Effect of polyester polyol chain length on the properties of transparent poly (ester-urethane-acrylate)/MMA copolymer for optical applications

A series of poly(ester-urethane acrylate)/methyl methacrylate (PEUMA) crosslinked copolymers were prepared using hydroxyl terminated aromatic polyesters (PEs) with varying chain lengths. Four kinds of PEs with terminal hydroxyl groups were synthesized by reacting phthalic anhydride (PA) with 1,2-propanediol (PDO), 1,4-butanediol (BDO), 1,6-hexanediol (HDO) and diethylene glycol (DEG) respectively. The resultant PEs were reacted with isophorone diisocyanate (IPDI) in the presence of dibutyltin dilaurate (DBTDL) catalyst and end capped with 2-hydroxyethyl methacrylate (HEMA) to obtain ester-urethane-acrylate (EUA) prepolymer. Thereafter, crosslinked PEUMA copolymer were synthesized by reacting the EUA prepolymer with 40% (w/w) methyl methacrylate (MMA) in the presence of 1% azobisisobutyronitrile (AIBN) chain initiator. The PEs and EUA prepolymer were characterized by Fourier transform infrared (FT-IR) spectroscopy, H-1 NMR, and gel permeation chromatography (GPC) techniques. The average molecular weights (Mc) between two crosslinks of the samples were determined by using the Flory Rehner equation. The tensile modulus, flexural strength, thermal properties and transparency of PEUMA copolymers were also determined and correlated with the average molecular weight and crosslinked density. The transparency of PEUMAs was found to be above 90% and hence it is an excellent alternative to glass for optical applications.