Polymer particles comprising a polymer matrix having a coating of an inorganic semimetal oxide or metal oxide, wherein the polymer matrix has at least one first functional group A and at least one second functional group B, both functional groups A and B being able to enter into at least one covalent bond with one another, said functional group A being selected from the group consisting of an azide group, C—C double bond, C—C triple bond, aldehyde group, ketone group, imine group, thioketone group and thiol group, and said functional group B being selected from the group consisting of a C—C double bond, C—C triple bond, C—N triple bond, diene group, thiol group and amine group.