Silicon Symposium

New Hydrophilic Polymeric Coupling Agents Derived from Epoxy Functional Monomers

Ferdinand Gonzaga, Jonathan Goff and Gerald L. Larson

Gelest, Inc.

Gelest - Enabling Your Technology

Coupling Agents

Molecules which have the ability to create a durable bond between organic and inorganic materials.

Silane coupling agents: Model structure:

(CH 2 ) n

R

Si

X X X

R: organofunctional group

Spacer

X: Hydrolyzable groups: • Alkoxy • Acyloxy • Halogen • Amine (cyclic azasilanes)

Properties of Coupling Agents

Control and tailor surface or interfacial properties of inorganic materials

Properties:

• Wettability: • Hydrophilicity • Hydrophobicity • Omniphobicity

• Adhesion • Ordering (monolayers) • Reactivity • Refractive Index

Substrates:

• Siliceous materials: •Silica •Glass

• Aluminium oxides • Zirconium oxides • Tin, Nickel Oxides • Titanium oxides • Boron, Iron and Carbon oxides

B. Arkles, Chemtech, 7(12), 766,1977.

Bonding Mechanism

Hydrolysis Condensation

Hydrogen Bonding

Bond Formation

Coating Degradation

• Hydrolytic stability of the oxane bond between silane and substrate

• Application in an aggressive environment (acidic/basic/saline)

(CH 2 ) n

R

Si

X X X Conventional Silane

• Gelest solution: dipodal silane coupling agents

Improved Stability from Dipodals

40

60

80

100

120

0 20 40 60 80 100 120 140 160 180

Stat

ic W

ater

Con

tact

Ang

le ,θ

(°)

t (days in 6 M HCl)

SiOC2H5

OC2H5OC2H5

Si SiOCH3

OCH3

OCH3OCH3H3CO

• Tighter networks • Up to X105 greater hydrolytic resistance

Multipodals coupling agents?

• Dipodals synthesis: • Synthetic challenges • Time consuming • Cost

• Polymerization of available monomers • Mild, tolerant to functional groups • Simple, cost-effective

Polymeric, multipodal coupling agents?

Polymerization of Epoxides

SiX3 SiX3

SiX3

R

R

R R

Ring Opening Epoxide Polymerization • Anionic ROP:

• Cationic ROP:

• Lewis Acid Catalyzed (Coordination catalyst):

• No strong nucleophile/electrophile • No formal charge • No hydrolytic conditions

Tris(pentafluorophenyl) Borane • Active at very low loadings • Robust and easy to handle (Air, Moisture) • Commercially available

• Widely used in Silicon chemistry:

• Dehydrogenative coupling of silanes and alcohols • Hydrosilylation of ketones • Piers-Rubinsztajn reaction

Proof of Principle Polymerisation

SIG5820.0

Conditions: Initiator (methallyl alcohol): 1 equiv. Monomer: 10 equiv. Catalyst: 0.8 mol% Slow monomer addition

Results: Mw:2,600g/mol Mn:1,702 Mw/Mn: 1.49 Yield: 96% Complete conversion (1H NMR)

Exotherm!

SIG5820.0

Conditions: Initiator (methallyl alcohol): 1 equiv. Monomer: 20 equiv. Catalyst: 0.8 mol% Slow monomer addition 2nd charge of catalyst required

Milder exotherm

Proof of Principle (2)

Results: Mw:2,391g/mol Mn:1,440 Mw/Mn: 1.66 Yield: 93%

Copolymerization with Trialkoxysilanes

Conditions: Initiator (methallyl alcohol): 1 equiv. Monomer: 20 equiv. (9:1 ratio) Catalyst: 0.8 mol% Slow monomer addition

Results: Mw:4,388g/mol Mn:2,334 Mw/Mn: 1.88 Yield: 85%

9 1

Triethoxysilyl groups unaffected during process

PEG as Polymerization initiator

Conditions: Initiator (methallyl alcohol): 1 equiv. Monomer: 6 equiv. (2:1 ratio) Catalyst: 0.8 mol% Slow monomer addition

Results: Mw:2,464 g/mol Mn: 1,388 Mw/Mn: 1.78 Yield: 86%

4 2

Access to functional block-copolymers

NMR Analysis

a

a b

b

c

c

d d

e, e’, h, h’

e

e e’

f

f’

g’

f, f’

g

g, g’

h

h’ e’

i

i

j

j

Epoxy-PEG monomers

Conditions: Initiator (methallyl alcohol): 1 equiv. Monomer: 20 equiv. (1:1 ratio) 60°C, Catalyst: 5 mol%

Results: Mw: 4,152 g/mol Mn: 1,269 Mw/Mn: 3.27 Yield: 78%

Need to optimize reaction conditions

10 10

Synthesis Conclusions • Epoxides efficiently polymerized by B(C6F5)3 • Polymerization orthogonal to Alkoxysilanes

• Access to various architectures/functionalities:

• Reaction sensitive to experimental conditions:

• Moisture • Induction time and exotherm variability • Discrepancy calculated/experimental MW

Polymeric Coupling Agents Efficiency

• Objective: assess wetting behavior of 3 PCA thin films. • Plan of Action:

• Design experimental procedure for surface modification • Treat BoroSilicate glass with PCA (3) • Analyze efficiency using Contact Angle measurements

PCA-TMS mPEG-PCA PCA-(PEG)m PCA-TMS

Experimental Procedure

• Borosilicate glass slide cleaning: Ethanol wash / Nitrogen dried • Acid Etch:

1. Glass slides dipped for 45minutes in 4% aqueous HCl 2. Rinse (DI / Ethanol / Acetone) 3. Nitrogen dried • Coating:

1. Glass slides dipped for one hour in reactive formulation (90% Ethanol, 5% Deionized Water, 5% PCA, 0.05% Acetic Acid) 2. Rinse (Ethanol) / Dry (N2) 3. Cure (80°C; 1 hour) 4. Cool down (dessicator) • Contact Angle measurement

Results

PCA-TMS mPEG-PCA

57

24

41

2121

30

0

10

20

30

40

50

60

PCA-TMS mPEG-PCACoupling Agent

Con

tact

Ang

le (D

egre

es)

WaterDiiodomethaneHexadecane

PCA-(PEG)m

Results

( 6 measurements averaged, 6 slides)

57

24

5

0

10

20

30

40

50

60

PCA-TMS mPEG-PCA PCA-(PEG)n

Coupling Agent

Cont

act A

ngle

(Deg

rees

)

Water

Super-wetting coupling agent

Conclusions / Future Work

• New synthetic route to polymeric coupling agents • Mild, versatile process

• Access to various architectures/functionalities

• Future work:

• Improve experimental conditions • Extend methodology to new monomers / initiators • Formulate new coatings • Durability tests