narrow molecular weight distribution of block co polymer. What does it mean ?
Dear Anil,
A lot of researchers have investigated molecular weight distribution) MWD using mean field theory and predicted compositional fluctuations and segregation strength to increase with MWD breadth.
Furthermore, if you read the work of Sides and Fredrickson (Sides, S. W.; Fredrickson, G. H.J. Chem. Phys. 2004, 121, 4974–4986), you will know that they demonstrated the phase boundaries in block copolymers (BCP) with block-selective broad MWD to be
shifted when compared with BCP systems with narrow MWD such that the intermaterial dividing surface bends toward the broad MWD domain. Moreover, the authors observed block-selective broad MWD to induce molecular segregation processes that can influence microstructure formation.
These results mean that molecular segregation can give rise to the thermodynamic stabilization of lamellar and cylindrical phase coexistence. Usually, broad MWD block copolymers result in the increase in domain spacing as well as the compositional shift of the structure stability regions.
I hope you find the answer in the mentioned Article above and the references.
Dear all;
in general, for all kinds of polymers it is the polydispersity index (PDI) is the reference to know the MWD. the PDI=Mw/Mn. In the MWD curve, and for an ordinary polymer, the MWD is a gaussian curve, which means that Mw and Mn are far from each other making the PDI>1. As far as they are close to each other the PDI becomes close to 1; and the ideal case is when PDI=1, this means that the plot of the MWD is a sharp peak.
So as a conclusion narrow MWD polymers including copolymers have a PDI close to one.
This type of copolymers are prepared via living/controlled polymerization techniques, mainly NMP (SFRP), ATRP; RAFT (MADIX), SET-LRP, and other degenerative techniques. Regards
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