Block copolymer synthesis mechanisms

Tetraethylthiuram disulfide (13) induces St polymerization by the photodissociation of its S-S bond to give the polymer with C-S bonds at both chain ends (15). The C-S bond further acts as a polymeric photoiniferter, resulting in living radical polymerization. Eventually, some di- or monosulfides, as well as 13, were also examined as photoiniferters and were found to induce polymerization via a living radical polymerization mechanism close to the model in Eq. (18), e.g., the polymerization of St with 35 and 36 [76,157]. These disulfides were used for block copolymer synthesis [75,157-161] ... 

Figure 8 Monomers for the block copolymer synthesis by transformation of mechanisms.

The use of the dual initiator strategy has opened up a whole new area of block copolymer synthesis using enzymes and over the previous five years many reactions and systems have been extensively reported. In general, the previous reports have shown that the use of supercritical C02 has allowed the two reaction mechanisms of eROP and free radical polymerization to occur simultaneously to yield well-defined block and graft copolymers. 

Grubbs and coworkers [127,128] reported two independent transformation reactions for block copolymer synthesis. The first report [128, 129] involved changing the mechanism from hving metathesis polymerization of cycloalkene to a group transfer polymerization of silyl vinyl ether. In a second report, block copolymers of NB and ethylene were prepared by transforming a metathesis polymerization to a... 

Guo, Y.-M., Pan, C.-Y., and Wang, J. (2001). Block and star block copolymers by mechanism transformation. VI. Synthesis and characterization of A4B4 miktoarm star copolymers consisting of polystyrene and polytetrahydrofuran prepared by cationic ring-opening polymerization and atom transfer radical polymerization. J. Polym. Sci., Part A Polym. Chem., 59(13) 2134-2142. 

More specific topics, such as block copolymer synthesis by changing the polymerization mechanism [18], by step-growth polymerization [19], via macroinitiators [20], living free-radical polymerization [21, 22] or ionic polymerization [23] were reviewed later on, as well as the synthesis of selected block copolymer types, for example hydrophilic-hydrophilic copolymers [24], copolymers based on PEO [10,16]. 

Feng, X.S. and Pan, C.Y. (2002) Block and star block copolymers by mechanism transformation. 7. Synthesis of polytetrahydrofuran/poly(l,3-dioxepane)/polystyrene ABC miktoarm star copolymers by combination of CROP and ATRP. Macromolecules, 35,2084—2089. 

Yijin X. and Caiyaun P., Block and star-hlock copolymers by mechanism transformation. 3. S-(PTHF-PSt)4 and S-(PTHF-PSt-PMMA)4 from living CROP to ATRP, Macromolecules, 33, 4750, 2000. Feldthusen J., Ivan B., and Mueller A.H.E., Synthesis of linear and star-shaped block copolymers of isobutylene and methacrylates hy combination of living cationic and anionic polymerizations. Macromolecules, 31, 578, 1998. 

By employing anionic techniques, alkyl methacrylate containing block copolymer systems have been synthesized with controlled compositions, predictable molecular weights and narrow molecular weight distributions. Subsequent hydrolysis of the ester functionality to the metal carboxylate or carboxylic acid can be achieved either by potassium superoxide or the acid catalyzed hydrolysis of t-butyl methacrylate blocks. The presence of acid and ion groups has a profound effect on the solution and bulk mechanical behavior of the derived systems. The synthesis and characterization of various substituted styrene and all-acrylic block copolymer precursors with alkyl methacrylates will be discussed. 

Every polymerization method is limited to a certain type and number of monomers, thus preventing the possibility to synthesize block copolymers with a wide combination of monomers. However, recent advances in polymer synthesis enabled the switching of the polymerization mechanism from one type to another, thereby permitting the preparation of block copolymers composed of monomers that can be polymerized by different techniques. 

SANS study of the mechanisms and kinetics of the synthesis of mesoporous materials from micelles of tri-block copolymers... 

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