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Effect of TPEG concentration on the polymerization rate of polycarboxylate superplasticizers and the number of reaction order

Polycarboxylate superplasticizers (PCE) are the most important admixtures in modern high-performance concrete. Isopentenyl polyoxyethylene ether (TPEG) is the dominant macromonomer used in industrial PCE synthesis. Understanding how TPEG concentration influences polymerization behavior is critical for stabilizing production, improving conversion rate, and ensuring consistent product performance.

This study uses aqueous free-radical copolymerization to analyze TPEG concentration, polymerization rate, reaction order, monomer reactivity, and molecular weight of PCE. The results provide a clear kinetic basis for optimizing industrial PCE manufacturing.

Experimental Basics: Materials & Synthesis

Raw Materials

TPEG 2400: main macromonomer
Acrylic acid (AA): small monomer
Ammonium persulfate (APS): initiator
Sodium methallyl sulfonate (MAS): chain transfer agent
Deionized water: reaction medium

Synthesis Method

One-shot feeding aqueous free-radical copolymerization
Fixed reaction volume, constant AA/APS/MAS dosage
Only the TPEG initial concentration is varied.
Sampling every 5 minutes in the first hour to track the reaction

Characterization Methods

FT-IR: confirm functional groups
GPC: measure residual TPEG, molecular weight
¹H-NMR: calculate actual acid‑ether ratio
Kinetic fitting: determine reaction order

Core Findings: TPEG Concentration & Polymerization Behavior

TPEG Concentration vs. Reaction Rate

As the TPEG initial concentration increases, the polymerization rate rises.
Rate increases from 4.1×10⁻⁵ to 6.9×10⁻⁵ mol/(L·s)
Higher TPEG → faster early‑stage reaction

Conversion vs. Time

TPEG conversion rises quickly in 0–30 minutes, then slows
Higher TPEG loading → lower final conversion
Reason: TPEG cannot homopolymerize; it only copolymerizes with AA. Fixed AA limits total conversion.

Polymerization Rate Trend

Rate rises first, then falls.
Early: high monomer/initiator concentration + gel effect → acceleration
Late: monomer depletion + high viscosity → rate decreases.

TPEG Reaction Order: 0.68

A key kinetic result:

The reaction order of TPEG in PCE copolymerization is 0.68
Kinetic equation:
Rp ∝ [TPEG]^0.68
This means the polymerization rate is moderately dependent on TPEG concentration.

Monomer Reactivity: AA > TPEG

¹H-NMR data show:

Actual acid‑ether ratio > feed acid‑ether ratio
Acrylic acid (AA) reacts faster and more completely.
TPEG has lower reactivity and is left partially unreacted

This explains why AA dominates both the polymerization rate and the structure formation.

Molecular Weight Changes

Higher TPEG concentration → lower molecular weight (Mw/Mn)
Higher TPEG → higher residual macromonomer
The acid-ether ratio strongly controls the final molecular weight.
PDI remains relatively stable under optimized conditions

Why This Matters for Industrial Production

For PCE Manufacturers

Control TPEG dosage to stabilize the rate
Excess TPEG speeds reaction but lowers conversion and increases residue.

Balance the acid‑ether ratio
Ensure sufficient AA to consume TPEG and achieve the target molecular weight.

Predict reaction speed
Use a 0.68 reaction order to design temperature and feeding profiles.

Improve product consistency
Reduce fluctuation in fluidity, slump retention, and compatibility.

For Concrete Performance

Proper TPEG concentration ensures:
High dispersing ability
Good slump retention
Low unreacted monomer content
Stable compatibility with cement, fly ash, and machine‑made sand

Conclusion

Increasing TPEG concentration accelerates polymerization but reduces the final conversion.
The reaction order of TPEG is 0.68, providing a key kinetic parameter.
AA reactivity > TPEG reactivity, so the actual acid‑ether ratio is always higher than the feed ratio.
Moderate TPEG dosage achieves the best balance of rate, conversion, molecular weight, and stability.

This study gives manufacturers a science‑based tool to optimize TPEG‑based polycarboxylate superplasticizer production.