Methylmethacrylate production

In the petrochemical industry the introduction of unsaturations in hydrocarbons is mainly obtained by dehydrogenation. This kind of reaction is less suitable for the functionalization of fine chemicals, because the high temperature necessary for the endothermic reaction can lead to the decomposition of thermally unstable compounds. An alternative reaction consists in the oxidative dehydrogenation, that can be carried out at lower temperatiu es. An example of this kind of reaction is constituted by the synthesis of methacrylic add (MAA, intermediate of methylmethacrylate production) via the oxidative dehydrogenation of isobutyric add (IBA), itself obtained from isobutyraldehyde (by-product of the oxo synthesis of nbutyraldehyde from propylene). This process constitutes one of the economically most interesting routes, alternative to the acetone-cyanohydrin process, which nowadays is the predominant process for the MAA production. 

Figure 31 The radical initiator (47) based on the oxidation adduct of an alkyl-9-BBN used for the production of poly(methyhnethacrylate) (48) from methylmethacrylate monomer by the radical polymerization route. (Adapted from ref. 69.)...

Transesterification is a crucial step in several industrial processes such as (i) production of higher acrylates from methylmethacrylate (for applications in resins and paints), (ii) polyethene terephthalate (PET) production from dimethyl terephthalate (DMT) and ethene glycol (in polyester manufacturing),... 

The [VO]+ ion has been reacted with methylmethacrylate and the dimer of methylmethacrylate (157). Sequential addition of up to three methylmethacrylate molecules was observed, there were also several products involving bond cleavage such as loss of Me groups. Up to two molecules of the dimer of methylmethacrylate were added to [VO]+ and some final product ions involved the addition of other groups such as two methoxide groups. High coordination may be attained by vanadium in these product ions. 

Polymethylmethacrylate production currently amounts to more than 2.8 milhon tons per year on a worldwide scale, and the average yearly demand has been steadily increasing in recent years by more than 0.2 million tons. In contrast to the majority of bulk chemicals, for which the number of competitive processes is limited to one or two technologies, in the case of methylmethacrylate (MMA), the monomer for polymethylmethacrylate production, there are several different technologies that are currently successfully applied, and others have been claimed or are under investigation. The main characteristics of these technologies are reported in Table 14.1. ... 

Butyllithium initiation of methylmethacrylate has been studied by Korotkov (55) and by Wiles and Bywater (118). Korotkov s scheme involves four reactions 1) attack of butyllithium on the vinyl double bond to produce an active centre, 2) attack of butyllithium at the ester group of the monomer to give inactive products, 3) chain propagation, and 4) chain termination by attack of the polymer anion on the monomer ester function. On the basis of this reaction scheme an expression could be derived for the rate of monomer consumption which is unfortunately too complex for use directly and requires drastic simplification. The final expression derived is therefore only valid for low conversions and slow termination, and if propagation is rapid compared to initiation. The mechanism does not explain the initial rapid uptake of monomer observed, nor the period of anomalous propagation often observed with this initiator. The assumption that kv > kt is hardly likely to be true even after allowance is made for the fact that the concentration of active species is much smaller than that of the added initiator. Butyllithium disappears almost instantaneously but propagation proceeds over periods from tens to hundreds of minutes. The rate constants finally derived therefore cannot be taken seriously (the estimated A is 2 x 105 that of k ) nor can the mechanism be regarded as confirmed. 

Copolymerizations initiated by lithium metal should give the same product as produced from lithium alkyls. Usually the radical ends produced by electron transfer initiation have so short a lifetime they can have no influence on the copolymerization. This is true for instance in the copolymerization of isoprene and styrene (50). The product is identical if initiated by lithium metal or by butyllithium. With the styrene-methylmethacrylate system, however, differences are observed (79,80,82). Whereas the butyllithium initiated copolymer contains no styrene at low conversions, the one initiated by lithium metal has a high styrene content if the reaction is carried out in bulk and a moderate one even in tetrahydrofuran. These facts led O Driscoll and Tobolsky (80) to suggest that initiation with lithium occurs by electron exchange and that in this case the radical ends are sufficiently long-lived to produce simultaneous radical and anionic reactions at opposite ends of the chain. Only in certain rather exceptional circumstances would the free radical reaction be of importance. Some of the conditions required have been discussed by Tobolsky and Hartley (111). The anionic reaction should be slow. This is normally true for lithium based catalysts in hydrocarbon solvents. No evidence of appreciable radical participation is observed for initiation by sodium and potassium. The monomers should show a fast radical reaction. If styrene is replaced by isoprene, no isoprene is found in the copolymer for isoprene polymerizes slowly by free radical initiation. Most important of all, initiation should be slow to produce a low steady concentration of radical-anions. An initiator which produces an almost instantaneous and complete electron transfer to monomer produces a high radical concentration which will ensure their rapid mutual termination. 

In this paper we would like to describe a new design, based on gas chromatographic analysis of the monomer mixture, for production of constant composition copolymers and its application to emulsion copolymerization. This design was already shortly described and applied to solution copolymerization (3) of methylmethacrylate and vinylidene chloride. Since then, the apparatus was made more simple, more reliable and more accurate. It is actually monitored by an analogic computering system which keeps the ratio of the monomers constant by controlling the addition of one of them. The process based on it can be called corrected batch process because the initial value of this ratio is kept up to the end. 

Ans. In the homogeneous catalytic process for PO the by-product is f-butanol, which has an attractive market. The atom utilization by the old route for PO is 31%. The atom utilizations by the new route are 44 and 56% for PO and f-butanol. For methylmethacrylate the atom utilization by the new route (methyl acetylene plus carbon monoxide and methanol) is 100%, and by the old route is 46% (see R. A. Sheldon, Chemtech, 1994, March, 38-47). 

These copolymers use about 70wt% of acrylonitrile and 30% of methylmethacrylate repeat units. ANM are used for thick transparent products, such as glazing, which require high-impact properties and good chemical and weathering resistance. 

Lignin has been grafted with ethenylbenzene [43,44] (styrene), 4-methyl-2-oxy-3-oxopent-4-ene [45,46] (methylmethacrylate), 2-propenamide (acrylamide), 2-propene nitrile [47] (acrylonitrile), cationic monomers, anionic monomers, and propenoic acid ethoxylates. An index of compounds listing structure, product name, and trivial name is given in Table 3. Two types of... 

The Step 1 product was dissolved in roughly 10 ml of n-butyl acetate and then treated with CuCl (0.0396 g) complexed with 108.8 pi of 1,1,4,7,10,10-hexamethyl-triethy-lenetetramine), 2 ml of methylethylketone, and 4 ml of methylmethacrylate. The mixture was then heated to 60°C for 24 hours, cooled, dissolved in THF to 20% solids, and filtered through alumina to remove residual catalyst. The product poly(methyl-methacrylate)-b-poly(butyl acrylate)-b-poly(methylmethacrylate) was isolated having molecular weight segments of 10,000/60,000/10,000 daltons, respectively. 

Methyl methacrylate (MMA) is an important commodity since it is polymerized to give poly methylmethacrylate (PMMA), a strong, durable and transparent polymer sold under the trade-names Perspex and Plexiglas. Since the conventional routes to MMA involve either the reaction of acetone with HCN to give the cyanohydrin (which has environmental problems), or the oxidation of isobutene, alternative carbonylation routes to MMA are being developed. One of these is the Lucite Alpha process which is claimed to decrease production costs by ca. 40%. This first synthesizes methyl propionate by a methoxycarbonylation of ethylene (Equation 23), using a palladium catalyst with very high (99.8%) selectivity. In the second step, MMA is formed in 95% selectivity by the reaction of methyl propionate with formaldehyde (Equation 24). 

Some pyrolysis products have high value. These are mainly monomers, such as methylmethacrylate, caprolactam (the monomer of PA 6), tetralinorethylene, or styrene. Others are comparable to standard prodncts with specifications of naphtha, kerosene, or gas-oil. Snch fractions have a well-known market, as follows from Table 1.7. 

The progress of the reaction with methylmethacrylate depends somewhat on initiator, temperature and solvent. Investigations have been carried out using fluorenyllithium [167, 168, 170], phenylmagnesium bromide [171, 172], butyllithium [173] and 1,1-diphenylhexyllithium [174] in toluene solution with or without the presence of ethers. Product analysis shows that two basic reactions occur with the monomer both with magnesium compounds [171, 175] and with butyllithium [176], viz. 

An examination of reported reactivity ratios (Table 6) shows that the behaviour rj > 1, r2 1 or vice versa is a common feature of anionic copolymerization. Only in copolymerizations involving the monomers 1,1-diphenylethylene and stilbene, which cannot homopolymerize, do we find <1, r2 <1 [212—215], and hence the alternating tendency so characteristic of many free radical initiated copolymerizations. Normally one monomer is much more reactive to either type of active centre in the order acrylonitrile > methylmethacrylate > styrene > butadiene > isoprene. This is the order of electron affinities of the monomers as measured polarographically in polar solvents [216, 217]. In other words, the reactivity correlates well with the overall thermodynamic stability of the product. Variations of reactivity ratio occur with different solvents and counter-ions but the gross order is predictable. 

CO and abstraction or recombination products cf alkyl fragments derived from the ester side chain fragments. The Norrlsh II process Is unimportant for short chain esters, (e.g. methylmethacrylate), for longer chain esters It should be considered. 

Polymerizations of methylmethacrylate initiated by organo-magnesium compounds also give rise to stereoregular products, although the active centre is almost certainly a covalent entity. Nevertheless, considerable similarities exist between these and conventional anionic systems. This is also true of polymerizations of alkyl vinyl ketones initiated by zinc and magnesium alkyls, and progress in this area has also been reported recently. ... 

A few other methods have been used to prepare polypeptide hybrid copolymers. Inoue polymerized Bn-Glu NCA off of amine-functionalized styrene derivatives, and then copolymerized these end-functionalized polypeptides with either styrene or methyl methacrylate using free radical initiators to yield hybrid comb architecture copolymers [38]. Although unreacted polypeptide was identified and removed by fractionation, copolymers were obtained with polypeptide content that increased with feed ratio. There was no mention if the polypeptide interfered with the radical chemistry. In similar work, Imanishi and coworkers converted the amine-ends of polypeptides to haloacetyl groups that were used to initiate the free radical polymerization of either styrene or methylmethacrylate to yield hybrid block copolymers [39]. Studies using CPC showed that the crude product contained mixtures of copolymers and homopolymers, and so removal of the homopolymers by extraction was necessary. 

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