Positron annihilation properties of copolyimides and copolyamides with microphase-separated structures

Citation
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
Citations number
28
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS
ISSN journal
0887-6266 → ACNP
Volume
38
Issue
9
Year of publication
2000
Pages
1123 - 1132
Database
ISI
SICI code
0887-6266(20000501)38:9<1123:PAPOCA>2.0.ZU;2-B
Abstract
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.