Polyurethanes (PU) are polymers composed of organic units joined by urethane links. PU polymers are generally formed by the reaction of a poly-isocyanate with a polyol. Polyurethanes which include carbonate linkages are called polycarbonate-polyurethanes (PC-PU). These PUs are extremely durable, high-performance materials that exhibit superior properties when compared to polyether-diol or polyester-diol based polyurethanes.
In relation to properties that are provided, PC-PU are used mainly in the manufacture of high-performance polyurethanes. The origin of these higher performances in the final polycarbonate-based polyurethanes, compared to their traditional counterparts as polyester- or polyether-based, is due to the presence of carbonate group in the polymer.
This group is much more stable against hydrolysis than the ester group and has greater stability against UV radiation and high temperatures that the ether group. Thus, the final polyurethane products including polycarbonate moieties present the advantage compared to those prepared with traditional
polyurethanes, a very high durability against degradation agents such as hydrolysis, chemicals, thermal degradation effect or UV.
Polycarbonate diols are generally used to produce polyurethanes that incorporate the carbonate linkages for superior performance. Polycarbonate-polyurethanes can also be produced through the use of polycarbonate-based polyurethane prepolymers.
A polycarbonate-based polyurethane prepolymer is a derivative of the corresponding polycarbonate diol in which all the polyol hydroxyl (OH) end groups have been reacted with an isocyanate leaving isocyanate groups (NCO) at the termini instead of hydroxyls.
There are several advantages of using PC-PU prepolymers in the production of Polycarbonate polyurethanes.
- Prepolymers are easier to handle as they are generally liquids or low-melting solids.
- In the absence of moisture, prepolymers are storage stable and provide a source of isocyanate functionality with lower vapor pressure (low volatility) as compared to free isocyanates.
- Prepolymers typically provide better compatibility with other PU formulation components due to their lower surface tension.
- Prepolymers also help produce a more uniform final polyurethane structure leading to improved polymer properties. They have a working pot life useful for both machine and hand-batching procedures.
Formulation Tips for PC-PU Prepolymers
PC-PU prepolymers are offered in a variable range of free NCO content to suit the desired polyurethane properties. About the formulation advice, PC-PU can directly replace current prepolymers in formulations in water-based, solventborne and 100% solids polyurethanes, just requiring minor modifications to adjust the formulation to the new prepolymer.
The prepolymer is cured by the addition of one or more diols, in proportion to the free NCO content, to complete the polymerization reaction. Even PC-PU prepolymers can be cured the adequate polycarbonate diol itself, here to obtain a system fully based on polycarbonate diol, not only the prepolymer but also the
crosslinking agent, that will avoid any weak group against sever aging conditions and maximize the properties retention in harsh environments. The properties of polyurethanes based on PC-PU prepolymers can be adjusted by using a single diol as a curative agent or a mixture of diols depending upon the desired properties.
A polycarbonate diol can be used as a single polyol, as well as blended with other standard polyols for curing. For maximum performance, in terms of durability, the use of a polycarbonate diol is recommended. Blending with other polyols allows formulators to incorporate the properties of polyester or polyether diols and reduce cost. The properties of PUs are considerably improved when polycarbonate diols constitute more than half of the polyol content.
PC-PU prepolymers can be used to formulate highly durable, high-performance polyurethane elastomers, coatings and adhesives. These materials retain their designed performance parameters even in harsh environments with little or no loss of initial properties.
What are the Top 3 Application Domains for Polycarbonate-based Prepolymers?
1. PU Elastomers
When compared to polycaprolactone and PTMEG based polyurethanes, PU elastomers based on PC-PU prepolymers exhibit:
- Extreme durability
- Higher chemical resistance
- Improved hydrolytic stability
- Greater thermal resistance
- Better abrasion resistance, and
- Superior mechanical properties
For instance, heating polycarbonate based polyurethanes in an oven at 120°C for 50 days typically causes only a 15-20% reduction in tensile strength, immersion in water at 80°C for 40 days leads to a less than 10% loss of tensile strength and weathering in a climate chamber for 1200 hours causes only a 5% decrease in strength.
Similarly, up to 91% of the original mechanical properties are retained after prolonged exposure to a harsh chemical environment.
Polycarbonate-based polyurethanes elastomers find applications in:
- Production of PU composites
- Cast urethane elastomers
- Rigid and flexible foams
- Sporting goods
- Shoe components
- High transparency PUs
- Wheels and tires
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- Thermoplastics PUs (TPUs)
- Waterproofing membranes
- Castable films
- Industrial parts
- Transport rollers, and
- High pressure nip rollers
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PC-PU elastomers have been successfully used to improve the performance and endurance of PU based elastomer rollers, boost the durability of composites in extreme conditions, and to enhance the durability of vibration reducing materials.
2. PU Coatings
PU coatings, based on PC-PU prepolymers have high thermal stability, exceptional scratch and abrasion resistance, super gloss retention, and are highly resistant to water, chemicals and staining.
These coatings show more than 85% reduction in yellowing due to weathering, more than 50% reduction in water absorption, almost 90% reduction in coating volume loss when exposed to harsh abrasion and almost 100% gloss retention after heat ageing as compared to polyether-diol or polyester-diol based polyurethanes.
PC-PU prepolymers are used in the production of high-performance coatings for wood, leather and automobiles. They also find applications in the production of inks, and specialized coatings for pavements, transparent glass, sports flooring and lining of abrasion-resistant pipes for the oil & mining industries.
3. PU Adhesives
PU adhesives formulated on PC-PU prepolymers exhibit enhanced adhesion properties, high thermal stability, superior hydrolytic stability and improved chemical resistance. These adhesives show up to 80% improvement in adhesion properties, 67% reduction of variation in initial adhesion properties after exposure to harsh hydrolytic conditions and 85% retention of initial adhesion properties after prolonged exposure to high temperatures.
PC-PU adhesives also show more than 85% reduction in yellowing due to weathering compared to PUs based on standard diols.
PC-PU prepolymers are used in the formulation of adhesives and sealants for the aerospace, automotive and footwear industries among other harsh and demanding environments. They also find applications in the production of adhesives for tapes, labels, packaging and lamination, and sealants for repairing cracks in floors & buildings.
Where can we find Polycarbonate-based Polyurethane Prepolymers?
Polycarbonate-based prepolymers and
polycarbonate diols are available from several suppliers, including:
UBE Industries Ltd offers a range of polycarbonate-based prepolymers under its brand name
ETERNATHANE®. They also offer the
ETERNACOLL® series of polycarbonate diols for the production of polycarbonate polyurethanes.
UBE Corporation Europe S.A. is the wholly owned subsidiary of UBE Industries, Ltd. for Europe and Latin America. Headquartered in Castellon (Spain) and with offices in Madrid, Düsseldorf, Mexico City and Sao Paulo, it manufactures and distributes caprolactam, polyamides, fertilizers and fine chemical products. The drive for product and manufacturing technology innovation and a commitment to sustainability and corporate responsibility are key management principles of the company.
