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Addition of Carbenes

المؤلف:  A. Ravve

المصدر:  Principles of Polymer Chemistry

الجزء والصفحة:  p575-576

2026-02-21

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Addition of Carbenes

Polyisoprenes and polybutadienes can also be modified by reactions with carbenes. Dichlorocarbene adds to natural rubber dissolved in chloroform in a phase transfer reaction with aqueous NaOH . A phase transfer reagent must be used with the aqueous NaOH. Solid sodium hydroxide can be used without a phase transfer reagent. There is no evidence of cis–trans isomerization and the distribution of the substituents is random . Difluorocarbene, generated under mild neutral conditions, adds to 1,4-cis- and 1,4-trans polybutadienes to give materials containing cyclopropane groups . The addition takes place randomly, to give atactic stereo sequence distributions:

Fluorocarbene, formed from phenyl (fluoro, dichloromethyl) mercury by thermolysis in situ, also adds to 1,4 cis-andtrans-polybutadienes. The carbene can add at various levels . The addition is stereospecific and preserves the alkene geometry of the parent polybutadiene. Also, the addition is random, showing that the reactivity of the double bonds is independent of the sequence environment. Dichlorocarbene, generated in situ from an organomercury precursor, phenyl(bromo, dichloromethyl)mercury (Seyferth reagent), adds to polybutadiene in a similar manner . The reactions take place under homogeneous conditions. They can be carried out on 1% solutions of the polymer in benzene, using 10–20% mol excess of the reagent.