Polymer composites present a group of materials that have very wide use and provide improvement in many areas such as materials for packaging, foils, films, construction materials and others. Nanocellulose, one of the natural and renewable polymers that contribute to environmental sustainability, is becoming very important because of its easy application possibilities and good properties. It is used as a filler in a synthetic polymer and it aims to replace it in the largest quantity possible and thereby does not worsen its properties. The purpose of this work is to prepare polymer composites based on the methyl methacrylate copolymer and functional methacrylates with crystal nanocellulose and to test their main properties. The copolymerization was conducted in a green solvent obtained from renewable biomass. Dihydrolevoglucosenone, which was used in this work, also known as CyreneTM, is a completely biodegradable solvent obtained through pyrolysis from cellulose. In the polymerization high conversions of the monomers, high molecular weights and low polydispersity are achieved. The glass transition temperature of the polymer nanocomposites increases with an increased addition of cellulose nanocrystals. The modulus of elasticity of composite materials is slightly higher or lower in regard to the pure copolymer and does not have a significant impact on the application properties. The influence on the breaking strength of the copolymer with the addition of cellulose nanocrystals is not big except for the copolymer methyl methacrylate with hydroxyethyl methacrylate. The research confirmed that by using a green solvent and cellulose as a filler, polymer materials can be produced with higher renewability and the harmful impact on the environment is significantly lesser.