Lubricant Additives

Olefi n Copolymer Viscosity Modifi ers 291

Polyethylene is a rigid, high-modulus solid at room temperature. Amorphous E/P rubber is

a relatively soft material under ambient conditions, which, cold, fl ows and exhibits a tacky feel.

The degree of tack is inversely proportional to its molecular weight and can be reduced by the

incorporation of long-chain branching. Solid bales of this type of rubber are easily compressed

and further densify during storage. Semicrystalline OCPs hold their shape during storage but are

slightly tacky to the touch. Higher compression pressures, longer compression times, and higher

fi nishing temperatures are required to successfully produce dense bales. Typical physical properties

of E/P copolymers are summarized in Table 10.1.

FIGURE 10.6 The effect of ethylene content (wt% as measured by NMR) on ethylene–ethylene (EE) and

ethylene–propylene (EP) dyad concentration.

0.2

0.3

0.4

0.5

0.6

0.7

0.8

45 55 65 75 85

Ethylene content (wt%)

Dyad mole fraction

fEp+fEp*

fEE

FIGURE 10.7 The effect of ethylene content (wt%) on crystallinity as measured by differential scanning

calorimetry (DSC) for a range of experimental EPDM copolymers.

DSC heat of fusion (J/g)

0

10

20

30

40

%Ethylene

50 60 70

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