PIB Bis-Succinimide at 5–10 wt% is the primary dispersant component in modern API CK-4/ACEA E9 HDEO packages - its superior shear stability and high-soot viscosity control make it the standard choice for long-drain applications where mono-PIBSI performance is insufficient at end-of-drain. At 7 wt% treat of a PIB MW 1100 grade (N% 2.0%): total N contribution to finished oil ≈ 0.14 wt%; viscosity contribution ≈ +20 cSt @100°C to be accounted for in finished oil SAE grade calculation; S/A, S, P contribution = 0. In EGR-intensive 15W-40 HDEO (typical truck fleet lubricant), bis-succinimide provides the dispersancy backbone that enables compliance with API CK-4 Mack T-13 viscosity increase ≤12 cSt @100°C at 4 wt% soot loading.

Premium European long-drain PCMO specifications (VW 504.00/507.00 up to 30,000 km; BMW LL-04 up to 25,000 km) require dispersancy capacity that is sustained through the entire extended drain - a challenge that exposes the shear degradation weakness of mono-succinimide. Bis-succinimide at 4–8 wt% provides the shear-stable dispersant backbone for these long-drain formulations, typically used alongside a smaller treat of mono-PIBSI to achieve the optimal balance of Sequence VH sludge rating (mono-favoured at low soot) and long-drain soot viscosity control (bis-favoured at high soot and end-of-drain). In ACEA C3 formulations (S/A ≤0.8%, S ≤0.3%), bis-succinimide treat rate can be freely optimised without any SAPS impact.

Bis-succinimide is the preferred dispersant in automatic transmission fluids (ATF), CVT fluids, and high-performance manual gear oils where the extreme shear environment of the transmission requires a dispersant that maintains molecular integrity throughout the transmission fluid's service life. In ATF, bis-succinimide at 3–6 wt% provides the dispersancy needed to prevent varnish fouling of valve body passages and clutch plates - conditions where mono-succinimide's lower shear stability results in progressive dispersancy loss over the first 30,000–50,000 km of transmission use. The dual PIB anchor of bis-succinimide survives transmission shear conditions far better, providing consistent varnish and sludge control throughout the fluid's lifetime.

In marine TPEO and gas engine oils where service intervals of 1,000–4,000 hours create sustained thermal and mechanical stress on the dispersant molecule, bis-succinimide's superior thermal stability (the fully closed both-end imide structure has fewer reactive sites for thermal decomposition vs. the one-end-open mono-succinimide) provides better sustained dispersancy over the extended service period. In gas engine oils, bis-succinimide effectively disperses nitrated polar by-products from NOₓ blow-by - the internal –NH groups of the polyamine bridge H-bond with nitro-compounds, maintaining them in suspension and preventing varnish formation on piston crowns and valve train surfaces over the 2,000-hour drain intervals typical of premium gas engine oil service.

Q: Why does PIB Bis-Succinimide have higher N% (1.5–3.5%) than mono-PIBSI (0.8–2.5%) when the bis structure closes both terminal amine groups into imide rings?

This is a common source of confusion. The higher N% in bis-succinimide does not come from having more free terminal –NH₂ groups (in fact, the bis structure has fewer free terminal amines than mono - both ends are ring-closed). The higher N% arises from two sources: (1) the polyamine chain used in bis-succinimide synthesis is longer (e.g. TEPA = tetraethylenepentamine with 5 N atoms, or PEHA = pentaethylenehexamine with 6 N atoms) - the longer chain is necessary to allow both ends to reach and react with their respective PIBSA units, and this longer chain brings more internal –NH nitrogen atoms per molecule; (2) the bis-succinimide molecule contains two imide ring nitrogen atoms vs one in mono-succinimide. The net effect is that although the percentage of free terminal –NH₂ is lower (those are ring-closed), the total N content per unit mass is higher. The active dispersant sites are the internal secondary amine groups (–NH–) along the polyamine bridge, not the terminal positions - these remain chemically active for H-bonding with soot surfaces in both mono- and bis-succinimide.

Q: In a new HDEO formulation, should I use mono-succinimide, bis-succinimide, or a blend?

The industry-standard answer for modern API CK-4/ACEA E9 HDEO is a blend of both, with bis-succinimide as the majority component. The practical guide: if your formulation must pass both Mack T-13 (high-soot viscosity - requires bis-succinimide's shear stability) and Sequence VH equivalent (sludge at low soot - mono-PIBSI's free terminal N is marginally better), a blend ratio of 60–70% bis / 30–40% mono typically achieves both simultaneously. If the primary driver is long-drain EGR-heavy duty (e.g. Volvo T-13, Shell Rotella long-drain spec), increase bis-succinimide ratio to 70–80%. If the primary driver is PCMO sludge/varnish (Sequence VH dominant), increase mono-PIBSI ratio to 50–60%. For ATF or CVT fluid, use 80–100% bis-succinimide due to the shear stability requirement. Sinolook can supply both grades and provide technical formulation support for optimising the mono:bis ratio for your specific application.

Q: Does PIB Bis-Succinimide contribute to finished oil viscosity grade, and how should it be accounted for in SAE grade formulation?

Yes - PIB Bis-Succinimide at 100–600 cSt @100°C contributes meaningfully to finished oil kinematic viscosity, especially at the 5–10 wt% treat rates typical in HDEO. At 7 wt% treat of a grade with viscosity 350 cSt @100°C, the dispersant's contribution to finished oil viscosity at 100°C is approximately 7% × (350 − 4) cSt ≈ +24 cSt above the base oil contribution - significant relative to the SAE 40 target of 12.5–16.3 cSt. This contribution must be included in the blending calculation: use the blending viscosity formula (Refutas index or ASTM D341 blending) with each component's viscosity at the blend temperature. Higher MW bis-succinimide grades (PIB >1500) have proportionally higher viscosity contributions - at 10 wt% treat of a 500 cSt grade, the contribution approaches +49 cSt, which would make it impossible to formulate a SAE 30 or 40 grade without compensating with a lower-viscosity base oil. For SAE 30/40 HDEO, use PIB MW 900–1100 bis-succinimide (viscosity 150–300 cSt) at 5–8 wt% to keep viscosity contribution manageable.

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