Orientation and Birefringence Compensation of Trunk and Graft Chains in Drawn Films of Cellulose Acetate-graft-PMMA Synthesized by ATRP

We examined the molecular orientation and optical anisotropy that are induced by the stretching of cellulose acetate (CA)-graft-poly(methyl methacrylate) (PMMA) films, in connection with the side-chain contents. The copolymers were prepared by atom transfer radical polymerization. The molecular characterization was successfully performed by NMR and GPC analyses, before and after deliberate cleavage of the PMMA grafts. Even if the molecular weight of the grafts increased, the dispersity index remained below 1.2. The molecular orientation behavior in uniaxially drawn films of the copolymers was estimated by a fluorescence probe technique. The measurement revealed a declining tendency of the orientation development with an increase in degree of the molar substitution (MS) of MMA unit of the copolymers. In comparison of birefringence (Δn) at a given stage of elongation of the films, the value of Δn decreased rapidly with increasing MS, which eventually led to the conversion from a positive Δn for pristine CA (acetyl DS = 2.15) to a negative one for the composition containing >65 wt % PMMA that corresponded to the highest MS in the graft series used. This type of graft copolymer may deserve to be a high-functional material whose optical anisotropy is controllable variously in terms of birefringence compensation between the oriented trunk and graft chains.