Block polymerization, experimental details

The present chapter deals with the synthesis of conjugated polymers with various kinds of fused heterocyclic units, focusing on the experimental details of their synthesis. Taking into account that the structure of the monomeric building block affects the properties of the final polymer and defines the methods that can be used for its synthesis, the discussion of the available polymerization methods will be closely related to the type of heterocyclic unit incorporated in its backbone (Table 18.1). 

In this chapter, the focus is largely on experimental and theoretical studies of micellization in a range of solutions of model block copolymers prepared by anionic polymerization. A discussion of both neutral and ionic block copolymers is included, and features specific to the latter type are detailed. The adsorption of block copolymers at the liquid interface is also considered in this chapter. Recent experiments on copolymer monolayers absorbed at liquid-air and liquid-liquid interfaces are summarized, and recent observations of surface micelles outlined. Thus this chapter is concerned both with bulk micellization and the surface properties of dilute copolymer solutions. 

A number of theories of the contribution of interdomain polymeric material to the stress-strain, modulus, and swelling behavior of block copolymers and semicrystalline polymers are examined. The conceptual foundation and the mathematical details of each theory are summarized. A critique is then made of each theory in terms of the validity of the theoretical model, the mathematical development of the theory, and the ability of the theory to explain experimental findings. 

The improvement in the first two areas has been possible because of the progress made in understanding the mechanism and kinetics of radical polymerization and the stracture of radical intermediates. Further advancement requires detailed structure-reactivity correlation for radicals and also for dormant species. Both experimental measurements of rate and equilibrium constants as well as computational evaluation of thermodynamic (bond dissociation, redox properties) and kinetic properties of the involved species is needed. This will help to establish order of reactivities for various species and will assist selection of the efficient initiators or sequence of monomer addition for block copolymerization. 

The present chapter has centered on experimental efforts performed to study confined polymer crystallization. However, molecular dynamics simulations and dynamic Monte Carlo simulations have also been recently employed to study confined nucleation and crystallization of polymeric systems [99, 147]. These methods and their application to polymer crystallization are discussed in detail in Chapter 6. A recent reference by Hu et al. reviews the efforts performed by these researchers in trying to understand the effects of nanoconfinement on polymer crystallization mainly through dynamic Monte Carlo simulations of lattice polymers [147, 311]. The authors have performed such types of simulations in order to study homopolymers confined in ultrathin films [282], nanorods [312] and nanodroplets [147], and crystallizable block components within diblock copolymers confined in lamellar [313, 314], cylindrical [70,315], and spherical [148] MDs. 

A brush-type theory was developed by DiMarzio et al. [168] and a self-consistent field theory by Whitmore and Noolandi [169]. The latter approach predicts a scaling for the overall domain spacing d I V- ATAa (where N is the total degree of polymerization and ATa is that of the amorphous block) that is in good agreement with experimental results [170], as detailed elsewhere... 

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