Nucleophilic and Electrophilic Substitutions

Many other conversions of functional groups of acrylic and methacrylic resins were reported. One of them is a conversion of methyl acrylate to a hydrazide by a direct reaction with hydrazine [244]:

The above reaction requires a 10:1 ratio of hydrazine to the ester groups. In the laboratory, it can be carried out on a steam bath over a period of 2–3 h. Approximately 60–80% of the ester groups convert [244]. The hydrazides can form various hydrazones through reactions with aldehydes and ketones:

The hydrazide can also be converted to an azide [244]:

A Hoffman reaction of the azide yields a cross-linked polymer [244]. Syndiotactic poly (methyl methacrylate) converts to a hydrazide in a similar manner [245]. Nucleophilic substitution reactions can be carried out on poly (methyl methacrylate) with hetero cyclic organolithium reagents [246]. The reactions are conducted in homogeneous solutions in tetrahydrofuran or in benzene combined with hexamethyl-phosphoramide. Copolymers will form with tautomeric keto-b-heterocyclic structures. Following heterocyclic reagents are useful [246]: 2-picolinyllithium, [(4,4-dimethyl-2-oxazole-2-yl) methyl] lithium, quinaldinyllithium, and [2-thia zole-2-yl-methyl] lithium. In attempts to carry out Arndt-Eister reactions on poly (methacryloyl chloride), the polymer was reacted with diazomethane in various molar ratios and at different temperatures [247]. Initially, acid chloride groups do react with diazomethane as expected. The products, however, undergo subsequent reactions with neighboring acid chloride groups and form cyclic structures [247]:

When Curtius and Lossen rearrangement reactions are attempted on poly (acryloyl chloride) [248], the products are fairly regular polyampholytes:

Somewhat similar results are obtained with a Hoffman reaction on polyacrylamide [279]. A Schmidt reaction on poly (acrylic acid) also yields mixed results [250]. When it is run in acetic acid, the intermolecular reactions appear to predominate over the intramolecular ones. Also, the products formed in acetic acid have higher nitrogen content that those formed in dioxane [250]. The NMR spectra show presence of some acid anhydride groups. This has an additional effect of lowering the yield. Diels-Alder reactions can be carried out on poly (furfuryl methacrylate) with dienophiles like maleic anhydride or a maleimide [252]. Dilute solutions (10%) of the polymers in benzene can be used, requiring up to 30% molar excess of the dienophiles:

The additions take place at room temperature and the reactions take from 7 to 30 days [252] to complete. Polyacrylonitrile reacts with hydroxylamine and the product can be metalated by elements from Group IV (Sn, Ge, and Si). This is a convenient route to formation of polymers with such pendant organometallic groups [253]:

The yields are high when the reactions are carried out on dilute solutions of polyacrylonitrile in dimethylformamide at 75C. The solutions must contain 1.5 mol each of hydroxylamine hydrochloride and sodium carbonate per mole of acrylonitrile groups [253]. A Ritter reaction can be carried out on atactic polyacrylonitrile with N-hydroxymethylamides of acetic, benzoic, and benzene-sulfonic acids [254]. When the same reactions are carried out with N hydroxymethylimides of succinic or phthalic acids in tetramethylene sulfone, there is a stronger tendency toward cross-linking. Copolymers of methacroyl chloride will undergo an Arbuzov rearrangement in reactions with triethyl phosphite in dimethylformamide, dioxane or benzene at 75C [255]. The conversions are high, ranging between 96 and 98%. The aldehyde groups of polyacrolein can be reduced by the Meerwein-Ponndorf reaction. There is a limit, however, to the amount of alcoholate that can be used and to the concentrations of free aldehyde groups in the starting material [256]. Also, ester condensations take place (Tischenko reaction) at the same time as the reductions occur [256].

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مواضيع ذات صلة

Reduction of the Ester Groups

Metalation Reactions

Nitration, Reduction, and Diazotization

Sulfonation Reactions

Reactions of Halomethylated Polymers

Chloromethylation Reactions

Reactions of Polystyrene

Substitution Reactions of Halogen-Bearing Polymers

Substitution Reactions of Saturated Polymeric Hydrocarbons

Cyclizations and Intramolecular Rearrangements

Isomerization Reactions

Epoxidation Reactions