Dendritic triblock copolymer

Nguyen PM, Hammond PT. Amphiphilic linear-dendritic triblock copolymers composed of poly(amidoamine) and poly(propylene oxide) and their micellar-phase and encapsulation properties. Langmuir 2006 22 7825-7832. 

Figure 5.2. Linear dendritic triblock copolymers prepared via anion trapping with benzyl bromide focal groups.

Gitsov and Frechet [11] reported the syntheses of novel linear-dendritic triblock copolymers achieved via anionic polymerization of styrene and final quenching with reactive dendrimers. For the characterization of the products in the reaction mixture, SEC with double detection was performed at 45°C on a chromatography line consisting of a 510 pump, a U6K universal injector, three Ultrastyragel columns with... 

A PAMAM-PEG-PAMAM dendritic triblock copolymer has also been shown to be an efficient gene delivery agent [40 ]. Plasmid DNA was found to assemble with the copolymer forming compact nanosized particles with a narrow size distribution. The resulting complex exhibited high solubility when compared to PAMAM dendrimers, low-cytotoxidty... 

Figure 4. a) polyester dendrimer and drug conjugate b) hyperbranched aliphatic polyester and c) dendritic-linear-dendritic triblock copolymer... 

In order to explore the properties that may be obtained by hybridizing the linear and dendritic architectural states, both diblock and triblock copolymer... 

Ishizu et al.194 synthesized hyperbranched macromolecules that resemble dendrimers. The synthetic approach involved the preparation of poly(4-methyl-styrene-b-PS-b-poly(4-methylstyrene) triblock copolymer by using naphthalene lithium as difunctional initiator. The 4-methyl groups of the terminal blocks were metalated with s-BuLi/tetramethylethylenedi-amine (TMEDA) complex in a molar ratio of 1 2. After removal of the excess s-BuLi by repeated precipitation of the living polymer and transfer of supernatant solution to another flask under high vacuum conditions, the polymer was dissolved in THF and was used as the initiator of a-methylstyrene at —78 °C. After the polymerization of a-methylstyrene, a small amount of 4-methylstyrene was added. The procedure of metalation of the a-methyl groups and polymerization of a-methylstyrene can be repeated many times to form a dendritic type hyperbranched polymer (Scheme 99). The characterization of the inter-... 

Later work by Frechet et al. attempted to prepare ABA diblock copolymers using the same methodology [255]. Two polyether dendrons were connected to a dihydroxy functional TEMPO moiety, which was then used to initiate, as well as control, the polymerization of St and formed dumbbell-shaped block copolymers (Scheme 29). The ABA block copolymers were formed however, there was some initial contamination from mono- and bis-dendritic species, which were removed by column chromatography. In addition, XH NMR analysis determined that the purified ABA triblock copolymers were also contaminated with AB diblock copolymers. This was attributed to the persistent radical effect, as well as inherent problems with the mobility of the bulky dendron counter radical, both of which will result in the AB diblock copolymers. Thermal polymerization may also contribute to diblock formation, as the radicals generated will be trapped by the counter radical dendron, but would not contain the initiating dendron moiety. Pure ABA triblock copolymer was obtained after two purification cycles using column chromatography [255]. 

A similar approach was used to construct a unique triblock copolymer having dendritic termini connected by linear segment. The synthesis of the dendritic-fe/oc/c-linear-fetocA -dendritic PS, referred to as the pom-pom structure due to its dumbbell-like shape, results from a convergent anionic polymerization procedure using dichlorodimethyl-silane as a coupling agent [119]. 

Figure 2. Structure of liquid crystalline block copolymers (LC-BCPs) (A) rod-coil diblock copolymer (B) rod-coil diblock copolymer with flexible spacer in the rod block (C) side group liquid crystal-coil (SGLC- coil) diblock copolymers (D) coil -rod-coil ABC triblock copolymers (predicted to be novel ferroelectric fluid by R. G. Petschek and K. M. Wiefling, Phys. Rev. Lett., 1987, 59(3), 343-346) (E) rod-rod diblock copolymer (one example of well-defined po-ly(n-hexyl isocyanate-fc-n-butyl isocyanate) rod-rod diblock copolymer was given by Novak et al. [68], however, no morphology studies were reported) (F) dendritic liquid crystal-coil (DLC-coil) diblock copolymer (not reported).

He X, Wu X, Cai X, Lin S, Xie M, Zhu X, Yan D (2012) Functionalization of magnetic nanoparticles with dendritic-linear-brush-like triblock copolymers and their drug release properties. Langmuir 28 11929-11938... 

FIGURE 11.3 Schematic architectures of polymers with semifluorinated segments (a) sf triblock copolymers (b) i/main chain polymers (c). side chain polymers (d) polymers with randomly distributed sf side chains (e) di- and triblock copolymers with one rf block (f) copolymers with dendritic segments. 

JH NMR) studies confirmed the presence of the AB diblocks in the product. This determination was facilitated by the fact that the dendritic nitroxide could be differentiated from the nonnitroxide-bearing dendron by NMR spectroscopy. Careful analytical studies confirmed that the pure ABA copolymers could be separated by column chromatography and that the undesired diblock impurity resulted mainly from the loss of the dendritic nitroxide during the course of the reaction. Obviously, this approach to ABA triblocks has rather limited practical value since the thermal stability of the final product is quite low. 

The addition of large linear blocks to dendrons with opposite polarity creates a desymmetrized structure predisposed to sequester insoluble components by aggregation rather than intramolecular hydrogen-bonding. Amphiphilic, linear-dendritic diblock (AB) and triblock (ABA) copolymers self-assemble into multimolecular micelles with CMC values that are well below those of low molecular weight surfactants. Typically, a hydrophilic linear block such as PEG is attached to the focal point... 

Emrick, T., Hayes, W., and Frechet, J. M. J. (1999). A TEMPO-mediated living free-radical approach to ABA triblock dendritic linear hybrid copolymers. J. Polym. Sci., Part A Polym. Chem., 57(20) 3748-3755. 

---