The bonding of alkoxysilanes to dehydroxylated silica surfaces: A new adhesion mechanism

Conference · Fri Dec 31 04:00:00 EST 1993

OSTI ID:141445

Dubois, L H; Zegarski, B R ^[1]

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1. AT&T Bell Laboratories, Murray Hill, NJ (United States)

Alkoxysilane coupling agents are commonly used to bond polymers to glass surfaces by the following reaction: R`Si(OR){sub 3} + HOSi{triple_bond} {yields} R`Si(OR){sub 2}-Si{triple_bond} + ROH. R is typically a methyl or ethyl group and R` contains a functionality that can react readily with the polymer. Until now it was thought that hydroxyl groups must be present on the surface in order for a reaction to take place. In this work the authors demonstrate, using infrared spectroscopy, that a series of seven alkyalkoxysilanes (R`{sub n}Si(OR){sub 4{minus}n}; R, R` = H, Me, Et; n = 1-3) react directly with highly strained siloxane (Si-O-Si) bonds present on dehydroxylated silica at room temperature, thus yielding a new mechanism for polymer-surface adhesion. This reaction takes place by nucleophilic attack of the adsorbates on the strained siloxane rings of the substrate resulting in adsorbed alkysiloxanes and alkoxides (i.e. R`Si(OR){sub 3} + {triple_bond}Si-O-Si{triple_bond} {yields} {triple_bond}Si-O-SiR`(OR){sub 2} + {triple_bond}Si-O-R). The driving force is the release of this strain energy. Surface silanol groups are not involved in the reaction. The resulting products are stable on the silica surface to temperatures in excess of 600 K and do not react with water vapor at low ({approx_lt}1 Torr) pressures. Typical R` groups (including mercaptans and epoxides) are not reactive toward these strained bonds thus leaving them free to bind into the polymer network.

• OSTI ID: 141445
• Report Number(s): CONF-930304--
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
ADHESION
ALKOXY RADICALS
CHEMICAL BONDS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
SILANES
SILICA
SORPTIVE PROPERTIES
TEMPERATURE DEPENDENCE