Crosslinked poly(methyl methacrylate) (PMMA) with high glass transition temperature (T_g) and thermal decomposition temperature was prepared by simple thermal crosslinking of PMMA-containing random copolymers bearing aryl trifluorovinyl ether (TFVE) moieties. A methacrylate monomer consisting of aryl TFVE moiety, 4-((1,2,2-trifluorovinyl)oxy)phenyl methacrylate (TFVOPMA), was first synthesized followed by radical copolymerization with methyl methacrylate (MMA) initiated by AIBN, providing the random copolymer containing aryl TFVE moieties, poly(4-((1,2,2-trifluorovinyl)oxy)phenyl methacrylate)-co-poly(methyl methacrylate) (PTFVOPMA-co-PMMA). Finally, crosslinked PMMA polymer with perfluorocyclobutyl (PFCB) aryl ether moieties as crosslinking units was obtained by [2π + 2π] cycloaddition reaction of aryl TFVE moieties in PTFVOPMA-co-PMMA copolymer. Thermal properties of both PTFVOPMA-co-PMMA and crosslinked PTFVOPMA-co-PMMA were examined by TGA and DSC. Compared to pure PMMA, T_g of PTFVOPMA-co-PMMA increased by 15.1 °C and no T_g was found in the DCS test of the crosslinked PTFVOPMA-co-PMMA. Thermal decomposition temperature (T_d,5%) of crosslinked PMMA was 47 °C higher than that of pure PMMA. Furthermore, the water absorption of crosslinked PMMA film greatly reduced in comparison with that of pure PMMA.