Poly linear block

Figure 7.3 Growth of poly(caprolactone) linear block from a dendritic macroinitiator...

Dendrimers, or arborols, or cascade, or cauliflower, or starburst polymers, were first synthesized in the early 1980s [3,4]. In 1985 Tomalia et al. [5] and Newkome et al. [6] presented the first papers dealing with dendrimers. A multitude of dendrimers have been presented in the literature ranging from polyami-doamine [7,8],poly(propylene imine) [9,10], aromatic polyethers [11-13] and polyesters [14, 15], aUphatic polyethers [16] and polyesters [17], polyalkane [18-19], polyphenylene [20], polysilane [21] to phosphorus [22] dendrimers. Combinations of different monomers as well as architectural modifications have also been presented. For example, chirality has been incorporated in dendrimers [23,24]. Copolymers of linear blocks with dendrimer segments (dendrons) [25-27] and block-copolymers of different dendrons have been described [28]. 

Based on this approach Schouten et al. [254] attached a silane-functionalized styrene derivative (4-trichlorosilylstyrene) on colloidal silica as well as on flat glass substrates and silicon wafers and added a five-fold excess BuLi to create the active surface sites for LASIP in toluene as the solvent. With THF as the reaction medium, the BuLi was found to react not only with the vinyl groups of the styrene derivative but also with the siloxane groups of the substrate. It was found that even under optimized reaction conditions, LASIP from silica and especially from flat surfaces could not be performed in a reproducible manner. Free silanol groups at the surface as well as the ever-present impurities adsorbed on silica, impaired the anionic polymerization. However, living anionic polymerization behavior was found and the polymer load increased linearly with the polymerization time. Polystyrene homopolymer brushes as well as block copolymers of poly(styrene-f)lock-MMA) and poly(styrene-block-isoprene) could be prepared. 

The synthesis of giant amphiphiles was recently reported by Meijer et al, who linked a linear hydrophobic poly(styrene) block to a dendritic poly(propyleneimine) as a polar head group. The association structure was found to vary with the dendrimer generation changing Irom inverse micelles for poly(styrene-JenJr-(NH2)4) through vesicles and rod-like micelles to spherical aggregates for poly-(styrene-fife fi r-(NH2)32 [210]. 

Poly(ether.siloxanes) contain a poly(methyl.siloxane) polymer, which may be branched, and poly(eiher)-blocks. Its structure may be linear or comblike. The blocks are connected by Si-O-C- or Si-C- bridges., Si-0-C- linked products can, for example, be produced by reacting branched dimethyl(chloro)siloxy-lerminated poly(methyl-siloxanes) (see Section 4.3.3) with monohydroxy-functional polyCethers. 

In another study, Selb and Gallot investigated the conformational properties of poly(styrene-g-4-vinyl-N-ethylpyridinium bromide) in water/methanol/LiBr mixtures [306]. The graft copolymers did not show intermolecular association in contrast to the linear block copolymers. Viscometric results showed that these graft copolymers also form compact, star-like monomolecular micelles with polystyrene cores and poly(4-vinyl-V-ethylpyridinium bromide) coronas, which resemble the polymolecular micelles of diblock materials. 

The linear-dendritic copolymer [G-3]-PE013k has a linear poly-(oxyethylene) block with molecular weight of 13,000 Da (PE013k) and was formed via living anionic polymerization of ethylene oxide initiated by a... 

Various linear block copolymers of the AB, ABA and ABC type with enzymatically polymerized amylose blocks were reported. Ziegast and Pfannemuller converted the hydroxyl end groups of poly(ethylene oxide) into amino groups via tosylation and further reaction with 2-aminoalkylthiolate. To the resulting mono- and di-amino functionalized poly(ethylene oxide) maltooligosaccharide lactones were attached and subsequently elongated to amylose via enzymatic polymerization. Pfannemuller et al. performed a very detailed study on the solution properties of the synthesized A-B-A triblock... 

Fig. 4 Novel drug delivery systems using stimuli-responsive polymers, (a) Morphology changes of poly(2-isopropyl- 2-oxazoline) (PiPrOx) and poly(benzyl ether)dendrons dendritic-linear block copolymers conjugates are Temperature- and pH-dependent.[105] (Copyright 2012, Royal Society of Chemistry) (b) Protein-binding-induced disassembly of dendron-based micelles. This inducible micelle disassembly is selective to the targeted protein and the disassembly can mediate release of the encapsulated therapeutic drugs.[106] (Copyright 2010, American Chemical Society)...

An alternative approach is the so-called hypergrafting that relies on the use of a linear block copolymer with a poly-ftmctional (usually relatively short) second block that acts as an initiator in the grafting polymerization of the branching monomer even for a step-growth mechanism. In this case the polyfimctionality of the initiator permits control over molecular weights and polydispersity and suppresses homopolymetization. 

The most convenient polymeric surfactants are those of the block and graft copolymer type. A block copolymer is a linear arrangement of blocks of variable monomer composition. The nomenclature for a diblock is poly-A-block-poly-B, and for a triblock it is poly-A-block-poly-B-poly-A. One of the most widely used triblock polymeric surfactants are the Pluronics (BASF, Germany) or Synperordc PE (ICI, U.K.), which consists of two poly-A blocks of poly(ethylene oxide) (PEO) and one block of poly(propylene oxide) (PPO). Several chain lengths of PEO and PPO are available. More recently, triblocks of PPO-PEO-PPO (inverse Pluronics) became available for some specific applications. 

Domb, A., Elmalek, 0., Gref, R., Minamitake, Y., Peracchia, M., and Danger, R., 1996, Synthesis and applications of non-linear block copolymers of PEG and poly(hydioxy add) esters. Paper in preparation. 

Figure21 Generalized phase diagram including morphologies found in polystyrene-block-poly(Z-L-lysine), linear block copolymers, O bottle-brush shaped block copolymers, and schematic presentation of the undulated lamellar morphology. (Reprinted from H. Schlaad, H. Kukula, B. Smarsly, M. Antonietti, and T. Pakula. Polymer 43 5321,2002. Copyright [2002], with permission from Elsevier Science.)...

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