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Polyurea: The slower dimension of a fast reaction





Polyurea, as considered in this paper, is the reaction product of primary or secondary amines with an isocyanate. By definition, the Polyurea has to have 100% reactive amines and no hydroxyl group containing materials are included. The reactive amines react with a quasi-prepolymer with typically 13 – 16% remaining NCO content. The name “Polyurea” is often misused for hybrid systems containing polyol blends or other hydroxyl group materials which lead to a two-step reaction profile and limited physical properties.


The demand for shorter turn around and processing time, good resistance against chemical attack, abrasion and thermal shock as well as the adjustable properties for elongation (< 200 % to > 1200%), tear and tensile strength or hardness (< Shore A 70 to > Shore D 65) make polyurea more and more often the best choice for various applications including vertical and fibre reinforcement installations.


fibre reinforced spray application


The broad application window for polyurea under various environmental conditions (e.g. temperature, humidity and various substrates) allows it to perform throughout the year. Legislation on reducing volatile organic compounds (VOC) in coatings has recently increased the market interest in polyurea coatings because they are 100% solids and autocatalytic thus they do not emit VOCs.


Typical elastomer properties are:

Tensile strength

up to 35 MPa

Shore hardness

A 70 – D 65


up to 1200 %

Tear strength

up to 40 N/mm

Tear resistance

up to 125 N/mm

Abrasion resistance

0.1 mg / cycle and up

Cure time

3 seconds up to
approx. 8 minutes


1 g/cm³


History …

Polyurea has been used in the industry since the late eighties. Initially, the main polyurea application was the production of RIM (Reaction Injection Moulding) parts for the automotive industry, e.g. as bumpers and fascia parts. The main advantages of these RIM parts were: 1) continuous production-line painting along with the conventional steel parts and 2) excellent impact resistance.

Although the polyurea technology was quickly proven in industrial production, a pause occurred due to adjustment problems between the highly reactive chemistry and the available RIM-equipment. However, in the past five years new applications for thin automotive fascia parts with excellent production-line paintability have gained a larger share in industrial production.

In addition to the RIM application, chemical and technical advances in the early nineties allowed new application options for spraying polyurea systems which found application in various types of protective coatings, e.g. flooring, roofing, pipelines, tank and marine linings or insulation foam protection; typical products for these applications are PC® DMD 16 and PC AMINE® DAX 126 D or on concrete PC AMINE® DAX 126 DS. Polyurea fulfilled the desire to return the facility back into service shortly after the coating is applied. Widest known applications are corrosion protection, e.g. for rail cars or steel constructions, and concrete coatings. Most prominent are secondary containments due to the good adherence to pipes, tank fittings or the concrete. More recently polyurea products like PC® MD 15 and PC AMINE® DAX 6 or PC AMINE® DAX 7 have been applied to parking decks or traffic areas incorporating a non-skid type aggregate material for grip and traction purposes or using an appropriate spray technique. Often, polyurea spray systems are used in combination with adhesion promoters like PC® ADD EAP 236 or PC® ADD SAP 220 to further improve the already good adhesion.


Steps to success …

Although polyurea applications have become more and more “forgiving” from an end user’s point of view, it should be mentioned that this is dependent on three major considerations:

1. The continuous training of the
    applicator or contractor
2. The equipment and maintenance
3. The right formulation, adjusted to
    the application


Among a number of other variables, these three are the decisive factors for either a successful application or costly coating failures.

To avoid health hazards protective pre-cautions should be followed and protective clothing, eye protection and respirators are necessary in many cases.


The evolution…

Due to the high and autocatalytic reactivity of the amine with the isocyanate and the co-existing mixing problems of the polyoxyalkyleneamines (PC AMINE® DA and TA series) with aromatic isocyanates, it became necessary to use the amine in combination with these so called curatives such as DETDA (Diethylenetoluene diamine, PC AMINE® ADA 180). The main function of curatives is the better miscibility of the amine blend with the aromatic isocyanate prepolymers.


Unfortunately, another effect of the use of DETDA (using typically 20-30% on the amine resin side) is the acceleration of the reaction, and the processing time is less than 5 seconds. The limitations resulting from the reaction speed lead to the requirement of high pressure equipment, preheated products (typically 70°C) for reduced viscosity, heated hoses and impingement mixing for fast spray application of the rapidly setting material. This sophisticated equipment is  needed specifically to insure a complete reaction and also to achieve a 100% mixture of the linear amines and the aromatic isocyanates. Today a wide variety of such equipment is available including parallel injection of reinforcement fibres or rotational spray equipment for vertical and horizontal pipes using circular spray or centrifugal spinners.


high pressure spray gun

typical high pressure machine equipment


Finding the right balance of the reaction is the major problem in daily application. In order to achieve the desired final properties, the good mixing operation is essential. For achieving slower and more balanced reaction profiles various attempts have been made. Only very few of those followed the polyurea chemistry, while most attempts were modifications with hydroxyl groups containing products which lead to a hybrid system with weaker physical properties and application troubles like pin holes et cetera. These hybrid formulations eliminate the most significant advantage of polyurea which is the autocatalytic reaction. That means no catalysts are used and so, without catalysts, the isocyanate reaction with humidity or water is not accelerated, reducing or even eliminating the risk of pin holes or side reactions and providing a good hydrolysis stability.


Amine resin side


46,7 %


24,6 %


27,8 %

Adhesion promoter like PC® ADD EAP 236

0,9 %

Quasi Prepolymer with 15% free NCO

typical spray coating formulation

This paper will only consider formulations within the previously defined polyurea scope and no hybrid formulations or systems containing carbonates.


First steps for slower curing and balanced reaction…

Some improvements have been done so far:

1.      In some instances, DETDA (PC AMINE® ADA 180) was replaced by either secondary amines with steric hindrance such as Unilink 4200 and halogen containing curatives as MCDEA or sulphur containing products like Ethacure 300. These DETDA substitutes show slower reaction speeds and allow a better, more self-levelling spray pattern as well as better surface wetting and thus better adhesion performance.

2.      A more efficient approach is the use of sterically hindered isocyanate prepolymers (like the PC® MD and DMD series) with a high content (if possible in the range of 50%) of 2,4’-MDI instead of 4,4’- MDI. This allows the highly reactive (4,4’- MDI) group to react first during the prepolymer formation. Then the less reactive (2,4’- MDI) groups remain for a smoother reaction with the amine, allowing a more homogenous Polyurea formation.


Based on this hindered isocyanate prepolymer approach, Nitroil® Performance Chemicals introduced recently a range of high 2,4’- MDI content prepolymers like PC® MD 13, DMD 13, MD 15, DMD 16 or MD 20 to the market in combination with amine resin formulations like PC AMINE® DAX 6, 7 or 120, 123, 127, 128. These allow an increase of the reaction time up to 25 seconds without any OH groups from polyols or carbonates which create the well-known problems in the application.

The extended urea formation period allows a better wetting and penetration of the surface, better chemical linkage development and self-levelling properties for smoother surface structures. These steps achieved the desired performance for most high pressure spray applications. However, the achievement of increased reaction times for spray systems created the desire to retard the polyurea reaction even further so that slower, castable formulations could be obtained.


The second step towards controlled reaction…

Following this first generation of slower curing polyurea (PC® MD / DMD series and PC AMINE® DAX 127 / DAX 127 D) we set about the task of developing a new, slow dimension of low reactivity without any halogen groups or sulphur substituted / sterically hindered secondary amines.

The newly developed “oligoamines” are tailor made products which combine excellent reactant miscibility with smoother processing  and bring about the finished product flexibility and excellent elasticity all in just one amine.

This new generation of “oligoamines” can be adjusted to the prepolymers to be used solely on the amine side e.g. as PC AMINE® ADA 520 D or for combination with standard amines such as the polyoxyalkyleneamines (PC AMINE® DA and TA series) in form of the PC AMINE® ADA 355 among others.


The following PC AMINE® ADA types are two examples of such tailor made products for both single use and complimentary formulation from a broad series of PC AMINE® ADA amines and curatives.




Formulation 1

Formulation 2

Amine side

100 % PC AMINE® ADA 520 D

45,7 % PC AMINE® ADA 355
54,3 % PC AMINE® DA 2000


PC® DMD 16

PC® MD 13

Typical properties

Shore A           : 90

Shore D           : 40

Pot life             : 30 sec

Elongation        : 450 %

Shore A           : 89

Shore D           : 36

Pot life             : 30 sec

Elongation        : 1000 %

(Table: typical formulations / typical properties)


cartridge application for control samples




application of PC AMINE® ADA 520
with PC® DMD 16


Almost limitless versatility…

 (Table: variability in elongation properties, PC AMINE® DAX types in combination with PC® MD 13)



From the above chart it can be seen that the various products demonstrate different elongation properties, especially for the scope of castable materials. For many applications, it is essential to determine the right elongation to maintain sufficient durability and flexibility at various stages of expansion or contraction. The same considerations apply for crack bridging applications where the selection of the right product with the right elongation, cohesion and adhesion properties is the decisive factor for either a successful application or costly coating failure.

Other criteria apply where perpendicular force properties are essential for normally spray-applied coatings being exposed to physical surface impacts. For such applications products like PC® MD 15 and PC AMINE® DAX 6 S and PC AMINE® DAX 7 S are recommended. These allow the polyurea coating to offer enhanced resistance to movement or displacement when exposed to intense or concentrated surface forces or impacts.


The slower reacting products allow a significantly better wetting and penetration of substrate surfaces to achieve significantly better mechanical bonding. In addition, the application is much easier and does not necessarily require pre-heated components or the specialized, large, heavy, heated, plural-component, high pressure, impingement mixing spray equipment.

The use of smaller, easier portable equipment and products like PC® MD 15 and PC AMINE® DAX 12 S allows a new dimension also of Polyurea coatings, e.g. for plant maintenance, balconies, small repair jobs, mining applications and more.


PC® OL 220 spray assembly

However, the major advantage of this development is the suitability of Polyurea for many additional non-spray applications, e.g. for cast applications as joint-filler, sealants and for electronic encapsulation.


PC AMINE® DAX 12 DS and PC® DMD 16
used as cable casting


PC AMINE® DAX 117 BL and PC® MD 15

control cable sealant for airport runways, suitable for highway applications as well


In the use as a residential, industrial or communal repair material polyurea catches more and more attention. As can be seen in above reference pictures the synthesis of fast installation and an expected service life of far more than a decade as well as adjustable properties towards the specific requirements as flame retardancy, elasticity or adhesion offer daily new fields of application.


Furthermore, this technology makes polyurea very attractive for two additional fields of application: as very reliable adhesive or for smaller mould parts such as gaskets. 
Especially in the application as adhesive or binder with small single use cartridge systems, it has the distinct advantage over other alternatively used materials in that the final curing is faster and it is significantly more resistant to climate influences during the application.


The flexibility and physical properties provide an excellent suitability for various applications including automotive, industrial and residential where long-lasting working/service life is essential.

PC AMINE® DAX 117 and PC® MD 15

polyurea impregnated glass fibre mats for
extremely increased dimension stability


Due to its excellent compatibility with reinforcements like glass fibres, it is also appropriate for applications where very high dimensional stability is essentially required. The advantages of this are even advanced impact resistance and structural stability. For the application these could be either automatically injected fibres in high pressure spray applications (standard equipment combined with a glass fibre chopper) in combination with products like PC® MD 15 and PC AMINE® DAX 6 or manually applied impregnated glass fibre mats e.g. for patch repair in waste water channels or industrial pipes using materials
like PC® MD 13 and PC
AMINE® DAX 117 along with low pressure casting equipment. The reinforcement of polyurea materials is especially enhancing the tear and puncture resistance in the final product.

An additional advantage of the castable polyurea is the simpler and more cost effective equipment that can be used. The newly engineered PC® OL 220 low pressure machine handles casting, sealing and spraying at comparably very low cost.



joint sealant application using the PC® OL 220 joint filler assembly



PC® OL 220 machine equipment


spray kit for the PC® OL 220 allowing fast conversion from cast to spray

and easy maintenance


Polyurea moulded parts are produced in two different methods: in a production line or in the field on the construction site. There are various potential applications, the following were introduced about one year ago:

In the production of moulded parts for railroad construction, both methods are employed. Rail track mounts are an example of an industrially moulded part, produced in a production line. These track mounts provide the unique polyurea properties of high impact resistance, sound and shock absorption, and provide long product service life. Rail cushions are an example of a moulded polyurea part, produced on site in various shapes to relaxed tolerances, for use in rails carrying slower, inner city or underground trains.


A novel developmental use for moulded polyurea parts has been in the electronic and electric office appliances areas as gear wheels for various paper feeders in platens for printers, copiers and fax machines as well as in full scale newspaper printing units. Polyurea has also been used as a sealant to aggressive printing inks and toner compounds; here the properties of polyurea in terms of high heat resistance, long lasting elastic properties and chemical resistance provide the essentially needed product parameters and offer prolonged service life.

Furthermore, in fields of the composite industry, polyurea is used to replace the unsaturated vinyl esters in open mould spray or reinforced layer applications. Here, the main advantages are no VOCs or emissions and significantly shorter manufacturing times.


Flame retardancy in polyurea applications is quite often a critical issue and spray coating applications are normally used to match extreme demands in physical resistance, as abrasion, impact or thermal stability. That reduces the options for the use of flame retardants, especially since many materials convert the polyurea into a hybrid. Others, TCPP, as an example, besides their emissions are known to negatively influence the mechanical properties, acting as a softener. Several other flame retardants do as well. PC® ADD FR P1 as a reactive type (in combination with selected hardeners), prevents such effects: physical parameter deterioration as well as emissions. An alternative way for polyurea flame protection is to increase its content of aromatic rings. Different amine resins developed by Nitroil® Performance Chemicals, normally used in castable systems, have been tested, and, among others, especially some of the higher-aromatic PC AMINE® ADA grades, proved to be remarkably supportive in flame retardancy. Nevertheless, due to its price this material will be used mostly for high-end applications at the moment.


There is an almost limitless degree of versatility for polyurea applications using the newest developments in quasi-prepolymers and amine chain extenders or amine compounds.

We hope that our raw materials or preblended components will interest various industries and application designers and support polyurea chemistry to continue on its growing success across industry. So far, imagination seems to be the strongest limitation to applying this versatile chemistry.

The two steps of speed reduction discussed in this paper will hopefully help to bring the numerous advantages of pure polyurea materials to such applications where pure polyurea formulations have so far not been used because they were too fast in the past or hybrid systems with weaker physical properties had been used. Thus, the slower curing polyurea presented shall bring the significantly better properties to those applications commonly served by other materials.



The authors wish to thank Michael Bader of INPUT – Institute for Polyurethane and Polyurea Technology for his work in formulation, preparation of samples and operating the cast equipment.


1.      “Polyurea Systems for Casting and Adhesives”, M. Bader, Institute for Polyurethane Technology, presented by R. Milian on the PDA 2001 Meeting

2.      tensile strength test methods: DIN 53504 or ASTM D 412


Unilink is a registered trademark of UOP Corp.
Ethacure is a registered trademark of Albermarle Corp.
PC and PC AMINE are registered trademarks of Performance Chemicals, Germany