Resin-Fortified Emulsion Polymerizations

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Resin-Fortified Emulsion Polymerizations

Doug-Youn Lee

(polylab1@yonsei.ac.kr)

Nanosphere Process & Technology Laboratory

Department of Chemical Engineering, Yonsei University

Emulsion Polymerization

 Production

Billions of metric tons/year

 Advantages

- High rate of polymerization - High molecular weights

- Low viscosity

- Excellent heat transfer - High conversions

- Continuous production possibility

Applications of Latexes

 Synthetic elastomer

 Surface coatings

 Adhesive

 Carpet backing

 Paper additives & coatings

 Well-characterized monodisperse particle for fundamental colloid research

 Medical uses

Diagnostic test Smart bombs

Pore size measurements

 Electron microscope calibration standards

 Mortar reinforcement

• Wetting and adherency problems

• Low gloss or mudcaking of resulting films

• Mechanical instability

• Freeze-thaw instability

• Shear thinning property

• Poor physical properties of the resulting films

Drawbacks of Emulsion Polymers

• Poor water and corrosion resistance of resulting films

• Poor adhesion especially to metal surfaces

Disadvantage of Surfactants

Resin-Fortified Emulsion Polymers

Emulsion Polymer

• High Molecular Weight

• Toughness

• Mechanical Strength

Low Mw Resin

• Stability

• Physical properties

• Alkali Dispersibility

• Gloss

• Crosslinkability

• etc.

Resin-fortified Emulsion Latex

• Fine particle size emulsions

• Excellent film property

• High gloss property

• Newtonian-like rheological property

• Excellent mechanical stability and freeze-thaw stability

• Excellent wetting property

Resin-Fortified Emulsion Polymerization

Fig. Schematic Representation of Emulsion Polymerization of Styrene in the Presence of Carboxylated Alkali-Soluble

Aggregate of Fuctional Resins in Aqueous Phase

Resin-Fortified Latex Particles

• Type of ASRs

- Acrylic Resin (St/AMS/AA or BA/AA etc.) - SMA (Styrene Maleic Anhydride) Resin - EAA (Ethylene Acrylic Acid) Resin

- Polyurethane Resin, etc.

• Number Average Molecular Weight : 500 - 20,000

(Preferably : 2,000 - 4,000)

• Acid Number : 50 - 300

• Soluble or Dispersible in Water or Alkali

• Useful as Emulsifier, Leveling agent, and Film-former

• *acid number: the number of mg of KOH required to neutralize 1g of resin

Alkali-Soluble Resin (ASR)

Acrylic Resin

Fig. Schematic Representation of

Low MW SAA.

• Low Mw Polymer Containing Carboxyl Groups

-

poly(styrene/alpha-methylstyrene/acrylic acid) (SAA)

(St : AMS : AA = 35 : 33 : 32) - Mn : 4,300 , Mw : 8,600 , PDI : 2.0

• Acid Number : 190

• Tg : 115 ^oC

• Soluble in water and amine or alcohol, etc

• Useful as emulsifier, leveling agent, and film-former

• Applications

- Floor Polishing - Adhesive

- Paper Coating & Metal Coating - Binder & Sizing

- etc.

HOOC

COOH

COOH

HOOC COOH

COOH

• Pigment Dispersion

• High Gloss & Excellent Clarity

• Transfer Property & Printability

• Solublility

- soluble in water and amine or alcohol, MEK etc.

• Compatibility

- excellent compatibilty with styrene-acrylic emulsions, as well as SMA and maleic resins.

• Viscosity Stability

• Applications

- multi-functional properties in water and solvent based ink and coatings.

- source of carboxyl functionality so that inks and coatings can be further crosslinked to provide heat and chemical resistance.

Properties and Characteristics of SAA



Excellent stability and physical properties



System having most of the advantages of both bulk and emulsion polymer system without their disadvantages

• Fine particle size emulsions

• Excellent film property

• High gloss property

• Newtonian-like rheological property

• Excellent mechanical stability and freeze-thaw stability

• Excellent pigment dispersity and wetting property

SAA Resin-Fortified Emulsion Polymer System

Latex Particle

Mw

10³ 10⁴ 10⁵ 10⁶

Area (%)

0 1 2 3 4 5

Fig. Molecular Weight Distributions of Resin-Fortified Latexes Prepared Using SAA.

SAA Resin-Fortified Emulsion Polymer System

Fig. TEM photographs of PMMA latex prepared with 35 wt % of SAA.

• Graphic Art

• Ink Binder

• Pressure Sensitive Adhesive

- Excellent adhesion

• Paper Coating

- High gloss property - Crosslinkable

W. J. Blank, R. E. Layman, US patent 4,151,143 (1979) S. L. Tsaur, US patent 4,820,762 (1989)

G. R. Frazee, US patent 4,845,149 (1989)

Applications of SAA Resin-Fortified Polymer System

Table Basic Recipe of PSA in the Presence of ASR

Components Wt %

D.D.I Water 49.14

Alkali-Soluble Resin(ASR)

[poly(BA(70%)/AA(30%)] Mn: 2000 11.93

Ammonium Hydroxide (NH⁴OH) 2.39

Nonionic Surfactant 0.48

Monomer

MMA(10)/2-EHA(77)/BA(10)/TEGDA(3) 35.81 Initiator

Ammonium Persulfate 0.25

Resin-Fortified PSA Formulation

• Excellent water resistance, tack and adhesion

• Fine particle size emulsions

• Emulsion viscosities which can be varied from low to high with no sacrifice in stability

• Emulsion viscosities which are stable under high shear conditions in roll coating operation

- Newtonian-like flow characteristics

• Low foam production which is desirable in roll coating operation

Advantages of Resin-Fortified PSA

Emulsion Polymerization

Using SAA Resin

SAA Concentration (wt%)

10^-6 10^-5 10^-4 10^-3 10^-2 10^-1 10⁰

Surface Tension (dyne/cm)

45 50 55 60 65 70 75

UV Absorbance

0.0 .2 .4 .6 .8

Aggregate Formation of SAA in Aqueous Solution

Fig. UV absorbance of pyrene at 360nm and surface tension of SAA solution as a function of SAA concentration. (wt% based on total)

• Critical Micelle Concentration : 10^-2 wt %

• The increase in pyrene solubility with

SAA concentration indicated the formation of SAA aggregates like micelles in aqueous solution.

• Also, a gradual decrease and leveling off of surface tension indicated that SAA formed aggreagtes.

Degree of Neutralization of SAA Resin

Effect of Neutralization Degree on Emulsion Kinetics

Degree of Neutralization (%) Low Degree

of Neutralization

Excess Addition

of Neutralization Agent

Solubilizing ability,

Emulsion Polymerization Using ASR as Emulsifier

1. Formation of Aggregates

HOOC

COOH

COOH

HOOC COOH

COOH

Neutralization

Important Factors determining the Characteristics of Aggregates

1. Acid Number

2. Degree of Neutralization

3. Molecular Weight & Structure 4. Temperature,…, etc.

: Monomer

Swelling

2. Emulsion Latexes in the Presence of ASR

. Core/Shell Morphology

ASR

Grafted ASR

Polymerization

Figure TEM photographs of PMMA latex prepared with 35 wt % of ASR:

degree of neutralization of ASR; (a) 80 %, (b) 100 %.

SAA Concentration

0 5 10 15 20 25 30 35 40

D n (nm)

32 34 36 38 40 42 44 46 48

Fig. Polystyrene latex particle size as a function

Particle Size of Polystyrene Particles

• The PS latex particle size decreased with increasing the concentration of ASR

• This result was similar to that obtained in the emulsion polymerization using conventional surfactant

Grafting Reaction of SAA

-

1st Ammonia Water 2nd Toluene

1st, 2nd developed solvent

0 10

0 10

ASR

PS &

ASR-g-PS

ASR

ASR-g- PS PS TLC

Column Glass Box

1st 2nd

TLC-FID

Separation Technique Iatroscan MK-5 TLC/FID analyzer

Fig. TLC-FID chromatographic scanning showing separation of the polystyrene latexes into three

components; the ungrafted ASR, ungrafted polystyrene, and the ASR-grafted polystyrene.

Fig. Schematic Representation of Latex Particle Grafted and Adsorbed

Latex Particle Stabilized with SAA

• In emulsion polymerization using SAA, SAA containing a large number of carboxyl groups results in electrosterically stabilized latexes

Stabilization Mechanism

- Electrosteric Stabilization

• SAA was adsorbed and grafted on the surface of the final latex particle, which resulted in small-sized carboxylated latex

• The zeta potentials of final latexes

showed high values due to SAAs which were concentrated on the surface of latex particle

pH

3 4 5 6 7 8 9 10 11

Zeta Potential (mV)

-70 -60 -50 -40 -30 -20 -10

[ASR] = 35 wt%

[ASR] = 10 wt%

Fig. pH dependence of zeta-Potential of PS Latex Particle Prepared at Different Concentration of SAA

Zeta-Potential of SAA-Fortified Latex Particle

Rate of Polymerization

Measure heat of reaction, ,from reaction calorimeter

Rate of Polymerization, Rp

R Q

V H

p

r

H O p

=

2

Δ

:

:

:

Calorimetric Conversion

( ) ( )

( ) ( )

X t Q t dt

Q t dt X t

c

r t

r

t_f c f

=





0

0

:

:

:

- Reaction Calorimetric Technique

ΔHp

V_{H O2} Qr

( )

X_c t

( )

Q t_r

( )

X t_{c f}

R p in SDBS vs. SAA Systems

• Despite the almost same particle size Rp in SAA system was lower than that in SDBS system.

• This result can be explained by the adsorp -tion of SAA onto the latex particles, which can influence the entry and exit of radicals.

• Average Partcle Size

D_n ([SDBS] = 10 wt %) = 54 nm D_n ( [SAA] = 15 wt %) = 52 nm

• Rp is proportional to average number of radicals per particle.

Reaction Time (min)

0 20 40 60 80 100

Rp (x10-4 moles/L. s)

0 1 2 3 4 5 6 7

Calorimetric Conversion

0 20 40 60 80 100

SDBS System SAA System

Fig. Rate of polymerization in emulsion

polymerization of styrene using SDBS and SAA respectively.

The kinetic of emulsion polymerization using SAA and conventional ionic emulsifier was conducted to study directly any effect of SAA.

Radical Diffusion in SDBS and SAA Systems

SDBS(Anionic Surfactant) System SAA System

• Thin Electrical Double Layer

• Higher radical entry rate

• Thicker Electrosteric Layer (Hairy Structure)

• Decrease in radical entry in the electrosterically stabilized latex is ascribed to hairy layer around the particle surface.

monomeric radical

Monomer Swollen Polymer Particle

monomeric radical

Electrosteric Layer

• It was assumed that the system enters Interval III after the maximum heat of polymerization.

• Rate expression for emulsion polymn.

• This supports that SAA has an influence on radical entry & exit, which lowers the average number of radicals per particle.

• n for the SAA system is lower than that for the SDBS system.

Fractional Conversion

.3 .4 .5 .6 .7 .8 .9

Average Number of Radicals per Particle

0.0 .1 .2 .3

SDBS System SAA System

Fig. Average number of radicals per particle ( n ) vs. conversion in emulsion polymerization of styrene using SDBS and SAA respectively.

n

[ ]

p A

p p p

=

n Calculation in SDBS vs. SAA Systems

Effect of SAA Concentration on R p

• This result is quite different from that of conventional emulsion polymerization of

styrene run earlier.

SAA Concentration

10 15 20 25 30 35 40

Particle Size [Dn (nm)]

40 42 44 46 48 50 52 54

• Although a decrease in particle size was observed, the Rp decreased with increasing SAA concentration.

Reaction Time (min)

0 20 40 60 80 100

Rp (x10-4 moles/L. s)

0 1 2 3 4 5 6

[SAA] = 15 wt % [SAA] = 25 wt % [SAA] = 35 wt %

Fig. Rate of polymerization in emulsion polymerization of styrene for different

Low Concentration SAA System High Concentration SAA System

• Thin electrosteric SAA Layer

• Relatively higher radical entry rate

• Thicker electrosteric SAA Layer

• More difficult for radicals to reach the particles

• This effect lowers the average number of radicals per particle.

monomeric radical Monomer Swollen

Polymer Particle

monomeric radical

Radical Diffusion For Different SAA Concentrations

Reaction Time (min)

0 20 40 60 80 100

Rp (x10-4 moles/L. s)

0 1 2 3 4 5 6

80 % Neutralization 100 % Neutralization

Fig. Rate of polymerization in emulsion

polymerization of styrene for different degree of

• The increase in Rp may be explained by the solubilizing ability of SAA aggregate and the radical entry into the particle.

• With increasing the neutralization

degree of SAA, the Rp of styrene decreased.

• As the degree of neutralization increased, the SAA micelles of low neutralization is less efficient in capturing radicals and solu- bilizing the monomer.

Effect of % Neutralization of SAA on R _p

Emulsion Polymerization Using SAA Resins

Effect of Neutralization Degree

Degree of Neutralization (%) Low Degree

of Neutralization

Excess Addition

of Neutralization Agent

A B C

R_p& n increased R_p& n

increased

Note: Low rate of instantaneous termination or radical exit from the particle may be due to viscose and

dense shell

Effect of Electrolyte Contents on R p

Time (min)

0 20 40 60 80 100

Rp (x10-4 moles/L. s)

0 1 2 3 4 5 6

No NaCl

[NaCl] = 0.086 M

Fig. Rate of polymerization vs. time in emulsion polymerization of styrene for different electrolyte contents. [SAA]=15

• Significant increase in Rp as the electrolyte contents increased with little change in

particle size.

• Effect of electroytes

- solubilization ability of SAA aggregates - capture efficiency of radical

• The effect was explained as a consequence of an increase in solubilization ability of

SAA aggregates and enhanced rate of radical entry.

Film Formation & Properties

Temperature (oC)

-50 0 50 100 150 200

log E' (Pa)

3 4 5 6 7 8 9

tan δ

0 1

Fig. Dynamic mechanical properties of 10 wt% SAA-blended

PBMAlatex film as a function of temperature; storage modulus (E’);

• The spectrum shows distinct relaxations due to immiscibility between PBMA and SAA

Dynamic Mechanical Property for Blend System

Figure Schematic of an atomic force microscopy (AFM) showing the force sensing cantilever.

Nanoscope III AFM

(Digital Instruments, Inc, USA)

Atomic Force Microscopy

AFM Images of PBMA+10%SAA Before Annealing

Fig. Atomic force micrographs of PBMA latex film containing 10% SAA before

Fig. Three-dimensional AFM surface images of PBMA latex film containing 10% SAA and annealed for 10 min at 90 ^oC.

AFM Images of PBMA+10%SAA, 90

C for 10min

ATR FTIR Spectra

(A) before annealing

(B) after annealing for 60 min at 90

C

710 to 690 cm

region :

typical absorption peak for benzene ring

Attenuated total reflectance FTIR:

(Perkin-Elmer model 2000)

Wavenumbers (cm^-1)

800 1000

1200 1400

Intensity

Before annealing After annealing

690-710 cm^-1

(A)

(B)

Fig. ATR FTIR spectra showing the 710 to 690 cm^-1 region of the air/film interface of PBMA latex film containing 10% SAA.

Grafting Reaction in Resin-Fortified Polymer System

Ungrafted PBMA Ungrafted SAA

Ungrafted SAA

Ungrafted PBMA

SAA-g- PBMA

(a)

(b)

Fig. TLC/FID chromatographic scanning curves of PBMA latex prepared with SAA

; (a) 10 wt % SAA-blended PBMA latex film, (b) 10 wt % SAA-fortified latex film.

Grafting Efficiency:

50 - 80%

Dynamic Mechanical Properties of SAA-fortified PBMA

Temperature (oC)

-50 0 50 100 150 200

log E' (Pa)

5 6 7 8 9

tan δ

0.0 .4 .8 1.2

(a)

Temperature (^oC)

-50 0 50 100 150 200

log E' (Pa)

5 6 7 8 9

tan δ

0.0 .4 .8 1.2

(b)

Fig. Dynamic mechanical properties of SAA-fortified PBMA latex films as a function of temperature; storage modulus (E′); damping curve (tanδ); (a) 10 wt % of SAA, (b) 20 wt % of SAA

Other Resin-Fortified Systems

Polyurethane Resin

1. Basic Urethane Chemistry



Polyaddition between di(poly)ol and di(poly) isocyanate group

 Segmented structure: soft and hard segments

 Various kinds of polyurethanes can be synthesized

2. Water-soluble Polyurethane Resin



Polyurethane resins have carboxylic acids (DMPA) and they located randomly at polymer backbone

Characteristics :

•Water-dispersible or water-soluble

•Low CMC and high solubilizing ability

•Molecular Weight: 5,000 - 15,000;

•Acid Number: 31 - 50 mg KOH/g PUR

OH + OCN N

H O

O

HOOC

COOH

HOOC COOH

COOH

Preparation of Polyurethane Resins

Synthetic Procedure

O H

O H

OH O

DMPA

NCO

OCN

IPDI

+



Non-reactive polyurethane resin : PUR-750 and PUR-2000

NH O NH

O O

O NH O

n

O O O H

O N

H O

O O

H n

O H

O nH

PPG

+

Stoichiometric balance in NCO and OH values

O OH

O O

H

O H n

PPG

+ Excess residual NCO

+ 2-hydroxyethyl methacrylate (HEMA)



Reactive polyurethane resin : PUR-750HEMA

O O

NH O NH

O

O O NH

O

n

O

O O H

O N

H O

O

Concentration dependence of the I₁/ I₃ Ratio of pyrene fluorescence for PU Resins(25^oC)

Concentration of PU resins (g/dm³ water)

10^-6 10^-5 10^-4 10^-3 10^-2 10^-1 10⁰ 10¹ I1 / I3

1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0

7.5x10^-4 2.1x10^-3

PU2000 PU750

Polyurethane Resin

PUR-2000 PUR-750

TEM Photo of Polyurethane Resins (× 30 K)

 Non-reactive type polyurethane resins at 100% neutralization degree

 Amorphous structure due to low Mw and low T



Polyurethane Resin Aggregates

Emulsion Polymerization Using Polyurethane Resins

Electron Microscopy Analysis

[SDS]_o = 5wt.%(monomer) [KPS]_o = 0.93mM water

[PUR750]_o = 5wt.%(monomer) [KPS]_o = 0.93mM water

Suggested driving forces

affecting continuous nucleation 1. Low CMC and small

aggregation number of the polyurethane resin

2. High solubilization ability for hydrophobic materials

 Remark

Self-aggregate of polyurethane molecules can be polymerization locus, even below CMC

Properties of Ethylene-Modified Latex

Using Ethylene-Acrylic Acid Resin

Emulsion Polymer

• High Molecular Weight

• Toughness

• Mechanical Strength

EAA resin

• Alkali Dispersibility

• Crosslinkability

• Barrier

• Chemical Resistance

Ethylene-modified Latex

• PAPER COATING

- Excellent water, grease and oil resistance - Excellent adhesion

- Repulping property - High gloss property - Crosslinkable

- High wet strength retention

• PAPER AND PAPERBOARD SATURATION AND SIZING

• METAL COATING, etc.

EAA Resin-Fortified Emulsion Polymer

Particle size (nm)

0 50 100 150 200

Intensity

0 20 40 60 80 100 120 140

EAA 60 wt% ; D_n = 69.1nm, D_w = 74.7nm EAA 50 wt% ; D_n = 75.6nm, D_w = 81.2nm EAA 40 wt% ; D_n = 82.4 nm, D_w = 101.1 nm

Figure. Particle size and size distribution of ethylene -modified polystyrene with different EAA concentration at 140% degree of neutralization of EAA.

Latex Particle Size with Concentration of EAA

• As the concentration of EAA as a polymeric emulsifier increases, particle size is smaller and size distribution becomes narrow.

• Polydispersity is affected by : - water solubility of monomer - concentration of EAA as a

polymeric emulsifier.

EAA content (wt%)

10 20 30 40 50 60 70

Permeability (g mm/m2 day)

3.0 3.5 4.0 4.5 5.0

Effect of EAA Concentration on Permeability

Figure. Permeability of ethylene-modified

PBMA latex film with different EAA concentration.

PBMA film EMPB-E20 film EMPB-E40 film EMPB-E60 film EAA film

8.1267 4.2276 3.9046 3.5568 0.2275 Permeability^a (g mm/m² day)

Table. Permeability of PBMA Films and Pure EAA Film.

a measured at 20^oC and 90% RH.

b % based on monomer.

* All sample drying at 40^oC.

EAA concentration (wt% based on PS)

20 40 60

Weight Loss (%)

0 10 20 30 40 50 60

Ethylene-Modified PS The Simple Blends

Figure. Weight loss of ethylene-modified PS and the simple blends of PS/EAA as a function of EAA concentration after their immersion to methyl ethyl ketone for 5 hours.

Table. Percentage Weight Losses of

Ethylene-Modified Latex Films and the Simple Blending Films of PS and EAA after Their Immersion to Methyl Ethyl Ketone for 5 Hours

Weight Loss %

Weight Loss % EMPS-

E60 1.72 SBPS-

E60 41.0%

EMPS-

E40 2.26 SBPS-

E40 46.8%

EMPS-

E20 6.61 SBPS-

E20 55.8%

Chemical Resistance

The chemical resistance of ethylene-modified PS films is about 20 times higher than that of simple blends.