Thermo-responsive behavior of propynyl-containing hydroxyethyl starch

Highly branched thermoresponsive polysaccharide derivative in water. Partly substituted highly branched cyclic dextrin ethylcarbamate

A thermoresponsive highly branched polysaccharide derivative was revealed from commercially available highly branched cyclic dextrin (HBCD), originally synthesized from amylopectin. Eight samples of partially substituted ethyl carbamate derivatives of HBCD (HEC) were prepared with a degree of substitution DS ranging from 0.27 to 1.46. Three samples with DS = 0.88, 1.05, and 1.22 showed LCST type phase separation in water. The intrinsic viscosity and form factor in water were typical of the hyperbranched structure. The intermolecular interactions between HEC and iodine or 1-anilinonaphthalene-8-sulfonic acid (ANS) were appreciably different from those of the linear analog (AEC), suggesting that the locally bent helical conformation of highly branched HEC chains has a different interaction with small molecules. The phase diagram of HEC-water systems was accidentally similar to that of the linear chain with the same molar mass and DS, although the one phase region of the branched polymer chain-poor solvent system is usually wider than that of the corresponding linear chain. This is likely due to the lower hydration nature of the polymer segment of HEC chains than that of the corresponding linear chain.

Temperature responsive crosslinked starch-kraft lignin macromolecule

Starch is a natural polymer with a relatively simple structure and limited solubility in water. Kraft lignin (KL) is a complex biopolymer obtained as a by-product from the delignification of wood and grasses. The present work reports developing a temperature-responsive high molecular weight macromolecule from crosslinking KL and starch (KLS). The NMR and XPS analyses quantified the changes in the aromatic and anhydroglucose units of KL and starch, observing a higher content of C-O-C bonds, which confirms the presence of glycerol ether cross-linkages between starch and KL in KLS. The rheological analysis of KLS dispersions revealed the formation of a thermo-responsive structured network. The temperature-dependent water solubility and rheological characteristics of KLS were related to the presence of hydrophilic starch chains, crosslinking degree, and physicochemical characteristics of KL. The incorporation of KL and ether crosslinks increased the thermal stability of KLS. Because of its multiple functional groups and large molecular weight (3.6-4.2 × 10⁵ g/mol) that was arranged in an extended globular shape, KLS-5 formed a gel-like structure after a heating-cooling treatment. Overall, the results confirmed that incorporating lignin in starch would fabricate sustainable materials with potentially altered applications, such as temperature-responsive hydrogels and films.

To the Methodology of Phase Transition Temperature Determination in Aqueous Solutions of Thermo-Sensitive Polymers

An advanced methodology of phase transition determination in aqueous solutions of thermo-sensitive polymers by using of the phase portraits method has been suggested. The methodology allows highly accurate determining the temperature when exactly a half of molecules loses solubility (from the maximum number that can go to another phase state under given conditions). It is shown that since phase transition passes usually in a wide enough temperature interval this indicator should be used as a quantitative parameter that characterizes phase transition process. Additionally the suggested methodology allows introducing one more quantitative parameter that reflects a sharpness of phase transition. The methodology is verified by an example of phase transitions study in aqueous solutions of thermo-sensitive copolymers based on N-vinylpyrrolidone and vinyl propyl ether.