Investigating the surface photografting polymerization of styrene (St), it was found that in the absence of photoinitiator and at high temperatures, a remarkable amount of St-grafted polymer is formed. The initiation performance of St was further confirmed by surface photografting polymerization of acrylic acid, where St was used as the photoinitiator. This finding is useful to investigate the reaction mechanism of aromatic compounds under UV radiation and develop photoinitiator-free polymerization systems.