Polyethylene Glycol (PEG 200 to 8000) Manufacturer: Pharma & Industrial portfolios are differentiated by molecular weight distribution, residual catalyst content, peroxide load, endotoxin level, and packaging controls rather than nominal grade alone. The product is a linear polyether diol, CAS 25322-68-3, general formula H(OCH₂CH₂)_nOH, produced through base-catalyzed ring-opening ethoxylation of ethylene glycol, diethylene glycol, or lower-molecular-weight PEG. Liquid grades 200 through 600 and solid grades 1000 through 8000 are water-soluble at ambient temperature, with solubility exceeding 50 wt% across most of the range. Pharmaceutical release is controlled by USP-NF Polyethylene Glycol and Ph. Eur. 1444; industrial material is released under ISO 9001:2015 and REACH Regulation (EC) 1907/2006. The technically significant batch variables are ethylene oxide residual, 1,4-dioxane residual, ethylene glycol/diethylene glycol, formaldehyde, water, pH, and peroxide value.

Representative grade properties for PEG 200–8000

Grade	Average molecular weight (Da)	Viscosity at 25°C or melting range	Hydroxyl value (mg KOH/g)
PEG 200	190–210	4.3 cSt liquid	535–590
PEG 300	285–315	5.9 cSt liquid	340–394
PEG 400	380–420	7.3 cSt liquid	267–295
PEG 600	570–630	15.7 cSt liquid	178–197
PEG 1000	950–1050	melting 37–40°C	107–118
PEG 1450	1300–1600	melting 43–46°C	70–85
PEG 3350	3015–3685	melting 53–57°C	30–38
PEG 4000	3600–4400	melting 53–59°C	25–35
PEG 6000	5400–6600	melting 55–61°C	16–22
PEG 8000	7000–9000	melting 60–63°C	12–16

How Does Ethylene Oxide Ring-Opening Control the 200 to 8000 Molecular Weight Band?

The molecular weight band is set by the ethylene oxide-to-starter hydroxyl ratio in a closed stainless-steel reactor operated under nitrogen pressure between 1.5 bar and 4.0 bar at 120°C to 160°C. Potassium hydroxide at 0.2–0.5 wt% is preferred over sodium hydroxide because it yields faster propagation and lower residual sodium after neutralization with lactic acid. Ethylene oxide is added sequentially until the targeted hydroxyl value is approached; for PEG 400, the molar ratio is near 9:1, while PEG 8000 requires a proportionally higher ratio and longer feed time. Post-reaction neutralization, adsorption filtration, and vacuum stripping at 80–120°C reduce catalyst residues and volatiles. Ethylene oxide residual and 1,4-dioxane are not eliminated by simple distillation alone in high-MW grades; thin-film strippers or wiped-film evaporators with high liquid turnover are required because the impurities partition into the polymer phase. Published data for specific EO-to-initiator ratio charts at manufacturing scale is limited, and each reactor train must be validated for residual ethylene oxide and 1,4-dioxane under worst-case feed interruption conditions.

Neutralization of the alkaline catalyst with lactic acid or glycolic acid produces soluble salts; if potassium lactate remains above 0.1 wt%, it can precipitate in high-MW solid grades during flaking and increase conductivity. Filtration through activated carbon at 70–85°C reduces color and peroxide precursors, but over-bleaching increases ethylene glycol and diethylene glycol through hydrolysis. Contact time is therefore restricted to 30–60 min, and pH is maintained between 4.5 and 7.5.

In pharmaceutical high-shear granulation on a 600 L vertical granulator, PEG 6000 is milled to a mass median particle size near 250 µm and dry-blended before water addition. The endpoint is not viscosity-controlled; impeller torque and chopper power draw define the water endpoint. The process window narrows when PEG 6000 content exceeds 8 wt% because friction-induced heating above 45°C partially melts the binder, and recrystallization during cooling forms dense agglomerates. Drying at 40°C is preferred over 60°C to avoid surface blooming. Dissolution is evaluated by USP <711> Apparatus 2 at 50 rpm in 900 mL of 0.1 N HCl; tablets containing more than 15 wt% PEG typically require a swelling disintegrant such as croscarmellose sodium at 3–5 wt% to maintain disintegration times below 15 min. The same solid grades are used in suppository bases, where the melting range of 55–61°C for PEG 6000 is blended with PEG 1000 or PEG 1450 to achieve a 37–45°C melting suppository mass.

When PEG 400 Substitutes for Glycerol in Softgel Fill Compounding

PEG 400 is accepted as a hydrophilic softgel fill vehicle when glycerol or propylene glycol is excluded because of aldehyde content or viscosity mismatch. The liquid has a viscosity range of 6.8–8.0 cSt at 25°C and is preheated to 35–40°C before deaeration under −0.08 MPa to remove air bubbles from the ribbon fill. Neat PEG 400 has low water content after vacuum drying, typically below 1.0 wt%, and will abstract moisture from the gelatin shell; shell plasticizer ratios are adjusted by 0.3–0.5 parts glycerol per part PEG in the fill to limit embrittlement. Water activity is measured by chilled-mirror dew point according to USP <1112>. Published data for specific capsule dimensions and rib thickness in PEG-filled softgels is limited; ribbon moisture index and seal temperature are established on a per-die basis.

Industrial synthetic coolants and metalworking fluids use PEG 400 and PEG 600 at 2–8 wt% as water-soluble lubricity additives because the polyether chain provides hydrodynamic film strength without mineral oil. Closed-cup flash points for PEG 400 and PEG 600 typically exceed 200°C, but aqueous dilution reduces fire risk only above 70 wt% water. Textile spin finishes and rubber release agents use PEG 300 to 600 for uniform film formation; high-MW solid grades are used as anti-redeposition agents in detergent bars and as humectants in leather processing. The addition of PEG 3350 or PEG 8000 to water-based drilling fluids at 1–3 wt% can reduce fluid loss, but the polymer is incompatible with high concentrations of borate crosslinkers, which can form shear-thickening complexes and plug shaker screens.

In osmotic pump tablet coatings, PEG 3350 and PEG 8000 are used as pore formers in cellulose acetate membranes at 10–30 wt%. During aqueous coating, the water-soluble PEG leaches to form pores; pore size distribution depends on PEG molecular weight and coating annealing temperature. Coating pan inlet air temperature is maintained at 50–60°C, exhaust relative humidity at 20–35%, and atomization pressure at 1.5–2.0 bar. Published data for specific core geometry is limited; dissolution of the core is evaluated by USP <711> Apparatus 2 under conditions relevant to the dosage form.

Thermal-Oxidative Degradation Limits in Hot-Melt Extrusion with PEG 6000

Hot-melt extrusion with PEG 6000 at 10–30 wt% as a plasticizer is constrained by autoxidation at barrel residence temperatures above 90°C. Peroxide content increases during aerated holding at 80°C; oxidative chain scission produces formaldehyde and formic acid, which degrade acid-labile APIs. Nitrogen blanketing of the feed hopper and limiting melt residence time to 2–4 min reduce peroxide accumulation. Stabilizer additions such as butylated hydroxytoluene at 0.01–0.05 wt% are used when elevated barrel temperatures above 100°C are unavoidable. Amine-based additives are incompatible because amine-catalyzed autoxidation raises aldehyde and formic acid levels. On a co-rotating twin-screw extruder with L/D 40:1, screw speed is often set between 100–300 rpm; published data for specific screw configurations is limited.

Release testing for pharmaceutical PEG grades is governed by the USP-NF Polyethylene Glycol monograph and Ph. Eur. 1444. Industrial grades are not automatically suitable for pharmaceutical use, even when average molecular weight overlaps, because endotoxin, residual solvent, and peroxide specifications differ. The matrix below summarizes routine release parameters.

Release parameters and test methods for PEG 200–8000

Parameter	Test method	Typical pharmacopeial criterion
Average molecular weight	USP-NF PEG monograph /Ph. Eur. 1444	within ±10% of label for solid grades
Viscosity	USP <911> /Ph. Eur. 2.2.8	grade-specific range
pH of 5% solution	USP <791>	4.5–7.5
Hydroxyl value	Ph. Eur. 2.5.3	grade-specific range
Ethylene oxide residual	Ph. Eur. 1444 GC headspace	≤ 1 ppm
1,4-Dioxane residual	Ph. Eur. 1444 GC headspace	≤ 10 ppm
Water content	USP <921> Karl Fischer	≤ 1.0 wt% for solid grades
Endotoxin	USP <85>	≤ 2.5 EU/g for parenteral applications

For parenteral and ophthalmic applications, PEG 3350 and PEG 8000 are released with endotoxin below 2.5 EU/g and bioburden below 10² CFU/g; they are typically double-bagged with desiccanted polyethylene liners. Industrial material may have higher sodium, potassium, and reducing-substance levels, and cannot be recertified as pharmaceutical grade without validated purification and change control under ICH Q7. Residual ethylene oxide is not the only constraint; formaldehyde carries classification under CLP at or above 0.1%, and must be controlled in both pharma and industrial batches. Storage of solid PEGs above 40°C in bulk bags leads to compaction and caking; storage below 20°C avoids fusion of low-melting PEG 1000 and PEG 1450. Oxidative stability during storage is improved with nitrogen-flushed packaging and reduced peroxide headspace, particularly for grades used in polyvinyl alcohol film and hot-melt adhesives.