Block copolymer brush

Similarly, core-shell cylindrical brushes were prepared via block copolymerization [308,313]. They consist of the soft pnBA cores and hard pSt shells [308]. The high resolution AFM micrographs of the block copolymer pBPEM-g-(pnBA-fc-pSt) brushes shows a necklace morphology. The synthesis of well-defined brush block copolymers demonstrates the synthetic power of ATRP. It was used to create a well-defined backbone with a degree of polymerization of 500, which was followed by a transesterification and the subsequent grafting of pnBA chains using ATRP. A final chain extension with St produced the block copolymers. 

Figure 10.4 Schematic illustration of the synthesis of brush block copolymers through the sequential addition (upper row) and brush random copolymer through random copolymerization (lower row) of macromonomers [39]. (Reproduced with permission of the American Chemical Society.)...

Figure 11 Schematic illustration of the synthesis of a brush block copolymer through sequential addition of macromonomers (top) and that of a random copolymer brush through random copolymerization (bottom) of macromonomers. Reprinted from Xia, Y. Olsen, B. D. Kornfield, J. A. Grubbs, R. H. J. Am. Chem. Soc. 2009, 131 (51), 18525-18532, with permission from ACS." ...

Figure 35 Schematics and AFM micrograph of micelles formed by linear-brush block copolymer PS-f>(PIBEMA-g(-PAA) spin cast from aqueous CsBr solution (lO M). Reprinted from Nelser, M. W. Muth, S. Kolb, U. etal. Angew. Chem. Int. Ed. 2004, 43 (24), 3192-3195, with permission from Wiley-VCH. ...

Fig. 13 TEM images of polymer/DNA complexes prepared in phosphate buffer (20 mM pH = 6.5) atN P20for(a) diblock copolymer PDMAEMA-h-PEG(x = 49,m = 47), (b) statistical copolymer P(DMAEMA-rtat-OEGMA) (x = 46, y = 7), (c) statistical copolymerP(DMAEMA-sta/-OEGMA) (x = 61, y = 9), (d) statistical copolymer P(DMAEMA-s/a/-OEGMA) (x = 90, y = 12) and (e) brush-block copolymer PDMAEMA-b-POEGMA (x = 53, y = 1, m = 8.5). Reprinted with permission from [181]. Copyright 2011 Elsevier...

Figure 4 DNA-synthetic polymer conjugates, (a) Incorporating extended aromatic molecules into DNA creates folded stmctures through jT-stacking. (b) Block copolymers consisting of DNA and synthetic polymers can be assembled into micelles via microphase separation of incompatible blocks, (c) A PEG-DNA-brush block copolymer can shape shift between spherical and cylindrical micelles depending on the specific DNA input, (d) Dendritic DNA, created by covalently modifying short DNA strands with dendritic oligoethylene moieties, self-assembles into long-range fibers without the need for sticky-end cohesion.

Figure 5.10 Two brush block copolymers reported by Bowden to self-assemble with domain sizes greater than 100 nm. (Adapted from Refs. [43, 44].)...

Figure 5.13 (a) Reflection spectra of photonic crystals produced through the self-assembly of molecular brush block copolymers plotted for films of one brush BC, prepared by controlled evaporation from DCM (blue), or TFIF, before (green), and after (red) thermal treatment, as well as via thermal annealing under compression (orange). 

Figure 5.14 Isocyanate-based brush block copolymers assembled to large lamellar nanostructures, with reflection peaks into the near infrared. (From Ref. [50].)...

Figure 5.16 A collection of brush block copolymers synthesized utiiizing the grafting-through ROMP approach, which all assemble to photonic crystals. (Adapted from Ref. [47, 48, 50, 55].)...

Miyake CM, Piunova VA, Weitekamp RA, Grubbs RH (2012) Precisely tunable photonic crystals from rapidly self-assembling brush block copolymer blends. Angew Chem Int Ed 51 (45) 11246-11248... 

Ishizu, K., Hatoyama, N., and Uchida, S. (2008) Architecture of rod-brush block copolymers synthesized by a combination of coordination polymerization and atom transfer radical polymerization. Journal of Applied Polymer Science, 108,3346-3352. 

Highly branched polymers, polymer adsorption and the mesophases of block copolymers may seem weakly connected subjects. However, in this review we bring out some important common features related to the tethering experienced by the polymer chains in all of these structures. Tethered polymer chains, in our parlance, are chains attached to a point, a line, a surface or an interface by their ends. In this view, one may think of the arms of a star polymer as chains tethered to a point [1], or of polymerized macromonomers as chains tethered to a line [2-4]. Adsorption or grafting of end-functionalized polymers to a surface exemplifies a tethered surface layer [5] (a polymer brush ), whereas block copolymers straddling phase boundaries give rise to chains tethered to an interface [6],... 

More detailed investigations with planar brushes, obtained from A-B block copolymers, where one component is able to crystallize on the surface of crystalline PE cores of platelet-like aggregates, have been reported recently [175]. 

The interest in these block copolymer micelles arises from the polyelectrolyte coronal block whose intrinsic properties are strongly influenced by many parameters including pH, salt concentration, and polar interactions. Moreover, they provide a unique model to mimic polyelectrolyte brushes at a high segment concentration, as noted by Forster [15]. 

Salt effects in polyelectrolyte block copolymer micelles are particularly pronounced because the polyelectrolyte chains are closely assembled in the micellar shell [217]. The situation is quite reminiscent of tethered polymer brushes, to which polyelectrolyte block copolymer micelles have been compared, as summarized in the review of Forster [15]. The analogy to polyelectrolyte brushes was investigated by Guenoun in the study of the behavior of a free-standing film drawn from a PtBS-PSSNa-solution [218] and by Hari-haran et al., who studied the absorbed layer thickness of PtBS-PSSNa block copolymers onto latex particles [219,220]. When the salt concentration exceeded a certain limit, a weak decrease in the layer thickness with increasing salt concentration was observed. Similar results have been obtained by Tauer et al. on electrosterically stabilized latex particles [221]. 

Fig. 9.19 Preparation of polymer brushes on solid surfaces by a) chemical grafting of end-functionalized linear polymers or selective adsorption of asymmetric block copolymers and b) by surface-initiated polymerization (SIP) using initiator functions on the solid surface. The depicted SAM bearing to-functionalities...

In this method, a reactive group on the surface initiates the polymerization, and the propagating polymer chain grows from the surface (Fig. 9.19b). In principle, it can be employed with all polymerization types, and a number of papers have reported high amounts of immobihzed polymer using surface-initiated polymerization with various initiator/monomer systems. If controlled or Hving polymerization techniques are used, block copolymer or end-functionahzed polymer brush systems can be prepared in consecutive reaction steps (Fig. 9.19c). 

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. 

Besides homogeneous and uniform SAMs or polymer brushes, systems of tailored heterogeneity such as mixed monolayers of two or more compounds, gradients, block copolymer brushes etc. are now under investigation. Especially, the development of patterned surfaces offers the exciting possibility to perform multiple parallel experiments on a single substrate or cascade reactions. 

The benefits of utihzing combinatorial methods for investigating polymer properties have been outlined recently [19,166,167]. Polymer gradient brush assemblies are expected to play an active role in further combinatorial material effort. Possible areas of interest include (but are not hmited to) study of phase behavior (stability) in hquid [168] and polymer blend [169] systems, morphological transitions in block copolymers [170,171], cell culturing [58,172], and others. 

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