292 Lubricant Additives: Chemistry and Applications10.5.2 EFFECT OF COPOLYMER COMPOSITION ON RHEOLOGICAL PROPERTIES IN SOLUTION
10.5.2.1 Low-Temperature Rheology
Rubin et al. [95–101] and others [102] measured the intrinsic viscosity [η] of EP copolymers
as a function of temperature in various solvents (Figure 10.9). Intrinsic viscosity, a measure of
polymer coil size in dilute solution, is fairly insensitive to temperature for noncrystalline OCPs.
Semi crystalline copolymers undergo a precipitous drop in [η] as temperature drops below ∼10°C. In
this region, the polymer begins to crystallize, forming intermolecular associations that effectively
cause the molecule to shrink in on itself, yet remain suffi ciently solvated to remain suspended in
oil solution.
The viscosity of a dilute polymer solution often follows the Huggins equation [103]sp cc[]k′[]
2FIGURE 10.8 Schematic illustration of solid-state morphologies of four types of poly(ethylene-co-octene)
copolymers. # SCB/1000 C is defi ned as the number of side chain branches per 1000 backbone carbon atoms.
(Minick, J., Moet, A., Hiltner, A., Baer, E., and Chum, S.P., J. Appl. Poly. Sci., 58, 1371–1384, 1995. Reprinted
with permission of John Wiley & Sons, Inc.)# SCB/1000 CCrystallinity (%)Density (g/cc)45103020 30 40 5014 2 0700.86 0.87 0.88 0.89 0.90 0.91 0.92 0.96Type IType IType IIType IIType IIIType IIIType IVType IV
Fringed micelles
No lamellaeFringed micelles
LamellaeNo fringed micelles
LamellaeNo fringed micelles
Lamellae
No spherulites Spherulites Spherulites SpherulitesTABLE 10.1
Typical Physical Properties of Ethylene–Propylene Copolymers
Property Typical Value
Density (kg/m^3 ) 860
Heat capacity (cal/g °C) 0.52
Thermal conductivity (cal/cm s °C) 8.5 × 10 − 4
Thermal diffusivity, (cm^2 /s) 9.2 × 10 − 4
Thermal coeffi cient of linear expansion (per°C) 2.2 × 10 − 4
Source: Adapted from Corbelli, L., Dev. Rubber Tech., 2, 87–129, 1981.CRC_59645_Ch010.indd 292CRC_59645_Ch010.indd 292 12/6/2008 10:10:13 AM12/6/2008 10:10:13 AM