Hybrids, 32 depolymerization

One critical issue is the evaluation alternative. In the case of methanolysis, the alternatives are to make DMT and EG by depolymerization or secure materials from traditional petrochemical sources. For hydrolysis, the alternatives are TPA and EG by depolymerization or from traditional sources. For both technologies, the amount of copolymerizing isophthalate and/or 1,4-cyclohexane dimethanol is likely to be too little to justify the cost of recovery. For the various forms of glycolysis and the methanolysis/BHET hybrid, the alternative is the BHET and BHET-like materials made by the combination of a terephthalate and isophthalate plus EG and various glycols. Market prices exist for TPA and EG. BHET is not an item of commerce, and so the value must be imputed from the market price for TPA (the modern terephthaloyl) and EG, plus a conversion cost. 

Random copolymers may lead to depolymerization like (B) homopolymers. On the contrary, alternated copolymers present a much better resistance to reversion. Copolymers exhibit a lower Tg (of 10 to 20 °C) than that of the hybrid homopolymer (A) . Thermogravimetric analyses of random and alternated copolymers show that they are more stable than each homopolymer (A) or (B) . 

Figure 15.1 Schematic representation of (a) a six-centered mechanism for depolymerization of siloxanes and (b) hybrid siloxanes...

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