By Csongor Szabo, BASF product manager Capromer
Introduction
Polycaprolactones, or rather poly-ε-caprolactones, are used as synthetic building blocks to enhance the properties of coatings, thermoplastics, adhesives and elastomers so that the finished product meets the most demanding requirements. This makes new applications accessible and allows new products to be developed.
Polycaprolactones are formed by ring opening polyaddition of epsilon (ε)- caprolactone. The starting molecules are multifunctional alcohols such as neopentyl and diethylene glycol or trimethylolpropane. This has the advantage of not generating any byproducts such as water, for example.
The ring-opening polymerisation proceeds at temperatures ranging from about 120°C to 200°C, and can be accelerated by means of special catalysts.
This process gives low-viscosity products of defined functionality that are easy to process.
The additional benefits in terms of application include low-temperature flexibility and weathering resistance, as well as low viscosity.
BASF recently entered the market for polymeric intermediates by offering the polycaprolactone (PolyCLO) speciality polyester.
Under the Capromer product line brand, the company supplies several high-quality grades of polycaprolactone that are used as building blocks to produce high-grade coatings, TPUs, adhesives and cast elastomers.
Capromer bestows these products with excellent application properties and has convincing benefits in application, including consistent reactivity and low viscosity. Moreover, these polycaprolactones are biodegradable, so they can be used in bio-applications.
Properties
The polymeric intermediates of the Capromer line lend excellent processing and outstanding rheological properties to formulated products.
The highlights include low melt viscosity, which facilitates high-solids product formulations, and the outstanding batch-to-batch reproducibility of these properties.
Compared to conventional polyester polyols, Capromer products are distinguished by pronounced hydrolytic stability. Major characteristics that set them apart from polyether polyols are their excellent UV stability, well-balanced resistance to water and hydrocarbons, and high low-temperature flexibility. Capromers enable the production of high-solids formulations that feature low-VOC (volatile organic compound) levels.
Various product types are currently available that are based on a range of starter polyols including, for example, neopentyl glycol (NPG), diethylene glycol (DEG) or trimethylolpropane (TMP) and feature a range of low molecular weights (Table 1).
Additional grades are being developed continuously, in close cooperation with our customers.
All Capromer products have primary hydroxyl groups that guarantee consistent reactivity in reactions with isocyanates. NPGbased polycaprolactones with a molar mass of 1000 or 2000 are available in two different grades distinguished by their residual acid values.
The lowest acid values guarantee that the polyurethanes made from these products will feature the highest hydrolytic stability as specified for sealing applications, for example.
Table 1 shows an overview of product data.
The range also includes top-quality product grades (marked ‘A’) with extremely low acid values (<0.05).
Applications
Capromer polycaprolactones present benefits when used as binders to formulate high-quality paints and coatings.
They also serve to produce thermoplastic polyurethane (TPU) resins for the automotive industry and for sports and leisure applications.
Moreover, they are used as curing agents for polyurethane adhesives for applications such as the shoe and packaging industries.
Coatings
In high-performance PU coatings, the low viscosity and high reactivity of polycaprolactones of low molar mass are ideal for developing high-solids formulations or solvent-free PU coatings.
Outstanding weathering resistance, flexibility at low temperatures and hydrolytic stability are the properties that make Capromer products the ideal choice for these applications. In leather and textiles, hydrolytic stability and excellent flex-cracking behaviour at low temperatures are essential.
Capromer polycaprolactones can be used for clear and pigmented PU coatings, for example for automotive and industrial coatings.
In aerospace applications, too, polycaprolactones are used when VOC-reduced coatings are specified that must feature good UV and chemical resistance over a broad range of temperatures.
In two-component coatings, Capromer products are reacted with aromatic and aliphatic isocyanates, the advantage being the high reactivity of the primary hydroxyl group in polycaprolactones.
Typical end products include synthetic leather coatings or flooring for sports halls.
The benefits of Capromer polycaprolactones in coatings and textile coating applications can be summarised as listed below: • Outstanding weathering resistance and hydrolytic stability; • Chemical resistance; • Excellent flexibility, even at low temperatures; • Mechanical resistance (excellent resistance to impact, cutting, cracking and abrasion); • Low viscosity – which is essential in highsolids formulations; • Precise, controlled functionality with consistent reactivity as a result; • Excellent performance at high and low temperatures.
Thermoplastic polyurethanes (TPU)
Most of the advantages of using Capromer polycaprolactones that are explained above are also relevant in TPU applications.
This applies in particular to automotive industry uses, where high mechanical strength and low-temperature flexibility, chemical and UV resistance, excellent adhesion to a multitude of substrates and very good application properties are required.
Other benefits of polycaprolactones are also appreciated in this area:
• Low viscosity and ease of application;
• Stable, liquid prepolymer building blocks;
• Marginal fogging;
• Hardly any smell;
• Exceptional cut resistance and tensile strength;
• Good chemical resistance to aqueous media, oil and solvents.
Water- and solvent-based adhesives
Capromer polycaprolactones are frequently used as soft segments in the production of aqueous PU dispersions. Their use is supported by benefits relevant to processing, such as a narrow molecular-weight distribution and low viscosity, and by properties relevant to the product. These include good temperature resistance and hydrolytic stability, and very good adhesion properties on a range of substrates, including leather.
Polycaprolactones are equally used to produce solvent-based PU adhesives.
Capromers are a preferred ingredient because of their low viscosity, which enables developers to formulate high-solids adhesives, and because their potlife can be controlled. Typical applications are in the textile and leather industries, as well as in laminated packaging.
The major benefits Capromer polycaprolactones offer in adhesive applications include: • Good adhesion to polar and non-polar substrates; • Very good hydrolytic stability compared to other polyester polyols; • Resistance to oil, solvent and UV light; • Outstanding strength; • Suitability for low-temperature applications; • Non-toxic and biodegradable.
Polyurethane cast elastomers
Finished products made of cast PU can be found mainly in sports and leisure applications, for example as soles of sport shoes or wheels for skateboards. The key properties that make these prepolymers — which are stable and liquid at room temperature — a good choice for these applications include:
• Low initial viscosity;
• Narrow molecular-weight distribution;
• Excellent flex cracking properties at low temperatures;
• Outstanding cut resistance and tensile strength;
• High abrasion resistance: and
• Hydrolytic stability.
In the production of sport shoes, sports goods and automotive components, manufacturers can speed up automatic processing by using Capromers.
BASF — intermediates and service
This innovative BASF Capromer range is valuable for applications in coatings, TPU and adhesives around the world. The portfolio is being developed continually to better meet the needs of users. In addition, BASF’s integrated Verbund system in manufacturing and logistics guarantees flexible and reliable supply.
Where monomers with polyalcohol functionality are used in polymeric systems instead of polycaprolactones, 1,6-hexanediol (HDO) is a key intermediate.
A difunctional linear alcohol, HDO is used in manufacturing polyester polyols for PU elastomers, coatings and adhesives. BASF is a leading global supplier of HDO, producing 1,6- hexanediol at Verbund sites around the world by means of proprietary processes.
Backward integration into raw materials and intermediates ensures a maximum of resource conservation and environmental sustainability.
As for all of these key intermediates, the knowledge and expertise of BASF’s global experts is crucial, supplemented by BASF’s worldwide presence and service offering.
Cooperating closely with customers, the company develops new intermediates, tailored to suit the specific requirements of the any application at hand.
Hosting professional innovation workshops, developing new products in joint projects, running a dedicated application laboratory to offer technical assistance: these are just some of the efforts BASF makes to raise the added value for its customers.
