Phosphorous containing benzoxazine-based monomer

Provided is a phosphorous containing benzoxazine-based monomer represented by Formula 1 below: wherein R 1 and R 2 are each, independently, one selected from the group consisting of a C1-C20 alkyl group, a C1-C20 alkoxy group, a C6-C20 aryl group, a C6-C20 aryloxy group and a group represented by the formula below, wherein R 3 is one selected from the group consisting of a hydrogen atom, a C1-C20 alkyl group, a C1-C20 alkoxy group, a C6-C20 aryl group, a C6-C20 aryloxy group, a halogenated C6-C20 aryl group, a halogenated C6-C20 aryloxy group, a C1-C20 heteroaryl group, a C1-C20 heteroaryloxy group, a halogenated C1-C20 heteroaryl group, a halogenated C1-C20 heteroaryloxy group, a C4-C20 cycloalkyl group, a halogenated C4-C20 cycloalkyl group, a C1-C20 heterocyclic group and a halogenated C1-C20 heterocyclic group.