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Introduction to Light-Curable Monomers and Their Applications

Release time:

2016-01-05 09:08

Introduction to Light-Curable Monomers and Their Applications

I. Introduction to Light-Curable Monomers

1. Definition

Monomer: From a chemical structural perspective, it is a small molecule containing a polymerizable functional group.

Active diluent: A diluent that can participate in the film-forming reaction.

2. Function

(1) Reduce viscosity;

(2) Determines the curing speed of the system;

(3) Increase crosslinking density;

(4) Control the adhesion and flexibility of the cured film.

3. Classification

(1) Acrylate-based; (2) Methacrylate-based; (3) Vinyl-based; (4) Vinyl ether-based; (5) Epoxy-based.

II. Monoalkyl acrylate

1. Single-officer, single-entity characteristics

(1) High conversion rate: Low content of carbon-carbon double bonds, allowing most of them to participate in free-radical polymerization;

(2) Low volumetric shrinkage: Low content of double bonds results in minimal volumetric shrinkage.

(3) Low crosslink density: No crosslinking points are formed during the curing process, which can enhance the flexibility of the cured film.

(4) Slow curing speed: Low double-bond content leads to slow curing.

(5) Low viscosity: strong diluting ability;

(6) Lower molecular weight: Consequently, it exhibits high volatility, and accordingly, high toxicity, strong odor, and flammability.

2. HEA/Hydroxyethyl Acrylate

Molecular weight	Appearance	Density	Flash point
116.12	Colorless, transparent liquid	1.106	99℃
Boiling point	Melting point	Refractive index
90-92℃ 12 mm Hg	-60℃	1.449–1.451
Feature	Primarily used for synthesizing light-curable resins, rarely used in the coatings and ink industry.
Molecular formula

3. HEMA/Hydroxyethyl methacrylate

Molecular weight	Appearance	Density	Flash point
130.14	Colorless, transparent liquid	1.073	207°F
Boiling point	Melting point
67℃ 3.5 mm Hg	-12℃
Feature	Used as a diluent monomer for the synthesis of UV-curable resins, coatings, inks, and adhesives.
Molecular formula

4. HPA/Hydroxypropyl Acrylate

Molecular weight	Appearance	Density	Flash point
130.1418	Colorless, transparent liquid	1.044	193°F
Boiling point	Melting point	Refractive index
77℃	/	1.4443
Feature	Used for synthesizing UV-curable resins and acrylic resins.
Molecular formula

5. HPMA/Hydroxypropyl methacrylate

Molecular weight	Appearance	Density	Flash point
144.17	Colorless, transparent liquid	1.066	96℃
Boiling point	Melting point	Refractive index
57℃ 0.5 mm Hg	-58℃	1.4470
Feature	Used for synthesizing UV-curable resins and acrylic resins.
Molecular formula

6. ACMO/Acrylamide morpholine

Molecular weight	Appearance	Density	Viscosity
141.17	Pale yellow to yellow liquid	1.122	10–15 cps/25℃
Tg	Melting point	Flash point
145℃	-35℃	110℃
Feature	UV rapid curing, odorless, highly durable, hydrolysis-resistant, with a low P.I.I. value, excellent dispersibility and wetting properties, and outstanding adhesion. Recommended for use in UV adhesives, UV inks, and UV coatings.
Molecular formula

7. IBOA/Isobornyl Acrylate

Molecular weight	Surface tension	Specific gravity (25℃)	Viscosity (25℃)
208	29.5	0.98–1.00	5-15cps
Appearance	Boiling point	Flash point	Refractive index
Colorless, transparent liquid	244.5℃ at 760 mm Hg	94.6℃	1.474
Feature	This product is used in adhesives and specialty coatings, offering excellent adhesion, heat resistance, toughness, water resistance, and abrasion resistance.
Molecular formula

8. IBOMA/Methyl methacrylate isobornyl ester

Molecular weight	Appearance	Density	Viscosity (25℃)
222.3233	Colorless, transparent liquid	0.980 g/cm³ (20℃)	8.5 mPa·s (20℃)
Boiling point	Melting point	Flash point	Refractive index
117℃ (0.93 kPa)	-50℃	127℃	1.477 (20℃)
Feature	Low viscosity, high boiling point, low surface tension (low shrinkage), high glass transition temperature.
Molecular formula

9. THFA/ Tetrahydrofuran Acrylate

Molecular weight	Surface tension	Specific gravity (25℃)	Viscosity (25℃)
154	34.9	1.06–1.07	5-6cps
Boiling point	Flash point	Refractive index (25℃)
87℃/9 mmHg	93℃	1.455
Feature	It exhibits excellent adhesion to a variety of substrates, features good dilution and viscosity reduction properties, forms a soft, pressure-sensitive film, and demonstrates superior water and chemical resistance. It is recommended for use in UV adhesive applications.
Molecular formula

10. EOEOEA/Ethoxyethoxyethyl acrylate

Molecular weight	Surface tension	Specific gravity (25℃)	Viscosity (25℃)
188	31.2	1.01-1.03	3-8cps
Appearance	Refractive index (25℃)
Colorless or yellow	1.436
Feature	Low shrinkage, excellent dilutability, and good flexibility; this product is suitable for inks, wood coatings, plastic coatings, paper coatings, and solder mask inks.
Molecular formula

11. PHEA/2-phenoxyethyl acrylate

Molecular weight	Surface tension	Specific gravity (25℃)	Viscosity (25℃)
192	38.4	1.10–1.11	5-15cps
Boiling point	Refractive index (25℃)	Flash point
275.981℃ at 760 mm Hg	1.515	110.543℃
Feature	Excellent dilutability, high reactivity, low viscosity—suitable for UV screen-printing inks.
Molecular formula

12. CTFA/Trimethylolpropane Trimethylolpropanal Acrylate

Molecular weight	Surface tension	Specific gravity (25℃)	Viscosity (25℃)
200	35.5	1.08–1.11	12-18cps
Tg	Refractive index (25℃)
40℃	1.462
Feature	Low odor, fast curing speed, excellent chemical resistance, high hardness, and excellent abrasion resistance.
Molecular formula

13. DMAA/N,N-dimethylacrylamide

Molecular weight	Appearance	Density	Viscosity (25℃)
99.13	Colorless, transparent liquid	0.96	1-3cps
Boiling point	Flash point
46 (0.27 kPa)	71℃
Feature	Primarily used in UV adhesives and UV inkjet applications, this product features low viscosity, water solubility, high adhesion, chemical resistance, antistatic properties, and excellent bonding performance on plastic and glass substrates.
Molecular formula

14. TMCHA/3,3,5-Trimethylcyclohexyl acrylate

Molecular weight	Surface tension	Specific gravity (25℃)	Viscosity (25℃)
196	27.1	0.91–0.95	2-8cps
Appearance	Refractive index (25℃)
Colorless and transparent	1.453
Feature	High Tg, low curing shrinkage, excellent adhesion, low surface tension
Molecular formula

15. ODA/Octyl Acrylate/Decyl Acrylate

Molecular weight	Surface tension	Specific gravity (25℃)	Viscosity (25℃)
184-212	27.1	0.86–0.89	2-8cps
Refractive index
1.434
Feature	Low shrinkage, excellent flexibility, excellent weather resistance, and excellent water resistance.
Molecular formula

III. Bis-acrylate

1. Dual-governor monomer characteristics

(1) Relatively fast curing speed; (2) High cross-linking density of the film formed; (3) Good dilutability; (4) Low volatility and low odor.

2. TPGDA/Tripropylene Glycol Diacrylate

Molecular weight	Surface tension	Specific gravity	Viscosity
300	32	1.03–1.05	8-16cps
Refractive index
1.448
Feature	Excellent flexibility, low volatility, and low viscosity. Primarily used as an active diluent, it can significantly reduce the viscosity of resin systems.
Molecular formula

3. DPGDA/Di(propylene glycol) diacrylate

Molecular weight	Surface tension	Specific gravity	Viscosity
242	32.4	1.04–1.10	7-13cps
Boiling point	Flash point	Refractive index
119–121℃ 0.8mm	110℃	1.449
Feature	Excellent dilution power, low volatility, low viscosity, and fast curing speed.
Molecular formula

4. NPGDA/Neopentyl Glycol Diacrylate

Molecular weight	Surface tension	Specific gravity	Viscosity
212	31.0	1.02–1.05	4-12cps
Appearance	Refractive index
Colorless and transparent	1.450
Feature	High reactivity, excellent dilutability, excellent scratch resistance, and excellent solvent resistance.
Molecular formula

5. HDDA/1,6-Hexanediol Diacrylate

Molecular weight	Surface tension	Specific gravity	Viscosity
226	34.5	1.01-1.03	5-10cps
Appearance	Refractive index
Colorless, transparent liquid	1.455
Feature	Excellent dilution performance, excellent adhesion to plastics, and excellent weather resistance.
Molecular formula

6. DCPDA/Tri-cyclo-decane diol diacrylate

Molecular weight	Surface tension	Specific gravity	Viscosity
304	37.9	1.09–1.11	110-150
Appearance	Refractive index
Colorless, transparent liquid	1.501
Feature	High Tg, low shrinkage, fast curing speed, excellent yellowing resistance, outstanding toughness, high hardness, and superior heat and chemical resistance.
Molecular formula

Four, San Guan Acrylate

1. Characteristics of the San Guan monomer

(1) Fast photopolymerization speed; (2) High hardness and high brittleness of the cured product; (3) Low volatility; (4) Relatively high viscosity and poor dilution effect.

2. TMPTA/Trihydroxymethylpropane Triacrylate

Molecular weight	Surface tension	Specific gravity	Viscosity
296	35.0	1.09–1.12	70-110cps
Appearance	Refractive index
Pale yellow, transparent liquid	1.501
Feature	High gloss, excellent hardness, high reactivity, high cross-linking density, and excellent wear resistance.
Molecular formula

3. TMPTMA/Trihydroxymethylpropane Trimethacrylate

Molecular weight	Surface tension	Specific gravity	Viscosity
338	32.2	1.06–1.07	35-50cps
Appearance	Refractive index
Pale yellow, transparent liquid	1.471
Feature	High cross-linking density, excellent heat and solvent resistance, and good hardness and scratch resistance.
Molecular formula

4. TMP3EOTA/Ethoxylated Trimethylolpropane Triacrylate

Molecular weight	Surface tension	Specific gravity	Viscosity
428	36.9	1.10–1.11	50-70cps
Appearance	Refractive index
Pale yellow, transparent liquid	1.469
Feature	Excellent hardness, more flexible than TM, low skin irritation.
Molecular formula

5. PET3A/Pentaerythritol triacrylate

Molecular weight	Surface tension	Specific gravity	Viscosity
298	38	1.168–1.190	600-900
Appearance	Refractive index
Colorless, transparent liquid	1.484
Feature	Excellent hardness, high cross-linking density, rapid curing, and excellent solvent resistance.
Molecular formula

6. G3POTA/Propoxylated glycerol triacrylate

Molecular weight	Surface tension	Specific gravity	Viscosity
428	34.1	1.082–1.105	70-100
Appearance	Refractive index
Pale yellow, transparent liquid	1.461
Feature	Fast curing, excellent hardness and flexibility, low skin irritation, and excellent pigment wetting and dispersibility.
Molecular formula

Five, Four-Official to Six-Official Acrylate

1. Single-organ characteristics of the Four Officials and Six Officials

(1) Fast photopolymerization speed; (2) High hardness and high brittleness of the cured product; (3) Low volatility; (4) High viscosity and poor dilution effect.

2. PET4A/Pentaerythritol Tetraacrylate

Molecular weight	Surface tension	Specific gravity	Viscosity
352	37.6	1.17–1.18	400-650cps
Appearance	Refractive index
Pale yellow, transparent liquid	1.483
Feature	Low volatility, high cross-link density, rapid curing
Molecular formula

3. Di-TMPTA/Di-trimethylolpropane tetraacrylate

Molecular weight	Surface tension	Specific gravity	Viscosity
482	35.0	1.09–1.11	400-700cps
Appearance	Refractive index
Pale yellow, transparent liquid	1.476
Feature	Fast curing, high cross-link density, excellent wear resistance, and superior chemical and water resistance.
Molecular formula

4. DPHA/Dipentaerythritol Hexaacrylate

Molecular weight	Surface tension	Specific gravity	Viscosity
578	42.0	1.17–1.19	5000-7000
Appearance	Refractive index
Pale yellow, transparent liquid	1.478
Feature	High reactivity, high cross-linking density, excellent abrasion resistance, and superior chemical and water resistance.
Molecular formula

VI. Principles for Selecting Photocurable Monomers

1. Principles for Selecting Photocurable Monomers

(1) Dilution; (2) Reactivity; (3) Toxic odor; (4) Surface tension; (5) Shrinkage; (6) Cost.

2. Selection Principle 1: Dilution Effect

(1) One of the main functions of the monomer is to reduce viscosity.

(2) If the monomer has a strong ability to reduce viscosity, its dosage can be minimized. In this way, the influence of the matrix-oligomer on the cured material’s properties can be maximized through volatilization.

(3) It should be noted that a monomer with low viscosity does not necessarily have a stronger ability to reduce viscosity.

(4) The dilution capacity of the same monomer often varies significantly across different systems.

(5) High-viscosity monomers are generally not used much for the purpose of reducing viscosity.

(6) As for solubility, it encompasses both the ability to dissolve photoinitiators and their mutual solubility with other components in the system.

3. Viscosity of Common Monomers

Monofunctional monomer	Abbreviation	Viscosity (cps/25℃)
Hydroxyethyl acrylate	HEA	<2
Isobornyl acrylate	IBOA	5-10
Tetrahydrofuran acrylate	THFA	5
Difunctional monomer	Abbreviation	Viscosity (cps/25℃)
1,6-Hexanediol diacrylate	HDDA	5-10
Tripropylene glycol diacrylate	TPGDA	8-16
Di(propylene glycol) diacrylate	DPGDA	7-13
Multifunctional monomer	Abbreviation	Viscosity (cps/25℃)
Trimethylolpropane triacrylate	TMPTA	70-100
Pentaerythritol triacrylate	PET3A	600-900
Dipentaerythritol hexaacrylate	DPHA	5000-7000

4. Comparison of Dilution Capacities of Different Monomers

5. Selection Principle 2: Reactivity

(1) The higher the reactivity of a monomer, the greater its promoting effect on the curing of the entire system.

(2) It should be noted that the double-bond content of a monomer does not have a strictly proportional relationship with its reactivity.

(3) Methyl acrylate monomers exhibit the highest reactivity; among them, acrylate monomers are more reactive than methacrylate monomers (the electron-withdrawing effect and steric hindrance of the methyl group on the double bond reduce their reactivity).

(4) Polyfunctional acrylate monomers generally exhibit relatively high photopolymerization rates, and the residual amount of the ultimate reactive groups may be relatively high.

(5) Although monofunctional acrylate monomers have a relatively low polymerization rate, given sufficient energy input, their final polymerization conversion can often reach over 80-90%.

6. Schematic diagram of monomer conversion rate

7. Selection Principle 3: Toxicity, Irritancy, and Odor

(1) The toxicity of the monomer can damage human organs and even be fatal;

(2) Irritation usually causes only discomfort to sensitive areas such as the skin and eyes and does not cause long-term harm.

(3) Generally speaking, the damage inflicted by individual units follows this order: single-officer unit > dual-officer unit > triple-officer unit > high-ranking officer unit;

(4) Reducing volatility can decrease the monomer’s toxicity, irritancy, and odor.

(5) Compared to TMPTA, the introduction of ethoxy groups into TM3EOTA reduces its volatility and thus diminishes its irritancy.

8. Selection Principle 4: Surface Tension

(1) The wettability, adhesion, permeability, and leveling properties of coatings and inks are all related to surface tension.

(2) Liquids with low surface tension can wet and spread on surfaces with high wettability.

(3) Conversely, if the surface tension of the liquid is greater than the wetting energy of the substrate, effective wetting and spreading cannot occur.

(4) Using monomers with appropriate surface tension as reactive diluents is one effective way to regulate the surface tension of a system.

9. Surface tension of different monomers

Active diluent	Abbreviation	Surface tension (dyne/cm)
Isobornyl acrylate	IBOA	29.5
Tetrahydrofuran acrylate	THFA	34.9
Ethoxyethoxyethyl acrylate	EOEOEA	31.2
Tripropylene glycol diacrylate	TPGDA	32
Di(propylene glycol) diacrylate	DPGDA	32.4
1,6-Hexanediol diacrylate	HDDA	34.5
Trimethylolpropane triacrylate	TMPTA	35
Pentaerythritol triacrylate	PET3A	38
Dipentaerythritol hexaacrylate	DPHA	42

10. Selection Principle 5: Contractility

(1) When coating and curing on substrates such as metal, glass, and plastic, significant shrinkage can lead to reduced adhesion.

(2) For applications on soft substrates such as paper and plastic films, the shrinkage during curing will cause the substrate to wrinkle.

(3) The higher the functionality, the more double bonds participate in the curing reaction, and the greater the shrinkage will be.

(4) Radiation curing is significantly faster than thermal curing, and the stresses generated during curing do not have enough time to dissipate, thereby affecting its adhesion performance.

11. Contractility of different monomers

Active diluent	Abbreviation	Functionality	Average percentage of shrinkage of the cured film
Tripropylene glycol diacrylate	TPGDA	2	11.9
Neopentyl glycol dipropoxypolyacrylate	(2PO) NPGDA	2	6.8
Trimethylolpropane triacrylate	TMPTA	3	26
Propoxylated glycerol triacrylate	GPTA	3	15.4
Polyethylene glycol (200) diacrylate	PEG200DA	2	19.7

12. Selection Principle 6: Cost

(1) The cost of a monomer affects the proportion it occupies within the system;

(2) The cost of the monomer affects the selling price and profit of the finished product in the market.

(3) As market competition intensifies, costs are troubling engineers in formulation design and affecting the final performance of products.

(4) Cost also determines the product’s popularity and sales volume in the market.

13. Single-unit feature compass

14. Top three single units by annual output

(1) TMPTA; (2) TPGDA; (3) HDDA.

Disclaimer

The above-mentioned indicators and recommended performance levels are measured under fixed conditions and do not guarantee suitability for all intended applications. For different application purposes and operating conditions, users must independently verify the formulations to ensure compliance with requirements.

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