Periodic Reporting for period 1 - SPRUT (Synthesis of bio-based non-isocyanate polyurethanes and their modification towards industrial application)
Berichtszeitraum: 2022-05-01 bis 2024-04-30
Polyurethanes (PUs) are a diverse family of plastics that we can find in wide variety of objects that surround us in everyday use. For example, foams in sleeping mattresses and shape memory pillows are PU foams, and so are the foams that are used for insulation of window frames and doors during construction. Thermoplastic PUs (TPUs) are extensively used in the production of shoe soles due to their durability, flexibility, and resistance to wear and tear. In the automotive industry, TPUs are used while making interior and exterior parts such as dashboards, door panels, and protective coverings. Their impact resistance and aesthetic qualities make them suitable for these applications. PUs also have many other useful applications in textiles, industrial insulation, medical devices, electronics etc.
The main issue with PUs is that they are produced from isocyanates – chemical compounds which are highly toxic and cancerogenic. They present significant respiratory and dermal hazards and can cause chronic illness or even death upon overexposure. Scientists are trying to substitute isocyanates with other compounds in order to reduce occupational hazards for workers who are frequently exposed to isocyanates.
One of the potential solutions is to use cyclic carbonates and diamines to produce polyhydroxyurethanes (PHUs) that are similar in structure to PUs and are usually considered as their greener alternative. However, current state of the art PHUs possess insufficient molecular weights and are very hydrophilic. These two factors combined result in poor mechanical properties and thus limit the practical utility of PHUs.
The SPRUT project was aimed at improving methods for PHU synthesis and developing method for their modification in order to reduce their hydrophilicity. The combined success of these two main goals will bring PHUs closer to industrial requirements and may allow to facilitate the substitution of toxic isocyanates at workplaces and everyday lives.
The main issue with PUs is that they are produced from isocyanates – chemical compounds which are highly toxic and cancerogenic. They present significant respiratory and dermal hazards and can cause chronic illness or even death upon overexposure. Scientists are trying to substitute isocyanates with other compounds in order to reduce occupational hazards for workers who are frequently exposed to isocyanates.
One of the potential solutions is to use cyclic carbonates and diamines to produce polyhydroxyurethanes (PHUs) that are similar in structure to PUs and are usually considered as their greener alternative. However, current state of the art PHUs possess insufficient molecular weights and are very hydrophilic. These two factors combined result in poor mechanical properties and thus limit the practical utility of PHUs.
The SPRUT project was aimed at improving methods for PHU synthesis and developing method for their modification in order to reduce their hydrophilicity. The combined success of these two main goals will bring PHUs closer to industrial requirements and may allow to facilitate the substitution of toxic isocyanates at workplaces and everyday lives.
The work on this project was distributed between three main areas.
First, the method for synthesis of cyclic dicarbonate monomers, which are a crucial precursor for PHU synthesis, have been established and optimized. During this process overall efficiency, toxicity and sustainability were thoroughly considered as well as the potential for further industrial scaling up.
Then, PHU polymers have been prepared using cyclic dicarbonates prepared on the first stage and various commercially available diamines. The method for PHU synthesis using reactive extrusion was optimized in order to produce polymers with molecular weight as high as 27000 kDa. These results are in line with the state-of-the-art publications and patents. However, several limitations such as side reactions don’t allow to further increase PHU molecular weight despite the optimization efforts.
Finally, method for modification of PHU polymers with aldehydes and boronic acids have been developed and optimized. Several PHU and aldehyde structures have been tested in order to understand structure-property relationships in final modified PHUs. It was shown that aromatic aldehydes provide the best effect in terms of retaining polymer mechanical properties and reduction of water adsorption at elevated humidities. However, aliphatic aldehydes allowed to obtain best modification degrees. Method was further optimized later to improve the modification with aromatic aldehydes without compromising other parameters of the modification process or properties of modified polymers. This method was additionally extended to use boronic acids and preparation of PHU vitrimers with boronic cross-links.
First, the method for synthesis of cyclic dicarbonate monomers, which are a crucial precursor for PHU synthesis, have been established and optimized. During this process overall efficiency, toxicity and sustainability were thoroughly considered as well as the potential for further industrial scaling up.
Then, PHU polymers have been prepared using cyclic dicarbonates prepared on the first stage and various commercially available diamines. The method for PHU synthesis using reactive extrusion was optimized in order to produce polymers with molecular weight as high as 27000 kDa. These results are in line with the state-of-the-art publications and patents. However, several limitations such as side reactions don’t allow to further increase PHU molecular weight despite the optimization efforts.
Finally, method for modification of PHU polymers with aldehydes and boronic acids have been developed and optimized. Several PHU and aldehyde structures have been tested in order to understand structure-property relationships in final modified PHUs. It was shown that aromatic aldehydes provide the best effect in terms of retaining polymer mechanical properties and reduction of water adsorption at elevated humidities. However, aliphatic aldehydes allowed to obtain best modification degrees. Method was further optimized later to improve the modification with aromatic aldehydes without compromising other parameters of the modification process or properties of modified polymers. This method was additionally extended to use boronic acids and preparation of PHU vitrimers with boronic cross-links.
The SPRUT project has pushed the boundaries of PHU research in several aspects (Figure 1).
First, the unique method for modification of PHUs has been developed. It allows to modify specifically designed PHU polymers with any aldehyde thus modifying their properties and behaviour. Using this method and aromatic aldehydes we were able to produce PHUs with 2-3 times reduced hydrophilicity. Such polymers now may be used in various environments without the loss of their mechanical properties due to water adsorption.
Second, this method was extended to prepare PHUs with task specific properties, such as fluorescence or ability to adsorb CO2. This is a clear illustration of universality of the developed approach which allows to impart any required property to the tailored PHU by designing functional aldehyde bearing this property.
Finally, the developed method was utilized for the preparation of PHU-based vitrimers. Vitrimers are a new generation of thermosetting materials that simultaneously have the advantages of recycling and reshaping, like thermoplastics. These new vitrimers exhibited high mechanical properties similar to industrial epoxy resins and can be potentially used in the preparation of new generation of recyclable composite materials with bio-based fibers. These PHU vitrimers can also be mechanically recycled up to 3 times without significant decrease in their properties as well as chemically in order to recover pristine PHU polymer, which can be further reused in the same or other applications.
First, the unique method for modification of PHUs has been developed. It allows to modify specifically designed PHU polymers with any aldehyde thus modifying their properties and behaviour. Using this method and aromatic aldehydes we were able to produce PHUs with 2-3 times reduced hydrophilicity. Such polymers now may be used in various environments without the loss of their mechanical properties due to water adsorption.
Second, this method was extended to prepare PHUs with task specific properties, such as fluorescence or ability to adsorb CO2. This is a clear illustration of universality of the developed approach which allows to impart any required property to the tailored PHU by designing functional aldehyde bearing this property.
Finally, the developed method was utilized for the preparation of PHU-based vitrimers. Vitrimers are a new generation of thermosetting materials that simultaneously have the advantages of recycling and reshaping, like thermoplastics. These new vitrimers exhibited high mechanical properties similar to industrial epoxy resins and can be potentially used in the preparation of new generation of recyclable composite materials with bio-based fibers. These PHU vitrimers can also be mechanically recycled up to 3 times without significant decrease in their properties as well as chemically in order to recover pristine PHU polymer, which can be further reused in the same or other applications.