Block polymer synthesis

Corpart P, Charmot D, Biadatti T et al. (1999) Block polymer synthesis by controlled radical polymerization. (W09858974) Chem Abstr 130 82018... 

Kinetic Study and (he Possibility of Block Polymer Synthesis Mechanisms of Initiation and Propagation Reactions... 

Firstly, to prove the possibility of block polymer synthesis between the acrolein and a second monomer. 

Copolymers with only short acrolein blocks can by synthesized. In these conditions, the formation of homopolyacrolelns can be avoided (differences between the PAI3 and the chromatograms Figures 1 and 7). In fact, it would better to define this approach as functionalization rather than block polymer synthesis. 

The phenomenal growth in commercial production of polymers by anionic polymerization can be attributed to the unprecedented control the process provides over the polymer properties. This control is most extensive in organolithium initiated polymerizations and includes polymer composition, microstructure, molecular weight, molecular weight distribution, choice of functional end groups and even monomer sequence distribution in copolymers. Furthermore, a judicious choice of process conditions affords termination and transfer free polymerization which leads to very efficient methods of block polymer synthesis. 

In a process related to GTP, aldehydes initiate the polymerization of silyl vinyl ethers and silyl diene ethers. Here the silyl group is present in the monomer and transfers to the aldehyde ended chains regenerating aldehyde ends [17] (Scheme 8). A Lewis acid catalyst is required. terf-Butyldimethylsilyl works best as a transfer group for vinyl ether while trimethylsilyl is suitable for diene ethers [18]. Even though aldol GTP provides a route to polyvinyl alcohol segments in the subsequent block polymer synthesis, the projected cost of the monomers discouraged further research aimed at commercialization. 

Haggard and Lewis have shown that tetrabutylammonium alkoxides polymerize methacrylates in alcohol solution [68]. Block polymer synthesis is not possible since the ester groups on the monomer exchange with the solvent. 

In a process related to RAFT, BASF workers have shown that 1,1-diphenylethylene will control the molecular weight of PMMA and polystyrene, and permit block polymer synthesis [92]. They propose that radical chain ends add to the diphenylethylene to form a stable diphenylalkyl radical that does not add more monomer but can reverse to diphenylethylene and the same radical chain end for addition of more monomer. The diphenylalkyl radical cap has the additional possibility of forming a reversible dimer (Scheme 35). 

Anionic Methods. Of the various methods used for nonpolar block polymer synthesis, the anionic approach is by far the most useful and most precise in producing a given segmented chain design [A-B-A, (A-B)j, A-B-C, etc.]. The linear A-B-A block polymer may be synthesized by two basic routes, sequential polymerization of all three blocks or sequential polymerization of two blocks, followed by coupling. The "sequential" method is illustrated in Reaction la for the preparation of S-B-S the "coupling" process is depicted in Reaction lb. 

The use of protecting groups in polymerization is the preferred laboratory method for preparing many functional polymers. Protecting group methods have allowed the synthesis of otherwise difficult to synthesize functional and reactive polymers. Industrial applications are expected to be more in the specialty rather than commodity polymer area because of the costs associated with the protection and deprotection steps. For exanple, FMC has just announced a new line of protected functional anionic initiators for use in specialty block polymer synthesis. Commodity polymer applications will have to await the development of new catalysts that not only tolerate functionality but also incorporate it in a single step. 

This methodology is amenable to use in block polymer synthesis, as hydrocarbon based "living pol3rmers" will readily add across the DPE double bond to form the macro-molecular initiator. ... 

Anionic Processes.— The methods of block polymer synthesis from living polyanions are now well understood and the recently reported syntheses are summarized in Tablet. 

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