From 09/23/2014 through 6/28/2012
1. “A star shaped polymer is a polymeric structure in which several chains emanate from a single junction point known as the core. The control offered by anionic polymerization makes it a very popular pathway to synthesize molecules with such complex geometry. It allows quantitative studies of the degree of branching of the polymer on the overall properties of the substance.
One of the first pathways explored was the use of a multifunctional initiator , but it was limited by the insolubility of such compounds and there was no control over the reactivity of each branch. A second, more efficient way was proposed - the addition of a multifunctional electrophilic terminator at the end of the polymerization of a linear polymer. This is analogous to the convergent synthesis of dendrimers, and is efficient as long as the stoichiometry between the terminating agent and the starting monomers are maintained.
The third route is through the addition of small amounts of cross – linking agents to the polymeric precursor (for example, addition of divinyl benzene to polystyryl lithium). There are three prime reactions that take place:
The crossover of the polystyryl chain to divinylbenzene
The block copolymerization of divinylbenzene
The reaction of the pendant vinyl groups of divinyl benzene with linear polystyryl branches
The uniformity in the structure is a function of the rate of the crossover reaction compared to the other two reactions. The number of branches of the star molecules cannot be precisely predicted, as it is a complex function of the reaction variables. For example, the amount of divinyl benzene added in the above pathway, compared to the number of active chains, is a key factor governing the overall degree of branching of the polymer.
The method is widely used for the synthesis of star shaped polystyrene with divinyl benzene with low molecular weight distributions. Star shaped polymethyl methacrylate was similarly synthesized using ethylene glycol dimetthacrylate as a crosslinker. The molecular weights obtained are comparatively high (~40kDa), which is thought to be necessary to avoid the gelation due to inter core reactions. The protection of the core groups by the branches gave such polymers the name "porcupine polymers".”
(Wikipedia, Star Polymers, 6/28/2012)
2. The range of polymers can be greatly expanded by hybrid inorganic /organic copolymers. Mannle et al produced a star copolymer based on an inorganic silane core with organic polymer branches with specific functional groups. The core is produced by controlled hydrolysis of a silane with functional groups and the branches developed by amine condensation reactions. The resulting products are useful as antioxidants, UV absorbers, radical scavengers or cross-linking agents.
US Patent 8,802,807 (August 12, 2014), “Method for the Manufacture of Polybranched Organic/Inorganic Hybrid Polymers,” Ferdinand Mannle, Christian Simon, Jest Beylich, Keith Redford, Britt Sommer, Einar Hinrichsen, Erik Andreassen, Kjell Olafsen, and Terje Didriksen (Sinvent AS., Trondheim, Norway).
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Roger D. Corneliussen
Maro Polymer Links
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Copyright 2012 by Roger D. Corneliussen.
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* Date of latest addition; date of first entry is 6/28/2012.