Jh. Fang et al., Positron annihilation properties of copolyimides and copolyamides with microphase-separated structures, J POL SC PP, 38(9), 2000, pp. 1123-1132
The positron annihilation lifetime (PAL) of a series of copolyimides and co
polyamides with microphase-separated structures was measured to investigate
the effects of different hard-segment polymers on the PAL properties of so
ft-segment domains of poly(dimethyl-siloxane) (PDMS) and poly(ethylene oxid
e) (PEG). The lifetime (tau(3)) and intensity (I-3) of the long-lived compo
nent are given as a function of the PDMS or PEG content for a series of cop
olymers, of which the density roughly obeys the additive rule except for th
e PDMS-segmented copolyamides. The PDMS-segmented copolyimides and copolyam
ides show much smaller I-3 values than those estimated from the additive ru
le. The lifetime distribution of the long-lived component for the PDMS-segm
ented copolyamides is composed of two components. The longer-lifetime compo
nent is attributed to pure PDMS domains, and the shorter-lifetime component
is attributed to the polyamide domains, intermediate phases, and PDMS doma
ins containing small amounts of short amide blocks. Despite the high PDMS c
ontent, the latter component is rather large. Thus, the positronium formati
on in the PDMS domains of the copolyimides and copolyamides is effectively
reduced. This can be explained by the combination of the difference in the
electron affinity of the PDMS and polyimide or polyamide segments and the i
ncomplete phase separation. The PEG-segmented copolyimides show much smalle
r I-3 values than those predicted from the additive rule. This is likely at
tributable to the effects of the intermediate phases. (C) 2000 John Wiley &
Sons, Inc.