Diblock copolymers monodisperse

Recent attempts to prepare 26 by RAFT, however, failed [153]. Double hydrophilic block copolymers of NIPAM and 23e [154], as well as of N,N-diethylacrylamide and 23b [155], were prepared with the CTA benzyl dithiobenzoate, and exhibit LCST and UCST behavior in water. The new polymer 51 is also part of amphiphiUc di- and triblock copolymers [152]. Diblock copolymers with poly(ethylene glycol) methyl ether acrylate, dimethylacry-lamide, or 4-vinylstyrene sulfonate are macrosurfactants with a switch-able hydrophobic block. Triblock copolymers containing additionally 4-vinylbenzoic acid differ in the nature of the hydrophilic part [152]. Near-monodisperse block copolymers of N,N-dimethacrylamide and 49a were synthesized in different ways via macro-CTAs of both monomers as the first step. Such sulfobetaine block polymers form aggregates in pure water but are molecularly dissolved after addition of salt [152,156,157]. 

The previously discussed theories were developed for monodisperse diblock copolymers, which are not TPEs. However, Leibler s mean-field theory has been extended to include polydispersity (Leibler and Benoit, 1981) and to include triblock, star, and graft copolymers (Olvera de la Cruz and Sanchez, 1986 Mayes and Olvera de la Cruz, 1989). In the former case, polydispersity corrections tend to lower x N corresponding to the ODT. As would be expected from the analogy between blends and diblocks, triblocks will phase separate at higher xN values than the corresponding diblocks. This theory predicts a monotonic increase in the critical value of x A as the symmetry of the triblock increases, to a maximum of about 18 for the symmetric triblock. Surprisingly, the minimum xN value that separates the order and disordered regions in triblocks does not necessarily correspond to the critical point. 

Among the few examples it is worth mentioning the work of Seo et al. [84] that studied the structures formed at the air/water interface of BCP/BCP blends using a symmetric monodisperse diblock copolymer of poly(styrene-b-ferrocenylsilane)... 

Triblock copolymers of the ABA type may be analyzed similar to the analysis of diblock copolymers. The two possible cases for this type of investigation are (a) the analysis with respect to the inner block B using the critical conditions of the outer blocks A and A, and (b) the analysis of the outer blocks A and A using the critical conditions of the inner block B. It is particularly useful to carry out experiments at the critical point of A and A. The separation then occurs with respect to the chain length of B, yielding fractions that are monodisperse with respect to B and polydisperse with respect to A and A. These fractions can be analyzed selectively with respect to the outer blocks A and A in separate experiments (Entelis et al., 1986 Adrian et al., 1998 Pasch and Augenstein, 1993, 1994, 2002 Pasch, 1997, 2000, 2004 Kilz and Pasch, 2000). 

As a final example of catalytic hydrogenation activity with polymer-stabilized colloids, the studies of Cohen et al. should be mentioned [53]. Palladium nanoclusters were synthesized within microphase-separated diblock copolymer films. The organometallic repeat-units contained in the polymer were reduced by exposing the films to hydrogen at 100 °C, leading to the formation of nearly monodisperse Pd nanoclusters that were active in the gas phase hydrogenation of butadiene. 

There have been a number of computer simulations of block copolymers by Binder and co-workers (Fried and Binder 1991a,ft), and this work was reviewed in Binder (1994). Although computer simulations are limited due to the restriction on short chain lengths that can be studied, finite size effects and equilibration problems at low temperatures, the advantages are that the models are perfectly well characterized and ideal (monodisperse, etc.) and microscopic details of the system can be computed (Binder 1994). In the simulations by Binder and co-workers, diblocks were modelled as self- and mutually-avoiding chains on a simple cubic lattice, with chain lengths N = 14 to 60 for/ = 1.A purely repulsive pairwise interaction between A and B segments on adjacent sites was assumed. A finite volume fraction of vacancies was included to speed the thermal equilibration process (Binder 1994). 

A typical procedure for the synthesis of a propylene-MMA diblock copolymer is as follows. A living polypropylene (Mn = 16,000, Mw/Mn = 1.2) was prepared at —78 °C in a toluene solution of the V(acac)3/A1(C2H5)2C1 catalyst, followed by the addition of MMA. The block copolymerization with MMA was carried out for 5 h at 25 °C, resulting in the formation of an almost monodisperse block copolymer (K I0 = 18,000, Mw/Mn = 1.2). The block copolymer was treated with acetic acid in which the homopolymer of MMA would be soluble. No soluble polymer was detected. In addition, the insoluble polymer was treated with boiling acetone. Again, no soluble polymer was found. These results indicate the formation of a diblock copoly-... 

In this system using a polystyrene containing block copolymer, the polystyrene segment should readily partition into the lipophilic polystyrene particle core while the poly(FOA) or PDMS block is solubilized in the CO2 continuous phase to provide steric stabilization and prevent coagulation. In comparison of the polystyrene-b-poly(FOA) diblock copolymers to the polystyrene-b-PDMS diblock copolymers, it was found that the use of a polystyrene-b-PDMS stabilizer gives much more monodisperse particles. This most likely arises from the synthetic technique employed in the surfactant synthesis. The blocks in the polystyrene-b-PDMS block copolymers have a much narrower polydispersity than the blocks in the polystyrene-b-poly(FOA) block copolymers. It was noted that the particles obtained in... 

Since reactive systems have a great practical relevance, many attempts have been made in recent years to adapt the techniques used for pre-made block copolymers to obtain more detailed information on the correlation between the interfacial structure and fracture toughness. The simplest case is that of a dilute solution of monodisperse chains with one reactive group per chain, located at the chain end. In this case, the mechanical problem of reinforcement becomes similar to that of single connector diblock copolymers discussed earlier. The important issues are then mostly related to the competition between grafting ki-... 

Butun, V. Armes, S. R BrUingham, N. C. Synthesis and aqueous solution properties of near-monodisperse tertiary amine methacrylate homopolymers and diblock copolymers. Polymer 2001, 42, 5993-6008. 

Rod-Coil Diblock Copolymers Based on Perfectly Monodisperse Rods. . . 65... 

In contrast to the rod-coil diblock copolymer consisting of perfectly monodisperse rods, the liquid crystalline morphologies of rod-coil diblock copolymer containing polydisperse rods seem to be studied in less detail. In certain cases, the polydisperse nature of the rod-segments could hinder self-assembly into regularly ordered supramolecular structures. However, due to relatively simple synthetic procedures, liquid crystalline polymer can be of benefit for new materials with controlled internal dimensions ranging from the nanometer to macroscopic scale. 

Living polymerization of azo monomers is one of the most effective ways to prepare well-defined azo BCs. Generally, a monodispersed macroinitiator should be prepared first. It is then used as an initiator for the subsequent polymerization of azo monomers. Finkelmann and Bohnert (1994) first reported the synthesis of LC-side chain AB azo BCs by direct anionic polymerization of an azo monomer. As shown in Scheme 12.1, the polymerization of polystyrene (PS)-based diblock copolymers was carried out from a PS-lithium capped with 1,1-diphenylethylene (DPE), whereas the poly(methyl methacrylate) (PMMA)-based diblock copolymers were prepared by addition of methyl methacrylate (MMA) monomers to the living azo polyanion, obtained by reaction of l,l-diphenyl-3-methylpentylithium (DPPL) with the azo monomer in tetrahydrofuran (THF) at lower temperature. By this method, a series of well-defined azo BCs were obtained with controlled molecular weights and narrow polydispersities (Lehmann et al., 2000). 

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