This Small Business Innovation Research (SBIR) Phase I project aims to use a cost-effective process of polymeric evolution to yield hydroxyl-terminated aliphatic polycarbonate dendrimers of precise shape to be used in formulating 100% solids two-component polyurethane coatings. The highly-crosslinked core will provide hardness, chemical resistance and toughness in the cured coating. The surface will be chemically modified to reduce viscosity and improve flow. The shape of the dendrimers will be designed to delay the activity of the catalyst, extending the pot life, while also allowing the release of the catalyst for a quick cure.
The broader/commercial impact of this project will be the potential to make 100% solids two-component polyurethane coatings more widely accepted. Currently the short pot life of two-component polyurethane coatings relative to the cure time has limited their applications. By providing extended pot life and increased performance, the dendrimers to be developed in this project is expected to enable the widespread adoption of zero-volatile, thus more environmentally-friendly, two-component polyurethane coatings.
The intellectual merit of this Phase I project was to demonstrate the use of a proprietary natural growth process to produce nanotechnology of specifically complex structure in a cost effective manner. Synthesis of high molecular weight molecules for use in nanotechnology is very expensive because of the conventional synthetic approach used. Consequently their applications are limited to markets such as medicine or microelectronics which can absorb their high cost. Within this project, dendrimers, spherical polymers with a specific core and surface like a living cell, were produced and their application to form high performance polyurethane coatings with little or no solvent was demonstrated. Unlike conventional chemical synthesis which treats molecules as building blocks that can be forced together, natural processes undergo a stochastic process of cyclic patterns of growth, destruction and regrowth until complex molecules and structures evolve by selective advantage. Within this project we were able to demonstrate the cost effective production of aliphatic polycarbonate dendrimers in which the dendrimer shape evolves due to the selective advantage of thermodynamic stability. We were also able to demonstrate unique chemical considerations behind such natural growth process which can be utilized to design other natural growth systems. 1. Dendrimer Synthesis: The first step of the project was to demonstrate the cost effective synthesis of large dendrimers using our proprietary process we call evolution polymerization. The environment of the core and surface of dendrimers were studied by graduate students at Princeton University Department of Chemistry, who determined specific hydrophobic and hydrophilic regions using fluorescence probes. An important finding during this project was how to consider multiple competing reactions which are common in natural growth processes. The natural growth studied consisted of two chemical processes; polycarbonate polyol growth and polymer evolution into a dendrimer. We found it was incorrect to consider the polymer growth as a first step followed by evolution into a dendrimeric shape. Rather, the optimum process for forming large dendrimers did not force the polymer growth first, but let both the size and the shape of the dendrimer evolve together. We believe this was the first example of harmonic addition of chemical processes. In this manner large dendrimers could be formed without significant flaws within the core. The optimized process proved consistent with many natural processes in which specific thermal conditions are required for "incubation" in order to be warm enough for the process to proceed, but not high enough to form irreversible byproducts. 2. Derivatizing Dendrimer Surface: We were able to attach alkyl groups to the surface of the dendrimer, via linkage to the hydroxyls, in order to make them more compatible with isocyanate reactants. This is essential for forming two-component urethane coatings. Alkylation of the dendrimers was also shown to dramatically reduce the viscosity of the dendrimers; essential for forming coatings with no solvents. In a broad sense this demonstrated the ability to manipulate the surface of a dendrimer in order to make it compatible with its environment. 3. Testing in urethane coatings: Two-component polyurethane coatings are formulated by blending a high molecular weight polyol with an isocyanate reactant. We were able to demonstrate that the low viscosity of the dendrimers produced in this project helped reduce the amount of solvent required to formulate a polyurethane coating. The highly branched polycarbonate core was also shown to offer performance characteristics above those of commercially available polyurethane coatings. Furthermore, the cost of the dendrimers made their price competitive to current polyol technology. Samples were given to coatings manufacturers who were hungry for a means to formulate polyurethane concrete coatings in order to meet new Southern California Air Quality Management District (SCAQMD) regulations. The high performance of these dendrimers in urethane coatings, along with their low cost, has already resulted in orders for some of the more primitive forms of technology developed within this project. 4. Environmental impact: All raw materials used to produce this technology can be derived from natural, sustainable sources. The only byproduct of the synthesis is methanol which can be sold to produce biodiesel. The high performance such as durability and adhesion seen with urethane coatings made using this technology will minimize repainting and will eliminate the use of primers in many applications. The dendrimers produced within this project will specifically be utilized to formulate low cost, high performance polyurethane coatings with little or no volatile solvents. However, from a broader sense these dendrimers can be utilized in other markets. Like the natural cycle of carbon dioxide, water, sugars and oxygen has led to the proliferation of a wide range of complex natural structures, we ultimately will also be able to design the production of a wide range of complex structures using the technology within this project. We also expect the harmonic addition of other natural growth processes will broaden the potential of this technology.
