What is the intellectual merit of the proposed project? This Small Business Innovation Research Phase I project will establish the feasibility of producing a novel class of amphiphilic graft copolymers to serve as thermoplastic hydrogel copolymers. Thermoplastic hydrogels are not available commercially and would be of great interest because, unlike conventional cross-linked hydrogel materials, they can be processed from solution or thermally into any form/shape via solvent casting, extrusion, thermoforming or hot melt injection. The proposed technology innovation will be achieved by the design of a series of amphiphilic graft copolymers with well-defined, adjustable macromolecular architectures with and without antimicrobial pendant groups along the chain. The project will explore a range of chemical compositions with variations in the chemical nature and concentration of hydrophobic grafts. The base polymer, poly(2-ethyl-2-oxazoline), is a commercially available polymer that is thermally stable, amorphous, water soluble, extrudable polymer. Physical crosslinks will be achieved by microphase separation. In the presence of water the hydrophilic backbone will swell. The degree of swelling and mechanical properties will be controlled by adjusting the macromolecular architecture tailored to the desired application requirements.
What are the broader/commercial impacts of the proposed project? The broader/commercial impact of this project will be to develop processible hydrogels tailored for specific applications for wound care, water purification membranes, ink jet receptive layers for printing and thermoform contact lenses. The ability to tailor the properties of these materials by controlled synthetic methods using living polymerization methods will greatly enhance their utility to serve these diverse industries. Thermoplastic hydrogels can be processed, whereas cross-linked hydrogels are insoluble and infusible. Low cost processing methods such as thermoforming, injection molding or extrusion offer significant economic advantage over many current hydrogel products on the market. Moreover, the ability to adjust the composition and tailor the hydrophilic/hydrophobic nature and microphase separation, which controls the degree of swelling, will enable the optimization of performance for a wide range of potential applications. The incorporation of non-leaching antimicrobial groups along the chain will enhance their utility in wound care and water purification membranes. Investigation of the surface and bulk morphology correlated to physical and thermo-mechanical data will help to obtain a better understanding of structure-property relationship of amphiphilic graft copolymers as a function of composition and observed morphology.
The proposed research aimed to address the need for a new class of commercially available hydrogel materials processible from solution or by thermal methods such as extrusion, injection molding or thermoforming. Typical hydrogels are chemically (covalently) crosslinked and therefore cannot be solution or thermally processed into desired shape/form after they are prepared. Thermoplastic hydrogels, such as those proposed in our research, are not commercially available and would be of significant interest for a wide range of applications due to their ability to be processed at any stage. The technology innovation proposed in this project aimed to utilize a combination of well established chemistry and new methods to prepare a novel series of amphiphilic graft copolymers as thermoplastic hydrogels with well-defined macromolecular architectures. These amphiphilic graft copolymers were to be designed with a hydrophilic backbone and phase separated hydrophobic graft segments that would act as physical crosslinks. In the presence of water these copolymer would swell but not dissolve. More specifically, these amphiphilic graft copolymers would have tailored chemical architectures comprised of Aquazol®, poly(2-ethyl oxazoline), as the main component (polymer backbone component). Aquazol® is Polymer Chemistry Innovations’ (PCI's) commercial product and is ideal as the major phase because of its unique properties such as: water solubility, amorphous character, well known polymer compatibilizer properties, excellent thermal stability and thermo-processing capabilities. Moreover, Aquazol® is a nontoxic polymer with FDA approval for indirect food additive, adhesive applications under 21 CFR 175.105. The hydrophobic graft segments were to be comprised of oxazoline-terminated polystyrene and/or oxazoline-terminated poly(benzyl methacrylate). The hydrophobic grafts are necessary to create the microphase separation in the presence of water. By selecting hydrophobic graft with high glass transition temperature mechanical integrity would be achieved. The properties of the thermoplastic hydrogels can be tailored by varying the chemical composition of the amphiphilic graft copolymers (the number of grafts per chain), the hydrophobic graft length (i.e. molecular weight) and the overall molecular weight of the poly(2-ethyl-oxazoline backbone polymer. The key technical objectives were to: Prepare a series of amphiphilic graft copolymers by living cationic copolymerization of oxazoline-terminated macromonomer and 2-ethyl-2-oxazoline comonomer; Chemically modify a select number of the amphiphilic graft copolymers with quaternary ammonium moieties for potential application in water purification and other membranes; Characterize the amphiphilic graft copolymers with and without quaternary ammonium groups to understand the structure-property relationship between a wide variety of chemical compositions and their resulting morphology. Investigate morphology variations of the copolymers when prepared from solution and melt mixing. Assess the properties of the copolymers in terms of their proposed commercial interests (i.e. film forming ability for coatings applications, membrane performance for water purification, and tensile properties and swell characteristics for other hydrogel applications). Four different synthetic approaches were investigated to prepare oxazoline-terminated macromonomer for the project. Three routes have been reported in literature and the forth was based on a novel approach using established chemistry. The three reported routes were all based on the concept of creating an oxazoline initiator and use that initiator to polymerize vinylic monomer such as styrene to create the oxazoline-terminated macromonomer. The novel approach prepared the polystyrene first and then reacted the oxazoline initiator onto the polystyrene containing a good leaving group. Unfortunately, PCI encountered unexpected synthetic challenges in preparing the oxazoline-terminated macromonomers. Several different synthetic routes were extensively investigated; however, initiator stability, percent functionalization and purity limitations of the oxazoline-terminated macromonomer prevented PCI from preparing the desired thermoplastic hydrogel proposed in this project goal. Low percent oxazoline functionality on the polystyrene macromonomer was unable to copolymerize with oxazoline monomer to form amphiphilic graft copolymers to serve as a thermoplastic hydrogel. Initial success in achieving this goal to create the oxazoline-terminated polystyrene was later determined to be physically bound to the polystyrene and not covalently attached. Repeated purification could not physically remove the impurity; however, when reacted with ethyl oxazoline monomer, thermoplastic hydrogel were not generated as determined by 1H NMR and swelling experiments. The polymer obtained dissolved in water and did not contain polystyrene phases. However, PCI will continue to evaluate alternative synthetic routes without public funding to achieve this goal and hopes to create the targeted product in the future. An unexpected positive result was that one new product (tosylate-terminated polystyrene macromonomer) was prepared during the project and may be commercialized by PCI in the future. Another positive outcome was the undergraduate technicians and graduate students hired for the project gained industrial experience in a chemical manufacturing company and had the opportunity to learn advanced level synthetic techniques during the project. In part, this experience enabled of all the students to secure full-time positions in the chemical industry.
