A novel hyperbranched polyisophthalate used as polymeric binders in holographic diffraction gratings

A novel photopolymerizable hyperbranched polyisophthalate (HPIP-A) was synthesized from 1,3,5-benzenetricarboxylic acid as a “core” molecule, 5-hydroxyisophthalic acid as an AB2 monomer, and 2-hydroxyethyl acrylate as an endcapping reagent. This material containing the unsaturation concentration of 5.29 mmolCC g−1 measured by 1H NMR has a wide molecular weight distribution of 2.05 and a degree of branching of 0.45. The refractive index at the wavelength of 650 nm was measured to be 1.562 using an autoretarder ellipsepsometer. The diffraction efficiency (DE) of holographic diffraction grating in the cured film was found to be strongly dependent on writing beam intensity, film thickness, monomer structure and content added in the resin. For a 25 μm thickness HPIP-A film added 30 wt.% methyl acrylate, a high diffraction efficiency of 92.3% was obtained at the writing beam intensity of 0.4 mW cm−2.