NEW DEVELOPMENTS IN SYNTHESIS OF STAR POLYMERS WITH POLY(ETHYLENE OXIDE) ARMS

The synthesis of star molecules consisting of small polydivinylbenzene (DVB) cores carrying a number of hydrophilic poly(ethylene oxide) bra nches hag been investigated. Two different methods are discussed: The 'core-first' technique, in which living poly(DVB) cores are used to in itiate the polymerization of oxirane. This method is flexible and effi cient, but the samples obtained exhibit broad molecular weight distrib utions, arising from large fluctuations of the core functionalities (a nd core sizes). The same method has been applied successfully to the s ynthesis of star-block copolymers, in which each branch consists of a polystyrene (PS) block and a poly(ethylene oxide) (PEO) block. The 'th ree-step'' method (''In-Out'') involves the use of living polystyrene 'seed-star'' molecules as initiators for the polymerization of oxirane . The 'seed-stars' themselves arise from a classical 'arm-first' proce ss. This method allows a better control of the functionality of the co res. The number of branches of either kind attached to a given core is equal. Hetero-star PS-PEO copolymers are obtained, but the length of the branches of either kind can be chosen at will within broad limits.