A set of double hydrophilic block copolymers was synthesized on the basis of a branched poly(ethylene glycol)-block-poly(ethyleneimine) (PEG-b-PEI) block copolymer by polymer analogous reactions. Different hydrophobic moieties were successfully introduced as well as carboxylate, phosphonate, sulfonate and thiol groups leading to a library of only partially differing block copolymers. The analysis of the block copolymers by GPC turned out to be extremely difficult, as the multifunctional polymers tend to interact with various column materials. However, characterization of PEG-b-PEI was possible with 1H NMR and analytical ultracentrifugation as well as with elemental analysis. These techniques revealed a significant amount of unbound PEG due to side reactions with PEI monomers or oligomers. The degree of the various functionalizations of PEG-b-PEI was determined by elemental analysis indicating that the sterically big phosphonic or sulfonic acid groups are only attached to the primary amino groups of the PEI block whereas the smaller thiol and carboxy groups can additionally be bound to secondary amino groups. The set of polymers was applied as additive in the crystallization of CaCO3 yielding microparticles in all cases. Under the basic conditions of the experiment (pH > 8.5), both hydrophobically modified and unmodified polymers show almost the same influence on the CaCO3 morphology, whereas the stabilization of the formed microparticles varies. However, the kind of functional group has a strong influence, with phosphonate and sulfonate as the substituents leading to the most significant changes in the CaCO3 morphology.
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Sedlák et al. (2001) studied this question.