Direct block copolymers

Fig. 14 Graphoepitaxy vs epitaxial self-assembly, (a) Graphoepitaxy utilizes topographic substrate pattern for directed block copolymer assembly. The substrate pattern remains in the finally formed nanopattemed morphology, (b) Epitaxial self-assembly utilizes nanoscale chemical pattern to register block copolymer assembly. Ultrafine chemical patterning requires e-beam lithography or other high-cost lithography such as EUV. Reprinted with permission from Jeong et al. [153]. Copyright 2010 American Chemical Society...

Ruiz R, Kang H et al (2008) Density multiplication and improved lithography by directed block copolymer assembly. Science 321 936-939... 

Molecular recognition was used in a very elegant way to direct block copolymer morphology by Shenhar et al. [80]. Upon addition of dendritic wedges with thymine units to a lamellar block copolymer with diaminopyridine units, a block copolymer morphology was obtained after evaporation of the solvent. 

C) Block copolymer thin film. (D) Guided self-assembly in registration with the underlying chemical pattern. (Reproduced with permission from R. Ruiz, H. King, F.A. Detcheverry et al., Density multiplication and improved lithography by directed block copolymer assembly, Science, 321, 936-939, 2008. 2008 American Association for the Advancement of Science.)... 

Yang, X., Wan, L. et al. (2010) Directed block copolymer assembly versus electron beam lithography for bit-patterned media with areal density of 1 terabit/inch and beyond. ACS Nano, 3,1844. 

Amide interchange reactions of the type represented by reaction 3 in Table 5.4 are known to occur more slowly than direct amidation nevertheless, reactions between high and low molecular weight polyamides result in a polymer of intermediate molecular weight. The polymer is initially a block copolymer of the two starting materials, but randomization is eventually produced. 

The second front originates in the polymer synthesis community. Efforts are mainly directed toward production of monodisperse block copolymers by living polymerizations. These stmctures typically result in microphase separated systems if one block is a high T material and the other is elastomeric in... 

Copolymerizations of benzvalene with norhornene have been used to prepare block copolymers that are more stable and more soluble than the polybenzvalene (32). Upon conversion to (CH), some phase separation of nonconverted polynorhornene occurs. Other copolymerizations of acetylene with a variety of monomers and carrier polymers have been employed in the preparation of soluble polyacetylenes. Direct copolymeriza tion of acetylene with other monomers (33—39), and various techniques for grafting polyacetylene side chains onto solubilized carrier polymers (40—43), have been studied. In most cases, the resulting copolymers exhibit poorer electrical properties as solubiUty increases. 

The synthesis of block copolymers by macromonotner RAFT polymeriza tion has been discussed in Section 9.5.2 and examples are provide in Table 9.9. RAFT polymerization with thioearbonylthio compounds has been used to make a wide variety of block copolymers and examples arc provided below in Tabic 9.28. The process of block formation is shown in Scheme 9.59. Of considerable interest is the ability to make hydrophilic-hydrophobic block copolymers directly with monomers such as AA, DMA, NIPAM and DMAEMA. Doubly hydrophilic blocks have also been prepared.476 638 The big advantage of RAFT polymerization is its tolerance of unprotected functionality. 

I he method of polymerization needs to be chosen for compatibility with functionality in the cores and the monomers to be used. Star block copolymers have also been reported. Mulli(bromo-compounds) may be used directly as ATRP initiators or they can be converted to RAFT agents. One of the most common... 

Comprehension of the interactions among microstructures composed of tethered chains is central to the understanding of many of their important properties. Their ability to impart stability against flocculation to suspensions of colloidal particles [52, 124, 125] or to induce repulsions that lead to colloidal crystallization [126] are examples of practical properties arising from interactions among tethered chains many more are conceivable but not yet realized, such as effects on adhesion, entanglement or on the assembly of new block copolymer microstructures. We will be rather brief in our treatment of interactions between tethered chains since a comprehensive review has been published recently of direct force measurements on interacting layers of tethered chains [127]. 

Measurements of diffusion of tracer polymers in ordered block copolymer fluids is another potentially informative activity, since molecular diffusion is one of the most basic dynamic characteristics of a molecule. Balsara, et al. have measured the retardation of diffusion due to ordering in the diffusion of polystyrene tracer homopolymers in polystyrene-polyisoprene matrices of various domain sizes [167]. Measurement of the tracer diffusion of block copolymer molecules will also be important. Several interesting issues are directly addressable via measurements... 

Another consequence of the absence of sponataneous transfer and termination reactions is that the polymer chains formed remain living 3), i.e. they carry at the chain end a metal-organic site able to give further reactions. Block copolymer synthesis is probably the major application 12 14), but the preparation of co-functional polymers, some chain extension processes, and the grafting onto reactions arise also directly from the long life time of the active sites. 

Perrier RJ (2001) Direct Conversion of 5,6-Unsaturated Hexopyranosyl Compounds to Functionalized Glycohexanones. 215 277-291 Frey H, Schlenk C (2000) Silicon-Based Dendrimers. 210 69-129 Forster S (2003) Amphiphilic Block Copolymers for Templating Applications. 226 1-28 Frullano L, Rohovec J, Peters JA, Geraldes CFGC (2002) Structures of MRI Contrast Agents in Solution. 221 25-60... 

Micellar nanocarriers have already been applied successfully for delivery of hydro-phobic drugs [86]. These carriers are usually the product of self-assembled block copolymers, consisting of a hydrophilic block and a hydrophobic block. Generally, an ELP with a transition temperature below body temperature is used as hydrophobic block and the hydrophilic block can be an ELP with a transition temperature above body temperature or another peptide or protein. The EPR effect also directs these types of carriers towards tumor tissue. 

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