Correlation between positron annihilation lifetime parameters and T1ρ relaxation times determined from solid state NMR at the compositional phase segregation point of graft copolymers

Abstract

A series of poly(methyl methacrylate)-graft-polystyrene copolymers were prepared using the macromonomer “grafting through” technique. The branch density was varied by variation of the feed ratios in the free radical copolymerization. The macromonomer branch length was controlled by using the living anionic polymerization technique. The graft copolymers were characterised by solution 1H NMR and SEC-MALLS to determine the composition of the graft copolymers. Positron annihilation lifetime spectroscopy (PALS), and solid state NMR (SS-NMR) were used to investigate the solid state morphology of the graft copolymers. The ortho-positronium lifetime (τ3) and the T1ρ relaxation times from solid state NMR analysis was used to determine the compositional phase segregation point in the copolymer series. The result shows that the information from these two techniques is complimentary and provides useful information to explain the variation in the Tg and positron lifetime parameters as a function of composition.