How Do Isocyanates and Polyols Affect the Performance of Polyurethane Coating Films: Structure, Raw Material Selection, and Performance Design Essentials

Introduction

The performance of polyurethane (PU) coating films originates first and foremost from the structure of the raw materials.

In polyurethane systems, isocyanates and polyols are the two most essential classes of raw materials. Isocyanates provide isocyanate groups, namely NCO groups, —N=C=O, while polyols provide hydroxyl groups, namely OH groups, —OH. The reaction between NCO and OH forms urethane linkages, which constitute the fundamental chemical basis for the formation of polyurethane structures.

R-NCO + R′-OH → R-NH-COO-R′

When analyzing the performance of polyurethane coating films, the following factors should be further considered:

1. Which type of isocyanate is used;

2. Which type of polyol is used;

3. The functionality, molecular weight, structural rigidity, and polarity of the raw materials;

4. The soft/hard segment structure and crosslinked structure formed after combining the raw materials.

Raw Material	Main Function
Isocyanate	Determines reaction activity, crosslinking capability, hardness, yellowing tendency, and weather resistance
Polyol	Determines flexibility, hydrolysis resistance, abrasion resistance, chemical resistance, hand feel, and film-forming characteristics
Chain extender	Adjusts hard segment content, segment regularity, and mechanical strength
Crosslinking polyol or polyisocyanate	Increases network density and affects hardness, solvent resistance, and chemical resistance

1. Isocyanates Determine the Reactive Ends and Hard Segment Characteristics of Polyurethane

Isocyanates are among the important reactive raw materials in polyurethane systems. Their core function is to provide NCO groups, which react with hydroxyl groups, amino groups, water, and other active-hydrogen-containing groups. In coatings, isocyanates not only determine reaction activity, but also affect coating film hardness, crosslink density, weather resistance, yellowing tendency, and chemical resistance.

1.1 From the Perspective of Structural Type: Aromatic and Aliphatic Isocyanates Differ Significantly

Common isocyanates used in coatings can be classified into aromatic isocyanates, aliphatic isocyanates, and cycloaliphatic isocyanates.

Type	Common Examples	Structural Characteristics	Effect on Coating Film Performance
Aromatic isocyanates	TDI, toluene diisocyanate; MDI, diphenylmethane diisocyanate	Contain benzene rings and have relatively strong structural rigidity	High reactivity, good hardness and strength, but yellowing resistance and outdoor weatherability are usually not their advantages
Aliphatic isocyanates	HDI, hexamethylene diisocyanate	Linear aliphatic structure	Good weather resistance, gloss retention, and color retention; commonly used in high-weatherability coating systems
Cycloaliphatic isocyanates	IPDI, isophorone diisocyanate; HMDI, hydrogenated MDI	Contain cycloaliphatic structures and combine rigidity with weather resistance	Help improve weather resistance, hardness, and chemical resistance; reactivity is generally lower than that of aromatic isocyanates

Because aromatic isocyanates contain aromatic rings, they usually have relatively high reactivity and strong rigidity, but they are more prone to yellowing under light exposure. Aliphatic and cycloaliphatic isocyanates are generally more suitable for coating film systems requiring high weather resistance, gloss retention, and color retention.

2. Isocyanate Functionality and NCO Content Affect the Crosslinked Structure

Functionality refers to the number of functional groups in a molecule that can participate in reactions. For isocyanates, provided that the NCO/OH equivalents are properly matched, the reaction proceeds sufficiently, and the system is capable of forming a network structure, higher functionality is more conducive to forming more branched structures or crosslinking points. As the number of crosslinking points increases, the coating film typically exhibits higher hardness, solvent resistance, and chemical resistance, but flexibility, impact resistance, and application tolerance may decrease.

Isocyanate Characteristic	Typical Effect on Coating Film
Difunctional isocyanate	Mainly forms linear or lightly branched structures, which is beneficial for flexibility
Polyfunctional isocyanate	Helps form crosslinked networks and improves hardness and chemical resistance
Higher NCO content	Indicates more reactive NCO equivalents per unit mass, but must be matched with hydroxyl content, functionality, and the target NCO/OH equivalent ratio
Stronger structural rigidity	Beneficial for hardness and heat resistance, but may reduce flexibility

In coating formulations, what is commonly used is usually not free low-molecular-weight diisocyanate monomers, but rather polyisocyanate curing agents, isocyanurate trimers, biurets, uretdiones, or prepolymers. These structures can reduce free monomer content and volatile exposure risks, while also providing viscosity, reactivity, and crosslinking capability more suitable for coating applications. It should be noted that NCO-containing isocyanate products still need to be handled, ventilated, protected, stored, and managed in accordance with SDS requirements.

3. Polyols Determine the Flexibility and Main Body Performance of Polyurethane

Polyols are another core class of raw materials in polyurethane structures. Compared with isocyanates, polyols have a more direct influence on coating film flexibility, elasticity, hand feel, hydrolysis resistance, abrasion resistance, and chemical resistance. If isocyanates mainly determine the reactive ends and crosslinking characteristics, then polyols mainly determine the main body performance of polyurethane coating films.

The influence of polyols mainly comes from the following factors: backbone structure; molecular weight; hydroxyl value; functionality; polarity and crystallinity; and glass transition temperature.

4. Polyester Polyols: Improving Strength, Adhesion, and Chemical Resistance

Polyester polyols are usually obtained through polycondensation of polyacids and polyols. Their structures contain ester bonds and show strong intermolecular interactions, which tend to provide polyurethane with good mechanical strength, adhesion, abrasion resistance, oil resistance, and chemical resistance.

Performance Direction	Effect of Polyester Polyols
Hardness	Usually helps increase hardness
Mechanical strength	Usually good
Adhesion	Strong polarity is beneficial for adhesion
Abrasion resistance	Usually good
Oil resistance and chemical resistance	Usually good
Hydrolysis resistance	Hydrolysis stability should be considered for conventional polyester structures

Polyester-based polyurethane coatings are widely used in automotive, industrial, architectural, and plastic coatings, mainly because of their good mechanical properties, adhesion, oil resistance, and chemical resistance. However, conventional polyester polyols contain ester bonds in their structures and may undergo hydrolysis under humid-heat or strongly alkaline conditions. Therefore, when used in systems requiring high hydrolysis resistance, more hydrolysis-resistant polyester structures should be selected, or other polyol structures should be used instead.

5. Polyether Polyols: Improving Flexibility and Hydrolysis Resistance

Polyether polyols contain ether bonds in the main chain and have relatively flexible chain segments. Compared with conventional polyester polyols, polyether polyols generally provide better low-temperature flexibility and hydrolysis resistance.

Performance Direction	Effect of Polyether Polyols
Flexibility	Usually good
Low-temperature performance	Usually good
Hydrolysis resistance	Usually better than conventional polyester polyols
Elasticity	Usually good
Mechanical strength	Should be evaluated together with structure and degree of crosslinking
Oil resistance and solvent resistance	Usually inferior to highly polar polyester or polycarbonate structures

Polyether-based polyurethane is suitable for systems requiring flexibility, elasticity, and hydrolysis resistance. However, if the coating film requires higher hardness, oil resistance, or stain resistance, reinforcement is usually needed through isocyanate structure design, crosslinking design, or blending with other resins. The key advantage of polyether polyols lies in their significant value in flexibility and hydrolysis resistance.

6. Polycarbonate Polyols: Improving Hydrolysis Resistance, Weather Resistance, and Abrasion Resistance

Polycarbonate polyols are a class of high-performance polyols whose backbones contain carbonate structures. Compared with conventional polyester and polyether polyols, polycarbonate polyols are generally conducive to improving the hydrolysis resistance, mechanical strength, heat resistance, and durability of polyurethane. However, weather resistance, abrasion resistance, and chemical media resistance still need to be comprehensively evaluated together with the isocyanate type, hard segment structure, crosslink density, and additive system.

Performance Direction	Effect of Polycarbonate Polyols
Hydrolysis resistance	Usually good
Weather resistance	Usually good
Abrasion resistance	Usually good
Heat resistance	Usually good
Mechanical strength	Usually good
Cost	Usually higher than conventional polyester and polyether polyols

Polycarbonate polyols are commonly used in polyurethane systems with high durability requirements. In actual formulations, however, whether to select polycarbonate polyols should be comprehensively judged according to performance targets, cost requirements, and application conditions.

7. Acrylic Polyols: Improving the Balance of Appearance, Weather Resistance, and Hardness

Acrylic polyols are hydroxyl-containing acrylic resins that commonly react with polyisocyanates to form crosslinked polyurethane coating films. Compared with polyester or polyether polyols, acrylic polyols are generally more favorable for coating film gloss, fullness, color retention, hardness, and chemical resistance. Their performance depends on the acrylic monomer composition, hydroxyl value, acid value, glass transition temperature, and molecular weight.

Structural Factor	Main Influence
Hydroxyl value	Affects the number of crosslinkable sites and the network density after curing
Glass transition temperature	Affects hardness, flexibility, and film-forming characteristics
Monomer composition	Affects weather resistance, adhesion, chemical resistance, and cost
Molecular weight	Affects viscosity, film formation, drying behavior, and mechanical properties

8. Chain Extenders and Low-Molecular-Weight Polyols Affect the Hard Segment Ratio

In addition to polymeric polyols, polyurethane systems often use low-molecular-weight diols, diamines, or polyfunctional alcohols as chain extenders or crosslinking components. Among them, diamines mainly form urea bonds when reacting with NCO groups, so strictly speaking, they introduce polyurethane-urea structures. The main function of chain extenders is not to independently provide film-forming properties, but to adjust the hard segment ratio, segment regularity, and intermolecular interactions.

Chain Extender Influence Factor	Effect on Coating Film Performance
Increased dosage	Increases the hard segment ratio; hardness and strength may increase
Increased structural rigidity	Beneficial for hardness, heat resistance, and deformation resistance
Increased functionality	Helps increase crosslink density
Excessive dosage	May cause the coating film to become brittle, reduce flexibility, or make film formation difficult

The influence of chain extenders on polyurethane performance should be considered together with the isocyanate type, polyol molecular weight, and overall hydroxyl content.

9. Hydroxyl Value, Functionality, and Molecular Weight Are Key Indicators for Polyol Selection

When selecting polyols, it is not enough to consider only the polyol type; specific indicators must also be evaluated. Even for polyols of the same type, differences in hydroxyl value, molecular weight, and functionality can lead to significant differences in the final coating film performance.

9.1 Hydroxyl Value

Hydroxyl value indicates the hydroxyl group content in a polyol and is commonly expressed in mg KOH/g. The higher the hydroxyl value, the more OH groups per unit mass of polyol are available to participate in the reaction. For reactive polyurethane systems, hydroxyl value affects formulation calculations, crosslink density, hardness, chemical resistance, and coating film brittleness.

Change in Hydroxyl Value	Possible Effect
Higher hydroxyl value	More crosslinking points; hardness and chemical resistance may increase
Lower hydroxyl value	Longer chain segments; flexibility may improve
Excessively high hydroxyl value	May cause the coating film to become too hard, brittle, or shorten the application window
Excessively low hydroxyl value	May lead to insufficient crosslinking and reduced solvent resistance and chemical resistance

9.2 Functionality

The higher the functionality, the more branched or crosslinked structures a polyol can form. Difunctional polyols tend to form linear chain segments, while polyfunctional polyols are more likely to form crosslinked networks.

Functionality	Structural Tendency	Effect on Coating Film
Difunctional	Mainly linear chain segments	Beneficial for flexibility and elasticity
Trifunctional and above	Increased branching or crosslinking	Beneficial for hardness, solvent resistance, and chemical resistance
Excessively high functionality	Network becomes too dense	May increase brittleness

9.3 Molecular Weight

The molecular weight of a polyol affects soft segment length and chain segment mobility. A higher molecular weight is usually beneficial for flexibility and elasticity, while a lower molecular weight provides more reactive sites per unit mass and more readily forms coating films with higher hardness and higher crosslink density.

Change in Molecular Weight	Possible Effect
Higher molecular weight	Better flexibility, elasticity, and low-temperature performance
Lower molecular weight	Hardness, strength, and chemical resistance may increase
Broader molecular weight distribution	May affect viscosity, application properties, and film-forming uniformity

10. Raw Material Combinations Determine Coating Film Performance

The effects of isocyanates and polyols on polyurethane performance are not simply additive. Actual coating film performance comes from the structural result formed by combining the two. For example:

Raw Material Combination	Coating Film Performance Tendency
Aliphatic isocyanate + acrylic polyol	Beneficial for weather resistance, gloss and color retention, hardness, and appearance
Aliphatic isocyanate + polycarbonate polyol	Beneficial for weather resistance, hydrolysis resistance, abrasion resistance, and durability
Aromatic isocyanate + polyester polyol	Beneficial for hardness, strength, and cost control, but yellowing should be considered
Cycloaliphatic isocyanate + polyether polyol	Beneficial for flexibility, elasticity, and a certain degree of weather resistance
High-hydroxyl-value polyol + high-functionality polyisocyanate	Beneficial for hardness and chemical resistance, but brittleness should be considered
High-molecular-weight polyol + low-crosslinking structure	Beneficial for flexibility and elasticity, but solvent resistance may be limited

The performance of polyurethane coating films cannot be judged from a single raw material alone. The correct approach is to consider the following factors together: isocyanate type; polyol type; functionality; hydroxyl value, NCO content, and NCO/OH equivalent ratio; molecular weight; soft/hard segment ratio; and crosslinked structure.

11. Different Performance Targets Correspond to Different Raw Material Design Directions

Performance design for polyurethane coating films should work backward from the target performance to the raw material structure.

Target Performance	Raw Material Design Direction
Improve hardness	Select structures with stronger rigidity, higher-hydroxyl-value polyols, or higher-functionality components
Improve flexibility	Select higher-molecular-weight polyols, flexible chain segments, or lower-crosslink-density structures
Improve weather resistance	Prefer aliphatic or cycloaliphatic isocyanates, combined with polyols that offer good weather resistance
Improve hydrolysis resistance	Select polyether, polycarbonate, or hydrolysis-resistant modified polyester polyols
Improve abrasion resistance	Use an integrated design based on hard segment structure, crosslink density, and abrasion-resistant polyols
Improve chemical resistance	Increase crosslink density and select backbone structures with better solvent resistance and chemical resistance
Improve hand feel and elasticity	Select flexible chain segments and control the hard segment ratio and crosslink density
Improve appearance and gloss	Select resin structures with good compatibility, stable color, and uniform film formation

It should be noted that different performance properties often restrict one another. High hardness does not necessarily bring high flexibility; high crosslinking does not necessarily improve impact resistance; and highly weather-resistant raw materials may not meet the lowest-cost requirement. The key to polyurethane formulation design is to find a reasonable balance among target properties, rather than pursuing the maximization of a single performance indicator.

12. Product Classification Tables Related to Performance Control of Polyurethane Coating Films Based on Isocyanate–Polyol Systems — Tables 1–4

Table 1. Isocyanate Curing Agents and Hard Segment Structure Sources

Category	CAS No.	Aladdin Cat. No.	Name	Specification or Purity	Product Features and Applications
Aliphatic diisocyanate	822-06-0	H106723	Hexamethylene diisocyanate (HDI)	Moligand™, ≥99%	Used for preparing weather-resistant polyurethane coating films, aliphatic polyurethane elastic coatings, HDI trimers, and biuret curing agents; suitable for studies on NCO/OH ratio, crosslink density, flexibility, and yellowing resistance.
Aliphatic polyisocyanate curing agent	4035-89-6	T770979	1,3,5-Tris(6-isocyanatohexyl)biuret	NCO content: 21–22.5%	Used in two-component polyurethane clearcoats, industrial protective coatings, and elastic coating curing systems; related to studies on high-functionality NCO sources, crosslinked film formation, solvent resistance, and abrasion resistance.
Aliphatic isocyanurate curing agent	3779-63-3	H694586	1,3,5-Tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione	≥95%	Used in HDI trimer-type polyurethane curing systems; suitable for studies on coating film hardness, weather resistance, chemical media resistance, crosslinked network structure, and transparent coating performance.
Aliphatic HDI uretdione / latent isocyanate structure	23501-81-7	B1234624	1,3-Bis(6-isocyanatohexyl)-1,3-diazetidine-2,4-dione	—	Used for HDI uretdione-structure curing agents, thermally activated polyurethane coating films, and low-free-monomer systems; related to storage stability, latent curing, thermal dissociation behavior, and coating film crosslinking behavior.
Cycloaliphatic diisocyanate	4098-71-9	I109582	Isophorone Diisocyanate (mixture of isomers) (IPDI)	≥99%	Used in weather-resistant polyurethane dispersions, elastic coatings, and transparent coating curing systems; suitable for studies on asymmetric NCO reactivity, hard segment structure, yellowing resistance, and mechanical balance.
Cycloaliphatic diisocyanate	5124-30-1	D155475	Dicyclohexylmethane 4,4′-Diisocyanate (mixture of isomers) (HMDI)	≥90% (GC)	Used in cycloaliphatic polyurethane coating films, weather-resistant elastic coatings, and waterborne polyurethane prepolymers; related to studies on hard segment regularity, light stability, flexibility, and water resistance.
Aromatic diisocyanate	26471-62-5	T135411	Tolylene Diisocyanate (2,4, 2,6) (TDI)	≥98% (GC)	Used in aromatic polyurethane coating films, prepolymers, elastomers, and adhesive coatings; suitable for studies on NCO reaction rate, hard segment content, coating film strength, abrasion resistance, and yellowing behavior.
Aromatic diisocyanate	91-08-7	T769897	Tolylene-2,6-diisocyanate	≥98%	Used for comparing the reactivity of TDI isomers, constructing polyurethane hard segments, and studying coating film curing kinetics, microphase separation, and mechanical properties.
Aromatic diisocyanate	101-68-8	M106783	4,4′-MDI (MDI)	≥98%	Used in high-strength polyurethane coating films, elastomers, prepolymers, and reactive coatings; related to studies on rigid hard segments, tensile strength, adhesion, abrasion resistance, and crosslinked structures.
Polymeric aromatic polyisocyanate	9016-87-9	P304914	Polymethylene polyphenyl polyisocyanate	NCO content ~30%; viscosity ~200 mPa·s (25 °C)	Used in highly crosslinked aromatic polyurethane systems, hard coatings, adhesives, and composite material coatings; suitable for studies on high NCO content, network densification, hardness, and chemical resistance.
Araliphatic diisocyanate	3634-83-1	M158033	m-Xylylene Diisocyanate (MXDI)	≥98% (GC)	Used in polyurethane coating films combining aromatic ring rigidity with aliphatic NCO reaction characteristics; related to studies on transparency, adhesion, hardness, and media resistance.
Hindered araliphatic diisocyanate	2778-42-9	B152785	1,3-Bis(2-isocyanato-2-propyl)benzene	≥97% (GC)	Used in low-yellowing araliphatic polyurethane coating films, reactivity-control systems, and elastic coating research; related to sterically hindered NCO groups, pot life, hard segment structure, and weather resistance.

Table 2. Polyether, Polyester, and Natural Oil Polyol Soft Segment Sources

Category	CAS No.	Aladdin Cat. No.	Name	Specification or Purity	Product Features and Applications
Hydrophilic polyether / PEO-type soft segment source	25322-68-3	P615493	Poly(ethylene oxide)	Viscosity 65–115 cps	Used in hydrophilic polyurethane coating films, waterborne polyurethane modification, and water-absorbing breathable coating studies; related to flexibility, hydrophilicity, ion migration, and surface wetting behavior. When the hydrophilic segment content is high, coating film water resistance should be considered.
Polyether diol soft segment	25322-69-4	P103212	Poly(propylene glycol) (PPG)	Average molecular weight 4000	Used in flexible polyurethane coating films, elastic coatings, and low-glass-transition-temperature soft segment systems; suitable for studies on chain segment mobility, resilience, hydrolysis resistance, and phase separation.
Polyester diol soft segment	36890-68-3	P478032	Polycaprolactone diol	Average Mₙ 10,000	Used in highly flexible polyester-type polyurethane coating films, elastomer coatings, and bio-related coating studies; related to crystalline soft segments, abrasion resistance, oil resistance, and mechanical reinforcement.
Polyether diol soft segment	25190-06-1	P432410	Polytetramethylene Ether Glycol (PTHF)	Average Mₙ ~2900	Used in highly elastic polyurethane coating films, low-temperature-resistant coatings, and abrasion-resistant elastomer systems; suitable for studies on soft segment regularity, tensile recovery, hydrolysis resistance, and microphase separation.
Natural oil polyol	8001-79-4	C110663	Castor oil	Chemically pure (CP)	Used in bio-based polyurethane coating films, flexible protective coatings, and crosslinked alkyd-modified systems; related to studies on hydroxyl functionality, hydrophobicity, flexibility, and adhesion.

Table 3. Low-Molecular-Weight Polyols, Chain Extenders, Crosslinkers, Hydrophilic Monomers, and Polymerizable Hydroxyl Monomers

Category	CAS No.	Aladdin Cat. No.	Name	Specification or Purity	Product Features and Applications
Linear diol chain extender	110-63-4	B1508458	1,4-Butanediol (BDO)	Anhydrous, ≥99%	Used for polyurethane hard segment chain extension, elastic coating films, and prepolymer post-chain-extension studies; related to hard segment regularity, tensile strength, abrasion resistance, crystallinity, and coating film toughness.
Trifunctional crosslinking polyol	56-81-5	G755728	Glycerol	Anhydrous, UltraBio™, molecular biology grade, ≥99.5% (GC)	Used for trifunctional polyurethane crosslinked networks, branched polyol synthesis, and coating film crosslink density adjustment; related to hardness, water resistance, adhesion, and gel content studies.
Short-chain diol chain extender	107-21-1	E119700	Ethylene glycol	Anhydrous, ≥99.8%	Used for short-chain hard segment construction, polyurethane coating film chain extension, and polyester polyol synthesis; related to studies on hardness, modulus, solvent resistance, and hydrogen bond density.
Hydroxy methacrylate monomer	868-77-9	H140643	2-Hydroxyethyl methacrylate (HEMA)	Anhydrous, ≥99%, contains 200 ppm MEHQ stabilizer, water ≤0.1%	Used in UV-curable polyurethane acrylates, waterborne polyurethane grafting, and hydroxyl-reactive modification; related to studies on photocuring crosslinking, adhesion, and scratch resistance.
Ether-type diol chain extender	111-46-6	D476199	Diethylene glycol	UltraBio™, ultrapure, ≥99% (GC)	Used in flexible polyurethane chain extension, polyester polyol synthesis, and coating film toughness adjustment; related to ether bond flexibility, low-temperature flexibility, and hydrolysis resistance studies.
Tetrafunctional crosslinking polyol	115-77-5	P103696	Pentaerythritol	AR, ≥98%	Used for high-functionality polyurethane crosslinking, alkyd resin polyol construction, and high-hardness coating film studies; related to branched structures, crosslink density, solvent resistance, and heat resistance.
Cycloaliphatic diol chain extender	105-08-8	C105684	1,4-Cyclohexanedimethanol (CHDM)	≥99%, mixture of cis and trans	Used in cycloaliphatic polyester polyols, weather-resistant polyurethane coating films, and highly transparent coating studies; related to rigid ring structures, heat resistance, hardness, and flexibility balance.
Hindered diol chain extender	126-30-7	N103689	Neopentyl glycol	≥99%	Used in hydrolysis-resistant polyester polyols, polyurethane coating film chain extension, and powder coating resins; related to branched alkyl structures, water resistance, weather resistance, and coating film hardness.
Linear diol chain extender	629-11-8	H103708	1,6-Hexanediol	≥98%	Used in flexible polyurethane coating films, polyester polyol synthesis, and long-chain hard segment chain-extension studies; related to chain segment flexibility, crystallinity, abrasion resistance, and low-temperature performance.
Carboxylic acid-type internal emulsifying monomer	10097-02-6	B115196	2,2-Bis(hydroxymethyl)butyric acid (DMBA)	≥98%	Used in waterborne polyurethane internal emulsification, anionic prepolymers, and self-dispersing coating film studies; related to carboxyl content, particle size, dispersion stability, and water resistance.
Carboxylic acid-type internal emulsifying monomer	4767-03-7	B104539	2,2-Bis(hydroxymethyl)propionic acid (DMPA)	≥98%	Used in waterborne polyurethane dispersions, anionic hydrophilic chain extension, and waterborne coating film preparation; related to emulsion stability, solids content, film formation, and adhesion studies.
Trifunctional crosslinking chain extender	77-99-6	T110597	1,1,1-Tris(hydroxymethyl)propane	≥98%	Used for branched crosslinking in polyurethane coating films, hydroxyl components of two-component coatings, and prepolymer modification; related to network density, hardness, chemical resistance, and scratch resistance.
Hydroxy methacrylate monomer	27813-02-1	H109880	Hydroxypropyl methacrylate (HPMA)	≥97%, contains 0.02% 4-methoxyphenol stabilizer	Used in polyurethane acrylates, hydroxyl acrylic resins, and photocurable coating film studies; related to hydroxyl reactions, free-radical copolymerization, adhesion, and water resistance.
Hydroxy acrylate monomer	2478-10-6	H156908	4-Hydroxybutyl Acrylate (4HBA)	≥97% (GC), contains MEHQ stabilizer	Used in flexible polyurethane acrylates, hydroxyl-reactive acrylic resins, and photocurable coatings; related to flexible chain segments, crosslinking reactions, adhesion, and impact resistance.
Hydroxy acrylate monomer	818-61-1	H104535	2-Hydroxyethyl acrylate	≥96%, contains 200–600 ppm MEHQ as inhibitor	Used in hydroxyl acrylic resins, polyurethane acrylates, and waterborne coating film modification; related to NCO reaction grafting, photocuring activity, hardness, and adhesion.
Hydroxy acrylate monomer	25584-83-2	H156905	Hydroxypropyl Acrylate (mixture of 2-Hydroxypropyl and 2-Hydroxy-1-methylethyl Acrylate)	≥90% (GC), contains MEHQ stabilizer	Used in hydroxyl acrylic resins, polyurethane acrylates, and waterborne polyurethane graft modification; related to flexibility, photocuring reactions, water resistance, and adhesion.

Table 4. Polyester Polyols, Alkyd Resins, and Structure-Regulating Monomers

Category	CAS No.	Aladdin Cat. No.	Name	Specification or Purity	Product Features and Applications
Aromatic anhydride monomer	85-44-9	P116466	o-Phthalic anhydride	Premium reagent, ≥99%	Used in the synthesis of alkyd resins, aromatic polyester polyols, and hydroxyl resins for polyurethane coatings; related to coating film hardness, adhesion, solvent resistance, and drying performance.
Aliphatic dicarboxylic acid monomer	124-04-9	A108267	Adipic acid	Pharmaceutical grade, PharmPure™, ≥99.6%	Used in aliphatic polyester polyols, flexible polyurethane coating films, and elastic coating studies; related to soft segment flexibility, low-temperature resistance, and abrasion resistance. Hydrolysis stability should be comprehensively improved through diol structure, hydrophobic modification, and formulation design.
Aromatic dicarboxylic acid monomer	121-91-5	I104311	Isophthalic acid	AR, ≥99%	Used in chemical-resistant polyester polyols, hydroxyl resins for polyurethane coatings, and high-hardness coating film studies; related to aromatic ring rigidity, heat resistance, water resistance, and adhesion.
Cyclic ester monomer	502-44-3	C109521	ε-Caprolactone	≥99%	Used in polycaprolactone polyol synthesis, flexible polyurethane coating films, and degradable polyurethane material studies; related to ring-opening polymerization, crystalline soft segments, abrasion resistance, and elasticity.
Aromatic dicarboxylic acid monomer	100-21-0	P108506	Terephthalic acid (PTA, benzene-1,4-dicarboxylic acid)	≥99%	Used in high-rigidity polyester polyols, hydroxyl resins for polyurethane coatings, and heat-resistant coating film studies; related to linear aromatic structures, hardness, chemical resistance, and dimensional stability.

Safety Note: Isocyanates and polyisocyanates are highly reactive and may cause irritation to the skin, eyes, nose, throat, and respiratory tract. They may also pose risks of respiratory or skin sensitization and occupational asthma. Experiments, formulation work, and spraying operations involving free NCO groups should be carried out under good ventilation or local exhaust conditions, and appropriate gloves, goggles, protective clothing, and respiratory protection should be used in accordance with the product SDS.

Note: The products listed above are representative Aladdin products. For more product specifications, please search by product name, CAS number, or catalog number on the Aladdin website.

References

[1] SpecialChem. Polyurethane Paint & Coatings: Uses, Chemistry, Process & Formulation.

[2] Wang, H.; Cao, L.; Wang, X.; Lang, X.; Cong, W.; Han, L.; Zhang, H.; Zhou, H.; Sun, J.; Zong, C. Effects of Isocyanate Structure on the Properties of Polyurethane: Synthesis, Performance, and Self-Healing Characteristics. Polymers, 2024, 16(21), 3045.

[3] Covestro. Polyisocyanates and Prepolymers.

[4] Zhang, Z.; Ni, N.; Xu, Y. Effects of Different Polyols with Functions on the Properties of Polyester Polyol-Based Polyurethane Coatings. Coatings, 2025, 15(1), 61.

[5] SpecialChem. Polyester Polyols for Water-Resistant Polyurethane Coatings.

[6] Liu, N.; Zhao, Y.; Kang, M.; Wang, J.; Wang, X.; Feng, Y.; Yin, N.; Li, Q. The Effects of the Molecular Weight and Structure of Polycarbonatediols on the Properties of Waterborne Polyurethanes. Progress in Organic Coatings, 2015, 82, 46–56.

[7] Tran, K.; Liu, Y.; Soleimani, M.; Lucas, F.; Winnik, M.A. Waterborne 2-Component Polyurethane Coatings Based on Acrylic Polyols with Secondary Alcohols. Progress in Organic Coatings, 2024, 190, 108374.

For more related articles, please see below:

A Panorama Guide to Synthetic Resins: Definitions & Polymerization Mechanisms, Classification Frameworks, Common Resins and Applications, Packaging Codes, and a Selection Roadmap (Tables 1–3)

Isocyanate-Functional Silane Coupling Agents: Structural Features, Classification, Applications, and Selection

Formulation Design and Selection of Amine Curing Agents in Epoxy Systems