Polymer depolymerization of the

X-ray crystallographic studies during the course of the reaction have demonstrated that the reaction is a typical topochemical process involving a direct rearrangement of the monomer crystal to the polymer crystal having an extended rigid rod-like structure. By x-ray analysis and DSC on the thermal depolymerization of the polymer crystal, a reversible topochemical process has been demonstrated for monomer and polymer crystals. 

The mass spectroscopic analysis of the gases formed in thermal development of the UV exposed poly(l-butene sulfone)/pyridine N-oxide revealed only 1-butene and S02 as the products, which indicated depolymerization of the polymer initiated by energy transfer form the sensitizer. These photosensitized poly(olefin sulfones) are not suitable for dry etching processes, and they are not reactive ion etching resistant. Resists made of poly(olefin sulfones) and novolac resins which will be described next are CF plasma etch resistant with reasonable photosensitivities. 

Heterogeneous process mainly involves chemolysis/solvolysis, and it uses chemical reagents or solvents for depolymerization of the polymer into monomers. It is a secondary recycling technique depending on the nature of polymers, a wide variety of solvents are used for the depolymerization process. Based on the nature of solvents, it is named as alcoholysis, methanolysis, glycolysis, etc. 

Plastics such as polystyrene undergo facile-catalyzed thermal depolymerization or pyrolysis yielding very high yields of styrene monomer. Base-catalyzed depolymerization of the polymer is as follows. 

Becanse PMMA has a low ceiling temperature, the formation of propagating radicals on radiolysis at 453 K, with G(S) = 10, Charlesby and Moore (40) found spontaneons depolymerization of the polymer to monomer at this temperature. In a later article, David and co-workers (239) showed that depol5mierization also occnrred when PMMA was irradiated at ambient temperatnre and then heated to 433 K, and that the jdeld of monomer was independent of the absorbed dose and the initial molecular weight of the PMMA. 

The thermal degradation of PLA has been claimed to mainly occur via random scission based on a linear relationship between inverse of the number-average degree of polymerization P and time as shown in Equation 23.2 [28]. Recently, Aoyagi et al. [9] and Abe et al. [29] suggested that the isothermal degradation of PLLA at 220, 290, and 330°C proceeded not only via simple random scission, but also via an unzipping depolymerization of the polymer chain based on the nonlinear relationships of l/P and P with time. 

Although the most common reverse reaction, p-elimination (extrusion of an olefin) is (3-H elimination forming a terminal olefin, p-alkyl elimination is sometimes observed with d° metal-alkyls of the early transition metals and the rare-earth metals. This reaction is the basis for depolymerization of the polymers. 

Microbial degradation in polyesters proceeds in two steps the first step is depolymerization of the polymer chain by extracellular enzymes and the second is metabolism of the depolymerized fragments [891]. 

Figure 35 (Top) structure of PPA which is in reversible equilibrium with its monomer when polymerized and which possesses a low ceiling temperature of only -40 °C. (Bottom) end-capping of PPA greatly increases its thermal stability and has been used to produce reasonably stable photoresists that function based on depolymerization of the polymer main chain upon exposure to radiation.

What is a big deal is when exposure to the environment causes irreversible changes in the material itself. These changes include chemical reactions, structural changes in the polymer matrix, degradation of the polymer, and sometimes even a complete depolymerization of the polymer molecules (a breakdown of the polymer chain into its base monomers). 

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