Controlled Cationic Photo-curing And Application

Photopolymerization has emerged as an inexpensive and efficient method for producing thin polymeric films and coatings.The main shortcoming of this process lies in the limited penetration of UV radiation into organic materials.In a clear formulation,the incident light is mainly absorbed by the photoinitiator,which leads to a top to bottom gradient for the photogenerated initiating species,and also for the monomer conversion.In this research,the cationic photopolymerization of 1,4-butanediol diglycidyl ether was found to have an infinitely long induction period due to the sustained stability of the secondary oxonium ions species at low temperature.The active decomposed from the secondary oxonium ions species would initiated polymerization with rising temperature.Based on this,the system could be separated into two steps:photolysis of the photoinitiator without polymerization under irradiation and polymerization in the dark.Under irradiation,only the secondary oxonium ion species was generated at low temperature,whereas the polymerization could proceed and auto-accelerate at room temperature without irradiation.The two steps could be monitored by the significant change of the temperature.Temperature controlled cationic mechanism resolved the issue of light penetration in colored thick composites.Through temperature control,the infinitely thick and dark material,even the carbon fibre reinforced polymer composite could be prepared by cationic photopolymerization.