Star-shaped polymers, cross-linking

Other synthetic possibilities provided by the living polymer technique may permit syntheses of star-shaped polymers, uniform networks of cross-linked polymers, regular branched polymers, etc. 

H. Gao, M. C. Jones, J. Chen, R. E. Prud homme and J. C. Leroux, Core cross-linked reverse micelles from star-shaped polymers. Chem. Mat., 20, 3063-3067 (2008). 

In the case of the application of p-divinylbenzene for this purpose the core macromolecule is a cross-linked polymer. Despite that the presence of long, linear arms, derived from the living polymer makes the macromolecule soluble. It turned out that not all active centers in the cross-linked core of poly divinylbenzene are accessible in the same way. For this reason the initiation of the reaction proceeds slowly and leads to the star-shaped polymer with arms of different lengths. An important advantage of this method is the possibility to obtain the star block copolymers. An example of such a compound is a copolymer containing up to 30 arms. Each of them is a block copol5mer of st3Tene (M = 2700-30,000) and ethylene oxide (M = 3000-6000). In addition to this information it should... 

Polymers are normally classified into four main architectural types linear (which includes rigid rod, flexible coil, cyclic, and polyrotaxane structures) branched (including random, regular comb-like, and star shaped) cross-linked (which includes the interpenetrating networks (IPNs)) and fairly recently the dendritic or hyperbranched polymers. I shall cover in some detail the first three types, but as we went to press very little DM work has been performed yet on the hyperbranched ones, which show some interesting properties. (Compared to linear polymers, solutions show a much lower viscosity and appear to be Newtonian rather than shear thinning [134].) Johansson [135] compares DM properties of some hyperbranched acrylates, alkyds. and unsaturated polyesters and notes that the properties of his cured resins so far are rather similar to conventional polyester systems. 

Electropolymerization of star-shaped oligomers 5.18a-c resulted in the formation of highly redox active, cross-linked hyperbranched polymers which led to systems with good conductivities, indicating the presence of multiple pathways for charge carriers provided by the branching units [472],... 

Elbert, D. L., and J. Hubbell. 1996. Surface treatments of polymers for biocompatibility. Annual Review of Materials Science. 26 365-370. GroU, J., E. V. Amirgoulova, T. Ameringer, C. D. Heyes, C. Rocker, G. U. Nienhaus, and M. Moller. 2004. BiofimctioDalized, ultrathin coatings of cross-linked star-shaped poly(ethylene oxide) allow reversible folding of immobilized proteins. J. Am. Chem. Soc. 126 4234-4239. 

In a comparison (14) of the polyesterification of silylated 5-acetoxyisophthalic acid and of free 5-acetoxyisophthalic acid, the nonsilylated monomer yielded insoluble products, indicating that a cross-linked material was obtained. The degree of branching for these materials was found to be close to 0.6 and independent of reaction conditions. Star-shaped and hyperbranched polyesters have also been synthesized by polycondensation of trimethylsilyl 3,5-diacetoxybenzoate (15) and a number of hyperbranched polymers based on the trimethylsilylester of )3-(4-hydroxyphenyDpropionic acid have been reported (16). 

More recently, the same photodimerization was exploited by Yagci et al, who functionalized linear or three-armed star-shaped poly(propylene oxide)s with two or three terminal benzoxazine coumarin functions, respectively [KIS 14], These products were used as multifunctional macromolecular precursors for the preparation of self-healing pol5mier films. Under irradiation at wavelengths over 300 nm, the formation of cyclobutane junctions from the chain-end chromophores of the macromonomers resulted in cross-linking. Regarding the recovery of mechanical properties, a healing efficiency up to 44% was obtained in the case of a cracked polymer sample studied in this work. 

Various types of block copolymers such as ABA triblock [93,94,105,108], ABC triblock [109-111], PNIPAM-dendrimer [112], and PNIPAM-[star-shaped (or hyperbranched) polymer] [65], and PNIPAM-polyrotaxane-PNIPAM [66] have also been designed/synthesized. For example, Armes et al. have synthesized biocompatible, thermoresponsive ABC and ABA triblock copolymers such as PPO-PMPC-PNIPAM via ATRP using a PPO-based macroinitiator. McCormick et al. have reported the RAFT synthesis of thermally responsive ABC triblock copolymers incorporating M-acryl-oxysuccinimide for facile in situ formation of micelles with cross-linked shells. 

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