Polystyrene bond breaking

It is interesting to note that the conversion of electronic to vibrational energy results in scission of the more stable pendant C—H bond rather than the main chain C—C bond. The observed results are consistent with this process because of the glassy nature of the polymer at room temperature. Almost certainly the main-chain bonds break and make . This proposal is supported by the observation that p-halogenated polystyrenes yield the halogen hydride, hydrogen and a cross-linked polymer on photolysis. 

The photoablation process consists of the absorption of a short-wavelength laser pulse to break covalent bonds in polymer molecules and eject decomposed polymer fragments. Channels of various geometries and dimensions can be obtained using an appropriate mask. Many commercially available polymers can be photoablated, including polycarbonate, poly(methyl methacrylate) (PMMA), polystyrene, nitrocellulose, poly(ethylene terphtalate) (PET), and poly(tetrafluoroethylene) (Teflon). ... 

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. 

Real-World Question what liquids will break the covalent bonds of polystyrene ... 

The chain scission also can start truly randomly and not only at the weaker bond. For polymers containing linear backbones, in addition to p-scissions, it is possible to have a-scissions, methyl scissions or even hydrogen scissions. The scission of a C-H bond is thermodynamically unfavorable at low temperatures and is not too common at temperatures where the other scission can take place. The a-scission is more frequent. It refers to the breaking of a o bond to an sp2 carbon. For polystyrene for example, the a-scission leads to the formation of a phenyl radical and a polymeric radical (and it is not a chain scission). 

To synthesize polyethylene a double carbon bond in the starting material ethylene (CH2=CH2) breaks to allow attachment to other ethylene molecules resulting in a high molecular weight material or macromolecule. Other polymers which are formed by a similar process include polystyrene (repeat unit or monomer is styrene), polypropylene (monomer propene), poly (methyl methacrylate) where the monomer is methyl methacryalate, 1,4-polybutadiene (monomer is buta-1,3-diene) and 1,4-polyisoprene (monomer is isoprene) which has the same formula as natural rubber. Detaik of how polymers are prepared and processed are presented in Chapter 3. 

One method of classifying plastics is by their response to heat. Thermoplasts, also known as thermoplastic polymers, soften and liquefy on heating and harden again when cooled. The process is reversible and can be repeated. On heating, the weak secondary bonds between polymer chains are broken, which facilitates relative movement between the chains. If the molten polymer is further heated until the primary covalent bonds also break, degradation of the thermoplast follows. Thermoplastic polymers are linear or exhibit branching with flexible chains and include polyethylene, polystyrene and polypropylene (Figure 4.10). 

Table 8.2 gives approximate ranges of values of y for poly(methyl methacrylate) and polystyrene deduced from various experiments and compares them with the value estimated from the energy required to break a typical bond and the number of polymer chains crossing unit area. 

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