Synthesis polysiloxane block copolymers

Information on the synthesis of the polyetherimide—polysiloxane block copolymers has not been disclosed. Many other synthetic methods for preparing block copolymers have been described (19,20,25) but are currendy not beheved to be commercially important. 

The principle of random block polymerization has been used for polysiloxane block copolymer synthesis as in equation (27) where the block connection is made by condensation between two types of silanol groups. This reaction, which is catalyzed by weak bases such as hexylamine carboxylate salts or tetramethylguanidine to avoid Si—O bond randomization, leads to multiblock polymers (35) having p-phenylene groups in the main chain. ... 

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. 

Various properties (3,4,5,15,16,18-32) as well as the morphology ( L iJL, 19.,23 33) of such copolymers were investigated in great detail. Synthesis of these block copolymers, while complex, is potentially not costly since materials and methods used in the manufacturing of polysiloxanes and polycarbonates can be used. 

Condensation reactions of silanols provides another method for polysiloxane synthesis. Hydroxy-terminated siloxane oligomers or polymers can be further condensed to polymers of higher molecular weight by condensation with loss of water (equation 23). This reaction is catalyzed by various metal salts tin salts have been widely used. Mixtures of two different a, co-dihydroxysiloxane oligomers may be condensed to give block copolymers. 

Not all copolymers which are produced by step-growth processes are random in nature. Block copolymers are also of major interest. An example of the synthesis of elastic polyurethane fibers was given in Section 1.5.4. Block and graft copolymers of polysiloxane-poly(alkylenc ethers) with segments like5-9 are used as surfactants in the production of polyurethane foams with uniform cell sizes. 

More recently, we have also reported the synthesis of thermoplastic siloxane elastomers based on hybrid polysiloxane/polyimide block copolymers (the hybrid polysiloxane being fluorinated or not) that were obtained through polyhydrosilylation of dienes with a,dihydrooligosiloxanes [76-78], as follows ... 

There have been other types of approaches also for the synthesis of hybrid polymers. Block copolymers containing polysiloxane segments and polyphosphazene segments have been synthesized by the reaction of hydride-terminated polysiloxane H-[Si(Me2)-0]n-SiMe2H with the telechelic polyphosphazene containing an amino end-group (Fig. 6.28) [33]. 

The application of polymer-supported catalysts has now been extended to the synthesis of complexes between transition metal derivatives and structurally ordered macromolecular ligands to give catalytic systems exhibiting high activity and stereoselectivity. Polystyrene and polymethacrylate resin and polystyrene-divinylbenzene-polystyrene-polybutadiene block copolymers, as well as vinyl-functionalized polysiloxanes grafted onto silica, are very suitable polymers for heterogenization of mostly Pt and Rh complexes. Moreover, polyamides exhibit much higher thermal stability than conventional polystyrene supports (114). 

The preparation of polymeric materials from renewable resources is of great economic and ecological significance. Oils and fats are one of the most important renewable materials since they offer a large number of possibilities for application that can be rarely met by petrochemistry. Although the hydrosilylation of olefins has been widely studied, a few reports have appeared on the fatty acid esters (4). Carbohydrate-modified polysiloxanes are another very important group of hybrid materials. Some examples of such modified, comb-structured polysiloxanes and also a few examples of carbohydrate-segmented polydimethylsiloxane block copolymers have been described. Hydrosilylation has also been used for the synthesis of silylated polycarbonates or polycarbonate-disiloxane-polycarbonate triblock copolymers. 

Except for ozonides obtained from vinylsiloxanes, the ozonides that result from these reactions are surprisingly stable. Figure 1 shows the C-NMR spectrum of an ozonide that was prepared from DC 7697 (n = 30). It contains resonances at 1, 18, 23, 29, 41, 94 and 104 ppm. Chemical shifts calculated for the carbon atoms in this compound (1.5(3,4), 15.7(1),24(2),26.3(6),30.4(7),97.3(5) and 99.3(6) ppm) correspond reasonably well with those observed. Polysiloxanes containing the ozonide functionality can, in fact, be used as macroinitiators for block copolymer synthesis (13). 

Table II. Synthesis and Properties of Block Copolymers Containing Polysiloxane...

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