Copolymers, block model polymerization methods

The present chapter reviews recent developments (work published in 1997 and later) in the synthesis of model block copolymers with a primary focus on ionic polymerisations. During this period controlled radical polymerisation techniques have attracted considerable interest and are emerging as a new method providing the synthesis of model polymers and copolymers. It is not the purpose of this chapter to cover this development since ionic methods still allow for better control of the polymers synthesised. Radical polymerization methods are the subject of Chapter 3. The question of how important differences in the widths of the molar mass distributions are has prompted the inclusion of a section on the MMD of model block copolymers. 

Cationic synthesis of block copolymers with non-linear architectures has been reviewed recently [72]. These block copolymers have served as model materials for systematic studies on architecture/property relationships of macromolecules. (AB)n type star-block copolymers, where n represents the number of arms, have been prepared by the living cationic polymerization using three different methods (i) via multifunctional initiators, (ii) via multifunctional coupling agents, and (iii) via linking agents. 

Polymeric supports can also be used with advantage to form monofunctional moieties from difunctional (Hies. Leznoff has used this principal in the synthesis of sex attractants on polymer supports (67). Starting from a sheap symmetrical diol he blocked one hydroxyl group by the polymer. Functionalization of cross-linked polymers is mostly performed by chloromethylation (65). A very promising method to introduce functional groups into crosslinked styrene-divinylbenzene copolymers is the direct lithiation with butyllithium in presence of N,N,N, N -tetramethyl-ethylenediamine (TMEDA) (69, 70). Metalation of linear polystyrene with butyl-lithium/TMEDA showed no exchange of benzylic hydrogen and a ratio of attack at m/p-position of 2 1 (71). In the model reaction of cumene with amylsodium, a kinetic control of the reaction path is established. After 3h of treatment with amyl-sodiuni, cumene is metalated 42% in a-, 39% m-, and 19% p-position. After 20h the mixture equilibrates to affort 100% of the thermodynamically more stable a-prod-uct (72). 

The properties of block copolymers, on the other hand, cannot be calculated without additional information concerning the block sizes, and whether or not the different blocks aggregate into domains. The results of calculations using the methods developed in this book can be inserted as input parameters into models for the thermoelastic and transport properties of multiphase polymeric systems such as blends and block copolymers of immiscible polymers, semicrystalline polymers, and polymers containing various types of fillers. A review of the morphologies and properties of multiphase materials, and of some composite models which we have found to be useful in such applications, will be postponed to Chapter 19 and Chapter 20, where the most likely future directions for research on such materials will also be pointed out. 

Both the 2,2-diphenyl vinyl and the l-methoxy-l,l-diphenylethyl chain ends are potential endgroups for the anionic polymerization of a variety of monomers by metalation. Our earlier results indicate that quantitative metalation of the 2,2-diphenylvinyl endgroups with alkyllithium cannot be achieved, most likely because of steric hindrance. However, as described recently, the ether cleavage of 1-methoxy-l,l-diphenyl-3,3,5,5-tetramethylhexane or electron transfer to 3,3,5,5-tetra-methyl-l,l-diphenylhex-l-ene by K/Na alloy, Cs or Li led to quantitative metalation resulting in nearly quantitative initiation of the polymerization of methacrylic monomers. Both precursors led to identical (macro)initiators verified by H NMR. These compounds can be considered as models of PIB chain ends formed by LCCP of IB and subsequent end-capping with DPE. The present study deals with the application of this method to the synthesis of different AB and ABA block copolymers by the combination of LCCP and living anionic polymerization. 

The major forte of anionic polymerization has been the ability to prepare polydlene and polystyrene polymers and copolymers with control over the major variables affecting polymer properties. Researchers continue to exploit this method for the preparation of model block copolymers, graft copolymers, and branched copolymers, and homopolymers with controlled, well-defined structures. The ability to prepare well-defined polymers and copolymers with functionalized end groups, especially ionic or ionizable groups, is also generating considerable current interest. Methods are also being explored to anionically pol)rmerize and copolymerized a variety of polar monomers with controlled structures. The current interest in blends and... 

Note, however, two recent review papers, one on off-lattice MC methods for coarse-grained models of polymeric materials [71] and one on MC applied to block copolymer systems [61], in which off-lattice simulations pertaining to self-assembly are discussed. 

Segura el al. combines Tarazona s WDA DFT for hard-spheres with Wertheim s thermodynamic perturbation theory and has been used in a number of studies of associating fluids in pores and with functionalized walls in the limit of complete association a DFT for polymeric fluids is obtained in this method. Based on these works, Chapman and co-workers have presented the interfacial-SAFT (iSAFT) equation, which is a DFT for polyatomic fluids formulated by considering the polyatomic system as a mixture of associating atomic fluids in the limit of complete association this approach allows the study of the microstructure of chain fluids. Interfacial phenomena in complex mixtures with structured phases, including lipids near surfaces, model lipid bilayers, copolymer thin films and di-block copolymers, have all been studied with the iSAFT approach. 

In conclusion, by overcoming the disadvantage of the previous synthetic methods for the preparation of hyperbranched polymers, we designed an all-new Seesaw-type macromonomer strategy to construct perfect hyperbranched model samples with uniform subchains. In onr stndy, we successfully prepared various kinds of Seesaw-type macromonomers, snch as homopolymers, triblock copolymers and diblock copolymers. Using these maCTomonomers as precursors, we have further prepared a series of perfect hyperbranched homopolymers, block copolymers, graft copolymers and hetero-snbchain copolymers by a combination of controlled/ living polymerization and click chemistry. Various solution properties of these novel hyperbranched (co) polymers in dilnte and semidilute solntions have been studied in detail. More specifically, the main achievements of this work are as follows ... 

Here, is the volume fraction of A block in diblock copolymer. To study the dynamics of phase separation, the polymeric external potential dynamics (EPD) method can be employed, which was proposed by Maurits and Fraaije [23] in dynamic density functional theory (DDFT) method (bead-string model). In EPD, the monomer concentration is a conserved quantity, and the polymer dynamics is inherently of Rouse type. The external dynamical equation in terms of the potential field m,- is expressed as... 

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