In order to control the properties of paper, several different routes of chemical modification have been used to tailor the properties of paper to specific needs. Such paper modification additives can, for example, make paper hydrophobic, control protein adsorption or improve it’s mechanical properties. Most paper modification processes use physically adsorbed polymers in which the polymeric additive is simply deposited on the surface of the paper fibrils. Such physically deposited molecules are inherently at risk of being replaced by competing adsorbents and may eventually be released into the environment. An alternative and important route is based on chemical modification reactions and makes use of the abundant number of hydroxyl groups in cellulose, for example through the formation of ethers or esters. However, removing a significant number of hydroxyl groups from the cellulose greatly alters the properties of the paper. In  addition, many of the substances used to modify paper are not environmentally friendly. Examples include wet strength agents based on epichlorohydrin or formaldehyde resins. They also make it rather difficult to recycle the paper, a  problem well known for wet-strengthened paper.
We describe a novel approach to paper modification using C,H insertion reactions. The paper is coated with a thin layer of a prepolymer containing dormant crosslinking units. These crosslinkers can be activated by heat or light, leading to  crosslinking of the polymer and simultaneously to insertion reactions with the cellulose molecules, thus covalently immobilizing the forming network. The crosslinker moieties comprise benzophenone, anthraquinone or diazoester  chemistries. By tuning the details of the chemical composition of the crosslinker units we can reduce the energy input for the chemical reactions very strongly. We describe the preparation and characterization of papers with very unusual  properties and give some initial results on how the use of dynamic linkages can make such papers easier to recycle.