Star polymers with vinyl polymer arms have been synthesized traditionally by the reaction of an anionic living chain end of the vinyl polymer with a multi-functional compound. Silicon tetrachloride was the first such multi-functional compound to be reacted with living chains to yield a star molecule. Other silyl chloride compounds have been used to form stars with a greater number of arms. The reaction of an anionic living chain end with a divinylic monomer such as divinyl benzene was the next innovation in the synthesis of star polymers. The anionic sites of the living polymer react with the divinylic monomer to form stars with small crosslinked cores. Modification of this synthetic route has been analogously applied to living cationic chains. Both of these syntheses can lead to soluble, star-shaped polymers with highly crosslinked cores. Although the core is crosslinked, the polymer remains soluble due to the solubilizing effect of the arms. This core is also usually considered to be negligible in size relative to the weight fraction of the arms and the core fraction is typically less than five percent of the total weight of the molecule. Materials have also been formed by increasing the weight fraction of the star's core while still obtaining materials that are soluble or colloidally dispersible. For example, a large, calculated amount of divinylbenzene can be added to living polystirene chains, resulting in stars with crosslinked cores of varying weight fraction. It has been found that in this manner stars with crosslinked cores of 30 percent by weight of the total star could be formed while still retaining solubility of the material. Similarly and more recently, living cationic polymerizations were utilized to form stars with polyvinyl polymer arms with crosslinked cores on the order of 35 weight percent. These materials also remained soluble with the large core allowing a large number of arms to fit around it. These multiarm stars showed interesting solution properties due to their architecture. Other syntheses of stars with large, crosslinked cores include synthesizing them from block copolymers where one of the blocks contains crosslinkable functionalities. These block copolymers can form micellar structures in the proper solvent and if the crosslinkable block forms the core of the micelle, the structure of the micelle can be locked in through subsequent crosslinking reactions resulting in star polymers or nanoparticles. This method requires the synthesis of well defined block copolymers by living techniques similar to the requirements of living techniques for other known methods of star formation.
The prior star polymer work involved only vinyl polymers, which severely limits the usefulness of the prior synthesis techniques. This is because vinyl starting materials tend to be expensive and because vinyl polymers are less than ideal for many applications. There is a significant need for techniques to synthesize star polymers of non-vinyl materials and the star polymers that may be made by such techniques.
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