Block copolymer synthesis diblock copolymers prepared

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... 

Due to the lack of vinyl monomers giving rise to crystalline segment by cationic polymerization, amorphous/crystalline block copolymers have not been prepared by living cationic sequential block copolymerization. Although site-transformation has been utilized extensively for the synthesis of block copolymers, only a few PIB/crystalline block copolymers such as poly(L-lactide-fc-IB-fc-L-lactide) [92], poly(IB-fr- -caprolactone( -CL)) [93] diblock and poly( -CL-fr-IB-fr- -CL) [94] triblock copolymers with relatively short PIB block segment (Mn< 10,000 g/mol) were reported. This is most likely due to difficulties in quantitative end-functionalization of high molecular weight PIB. 

Using the more successful arm-first approach, in-chain functionalized stars were prepared. 2,3-Dicarbomethoxynor-bomadiene was polymerized with the same catalytic systems followed by the addition of the difunctional monomer, leading to the desired functionalized star polymers. SEC revealed the presence of 10-20% unreacted homopolymers. Using the same procedure, star-block copolymers can also be prepared. 2,3-Dicarbomethoxynorbomadiene was initially polymerized followed by the addition of norbomene for the synthesis of the living diblock copolymers. Reaction of these living diblocks with the difiinctional monomer afforded the star-block copolymers with complete consumption of the living arms (Scheme 56). 

In the case of AB diblock copolymers prepared by the RAFT technique, the order of monomer addition must be taken into account. A characteristic example of such a block copolymer synthesis is demonstrated in Scheme 19. Initially, a poly(N, N-dimethylacrylamide) (PDMA) macro-CTA was prepared, followed by the use of PDMA-CTA as an initiator to polymerize successfully the second monomer N,N-dimethyl vinyl benzy-lamide (DMVBA). The final diblock copolymer is not contaminated with homopolymer. It has been discovered that the reverse approach is impossible, probably due to the slow fragmentation of the intermediate radical or due to the slow initiation efficiency of the intermediate radical (styrenic macroradical). 

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... 

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). 

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-... 

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-... 

Se et al. presented the synthesis of poly[(VS- -I)-b-S] block—graft copolymers.157 The backbone, a diblock copolymer of 4-(vinyldimethylsilyl)styrene (VS) and styrene, was prepared first by anionic polymerization. The VS monomer was polymerized selectively through the styryl double bond at low... 

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