Ester formation, isobutylene

Formation of products of rearrangement may be looked upon as occurring by way of loss of hydrogen from a carbon atom which is not adjacent to the carbon atom holding the phosphate radical. This results in the transitory formation of a cyclopropane or cyclobutane ring which then opens to yield the rearranged olefin. Thus, in the copolymerization of isobutylene with 2-butene, the intermediate ester may react in the following ways ... 

Terpolymers made from two different olefins and CO are known. They were first described in Brubaker s initial patent and involved the free radical initiated terpolymerization of CO and C2H with another olefin such as propylene, isobutylene, butadiene, vinyl acetate, diethyl maleate or tetrafluoroethylene More recently, in another patent, Hammer has described the free radical initiated terpolymerization of CO and C2H with vinyl esters, vinyl ethers or methyl methacrylate 26Reaction temperatures of 180-200 °C and a combined pressure of 186 MPa were employed. Typically a CO QH4 olefin molar ratio of 10 65 25 was observed in the terpolymers. In other patents, Hammer 27,28) has described the formation of copolymers with pendant epoxy groups by the free radical initiated polymerization of CO, QH4, vinyl acetate and glycidyl methacrylate. Reaction conditions similar to those stated above were employed, and a typical CO C2H vinyl acetate glycidyl methacrylate molar ratio of 10 65 20 5 was observed in the product polymer. 

In zeolites, this barrier is even higher. As discussed in Section II.B, the lower acid strength and the interaction between the zeolitic oxygen atoms and the hydrocarbon fragments lead to the formation of alkoxides rather than carbenium ions. Thus, extra energy is needed to transform these esters into carbonium ionlike transition states. Quantum-chemical calculations of hydride transfer between C2-C4 adsorbed alkenes and free alkanes on clusters representing zeolitic acid sites led to activation energies of approximately 200 kJ/mol for isobutane/tert-butoxide (29), 230-305 kJ/mol for propane/sec-propoxide, and 240 kJ/mol for isobutane/tert-butoxide (32), 130-150 kJ/mol for ethane/ethene (63), 95-105 kJ/mol for propane/propene, 88-109 kJ/mol for isobutane/isobutylene, and... 

The photoaddition of allenic esters (31) to the enone (32) has been studied. The major products from these reactions are the dienes (33) and the cyclobutanes (34) and (35). It seems likely that the addition proceeds by the traditional biradical path to an intermediate such as (36). Dis-proportionation affords (33) while C-C bond formation yields the two cyclobutanes.The cycloaddition of isobutylene to the enone (37a) in a variety of solvents affords the adduct (38, 20-40X) and the alkylated... 

Better control of grafting and less homopolymer formation is achievable in ionic reactions than can be obtained in free-radical reactions. Anionic grafting via backbone initiation has been demonstrated (22) with caprolacteim on macromolecular ester sites of styrene/methyl methacrylate copolymers. Cationic grafting of isobutylene onto poly(vinyl chloride) with the aid of aluminum alkyl has been carried out by J. P. Kennedy (23). 

None of the products formed in the reactions described above is considered to significantly change the reaction rates and product distributions by acting as a catalyst. However, Siskin et al. [106] reported that in the hydrolysis of methyl 1-naphthoate at 343 °C naphthalene was predominantly formed because the potential for autocatalysis arises. They concluded that decarboxylation of naphthoic acid, the main product at a lower temperature of 250 °C, led to the formation of naphthalene at 343 °C the reaction is catalyzed by the generated carbonic acid. In the hydrolysis of typical p-keto esters, ethylacetoacetate was completely converted to acetone, eAanol, and CO2 within 30 min at 250 °C. Under the same conditions, r-butyl acetate degraded into a bright red, insoluble mixture of unidentifled products resulting from polymerization of isobutylene [107]. 

Table 3.4 and Table 3.5 show the degradation products of the polymeric isomeric butyl esters. It is apparent with the products of poly-n-butyl acrylate that the identification of w-butyl formate, n-butyl acetate, the saturated and unsaturated dimers extends the earlier reports of Grassie and co-workers [42]. The formation of n-butyl acetate is consistent with that of methyl acetate formation and is simple scission at the chain end and hydrogen addition. With polyisobutyl acrylate the formation of isobutylene monomer and oligomers occurs. 

The reaction mechamism for isobutylene formation is derived from the general mechanism of Grassie and co-workers [42]. Polyisobutyl acrylate degradation produces more simple saturated esters than the other homologous polyermeric esters. 

There has been a slight increase in activity in this area compared with that in the previous two year period. For the polymeric esters of acrylic, methacrylic acids, and related polymers the simplest reaction, apart from thermal depolymerization, is hydrolysis, and one or two papers on this subject have appeared. One of these concerns a comparison of the kinetics of hydrolysis of a number of methacrylate esters and a further two deal with the formation of copolymers containing carboxylic acid functions. Methyl trifluoroacrylate forms alternating copolymers with cE-olefins (ethylene, propylene, isobutylene) and these are readily hydrolysed in boiling aqueous methanolic sodium hydroxide to yield hydrophilic fluoropolymers. Hydrolysis is reported to be nearly quantitative with no chain scission. An alternating copolymer is also formed by radical polymerization of maleic anhydride with A-vinyl succinimide. On hydrolysis this copolymer is... 

The autoaeeelerated character of P-i-BuMA degradation was linked to the ester group deeomposition, with isobutylene formation, which gives free radicals in the reaction with NO2 and thus promotes the degradation proeess. 

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