Download K-KAT 670 Silane Catalyst Presentation

Non-Tin Catalysts for Crosslinkable
Silane Terminated Polymers
K-Kat 670
King Industries, Inc.
Science Road
Norwalk, CT 06852
USA
Silane Chemistry
Terms and Applications
•
Organosilane compounds
– Monomeric silicon bonded with carbon
• Siloxane compounds (Si-O-Si)
– Polymeric organosilane compounds
• Silanol groups (Si-OH)
– Hydrolyzed silane group
• Promote adhesion and reinforcement of:
– Coatings
– Adhesives
– Sealants
– Fillers
Silane terminated Polymer Technologies
• Functionalized backbone with alkoxysilane terminal groups
• Silane terminated polymer backbone chemistries
– Polyether
– Polysiloxane
– Polyurethane
• Cured properties (Tg, flexibility…) depend on the backbone
Silane terminated Polyethers
CH3
Si
MeO
OMe
•
•
•
•
•
•
•
•
•
CH3
CH3
O
CHCH2O
Si
n
OMe
OMe
Polyether backbone provides low viscosity, low Tg, flexibility over a wide temp. range,
low color and odor.
Can produce versatile sealants and adhesives
Linear MS polymers produce very soft, low modulus sealant with superior workability
and adhesion.
Slightly branched structures provide a higher modulus, with fast and uniform cure.
Superior adhesion to a wide variety of materials without primer.
Excellent elastic behavior and durability.
Great mechanical properties.
Good storage stability, in the absence of catalyst and water.
Fast moisture cure with no bubbling.
Silane terminated Polyurethanes
CH3
Si
EtO
OEt
•
•
•
•
•
•
•
•
•
•
CH3
H
N
H
N
N
O
X
O
O
CHCH2O
CH3
H
N
N
n
H
N
Si
X
O
O
OEt
OEt
Urethane functionality provides compatibility and tear resistance
Polyoxypropylene backbone provides elasticity
Silane end groups serve as crosslinking/chain extension functionalities and an internal primer on
many surfaces.
Combine the benefits of silicones and polyurethanes
Odorless and NCO free and hence not classified
Sealants and adhesives have high mechanical strength and good elastic recovery
Excellent adhesion without primer
Paintability
Bubble-free crosslinking even in humid environment
Useful in
– Bodywork and vehicle construction
– Ship building
– Airconditioning and ventillation technology
– Construction and assembly applications
Market Drivers / Technology Trends
•
•
•
Organotin compounds such as, for example, dibutyltin dilaurate (DBTDL),and dibutyltin
bis(acetylacetonate) are widely used as condensation cure catalysts to accelerate the
moisture assisted curing of a number of different polyorganosiloxanes and non-silicone
polymers having reactive terminal silyl groups.
– Environmental regulatory agencies and directives, however, have placed
increasing restrictions on the use of organotin compounds in formulated products.
– While formulations with greater than 0.5 wt. % dibutyltin presently require
labeling as toxic with reproductive 1B classification, dibutyltin-containing
formulations are proposed to be completely phased out in consumer applications
during next several years.
Methanol emission from methoxysilane terminated polymers deemed harmful leading
to a switch towards ehtoxy silane terminated polymers.
Non-tin metal catalysts that accelerate the condensation curing of both methoxy and
ethoxy terminated moisture curable silanes would be highly desired.
Desired Catalyst Attributes
• Liquid Product
• Stability in 1K system during extended storage periods.
• Ambient moisture cure rate comparable to tin catalysts.
• Imparts good mechanical properties after cure.
• Excellent adhesion to a variety of substrates.
Silanol Formation
Hydrolysis of Alkoxysilanes
CH3
Polymer
CH3
H2O
Si
OMe
Polymer
Si
Polymer
OH
Catalyst
OMe
CH3
H2O
Si
Catalyst
OMe
OH
OH
Formation of Siloxane Crosslinks by
Condensation of Silanols
CH3
Polymer
Si
CH3
OH
+
Polymer
OMe
OH
OMe
CH3
CH3
Polymer
Si
Si
O
OMe
Si
OMe
Polymer
Formation of Siloxane Crosslinks by
Condensation of Silanol and Alkoxysilane
CH3
Si
CH3
OH
+
Polymer
OMe
OMe
OMe
CH3
CH3
Polymer
Si
Si
O
OMe
Si
OMe
Polymer
+
CH3OH
Acid Catalyzed Hydrolysis of Alkoxysilanes
Acid Catalyzed Hydrolysis of Alkoxysilanes
•
•
•
At neutral pH, alkoxysilanes hydrolyze at very slow rates, with half-lives > 14hrs
At pH < 4, the hydrolysis is rapid
At pH > 10, hydrolysis of the first intermediate, RSi(OR)2OH, is inhibited due to the ionization of the SiOH
group.
F. D. OSTERHOLTZ and E. R. POHL* J.Adhesion Sci.Technol.Vol.6, No. 1, pp 127-149(1992)
Acid Catalyzed Condensation of Silanols
CH3
Polymer
Si
H
OH
+
CH3
OH
Polymer
Si
+
Polymer
Si
OH
+
OH2
Polymer
Si
OH
OH
CH3
CH3
Si
OH
H2O
+
O
H
Si
OH
CH3
CH3
+
Polymer
+
OH2
+
OH
CH3
Si
H
H
OH
Polymer
CH3
+
O
+
O
H
+ H2O
Polymer
Si
OH
+
Polymer
OH
H2O
CH3
CH3
Polymer
Si
O
Si
OH
H3O+
Polymer
Base Catalyzed Hydrolysis of Alkoxysilanes
•General Base Catalysis: Any basic species accelerates the reaction by assisting the removal of a proton from water in
the transition state.
•Specific Base Catalysis: The hydroxide anion accelerates the reaction rate by directly attacking the substrate.
Base Catalyzed Condensation of Silanols
CH3
CH3
R
Polymer
Si
OH
+
OH
Si
OH
Polymer
NR2
+
H2O
+
Polymer
Si
OH
CH3
CH3
CH3
NR2
Si
R
OH
CH3
Polymer
N H
OH
Polymer
Si
O
Si
OH
OH
+
R
N H
R
Polymer
Acid and Base Catalyzed
Hydrolysis and Condensation
Effect of pH on Reaction Rates
Optimum pH for hydrolysis and condensation is different
-1
0
2
4
6
8
10
12
14
log pK
pH>10 hydrolysis inhibited due
to ionization of SiOH group
Condensation
minimum rate ~pH 4
Hydrolysis
minimum rate ~pH 7
-4.5
pH
Hydrolysis
Condensation
Acid and Base Catalyzed
Hydrolysis and Condensation
Effect of pH on Reaction Rates
•
Hydrolysis
– Rate minimum is at approximately neutral pH ( pH 7)
•
Condensation
– Rate minimum is at approximately pH 4
•
Each pH change of 1 unit in either direction produces a ten-fold rate acceleration
assuming an excess of available water (up to pH 10 for hydrolysis)
•
Both hydrolysis and condensation reactions are reversible. Alcohols will reverse the
silane hydrolysis
Mechanism of Tin catalysis
DBTDL Hydrolysis
R'
R'
O
O
O
R
O
Sn
O
R'
O
R
R
HO
Sn
R
O H
O
H
H
+
R'
O
DBTDL undergoes hydrolysis and forms an organotin hydroxide, which is the true
catalytic species
Frederik Willem, Makromol.Chem. 181, 2541-2548 (1980)
Mechanism of Tin Catalysis
Formation of Organotin Silanolates
R'
O
CH3
O
R
Sn
R
O
+
Polymer
Si
CH3
OMe
Polymer
Si
OMe
R
OMe
O
H
Sn
R
R'
Organotin hydroxide reaction with alkoxysilane
group to form organotin silanolates
O
+
CH3OH
Mechanism of Tin Catalysis
Formation of Silanol Group
CH3
Polymer
Si
R'
OMe
R
+
O
O
CH3
H2O
Polymer
Si
O
OH
Sn
+
R
OMe
R
Sn
R
O
H
R'
O
Tin silanolates react readily with alcohols and water
Mechanism of Tin Catalysis
Formation of Alkoxysilane
CH3
Polymer
Si
OMe
O
+
CH3
R
Polymer
Si
OH
Sn
OMe
R
R'
O
R'
CH3
CH3
O
O
Polymer
Si
O
OMe
Si
OMe
Polymer
+
R
Sn
R
O
H
Mechanism of tin catalysis
L
Sn
H2O
LH
O
OR
Si
OH
Si
Sn
OH
ROH
O
Sn
Si
Si
Si
Evaluation of K-Kat 670 in Silane functional
Polymer Formulations
•
Fully formulated single component moisture cure alkoxysilane systems were used
•
Uncatalyzed formulations were stored in dispense cartridges. Approximately 30 grams of uncatalyzed material was
dispensed into a speed mixer container with a caulk gun before addition of the catalyst. The material was mixed on
a speed mixer for 30 seconds at 1500 rpm then 2 minutes at 2200 rpm.
•
An adjustable doctor blade was used to apply 3 mm of the blend onto a paper substrate.
•
The degree of dryness was determined by using a Model 415 Drying Time Tester* in accordance with DIN 53 150.
•
The dryness test involved applying a force onto a paper disk that covered a test site on the casting for 60 seconds.
The results are based on the amount of tack and on visual impressions that develop from the applied force. The
dryness testing was done at approximately 25°C and 50% relative humidity.
•
Degree 1 of the DIN 53 150 method was substituted with a glove test to determine touch dry.
•
Hardness of the castings was determined with a Shore A** hardness tester after the castings were allowed to cure
under ambient conditions for 2 weeks. Other mechanical properties were measured on an Instron*** tester using
dogbone shaped samples cut from the fully cured 3 mm thick castings.
*Model 415 Drying Time Tester, Erichsen GmbH & Co. KG
**Instron Corporation, Shore A durometer
***Instron Corporation, Dual column table top model, 30 kN (6700 lbf) load capacity
Dryness Testing Ratings
Degree of dryness (DIN 53 150)
Rating
Description
1
Touch dry, no visible residue remaining on rubber glove
2
Paper does not adhere, but visible change with 20g load
3
Paper does not adhere, but visible change with 200g load
4
Paper does not adhere, but visible change to coated surface with 2Kg load
5
Paper does not adhere, no visible change to coated surface with 2Kg load
6
Paper does not adhere, but visible change to coated surface with 20Kg load
7
Paper does not adhere, no visible change to coated surface with 20Kg load
Dimethoxymethylsilane Polymer
Formulation
Component
%
Dimethoxymethylsilane polymer
32.8
Plastisizer
16.4
Filler
39.3
Titanium dioxide
6.6
Thixotrope
1.6
HALS
0.3
UVA
0.3
Moisture scavenger
0.7
Adhesion promoter
2.0
100.0
Dimethoxymethylsilane Formulation
Dryness Development
•
Levels of K-Kat 670 were adjusted to produce castings that dried at rates
similar to the system catalyzed with 0.6% dioctyltin diacetylacetonate
(DOTDAA).
•
The tin content of DOTDAA is approximately 21%. At 0.6%, the tin content in
the formulated control system is approximately 0.12% which would not
comply with EU regulations.
•
The systems dried similarly with each achieving the highest degree of dryness
(Paper does not adhere to 20Kg load, no visible change to coated surface) in
6 hours.
•
The DOTDAA and K-Kat 670 catalyzed castings developed similar tensile stress
(which can be associated with toughness), modulus (elastic modulus) and
strain (elongation).
Dimethoxymethylsilane Formulation
Dryness Development
7.0
Hours at 25 C/50% RH
6.0
5.0
4.0
3.0
2.0
1.0
0.0
1
2
3
4
5
Dryness degree(DIN 53 150)
0.6% DOTDAA
2.0% K-Kat 670
6
7
Dimethoxymethylsilane Formulation
Properties After 2 Week Cure
400
350
300
250
200
150
100
50
0
Shore A
Stress at max, psi
0.6% DOTDAA
Strain at max, %
2.0% K-Kat 670
Modulus, psi
Trimethoxysilane Formulation
Dryness Development
•
DOTDAA was compared to K-Kat 670 in a polyether backbone TMS polymer
system.
•
The DOTDAA system achieved the maximum dryness rating (passed 20Kg load
test) in 5 hours while K-Kat 670 required 6 hours to reach the 7 dryness
rating.
•
Both castings developed similar mechanical properties after the 2 weeks of
ambient cure
Trimethoxysilane Polymer
Formulation
Component
%
Trimethoxysilane polymer
32.8
Plastisizer
16.4
Filler
39.3
Titanium dioxide
6.6
Thixotrope
1.6
HALS
0.3
UVA
0.3
Moisture scavenger
0.7
Adhesion promoter
2.0
100.0
Trimethoxysilane Formulation
Dryness Development
7.0
Hours at 25 C/50% RH
6.0
5.0
4.0
3.0
2.0
1.0
0.0
1
2
3
4
5
Dryness Degree ( DIN 53 150)
0.6% DOTDAA
2.0% K-Kat 670
6
7
Trimethoxysilane Formulation
Properties After 2 Week Cure
400
350
300
250
200
150
100
50
0
Shore A
Stress at max, psi
0.6% DOTDAA
Strain at max, %
2.0% K-Kat 670
Modulus, psi
Diethoxysilane Formulation
Dryness Development
•
DOTDAA was compared to K-Kat 670 in a polyurethane backbone DES polymer system.
•
DOTDAA was essentially inactive in this system, at even 0.5% and 1.0% on total formulation weight.
•
Higher dosages were not evaluated since the tin level incorporated with the 1.0% dosage was more
than double the maximum allowed by EU regulations.
•
The 3 mm thick castings required more than 120 hours to achieve a dryness rating of 7.
•
Dibutyltin dilaurate (DBTDL) was similarly inactive.
•
Dry times of the DES system catalyzed with K-Kat 670 were significantly faster than the tin
catalyzed systems.
•
DOTDAA catalyzed system required a month of ambient cure before it was suitable for testing on
the Instron. Even so, the casting exhibited very poor mechanical properties.
The K-Kat 670 cure profile was unchanged after storage of the polymer containing 2% of the
catalyst at 500C for 4 weeks
•
Diethoxysilane Polymer Formulation
Component
%
Diethoxysilane polymer
20.2
Plasticizer
23.1
Calcium carbonate
49.2
Titanium dioxide
3.3
Antioxidant
0.3
HALS
0.3
Moisture scavenger
0.8
Fumed silica
1.4
Adhesion promoter
1.5
100.0
Diethoxysilane Formulation
Dryness Development
140
Hours at 25 C/50% RH
120
100
80
60
40
20
0
1
2
3
4
5
Dryness Degree (DIN53 150)
0.5% DOTDAA
2.0% K-Kat 670
6
7
Diethoxysilane Formulation
Cured Properties
700
Cure Schedule: K-Kat 670: 2 weeks, DOTDAA:1 month
600
500
400
300
200
100
0
Shore A
Stress at max, psi
0.5% DOTDAA*
Strain at max, %
2.0% K-Kat 670
Modulus, psi
K-Kat 670 for Crosslinkable Silane
Terminated Polymers
Conclusions
• Liquid Product
• Excellent Stability in 1K system during extended storage periods.
• Provides ambient moisture cure comparable to tin catalysts, in
methoxy silane terminated polymers.
• Provides superior moisture cure versus tin catalysts in ethoxy silane
terminated polymers.
• Imparts good polymer mechanical properties after cure.
• Excellent adhesion to a variety of substrates.
Non-Tin Catalysts for Crosslinkable Silane
Terminated Polymers
Thank You for your interest