Photodegradable plastics: end-of-life design principles

Figures & data

Figure 1.  The degradation kinetics behavior of a typical polymer (red) and an ideal photochemically degradable polymer (blue). Note the tunable onset of degradation and the rapid degradation in the ideal polymer.

short-legendScheme 1. The photochemical reactions of a ketone-containing polymer. Note that all of these pathways lead to polymer backbone cleavage.

short-legendScheme 2. Photochemical degradation of a polymer backbone with pendant carbonyl groups.

short-legendScheme 3. Photochemical degradation of a polymer with metal–metal bonds along its backbone.

short-legendScheme 4. The autoxidation process.

short-legendScheme 5. Examples of organic hydroperoxide reactions. Note that a carbonyl chromophore can form from reaction of the hydroperoxide. The carbonyl group is a chromophore and its formation leads to subsequent photochemical reactions.

short-legendScheme 6. Metal catalyzed degradation of hydroperoxides. Note that the RO and ROO radicals formed in the top set of reactions react further to eventually give alcohols, carboxylic acids, aldehydes, and ketones.

Figure 2.  Examples of inorganic photosensitizers attached to polymer chains through pendant groups.

short-legendScheme 7. Mechanism for the Norrish Type II photochemical reaction showing the formation of the six-membered ring intermediate.

Figure 3.  Plot of ln Φ versus T^–1 for polymer 2.

Source: See 99, Figure 2. With permission from Springer Science+Business Media.

short-legendScheme 8. Photochemical homolysis of a bond in a polymer and the subsequent trapping reaction depicting the caged radicals, where k c is the rate constant for the geminate recombination, k d is for diffusion from the radical cage, and k t is for the radical trapping step.

short-legendScheme 9. A generalized reaction scheme showing photolysis of a bond along the backbone in a polymer (M represents a generic atom, carbon or otherwise).

Figure 4.  Illustration of the reaction of photogenerated metal radicals with trapping atoms in a solid-state matrix. In case (a) there is a trap in the reactive sphere of the metal radical and (b) the trap is initially outside of the reactive sphere.

Daglen , B.C. , Harris , J.D. and Tyler , D.R. 2007 . Factors Controlling the Rate of Photodegradation in Polymers: The Effect of Temperature on the Photodegradation Quantum Yield in a PVC Polymer Containing Metal–Metal Bonds in the Polymer Chain . J. Inorg. Organomet. Polym. Mater. , 17 : 267 – 274 .

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