Amidoalkylations of polybutenes and of ethene-propene copolymer, catalyzed by trifluoroacetic acid, result in 5,6-dihydro-4H-1,3-oxazino-substituted polyalkenes with the 2-position of the oxazine ring unsubstituted or occupied by a vinyl or a phenyl group. The vinyl-substituted dihydrooxazino polymers thus obtained readily add butylamine to the vinyl fragment yielding alkylamino-substituted derivatives.