Star polymers, atom transfer radical polymerization

Star polymers are a class of polymers with interesting rheological and physical properties. The tetra-functionalized adamantane cores (adamantyls) have been employed as initiators in the atom transfer radical polymerization (ATRP) method applied to styrene and various acrylate monomers (see Fig. 21). 

Figure 21. Atom transfer radical polymerization (ATRP) synthetic route to tetrafunctional initiators of a star polymer with adamantyl (adamantane core). Taken from Ref. [91] with permission.

The synthesis of A2B miktoarm star polymers has been discussed and exemplified using PIB as a component. The synthesis involves a quasi living cationic polymerization of isobutylene from a monofunctional cationic initiator. This initiator also contains a blocked hydroxyl group. Eventually, the blocked hydroxyl group of the initiator is deblocked, and functionalized with a branching agent. This activated reagent is then used for an atom transfer radical polymerization process of /erf-butyl acrylate (18). 

L.K. Breland and R.F. Storey, Polyisobutylene-based miktoarm star polymers via a combination of carbocationic and atom transfer radical polymerizations, Polymer, 49(5) 1154-1163, March 2008. 

Pansier [2] used the bromomethyl analogue, (II), of the Step 2 product in the atom transfer radical polymerization of methyl methacrylate. Lewandowski [3] prepared the tribromomethyl analogue, (111), by reacting with trimethylolpro-pane and then used this reagent to prepare methyl methacrylate star polymers. A reaction profile is provided in Table 3. 

H) Atom transfer radical polymerization Numerous reports have been published regarding the synthesis of star polymers using multifunctional initiators capable of initiating the atom transfer radical polymerization (ATRP) of certain monomers, mainly styrene, methacrylates, and acrylates. The living character of the growing chain ends provides the possibility for the synthesis of star-block copolymers. 

Yuan et al. [165] reported the synthesis of well-defined dendrimer-star, block-comb polymers by the combination of living ring-opening polymerization and atom transfer radical polymerization on the basis of a dendrimer polyester. Star-shaped dendrimer PCLs were synthesized by the bulk polymerization of e-caprolactone with a dendrimer initiator. The dendrimer PCLs tiien were converted into macroinitiators via esterification with 2-bromopropionyl bromide. And the star-block copolymer dendrimer poly(s-caprolactone)-block-poly(2-hydroxyethyl... 

Guo, Y.-M., Pan, C.-Y., and Wang, J. (2001). Block and star block copolymers by mechanism transformation. VI. Synthesis and characterization of A4B4 miktoarm star copolymers consisting of polystyrene and polytetrahydrofuran prepared by cationic ring-opening polymerization and atom transfer radical polymerization. J. Polym. Sci., Part A Polym. Chem., 59(13) 2134-2142. 

Abraham, S., Ha, C.-S., and Kim, I. (2006) Self-assembly of star-shaped polystyrene-WocA -polypeptide copolymers synthesized by the combination of atom transfer radical polymerization and ring-opening living polymerization of a-amino acid-N-carboxyanhydrides. Journal of Polymer Science Part A Polymer Chemistry,... 

Reversible deactivated radical polymerization processes, which have been referred to as living/controlled radical polymerizations, allow for producing polymeric materials with controlled molecular masses, low dispersities, and complex maaomolecular architectures, such as block and comb-like copolymers as well as star-shaped (co)polymers. In addition to nitroxide-mediated polymerization (NMP) ° and atom-transfer radical polymerization (ATRP), ° reversible addition fragmentation chain-transfer (RAFT) polymerization is an attractive new method. " ... 

Han D, Tong X, Zhao Y (2012) Synthesis and characterization of six-arm star polystyrene-block-poly(3-hexylthiophene) copolymer by combination of atom transfer radical polymerization and click reaction. J Polym Sci A Polym Chem 50 4198-4205... 

A bewildering array of names are used to describe the various controlled/living radial polymerization techniques currently in use. These include stable free radical polymerization (SFRP) [35-38], nitroxide mediated polymerization (NMP) [39], atom transfer radical polymerization (ATRP) [40-42 ] and degenerate transfer processes (DT) which include radical addition-fragmentation transfer (RAFT) [43, 44] and catalyst chain transfer (CCT). These techniques have been used to polymerize many monomers, including styrene (both linear and star polymers) acrylates, dienes, acrylamides, methacrylates, and ethylene oxide. Research activity in this field is currently expanding at a very high rate, as is indicated by the many papers published and patents issued. 

Kamada,., Koynoy, K, Corten, C., Juhari, A, Yoon, J. A, Urban, M. W., Balazs, A. C Matyjaszewski, K. (2010). Redox responsive behavior of thiol/dlsulfide-ftinctionalized star polymers synthesized via atom transfer radical polymerization. Macromolecules, 43,4133-4139. 

This type of chemistry towards well-defined star-shaped (polymer)j,Qo is closely linked to progress made during this last decade in radical polymerization [3]. Indeed, the various controlled radical polymerizations such as nitroxide-mediated polymerization (NMP) or atom transfer radical polymerization (ATRP) allow us to produce polymer chains with tailored chain length and low polydisper-sities. Furthermore, the as-prepared chains bear at their end a function (stable radical or C—halogen bond) that can be converted under the right conditions into a macro-radical. If this latter is produced in the presence of Cgo, several chains should add to the fullerene. 

It has been reported that the reachon of azides with C o proceeds primarily through mono-addihon this has been widely used to attach fullerenes onto the side chains of polymers or copolymers [79-81]. Star-shaped macromolecules were obtained when PS chains prepared by atom transfer radical polymerization were converted into PS-N3 before reaction with Cgo- Even so, the mono-adducts were predominant. 

The introduction of monofunctional POSS macromers into an organic polymer by polymerization at the single reactive site leads to POSS-modified polymers. POSS macromers were incorporated in linear polymers, such as methacrylates, styrenics, norbomenes, ethylenes, propylenes, and urethanes in order to improve mechanical or thermal properties. If a multifunctional POSS with cross-linkable functions is used cross-linked materials are indeed formed. Star polymers are achieved if a multifunctional POSS unit contains initiator groups and a controlled polymerizatiOTi occurs, such as atom transfer radical polymerization. 

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