Department of Chemical Engineering

Synthesis of High-performance UV curable Crosslinked Coatings through the Grafting of

Methylene Malonate Chemistry

Mengfei Huang

Advisor: Jessica Schiffman, John Klier

University of Massachusetts, Amherst

Department of Chemical Engineering

2

Overview of Coatings

Decorative Coatings

Protective Coatings

Other applications

World coating market in 2011

http://news.jc001.cn/11/0809/628508.html

High crosslinking degree

High performance and mechanical strength

Fast curing

X High solvent level

X Release of volatile organic compounds (VOCs)

X Bad effects to environment and human health

X Pose fire and explosion hazard and need careful storage

3

Water Borne Coatings Market and Method of Synthesis

Global waterborne coatings Growing Emulsion polymerization to make latex

Environmentally friendly, low toxicity

Resist blocking, heat, abrasion and offer

minimal flammability

X Thermoplastic coating with low crosslinking

X Insufficient mechanical properties

Global market report from BCC Research

Waterborne Coating Binders

~ 85% Vinyl Addition Emulsion Polymers

~ 15% Other Dispersions

• Polyurethane

• Alkyd

• Epoxy….

4

Crosslinking Provides• Hardness• Chemical resistance• Moisture resistance• Abrasion & block Resistance• Higher gloss• Improved durability• Enables low VOC

• Crosslinking Agent

• Functional Latex

• 1K & 2K

• Crosslinked Latex

• Mechanical, Tg, Barrier,

Block….

Enhanced Waterborne Properties Thermoset

Current Technology• 1K heat cure: Amino formaldehyde

resins, phenolic resins…• 1K UV cure: Expensive and inefficient• 2K Isocyanate cure: Hazard concerns• 1K Sunlight cure: Low allyl group level,

limited crosslinking.

Opportunity for New Technology• Room temperature cure• Cure on demand after film formation

(UV, sunlight, O2)• No premature crosslinking in dispersion• High degree of crosslinking• One component

5

Covalent Modification: Reactive Functional Additives

Substrate with Anionic Groups- Dispersions- Surfaces

FunctionalGroup

Anionically PolymerizableGroup

F1

Mix

• Aqueous• Non-Aqueous

• Anionic Grafting• High Functional Group Density• Latex, POD, PUD etc.

High Density of

Functional Group

F1: Vinyl groups, PEG, PDMS segment,

Hydrocarbon segment, silane…

6

Covalent Modification: Reactive Functional Additives

Substrate with Anionic Groups- Dispersions- Surfaces

FunctionalGroup

Mix

• Aqueous• Non-Aqueous

• Anionic Grafting• High Functional Group Density• Latex, POD, PUD etc.

Anionically PolymerizableGroup

High Density of

Vinyl Group

7

Chemical Structure of HEMA-MM

Hydroxyethyl methacrylate methylene malonate (HEMA-MM)

for UV curable coatings– Post functionalization

Methylene Malonate (MM)

Anionic polymerization

HEMA：Free radical polymerization

Functionalized surface

PolyMM covalently bond on surface

Pendent HEMA groups

Easy method to introduce unsaturated

double bond

Enable UV crosslinking

Improvements on mechanical strength

8

Anionic polymerization of DEMM under mild conditions

• DEMM could undergo fast anionic polymerization under mild

conditions (i.e. room temperature, ambient environment).

Diethyl methylene malonate

(DEMM)

• Reaction mechanism

Nucleophile:• Carboxyl (R-COO-)

• Bronic (R-B(OH)3-)

• Phenolic (R-Ar-O-)

Huang, M. et cl, Anionic Polymerization of Methylene Malonate for High Performance Coatings. ACS Applied Polymer Materials 2019.

9

Study of connection bond using UV-vis

Functional groups initiate DEMM

DEMM Covalently Bonds with Anionic Functional Groups

0 2 4 16 18 200

20

40

60

80

100

VBA-Na

AA-Na

MAA-Na

BBA-Na

Catechol-NaDE

MM

Co

nve

rsio

n (

%)

Time (h)

• Sodium 2-vinylbenzoic acid (VBA-Na)

• Sodium acrylic acid (AA-Na)

• Sodium methacrylic acid (MAA-Na)

• Sodium benzeneboronic acid (BBA-Na)

• Sodium catechol (catechol-Na)

DEMM conversion rate by functional salts

• 5-fluoresceincarboxylate was covalently coupled to polyDEMM.

Are they covalently bonded

via anionic polymerization?

10

Carboxylated latex particles

Waterborne latex

Grafting of HMEA-MM on Latex: Carboxyl-MM Chemistry

Latex

Latex synthesized by emulsion polymerization

• Base monomer:

Methyl methacrylate (MMA), butyl acrylate (BA)

• Functional monomer:

Methacrylate acid (MAA) 10 wt%

• Surfactant

Sodium dodecyl sulfate (SDS)

• Room temperature

• Ambient environment

• Easy processing

HEMA-MM

11

Procedure: Directly adding 10%, 20%, 30% and 40% methylene malonate monomer into

MAA latex (to the solid weight of latex) at pH 6, stir for reaction.

• Particle size increases linearly with the addition of methylene malonate

monomer.

• Contact angle increases with MM grafting

• Less than 10 wt% MM could consume the carboxyl groups in the latex.

MM Grafting on MAA Latex Particles

0 10 20 30 40

85

86

87

88

89

90

91

92

93

Actual Particle Size

Theoretical Particle Size

Pa

rtic

le S

ize (

nm

)

DEMM Content (wt%)Methylene malonate content (wt%) Methylene malonate content (wt%)

• Particle size distribution • Contact angle

12

UV-curable Coating Synthesis： Carboxyl-MM Initiation

Coating performance

Neutralize latex pH to 6

MAA latex was grafted with 0%, 2.5%, 5%, 7.5% and 10% HEMA-MM.

Photoinitiator: 2,2-Dimethoxy-2-phenylacetophenone (DMPA)

Grafting of HEMA-MM

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0 2.5 5 7.5 100

50

55

60

65

70

After UV

Before UV

Wd

ry g

el /

Wdry

film

(%

)HEMA-MM (wt%)

2.5 5 7.5 100

10

20

30

40

50

Wsw

elli

ng

film

/ W

dry

film

(%

)

HEMA-MM (wt%)

Increasing HEMA-MM content

Swelling Ratio and Gel Content Increase with HEMA-MM

Procedure: Prepare UV curable coating with 0%, 2.5%, 5%, 7.5% and 10% HEMA-MM grafting.

Immerse coating film (m1) into DMF for 24h, weigh the gel as m2. Dry the swelling gel as m3.

Gel content =m3/m1

• Control sample completely dissolved in DMF.

• 100 wt% HEMA-MM formed a swelling gel.

• Swelling ratio result and gel content result

indicate the increasing of crosslinking degree

with more HEMA-MM incorporation.

Swelling ratio = m2/m1

Dry film

DMF

Swell

m1

Swelling gel: m2

14

Tg and Hardness Increase with More HEMA-MM

Hardness test: QBY-II, based on GB 1730-79

• Crosslinking density increases by introducing more HEMA-MM.

• The dense crosslinking network enabled an elevated hardness.

• The mechanical properties were significantly improved

Glass transition temperature change

• Small amount of MMA was used

to dissolve DMPA in this sample.

0 2.5 5 7.5 10

35

40

45

50

55

60 Before UV

After UV

Gla

ss T

ransitio

n T

em

pera

ture

(℃

)

HEMA-MM (wt%)

Acrylic polyurethane for car

coatings and industrial product.

https://www.atobo.com.cn/Products/Photo-8127030.html

15

0 200 400 600 8000

5

10

15

20

Str

ess (

MP

a)

Strain (%)

HEMA 0%

HEMA 2.5%

HEMA 5%

HEMA 7.5%

HEMA 10%

The Tensile Strength Greatly Improved

• The film becomes stronger with increased crosslinking.

• Young’s modulus and yield strength increase with more HEMA-MM.

Procedure: The coating film after UV crosslinking was cut by 5 cm*0.5 cm

for tensile test (Stable Micro Systems, TA-XT plus).

0 2.5 5 7.5 100

10

20

30

40

50

60

70

80

90

Young's modulus (MPa)

Yield strength (MPa)

HEMA-MM (wt%)

16

Conclusion

• Methylene malonate undergoes fast anionic polymerization initiated by

nucleophiles (Carboxyl, Bronic, Phenolic)

• HEMA-MM undergoes anionic polymerization under mild conditions, and it

provides pendent vinyl groups for free radical polymerization in latex system.

• The grafting of methylene malonate was demonstrated with particle size and

contact angle measurements, extraction studies, UV-vis, and NMR studies.

• Evidence of crosslinking is based on

• Decreased swelling ratio

• Increased gel content

• Increased glass transition temperature

• Improved hardness

• Increased Young’s modulus and yield strength

• HEMA-MM provides a simple in-situ method under mild conditions and with

easy-processing to introduce vinyl groups onto emulsion polymers and polymer

dispersions for subsequent free radical crosslinking.

17

Department of Chemical Engineering

19

Study of DEMM Initiated by Hydroxide Ions (OH-)

Hydroxide ion initiates DEMM

pH modified by sodium hydroxide

3 4 5 6 70

100k

200k

300k

400k

500k

Mo

lecu

lar

We

igh

t

pH

10 wt% DEMM

Molecular weight of water-initiated-

DEMM under different pH (3-7)

The conversion of DEMM initiated

by water at different pH

OH- in water could initiate DEMM

The conversion rate of DEMM and

molecular weight of polyDEMM

could be controlled by pH values

The anionic mechanism has been

demonstrated using NMR

Initiation: OH-

Termination: H+

Huang, M. et cl, Anionic Polymerization of Methylene Malonate for High Performance Coatings. ACS Applied Polymer Materials 2019.

20

NMR of low MW polyDEMM initiated by water at pH 4

-H connection bond -- 1H NMR -OH connection bond -- 13C NMRMatrix-assisted laser desorption/ionization

mass spectroscopy （MALDI-TOF ） test

with the discovery of two oligomers

Discovered initiation and termination

connection bond.

Verified the anionic polymerization

mechanism.

21

13C NMR study of carboxyl in water initiated MM

• 1 wt% carboxylate in water (pH 5) gives more than 80% grafting.

Procedure: Directly adding 10 wt% methylene malonate monomer into 1 wt% MAA

in water at pH 6, stir overnight for reaction. Dry the latex and measure 13C NMR.