve of this... 

A few polymers can be converted back to their monomers for purification and repolymerization. Polymers formed by ring-opening polymerization fall in this class, as shown in the foregoing by the conversion of nylon 6 back into caprolactam. When ethyl cyanoacrylate is used as a binder for metal and ceramic powders, it can be recovered for reuse by pyrolysis at 180°C.184 The monomer can be obtained by pyrolysis of polymethyl methacrylate in 92-100% yield,185 poly(a-methylstyrene) in 95-100% yield, and polytetraflu-oroethylene in 97-100% yield.186 Polystyrene can be de-polymerized to styrene containing some styrene dimer by heating with solid acids or bases at 350 400°C.187 It is pos sible that the dimer could be recycled to the next run to produce more monomer. The best yield (> 99% styrene) was obtained by passing polystyrene through a fluidized bed of a solid catalyst at 400 700°C, with a contact time of more than 60 s.188... 

The second mode is especially damaging. It causes not only a loss of the initiator but yields lithium alkoxide which, in turn, interferes with the propagation. In this respect butyl lithium is the most undesired initiator as it produces large amounts of the alkoxide in the first few seconds even at - 30 °C. Similar side reactions take place in the propagation of lithium polymethyl methacrylate, causing, e.g. ring formation or a false addition and branching371,372>. 

Copolymerisation reactions do not always succeed in the presence of phenols. Cardanol, converted to the acrylate (R = H) by reaction with acryloyl chloride, has been co-polymerised in the presence of benzoyl peroxide with methyl methacrylate leading to a product vrith improved thermal stability compared with polymethyl methacrylate alone (ref. 265). In a similar way an acrylate and a methacrylate (R = Me) have been synthesised from 3-pentadecylphenol. Polymerisation yielded moderately high molecular weight compounds of potential interest as pressure-sensitive adhesives (ref. 266). 

Patterning of hydrophilic/hydrophobic alkanethiols combining electron beam lithography (EBL) and self-assembly of alkanethiol molecules, (a) 150 nm thick polymethyl methacrylate (PMMA) resist spin coated onto the gold deposited on a silicon wafer (b) Patterned PMMA trenches were defined by electron beam and development (c) a hydrophilic ll-amino-l-un-decanethiol hydrochloride (MUAM) assembled in the PMMA trench area (d) PMMA resists were removed by acetone to produce patterned MUAM on gold (e) backfilled by hydrophobic octadecanethiol (ODT) yielding the final chemical pattern. (Reprinted with permission from Wiley.)... 

The thermal degradation of polymethyl methacrylate (PMMA) over the temperature range 150-500 °C gives virtually 100% yield of monomer. 

Dicapryl adipate n. C4H8(COOC8Hi7)2. A plasticizer for cellulosic and vinyl resins, yielding good low-temperature flexibility. Also compatible with polymethyl methacrylate and polystyrene. 

Plastics generally increase in strength and become more rigid at low temperature. However, many plastics will become brittle. Brittleness results when a material loses its yield. Brittleness can result from crystallization, although many linear polymers become brittle without crystallizing. Rubber-type materials exhibit brittle behavior similar to that of thermoplastics. It also should be noted that some plastics have useful properties below their brittle points (e.g., polystyrene and polymethyl methacrylate). 

The changes and yields in polymer irradiation are often similar to those found with lower-molecular-weight compounds with similar structural features. The radiolysis of linear polyethylene is similar to that of the -alkanes, polystyrene resembles the alkylbenzenes, and polymethyl methacrylate behaves like a branched chain ester. Lower-molecular-weight compounds are often used to model processes taking place in polymer irradiation. 

Studies involving the use of organically modified clay particles in heterophase polymerization are rather scarce. Indeed, we are aware of only two reports that combine the emulsion or suspension polymerization approaches and ion-ex-change reaction. In one of these reports, AI BA is immobiHzed in the clay interlayer region to yield exfoliation of MMT in the PMMA matrix through suspension polymerization [135]. In another relevant study, it was demonstrated that exfoliated structures could be obtained by post-addition of an aqueous dispersion of layered silicates (either MMT or laponite) into a polymethyl methacrylate latex suspension produced in the presence of suitable cationic compounds (cationic initiator, monomer or surfactant) [136]. Since the latex particles were cationic and the clay platelets anionic, strong electrostatic forces were developed at the polymer/clay interface. 

The 1930s marked the start of the poly era. It had been known since the nineteenth century that a number of organic compounds could yield tarry insoluble materials under certain conditions, but it was not until the 1930s that the chemical nature of these compounds was understood. It was Hermann Staudinger (1881-1965) who established that these materials, as well as natural rubber, consisted of very long-chain molecules. Commercial production of polyvinyl chloride (PVC) commenced in the 1930s with the development of suitable plasticisers, and other thermosoftening addition polymers which were first produced at this time include polystyrene, polyethylene (Polythene), polymethyl methacrylate (Perspex) and polychloroprene (Neoprene), which is similar to natural rubber except that the methyl side chain has been replaced by chlorine. 

A sheet of polymethyl methacrylate 0.20 in. thick is heated radiantly to a surface temperature of 2000°F for 519 s. The convective heat-transfer coefficient is 8.85 Btu/h F. What heat transfer would be needed to yield the same evenness index for the same time of exposure Explain the difference in the two situations. 

Synthesis of methyl methacrylate is fundamental to the production of the transparent plastic polymethyl methacrylate (PMMA), and is estimated at over two million metric tons per year. The monomer is most commonly synthesized via the well-established Acetone Cyanohydrin (ACN) process, as shown below, based on easily available raw materials such as, acetone, hydrogen cyanide, methanol and sulfuric acid. Reaction of acetone and hydrogen cyanide yields acetone cyanohydrin as an intermediate, which is then reacted with excess amount of concentrated sulfuric acid, followed by thermal cracking to form methacrylamide sulfate. The methacrylamide sulfate intermediate is then further hydrolyzed and esterified with aqueous methanol to form methyl methacrylate. 

Figure 12.20 Mohr circles for yield behaviour of polymethyl methacrylate obtained from results of Rabinowitz, Ward and Parry. The crosses are the results of Bowden and Jukes. (Reproduced with permission from Rabinowitz, S., Ward, I.M. and Parry, J.S.C. (1970) The effect of hydrostatic pressure on the shear yield behaviour of polymers. /. Mater. Sci., 5, 29. Copyright (1970) Springer Science and Business Media.)...

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