Controlled Polymerization Techniques

Previous sections discussed the micellization behavior of AB or ABA linear block copolymers. With the recent progress achieved in the field of controlled polymerization techniques, more sophisticated block copolymer architectures are now available. Investigation of the micellization behavior of such... 

The discovery of new controlled polymerization techniques in the mid-1990s and the progress achieved in living polymerization toward well-defined block copolymers with complex topologies have certainly played a key role in the development of block copolymer micelles. 

More specific libraries, such as polymer thin film (gradient) libraries or libraries prepared via controlled polymerization techniques, are not part of this overview, but will be discussed in detail in other chapters of this book [94, 95],... 

Apart from ATRP, the concept of dual initiation was also applied to other (controlled) polymerization techniques. Nitroxide-mediated living free radical polymerization (LFRP) is one example reported by van As et al. and has the advantage that no further metal catalyst is required [43], Employing initiator NMP-1, a PCL macroinitiator was obtained and subsequent polymerization of styrene produced a block copolymer (Scheme 4). With this system, it was for the first time possible to successfully conduct a one-pot chemoenzymatic cascade polymerization from a mixture containing NMP-1, CL, and styrene. Since the activation temperature of NMP is around 100 °C, no radical polymerization will occur at the reaction temperature of the enzymatic ROP. The two reactions could thus be thermally separated by first carrying out the enzymatic polymerization at low temperature and then raising the temperature to around 100 °C to initiate the NMP. Moreover, it was shown that this approach is compatible with the stereoselective polymerization of 4-MeCL for the synthesis of chiral block copolymers. 

Enzymatic polymerizations have been established as a promising and versatile technique in the synthetic toolbox of polymer chemists. The applicability of this technique for homo- and copolymerizations has been known for some time. With the increasing number of reports on the synthesis of more complex structures like block copolymers, graft copolymers, chiral (co)polymers, and chiral crosslinked nanoparticles, its potential further increases. Although not a controlled polymerization technique itself, clever reaction design and integration with other polymerization techniques like controlled radical polymerization allows the procurement of well-defined polymer structures. Specific unique attributes of the enzyme can be applied... 

Therefore, we searched for amphiphilic polymers that are available, through preparative methods, in various compositions via controlled polymerization techniques. In this report we... 

A possible way to overcome the hurdle of intrinsic defects could be synthesizing strictly linear, defect-free polymers with the use of modern, precisely controlled polymerization techniques and utilizing them as starting materials for dehydrohalogenation. 

Generally, there are two strategies to prepare star polymers the core-first strategy [37-44], and the arm-first strategy [45-52], The arm-first strategy starts with the linear arms first. Since the arms are prepared separately, many living/controlled polymerization techniques can be employed. Thus, the linear arms can be synthesized in a defined manner. Then one of the chain ends will be functionalized for further crosslinking reactions. Based on the functionalities of the chain ends, the arm-first methods can be divided into macroinitiator (MI) method and macromonomer (MM) method. 

For the grafting of the side chains, different controlled polymerization techniques were also applied. In addition to the rare cases of ring-opening polymerizations... 

Controlled polymerization techniques have enabled the preparation of well-defined polyelectrolytes of different architectures. Polyelectrolyte stars and cylindrical brushes are two typical examples with isotropic and anisotropic nature, respectively. Different synthetic strategies have been developed for these polyelectrolytes. However, the core first and grafting from strategies have turned out to be the most suitable methods for the synthesis of polyelectrolyte stars and cylindrical brushes. 

Since the discovery of living polymerizations by Swarc in 1956 [1], the area of synthesis and application of well-defined polymer structures has been developed. The livingness of a polymerization is defined as the absence of termination and transfer reactions during the course of the polymerization. If there is also fast initiation and chain-end fidelity, which are prerequisites for the so-called controlled polymerization, well-defined polymers are obtained that have a narrow molar mass distribution as well as defined end groups. Such well-defined polymers can be prepared by various types of living and controlled polymerization techniques, including anionic polymerization [2], controlled radical polymerization [3-5], and cationic polymerization [6, 7]. 

Since the development of soft ionization mass spectrometry [9], which allows to analyze large organic molecules without fragmentation, various polymer architectures were characterized by mass spectrometry. In principle, different parameters tailoring polymeric material properties such as molar mass (MJ, architecture (linear, branched, cyclic, star, etc.), monomer composition, degree of functionalization, end groups, and the presence of impurities or additives can be evaluated by mass spectrometry, however, with some limitations. The determination of molar masses of polymers by mass spectrometry is only possible for reasonable low dispersity polymeric architectures, which can be achieved by using controllable polymerization techniques such as anionic or... 

Synthetic glycopolymers of various architectures have been prepared in recent years using the fast development of controlled polymerization techniques and the very efficient coupling reactions in polymer analogous approaches. Both, linear and globular polymer structures that have been obtained by synthesizing dendritic, starlike, or micelle-like structures or nanogels have received much attention. 

The synthesis of a variety of linear diblock DHBCs structures has been realized by the vast majority of the so called controlled polymerization techniques. Herein, we describe recent achievements in the synthesis of DHBCs categorized according to the followed polymerization mechanism. 

The latest advances in controlled polymerization techniques have enabled the preparation of well-defined polymer cylinders of different morphologies. In terms of chemical compositions and architectures, CPBs with linear side chains can be classified into several main group structures (Figure 10.1). The fundamental structure is the homopolymer CPB (Figure 10.1a) based on this simple model, more complex and functional CPBs have been designed and synthesized. 

Living /controlled polymerization techniques are the most convenient and efficient methodologies to prepare various types of block copolymers. Four main synthetic routes have been developed (Figure 1) in order to prepare well-defined model diblock copolymers exhibiting low compositional and molecular heterogeneity. 

Synthesis of Rod-Coil Block Copolymers using Two Controlled Polymerization Techniques Simone Steig, Frauke Cornelius, Andreas Heise, Rutger J. I. Knoop, Gijs J. M. Habraken, Cor E. Koning, Henning Menzel ... 

Synthesis of Rod-Coil Block Copolymers using Two Controlled Polymerization Techniques... 

Living or controlled polymerization techniques have also been frequently used for the in-situ synthesis of polymer nanocomposites. Figure 1.20 shows the example of styrene polymerization in the presence of modified filler. The filler modification consisted of ammonium cation bearing a notroxide moiety [44]. Styrene was polymerized in bulk at 125 °C for 8h. No diffraction peaks were observed in the XRD confirming extensive exfoliation of the filler. TEM micrographs also confirmed the uniform distribution of filler in the matrix. Generation... 

PS nanocomposites, including bulk free radical plymerization, solution and emulsion polymerizations, as well as controlled polymerization techniques such as RAFT, NMP, and ATRP. 

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