Molecular weight distributions chain length distribution

More precise molecular weight development chain length and distribution. 

If the mass (weight)-firaction distribution w/W) is known, the average molecular weights and chain lengths can be determined ... 

Since all of the chains are intiated at about the same time and because growth continues until all of the styrene has been consumed, the chains will have similar lengths, i.e. there will be a narrow molecular weight distribution. In addition the chains will still have reactive ends. If, subsequently, additional monomer is fed to the reactor the chain growth will be renewed. If the additional monomer is of a different species to the styrene, e.g. butadiene, a binary diblock copolymer will be formed. 

The interdiffusion of polymer chains occurs by two basic processes. When the joint is first made chain loops between entanglements cross the interface but this motion is restricted by the entanglements and independent of molecular weight. Whole chains also start to cross the interface by reptation, but this is a rather slower process and requires that the diffusion of the chain across the interface is led by a chain end. The initial rate of this process is thus strongly influenced by the distribution of the chain ends close to the interface. Although these diffusion processes are fairly well understood, it is clear from the discussion above on immiscible polymers that the relationships between the failure stress of the interface and the interface structure are less understood. The most common assumptions used have been that the interface can bear a stress that is either proportional to the length of chain that has reptated across the interface or proportional to some measure of the density of cross interface entanglements or loops. Each of these criteria can be used with the micro-mechanical models but it is unclear which, if either, assumption is correct. 

In PLP the sample is subjected to a series of short (<30 ns) laser pulses at intervals t. Analysis of the molecular weight distribution gives the length of chain formed between successive pulses (v) and this yields a value for kp (eq. 13). 

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