Copolymers, triblock characterization

Controlled synthesis and detailed characterization of triblock copolymers of di-phenylsiloxane and dimethylsiloxane has been reported by Meier and co-workers147 148), who used lithium based initiators and the cyclic trimers of dimethyl and diphenyl-... 

Ban H.T., Kase T., Kawabe M., Miyazawa A., Ishihara T., Hagihara H., Tsunogae Y., Murata M. and Shiono T.A. New approach to styrenic thermoplastic elastomers S3Tithesis and characterization of crystalline styrene-butadiene-styrene triblock copolymers. Macromolecules, 39, 171, 2006. 

A series of poly(ester-urethane) urea triblock copolymers have been synthesized and characterized by Wagner et al/ using PCL, polyethylene glycol, and 1,4 diisocyanatobutane with either lysine ethyl ester or putrescine, as the chain extender. These materials have shown the elongation at break from 325% to 560% and tensile strengths from 8 to 20 MPa. Degradation products of this kind of materials did not show any toxicity on cells. 

Recent studies on PEO-PPO, PEO-PBO di- and triblock copolymers include the works of Bahadur et al. [121], who examined the role of various additives on the micellization behavior, of Guo et al. [122], who used FT-Raman spectroscopy to study the hydration and conformation as a function of temperature, of Booth and coworkers [ 123], who were mainly interested in PEO-PBO block copolymers with long PEO sequences, and of Hamley et al., who used in situ AFM measurements in water to characterize the morphology of PEO-PPO micelles [56,57]. 

Micelles of type (1) were the first investigated examples of ABC triblock copolymer micelles. These micelles are generally characterized by the so-called onion, three-layer, or core-shell-corona structures, i.e., the first insoluble A block forms the micellar core, the second insoluble B block is wrapped around the core, and the third soluble C block extends in the solution to form the micellar corona (Fig. 18). To the best of our knowledge, there are no known examples of ABC block copolymer micelles with A and C insoluble blocks and a B soluble block. 

ABC triblock copolymers have recently proven to be useful in constructing the so-called three-layer, onion, or core-shell-corona micelles, as described in Sect. 7.2. These micelles are characterized by a centrosymmetric structure and a micellar core with two different concentric compartments. Noncentrosymmetric structures from ABC triblock copolymers blended with AC diblocks have, however, been reported in bulk by Goldacker et al. [290]. 

Elabd, Y. A., Walker, C. W. and Beyer, F. L. 2004. Triblock copolymer ionomer membranes. Part 11. Structure characterization and its effects on transport properties and direct methanol fuel cell performance. Journal of Membrane Science 231 181-188. 

Elabd, Y. A. and Napadensky E. 2004. Sulfonation and characterization of poly(styrene-isobutylene-styrene) triblock copolymers at high ion-exchange capacities. Polymer 45 3037-3043. 

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. 

In the past several years, we have used the SAAP method to prepare different long multiblock copolymers. Generalities about the preparation and characterization of different end-functionalized triblock copolymers are first outlined. Then, the micellization of triblock copolymer as well as coupling efficiency with and without self-assembly method are discussed. 

Narrowly distributed Pl-ft-PS-i-PI triblock copolymer chains with both of their ends capped with bromobutyl groups were prepared by sequential addition of living anionic polymerization and terminated by excess of 1,4-dibromobutane (PS block Mw = 3.5 x 103 g/mol PI blocks Mw = 3.1 x 103 g/mol Mw/Mn = 1.12 The degree of end-functionalization was 92% characterized by HNMR). Figure 6 shows the SEC profile of such prepared triblock copolymer chains. The small but a detectable amount ( 5%) of Pl-i-PS-i-PI dimers, PI-Z>-PS-Z>-PI-c-PI-Z>-PS-Z>-PI, is presumably formed via the Wurtz-type coupling reaction. 

Y. Kwon, R. Faust, C.X. Chen, and E.L. Thomas, Synthesis and characterization of poly(isobutylene-b-pivalolactone) diblock and poly (pi va lolac tone-b-isobu tylene-b-pivalolactone) triblock copolymers, Macromolecules, 35(9) 3348-3357, April 2002. 

S.J. Taylor, R.F. Storey, J.G. Kopchick, and K.A. Mauritz, Poly[(styr-ene-co-p-methyIstyrene)-b-isobutylene-% textitb-(styrene-co-p-meth-ylstyrene)] triblock copolymers. 1. synthesis and characterization, Polymer, 45(14) 4719-4730, June 2004. 

Ge, H., Y. Hu, X. Jiang, D. Cheng, Y. Yuan, H. Bi, and C. Yang. 2002. Preparation, characterization, and drug release behaviors of drug nimodipine-loaded poly(s-caprolactone)-poly(ethyleneoxide)-poly(e-caprolactone) amphiphilic triblock copolymer micelldsPharm. Sci91 1463-1473. 

The substantial work on polystyrene/polybutadiene and polystyrene/ polyisoprene blends and diblock and triblock copolymer systems has lead to a general understanding of the nature of phase separation in regular block copolymer systems (5,6). The additional complexities of multiblocks with variable block length as well as possible hard- and/or soft-phase crystallinity makes the morphological characterization of polyurethane systems a challenge. 

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