Material guide: IPM (isopropyl myristate), the one with a vapour pressure 97 times below DPG

In short: a solvent with no smell of its own, whose use is decided by three physical-property fields. Where it earns its place is after the ethanol has evaporated, because it is still there.

Fields

Field	Value
CAS	110-27-0
Formula	C17H34O2, MW 270.456
Database category	carrier solvents/diluents for flavors and/or fragrances
Melting point	2-3 C
Boiling point	192-193 C @ 20 mmHg
Flash point	> 110 C
logP	7.20 (est)
Vapour pressure	0.000329 mmHg @ 25 C (est)
Specific gravity	0.840-0.860 @ 25 C
Refractive index	1.428-1.443 @ 20 C
Water solubility	0.01354 mg/L @ 25 C (est)
Solubility	amyris wood oil; benzyl benzoate; benzyl salicylate; clove leaf oil; ethyl lactate; paraffin oil; diluent for candle fragrances
Odour strength	none
Substantivity	400 hours
Shelf life	24 months
Occurrence	brandy; coriander seed; kumquat peel oil; witch hazel leaf oil @ 0.07%
Suppliers	54
Regulatory	JECFA, FEMA GRAS, CoE, FLAVIS
Oral toxicity	rat LD50 > 16000 mg/kg; mouse 49700 mg/kg
Note	used for microemulsions; flavour ingredient

Three fields

Vapour pressure 0.000329 mmHg. That sits at the low end among common carrier solvents. Against its peers:

	Vapour pressure @ 25 C
Ethanol	44.6 (@ 20 C)
DPG	0.0319
IPM	0.000329 (est)
Benzyl benzoate	0.000250
TEC	0.000175 (est)

IPM is 97 times below DPG.

The gap is invisible in the bottle. It shows up after the ethanol goes: on a nozzle, on skin, on a blotter. Some of the DPG leaves with it; the IPM barely moves.

logP 7.20. The highest of these four. DPG is -0.60, TEC is 0.10, benzyl benzoate 4.00.

A 7.20 means strongly lipophilic, which helps with fat-soluble solid aroma chemicals and hurts when mixing with water or high-proof ethanol. The solubility field lists oils and esters, and no water.

Melting point 2-3 C. An easily skipped field, and it decides whether a co-solvent sets on its own in winter. Benzyl benzoate's 18-21 C sits inside the room-temperature range.

Three together: it stays, it dissolves lipophilic material, and it does not set when cold.

When to reach for it

The mechanism Reid and colleagues described in Int J Pharm in 2009 applies to any spray format: a volatile solvent evaporates and creates supersaturation in situ. Taking the ethanol in their aerosol from 10% to 20% moved the onset of supersaturation from 30 minutes after application to the moment of actuation.

A perfume spray is the same event. The ethanol leaves, and what remains is either liquid or crystalline.

IPM's job is to keep the residue liquid.

The limit needs stating. Leichtnam and colleagues worked on a testosterone spray in J Pharm Sci in 2007, using antinucleant polymers to hold a supersaturated state. Calorimetry looked promising; once sprayed onto skin, delivery showed no improvement. Their conclusion was that the evaporation process during spray atomisation needs better characterisation. A co-solvent is a different move from an antinucleant, but that paper is a warning about the same thing: what happens past the nozzle is hard to predict.

What it takes away

Non-volatility cuts both ways. IPM staying on skin means the material dissolved in it stays there too, rather than going into the air. Projection drops.

The person on the forum who diagnosed the problem correctly said as much: IPM will decrease the performance of the perfume, so that has to be weighed in.

The substantivity field reads 400 hours, the ceiling value in this database and the same as DPG's. For a solvent that number carries limited meaning; it says this material does not leave on its own.

Corpus

Across 954 published formulas, IPM appears in 4, or 0.4%, at a median dose of 13.5%.

In the same corpus, benzyl benzoate appears in 43 (4.5%), DPG in 34 (3.6%) and TEC in 5 (0.5%).

IPM barely appears in professional formulas.

There is an explanation worth writing down. These 954 are concentrate formulas, dealing with dissolution and dilution. Nozzle residue is a finished-product problem, and the finished product's solvent system does not appear in a concentrate formula. Not seeing IPM in concentrates does not mean it is absent from finished perfumes.

The toxicity field

Rat oral LD50 above 16000 mg/kg, mouse 49700 mg/kg. Those are high numbers, at the low-toxicity end for this class of material.

For comparison in the same database: DPG rat 14850, TEC rat 5900, benzyl benzoate rat 1700 to 2800.

What IPM is argued about in cosmetics is comedogenicity rather than toxicity, and that is not a field in this database. I did not look into it.

What this doesn't establish

• I have not used it. This is database fields plus two papers.
• The vapour pressure and logP are both estimates. The 97-fold gap against DPG is one measurement against one estimate.
• Vapour pressure is not evaporation rate. Film thickness, airflow and surface area drive the real behaviour. I use it to rank, not to predict rates.
• I have no measured solubility for ambroxan or any aroma chemical in IPM. "logP 7.20, so it dissolves lipophilic material" is a rule of thumb.
• "IPM holds ambroxan at 25%" is a forum report, unreproduced here, and I cannot tell whether the two replies mentioning it are independent measurements.
• Leichtnam 2007 studied testosterone and antinucleant polymers, not a co-solvent and not a fragrance material.
• Reduced projection is a qualitative inference with no measurement behind it.
• Comedogenicity I did not check. This database has no such field.
• Four formulas is too small a sample. The 13.5% median should not be read as a recommended dose.