Polystyrene depolymerisation

Thermal depolymerisation of polystyrene is possible to given back the styrene monomer along with a number of low Molecular weight compounds. 

A-max = 525 run) has allowed both a determination of the depolymerisation rate and the number of break points (i. e. 2 DPPH molecules per bond breakage). Evidence for the formation of macroradicals in the degradation of polymethyl methacrylate, polystyrene and polyvinylacetate has also been provided by Tabata [63] using spin trapping and esr techniques. Taranukha [64] has also used spin traps to study the degradation of aqueous polyacrylamide. 

Polymerisation of styrene is associated with AH = -67.3 kj/mol and AS = -10.5 J/mol.K. Calculation leads to Tc = 641 K, i.e. 368 °C. This means that polystyrene is thermodynamically stable below this temperature and can be heated to be transformed into objects, e.g. by moulding, above its glass transition temperature Tg), located around 100 °C. However, polystyrene objects are not stable in a fire, resulting in depolymerisation, emission of gases and quick burning. 

Several polymers degrade primarily by a free radical depolymerisation, including polystyrene (PS) and polymethacrylates. When a free radical is produced in the backbone of polyethyl methacrylate, for example, the molecule undergoes scission to produce an unsaturated small molecule (ethyl methacrylate) and another terminal free radical. This radical will also cleave to form ethyl methacrylate and propagate the free radical. The net effect is often referred to as unzipping the polymer. 

Zuev and co-workers [16] also studied the isothermal degradation at 600 °C of a series of parasubstituted polystyrenes with electron donating (CH, NH ) and electron attracting (NO, Cl, Br) substituents. The temperature ranges over which degradation occurred were determined and the heat stability of these polymers compared with those of conventional PS. Thermal degradation was found to involve random chain scission and depolymerisation and heat stability was found to depend on the electronic nature of the substituents and the possible stabilisation of macroradicals formed upon chain scission. 

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