Introduction

The photodegradation of the polymer PPE (see figure 1) has been the subject of many experimental studies for the last 30 years. While in most of these studies the reaction mechanisms were deduced from an analysis of the photoproducts formed after a longer period of irradiation, direct evidence for the inital photochemical step is still missing.

Figure 1: Structure of polymer PPE

Different mechanisms have been proposed for the initial photochemical step. These can be grouped in two classes.

Intramolecular Mechanisms
- Photoinduced ether cleavage [1].
- 1,5-Hydrogen transfer in the excited state followed by ether cleavage [2].
Intermolecular Mechanisms
- Free radical mechanism, hydrogen abstraction from the methyl group by impurities [3].
- Photoinduced electron transfer from the polymer to oxygen [4].

In this contribution we will present theoretical and experimental studies which will give further insight into the photodegradation mechansims. The low temperature absorption spectra of model compounds allow a decision between intra- and intermolecular mechanisms. The relevance of the proposed intramolecular mechanisms, was studied using semiempirical calculations.

Contents

Computational Method

Experimental Method

Peter Gedeck, June 10th 1995