1.2- Elimination reactions, characteristics solvent effects

In a detailed study, the scope and limitations of the Diels-Alder reaction of amidines and related compounds with 1,3,5-triazines arc discussed.10 The reactions with the amidine hydrochlorides 15 (X = NH2) are best conducted at temperatures of 90-100 °C and in polar aprotic solvents (particularly in dimethylformamide). As expected for inverse electron demand Diels-Alder reactions, the reaction exhibits characteristic 1,3,5-triazine substituent effects (C02Et >HI> SMe). Thioimidates, e.g. 15 (X — SMe), undergo a similar reaction with 1,3,5-tri-azines with varying yields and competing amine or thiol elimination while imidates, e.g. 15 (X = OMe) are unreactive under the examined reaction conditions.10... 

Chain transfer to polymer is another important reaction that can greatly affect the structure of macromolecules and, hence, the properties of the polymers. Moreover, contrary to chain transfer to solvent that can be eliminated or at least suppressed by the use of another solvent, transfer to polymer is an inherent property of the polymerizing system. The effect of this reaction on molecular weight characteristics of polymers has been studied only for free radical polymerization [23-25]. In particular, it was shown that transfer to polymer may cause gelation if termination proceeds via combination. Principal results for living polymerization were obtained in Ref [26]. 

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