One-Component Heat Curable Urethane Liquid Elastomers
Abstract Quite clearly this study does not fully achieve the objectives stated earlier. The data show that fairly good quality storage stable one-component elastomers may be produced from acrylic modified urethane oligomers thermally cured with polyfunctional mercaptans and peroxide. Unfortunately, some of the advantages of a liquid system are lost because a reinforcing filler must be added in order to achieve acceptable physical properties. At the levels studied in this design, the filler and % hard segment play only a minor role in influencing the physical properties of the system. Those oligomers with low average functionality and low unsaturation appear to give the best physical properties, and further improvements may be achieved by looking at higher molecular weight polyols which, for a given functionality, will produce oligomers with lower unsaturation. Clearly, our screening study was not extensive enough to fully elucidate the utility of this concept. In order to determine what order of properties may be achievable by this approach, it will be necessary to design experiments that consider the effects of the other variables not evaluated in our initial study. For instance, we held the mercaptan constant throughout this work. It is trifunctional and was used at a 10% excess. Beneficial effects may be achieved with less than an excess or a greater excess or by evaluating mercaptans with reduced or elevated functionality. The cure conditions should be optimized and the effect of conventional rubber accelerators or additives screened. The oligomer for the most part consists of a polyol. We chose to evaluate only the 1500 equivalent weight polyether polyols for most of our preparations. We indicated earlier that it may be beneficial to look at higher equivalent weight polyols in order to minimize the unsaturation for a given functionality. Also, urethanes derived from polyester polyols generally possess superior physical properties compared to those based on polyethers, and it may be worthwhile to examine polyester polyol based oligomers. Carbon black, as well as fully adequate mixing, should be looked at to completely define the process.