In this study the flocculation efficiency of cationic starch derivatives of varying degrees of substitution (DS) and different amylose/amylopectin ratios was investigated and compared to structural properties. The molar masses, Mw, radii of gyration, RG, and the molar mass distributions of the starch samples were determined by applying the method of flow field‐flow‐fractionation combined with multi‐angle light scattering and interferometric refractometry. In dewatering experiments potato starch derivatives of differing DS have optimum dosages that correspond to their cationicity. The lowest flocculant dosage yielding maximum dewatering results was determined for the most strongly substituted sample (DS = 1.48), while the least substituted starch derivative (DS = 0.28) showed the highest flocculant demand. Furthermore, the molar mass distribution and coil dimensions of derivatives seem to have a great influence on flocculation efficiency, because a 1.5‐fold increase in molar mass can compensate a 1.5‐fold decrease in DS. Toxicological investigations on synthetic and natural flocculants employing hens fertile egg screening test (HEST) led to the conclusion that cationic starches of DS < 0.95 are less toxic than commercial synthetic flocculants. When the results of flocculation experiments and toxicological data were taken into account, a moderate DS of 0.6 was deemed to give the best compromise between dewatering efficiency, cost‐effectiveness and ecological safety.

Summary: Growing demand for environmentally friendly technologies promotes the interest in investigation of natural flocculants and development of new ways of their derivatization aimed to find a compromise between cost, efficiency, and safety in polyelectrolyte applications. Recent progress in cationization of natural starch [T. Heinze et al., Macromol. Mater. Eng. 2002, 287, 495] allowed obtaining cationic starch derivatives (2‐hydroxy‐3‐trimethylammoniumpropyl starch chloride) with very high substitution degrees (up to 1.54) that made them together with aminopolysaccharide chitosan the most promising candidates to replace synthetic flocculants in various industrial sectors. In this paper the flocculation efficiency of chitosan, cationic polyacrylamide copolymers (Praestols), and two series of cationic starch derivatives varying in substitution degree and amylose/amylopectin ratio is investigated to answer the following questions: do cationic polysaccharides and synthetic polymers show comparable efficiency; does high degree of starch functionalization significantly improve its flocculation behavior in comparison with commercially available starch products; and whether the amylose/amylopectin ratio (i.e. ratio of linear/branched polymers) plays a role in flocculation behavior of highly substituted cationic starch derivatives.

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Poly(butyl cyanoacrylate) (PBCA) is a biodegradable and biocompatible homopolymer which is used as a carrier matrix for drug delivery systems in the pharmaceutical industry. Typically, polymerization is carried out under aqueous conditions and results in molecular weights are mostly lower than 3000 g/mol due to the instability of the high molecular weight PBCA. However, the stability of polymer excipients is a major prerequisite for drug product development in the pharmaceutical industry. In this work, a reliable polymer synthesis strategy for PBCA was designed to control the molecular weight in a nonaqueous polymerization environment. The anionic polymerization process and the impact of key synthesis parameters were investigated. The results confirmed that the previously postulated depolymerization–repolymerization process (DPRP) in the literature can be used to tailor the molecular weight of PBCA. The amount of sodium methoxide present during the polymerization proved to be the key parameter to control the DPRP and the molecular weight as desired. In addition, it was discovered that end-capping the PBCA chain suppressed the DPRP and prevented monomer release by depriving the PBCA of its living character. Thus, neat PBCA polymer with varying molecular weights determined by Advanced Polymer Chromatography™ as well as end-capped PBCA were synthesized, and the improvement of the chemical and shelf-life stability were confirmed using NMR.

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