Main chains, block copolymers synthesis

The polymer coupling approach to block copolymer synthesis is seriously disadvantaged by the need to ensure stoichiometric equivalence of the reactive functional groups. These are in low concentration relative to the main chain units of the polymer chains and they are usually sensitive to trace impurities, particularly water (e.g. Si-Cl rapidly converts to Si-OH, Si rapidly converts to Si-H). Hence obtaining stoichiometric equivalents of the chain ends is extremely difficult and leads to poor reproducibility without scrupulous care using high vacuum line procedures. In... 

This chapter focuses on polyferrocenylsilanes (PFSs) where iron and silicon are in the main chain. Subsequently, PFS block copolymers will be reviewed. These materials represent an area of rapidly growing interest as a result of their self-assembly into phase-separated metal-rich nanodomain structures in thin films and micelles in block-selective solvents. The resulting nanostructured materials have a wealth of potential applications and recent breakthroughs in this area are discussed. The subject matter of the chapter is divided up into subsections covering PFS homopolymer and block copolymer synthesis, solution and solid-state self-assembly and applications of the latter, which have been extensively developed by ourselves and our collaborators and also by other research groups. 

The principle of random block polymerization has been used for polysiloxane block copolymer synthesis as in equation (27) where the block connection is made by condensation between two types of silanol groups. This reaction, which is catalyzed by weak bases such as hexylamine carboxylate salts or tetramethylguanidine to avoid Si—O bond randomization, leads to multiblock polymers (35) having p-phenylene groups in the main chain. ... 

Gilroy JB, Patra SK, Mitchels JM, Winnik MA, Manners I (2011) Main-chain heteaobi-metallic block copolymers synthesis and self-assembly of polyfiarocenylsUane-b-poly (cobaltoceniumethylene). Angew Chem Int Ed 50 5851-5855... 

They also synthesized polymeric iniferters containing the disulfide moiety in the main chain [149,150]. As shown in Eq. (30),polyphosphonamide,which was prepared by the polycondensation reaction of phenyl phosphoric dichloride with piperadine, was allowed to react with carbon disulfide in the presence of triethylamine, followed by oxidative coupling to yield the polymeric iniferter 32. These polymeric iniferters were used for the synthesis of block copolymers with St or MMA, with the composition and block lengths controlled by the ratio of the concentration of the polymeric iniferter to the monomer or by conversion. The block copolymers of polyphosphonamide with poly(St) or poly(MMA) were found to have improved flame resistance characteristics. 

Some particularities of the extraction of ions from an aqueous organic phase, and of the phase catalyzed polyetherification will be summarized. These will represent the fundamentals of our work on the synthesis of some novel classes of functional polymers and sequential copolymers. Examples will be provided for the synthesis of functional polymers containing only cyclic imino ethers or both cyclic imino ethers as well as their own cationic initiator attached to the same polymer backbone ABA triblock copolymers and (AB)n alternating block copolymers and a novel class of main chain thermotropic liquid crystalline polymers containing functional chain ends, i.e., polyethers. 

Three major topics of research which are based on phase transfer catalyzed reactions will be presented with examples. These refer to the synthesis of functional polymers containing functional groups (i.e., cyclic imino ethers) sensitive both to electrophilic and nucleophilic reagents a novel method for the preparation of regular, segmented, ABA triblock and (A-B)n alternating block copolymers, and the development of a novel class of main chain thermotropic liquid-crystalline polymers, i.e., polyethers. 

The main advantage of this type of initiator is the production of significantly longer polymer chains without reduction of the polymerization rate (compared with monofunctional initiators) [104]. When both functional groups are part of the same peroxide, they are both decomposed to the initiating radicals at practically the same rate. When the difunctional initiator is composed of peroxides decomposing at various rates, this property may be utilized for the synthesis of block copolymers. 

CRP is a powerful tool for the synthesis of both polymers with narrow molecular weight distribution and of block copolymers. In aqueous systems, besides ATRP, the RAFT method in particular has been used successfully. A mrmber of uncharged, anionic, cationic, and zwitterionic monomers could be polymerized and several amphiphilic block copolymers were prepared from these monomers [150,153]. The success of a RAFT polymerization depends mainly on the chain transfer agent (CTA) involved. A key question is the hydrolytic stability of the terminal thiocarbonyl functionaHty of the growing polymers. Here, remarkable progress could be achieved by the synthesis of several new dithiobenzoates [150-152]. 

In Table 10 we have gathered different 1,2-disubstituted tetraphenylethanes reported in the literature to get telechelic polymers. We can remark that few studies were undertaken in the area of telechelic polymers hence, despite a one-step reaction to get a telechelic structure, the main interest attributed to initer systems concerns the ability to restart a block copolymerization. The number of publications concerning the synthesis of diblock copolymers may prove this assumption. Under certain polymerization conditions, the chain ends, comprising the last monomer unit and the primary radical formed from the intiator, may split up into new radicals able to reinitiate further polymerization of a second monomer, leading to block copolymers. This is certainly the reason why 1,2-disubstituted tetraphenylethane does not present such interesting condensable functions (X in Scheme 10) for polycondensation reactions (Table 10). 

Most of the known photochemical procedures for the synthesis of block and graft copolymers are based on the modification of already existing polymers with photolabile groups incorporated at defined positions, i.e. at the chain end, at side chains, or in the main chain (see Chart 11.13) [84]. 

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