Ultraviolet-curable liquid natural rubber

Preparation of ultraviolet (UV)-curable liquid natural rubber was achieved by fixation of photosensitive molecule onto liquid natural rubber. The liqu id natural rubber (LNR) was prepared by oxidative degradation of natural ru bber latex, using the phenylhydrazine/O-2 system. The LNR was further treat ed with in situ performic acid, which leads to epoxidized liquid natural ru bber (ELNR). The progress of the addition reaction of photosensitive acryli c acid onto epoxide ring of the ELNR was followed by infrared spectroscopy. It was found that at 80 degrees C reaction temperature, epoxide ring openi ng reaction of ELNR came to completion within 2 h, which is faster than the reaction at 60 degrees C. The photocrosslinking reaction of the acrylated ELNR was studied by monitoring the exothermic heat of photocuring of acryla te double bond using a double beam photocalorimeter (DPA7). It was found th at the fast crosslinking-polymerization occurred when the rubber was expose d to UV irradiation in the presence of photocleavage initiator (Irgacure 18 4 and Darocur 1173) and liquid diacrylate monomer (1,6 hexanediol diacrylat e and tripropylene glycol diacrylate). The cure kinetics of the elastomers were also investigated, and it was found that the diacrylate monomer, photo initiator concentration play an important role on the rate and extent of th e reaction. (C) 2000 John Wiley & Sons, Inc.