For the first time, carboxymethyl starch (CMS) samples with a very high degree of substitution (DS CM ϭ 2.1) were synthesized by multistep carboxymethylation under heterogeneous reaction conditions in methanol/water with sodium hydroxide and monochloroacetic acid as an etherifying agent. The stepwise increase in the total DS CM value gradually decreased with an increasing DS CM value of the starting polymer. The determination of the functionalization pattern of CMS by 1 H-NMR spectroscopy after chain degradation indicated a high preference for

Hydrogels were synthesized through cross‐linking of carboxymethyl starch (CMS; Degree of Substitution DS = 0.45) using polyfunctional carboxylic acids (malic, tartaric, citric, malonic, succinic, glutaric and adipic acid). The syntheses used a cross‐linking agent ratio (ratio of the number of cross‐linking agent molecules to the number of monomer units constituting the polymer) of FZ = 0.05. After cross‐linking the gels were dried, ground and then hydrogels of a polymer concentration of 4 mass‐% were produced. These CMS‐hydrogels were then rheologically characterized using dynamic oscillatory measurements. From measurements of the plateau region storage modulus G'P, the network parameters molar mass between two entanglement points Me (Me ranging from 9.318 (citric acid) to 281.397 g/mol (tartaric acid)), the cross‐link density νe and the distance between two entanglement points ξ were calculated. Using carboxylic acids without other functional groups, a maximum in gel sturdiness is found at a spacer length of two CH2‐groups. The evaluation of the loss factor tan δ for the CMS‐hydrogels showed that values of tan δ = 0.2 varied only slightly with the frequency ω. Flow curves showed a pseudopIastic flow behavior for all CMS‐hydrogels (the shear viscosity η declining over five decades in the range of the shear rate γ of 10−3 to 103 s−1) The different polyfunctional carboxylic acids have a strong influence on the sturdiness of the synthesized CMS‐hydrogels.

Carboxymethyl starches (CMS) with a degree of substitution (DS) in the range of 0.5 to 1.5 and reagent yields about 70% were synthesised under heterogeneous reaction conditions. Starting from a standard procedure for manufacturing low substituted CMS the molar ratios of the reagents were increased. Under these conditions starch particles agglomerated during the reaction and the stirrer stopped. The reaction conditions (pulp density, addition of dispersing and water binding agents, pressure, sequence of reagents addition, reaction time, temperature, starch variety, etc.) were varied to find the best process conditions for optimum reaction efficiencies and product properties. If an amylose‐free starch, e.g. waxy corn starch is used as starting material, the obtained products are completely soluble in water to form a clear solution. The products are good viscosity regulators. Using a 2% aqueous solution a wide range of viscosity (1–90 000 mPa s) can be adjusted. The calcium‐binding capacity and the biodegradability of the products were investigated.

Hydrogels were synthesized by cross-linking of potato starch (PS) with dichloroacetic acid (DCA) in the presence of monochloroacetic acid (MCA) to form etherified carboxymethyl starch (CMS) gels, to be used for ultrasonic medical examinations. By etherification cross-linked CMS-hydrogels can be produced, that are stable in contrast to the in the long-term unstable esterified gels, that were presented in the last paper. The rheological benchmarks for the CMS-hydrogels were set in comparison with synthetic ultrasonic gels. Gels with potato starch contents in the reaction batch ranging from 12.5% to 20% showed the best compliance with the benchmark parameters. The DS values of these CMS-hydrogels vary from 0.42 to 0.49, increasing with decreasing amount of starch in the reaction mixture. The free swelling capacities (FSC) vary between 77 g/g for the 12.5% PS-gel and 34 g/g for 20% PS-gel, the turbidities of the samples being in the range from 14.5 NTU (Nephelometric Turbidity Units) (12.5% PS) up to 20.5 NTU (20% PS). The variation of the PS fraction in the reaction mixture showed that with an increased amount of PS in the reaction batch the number of cross-links of the CMS-gels increases, too. At a higher number of cross-links the swelling capacity is reduced and the concentration needed to form stable hydrogels is greatly increased. Thus a hydrogel of a polymer concentration of 5 mass-% from a 12.5% PS batch was produced, that showed the best accordance with the rheological benchmark parameters such as gelatinization time, visco-elastic and pseudoplastic properties and long-term stability. The ultrasonic pictures taken with this CMS-gel were not different from those taken with the synthetic gels. This hydrogel was then subjected to long-term-stability measurements performed over one year and to rheological temperature cycle tests. The tests showed that the long-term stability of the gels is sufficient for their use as ultrasonic gel.

Carboxymethyl starch (CMS) was prepared in a completely heterogeneous procedure in a methanol/water slurry activated with aqueous sodium hydroxide (45%, w/v) using monochloroacetic acid as the etherifying agent. The influence of the reaction conditions and the type of starting starch (amylose content and preactivation) was evaluated in regard to the formation of the main repeating units (i.e., unfunctionalized and mono-, di-, tri-, and tetra-O-carboxymethylated) and the pattern of functionalization within the anhydroglucose units (AGU). The reproducible synthesis gave products with a maximal degree of substitution of CM groups (DS CM ) of 0.66, which was reached in a one-step synthesis. Repeated carboxymethylation led to products with a DS CM of 0.88. As revealed by means of HPLC analysis after complete acidic depolymerization, in any sample the mono-O-carboxymethylated glucose (mono-O-CMglc) was preferably present while the di-O-CMglc was formed to a very low extent only. The tri-O-CMglc was found in some samples while tetra-O-CMglc was not detected. The mole fractions determined did not follow the simple Spurlin statistic as shown for CM cellulose synthesized under comparable conditions. Within the carboxymethylated AGUs a preferred functionalization at position 2 was analyzed by means of 1 H-NMR spectroscopy after hydrolytic chain degradation. Consequently, the CMS samples synthesized contained mainly 2-mono-O-CM-AGU.