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Slow Release Polycarboxylate Superplasticizer Synthesized with Functional Monomers

In modern concrete production, slow-release polycarboxylate superplasticizers have become essential for long-distance transportation, hot weather construction, and high-durability projects. Traditional slow-release products rely on expensive ester monomers, which increase production costs.

This study introduces a low-cost, high-performance slow-release polycarboxylate superplasticizer synthesized from a new ester-functional monomer derived from acrylic acid (AA) and ethylene glycol (EG). The research optimizes both monomer synthesis and superplasticizer formulation, delivering a cost-effective solution with excellent slump retention and water reduction.

Raw Materials & Synthesis Route

Functional Monomer Preparation (Esterification)

Reactants	Acrylic acid (AA) + Ethylene glycol (EG)
Catalyst	Concentrated H₂SO₄
Inhibitor	Hydroquinone (HQ)
Temperature	90 – 120 °C
Time	80 min (optimized)

The reaction produces ethylene glycol acrylate ester – a functional monomer that introduces hydrolyzable ester groups into the PCE molecular chain.

PCE-F Copolymerization

TPEG	Polyether macromonomer (steric stabilization)
AA	Carboxyl groups (adsorption on cement)
Functional monomer (EG-AA ester)	Slow-release ester groups
Mercaptopropionic acid (MPA)	Chain transfer agent (molecular weight control)
H₂O₂ + Vc	Redox initiation system (25 °C)

Dosing sequence: A: (AA + functional monomer) added over 2 h, B: (MPA + Vc) over 2.5 h.

Key Factors Affecting Esterification Rate

To maximize esterification yield while controlling cost, the study evaluated four variables.

Molar Ratio of EG to AA

1.0:1	78.73%
1.2:1	82.89%
1.3:1	83.01% (negligible gain)

Optimal: 1.2:1 – balances conversion with excess EG cost.

Reaction Temperature

95 °C → 79.07%
115 °C → 82.89% (best)
125 °C → 77.59% (side reactions increase)

Reaction Time

0–40 min: rapid increase
80 min: maximum esterification rate
80 min: no further gain (slight decline)

Catalyst (H₂SO₄) Dosage

1%	~78%
3%	82.89%
5%	drops (more side reactions)

Optimal esterification conditions:
EG:AA = 1.2:1, 115 °C, 80 min, 3% H₂SO₄.

Optimizing PCE-F for Slow-Release Performance

Acid-to-Ether Ratio (n(AA) : n(TPEG))

1.35	85	–	–
1.60	increases	–	–
1.85	160	245	210
2.10	higher initial	lower	lower
2.35	160	declines	declines

Best: 1.85 – provides good initial dispersion + excellent slow-release (peak at 1 hour).

Functional Monomer Dosage (% of TPEG mass)

9%	high	moderate	moderate	less slow-release
15%	100	245	220	optimal
18%	lower	lower	lower	too many ester groups → poor hydrolysis

At 15%, ester groups hydrolyze gradually, releasing carboxyl groups over time – ideal for slump retention.

Chain Transfer Agent (MPA) Dosage

MPA controls the polymer’s molecular weight – a critical factor for slow-release behavior.

0.2–0.3%	Molecular weight too high → ester groups buried → slow/no hydrolysis
0.4%	Best balance (initial 110 mm → 1h 245 mm → 2h 220 mm)
0.5–0.6%	Molecular weight too low → rapid hydrolysis → no sustained release

Optimal MPA: 0.4% of TPEG.

FTIR Confirmation

Functional monomer: Peaks at 1731 cm⁻¹ (C=O ester), 1265 cm⁻¹ & 1183 cm⁻¹ (C–O–C) → ester successfully formed.
PCE-F: No C=C peak at 1644 cm⁻¹ → monomers fully copolymerized. Ester and ether bands present.

Performance Comparison with Commercial Slow Release Polycarboxylate Superplasticizer

Test method: Cement paste fluidity over time (0–90 min).

PCE-HEA (commercial)	0	230	60	–
PCE-F (this study)	100	245	60	220

PCE‑F provides immediate initial dispersibility (unlike PCE‑HEA, which starts at 0 mm) while maintaining similar peak and retention.

Why This Matters for Ready-Mix & Long-Distance Transport

Lower raw material cost (EG is much cheaper than hydroxyethyl acrylate)
Balanced profile: initial dispersibility + sustained release + strength retention
Easy to synthesize at 25 °C (ambient copolymerization)
Compatible with standard PCE blending ratios

For concrete producers facing:

Long trucking times (1–2 h)
High ambient temperatures
Variable cement/admixture compatibility

PCE‑F offers a cost-effective, high-performance slow-release solution.

Conclusion

The slow release polycarboxylate superplasticizer synthesized with EG-AA functional monomer provides an excellent combination of cost efficiency and high performance.

With optimized esterification and polymerization conditions, it delivers:

Strong, slow-release slump retention
Good initial fluidity
High compatibility
Significantly lower production cost

This new type of PCE is ideal for ready-mix concrete, high-rise construction, hot-site casting, and long-transport projects requiring stable workability over time.