Process for Producing Polymerizable Polybranched Polyester

Title Process for Producing Polymerizable Polybranched Polyester 

A new transesterification stanoxane catalyst, tin (di(chlorodimethylsiloxy)-tin chlor-odimethylsilane), has been used to incorporate ethyl acrylate into the condensation polymer of 2,2-bis(hydroxymethyl)propionic acid. This catalyst is preferable because it allows the reaction to proceed under milder conditions than those using a condensation esterification reaction route and makes it likely for product crosslinking side reactions to occur. 

A reaction vessel equipped with a Dean-Stark decanter was charged with 10 parts of the condensation polymer of 2,2-bis(hydroxymethyl)propionic acid having a Mn of 2920 daltons, a Mw of4280 daltons, and a PDI of 1.47. This mixture was then treated with tin(di(chloro-dimethylsiloxy)-tin chlorodimethylsilane) (0.25 parts), ethyl acrylate (100 parts), and hydroquinone (0.05 parts). The mixture was then heated to between 92°C and 95°C so that the amount of distillate to the decanter was 15 to 20 parts per hour. Fresh ethyl acrylate was added to the reaction vessel as needed while the reaction continued for 20 hours. 

Following completion of the reaction, excess ethyl acrylate was removed by distillation and the residue dissolved in 70 parts of EtOAc. The solution was washed three times with 30 parts of hot water at 50°C to extract the catalyst. The solution was further washed four times with 20 parts of 5% aqueous NaOH to remove hydroquinone, followed by a single washing with 20 parts of 1 % aqueous H2SO4 and twice with 20 parts of water. The mixture was last treated with 0.0045 parts of methoquinone and distilled 13 parts of product were isolated having a Mn of 3880 daltons, Mw of 7730 daltons, which is equivalent to 25.5 vinyl groups/ molecule. 

The formula for the stanoxane catalyst is (ClSi(CH3)20)2Sn-Sn(CH3)2Cl. Hyperbranched polycarbonates, (1), with only marginal crosslinking side reactions were prepared by Bruchmann [1] by transesterification, using diethyl carbonate and trihydroxy methylmethane catalyzed by potassium carbonate. 

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