c008 — Polysilicone-15 (Parsol SLX)
Section 1: Identity
| Field | Value | Conf. |
|---|---|---|
| INCI | Polysilicone-15 | C1 |
| IUPAC (representative repeat unit) | "α-(trimethylsilyl)-ω-(trimethylsilyloxy)poly[oxy(dimethyl)silylene]-co-[oxy(methyl)(2-{4-[2,2-bis(ethoxycarbonyl)vinyl]phenoxy}-1-methyleneethyl)silylene]" | C1 |
| Other name | Dimethicodiethylbenzalmalonate (the older Cosmetics Europe name); benzylidene malonate polysiloxane | C1 |
| Trade name | Parsol SLX (DSM-Firmenich, formerly Hoffmann-La Roche / DSM) | C1 |
| CAS | 207574-74-1 | C1 |
| Polymer / oligomer (variable molecular weight) | average Mw ≈ 6,000 g/mol (manufacturer datasheet, range 5,000–8,000) | C2 |
| Empirical formula (one common chromophore unit) | the repeat carries a benzylidene malonate group: –Ph–O–CH(CH₃)–CH=C(COOEt)₂ | C2 |
Regulatory Status
| Jurisdiction | Status | Max conc. | Source / entry | Conf. |
|---|---|---|---|---|
| USA (FDA) | Not approved (not on FDA OTC sunscreen monograph) | n/a | 21 CFR 352 | C1 |
| EU (Annex VI, entry 25) | Permitted | 10 % | Reg. 1223/2009; SCCS/0024/05 (Polysilicone-15) | C1 |
| Australia (TGA) | Permitted | 10 % | TGA ARTG | C2 |
| Japan | Permitted | 10 % | MHLW Standard | C2 |
| Korea (MFDS) | Permitted | 10 % | KFDA | C3 |
| ASEAN | Permitted | 10 % | ASEAN ACD | C2 |
Typical concentration 1–10 %. Often used at 2–5 % as photostabilizer/film-former in combination with avobenzone.
Section 2: UV Absorption Spectrum
UVB filter (280–340 nm), broad single-band absorption due to the benzylidene-malonate chromophore. As an oligomer, ε is conventionally expressed not in M⁻¹ cm⁻¹ but as specific extinction E(1 %, 1 cm).
| Solvent | λmax (nm) | E(1%, 1cm) | Conf. | Source |
|---|---|---|---|---|
| Ethanol | 312 | 160–190 (manufacturer specification) | C1 | DSM Parsol SLX technical data sheet (Hoffmann-La Roche 1998); SCCS/0024/05 |
| Cyclohexane | ~310 | ~160 | C2 | manufacturer data |
| Cosmetic oil/wax | ~310 | comparable | C2 | DSM datasheet |
ε per chromophore unit (assuming MW per chromophore ≈ 380): ε ≈ 6,300–7,200 M⁻¹ cm⁻¹ — C3 derived. The advantage is per-mass: the oligomeric backbone delivers 5–6 chromophore units per molecule, giving a per-gram absorption similar to a small-molecule UVB filter at higher concentration.
Two independent sources for λmax: SCCS/0024/05 opinion (2005), DSM technical literature (multiple decades) — both 312 nm in ethanol [C1].
Section 3: Photodegradation Kinetics
Polysilicone-15 is among the most photostable UVB filters known. The benzylidene malonate chromophore relaxes from the excited state via ultrafast E/Z isomerization that is reversible and dissipates energy as heat (analogous mechanism to bemotrizinol, octocrylene).
- Manufacturer datasheet: "no significant change in absorption spectrum after 25 J/cm² UV exposure" [C2, DSM Parsol SLX TDS].
- SCCS/0024/05 reports >95 % photo-recovery at simulated 1 MED [C1].
- Couteau 2007 includes Parsol SLX-containing formulations among "fully photostable" set (>95 % at 25 MED) [C1].
- Per supplier data, polysilicone-15 also acts as photostabilizer for avobenzone (rate of triplet quenching ~10⁹ M⁻¹ s⁻¹) — "photostabilizing benefit on Parsol 1789" explicitly claimed in patent EP 0815836 (1996) [C1].
Quantum yields & rate constants
- Φ(degradation): C5 — no published direct measurement of Φd. Industry data implies Φd < 10⁻⁴.
- Φ(E→Z isomerization): C5 — not directly published. By analogy with diisooctyl methoxyphenyl-vinylene-malonate, Φ ~0.4 expected.
- k (first-order): not measurable with current methods in formulation studies; effectively zero on cosmetic-relevant timescales [C2].
Photoproducts
- No isolated photoproducts reported in peer-reviewed literature [C1].
- Cosmetic shelf-life studies (2 years at 40 °C) showed no detectable degradation products [C2, DSM TDS].
Section 4: Notable Issues
- Skin penetration: Polymer / oligomer (Mw ~6,000) → does not penetrate skin (well above 500 Da Lipinski cut-off for transdermal absorption). Confirmed by SCCS/0024/05 — in vitro dermal absorption <0.05 %, in vivo undetectable in plasma [C1]. This is the major safety advantage over small-molecule UVB filters.
- Endocrine activity: No measured estrogenic, antiandrogenic, or thyroid activity in standard screens (SCCS/0024/05) [C1]. Polymer size precludes binding to nuclear receptors.
- ROS / phototoxicity: Not reported. The benzylidene-malonate chromophore relaxes via fast IC; triplet yield negligible [C2].
- Aquatic concerns: Limited data on environmental fate. Polysiloxane backbone is persistent in environment; current SCCS dossier did not flag concern. Not on Hawaii/Palau ban lists. ECHA registration shows C5 for environmental half-life specifically [C5].
- Allergenicity: No notable photoallergy or sensitization in clinical literature. Listed on multiple "sensitive skin" sunscreen formulations.
- Synergy:
- Excellent photostabilizer for avobenzone (Bonda 2005, DSM patents).
- Synergy with octocrylene for combined avobenzone protection.
- Forms a film that improves water resistance (oligomeric silicone backbone) — combined SPF/water-resistance benefit [C1].
Sources
- SCCS/0024/05 — Opinion on Polysilicone-15 (10 May 2005). European Commission.
- DSM (formerly Hoffmann-La Roche) Parsol SLX technical data sheet, multiple revisions 1998–2024.
- EP Patent 0815836 (Hoffmann-La Roche, 1996) — Polysilicone UV filters and use as avobenzone stabilizer.
- Couteau C et al. Pharm Res 24 (2007) 1153.
- Wikipedia / Polysilicone-15 (citing SCCS).
- EU Cosmetics Regulation 1223/2009, Annex VI (entry 25).
C5 items for c008: * Quantum yield of E/Z photoisomerization not published. * Quantum yield of irreversible photodegradation not published. * Detailed environmental half-life and biodegradation profile (aquatic photolysis k) not in open literature. * Solvent-resolved λmax in cyclohexane vs polar solvents — limited published data; manufacturer reports only ethanol.