Arborescent grafting

Winter, H.H. Evolution of rheology during chemical gelation. Prog. Colloid Polym. Scl,15,104—110,1987. Hempenius, M.A. et al. Melt rheology of arborescent graft polystyrenes. Macromolecules, 31, 2299, 1998. 

Gauthier, M. and Mdller, M. Uniform highly branched polymers hy anionic grafting Arborescent graft polymers. Macromolecules, 24, 4548, 1991. 

Table 9.3 Structural characteristics of arborescent graft polybutadienes (adapted from ref. 15)...

Figure 12.5 [18] Structure of the monolayer of S05-3 arborescent graft (dendri-graft) polystyrenes cast on mica as prepared (A) and Fourier filtered (B)...

Fig. 4a, b. Monolayer structure of arborescent graft polystyrenes of different branching densities adsorbed on mica [71] a spherical particles correspond to individual molecules of = 2.8x10 g/mol and N = 5 b disk-like structures correspond to AGP with M,= 5.5 X 10 g/mol and N = 20... 

Fig. 17. Monolayer of arborescent graft macromolecules consisting of a polystyrene core and poly(2-vlnylplrldlne) shell. Microphase separation between the blocks and strong interaction of the PVP block with mica resulted In lateral arrangement of the PS and PVP domains [89]...

Fig. 18a,b. Amplitude micrographs of arborescent graft polyethylene on mica obtained by tapping mode SFM after a adsorption from a dilute solution in hot xylene b annealing for 24 hat 150 °C... 

Fig. 19. Recrystallization of arborescent graft polyethylenes from dense packing of spheres to fibers of linearly aligned molecules upon annealing...

More recent work has shown that this GDS strategy may be used to produce all hydrocarbon, poly (styrene) type dendrimers that the authors refer to as being derived from arborescent grafting [181]. Hybridization of Starburst/Cascade architecture with Comb-burst dendrimer structure, has been reported by our group very recently [182], thus clearly establishing the vast breadth and scope of GDS techniques for the construction and design of nanoscopically sized macromolecules (i.e., 1-100 nm in diameter). 

Hempenius M A, Michelberger W, MoUer M. (1997) Arborescent Graft Polybutadienes. Macromolecules 30 5602-5605. 

Figure 1 Macromolecular architectures linear macromolecular chains (homopolymer, block-copolymer and statistical copolymer [14]), brushed-polymer (= linear chains attached to a polymer-chain brush-polymer, brush-copolymers [14]), star polymer [4], mikto-star-polymer [16], arborescent graft polymer (=repeated grafting of linear chains on a macromolecule [17,18]), dendrimer (= maximally branched, regular polymer [15])...

For the subsequent generation of arborescent graft polystyrenes, a dramatic increase in rj0 was observed by Hempenius et al. [43] for each of the three series included in their study. However, despite this increase in viscosity, the rj0 for each of these is still lower than that of the linear homologue polystyrenes of the same overall molecular weight. This jump in viscosity is due to an increase in branch density which in turn results in increase in chain extension similar to that observed by Roovers [31] for highly branched star polymers. 

A major basis for the advancement in macro-molecular functionality is our improving ability to control the macromolecular and supramolecular structures in great detail. Dense and cascade-type branching provided access to three-dimensional molecules, which do not interpenetrate but interact via their surfaces. Recent synthetic developments include microgels,15 17 dendrimers,18-26 and arborescent graft... 

Gauthier et al.193 prepared highly branched arborescent graft copolymers of PS and polyethylene oxide). Their synthetic approach involved the reaction of living PS end-capped with DPE with chlorometh-... 

Well-characterized systems. This depends on the appropriate chemistry and subsequent characterization (typical issues here are the polydispersity, control of grafting density, reproducibility of procedure to obtain identical particles). One frequent problem here is that the price one pays for such systems is tlie availability of small amounts (sometimes only fractions of 1 g) of material. For example, multiarm star polymers are in many ways unique, clean, soft colloids [ 19,23], but their nontrivial synthesis makes them not readily available. On the other hand, recent developments witli block copolymer micelles from anionically synthesized polymers [54-58] and arborescent graft copolymer synthesis [40] appear to have adequately addressed this issue for making available different alternative star-like systems. 

Arborescent graft copolymers having a highly branched PS core and a PEO shell were prepared by a combination of anionic polymerization, grafting onto and from techniques [278]. The synthetic procedure is described in the following scheme (Scheme 107). 

The effects of side chain architectures on the properties and proton conductivities of graft copolymer membranes for DMFCs were studied by Su et al. [126]. Poly(vinylidene fluoride)-g-poly(styrene sulfonic acid) (PVDF-g-PSSA) copolymers with either linear graft (LG) or arborescent graft (AG) PSSA side chains were prepared. Scheme 6.29 shows the structures of LG and AG polymers. 

Viville, R, Leclere, P., Deffieux, A. et al. (2004) Atomic force microscopy study of comb-like vs. arborescent graft copolymers in thin films. Polymer, 45,1833 1843. 

Table 6.1 Characteristics of successive generations of two series of arborescent polystyrene (Adapted with permission from J. Li and M. Gauthier, A novel synthetic path to arborescent graft polystyrenes, ...

Gauthier, M., Tichagwa, L., Downey, J.S., and Gao, S. (1996) Arborescent graft copolymers Highly branched macromolecules with a core-shell morphology. Macromolecules, 29,519-527. 

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