Synthetic methods used to access poly(carbonate) block copolymers (PC-BCPs) from ring opening polymerizations are well controlled reactions that result in monomodal molecular weight distributions and low polydispersities. Despite these methodologies the synthesis of PC-BCPs often suffer from side reactions that result in homopolymer impurities that dramatically affect their performance in self-assembly applications. We will discuss the sources of these impurities in PC-BCPs produced from macroinitiators, sources that include: (i) monomer and macroinitiator quality, (ii) choice of catalyst (acid vs. base) and (iii) reaction conditions. With judicious attention to these considerations homopoloymer impurities can be dramatically minimized, however, the resulting polymers still contain homopolymer impurities and require fractionation methods for purification. The impact of these PC-BCP purification methods on thin film self-assembly will also be shown. Finally, detection of these impurities can be challenging for traditional methods of polymer characterization such as gel permeation chromatography (GPC) and <sup>1</sup>H-NMR as well as more specialized methods of characterization like adsorption based high performance liquid chromatography (HPLC). Therefore, we have developed an alternative strategy in impurity detection, contrast enhanced diffusion ordered spectroscopy (CEDOSY), which has proven a powerful tool in allowing one to resolve the presence of even small amounts of homopolymer impurities.

Origin and detection of impurities in ring-opened poly(carbonate) block copolymers for self-assembly

250th National Meeting (2015)

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