EP-4735484-A1 - METHOD OF PREPARING CONDUCTIVE MATERIALS WITH POLYPYRROLE COVALENTLY BOUND BY DIALDEHYDE POLYSACCHARIDES

Abstract

The method involves an environmentally friendly process that uses spontaneous aldol condensation between the aldehyde groups of dialdehyde polysaccharides (DAP) and pyrrole to prepare pyrrole-decorated DAP. This is further used to prepare conductive co-oligomers and copolymers of DAP and pyrrole, formed without the addition of an oxidizing agent by connecting the bound pyrrole cycles at higher temperatures into longer chains by —CH— bridges originating from the aldehyde groups of DAP. The DAP, pyrrole-decorated DAP, and the corresponding co¬ oligomers and copolymers of DAP and pyrrole can be further used to prepare conductive covalently cross-linked hydrogels, covalently bind PPy prepared by other methods, and for the creation of composites suitable especially for biomedical applications.

Inventors

• Vícha, Jan
• MÜNSTER, Lukás
• MARTÍNKOVÁ, Martina
• VÍCHOVÁ, Zdenka
• KASPÁRKOVÁ, Vera
• HUMPOLÍCEK, Petr

Assignees

• Tomas Bata University In Zlín

Dates

Publication Date

20260506

Application Date

20240617

Claims (3)

1. 1. A method for preparing conductive co-oligomers and copolymers of pyrrole and conductive composites or conductive hydrogels based on them, characterized by that the polysaccharide with at least one pyranose cycle carrying hydroxyl groups in positions 2 and 3 is at least partially oxidized by the action of an alkali metal periodate to form the dialdehyde of the given polysaccharide, then the residues of the oxidizing agents are completely removed from the dialdehyde polysaccharide by dialysis or repeated centrifugation, and the dialdehyde polysaccharide is isolated by filtration, centrifugation, or lyophilization, after which either a) for the preparation of co-oligomers and copolymers of pyrrole without the use of chemical or electrochemical polymerization, the obtained dialdehyde polysaccharide is exposed to aqueous solution of pyrrole in an amount corresponding to 1 to 20 times the molar amount of aldehyde groups in the dialdehyde polysaccharide for 3 to 48 hours in an acidic environment with a pH between 3 and 6.5, where a condensation reaction occurs between the carbonyl groups of the dialdehyde polysaccharide and pyrrole at laboratory temperature, namely the substitution of hydrogen atom or atoms in the a positions of the pyrrole cycle and the formation of a covalent bond between pyrrole and dialdehyde polysaccharide and thus the decoration of the dialdehyde polysaccharide with pyrrole, with the fact that at elevated temperatures or after subsequent heating, preferably to 50 to 75°C, bound pyrrole cycles are linked by the same condensation reaction into higher units via -CH- bridges formed from the original carbonyl groups of the dialdehyde polysaccharide and the chains of the dialdehyde polysaccharide thus function as a template for the formation of conductive co-oligomers and copolymers of pyrrole with dialdehyde polysaccharide, whereby if the dialdehyde polysaccharide is fully dissolved in water, the co-oligomers and copolymers of dialdehyde polysaccharide and pyrrole take the form of a conductive colloidal solution or dispersion, but if the dialdehyde polysaccharide is in an insoluble form, preferably in the form of surface-oxidized cellulose fibers, or if the dialdehyde polysaccharide is located on the surface of another insoluble polymer of hydrophilic nature carrying -OH, or -NH? groups with which the dialdehyde polysaccharides can react to form hemiacetals or imines, preferably cotton fabric, conductive co-oligomers and copolymers of dialdehyde polysaccharide and pyrrole are formed on the surface of such materials, and these thus become conductive or b) for the preparation of conductive composites, dialdehyde polysaccharide, in the form of fibers, nanofibers, or as a layer on insoluble natural or synthetic hydrophilic polymers, impregnated with dialdehyde polysaccharide solution, found in the form of fibers, nanofibers, or fabrics carrying -OH, -NH?, or -NH groups, with which dialdehyde polysaccharides react to form hemiacetals or imines, further referred to as matrices, is reacted with an aqueous solution of pyrrole in a molar amount corresponding to 0.1 to 10 times the amount of aldehyde groups present in the dialdehyde polysaccharide at laboratory temperature for 16 to 24 hours, during which the dialdehyde polysaccharide is decorated with pyrrole, followed by the initiation of in situ polymerization of the remaining pyrrole into polypyrrole by adding a suitable oxidizing agent, preferably FeCH in a 1.65 to 3 times molar excess relative to the pyrrole, with the reaction running for 4 to 24 hours, during which the pyrrole cycles covalently bound to the dialdehyde polysaccharide are incorporated into the forming polypyrrole chains, which are preferably forming on the surface of the dialdehyde polysaccharide or dialdehyde polysaccharide-impregnated matrices and become covalently connected with them, which leads to more effective coverage of dialdehyde polysaccharide or dialdehyde polysaccharide-impregnated matrices with polypyrrole at the given concentration of pyrrole when compared to unoxidized or unimpregnated matrices and to the increase of the resistance of the deposited polypyrrole layer against peeling from the matrix while maintaining the electrical conductivity of the composites thus prepared or c) for the preparation of conductive hydrogels, pyrrole is first added to the dialdehyde polysaccharide in a molar amount that is lower than the molar amount of aldehyde groups in the dialdehyde polysaccharide, preferably in a molar ratio of 0.5:1 for pyrrole: aldehyde groups in the dialdehyde polysaccharide, the mixture is stirred for at least 3 hours to decorate the dialdehyde polysaccharide with pyrrole, the solution of pyrrole-decorated dialdehyde polysaccharide is subsequently mixed with a solution of a water-soluble polymer carrying -OH, or-NH? groups, preferably polyvinyl alcohol, in an amount sufficient for its crosslinking, preferably 1 to 5 wt% relative to the polymer, poured into molds and left to crosslink during drying, with the resulting materials being washed in water and then again immersed in an excess of pyrrole solution until the formed hydrogel is saturated with pyrrole, preferably for 72 hours, after which the polymerization of pyrrole is initiated using a molar excess of FeCh relative to pyrrole in the solution, during which polypyrrole chains are formed inside the structure of the hydrogel and because these also include cycles from pyrroledecorated dialdehyde polysaccharide, chemical anchoring of polypyrrole molecules in the hydrogel and thus a secondary crosslinking of the hydrogel structure occurs, which improves mechanical properties of the hydrogel and leads to the acquisition of electrical conductivity or d) dialdehyde polysaccharide is used for the preparation of conductive composite hydrogels, where the dialdehyde polysaccharide is first used to crosslink soluble polymers carrying -OH, or -NH? groups, preferably chitosan, in an amount sufficient for its crosslinking, preferably 2 wt% relative to the amount of dissolved polymer, whereby a colloidal solution or suspension of polypyrrole particles, prepared without the presence of dialdehyde polysaccharide using known methods, is added to the polymer solution before its mixing with dialdehyde polysaccharide, preferably in an amount of 5 to 10 wt% relative to the amount of dissolved polymer, and, after mixing of all components, the resulting slowly solidifying solution is transferred into a mold and dried, during which bonds are formed both between the dialdehyde polysaccharide and the polymer and between the dialdehyde polysaccharide and the polypyrrole particles, which chemically anchors them in the structure and limits their possible leaching from thus prepared conductive composite hydrogels, which also accelerate wound healing in the form of hydrogel coverings.
2. 2. The method according to claim 1, characterized in that the polysaccharide with at least one pyranose cycle carrying hydroxyl groups in positions 2 and 3 is a polysaccharide from the group including cellulose, dextran, hyaluronic acid, alginate, dextrin, starch, amylose, pectin, schizophyllan, scleroglucan, or xanthan.
3. 3. The method according to claim 1, characterized in that the synthetic polymer of hydrophilic nature in the form of fibers, nanofibers, or fabrics carrying -OH, -NHz, or -NH groups is a polymer from the group including cellulose, chitosan, polyurethane, or polyamide.

Description

METHOD OF PREPARING CONDUCTIVE MATERIALS WITH POLYPYRROLE COVALENTLY BOUND BY DIALDEHYDE POLYSACCHARIDES Field of Invention The invention relates to a method of preparing conductive co-oligomers, copolymers, composites, and conductive hydrogels based on polypyrrole (PPy) and dialdehyde polysaccharides (DAP) with expected applications in sensors, biomedicine, power industry, and wearable electronics. The basis of the invention is the use of spontaneous formation of covalent bonds between DAP and pyrrole or PPy as a result of a condensation reaction between pyrrole cycles and aldehyde groups of DAP. This method allows a) direct decoration of DAP with pyrrole cycles without the need for prior modification of pyrrole or the use of other toxic organic agents and solvents, which are necessary for existing solutions, b) preparation of conductive co-oligomers and copolymers of pyrrole and DAP by increasing the temperature, without the addition of an oxidizing agent or the use of another polymerization method otherwise necessary for the preparation of PPy copolymers, because the poly aldehyde character and structure of DAP function as a template allowing the linking of bound pyrrole cycles by —CH— bridges into higher units, which can be used for the preparation of conductive colloidal particles and conductive fibrous materials, c) incorporation of pyrrole cycles covalently bound to DAP into PPy chains formed during in situ polymerization and subsequent formation of covalently bound conductive composites of DAP and PPy, without the need for the addition of organic agents, linkers, and toxic reactants, in which case the PPy preferentially grow on the oxidized matrix and resistance of the PPy layer to wear is increased compared to matrices not containing DAP, d) preparation of conductive composite materials by anchoring pre-made PPy particles into matrices using a reaction with DAP, e) simultaneously with points a) to d) to use the ability of DAP to react with natural or synthetic hydrophilic polymers carrying -OH, -NH2, or -NH groups such as cellulose, chitosan, polyvinyl alcohol, polyurethane or polyamide, which can be dissolved or undissolved in the form of various hierarchical structures, namely fabrics, fibers or nanofibers, in which case DAP can also serve as a crosslinking agent forming hemiacetal or imine bonds with these polymers, as well as for binding of pyrrole cycles and the associated formation of copolymers or composites with covalently anchored PPy. Description of the Prior Art Polypyrrole (PPy) is considered one of the most promising conductive polymers with a range of potential industrial uses in the field of sensors, wearable electronics, battery electrodes, and desalination of water, but also in medicine and biology as wound healing material or for preparation of conductive cellular scaffolds. The reason for the popularity of PPy is the ease of its preparation, good stability, low toxicity, and especially high electrical conductivity. The main disadvantages of PPy include its very low solubility in most solvents and limited processability. PPy is usually prepared by electropolymerization or chemical oxidative polymerization using various oxidizing agents, such as FeCh, in the form of thin layers or powder. While electropolymerized thin layers usually have high conductivity and purity, their use is limited by the mechanical properties of pure PPy and its weak interaction with the substrate, which leads to easy cracking or peeling of the PPy layer and reduction of conductivity. The limited size of electrodes usable for electropolymerization also prevents greater industrial applications of this technique. Chemical polymerization of pyrrole using various oxidizing agents is a difficult-to-control radical-involving process occurring in an acidic environment. When oxidizing a solution of pyrrole, nucleation of PPy particles occurs by random connection of monomers and oligomers of pyrrole throughout the volume of the solution. The resulting particles usually have a very wide size distribution, and therefore a high polydispersity index (PDI), which can affect their further properties and use. The conductivity of thus prepared PPy powder is given by the amount and extent of contacts between particles and is orders of magnitude lower than that of a homogeneous layer of PPy film deposited on an electrode. To expand the application potential, PPy is usually prepared in the form of composites with other materials. The simplest methods of preparing composites are the dispersion of pre- prepared PPy powder into a polymer matrix or the initiation of in situ polymerization of pyrrole directly in the matrix. Both often lead to the formation of a material with inhomogeneous properties, especially due to the different sizes and distribution of PPy particles. The electrical conductivity of such a composite is also significantly lower than that of a homogeneous layer of PPy due to the limited number of interactions b