| HS Code | 656766 |
| Chemical Name | Vinyl Acetate Monomer |
| Cas Number | 108-05-4 |
| Molecular Formula | C4H6O2 |
| Molecular Weight | 86.09 g/mol |
| Appearance | Clear colorless liquid |
| Purity | ≥ 99.5% |
| Stabilizer | Diphenylamine (DPA) |
| Stabilizer Content | 0.01 - 0.05% |
| Boiling Point | 72.7 °C |
| Flash Point | -8 °C |
As an accredited DPA Stabilized Industrial VAM factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | DPA Stabilized Industrial VAM is supplied in 200-litre steel drums, 180 kg net, under nitrogen blanket for purity. |
| Container Loading (20′ FCL) | DPA Stabilized Industrial VAM loaded in 20′ FCL as drums/IBCs, secured upright, ventilated, away from heat and ignition sources. |
| Shipping | DPA Stabilized Industrial VAM (vinyl acetate monomer) is a flammable, reactive liquid requiring careful transport. Ship in approved, grounded containers under inert gas, away from heat and oxidizers. Follow dangerous goods regulations, use proper labeling, and ensure secondary containment to prevent polymerization risks during transit. |
| Storage | Store DPA Stabilized Industrial VAM in a cool, dry, well-ventilated area away from heat, sparks, open flames, and direct sunlight. Keep containers tightly sealed and properly bonded/grounded to prevent static discharge. Maintain temperatures below 30°C, avoid contact with oxidizers, and monitor inhibitor levels to prevent polymerization. Use approved, compatible materials and inspect regularly. |
| Shelf Life | Store in a cool, dry area away from heat and ignition sources. Shelf life is 12 months from date of manufacture. |
DPA-stabilized industrial vinyl acetate monomer is supplied as a radical-initiated polymerization feedstock in which diphenylamine functions as a free-radical scavenger rather than a conventional phenolic inhibitor. The inhibitor package changes the radical budget in downstream polymerization because DPA is not removed by simple vacuum degassing at typical plant pressures and has a normal boiling point of 302°C at 101.3 kPa. A polymerization recipe qualified on hydroquinone-stabilized VAM cannot be transferred directly to DPA-stabilized VAM without re-establishing initiator demand and exotherm profile. Lot-specific DPA concentration is reported on the supplier certificate of analysis and must be entered into the recipe control model. Failure to compensate for DPA content produces extended induction periods, uneven monomer conversion, broad molecular weight distribution, and altered final-resin properties in several downstream segments.
In semi-batch emulsion polymerization for wood adhesives, polyvinyl acetate homopolymer emulsions are produced under a nitrogen blanket in jacketed glass-lined reactors equipped with an anchor impeller and a radial turbine. Deionized water, a protective colloid such as partially hydrolyzed PVOH with a degree of hydrolysis of 88–89 mol%, and a nonionic or anionic surfactant are charged before monomer feed. VAM is metered over 3–5 h while reactor temperature is maintained at 65–75°C. With DPA-stabilized VAM, the initial radical population is consumed until the inhibitor is depleted. If initiator feed is not adjusted, the expected exotherm onset shifts by 15–45 min and the batch may show a double exothermic peak due to accumulated monomer. Sodium persulfate or ammonium persulfate is metered at 0.2–0.5 wt% on total monomer, with the actual rate dependent on residual DPA in the monomer feed. A redox pair of sodium metabisulfite and persulfate is used when lower polymerization temperature is required. Process control relies on heat flow rather than time-based initiator additions. Final emulsions typically have solids of 50–60%, pH of 4.0–5.5, and Brookfield viscosity of 3,000–15,000 mPa·s at 23°C. Dry shear strength for D3-grade wood bonding is verified by EN 204 or ASTM D905. High residual DPA that is not accounted for produces low molecular weight fractions and reduced cohesive strength because initiation is delayed and polymer chains terminate under higher monomer concentration. Published data for the exact kinetic chain length reduction at a given DPA concentration in this specific configuration is limited; verification by gel permeation chromatography against a DPA-free control is recommended.
For polyvinyl alcohol production, methanol-based solution polymerization of VAM followed by alkali-catalyzed alcoholysis is the standard route. The DPA inhibitor entering the methanol solution must be treated as a chain-transfer-active contaminant in the molecular weight control scheme. Reaction temperature is commonly 60–65°C with azobisisobutyronitrile at 0.05–0.20 wt% on VAM. Polymerization is run to 50–70% conversion in a stirred, reflux-cooled reactor, after which residual VAM is removed by vacuum stripping. Because DPA has a boiling point well above the stripping temperature, it does not co-volatilize with methanol or unreacted VAM and can remain in the PVAc solution entering saponification. Industrial production of 88 mol% and 99 mol% hydrolysis grades uses methanolic sodium hydroxide in a kneader or belt saponifier. The gel is then ground, washed, and dried. Viscosity control of finished PVOH is based on a 4% aqueous solution measured at 20°C with an Ubbelohde capillary viscometer; commercial grades range from 3 mPa·s to 70 mPa·s. DPA residues can appear in final PVOH as trace nitrogen compounds and may affect thermal stability during melt processing. For textile warp sizing or paper surface sizing, nitrogen content and color after heat ageing are routine release checks. When high-clarity film-grade PVOH is required, the monomer specification must confirm DPA content and the saponification line must include a washing step sufficient to remove inhibitor-derived species. ISO 3105 is referenced for capillary viscometer procedure in dilute polymer solution testing.
At pressures of 1,000–3,000 bar and temperatures of 150–300°C, ethylene-vinyl acetate copolymers used in extrusion, film, and hot-melt compounding are produced in continuous high-pressure autoclave or tubular reactors. VAM acts as both a comonomer and a chain-transfer agent; typical VAM content ranges from 9 wt% to 40 wt%. DPA-stabilized VAM fed into the high-pressure radical process alters the radical balance in the first reactor zone. Because DPA is a relatively nonvolatile radical scavenger, its effect is more pronounced than volatile inhibitors that vaporize at reactor inlet temperatures. In an autoclave system, the result is a longer effective induction volume before stable copolymerization. In a tubular reactor, DPA-induced delay shifts peak temperature further down the tube and may require a reduction in initiator injection at the second or third injection point. Organic peroxide initiator is injected at multiple points along the reactor. Process control uses melt flow rate as the primary molecular weight indicator, measured by ASTM D1238 or ISO 1133-1. Vinyl acetate incorporation is determined by a calibrated Fourier transform infrared method or saponification number. Photovoltaic encapsulant grades demand VA content of 28–33 wt%, melt flow rate of 10–40 g/10 min at 190°C/2.16 kg, and peroxide-curable formulations. Residual nitrogen species from DPA may interact with peroxide cure systems unless diluted or flushed from the polymer. Production of ultra-low-gel encapsulant film requires close control over DPA carryover because impurities that disrupt gel content can reduce yield in downstream calendering and crosslinking.
In medium-pressure emulsion copolymerization for construction-grade vinyl acetate-ethylene dispersions, a reactor is charged with water, stabilizer, buffer, and a redox initiator. Ethylene pressure of 10–60 bar is applied. DPA-stabilized VAM increases the demand for the reducing agent in the redox pair because oxidized DPA species may consume radicals. Typical redox pairs are ammonium persulfate with sodium formaldehyde sulfoxylate or sodium metabisulfite. A production-scale pattern observed is that the first ethylene uptake occurs later when DPA content is not compensated; ethylene conversion then becomes uneven and the resulting dispersion shows lower wet adhesion in cement-modified mortars. The polymer composition is adjusted to a glass transition temperature between −15°C and +10°C. Dispersions are formulated into one-component and two-component cementitious tile adhesives. Performance is classified under EN 12004 as C1 or C2, with tensile adhesion after water immersion and heat ageing measured under EN 1348. The final dispersion typically contains 50–55% solids; residual VAM below 1,000 mg/kg may be required by local regulations. Because DPA has low volatility, it tends to remain in the dispersion after vacuum stripping. North American and EU production sites should verify residual monomer and inhibitor-derived compounds by gas chromatography–mass spectrometry when testing workplace exposure or disposal compliance.
When a binder must combine UV resistance with scrub resistance, vinyl acetate-acrylic copolymer emulsions are produced by staged monomer addition in which VAM is copolymerized with butyl acrylate or 2-ethylhexyl acrylate. DPA-stabilized VAM is acceptable only when DPA content is included in the monomer feed model; otherwise, the more reactive acrylate monomer may polymerize first and shift particle morphology. Reactor control uses a pre-emulsion feed over 4–6 h at 75–85°C with ammonium persulfate. Acrylic comonomer level commonly ranges from 10 wt% to 35 wt% of total monomer. The resulting latex can have minimum film-forming temperature lowered without external plasticizer. Scrub resistance is measured by ASTM D2486; exterior durability is compared by accelerated weathering under ASTM G155. Formulation with these binders commonly gives flat and satin coatings with pigment volume concentration of 35–55%. High DPA carryover can reduce polymerization rate, broaden particle size distribution, and produce coagulum in the reactor. Coagulum is measured as wet screen residue on a 150 µm screen and should remain below 0.05 wt% for acceptable production yield. This is a production line limitation: excessive coagulum forces filtration and reduces batch throughput. DPA-related inhibition must be compensated before the final monomer shot; otherwise, residual monomer can exceed permitted workplace or environmental release values.
| Application segment | Parameter | Standard or method | Typical constraint |
|---|---|---|---|
| PVAc wood adhesive | Dry shear strength | EN 204, ASTM D905 | D3 classification |
| Cementitious tile adhesive | Tensile adhesion after water immersion and heat ageing | EN 1348, EN 12004 | C1/C2 classification |
| Architectural coating | Scrub resistance and accelerated weathering | ASTM D2486, ASTM G155 | Cyclic scrub failure point |
| Photovoltaic EVA encapsulant | Melt flow rate at 190°C/2.16 kg | ISO 1133-1:2022, ASTM D1238 | 10–40 g/10 min |
Solution-grade vinyl chloride-vinyl acetate copolymers are produced by suspension or solution polymerization. Vinyl acetate comonomer content of 3–20 wt% lowers the crystallinity of polyvinyl chloride and improves solubility in ketone and ester solvents. DPA-stabilized VAM used as a comonomer introduces nitrogen-containing species that can affect the heat stability of the finished resin. Polymerization is performed in a pressure vessel with a free-radical initiator; temperature is controlled between 50°C and 70°C depending on target K-value. K-values of 45–60 are common for graphic arts and coil coating resins. Finished resins are dissolved in methyl ethyl ketone, methyl isobutyl ketone, or ethyl acetate. Solution viscosity and color are release parameters; heat stability is tested by static oven ageing at 160–180°C with color change measured against a reference. For printing inks, the resin provides pigment wetting and adhesion to polyolefin and metal substrates. For coil coatings, vinyl chloride-vinyl acetate copolymers are combined with melamine or blocked isocyanate crosslinkers. DPA-derived residues may interact with tin-based heat stabilizers or cause yellowing under high-temperature bake cycles above 180°C. When such interactions are suspected, the resin manufacturer should qualify a DPA-reduced VAM grade or adjust stabilizer type. Industrial DPA-stabilized VAM is not automatically suitable for direct or indirect food-contact polymer applications; compliance with FDA 21 CFR 175.300, FDA 21 CFR 176.170, or EU food-contact legislation must be confirmed on the final polymer and extraction profile rather than assumed from monomer grade.
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DPA Stabilized Industrial VAM is introduced as a diphenylamine-inhibited vinyl acetate monomer, CAS 108-05-4, supplied for downstream polymer synthesis where conventional hydroquinone stabilization creates color, oxygen-partitioning, or redox-initiation constraints. The product is not a single-model product; it is a stabilizer-defined industrial monomer grade. The backbone chemistry remains vinyl acetate, while the inhibition chemistry differentiates this grade from hydroquinone-stabilized and 4-methoxyphenol-stabilized commercial VAM. The material is specified as a clear, colorless liquid with a minimum assay of 99.9% by gas chromatography under ASTM D2190-07. Typical physical properties include molecular weight 86.09 g/mol, density 0.934 g/cm³ at 20 °C, boiling point 72.7 °C at 101.3 kPa, closed-cup flash point -8 °C, and vapor pressure 12.3 kPa at 20 °C. The stabilizer is diphenylamine, CAS 122-39-4, present at low mg/kg concentration. For comparison, hydroquinone-stabilized VAM uses CAS 123-31-9, and MEHQ-stabilized VAM uses CAS 150-76-5. The lower water solubility of DPA relative to hydroquinone is the primary technical basis for selecting this grade in solvent-borne or moisture-sensitive polymerization systems.
Commercial DPA-stabilized industrial VAM is supplied against a specification that limits water, acidity, color, and stabilizer content. A typical certificate of analysis reports water below 0.05% by mass when tested by Karl Fischer titration according to ASTM D1364-22, acidity below 0.005% as acetic acid by titration according to ASTM D1613-17, and color below 5 Pt-Co units under ASTM D1209-19. DPA content is commonly controlled to 3–15 mg/kg, with the exact loading negotiated according to intended storage duration and downstream initiator sensitivity. Low water content is critical because vinyl acetate hydrolyzes to acetaldehyde and acetic acid. Moisture ingress above 0.05% by mass increases acidity and reduces DPA efficiency through protonation of the aromatic amine stabilizer. The acidity specification also reduces corrosion in carbon steel equipment and limits consumption of the basic stabilizer. For UV-sensitive or radiation-curable downstream chemistry, the aromatic amine structure of DPA can be a relevant variable because it can absorb UV radiation and generate color in aged films. Users should evaluate this effect against the lower water solubility of DPA compared with hydroquinone.
The comparative stabilizer profiles for three industrial VAM grades are summarized in Table 1.
| Parameter | DPA-stabilized VAM | HQ-stabilized VAM | MEHQ-stabilized VAM |
|---|---|---|---|
| Inhibitor CAS | 122-39-4 | 123-31-9 | 150-76-5 |
| Inhibitor class | aromatic secondary amine | phenolic/quinone | phenolic ether |
| Typical commercial loading | 3–15 mg/kg | 3–25 mg/kg | 5–20 mg/kg |
| Approximate water solubility at 20–25 °C | 53 mg/L | 70 g/L | 40 g/L |
| Oxygen requirement | requires dissolved oxygen | requires dissolved oxygen | requires dissolved oxygen |
| Principal technical advantage | low water partitioning; less aqueous-phase inhibition | established inhibition history; cost-effective | low color; less phenolic discoloration |
| Potential limitation | protonation under acidic conditions; UV-absorbing residue | water-soluble; can partition into aqueous phase | may retard radiation-cure systems |
These differences are not merely analytical; they influence induction period, phase partitioning, and final polymer color. The data in Table 1 are representative commercial ranges, and a specific lot should be controlled by the certificate of analysis rather than by generic grade claims. Safety, transportation, occupational exposure, and emergency response requirements are provided in the supplier safety data sheet and are not replaced by the specification range.
DPA retards free-radical polymerization through hydrogen abstraction from the amine by peroxy radicals, forming diphenylnitrogen radicals and nitroxyl-type species that terminate propagating chains. The mechanism is oxygen-dependent. Without dissolved oxygen, the inhibitor is not regenerated effectively, and the monomer can undergo uncatalyzed radical polymerization. For this reason, storage and handling require vapor-space oxygen of 5–21 vol%. Nitrogen blanketing, sometimes used to reduce flammability, can deactivate the inhibitor unless the system is explicitly designed for oxygen-free storage. At temperatures above 30 °C, inhibitor consumption increases and the safe storage period shortens; above 50 °C, polymer formation in lines and storage tanks becomes significant even with oxygen present. Iron contamination above 0.5 mg/kg can shorten induction time by catalyzing peroxide decomposition. Glass-lined or stainless 316L vessels are preferred over carbon steel where long hold times are expected.
The induction period in a polymerization reactor is not directly predicted by DPA concentration alone. It depends on dissolved oxygen, temperature history, trace iron, and the initiator system. Batch-to-batch variation in DPA loading is commonly controlled to ±1 mg/kg, but downstream recipes should be adjusted using the actual certificate of analysis rather than the nominal grade value. In bulk and solution vinyl acetate polymerizations initiated by azo compounds at 60–80 °C, the induction period may range from minutes to hours when DPA loading is between 5 mg/kg and 15 mg/kg. The exact delay depends on initiator half-life at the selected temperature, dissolved oxygen concentration, and reactor surface-to-volume ratio. Published kinetic data for DPA inhibition in vinyl acetate under plant-scale conditions is limited, so induction-time screening with the intended initiator pair is required when substituting DPA-stabilized monomer.
In solvent-borne and bulk polymerization processes, the low water solubility of DPA reduces inhibitor transfer into the aqueous phase. In contrast, hydroquinone partitions strongly into water and can delay particle nucleation in emulsion and suspension systems. DPA remains predominantly in the monomer phase, which can make inhibition more consistent in monomer droplets but requires careful control of dissolved oxygen throughout the feed system. In a continuous vinyl acetate-ethylene emulsion line, substitution of HQ-stabilized monomer with DPA-stabilized monomer may shorten redox-initiation induction when oxygen is adequate, but it may also increase sensitivity to oxygen depletion caused by vacuum degassing or nitrogen stripping. Published data for specific plant configurations is limited; bench measurements using the actual redox pair are necessary before grade substitution.
Residual DPA in the polymer phase after drying may act as a radical scavenger during thermal aging, but it can also generate color under alkaline conditions. This trade-off is not present with hydroquinone to the same extent because hydroquinone is more readily removed from aqueous dispersions. Formulators should measure dry film color after accelerated aging at 60 °C for 14 days and compare the result against the incumbent HQ-stabilized grade. The use of ASTM D1209-19 or ISO 6271 is appropriate for color assessment of polymer solutions if the sample is compatible with the test cell.
In polyvinyl acetate homopolymer and vinyl acetate-ethylene copolymer emulsion processes, inhibitor type influences particle nucleation, coagulum, residual monomer, and dispersion color. Because DPA is hydrophobic, less inhibitor is present in the water phase during micelle formation; this can reduce inhibition of aqueous-phase radical species. The effect is particularly relevant in redox-initiated recipes using persulfate-bisulfite or iron-sulfoxylate couples, where water-phase initiation is sensitive to radical scavenging. At the same time, residual DPA in the polymer phase may act as a thermal antioxidant during later drying, but it can also contribute to color development if the dispersion is exposed to alkaline conditions or high heat. In polyvinyl alcohol production, residual diphenylamine may survive saponification and affect optical clarity of the resulting PVA film. Published comparative data for DPA residues in PVA optical properties is limited.
Manufacturers replacing HQ-stabilized VAM with DPA-stabilized VAM should measure coagulum, free monomer, dispersion viscosity, filter pressure rise, and dry film color as at-line critical-to-quality parameters. The monomer feed should not be held in oxygen-deficient conditions for more than 24 h at 25 °C; pre-reactor hold at 40 °C should be limited to 8 h unless stabilizer loading is verified for extended storage. In continuous lines with mass-flow-controlled monomer feed, the oxygen analyzer downstream of the monomer day tank is a critical control point. A decline in dissolved oxygen below 5% saturation in the liquid monomer may indicate inhibitor deactivation before a visible increase in viscosity occurs.
In polymers intended for medical, food-contact, or sensitive adhesive applications, residual phenolic stabilizers may be subject to specific migration limits. DPA is a different chemical class with its own toxicological profile and migration behavior. The replacement of hydroquinone by diphenylamine does not automatically produce a phenolic-free polymer because other formulation components may still contain phenolics. The downstream polymer must be tested against the applicable regulations such as REACH Regulation (EC) No 1907/2006 or FDA 21 CFR 175.105 only where the formulation falls within that scope. Published data for DPA migration kinetics from polyvinyl acetate matrices is limited; users should not assume that the lower water solubility of DPA reduces migration without experimental migration testing. The stabilizer loading in the monomer is low, but the low volatility of DPA can lead to accumulation in high-boiling recycle loops. This is an operational boundary in continuous solvent recovery systems, where DPA may concentrate in recovered solvent bottoms and contribute to color or fouling. Periodic analysis of recycle streams for DPA is recommended if the monomer is used in closed-loop solvent processes.
DPA-stabilized industrial VAM is a flammable liquid under NFPA 30 and OSHA 29 CFR 1910.106; it is transported as DOT Class 3, Packing Group II, with a closed-cup flash point of -8 °C. Lower and upper explosion limits are 2.6% and 13.4% by volume, respectively. Storage areas require grounding, bonding, and ventilation to maintain vapor concentrations below 10% of LEL. Pumps and electrical equipment in classified locations must meet NFPA 70 hazardous location requirements. The material should be stored under air, not under nitrogen, to preserve DPA inhibition. If an inert pad is required for process safety, the stabilizer package and storage duration must be validated by a reactivity study because oxygen depletion can reduce inhibitor activity.
Materials of construction should be stainless steel 316L, stainless steel 304L, or lined carbon steel; copper and copper alloys are avoided because trace copper can promote color formation and destabilization reactions, and carbon steel may release iron that accelerates inhibitor depletion. Peroxides, azo initiators, strong acids, strong bases, and oxidizing agents must be segregated from the monomer because these substances can initiate vinyl polymerization or degrade the inhibitor. Moisture ingress above 0.05% by mass accelerates hydrolysis to acetaldehyde and acetic acid, increasing acidity and reducing DPA efficiency through protonation. Weekly certification of oxygen analyzers and monthly verification of inhibitor content in long-term storage tanks are typical plant practices; the frequency is adjusted based on actual tank turnover and ambient temperature history.
For bulk transfers, the product should be moved through closed lines with positive-displacement or canned centrifugal pumps equipped with mechanical seals. Filling and emptying operations require vapor-space management only if the oxygen concentration can be maintained above 5%; otherwise, the activity of DPA must be confirmed before return to storage. The product is assigned a retest interval of 6 months from the date of analysis under typical storage conditions of 10–30 °C. Extended storage beyond 12 months may require retesting for acidity, water, color, and DPA content; published data for DPA-stabilized VAM beyond 12 months is limited.
For continuous vinyl acetate-ethylene emulsion lines producing pressure-sensitive adhesives and barrier coatings, DPA-stabilized VAM can be introduced through a mass-flow-controlled monomer feed to reduce pre-reactor gelation while maintaining low coagulum, provided the feed line oxygen content is maintained above 5% by volume. The stabilizer loading should be monitored against the certificate of analysis rather than assumed from the grade name; polymerization recipes may require adjustment of reducing agent concentration when residual DPA alters radical scavenging in the aqueous phase. Published data for this specific configuration is limited, and start-up after grade conversion should include a structured induction-period study at the intended reactor temperature and initiator concentration. The product remains subject to the same storage, flammability, and handling controls as other VAM grades, with the additional constraint that oxygen exclusion can defeat the diphenylamine stabilization system.
