Other methacrylates

In the early stages of degradation, polymethyl-a-phenylacrylate [97, 98] decomposes by random initiation and unzipping to monomer, as do poly-a-methylstyrene and anionic polymethylmethacrylate. Later in the reaction, chain-end initiation becomes important and predominates beyond about 45% conversion. Poly-n-butylmethacrylate yields appreciable amounts of monomer but the reaction is not quantitative [99]. Monomer production ceases at 30—50% conversion at 250° C, and at 

Poly-f-butylmethacrylate behaves in a very different way. If the pressure of the evolved gas is measured as a function of time [100] (Fig. 32) three maxima are observed. They correspond to three different stages in the degradation. The volatiles produced during each stage were analysed and the results obtained are shown in Table 5. These data can be 

PRODUCT YIELDS ASSOCIATED WITH MAXIMA C, D AND E (FIG. 32) IN THE THERMAL DEGRADATION OF POLY-f-BUTYLMETHACRYLATE 

Matsuzaki et al. [101] have found that isotactic poly-t-butylmethacrylate decomposes more rapidly into isobutene and polyanhydride than the corresponding syndiotactic polymer. This is in agreement with the above mechanism. 

Monomer production is a general reaction of the methacrylates. Ester decomposition yielding methacrylic acid and the corresponding olefin is possible when the alcohol residue has P hydrogen atoms it becomes the most important mechanism in the case of tertiary esters like poly-t-butylmethacrylate but is competitive with monomer formation in ethyl- and n-butylmethacrylates. 

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Appropriate protective clothing and equipment should be worn to minimize exposure to methacrylate liquids and vapors. Chemically resistant clothes and gloves and splash-proof safety goggles ate recommended. The working area should be adequately ventilated to limit vapors. Should chemical exposure occur, contaminated clothing should be removed and the affected area washed with copious amounts of water. Medical attention should be sought if symptoms appear. Eurther information about methyl methacrylate and other methacrylates is available (141). 

The uniqueness of methyl methacrylate as a plastic component accounts for its industrial use in this capacity, and it far exceeds the combined volume of all of the other methacrylates. In addition to plastics, the various methacrylate polymers also find appHcation in sizable markets as diverse as lubricating oil additives, surface coatings (qv), impregnates, adhesives (qv), binders, sealers (see Sealants), and floor poHshes. It is impossible to segregate the total methacrylate polymer market because many of the polymers produced are copolymers with acrylates and other monomers. The total 1991 production capacity of methyl methacrylate in the United States was estimated at 585,000 t/yr. The worldwide production in 1991 was estimated at about 1,785,000 t/yr (3). 

The addition—reaction product of bisphenol A [80-05-07] and glycidyl methacrylate [106-91-2] is a compromise between epoxy and methacrylate resins (245). This BSI—GMA resin polymerizes through a free-radical induced covalent bonding of methacrylate rather than the epoxide reaction of epoxy resins (246). Mineral fillers coated with a silane coupling agent, which bond the powdered inorganic fillers chemically to the resin matrix, are incorporated into BSI—GMA monomer diluted with other methacrylate monomers to make it less viscous (245). A second monomer commonly used to make composites is urethane dimethacrylate [69766-88-7]. 

The hindered carbon-centered radicals are most suited as mediators in the polymerization of 1,1-disubstituled monomers e.g. MMA,78,95 other methacrylates and MAA,06 and AMS97). Polymerizations of monosubstituted monomers are not thought to be living. Dead end polymerization is observed with S at polymerization temperatures <100°C.98 Monosubstituted monomers may be used in the second stage of AB block copolymer synthesis (formation of the B block).95 However the non-living nature of the polymerization limits the length of the B block that can be formed. Low dispersities are generally not achieved. 

Anionic Polymerization of Other Methacrylates and Their Copolymerization... 

Only fragmented data are available on polymerization of other methacrylates. Propagation constants and the respective Arrhenius parameters for the homopolymerization of various methacrylates initiated by sodium metallo-organics were reported recently +3,56) and are given in Table 2. 

Sawamoto et al. have revealed that the ruthenium complex induces the living radical polymerization of MMA [30,273-277]. For example, RuCl2(PPh)3 provided poly(MMA) with Mw/Mn 1.1 and the block copolymers. This system has a unique characteristic in that it is valid not only for MMA and other methacrylates, but also for acrylates and St derivatives. 

The majority of resins are composed of two dimethacrylate monomers, 2,2 -bis [4(2-hydroxy-3-methacryloyloxypropyloxy)phenyl] propane (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) [22-28]. Typically, TEGDMA or other methacrylate monomers are added as viscosity modifiers to Bis-GMA to make the solution less viscous and more appropriate for clinical use. These diluents also allow for better distribution of the components during manufacture of these composite systems. Another common monomer used to make dental composites, especially those manufactured in Europe, is urethane dimethacrylate [24,29, 30], Ethoxy bisphenol A dimethacrylate is another modification of the Bis-GMA monomer that can be used to make a more hydrophobic polymer that would better withstand the wet oral environment. Other diluents include low viscosity diacrylates and dimethacrylates. Table 1 lists some of these monomers [31-37]. 

Of key importance in the Lewis acid promoted living anionic polymerization of methacrylic esters with aluminum porphyrin is how to suppress the undesired reaction between the nucleophile (2j ) and the Lewis acid, leading to termination of polymerization (Fig. 11). As mentioned in previous sections, one of our approaches was to make use of sterically crowded Lewis acids such as methyla-luminum bis(ort/zo-substituted phenolates). This section focuses attention on the steric bulk of the nucleophile component (2 ), by using strategically designed aluminum porphyrins and some other methacrylates, for the purpose of understanding the scope and limitation of this method (Fig. 12). 

Polymerization. Poly (methyl methacrylate) was obtained commercially. The polymers of other methacrylates and their copolymers were prepared in toluene with 2,2 -azobisisobutyronitrile (AIBN) at 60 °C. All the polymers prepared free radically were syndiotactic or atactic. Isotactic poly(a,a-dimethylbenzyl methacrylate) was obtained using C6H5MgBr as the initiator in toluene at 0°C. Poly(methacrylic acid) was prepared in water using potassium persulfate at as the initiator 60 °C. The molecular weights, glass transition temperatures and tacticities of the polymethacrylates are summarized in Table I. 

The difference between the rotatory power of poly-1.3-dimethyl-butyl-methacrylate and of 1.3-dimethyl-butyI-pivalate used as a model compound, was attributed by Arcus (8,9) to the particular conformation assumed by the polymer chain in solution. A similar explanation can be given to the differences in rotatory power observed in the case of other methacrylic esters (134), and to the slight differences between the men-thyl-methacrylate polymers having different stereoregularity (131,135). 

Surfilcon-A copolymer of MATA, ATP, and other methacrylates 74 Permaflex Cooper Vision, Inc. 

Methyl methacrylate polymerises in the solid state to give an amorphous poly(methylmethacrylate), as do a number of other methacrylate monomers. Poly(oxymethylene) is a fibrous, oriented, crystalline polymer that is obtained by the ring opening polymerisation of cyclic oxymethylenes, -(CH20)-m, where m can be between 3 and 6. 

Recently, the miscibility of CO rubber with PMMA over the entire range of concentrations and molecular weights has been confirmed (1 ). There is a broadening of the glass transition which reaches a maximum at about 30% PMMA. However, even at that concentration, the polymers are truly miscible. Studies of compatibility of CO rubber and some copolymers have been reported with other methacrylate polymers and also with acrylate polymers over a wide variety of conditions (Llf 12). Another reason for blending with CO is that CO contains chlorine which tends to enhance x-ray absorption, especially near the absorption edge of 4.4 A. It was hoped that the in-rrease in absorption would produce more secondary... 

The temperature has a decisive effect on the anionic polymerization initiated by DPHLi (10) or benzyllithium in THF. As soon as the temperature is increased from —78 °C up to —40°C, the livingness is lost. Compared to MMA and other methacrylates, tBuMA is an exception for which the anionic polymerization remains under control at temperatures as high as 25 °C. This remarkable behavior is accounted for by the steric hindrance of the ester group, which prevents side reactions from occurring at an appreciable rate. 

Pyrolysis process for poly(2-hydroxyethyl methacrylate) occurs similarly to that for other methacrylic acid esters. The formation of 2-methyl-2-propenoic acid 2-hydroxyethyl ester, the monomer, shows that unzipping is a significant part of the process. Some other compounds in the pyrolysate also are generated from the polymer cleavage, such compounds including 2-methyl-2-propenoic acid ethenyl ester, propanoic acid, 2-methyl-2-propenoic acid, ethanol, etc. On the other hand, some compounds are not expected in the pyrolysate and they can be impurities or additives. Examples of such compounds are the hydrocarbons (undecene, dodecane, 1-dodecene, etc.), the esters of ethylene diol and the free 1,2-ethandiol, etc. The initiator AIBN and its decomposition products 2-methyl-2-propenenitrile and 2-methylpropanenitrile identified in the pyrolysate show that the polymer was obtained using AIBN as initiator. 

Other methacrylate-based copolymers are also possible with acrylamide (R-14)370 and maleimide (R-15),410 which can be prepared by ruthenium and copper catalysts, respectively. Both copolymers have amide groups randomly distributed in the PMMA chains. 

Methacrylates are the monomers most commonly utilized in CCT, and MMA seems to be the monomer against which all comparisons are made. It was discussed extensively in the section on catalysts. In addition to the methyl ester, many other methacrylate esters are mention in the literature. Table 9 lists... 

Dimethacrylate monomers and polymethacrylate monomers must be discussed separately from other methacrylates because of their ability to cross-link under normal free-radical polymerization conditions. Even at very low conversion, less than 1%, they produce completely cross-linked polymers that cannot be solvent-swollen and are insoluble. CCT agents reduce molecular weight and thereby move the gelation point to a much higher degree of conversion, though CCT cannot prevent gelation completely.320... 

The nine-line spectrum observed after irradiation of polymethylmethacrylate (PMMA) at room temperature has been the subject of much investigation and interpretation. It consists of five well-resolved narrow lines of approximately binomial distribution of intensities and four broader lines evenly distributed between the five (Fig. 14). Identical spectra are obtained at room temperature after UV irradiation or mechanical degradation [41]. A spectrum with similar general features is observed for the other methacrylic and methacrylate polymers. 

It is evident that a sinusoidal oscillation occurs about the steadily increasing transient value the plots previously shown were based on a smoothed transient curve for calculations of A. The period of oscillation is nearly independent of time. We have also observed constant periodicity for other methacrylate polymers. The period appears to be proportional to the strain rate, as judged from several experiments, so that the calculated spac-ings (see below) are independent of e. The magnitude of the fluctuations is typically 2-4% of the transient value in terms of... 

Other methacrylates snch as ethyl methacrylate (EtMA), isobomyl methacrylate (/-BMA) and t-bntyl methacrylate (t-BnMA) were successfully polymerised at 35 °C as well (Table 1). For PEtMA and Pt-BuMA, very low polydispersities of 1.15 and 1.14 were obtained. For polymerisations of isobomyl methacrylate, on the other hand, a significantly broader molecular weight distribution of PDI = 2.46 was fonnd. The two acrylates tested, -butyl acrylate ( -BnA) and t-bntyl acrylate (t-BuA), gave very low conversions (Table... 

The hindered carbon-centered radicals are most suited as mediators in the polymerization of 1,1-disubstituted monomers e.g. other methacrylates... 

Due to good optical and rheological characteristics, homopolymers of fluorine-containing methacrylates and their copolymers with other methacrylates are more often used in fibre-optic practice [2, 20-24, 26-34]. But selection of a polymer with the best optical and mechanical properties requires establishment of the dependence of the structure and properties of the polymers on the structure and reactivity of initial monomers. To solve this problem the study of the kinetics of block polymerisation and copolymerisation process of fluoroalkyl-(meth)acrylates is desirable. 

Similarly the coisotactic parameters were obtained in the copolymerizations between methyl methacrylate(Mi) with other methacrylates(M2), and between OK-methylbenzyl methacrylate(Mi) with trityl methacrylate(M2) by radical and BuLi initiators in THF. The parameters are shown in Table 20. 

Table 20. Coisotactic parameters in the copolymerization of methyl methacrylate(Mj) and other methacrylates(M2) by AIBN at 60 C and by BuLi at —78 C in tetrahydrofuran. Ref. l...

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