Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 29, 2018 | https://pubs.acs.org Publication Date: May 5, 1993 | doi: 10.1021/ba-1993-0236.ch022
22 Polymer Characterization Using Singlet Oxygen Phosphorescence as a Spectroscopic Probe Peter R. Ogilby , Maria P. Dillon , Yuanping Gao , Kai-Kong Iu , Marianne Kristiansen , Vicki L . Taylor , and Roger L . Clough 1
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Department of Chemistry, University of New Mexico, Albuquerque, NM 87131 Organic Materials Division (Org. 1811), Sandia National Laboratories, Albuquerque, NM 87185 1
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Singlet molecular oxygen ( ∆ O ) can be produced in solid organic polymers by a variety of different methods. The phosphorescence of singlet oxygen can be monitored in both steady-state and time-resolved experiments, yielding valuable information on the structure and properties of (1) the polymer and (2) solutes dissolved in the polymer. With this spectroscopic probe, we are also able to comment on specific processes that can have important practical ramifications including, for example, the degradation of polymers. In addition, this probe provides a method by which oxygen diffusion coefficients can rapidly and accurately be determined for easily prepared polymer films. 1
SINGLET
OXYGEN
(*Δ
0 2 ),
g
2
T H E LOWEST
EXCITED
ELECTRONIC
STATE
of
molecular oxygen, c a n b e p r o d u c e d i n solid organic polymers b y a variety o f different methods. O n c e f o r m e d , singlet oxygen w i l l follow one o f three general deactivation channels:
0065-2393/93/0236-0573$07.50/0 © 1993 American Chemical Society
Urban and Craver; Structure-Property Relations in Polymers Advances in Chemistry; American Chemical Society: Washington, DC, 1993.
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S T R U C T U R E - P R O P E R T Y R E L A T I O N S IN P O L Y M E R S
Singlet oxygen c a n return to t h e g r o u n d triplet state ( X ~ 0 ) b y either radiative (k , e q 1) o r nonradiative ( f c , e q 2) decay. T h e rates f o r b o t h processes d e p e n d o n the s u r r o u n d i n g m e d i u m i n c l u d i n g solutes (quenchers, population can also b e depleted b y a c h e m i c a l reaction w i t h either a solute molecule o r the p o l y m e r itself ( ( k ) , e q 3): A d d u c t s ( A 0 ) such as a n endoperoxide o r hydroperoxide are f o r m e d rather than regenerating t r i p l let oxygen. A l t h o u g h the q u a n t u m y i e l d o f phosphorescence is small (~ 1 0 ~ - 1 0 ~ , i.e., k
