Siloxane- Alkylene Oxide Copolymers

The interest in this type of copolymers is still very strong due to their large volume applications as emulsifiers and stabilizers in many different systems 43,260,261). However, little is known about the structure-property relationships of these systems 262) and the specific interactions of different segments in these copolymers with other components in a particular multicomponent system. Sometimes, minor chemical modifications in the PDMS-PEO copolymer backbone structures can lead to dramatic changes in its properties, e.g. from a foam stabilizer to an antifoam. Therefore, recent studies are usually directed towards the modification of polymer structures and block lengths in order to optimize the overall structure-property-performance characteristics of these systems 262). 

Controlled synthesis of AB, ABA and (AB)n type PEO (A) and PDMS (B) copolymers by hydrosilation of mono- or diallyl-terminated PEO oligomers and telechelic (Si—H) terminated PDMS oligomers were reported by Haesslin 263). Hydrosilation reactions were conducted in bulk, at 90 °C, in the presence of hexachloroplatinic acid catalyst. Completion of the reactions were monitored by H-NMR, GPC and VPO. The molecular weights obtained were in good agreement with theoretical expecta- 

---

There are several short reviews of the synthetic chemistry [15, 16] and physical properties for siloxane-alkylene oxide copolymers 3. The synthesis generally proceeds through two steps, the production of polymethylhydrosiloxane-dimethylsiloxane copolymers and the subsequent platinum catalyzed hydrosilylation of an allyl terminated polyether (Eq. 3). 

Hydrosilation reactions have been one of the earlier techniques utilized in the preparation of siloxane containing block copolymers 22,23). A major application of this method has been in the synthesis of polysiloxane-poly(alkylene oxide) block copolymers 23), which find extensive applications as emulsifiers and stabilizers, especially in the urethane foam formulations 23-43). These types of reactions are conducted between silane (Si H) terminated siloxane oligomers and olefinically terminated poly-(alkylene oxide) oligomers. Consequently the resulting system contains (Si—C) linkages between different segments. Earlier developments in the field have been reviewed 22, 23,43> Recently hydrosilation reactions have been used effectively by Ringsdorf 255) and Finkelmann 256) for the synthesis of various novel thermoplastic liquid crystalline copolymers where siloxanes have been utilized as flexible spacers. Introduction of flexible siloxanes also improved the processibility of these materials. 

Siloxane containing polyester, poly(alkylene oxide) and polystyrene type copolymers have been used to improve the heat resistance, lubricity and flow properties of epoxy resin powder coatings 43). Thermally stable polyester-polysiloxane segmented copolymers have been shown to improve the flow, antifriction properties and scratch resistance of acrylic based auto repair lacquers 408). Organohydroxy-terminated siloxanes are also effective internal mold release agents in polyurethane reaction injection molding processes 409). 

---