Poly , hyperbranched

Kim and Webster [57] were the first to show that trifunctional benzene-based monomers can also be used to synthesize poly(phenylene)s, in this case hyperbranched structures 31 based on 1,3,5-trisubstituled benzene cores. They self-condensed l,3-dibromophenyl-5-boronic acid leading to the formation of soluble, hyperbranched PPP-type macromolecule 31. 

Polyester chemistry is the same as studied by Carothers long ago, but polyester synthesis is still a very active field. New polymers have been very recently or will be soon commercially introduced PTT for fiber applications poly(ethylene naph-thalate) (PEN) for packaging and fiber applications and poly(lactic acid) (PLA), a biopolymer synthesized from renewable resources (corn syrup) introduced by Dow-Cargill for large-scale applications in textile industry and solid-state molding resins. Polyesters with unusual hyperbranched architecture also recently appeared and are claimed to find applications as crosstinkers, surfactants, or processing additives. 

Miller et al. were the first to report the synthesis of hyperbranched poly(arylene ether ketone)s.157 They used 3,5-bis(4-fluorobenzoyl)phenol as the starting material, as shown in Scheme 6.20. 

Dendrimers have structures similar to that of hyperbranched polymer and can be taken as the perfectly branched polymer with monodispersity. However, they need to be prepared by a multistep procedure. Therefore, very little work has been done on dendritic polyfarylcnc ether)s. Morikawa et al. prepared a series of monomers with a various number of phenylene units.164,165 These monomer were used to prepare poly(ether ketone) dendrons with graded structures (Scheme 6.24). 

Poly(arylene ether ketone)s (PEKs), 327 block and graft copolymers of, 359-361 hyperbranched, 349 modification of, 354 synthesis of, 340-345, 360 Poly(arylene ether phosphine oxide)s (PEPOs), 345... 

Poly(phenylenethylene), dendronized, 522 Poly(phenylenevinylene) optically active, 510-511 synthesis of, 495-496 Poly(/ ara-phenylenevinylene)s, 472 Polypheny lquinoxaline (PPQ) hyperbranched, 312-314 synthesis of, 309-313 Polyphosphoric acid, 333 Polypropylene oxide) polyol, 223 Polypropylene polyols, 220 Poly (pyridine), synthesis of, 503-505 Polyquinoxaline (PQ), synthesis of, 309-313... 

Hyperbranched poly(ethyl methacrylate)s prepared by the photo-initiated radical polymerization of the inimer 13 were characterized by GPC with a lightscattering detector [51]. The hydrodynamic volume and radius of gyration (i g) of the resulting hyperbranched polymers were determined by DLS and SAXS, respectively. The ratios of Rg/R are in the range of 0.75-0.84, which are comparable to the value of hard spheres (0.775) and significantly lower than that of the linear unperturbed polymer coils (1.25-1.37). The compact nature of the hyperbranched poly(ethyl methacrylate)s is demonstrated by solution properties which are different from those of the linear analogs. 

Experimental data on the solution properties and melt rheology of highly branched structures are scarcely found in the literature. This might be because of the structural nonuniformity of hyperbranched polymers, which makes it difficult to obtain reliable data. Because of the purely statistical nature of the poly-... 

Well-defined complicated macromolecular structures require complex synthetic procedures/techniques and characterization methods. Recently, several approaches leading to hyperbranched structures have been developed and will be the focus of this section. The preparation of hyperbranched poly(siloxysilane) has been reported [198] and is based on methylvinyl-bis(dimethyl siloxysilane), an A2B type monomer, and a progressive hydrosi-lylation reaction with platinum catalysts. An appropriate hydrosilylation reaction on the peripheral - SiH groups led to the introduction of polymeric chain (PIB, PEO) or functional groups (epoxy, - NH2) [199]. 

Hyperbranched polymers have also been prepared via living anionic polymerization. The reaction of poly(4-methylstyrene)-fo-polystyrene lithium with a small amount of divinylbenzene, afforded a star-block copolymer with 4-methylstyrene units in the periphery [200]. The methyl groups were subsequently metalated with s-butyllithium/tetramethylethylenediamine. The produced anions initiated the polymerization of a-methylstyrene (Scheme 109). From the radius of gyration to hydrodynamic radius ratio (0.96-1.1) it was concluded that the second generation polymers behaved like soft spheres. 

Van Koten and Frey used a hyperbranched poly(triallylsilane) as the support for palladium- pincer complexes.[63] The supported palladium-pincer complexes were applied in the catalytic aldol condensation of benzaldehyde and methyl isocyanate. Their activity was similar to that of single site Pd catalysts. According to the authors, the complex is suitable for continuous membrane applications, as demonstrated by their purification by means of dialysis. 

Over the past decade, literally dozens of new AB2-type monomers have been reported leading to an enormously diverse array of hyperbranched structures. Some general types include poly(phenylenes) obtained by Suzuki-coupling [54, 55], poly(phenylacetylenes prepared by Heck-reaction [58], polycarbosilanes, polycarbosiloxanes [59], and polysiloxysilanes by hydrosilylation [60], poly(ether ketones) by nucleophilic aromatic substitution [61] and polyesters [62] or polyethers by polycondensations [63] or by ring opening [64]. 

The preferred initiator is stannous octoate in catalytic amount [95, 96] and polymerizations occur in bulk at 110°C or in toluene. The synthesis was expanded to stars with 40 and 48 arms by means of a hyperbranched poly(2,2 -bis(hydroxymethyl)propionicacid) or classical dendrimer, respectively [97],... 

Commercially available hyperbranched polymer, a poly(ester-amide) is currently being marketed by DSM under the product name Hybrane [13] (Figure 8.2). It is also a hydroxyl-functionalized product, but contains both amide and ester linkages. The synthesis is accomplished in two steps cyclic anhydrides are reacted with diisopropanolamine to give an amide-intermediate, possessing two hydroxyl groups and one carboxylic acid. The subsequent polymerization takes places via an oxazolinium intermediate which results in the formation of a... 

Figure 8.2 A schematic representation of hydroxy-functional hyperbranched poly(ester-amide) Hybrane based on diisopropanolamine and an anhydride [11]...

Since these reports, a number of new approaches based on vinyl monomers and various initiating systems have been explored to yield hyperbranched polymers such as, poly(4-acetylstyrene) [26], poly(vinyl ether) [27] and polyacrylates [28], In view of the fact that free radical polymerizations are most widely used in industrial polymerization processes the development of these procedures for vinyl monomers has opened a very important area for hyperbranched polymers. 

Spin-coating films of other compositionally different dendritic macromolecules such as carbosilane dendrimers and hyperbranched poly(styrene) were studied by Sheiko et al. [20-22] using tapping mode AFM. 

POLY(ETHYLENEIMINE) SCAFFOLD TOWARD HYPERBRANCHED SIALOSIDES... 

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