Diblock copolymers block copolymer synthesis

Potentially, there are greater numbers of monomers that are suitable for cationic polymerization than for anionic, but the cationic method is less successful in block copolymer synthesis because, in many systems, the existence of a living carbocationic species is doubtful. Consequently, the involvement of carbocations in block copolymer synthesis tends to be limited to mixed reactions, e.g., the couphng of poly(tetrahydro-furan) cations with polystyryl anions to give an (A - B) diblock (Equation 5.19). 

Gianneschi and coworkers [29] have utilized a similar approach in functionalizing ROMP copolymers with hydrophilic peptides. This work involves a block copolymer synthesis incorporating a phenyl NBE moiety as the hydrophobic block and an NHS moiety as the chemically addressable block. Subsequent conjugation of peptides via their N-termini affords amphiphilic block copolymers in which the hydrophilic shell is defined by a short peptide sequence programmed to be an enzyme substrate. For graft-to functionalization, A/ ,A/ -diisopropylethylamine was added to the activated ester diblock copolymer in DMF, followed by the addition of peptide (with respect to NHS units). 

RAFT polymerization is recognized as one of the most versatile methods for block copolymer synthesis and numerous examples of block synthesis have now appeared in the literature. RAFT poljunerization proceeds with retention of the thiocarbo-nylthio group. Hiis allows an easy entry to the synthesis of AB diblock copolymers by the simple addition of a second mono-mer. ° Higher order (ABA, ABC, etc.) blocks are also possible by sequential addition of further monomer(s). 

Somewhat limited work has been reported over the last decade. There are several reports on the synthesis and physical and structural characterization of styrene-dimethylsiloxane 141 144) and methylmethacrylate-dimethylsiloxane145> diblock, triblock and multiblock copolymers. Several reports are also available on the thermal223), solution 224,2251 and surface196 2261 characterization of various styrene-dimethyl-siloxane block copolymers synthesized by anionic techniques. 

Kennedy J.P. and Shim J.S., Star-block polymers having multiple polyisobutylene containing diblock copolymers arm radiating from a siloxane core and a method of synthesis thereof. Disclosure 318, US Patent, Notice of Allowance, 2001. 

Abstract This review highlights recent (2000-2004) advances and developments regarding the synthesis of block copolymers with both linear [AB diblocks, ABA and ABC triblocks, ABCD tetrablocks, (AB)n multiblocks etc.] and non-linear structures (star-block, graft, miktoarm star, H-shaped, dendrimer-like and cyclic copolymers). Attention is given only to those synthetic methodologies which lead to well-defined and well-characterized macromolecules. 

Star-block copolymers are star polymers in which each arm is a block (diblock or triblock) copolymer. There are several methods used for the synthesis of star-block copolymers [142], and the most commonly used strategies are given in Scheme 67. 

Influence on the phase behaviour is observed if even small amounts (0.5 wt %) of hairy silica-like nanoparticles obtained by block-copolymer-directed sol-gel synthesis are added to a block copolymer [53,214]. On the example of a PS-fo-PI diblock copolymer a depression of the ODT of approx. 20 K was observed (Fig. 68), accompanied by a broadening of the transition. The largest depression was observed for rod-like nanoparticles, which is explained by the energy introduced by the defects [215]. 

The facility to introduce well-defined chain ends has been used to prepare star polymers557 and diblocks via reaction with macromolecular aldehydes.558 The synthesis of amphiphilic star block copolymers has also been described using a cross-linking agent.559 560 A similar strategy has recently... 

By covalent linkage of different types of molecules it is possible to obtain materials with novel properties that are different from those of the parent compounds. Examples of such materials are block-copolymers, soaps, or lipids which can self-assemble into periodic geometries with long-range order. Due to their amphiphilic character, these molecules tend to micellize and to phase-separate on the nanometer scale. By this self-assembly process the fabrication of new na-noscopic devices is possible, such as the micellization of diblock-co-polymers for the organization of nanometer-sized particles of metals or semiconductors [72 - 74]. The micelle formation is a dynamic process, which depends on a number of factors like solvent, temperature, and concentration. Synthesis of micelles which are independent of all of these factors via appropriately functionalized dendrimers which form unimolecular micelles is a straightforward strategy. In... 

Abstract This article reviews results from our group of the synthesis and characterization of diblock copolymer brushes. Results from the literature are also covered. We report a wide variety of diblock compositions and compare the miscibility of the two blocks with the tendency to rearrange in response to block-selective solvents. Also, we describe the types of polymerization methods that can be utilized to prepare diblock copolymer brushes. We have compared the molecular weight of free polymer and the polymer brush based on results from our laboratory and other research groups we have concluded that the molecular weight of the free polymer and that of degrafted polymer brushes is similar. 

In this review, synthesis of block copolymer brushes will be Hmited to the grafting-from method. Hussemann and coworkers [35] were one of the first groups to report copolymer brushes. They prepared the brushes on siUcate substrates using surface-initiated TEMPO-mediated radical polymerization. However, the copolymer brushes were not diblock copolymer brushes in a strict definition. The first block was PS, while the second block was a 1 1 random copolymer of styrene/MMA. Another early report was that of Maty-jaszewski and coworkers [36] who reported the synthesis of poly(styrene-h-ferf-butyl acrylate) brushes by atom transfer radical polymerization (ATRP). 

The designed set of 2-oxazoline monomers that was used for the synthesis of the triblock copolymers (MeOx, EtOx, PheOx, and NonOx) yielded polymers of different polarity [91], P(MeOx) and P(EtOx) are hydrophilic, whereas P(PheOx) and P(NonOx) are hydrophobic. All possible combinations of these four different monomers would result in 64 different structures. However, all polymers that would have two times the same block after each other were excluded since they do represent diblock copolymers. Additionally, some structures, which have NonOx as the first block and EtOx or MeOx as the second block, were excluded due to extensive side reactions. Consequently, 30 different triblock copolymers were synthesized, and they are listed in Table 13 with their corresponding structural characterization. 

Figure 6 Schematic representation of the problems that can be encountered during the synthesis of a zwitterionic diblock copolymer by aqueous ATRP. I represents the initiator fragment and represents the block junction...

ATRP is a powerful synthetic tool for the synthesis of low molecular weight (Dp < 100-200), controlled-structure hydrophilic block copolymers. Compared to other living radical polymerisation chemistries such as RAFT, ATRP offers two advantages (1) facile synthesis of a range of well-defined macro-initiators for the preparation of novel diblock copolymers (2) much more rapid polymerisations under mild conditions in the presence of water. In many cases these new copolymers have tuneable surface activity (i.e. they are stimuli-responsive) and exhibit reversible micellisation behaviour. Unique materials such as new schizo-... 

The architecture of copolymers can be controlled by the synthesis procedure, and it is possible to prepare diblock, triblock, multiblock, starblock and graft copolymers. These are illustrated in Fig. 1.1. Examples of other exotic architectures that have recently been synthesized are shown in Fig. 2.33. The possibilities for molecular design seem to be almost limitless, only being limited by the chemist s imagination. This book is concerned with block copolymers, and graft copolymers... 

---