Aldehyde functional polysiloxanes

Abstract Aldehyde functional polysiloxanes (1) (Fig. 1) can be selectively prepared in high yield and purity by oxidation of the corresponding carbinols with technical bleach and catalytic amounts of TEMPO. This simple oxidation method is also successfully used for the preparation of the corresponding carboxylic acids 2 (Fig. 1). The stability, reactivity and chemical properties of new compounds 1 and 2 are investigated. 

To date, three methods have been described for the synthesis of aldehyde functional polysiloxanes (1) in patent literature, but these are not practiced. The hydroformylation of olefinic siloxanes with carbon monoxide and hydrogen under high pressure and temperature conditions is possible (Scheme 1, eq. (1)), but produces a mixture of... 

Scheme 1 Methods for the synthesis of aldehyde functional polysiloxanes described in the literature [1-5] (1) hydroformylation, (2) and (3) ozonolysis, (4) hydrosilylation of acrolein acetals and acid hydrolysis...

Concern about redistribution reactions of the polysiloxane backbone and the formation of small amount of aldehyde-functional polysiloxane as side-product led the authors to explore several acid catalysts with the lowest moisture content possible, with activated clay being finally preferred. Size-exclusion chromatography was performed on some of the resulting polysiloxanes. 

Aldehyde-Functional Polysiloxane Synthesis. Poly (dimethylsiloxanes) containing 1-hexenyl-dimethylsiloxane end groups, DC 7691 (n = 200), DC 7692 (n = 100) and DC 7697 (n = 30), were dissolved in hexane or methylene chloride (1 g/ml) and the solutions were cooled to -20°C. Ozone was then bubbled through the solutions and then into a Nal solution to decompose any excess that had not been reacted and prevent its release to the atmosphere. Treatment of the reaction mixtures with ozone was stopped after the Nal solution developed a blue color indicating that all the unsaturation had been consumed. The reaction mixtures were then allowed to warm to room temperature and heated for one hour at 40 C with Zn powder/acetic acid (1 1 molar ratio) to convert the ozonized groups on the polymers to aldehyde groups. 

The reaction mixtures were then filtered to remove zinc oxide, washed with water to remove excess acetic acid and then dried. Removal of the solvent by distillation then yielded the aldehyde-functional polysiloxanes. Listed below are the polymers prepared for use in this study. The polymers exhibited characteristic aldehyde absorption at- 1733 cm . ... 

Reaction of ozonized polysiloxanes with zinc and acetic acid at 40° converts the ozonide groups to aldehyde groups. Table I provides information about the aldehyde-functional polysiloxanes that were employed in this investigation. 

When solutions of aldehyde-functional polysiloxanes, copper octanoate, trieth-ylamine, pyridine, triphenylphosphine and monomer in inert solvents such as benzene are heated, radicals can be generated at the polysiloxane ends and these can initiate polymerization. This is shown below, where M is a monomer unit. 

Aldehyde functionalities are very reactive toward amino and hydroxy groups. As a result, polymers 1 can bind to cellnlose or protein snrfaces. Their reactivity toward nucleophiles enables them to take part in varions crosshnking reactions, e.g. with amines. Carboxy fnnctional polysiloxanes 2 are also able to bind to surfaces because of the carboxy group s high polarity. They can nndergo crosslinking reactions, e.g. with epoxides. Their salts are good snrfactants. 

Polysiloxanes with terminal hexenyl groups were converted by ozonol-ysis into polysiloxanes with terminal aldehyde functionality. These were used in combination with copper octanoate, triethylamine, pyridine and triphenylphosphine to initiate the polymerization of styrene, methyl methacrylate and styrene/methyl methacrylate mixtures at 70°C. The polymerizations yielded block copolymers containing polysiloxane and vinyl (co)polymer segments. Depending on how the polymerizations terminated, the block copolymers had triblock or multiblock architectures. 

General Chemistry. Although polysiloxanes that bear aldehyde functionality have not been described previously, they can be prepared quite easily by ozonolysis of precursors that bear terminal olefmic groups. Hydrosilation can be used to prepare such materials from readily available precursors. The following series of reactions was thus used to prepare polysiloxanes with terminal aldehyde functionality. 

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