A microcapsule comprising an oil core and a microcapsule wall encapsulating the oil core, wherein the oil core contains an active material, the microcapsule wall is formed of an encapsulating polymer that is a reaction product of (i) a branched polyethyleneimine, a mixture of the branched polyethyleneimine and a polyfunctional amine, or a mixture of the branched polyethyleneimine and a polyfunctional alcohol, and (ii) a carbonyl crosslinker, or a mixture of a carbonyl crosslinker and a polyisocyanate, the carbonyl crosslinker has a first functional group and a second functional group, the first functional group is a carbonyl electrophilic group reactive towards the branched polyethyleneimine, the polyfunctional amine, or the polyfunctional alcohol, the second functional group is an electrophilic group reactive towards the branched polyethyleneimine, the polyfunctional amine, or the polyfunctional alcohol, the branched polyethyleneimine has a molecular weight of 750 to 50,000 Daltons, the carbonyl crosslinker has a molecular weight of 50 to 2,500 Daltons, the molar ratio between the branched polyethyleneimine and the carbonyl crosslinker is 1: 20 to 20: 1, the first functional group is formyl, an acyl halide group, a carboxylic anhydride group, and the second functional group is formyl, keto, carboxyl, a carboxylate ester group, an acyl halide group, an amide group, a carboxylic anhydride group, an alkyl halide group, an epoxide group, an aziridine group, an oxetane group, an azetidine group, a sulfonyl halide group, a chlorophosphate group, an isocyanate group, an α,β-unsaturated carbonyl group, an α,β-unsaturated nitrile group, or an α,β-unsaturated methanesulfonyl group. the oil core contains an active material, the microcapsule wall is formed of an encapsulating polymer that is a reaction product of (i) a branched polyethyleneimine, a mixture of the branched polyethyleneimine and a polyfunctional amine, or a mixture of the branched polyethyleneimine and a polyfunctional alcohol, and (ii) a carbonyl crosslinker, or a mixture of a carbonyl crosslinker and a polyisocyanate, the carbonyl crosslinker has a first functional group and a second functional group, the first functional group is a carbonyl electrophilic group reactive towards the branched polyethyleneimine, the polyfunctional amine, or the polyfunctional alcohol, the second functional group is an electrophilic group reactive towards the branched polyethyleneimine, the polyfunctional amine, or the polyfunctional alcohol, the branched polyethyleneimine has a molecular weight of 750 to 50,000 Daltons, the carbonyl crosslinker has a molecular weight of 50 to 2,500 Daltons, the molar ratio between the branched polyethyleneimine and the carbonyl crosslinker is 1: 20 to 20: 1, the first functional group is formyl, an acyl halide group, a carboxylic anhydride group, and the second functional group is formyl, keto, carboxyl, a carboxylate ester group, an acyl halide group, an amide group, a carboxylic anhydride group, an alkyl halide group, an epoxide group, an aziridine group, an oxetane group, an azetidine group, a sulfonyl halide group, a chlorophosphate group, an isocyanate group, an α,β-unsaturated carbonyl group, an α,β-unsaturated nitrile group, or an α,β-unsaturated methanesulfonyl group.