Effect of an added base on (4-cyanopentanoic acid)-4-dithiobenzoate mediated RAFT polymerization in water

The effect of an added base on the aqueous reversible addition-fragmentation chain transfer polymerization of a methacrylic glycomonomer with (4-cyanopentanoic acid)-4-dithiobenzoate was investigated. When sodium carbonate or sodium bicarbonate were used to dissolve the RAFT agent in aqueous solution at room temperature, an inhibition period of 60-90 min was observed at the beginning of the polymerization together with a marked decrease in the overall polymerization rate. Also, experimental M_n values were much higher than the calculated ones in both cases. When sodium carbonate was used, control over the polymerization process was lost within 43% conversion. Better results were obtained with sodium bicarbonate, in which case the molecular weight distribution remained narrow and unimodal up to 81% conversion. At that point, a higher molecular weight shoulder developed that kept growing in intensity at the proceeding of the reaction. Dramatically improved results were obtained by adding circa 10% ethanol to the polymerization mixture to facilitate the dissolution of (4-cyanopentanoic acid)-4-dithiobenzoate. Following this protocol, narrow polydispersity poly(methyl 6-O-methacryloyl-α-d-glucoside) was obtained possessing a molecular weight close to the predicted value.