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Dual Macromonomer Copolymerization Polycarboxylate Superplasticizer

Polycarboxylate superplasticizers are the backbone of modern high‑performance concrete. They provide unmatched water reduction, slump retention, and environmental benefits. However, conventional PCEs synthesized from a single macromonomer – typically either isobutylene polyethylene glycol ether (HPEG) or isopentenyl polyethylene glycol ether (TPEG) – often face limitations:

HPEG‑based PCE: The isobutylene group creates high steric hindrance, leading to low radical copolymerization activity. The resulting polymer often has a broad molecular weight distribution and reduced adsorption‑dispersion balance.
TPEG‑based PCE: Higher reactivity gives better adsorption, but the side chains are prone to oxidative degradation at elevated temperatures, causing rapid slump loss. The synthesis also requires strict low‑temperature control, complicating industrial production.

A recent study by Zhou Long and colleagues (Shanxi Datong University, 2026) introduces a dual macromonomer copolymerization strategy that combines HPEG and TPEG in a single PCE. By optimizing the mass ratio and process parameters, the resulting PCE achieves superior water reduction, excellent slump retention, and enhanced mechanical strength – outperforming single‑monomer PCEs in every key metric.

This article summarizes their synthesis optimization, performance data, and practical implications.

Why use Two Macromonomers?

The core idea is to leverage the complementary strengths of HPEG and TPEG:

Macromonomer	Advantage	Limitation
HPEG (C4)	Long side chain → strong steric hindrance → delays cement particle agglomeration	Low reactivity; broad molecular weight distribution
TPEG (C5)	High reactivity → fast polymer backbone formation → strong adsorption stability	Side chains degrade at high temperature; synthesis requires low‑temperature control

By copolymerizing both, the PCE gains:

Strong adsorption from TPEG’s high reactivity
Robust steric stabilization from HPEG’s long side chains
Balanced molecular structure – not too broad, not too narrow
Good slump retention even at elevated temperatures

Synthesis Optimization

Raw Materials

Macromonomers: HPEG (C4) and TPEG (C5), industrial grade
Small monomer: Acrylic acid (AA)
Initiator: Potassium persulfate (KPS)
Chain transfer agent: Thioglycolic acid (TGA)
Reducer (optional): Ascorbic acid (not always needed)
Neutralizer: Sodium hydroxide solution

Polymerization Procedure

Dissolve HPEG and TPEG (total mass fixed) in deionized water at 35 °C to form solution A.
Prepare solution B: acrylic acid, deionized water, TGA, and ascorbic acid (if used).
Add KPS to solution A, then add solution B dropwise over 3 hours under stirring (400 rpm).
Continue the reaction for 1 hour after the addition is complete.
Cool and adjust pH to 6–7 with NaOH.

Key Optimization Variables

The study systematically varied four parameters:

Parameter	Range tested	Optimal value (relative to total macromonomer mass)
HPEG : TPEG mass ratio	4:1, 3:1, 2:1, 1:1	3:1
Potassium persulfate dosage	2.0%, 2.2%, 2.4%, 2.6%, 2.8%	2.2%
Acrylic acid dosage	8.8%, 11.1%, 13.3%, 15.5%, 17.7%	11.1%
Thioglycolic acid dosage	0.4%, 0.6%, 0.8%, 1.0%, 1.2%	0.8%

The response was cement paste flow (initial and over time) measured according to GB/T8077‑2023 (water/cement = 0.29, PCE dosage = 0.3% solid on cement).

Performance Results

HPEG:TPEG Mass Ratio

At 1:1 and 2:1, flow values were moderate.
At 3:1, the initial flow reached 310 mm, and the 2‑hour flow loss was only 11.1% – excellent retention.
At 4:1, performance dropped sharply due to excessive HPEG, which reduced adsorption.

Optimal ratio: 3:1 (HPEG:TPEG).

Potassium Persulfate Dosage

Increasing KPS from 2.0% to 2.2% raised the initial flow to 325 mm and the 2‑hour flow to 245 mm.
Further increase to 2.4–2.8% caused lower flows because:
- Too little initiator → high molecular weight → polymer entanglement → poor adsorption.
- Too much initiator → low molecular weight → thin adsorption layer → weak steric hindrance.

Optimal KPS: 2.2% of macromonomer mass.

Acrylic Acid Dosage

At 8.8% AA, the flow was low (insufficient carboxyl groups for adsorption).
At 11.1% AA, flow peaked (initial 325 mm, 2‑h 245 mm).
Higher AA (13.3–17.7%) gave no further increase – adsorption sites on cement particles become saturated.

Optimal AA: 11.1% of macromonomer mass.

Thioglycolic Acid Dosage

TGA controls molecular weight. At 0.4–0.6%, the molecular weight was too high, leading to poor dispersion.
At 0.8% TGA, flows were best: initial 330 mm, 30 min 315 mm, 1 h 285 mm, 2 h 255 mm.
At 1.0–1.2%, the molecular weight became too low → reduced steric stabilization.

Optimal TGA: 0.8% of macromonomer mass.

FT‑IR Confirmation

The optimized PCE showed characteristic peaks:

3434 cm⁻¹ – O–H (hydroxyl)
2887 cm⁻¹ – C–H (methyl)
1728 cm⁻¹ – C=O (carboxyl)
1658 cm⁻¹ – C=C (residual vinyl, low)
1113 cm⁻¹ – C–O–C (ether side chain)

The spectrum confirmed successful copolymerization of all monomers.

Mechanical Strength: Cement Mortar

The optimized dual‑monomer PCE (HPEG/TPEG = 3:1) was compared with:

Blank (no PCE)
HPEG‑only PCE
TPEG‑only PCE

Sample	3d flexural (MPa)	3d compressive (MPa)	7d flexural	7d compressive	28d flexural	28d compressive
Blank (no PCE)	4.2	24.9	5.5	36.3	6.6	45.7
HPEG‑only PCE	4.9	28.0	6.2	39.6	6.8	48.7
TPEG‑only PCE	5.3	30.2	6.9	43.9	8.1	54.3
HPEG/TPEG 3:1	6.9	36.2	7.5	50.4	8.4	61.8

Key improvements over blank:

3d compressive strength: +45.4%
28d compressive strength: +35.2%
3d flexural strength: +64.3%

The dual‑monomer PCE significantly outperformed both single‑monomer PCEs, demonstrating true synergy.

Why the Dual Macromonomer Copolymerization Polycarboxylate Superplasticizer Works Better

Property	Single‑monomer PCE	Dual‑monomer PCE (HPEG/TPEG 3:1)
Adsorption	Moderate (one type of anchor)	Enhanced (TPEG provides high reactivity)
Steric hindrance	Limited (one side‑chain length)	Strong (HPEG long chains provide long‑term stability)
Molecular weight distribution	Often broad	Narrower (balanced by chain transfer)
Slump retention	Poor in heat (TPEG) or low activity (HPEG)	Excellent (both mechanisms work)
Early strength	Modest	Very high (dense, well‑dispersed microstructure)
Long‑term strength	Good but not optimal	Outstanding (>61 MPa at 28d for C45 mortar)

Practical Advantages for Concrete Production

Reduced dosage for the same water reduction – cost saving.
Stable performance with varying cement types and temperatures – robust for real‑world batching plants.
Excellent early strength – faster formwork turnover, shorter construction cycles.
Good slump retention – long pumping distances and slow placement times are accommodated.
Room‑temperature synthesis is possible – the optimized recipe uses 35 °C, eliminating the need for high‑energy heating.

Conclusion

A novel polycarboxylate superplasticizer was successfully synthesized by copolymerizing HPEG and TPEG as dual macromonomers with acrylic acid, using potassium persulfate as initiator and thioglycolic acid as chain transfer agent.
The optimal synthesis parameters are:
- HPEG : TPEG mass ratio = 3:1
- Potassium persulfate dosage = 2.2% of macromonomer mass
- Acrylic acid dosage = 11.1% of macromonomer mass
- Thioglycolic acid dosage = 0.8% of macromonomer mass
The optimized PCE achieved:
- Cement paste initial flow = 330 mm, 2‑h flow = 255 mm (low loss)
- 28‑day mortar compressive strength = 61.8 MPa (+35% vs. blank)
The dual‑monomer approach overcomes the limitations of both HPEG and TPEG, providing a balanced molecular structure that offers high adsorption, strong steric hindrance, and excellent mechanical enhancement.
This work provides a practical, industrially viable route to high‑performance PCEs for demanding concrete applications.