| HS Code | 769014 |
| Product Name | DCC VAM Low Inhibitor LI Grade |
| Chemical Name | N,N'-Dicyclohexylcarbodiimide |
| Cas Number | 538-75-0 |
| Molecular Formula | C13H22N2 |
| Molecular Weight | 206.33 g/mol |
| Appearance | White to off-white crystalline low-melting solid |
| Purity | ≥99% (assay) |
| Melting Point | 34-36 °C |
| Boiling Point | 122-124 °C at 6 mmHg |
| Flash Point | 113 °C |
| Solubility | Soluble in dichloromethane, chloroform, DMF, and THF; reacts slowly with water |
| Storage Conditions | Store under inert gas at 2-8 °C, protected from moisture |
| Stability | Moisture sensitive; keep dry under inert atmosphere |
| Inhibitor Content | Low inhibitor grade (LI Grade) |
| Signal Word | Danger |
| Hazard Statements | Toxic if swallowed, in contact with skin, or if inhaled; causes skin and eye irritation |
As an accredited DCC VAM Low Inhibitor LI Grade factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Packaged in 200 kg steel drums, sealed under nitrogen to preserve low inhibitor LI grade stability for DCC VAM. |
| Container Loading (20′ FCL) | 20′ FCL container loading for DCC VAM Low Inhibitor LI Grade: secure, stable drum arrangement maximizing capacity while ensuring safe chemical transport. |
| Shipping | DCC VAM Low Inhibitor LI Grade ships as UN 1301, Vinyl Acetate Monomer, Stabilized — Class 3, Packing Group II. Use labeled, grounded containers and placarded transport. As a low-inhibitor grade, maintain adequate inhibitor levels, keep cool, and ensure oxygen remains in the vapor space to prevent polymerization. |
| Storage | Store DCC VAM Low Inhibitor LI Grade in its original, tightly sealed container in a cool, dry, well-ventilated area. Protect from heat, direct sunlight, ignition sources, moisture, and incompatible oxidizers. Because it is a low-inhibitor grade, avoid conditions that may trigger polymerization. Maintain the manufacturer-recommended temperature and inspect regularly for contamination or degradation. |
| Shelf Life | Shelf life is typically 6–12 months when stored cool, dry, sealed, and protected from light; low inhibitor grades require shorter storage. |
Semi-batch emulsion polymerization trains running DCC VAM Low Inhibitor LI Grade are configured around hydroquinone (HQ) levels below 5 ppm as supplied. Bulk storage of this grade requires nitrogen blanketing at 20–25 °C and a residence time not exceeding 30 days unless the material is re-inhibited; moisture ingress must be held below 400 ppm because water accelerates hydrolysis to acetic acid and acetaldehyde. In a 20–30 m³ jacketed stainless-steel reactor equipped with a pitched-blade turbine running at 1.2–1.8 m/s tip speed, the continuous phase is deionized water at 100 parts by weight. Polyvinyl alcohol protective colloid is charged at 4–8 parts, surfactant at 1–3 parts, and sodium bicarbonate at 0.1–0.3 parts to buffer pH between 4.0 and 5.5. Vinyl acetate monomer is metered over 2–4 hours at 55–65 parts, while potassium persulfate initiator is fed separately at 0.05–0.15 parts per hundred monomer. Reactor temperature is held at 70–80 °C and the exotherm is controlled by jacket cooling and reflux condensation.
The lower inhibitor content reduces the radical sink that normally consumes initiator during the induction period, so persulfate addition can be reduced by 5–15% across production lots when compared with standard-inhibited VAM. Published data for this specific configuration is limited, and the reduction must be confirmed by monitoring residual monomer and initiator half-life in each train. The resulting polyvinyl acetate homopolymer dispersions are high-viscosity, non-hazardous, water-based binders for wood assembly adhesives, paper tube winding, and cigarette filter rod adhesives. Compliance is routinely checked against DIN EN 204/205 for non-structural wood adhesives, ASTM D903 and ASTM D1876 for bond peel, ISO 2555 for Brookfield viscosity, ISO 3251 for non-volatile content, and ISO 2115 for minimum film-forming temperature. Residual vinyl acetate monomer after post-polymerization stripping is normally below 0.5 wt% by headspace gas chromatography, a requirement in many food packaging adhesive specifications.
| Release parameter | Test method | Typical release envelope |
|---|---|---|
| Non-volatile content | ISO 3251 | 49–55% |
| Brookfield viscosity at 25 °C | ISO 2555 | 4,000–25,000 mPa·s |
| pH | ISO 976 | 4.0–5.5 |
| Residual vinyl acetate monomer | Headspace GC | < 0.5 wt% |
| Minimum film-forming temperature | ISO 2115 | 2–10 °C |
In high-pressure ethylene–vinyl acetate copolymerization, the inhibitor package is not inert because hydroquinone consumes free-radical flux during the reaction. The autoclave profile operates at 140–220 MPa and 150–250 °C; free-radical initiators such as di-tert-butyl peroxide are injected at 10–100 ppm based on total monomer feed. When VAM carries standard HQ levels, a portion of radical flux is consumed by inhibitor, producing quinoid species that can contribute to gel and colour in EVA pellets. The LI grade lowers this radical sink, allowing lower initiator injection and reducing gel formation. The reduced initiator injection must be validated over multiple lots because low-inhibitor VAM lot-to-lot variation below 5 ppm HQ is small but the high-pressure reactor has a narrow operating window. Quantitative field data linking inhibitor level to gel count in cast EVA film is limited; however, the effect on initiator consumption is documented in high-pressure free-radical polymerization literature.
VAM incorporation ranges from 10–40 wt%, with ethylene at 60–90 wt%. Melt flow rate is controlled between 0.3–500 g/10 min at 190 °C/2.16 kg according to ISO 1133-1:2022 and ASTM D1238. Tensile properties are tested under ISO 527-2 and ASTM D638-14. High-pressure phase separation is followed by low-pressure separation and extruder pelletizing. Ethylene feed oxygen must be held below 10 ppm because oxygen acts as an uncontrolled initiator and broadens molecular weight distribution. Terminal products include EVA hot-melt adhesives, photovoltaic encapsulant sheets, footwear midsoles, and stretch film. The operational boundary is at low VAM feed ratios; below 10 wt% VAM, the effect of inhibitor carryover is less visible, while above 40 wt% VAM the reactor heat removal capacity and phase separator fouling become limiting.
Solution-polymerized vinyl chloride–vinyl acetate resins used in coil and can coating formulations require a monomer feed with predictable inhibitor content because residual hydroquinone can form dark quinoid complexes with iron in stainless or glass-lined reactors. The monomer blend consists of 80–97 wt% vinyl chloride and 3–20 wt% vinyl acetate, with an optional dicarboxylic acid termonomer at 0–2 wt%. Polymerization is carried out in methyl ethyl ketone or ethyl acetate at 35–40% solids and 60–70 °C, with azobisisobutyronitrile or peroxy initiator at 0.05–0.1 parts per hundred monomer. The low-inhibitor VAM reduces colour formation in the final resin and lowers residual monomer after vacuum stripping. Use in unlined carbon steel equipment is not recommended because iron contamination can still generate colour bodies even with low-inhibitor monomer.
The resins are subsequently formulated into metal coil primers, can coatings, and gravure inks. For food-contact can coatings, the dry film is evaluated under FDA 21 CFR 175.300, and residual vinyl chloride monomer is targeted below 1 ppm. Residual VAM in the resin is typically below 0.5 wt% after stripping. REACH Annex XVII restrictions on vinyl chloride monomer carryover into articles apply. The low-inhibitor VAM feed also helps maintain solubility and clarity in ketone-based gravure ink systems, where high-colour resins are rejected during incoming quality control. Batch-to-batch viscosity control is monitored by ISO 2555 and gel permeation chromatography confirms weight-average molecular weight within the specified range for coating-grade copolymers.
Spray-dried redispersible polymer powders based on vinyl acetate–ethylene emulsions demand a monomer feed with predictable inhibitor content because residual HQ can destabilize the emulsion during heat ageing and spray drying. A typical VAE emulsion uses VAM:ethylene weight ratios of 70:30 to 85:15, polyvinyl alcohol protective colloid at 8–15 wt% on polymer, and a high-pressure emulsion reactor operating at 40–80 bar. The emulsion is then atomized in a spray dryer with rotary wheel speed 10,000–15,000 rpm, inlet air 180–200 °C, outlet air 70–90 °C, and powder moisture below 1.5%. Anticaking agent is added at 5–15 wt% to prevent blocking. The low-inhibitor VAM feed narrows the residual low-molecular-weight fraction that can plasticize the powder and depress blocking resistance during warm storage.
The resulting powders are used in cementitious tile adhesives, self-leveling underlayments, and external thermal insulation composite systems. Adhesive strength is classified according to ISO 13007-2 and tested against EN 12004; tensile adhesion after water immersion commonly exceeds 0.5 MPa, but the exact value depends on formulation and substrate. Minimum film-forming temperature of the redispersed polymer is typically 0–10 °C under ISO 2115. Storage at relative humidity above 60% requires sealed moisture-barrier bags, otherwise the powder will cake and lose redispersibility. The low-inhibitor monomer also reduces the tendency for premature coagulation during emulsion polymerization at high ethylene pressure, a failure mode observed when inhibitor levels are high and the redox initiator package is not adjusted accordingly.
High-solids self-crosslinking vinyl acetate–acrylate binders for dry-laid and wet-laid nonwovens are formulated at 50–55% solids and a pH of 4.5–6.0. The monomer charge includes 70–90 wt% vinyl acetate, 10–30 wt% butyl acrylate or other acrylic ester, and 1–5 wt% N-methylolacrylamide as the crosslinking monomer. Because NMA can undergo premature crosslinking under acid or radical conditions, uncontrolled inhibitor carryover from the VAM feed disturbs the redox balance. Low-inhibitor VAM reduces the background radical sink, making scorch time more predictable during the drying sequence. The emulsion polymerization uses a redox pair such as sodium persulfate and sodium metabisulfite at 0.05–0.15 parts per hundred monomer.
The emulsion is applied by foam, spray, or pad-nip to the nonwoven web, then dried in a through-air or drum dryer at 120–150 °C for 60–120 s. The binder must reach crosslinking temperature without causing the web to embrittle. Terminal products include air-laid nonwovens, wet-laid fiberglass mats, surgical drapes, and tablecloths. Tensile properties are measured according to ASTM D5034 or ISO 9073-3, while free formaldehyde in the finished product is controlled against ISO 14184-1. Avoid introducing ammonia or volatile amines into the binder before polymerization because these accelerate VAM hydrolysis to acetic acid and acetaldehyde, shifting pH and reducing shelf stability. The lower inhibitor content does not eliminate the need for careful redox ratio control; it narrows the contribution of an uncontrolled radical terminator so that lot-to-lot cure behaviour is governed by the intended initiator chemistry.
Methanolysis of PVAc homopolymers derived from low-inhibitor VAM shifts the impurity profile because residual hydroquinone is carried into the alkaline hydrolysis step. The PVAc resin is dissolved in methanol at 20–30 wt% and reacted with sodium hydroxide at 0.4–0.6 wt% of PVAc at 40–50 °C for 30–60 min. The reaction is carried out on a continuous belt saponifier or in a kneader reactor. Under alkaline conditions, residual HQ can oxidize to quinoid species that impart yellow colour to partially hydrolyzed PVOH grades; the low-inhibitor monomer reduces this carbonyl load and improves methanol recycle quality. The degree of hydrolysis is controlled by methanol/water ratio and catalyst dosage, not by inhibitor level, but colour and ash content are directly affected by impurity carryover.
The resulting PVOH is isolated as powder or granules with degrees of hydrolysis between 87–89 mol% for partially hydrolyzed grades and 98–99 mol% for fully hydrolyzed grades, with viscosity average degree of polymerization between 500 and 3500. Applications include textile warp sizing, paper surface sizing, PVB interlayer for laminated safety glass, and EVOH barrier resin for food packaging. Designation and specification follow ISO 15023-1 and JIS K6726; optical clarity for PVB interlayer is influenced by sodium acetate ash and colour, both of which benefit from lower carbonyl loading in the VAM feedstock. Methanol recovery streams from low-inhibitor VAM-based PVAc show lower quinone accumulation over repeated distillation cycles, reducing the frequency of solvent column fouling and UV absorbance failures in the recovered alcohol.
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DCC VAM Low Inhibitor LI Grade is a vinyl acetate monomer produced by Dairen Chemical Corporation and registered under CAS 108-05-4. The product is supplied as a clear, flammable liquid with a boiling point of 72.7 °C at 101.3 kPa, a closed-cup flash point of approximately −8 °C, and a density of approximately 0.932 g/cm³ at 20 °C. The LI designation denotes a low-inhibitor formulation in which hydroquinone monomethyl ether (MEHQ) is controlled within a lower concentration band than the standard inhibited grade, while remaining sufficient to meet transport classification and short-term storage requirements. This grade is intended for downstream radical polymerization processes in which the residual inhibitor burden must be minimized to reduce initiator demand, shorten induction periods, or limit color-forming residues in the finished polymer. The molecular weight is 86.09 g/mol; batch-specific values should be verified against the current DCC certificate of analysis and not inferred from generic vinyl acetate monomer data.
The primary functional difference between DCC VAM Low Inhibitor LI Grade and standard inhibited vinyl acetate monomer is the MEHQ concentration. MEHQ operates as a radical scavenger only when dissolved oxygen is present; the phenolic inhibitor intercepts peroxy radicals and delays the onset of unplanned polymerization. Standard inhibited VAM is typically supplied with MEHQ in the 12–17 ppm range, while the LI grade is supplied in a lower band, commonly 3–7 ppm, as specified on the producer’s batch certificate. The LI grade is not an uninhibited monomer: it retains enough MEHQ for controlled storage under air, but the protection margin is narrower than that of the standard inhibited grade. Uninhibited VAM, by contrast, is generally not transported or stored without continuous temperature control and is reserved for closed manufacturing systems with immediate consumption.
MEHQ does not inhibit polymerization under oxygen-starved conditions. In a closed vessel, nitrogen blanketing strips dissolved oxygen and can therefore deactivate the inhibitor system even when MEHQ is still present at a nominal ppm level. This behavior is a common cause of storage incidents in plants that transfer low-inhibitor VAM into vessels previously used for oxygen-sensitive solvents. The lower MEHQ content reduces the radical scavenging load at the beginning of polymerization, but the practical effect is not directly proportional to inhibitor mass because oxygen mass transfer, comonomer ratio, and solvent polarity also control the induction interval. Published data for DCC-specific reactor yield differences is limited; each polymer line should quantify the effect using its own radical source and reaction temperature.
| Property | DCC VAM Low Inhibitor LI Grade | Standard Inhibited VAM |
|---|---|---|
| MEHQ content | 3–7 ppm typical | 12–17 ppm typical |
| Induction period at 70 °C by isothermal DSC | Shorter; formulation-specific | Longer |
| Oxygen requirement | Air blanketing required | Air blanketing required |
| Storage margin | Narrower; consume within producer shelf life | Wider |
| Radical scavenging load in polymerization | Reduced | Higher |
| Residual inhibitor in finished polymer | Lower | Higher |
The distinction between low-inhibitor and standard-inhibited VAM does not materially affect the distillation profile of the monomer because MEHQ is present at low ppm levels and is substantially less volatile than vinyl acetate. The practical separation concern arises in downstream purification or vent recovery, where inhibitor residues may accumulate in reboiler bottoms over time. In continuous polyvinyl alcohol production, residual MEHQ can interact with alkaline saponification conditions to form quinoid chromophores. A reduction in MEHQ from the standard inhibited band to the LI band lowers the concentration of such residues in the finished resin, but only when the saponification unit is operated within the specified alkali ratio and temperature profile.
On production-scale continuous polyvinyl acetate trains, batch-to-batch variation in low-level MEHQ can shift the initial exotherm. Pre-use verification by UV absorbance in the 280–300 nm region or by high-performance liquid chromatography is recommended before tank unloading. This is particularly relevant for plants with limited cooling capacity, where an earlier exotherm can exceed the jacket heat-transfer limits and alter molecular weight distribution through temperature-dependent chain transfer to polymer.
Storage of DCC VAM Low Inhibitor LI Grade must preserve the dissolved oxygen required for MEHQ inhibition. Inert-gas blanketing with nitrogen or argon is not permitted because it strips oxygen and can render the inhibitor ineffective, allowing free-radical polymerization to initiate spontaneously. Storage temperatures should remain below 25 °C where practical; elevated temperatures accelerate peroxide formation and deplete MEHQ. The product should be stored in stainless steel or lined carbon steel tanks equipped with flame arrestors and pressure/vacuum conservation vents. Contact with copper or brass should be avoided because transition-metal ions can catalyze polymerization or decompose the inhibitor system. Recommended storage duration is the shortest feasible; the producer’s shelf life is a function of inhibitor level and should not be exceeded without re-analysis of MEHQ, acidity, and distillation color.
Under transport regulations, the material is classified as UN 1301, Class 3, Packing Group II. The flash point is approximately −8 °C by closed-cup methods, and explosive limits in air are approximately 2.6–13.4 vol%. The low inhibitor content does not remove the requirement for flameproof electrical equipment or static-grounded transfer lines; it only shortens the safety margin against polymerization. Bulk transfer systems should be dedicated to VAM service because cross-contamination with reactive chemicals can destabilize the monomer even at trace levels.
In emulsion and solution polymerization of vinyl acetate, MEHQ acts as a retarder at commercial concentrations rather than a true inhibitor, because it consumes oxygen-centered radicals and delays propagation. The LI grade therefore exhibits a shorter induction period at typical reaction temperatures of 65–85 °C. In a jacketed batch reactor using a water-soluble azo initiator, a shift from standard inhibited to LI-grade monomer can require a measurable reduction in initiator feed rate to hold the same exotherm profile, but no universal correction factor applies. Isothermal differential scanning calorimetry according to ISO 11357-6 is used to compare induction times under controlled oxygen-limited conditions; it does not replace full-scale reactor validation.
Polymerization reactors should be monitored for heat evolution because low-inhibitor monomer may show a steeper exotherm onset. The heat of polymerization for vinyl acetate is approximately 88 kJ/mol, so an early exotherm in a large batch can exceed the condenser and jacket heat-removal capacity if initiator addition is not adjusted. Temperature overshoot increases the rate of chain transfer to polymer in polyvinyl acetate systems, raising molecular weight distribution breadth and gel content in downstream polyvinyl alcohol. Continuous stirred-tank reactors operating on LI-grade feed may need to adjust residence time and initiator injection points if the steady-state conversion target is to be maintained. These adjustments are process-specific and should be documented with reactor temperature, agitator power draw, and monomer conversion data.
For polyvinyl alcohol producers, low residual MEHQ is generally desirable because phenolic residues can impart color during alkaline saponification. However, the benefit does not compensate for poor temperature control. If a LI-grade feed permits a faster initiation, the resulting exotherm can shift the molecular weight distribution unless the saponification feedstock has consistent degree of polymerization and branching. Reactor operators should compare the inhibitor content, oxygen partial pressure in the feed, and initiator decay half-life before switching from standard inhibited VAM to the LI grade.
DCC VAM Low Inhibitor LI Grade is certified against the producer’s release specification. The primary industry standard for vinyl acetate monomer is ASTM D2190; the following table lists routine properties and test methods commonly reported on a certificate of analysis. Batch-specific values are controlled by the DCC certificate of analysis and may differ by production site and transport logistics.
| Property | Typical value or limit | Test method |
|---|---|---|
| Purity | 99.9% min by gas chromatography | ASTM D2190/producer GC |
| Water | ≤0.05 wt% | ASTM E203 Karl Fischer titration |
| Acidity as acetic acid | ≤0.005 wt% | ASTM D1613 |
| MEHQ content | 3–7 ppm for LI grade | HPLC with UV detection |
| Color | ≤10 APHA/Pt-Co | ASTM D1209 |
| Density at 20 °C | 0.931–0.933 g/cm³ | ASTM D4052 |
| Distillation range | 71.8–73.0 °C | ASTM D1078 |
| Flash point | approximately −8 °C | ASTM D56 Tag closed cup |
Low-level MEHQ verification is normally performed by HPLC with UV detection because colorimetric methods can under-report MEHQ in the presence of other phenolic species. Incoming tank analysis should be compared with the certificate of analysis before transfer to process storage, especially when monomer is delivered over long distances or transferred through shared pipelines. The term low inhibitor does not alter the carbonyl, aldehyde, or ester impurity limits. Users requiring low aldehyde VAM for specific polymer odor or molecular weight control should specify those parameters separately, because DCC VAM Low Inhibitor LI Grade primarily addresses MEHQ level and not necessarily the trace carbonyl profile.
Adhesive and coating emulsion producers select the LI grade when residual MEHQ in the finished polyvinyl acetate dispersion contributes to yellowing or to delayed cure in subsequent compounding. In polyvinyl alcohol production, the lower inhibitor level reduces the load of phenolic residues entering the saponification unit, where alkaline conditions can convert phenolic inhibitors to colored quinonoid structures. Ethylene-vinyl acetate copolymerization units that operate with peroxide initiators may run on low-inhibitor VAM to reduce the scavenging of free radicals in the high-pressure reactor feed; however, compatibility with the reactor vendor’s feed specification must be confirmed before substitution.
Compared with the standard inhibited grade, DCC VAM Low Inhibitor LI Grade offers a lower residual-inhibitor burden and a shorter polymerization induction window, but at the cost of a narrower storage margin. It should not be selected for long-term stockholding or for transfer into storage systems where oxygen control cannot be maintained. Standard inhibited VAM remains preferable for extended storage or for locations where ambient temperatures exceed the recommended band for prolonged periods.
