The Architecture of Polymers

A promising solution for the mathematical prediction of chain flexibility is conformational analysis. Generally, conformational analysis identifies stable isomeric states for polymer chains and the energy barriers between them, which are the major elements needed to define chain flexibility in a precise manner. However for polymers, conformational analysis can become a cumbersome task, because the architecture of polymer chains allows a large number of degrees of freedom, which must be studied simultaneously. To obtain meaningful information, the analysis must be simplified, and only the most significant conformational elements must be studied. 

The second large group of chapters spedfically describes the synthetic aspects of ROP/ROMP. In this section, the architecture of polymers prepared by ROMP, functionalization of poly (ethylene oxide), chain extension by ROP, nonlinear polyethers, as wdl as ROP in heterogeneous media are discussed. It also describes methods of polymerization that provide regular and mostly spherical partides, and gives for the first time a review of the kinetics and mechanism of this particular system that resembles emulsion vinyl polymerization. The chapter on polymerization in confined space (encompassing matrix polymerization) summarizes results that may open the way to the replica polymerization, a process that is typical for the matrix synthesis of biomacromolecules in nature. 

The architectures of polymers synthesized using ROMP generally fall under four broad categories linear, cross-linked, branched, and dendritic. Linear polymers, as the name implies, possess chains that extend in one dimension, and encompass flexible coils, rigid rods, cycles, and polyrotaxanes, which can all be related to a string. Flexible coils may be imagined as a... 

The discovery and development of polypropylene, the one genuinely new large tonnage thermoplastics material developed since World War II, forms part of what is arguably the most important episode in the history of polymer science. For many years it had been recognised that natural polymers were far more regular in their structure than synthetic polymers. Whilst there had been some improvement in controlling molecular architecture, the man-made materials, relative to the natural materials, were structurally crude. 

As discussed in Section 7.3, conventional free radical polymerization is a widely used technique that is relatively easy to employ. However, it does have its limitations. It is often difficult to obtain predetermined polymer architectures with precise and narrow molecular weight distributions. Transition metal-mediated living radical polymerization is a recently developed method that has been developed to overcome these limitations [53, 54]. It permits the synthesis of polymers with varied architectures (for example, blocks, stars, and combs) and with predetermined end groups (e.g., rotaxanes, biomolecules, and dyes). 

Copolymerizations are processes that lead to the formation of polymer chains containing two or more discrete types of monomer unit. Several classes of copolymer that differ in sequence distribution and/or architecture will be... 

The microstructure and architecture of polymers can also gready influence die properties of die polymers. For example, poly(3-substituted thiophene)s could have three microstructure joints s-trans (head to tail), s-trans (head to head), and s-cis (head to tail) (Fig. 9.3). The regioregular head-to-tail poly(3-substituted thiophene)s exhibit higher electrical conductivity values and higher... 

The main chain of dendronized polymers, due to die large size of the mon-odendrons, is usually forced to take a stretched shape thus the whole molecule exists as a rigid rod architecture both in solution and in the solid state.32d Depending on the backbone stiffness, the degree of monodendron coverage, and the size of die monodendron, the architecture of these macromolecules is no longer a sphere but a cylinder this dictates die properties of the dendronized polymers. 

In summary, our new SEC system provides very useful information about branching. Together with selective link destruction, it is a very powerful tool in the analysis of polymer architectures. Further analysis of various model architectures is in progress in our laboratories. 

Recently, Teymour and coworkers developed an interesting computational technique called the digital encoding for copolymerization compositional modeling [20,21], Their method uses symbolic binary arithmetic to represent the architecture of a copolymer chain. Here, each binary number describes the exact monomer sequence on a specific polymer chain, and its decimal equivalent is a unique identifier for this chain. Teymour et al. claim that the... 

Hysteresis Behavior. The hysteresis behavior of the HBIB triblock copolymers are given in Figure 13A and of that of the inverted HIBI block copolymer is given in Figure 13B. The difference in the behavior of these two series of block copolymers is tremendous. The origin of these differences are again directly related to the morphology and the architecture of the polymers. 

The architecture of macromolecules is another important synthetic variable. New materials with controlled branching sequences or stereoregularity provide tremendous opportunity for development. New polymerization catalysts and initiators for controlled free-radical polymerization are driving many new materials design, synthesis, and production capabilities. Combined with state-of-the-art characterization by probe microscopy, radiation scattering, and spectroscopy, the field of polymer science is poised for explosive development of novel and important materials. New classes of nonlinear structured polymeric materials have been invented, such as dendrimers. These structures have regularly spaced branch points beginning from a central point—like branches from a tree trunk. New struc-... 

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