A novel material is provided herein which is suitable for use in a precursor of a polymer coating material that coats a polymer on a surface of a base material to provide the base material with surface modification and/or functionality assignment. A composite material characterized in that a compound having a polymerization initiation site containing a halogen group is incorporated in a crosslinked structure comprising a catechol derivative or a phenol derivative represented by the following formula (I). In the formula (I), R may be interrupted by an oxygen molecule and represents a hydrocarbon group with 2 to 20 carbons that has at least one double bond site, and A represents a hydrogen atom, a hydroxyl group, or an alkoxy group with 1 to 20 carbons.