Photopolymer For Holographic Recording Using Hyper-branched Polyester

Application of holography recording has achieved great success in many areassuch as high-density information storage and anti-counterfeit technology.Photopolymer is a promising holographic recording media, due to its high sensitivity,high diffraction efficiency, easy to process, storage stability. The mechanism ofholographic recording in photopolymer involves a complicated polymerization andmonomer diffusion process, which results in the change of optical properties byphoto-polymerization. Hyper-branched polymers are loosely packed and lack withmuch less inter-chain tangling. They are potentially important components inholographic recording materials, because small molecules could transport easilyinside. In this work, a new and high performance photopolymer system forholographic recording was developed. The material consisted of hyper-branchedpolyester end-capped with phenyl groups (HBPE-B) as polymeric binders, acrylatemonomers and a visible light sensitive photo-initiator (Irgacure784). In the synthesispart, hyper-branched polyesters (HBPE-A) with full -OH as the chain end groupswere synthesized from trimellitic anhydride (TMA) and epichlorohydrin (ECH) byone-step reactions in milder conditions. The OH groups on the HBPE-A weretransformed into benzoate groups via two routs: modification with benzoic acid/DCC,or with benzoyl chloride. The structure of the polyesters was characterized by FTIR,GPC, ~1HNMR, DSC and TG. The molecular weight of hyper-branched polyesterswas increasing while the anhydride value of TMA was improved, and finally reacheda constant level. Both the efficiency and the synthesizing arts of end-capping bybenzoyl chloride were better than that of benzoic acid; In the holographic recording,different HBPE-B photopolymer films were made and holographied. Effects ofphoto-monomers, such as AM, DAM, EA, BA, TFPMA, TPGDA, photo-initiatorIrgacure784 and the thickness of the photopolymer films, as well as the recordingconditions on diffraction efficiencies were studied. We found that an optimizedHBPE-B photopolymer films exhibited considerable DE of up to 98.9% and excellent spatial frequency response characteristics with resolution of over 3750lines/mm. The optimized composition of HBPE-B photopolymer system wasobtained as 78.8wt.% HBPE-B, 18.Swt.% TPGDA and 2.4wt.% Irgacure784.