®TMTrademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow Page 1 Reactivity and Mechanical Performance of Polyurethane Films Made With CASE Dow Polyols and Isocyanates

Whether you’re developing formulations for electrical encapsulants or shoe soles , Dow Polyurethanes is the raw

material source you can count on for many of your coating, adhesive, sealant, and elastomer ( CASE ) formulation needs.

Dow offers a wide range of polyurethane raw materials, including VORANOL TM polyether polyols, VORANATETM TDI,

PAPITM polymeric MDI, and ISONATETM pure and modified MDI. In addition, Dow’s backward integration into the basic

feedstocks used to produce polyurethane chemicals gives us an important advantage in ensuring high quality and

availability of the products we sell.

Polyurethane chemistry is very versatile, as seen by the multitude of uses from bowling balls to flexible foam and

windmill adhesives . By changing the polyol and isocyanate components, you can greatly impact the final properties of

the polyurethane r esin . This brochure characterizes a small s ampling of the possibilities

.

Adhesives and sealants can be prepared using a single component (1K) system or a two component (2K) system. In a 1K

system, a prepolymer is prepared in wh ich one or more polyol s is reacted with a stoichiometric excess of isocyanate.

This prepolymer retains isocyanate functionality , but has an increased shelf life and lower volatility compared to pure

isocyanates

. This prepolymer is then mixed with plasticizers, fillers, antioxida nts, adhesion promoters, and catalysts

.

When this system is dispensed, the prepolymer reacts with ambient moisture to cure. In a 2K system, the polyol ( s ) and

additives are blended together to make up one of the two components. The isocyanate or prepolymer makes up the

second component. The se two components are mixed on site to cure the system . A 2K system typically allow s for a

faster reaction and better control over the curing conditions , but requires the ability to mix separate components at the

proper ra tio

.

The data presented in this report was generated using one component systems with polyol s and isocyanate s only to

compare resin properties without the influence of additives

. A sampling of Dow polyols and isocyanates listed in Table 1

were used to acc omplish this goal. For a more complete listing of the Dow polyols for CASE applications, see the

brochure entitled “ Supplying a Multitude of Products for Measurable Results: Polyols for Coating, Adhesive, Sealant,

Elastomer, and Electronic Applications .”

Table 1: Raw Material Information

Polyol Functionality OH Number Average

Molecular

Weight Viscosity at

25 °C, cSt Viscosity at

100°F, cSt Water, % Max

VORANOL TM 220

- 056N 2 56 2000 300 150 0.03

VORANOL TM 221

- 050 2 50 22 00 360 200 0.04

VORANOL TM 222

- 056 2 56 20 00 321 170 0.04

VORANOL TM 230

- 056 3 56 3000 4 80 245 0.03

VORANOL TM 232

- 034N 3 34 5 000 860 415 0.05

VORANOL TM 4000LM 2 28 4000 920 480 0.03

VORANOL TM B

- 2000 2 56 2000 610 230 0.04

Isocyanate Functionality NCO Content

by weight, % I.E.

Weight Viscosity, cP Description

ISONATE TM 125M 2 33.5 125.5 5 at 43°C Pure MDI

ISONATE TM 50 O,P 2 33.5 125.5 10 at 25°C Pure MDI with 50% o,p content

ISONATE TM 143L 2.15 29.1 144.5 33 at 25°C CDI modified MDI®TMTrademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow Page 2 In these formulations, the polyol side was first heated in a round

- bottom flask to 50°C. Benzoyl chloride was added to

stabilize the system. The isocyanate was then weighed into the round

- bottom flask and the mixture was heated to 80°C

.

After running the reaction for six hours, the material wa s analyzed for viscosity and %NCO

. Prepolymer f ilms were drawn

down between 20 and 30mil onto polypropylene sheets and cured with ambient moisture. Samples were taken from

these films for mechanical property testing following standard ASTM D 1708. Prepolym er and mechanical performance

data is presented in Table 2.

Table 2: Formulation Data

Component Formulations (parts by weight)

A B C D E F G H I J K

VORANOL TM 220

- 056N 50 100 100 100 100

VORANOL TM 221

- 050 100

VORANOL TM 222

- 056 100

VORANOL TM 232

- 034N 100

VORANOL TM 230

- 056 50

VORANOL TM 4000LM 100

VORANOL TM B

- 2000 100 100

ISONATETM 125M 20.3 14.5 13.0 19.7 25.6 32.2 30.6 32.2 33.0

ISONATE TM 50 O,P 20.1

ISONATE TM 143L 23.0

Prepolymer Properties

Prepolymer %NCO 2 2 2 2 2 2 3.5 5 5 5 5

Prepolymer Viscosity at 25°c, Pa.s 68.8 81.7 16.6 123.0 95.8 40.4 22.0 10.7 7.3 8.2 14.7

Moisture Cured Film Properties

100% Modulus, psi 104 162 61 170 123 179 155 308 310 344 410

Tensile Strength, psi 953 275 168 342 379 320 978 700 473 685 1082

Max Elongation, % 1459 227 1980 281 505 693 1945 1051 1078 1298 755

Shore A Hardness 44 49 30 47 42 51 47 62 67 68 67

In moisture cured film s such as these , the free NCO groups on the prepolymer react with atmospheric water to form

urea crosslinks. If one desires to use the se prepolymers in a two component elastomer

, the atmospheric water could be

substituted with a chain extender such as 1,4

- butanediol.

As highlighted in formulations A and K, VORANOL TM B

- 2000 based resins provide excellent mechanical pro perties in

addition to their excellent hydrophobicity. The VORANOL TM 4000LM resin shown in formulation C achieves a maximum

elongation of nearly 2000% at 2% N CO, which is difficult to do with conventional polyols. Formulation C also has a

significantly lower prepolymer viscosity than other typical formulations at 2% NCO. As a whole, the formulations in Table

2 show that with increasing isocyanate content (%NCO) , the maximum elongation tends to decrease while the 100%

modulus tends to increase.

In creating these films of varying compositions, a correlation drawn between Shore A Hardness and 100% Modulus is

shown in Figure 1 . This allow s for a quick screening of test formulat ions using S hore A Hardness as a comparison without

immediately having to run the microtensile tests. The data used for the correlation is a series of samples that includes,

but is not exclusive to, the data from the formulations in Table 2.®TMTrademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow Page 3 Figure 1 : Comparison Between Shore A Hardness and 100% Modulus

System reactivity depends on four main factors : polyol reactivity, isocyanate reactivity, acid/base balance, and catalyst

type/ loading. System reactivity is very important for several reasons: open /handling time

, tack

- free time , and because

the morphology of the system can organize differently depending on how quickly it reacts. A slow er reacting system may

react so slowly that as the system reacts, there is too much phase separation between the polyol soft segment and the

growing urethane hard segment. Depending on the system, it may not be visible immediately, but mechanical properties

could suffer

.

One way of controlling the sy stem reactivity is by changing the polyol backbone . Typical polyether polyols are

polypropylene oxide with either some or no ethylene oxide (EO) capping. I ncreasing the level of EO capping on a polyol

increases the primary hydroxyl content, which subsequently increases the reactivity

.

Another consequence of increased EO content is a higher affinity for water. If one makes a prepolymer using a polyol

with a high EO content

, such as VORANOL TM 222

- 056, that prepolymer will have a much higher affinity for water than a

prepolymer made using all

- PO polyols such as VORANOL TM 220

- 056N. This high affinity for water will draw in more water

in a moisture

- cured system, significantly increasing the rate of cure of the p repolymer and subsequently decreasing the

open time. VORANOL TM B

- 2000 is a very hydrophobic polyol, so prepolymers made with this polyol will take longer to

bring in atmospheric moisture and cure. 

### 0 10 20 30 40 50 60 70 80

0 50 100 150 200 250 300 350 400 450Shore A Hardness



### 100% Modulus, psi®TMTrademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow Page 4 The following reactivity comparison was done by making low % NCO prepolymer s on a rheometer using ISONATETM 50

O P, Dabco 33LV catalyst, and several VORANOL TM ~2000MW diols

. Figure 2 show s viscosity growth as a function of time,

which can be correlated to the reactivity of the system. There is a clear difference betwee n the reactivity of the higher

EO

- capped polyols, VORANOL TM 221

- 050 and VORANOL TM 222

- 056, the all PO polyol, VORANOL TM 220

- 056N, and the

hydrophobic polyol, VORANOL TM B

- 2000. The prepolymer made with VORANOL TM 221

- 050 has a much lower final

viscosity because VORANOL TM 221

- 050 has a slightly higher molecular weight than the other polyols, at ~2200g/mol.

Figure 2 : Viscosity Build for Prepolymers with Different Polyols

Because of the differences in final viscosity, it is helpfu l to view the data in terms of percentage of final viscosity versus

time. As shown in Figure 3 , this gives us a normalized picture of how each of the polyols reacts

.®TMTrademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow Page 5 Figure 3 : Normalized Viscosity Build for Prepolymers with Different Poly ols

From this, the picture is a little more straightforward

. VORANOL TM 221

- 050 and VORANOL TM 222

- 056 are more reactive

than VORANOL TM 220

- 056N and VORANOL TM B

- 2000 because of their EO capping . On the other hand, VORANOL TM B

- 2000

has a slower reactivity profile than the other polyols and will provide for significantly longer open times in the base case.

F o r m N u m b e r : 109

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