Grafted block polymers, synthesis methods

The isopropyl group discourages P-H transfer, leading to the exclusive formation of Al-PEs. The Al-PEs can be readily transformed to a variety of functionalized PEs and to PE-based and polar polymer-based block and graft copolymers, using established methods. The selective synthesis of vinyl- and Al-terminated PEs with Zr-FI catalysts shows the critical importance of the substituent on the imine-N for polymerization catalysis. 

The mechanical synthesis of block and graft copolymer is a method of sizable versatility. It can be performed (as already stated) during polymer processing and in standard equipment. The reaction, also, can be carried out by subjecting a mixture of two or more polymers to mechanical degradation in either the solid, elastic-melt, or solution states. It is, also, possible to induce reaction mechanically between polymers and monomers. 

This review covered recent developments in the synthesis of branched (star, comb, graft, and hyperbranched) polymers by cationic polymerization. It should be noted that although current examples in some areas may be limited, the general synthetic strategies presented could be extended to other monomers, initiating systems etc. Particularly promising areas to obtain materials formerly unavailable by conventional techniques are heteroarm star-block copolymers and hyperbranched polymers. Even without further examples the number and variety of well-defined branched polymers obtained by cationic polymerization should convince the reader that cationic polymerization has become one of the most important methods in branched polymer synthesis in terms of scope, versatility, and utility. 

From the viewpoint of polymer synthesis, the multiplicity of the propagating species provides a possibility to synthesize polymers with varying structures from the different intermediates. In fact, the steric structure of, e.g., polystyrene, polyfvinyl ether)s, and poly(a-methylstyrene) can be controlled by selecting counteranions Recently, Kennedy and his associates studied in detail the control of chain transfer and termination by counteranions (initiators) in isobutene polymerization, and opened a new field of block and graft polymer synthesis (especially by their inifer method)... 

There are additional factors that may reduce functionality which are specific to the various polymerization processes and the particular chemistries used for end group transformation. These are mentioned in the following sections. This section also details methods for removing dormant chain ends from polymers formed by NMP, ATRP and RAFT. This is sometimes necessary since the dormant chain-end often constitutes a weak link that can lead to impaired thermal or photochemical stability (Sections 8.2.1 and 8.2.2). Block copolymers, which may be considered as a form of end-functional polymer, and the use of end-functional polymers in the synthesis of block copolymers are considered in Section 9.8. The use of end functional polymers in forming star and graft polymers is dealt with in Sections 9.9.2 and 9.10.3 respectively. 

Chapter 4 shows that the range of polymeric structures from enzymatic polymerization can be further increased by combination with chemical methods. The developments in chemoenzymatic strategies towards polymeric materials in the synthesis of polymer architectures such as block and graft copolymers and polymer networks are highlighted. Moreover, the combination of chemical and enzymatic catalysis for the synthesis of unique chiral polymers is discussed. 

Of all the methods for the production of block and graft polymers, the greatest importance, from the view of commercial simplicity, involves mechanical synthesis. The block and graft reactions can be potentially performed directly during polymer processing and in standard equipments, such as internal mixers, injection molding machines, and extruders. 

In the present paper we will review principally the different methods of synthesis which proceed through a radical or ionic mechanism. Condensation reactions will only be considered when they unite preformed polymer molecules into a graft or a block copolymer. 

Ionic polymerisation is a well-known technique for the preparation of graft copolymers but the fate of these reactions is determined by the reaction conditions. Since the discovery of living polymerisation , (anionic polymerisation) [67] it has become an excellent method for the synthesis of block and graft copolymers. In anionic polymerisation the graft copolymerisation is initiated by the anion generated by the reaction of bases with acidic protons in the polymer chain as shown in Scheme 2. 

Inifer type reactions have been applied to a large number of cationic synthesis, yielding functional polymers 70 72), block copolymers 73), graft copolymers, and even star-shaped polymers73). As far as macromonomer synthesis is concerned three different methods have been used which are described below ... 

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