Silicone Base Rubber: 107 and 110 Raw Gum
title: "Silicone Base Rubber: 107 and 110 Raw Gum" description: "Technical overview of 107 and 110 silicone base rubber—viscosity grades, end-group chemistry, and supply chain position between DMC and compounded silicone." section: "midstream"
From Monomer to Gum
Silicone base rubber—commonly called raw gum or base polymer—is the high-molecular-weight PDMS intermediate that sits between cyclic siloxane monomers and compounded, formulated silicone products. Two grades dominate industrial supply: 107 gum (hydroxyl-terminated) and 110 gum (vinyl-terminated).
107 gum (also written as 107 silicone rubber or α,ω-dihydroxypolydimethylsiloxane) has silanol end groups (–Si–OH). These reactive hydroxyl terminations allow room-temperature vulcanization (RTV) via condensation with crosslinkers such as TEOS or methyltrimethoxysilane. It is the feedstock for RTV-1 and RTV-2 sealants, potting compounds, and release coatings.
110 gum carries vinyl end groups (–Si–CH=CH₂) and may also incorporate vinyl side-chain substitution. Vinyl groups enable platinum-catalyzed addition cure at elevated temperatures, making 110 gum the backbone of liquid silicone rubber (LSR), high-consistency rubber (HCR), and medical-grade silicones.
Key Specification Parameters
| Parameter | 107 Gum (Condensation) | 110 Gum (Addition) |
|---|---|---|
| End group | Hydroxyl (–OH) | Vinyl (–CH=CH₂) |
| Molecular weight | 400,000–600,000 g/mol | 500,000–800,000 g/mol |
| Viscosity (raw) | 10,000–100,000 mPa·s | 5,000–80,000 mPa·s |
| Cure mechanism | Condensation (RTV) | Platinum addition (HTV/LSR) |
| Typical Pt inhibitor risk | None | Yes — avoid tin, amine, sulfur |
Viscosity is the primary commercial grade differentiator. Buyers specify gum viscosity (in mPa·s or centipoise) rather than molecular weight because viscosity is easier to measure in-line and correlates directly with processability in mixing equipment.
Supply Chain Position
Raw gum is produced by ring-opening polymerization of D4 or DMC in the presence of a base or acid catalyst, with chain-length controlled by the ratio of terminating agent to monomer. Production is tightly integrated with DMC manufacturing; the major Chinese silicone producers (Wynca, Xinyaquan, Dongyue, Jilin Chemours) do not sell 107 or 110 gum as primary merchant products—they convert it internally to compounded rubber, sealant bases, and emulsion polymers.
Merchant gum is available from mid-tier Chinese producers and from toll-polymerization converters. Quality variation centers on molecular weight distribution (PDI) and residual cyclic content—low-quality gum with high D4/D5 residuals causes fogging in automotive applications and blooming on cured silicone surfaces.