For solid powder PGMA with number-average molecular weight 40-80 Mn*103 (g/mol) manufactured in industrial plants, the exclusive mainstream mass-production process is solution free-radical polymerization followed by solvent precipitation powder-making and low-temperature vacuum drying.

Other polymerization routes are eliminated for large-scale commercial production of this specification, detailed as below.

1. Reason for selecting solution polymerization + precipitation process

Molecular weight matching logic (40,000–80,000 high molecular weight)

• Low chain-transfer system: Thiol molecular weight regulators are rarely or never added; low initiator dosage and prolonged polymerization at mild temperature are adopted to achieve high \(M_n\) above 40,000 steadily.

• Suspension polymerization: Fast heat transfer in aqueous phase causes severe chain transfer. Industrial suspension PGMA normally has \(M_n\) lower than 30,000, which cannot stably reach 40,000–80,000. Its product is rigid porous microspheres instead of loose ultrafine powder.

• Bulk polymerization: Ultra-high viscosity of high-molecular-weight system leads to runaway exotherm and crosslinking gelation, unfeasible for industrial scale-up.

• Emulsion polymerization + spray drying: Final powder contains residual emulsifiers, resulting in unstable epoxy groups; rarely used for high-epoxy solid PGMA.

• ATRP / RAFT controlled radical polymerization: High cost of catalysts and chain transfer agents, single-batch output limited to hundreds of kilograms. Only applied for small-batch special narrow-distribution products instead of mass-produced general PGMA powder with \(M_n\) 40–80 kDa.

Product morphology matching: white loose solid powder

1. Solution polymerization in reactors: Xylene, butyl acetate or toluene act as reaction solvents to form high-viscosity PGMA resin solution after polymerization.

2. Precipitation procedure (core step for powder formation): Diluted PGMA resin solution is slowly added into excessive cold methanol (poor solvent). High-molecular PGMA precipitates instantly into ultrafine flocculent powder.

3. Plate-and-frame filter press separates solids, followed by repeated washing with fresh methanol to remove residual GMA monomer and initiator residues.

4. Vacuum drying at 45–55 °C under negative pressure (strict temperature control to avoid epoxy ring-opening crosslinking). After crushing and sieving, loose white ultrafine solid PGMA powder is obtained.

2. Complete industrial production flow (for PGMA \(M_n\) 40–80 kDa solid powder)

Step 1 Raw material pretreatment

GMA monomer passes through alkaline alumina column to remove MEHQ polymerization inhibitor; water content controlled below 100 ppm. The whole system is protected by nitrogen to isolate oxygen (radical inhibitor).

Step 2 Polymerization stage (dropwise solution free-radical process)

1. Charge 60% total solvent into polymerization reactor, heat to 70–78 °C.

2. Hardly add thiol regulators (thiols sharply reduce molecular weight, minimal or zero dosage required for \(M_n\) above 40 kDa).

3. AIBN low-temperature initiator, dosage controlled at 0.2%–0.4% of monomer mass; low initiator loading favors high number-average molecular weight.

4. Dropwise feed pure GMA monomer uniformly over 2.5–4 hours. Low instant monomer concentration suppresses chain termination and raises final \(M_n\).

5. Hold temperature for 6–10 hours after feeding to reach monomer conversion ≥ 93%.

6. Cool down and dilute high-viscosity resin with supplementary solvent for subsequent precipitation.

Step 3 Precipitation & powder separation

1. Fill precipitation tank with excess cold methanol (-5 ~ 10 °C) under high-speed stirring.

2. Drizzle diluted PGMA resin solution slowly into cold methanol, white fine polymer powder precipitates out.

3. Stir for 1 hour to complete sedimentation, filter via plate-and-frame filter press.

4. Multiple methanol washing cycles to eliminate unreacted monomer and initiator byproducts.

Step 4 Drying & finished product treatment

Filter cake is sent to vacuum drying oven, dried at 45–52 °C under vacuum until volatile content < 0.5%. After crushing and sieving, solid PGMA powder finished goods with \(M_n \times 10^3 = 40\sim80\ \mathrm{g/mol}\) are packed.

3. Distinguishing features of this industrial process (for factory route verification)

1. Workshop supporting equipment: Polymerization reactors, methanol precipitation tanks, filter press units, low-temperature vacuum drying ovens, methanol recovery rectification tower.

2. Formulation characteristics: Zero or trace thiol regulators, low initiator dosage, long monomer feeding time + prolonged curing holding period.

3. GPC test indicators: Stable \(M_n\) 40,000–80,000, polydispersity index PDI = 1.7–2.3.

4. Appearance: No spherical microspheres, delicate white powder when rubbed between fingers, high & stable epoxy value.

4. Downstream applications of this PGMA powder

• Compatibilizer for engineering plastic alloys (PA / PBT / PC blends)

• Epoxy modifier for powder coatings

• Modifier for glass fiber & inorganic mineral fillers

Short One-Sentence Abstract (for catalog/TDS use)

Solid PGMA powder with molecular weight \(M_n = 40\sim80\ \mathrm{kDa}\) is industrially manufactured via solution free-radical polymerization, followed by solvent precipitation and low-temperature vacuum drying; suspension, emulsion and controlled polymerization cannot realize large-scale production of this specification.