Unzipping pure case

Unzipping was first considered in the context of DNA [10]. However the same ideas play a role here. Let us consider a pure case of a directed polymer with one end fixed at origin and with an attractive interaction with a line at r( ) = 0 (instead of being in a random medium). The Hamiltonian for a delta-function interaction can be written as... 

In cases where no additional oxygen is present, polystyrene can undergo nearly pure thermal degradation. The two prevalent mechanisms are sequential elimination of monomer units, which is called unzipping or depolymerization. In this case, styrene monomer is formed. Random chain scission can also occur. It is sometimes combined with unzipping at the reactive broken chain ends. At temperatures approaching 300 °C, up to 40 % of a polystyrene molecule can be converted to styrene monomer. 

Depolymerization is the reverse reaction to polymerization it consists of unzipping the monomeric units after initiation of the reaction either at random or at the chain ends. The initiation can be the consequence of a photochemical reaction but depolymerization itself is a purely thermal reaction which is discussed in Chapter 1 of this book. It is usually negligible at room temperature. Photochemically initiated depolymerization has been studied in the case of polymethylmethacrylate [9], poly-a-methylstyrene [10] and polymethylisopropenylketone [11]. 

If we consider a pure problem, there will be an unzipping transition as described in Sec. 7 above. The transition is first order in nature. In this particular case there is no thermal unbinding in one dimension but if we forbid crossing of the polymers, then a... 

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