📋 Table of Contents
1. 🔬 Chemical Identity: CAS Number, Structure & Nomenclature
Alpha-methylstyrene dimer (AMS dimer) is formed by the acid-catalysed or thermally initiated dimerisation of two alpha-methylstyrene molecules. The reaction is regioselective, predominantly yielding 2,4-diphenyl-4-methyl-1-pentene as the major isomer, with smaller proportions of the 2-pentene isomer also present in commercial grades.
| Identifier | Detail |
|---|---|
| IUPAC Name (major isomer) | 2,4-Diphenyl-4-methylpent-1-ene |
| CAS Number | 6362-80-7 (major isomer); commercial mixtures may cite 1,1-diphenyl compound variants |
| Molecular Formula | C18H20 (MW: 236.35 g/mol) |
| Common Trade Names | AMS Dimer; α-Methylstyrene Dimer; Dimethane |
| Parent Monomer | Alpha-Methylstyrene (AMS), CAS 98-83-9 |
| Physical Form | Clear, pale yellow liquid at room temperature; low viscosity |
💡 Why two isomers? The dimerisation of AMS is not perfectly regioselective. The 1-pentene isomer (2,4-diphenyl-4-methylpent-1-ene) is the dominant product and carries a terminal alkene group, making it reactive in polymerisation and as a chain-transfer agent. The 2-pentene isomer (2,4-diphenyl-4-methylpent-2-ene, internal alkene) is less reactive. Commercial AMS dimer specifications typically state the isomer ratio, and this ratio meaningfully affects performance in chain-transfer applications.
2. ⚗️ Physical & Chemical Properties
AMS dimer's liquid state at ambient temperature and its low volatility set it apart from the monomer and make it easier to handle in most industrial environments. The table below covers typical values for commercial-grade material.
| Property | Typical Value | Notes |
|---|---|---|
| Molecular Weight | 236.35 g/mol | Exactly 2× AMS monomer (MW 118.17) |
| Appearance | Clear, pale yellow liquid | Colour darkens on oxidation; store under inert gas |
| Boiling Point | ~290–295 °C (at 760 mmHg) | Very low volatility at ambient temperature |
| Flash Point | ~127–135 °C (closed cup) | Combustible liquid; not classified as flammable |
| Density | ~0.965–0.975 g/cm³ (at 20 °C) | Slightly less dense than water |
| Refractive Index (nD20) | ~1.555–1.565 | Useful purity/identity check |
| Viscosity | ~5–10 mPa·s (at 25 °C) | Low viscosity; easy pumping and dosing |
| Vapour Pressure | < 0.1 mmHg (at 20 °C) | Negligible at ambient; low inhalation hazard |
| Solubility in Water | Practically insoluble | Miscible with most organic solvents and lubricant base oils |
| Thermal Stability | Excellent up to ~200 °C | Key advantage over the monomer in high-temperature processing |
3. ⚖️ AMS Dimer vs AMS Monomer: Key Differences
Buyers frequently ask whether they should specify AMS monomer or AMS dimer for a given application. The answer depends almost entirely on the intended use. The comparison below clarifies where each product fits.
| Parameter | AMS Monomer (CAS 98-83-9) | AMS Dimer (CAS 6362-80-7) |
|---|---|---|
| Molecular Weight | 118.17 g/mol | 236.35 g/mol |
| Physical State (25 °C) | Liquid (low bp: 165 °C) | Liquid (high bp: ~292 °C) |
| Vapour Pressure | ~1.9 mmHg (20 °C) - volatile | <0.1 mmHg (20 °C) - negligible |
| Flash Point | ~53 °C - flammable liquid | ~130 °C - combustible only |
| Reactivity | Highly reactive; polymerises readily; requires inhibitor | Moderate; terminal alkene reacts as chain-transfer agent |
| Primary Use | Copolymer monomer; resin production; AMS dimer feedstock | Chain-transfer agent; lubricant additive; plasticiser |
| Shipping Classification | UN 2303 - Flammable Liquid, Class 3 | Not classified as dangerous for transport (standard conditions) |
| Storage Requirement | Inhibited; cool, dark location; nitrogen blanket recommended | Inert atmosphere preferred; less stringent than monomer |
🔗 Upstream relationship: AMS dimer is manufactured from AMS monomer. The quality of the dimer - particularly its isomer ratio and colour - is directly influenced by the purity of the AMS feedstock used. For more on AMS monomer specifications, see our Alpha-Methylstyrene product page.
4. 🏭 Industrial Applications
AMS dimer is a functionally versatile specialty chemical. Its combination of low volatility, reactive double bond (in the 1-pentene isomer), and excellent oil compatibility makes it useful across four major industrial sectors.
| Application | Typical Use Level | Key Benefit vs Alternatives |
|---|---|---|
| Chain-transfer agent (SBR, acrylates) | 0.1 – 2.0 phr | Odour-free; no sulphur residues vs. DDM |
| Lubricant additive | 1 – 5% | Low volatility; thermally stable; no flash-point suppression |
| Rubber plasticiser | 5 – 20 phr | Non-migrating; no surface blooming |
| Coating reactive diluent | 5 – 15% | Reduces VOC; reacts into polymer backbone |
5. 🦺 Safety, Handling & Storage
AMS dimer is considerably safer to handle than AMS monomer thanks to its low volatility and higher flash point. Nonetheless, standard chemical safety protocols apply. The following guidance reflects typical SDS information for commercial AMS dimer.
✅ Transport note: Under normal commercial conditions, AMS dimer does not meet the criteria for classification as a dangerous good under IMDG, IATA, or ADR regulations - significantly simplifying international shipping documentation compared to AMS monomer (UN 2303, Class 3, PG III).
6. 🌐 Sourcing & What to Ask Your Supplier
AMS dimer is a more specialised product than the parent monomer and available from fewer global sources. Evaluating suppliers on the following points will help you avoid quality issues and supply disruptions.
7. ❓ Frequently Asked Questions
📚 Related Articles in This Series
Enquire About Alpha-Methylstyrene Supply
Whether you need AMS monomer as a feedstock for dimer production, or sourcing guidance for finished AMS dimer, Sinolook Chemical's technical sales team is ready to assist. We export to 50+ countries with full documentation support.
