Block polymer defined

A block polymer is a polymer comprising molecules in which there is a linear arrangement of blocks, a block being defined as a portion of a polymer molecule in which the monomeric units have at least one constitutional or configurational feature absent from the adjacent portions [4]. In a block copolymer, the distinguishing feature is constitutional, i.e. each of the blocks comprises units derived from a characteristic species of monomer. 

Oxazolines undergo polymerization upon exposure to a variety of cationic initiators such as strong Lewis acids or strong protic acids. Copolymerization between different oxazolines of defined composition can be carried out in a random manner or in a controlled fashion resulting in block polymers. Alternatively, oxazolines can also be grafted onto other types of polymers. It is beyond the scope of this chapter to review in detail this enormous and important subject. Instead, the... 

Copolymers with only short acrolein blocks can by synthesized. In these conditions, the formation of homopolyacrolelns can be avoided (differences between the PAI3 and the chromatograms Figures 1 and 7). In fact, it would better to define this approach as functionalization rather than block polymer synthesis. 

Anionic polymerization has been the usual route for this type of special synthesis. Cationic [9], catalytic [10], and group transfer [11] polymerizations have been developed to produce well-defined blocks from different classes of monomers. Perhaps the richest and most technologically useful future route to the production of these materials is via so-called telechelic [12] or functionalized polymers. Generically, this refers to block polymers in... 

A new process, which Involves the conversion of polymeric oxyl-llthlum to oxyl-aluminum chain end as modified ring-opening site for lactones, has proven to be very effective In eliminating trans-esterlflcatlons. Therefore, uniform block polymers containing styrene, butadiene, and e-caprolactone can be prepared with well defined structure ... 

Recent advances in polymer synthetic chemistry have allowed the development of elegant and more complicated architectural polymers. This has been driven predominantly by the development of various controlled polymerization methodologies, particularly in the area of free radical polymerization [45-49]. This has equipped the polymer chemist with a rich and abundant synthetic toolbox. In general, these architectural polymers are based on the principle of being able to sequentially add different polymeric blocks with defined molecular weight into a single polymer chain [50]. The synthesis of block copolymers is particularly suited to the combination of two different polymerization techniques. This can be quite easily achieved by the use of a bifunctional initiator and is an elegant synthetic... 

S-B-S and S-I-S. Much of our discussion will refer directly to data for S-B-S and S-I-S block polymers. We justify this on several counts. These block polymers can be clearly defined as to structures, molecular weights, and compositions. They have served as model systems for much of the recent work in block polymers. They also comprise the largest volume of commercial block polymers. Finally, we believe that the discovery (20) of the S-B-S and S-I-S thermoplastic rubbers which are strong, resilient rubbers without vulcanization, and the concomitant, readily understood theory (21). provided a paradigm (terminology of T. S. Kuhn (2 2)) that significantly accelerated the scientific work on these polymers in recent years. 

The Commission on Macromolecular Nomenclature defined 52 terms related to polymer structure, including polymer, constitutional units, monomer, polymerization, regular polymer, tactic polymer, block polymer, graft polymer, monomeric unit, degree of polymerization, addition polymerization, condensation polymerization, homopolymer. 

Stereoblock polymers are defined analogously to constitutional block polymers each block has a different species of stereorepeating unit to the block preceding it, but has the same constitutional monomeric units. Tactic... 

Deviations of the parameter a from the theoretical value may be due to small variations in local structural properties of the activated complex during the expulsion process. Here, factors like screening of solvent/core polymer contacts by the corona block and ill-defined core-corona interfaces might come into play. However, discrepancies could also arise from small uncertainties in the determination of polymer characteristics. However, these discrepancies are obviously system-specific and depend on selective solvent, type of block polymer, temperature, and degree of polymerization and are thus of minor relevance for the general understanding of equdibrium kinetics. From the experimental point of view, a more systematic study... 

If one leaves water and gold to organic solvents as a medium, the situation will change. Biopolymers and synthetic block polymers form ill-defined clusters, nanometer helices are replaced by micrometer twisted ribbons, and sheets immediately crystallize. In the case of micellar assemblies bilayer sheets prevail, showing a tendency to roll up and form bulky scrolls. 

Living polymerizations do not have either transfer or termination reactions, that is, the active chain carrier remains bound to an individual polymer chain up to the yield determined by the monomer-polymer equilibrium. The ionic ends of the living polymer can thus be used to produce block polymers of defined structure. This ability, however, depends on the polarity of the growing macroanion and the monomer to be added on. To a first approximation, the polarity can be described in terms of what is known as the e values of the two monomers. Electron-poor monomers have high e values and electron-rich monomers have strongly negative e values (see also Section 22.2.5). For example, the poly(methyl methacrylic anion) (monomer e = 0.40) starts the polymerization of acrylonitrile e = 1.20), but not that of styrene e = —O.SO). Conversely, however, the poly(styryl anion) can start the polymerization of methyl methacrylate. 

One of the key features of the RAFT polymerization is the potential functionalization capability by carefully selecting the functional substituent Z of the RAFT agent (see Fig. 2.25). Quemener et al. [110] developed a clickable (1,3-dipolar cycloaddition) azide and alkyne functionalized RAFT agents and weU-defined block polymers of vinyl acetate and styrene were prepared by combining RAFT polymerization and click chemistry. A similar combination of RAFT and click chemistry has been successfully evaluated to generate various block polymers for polymer- protein and drug conjugations [111]. 

Chain-growth catalyst-transfer polycondensation (CTP) is a rapidly developing polymerization method, as it allows, in many cases, the above-mentioned limitations of step-growth polymerizations to be overcome. CTP provides a straightforward access to well-defined conjugated homopolymers (e.g., polythiophenes (1), polyfluorenes (2), polyphenylenes (3), etc.), alternate donor-acceptor copolymer e.g., 4) and all-conjugated block polymers (e.g., 5), Chart 20.1. 

Over a period of about 50 years, representation of polymer structures, both on paper and in databases, has developed from a virtually random system to a highly organized and sophisticated one. Polyoners are represented sometimes by structure-based methods, sometimes by source-based methods, and sometimes by both. Both methods survive because each offers advantages and disadvantages. Both methods involve structural representation of polymers by a precisely defined set of rules developed over several decades by CAS, lUPAC, and the Committee on Nomenclature of the Division of Polymer Chemistry of the ACS. Areas still in need of improved representation are copolymers of imterminated SRU types aftertreated (post-treated) polymers, and dendritic (52), hyperbranched, hyper-cross-linked, star, and star-block polymers. Also needed are hierarchical relationships between intellectually related polymers (53). 

The differences in the IR and Raman spectra of random copolymers, block copolymers, and polymer mixtures, A and B , will be covered in a moment. It should be appreciated that it is difficult to distinguish between polymer mixtures of the form A - - B and block copolymers defined as A -B from either IR or Raman spectra, because the chemical bonding between species A and B is only one of many bonds within a polymer chain. Column chromatographic separation followed by IR or Raman spectral identification or a GPC-IR method [16] is needed to determine whether a sample is a block copolymer or a mixture. In the case of a random copolymer in which component B is very small, B is mixed into the A A chain sequence in the form -A -B-A ,-. While the IR and Raman spectra of the A sequences may stay essentially the same as the A homopolymer, the spectra of B in an... 

Immobilized Ligands and Precatalysts Several attempts have been made to link NHCs or their corresponding rhodium complexes to sohd surfaces in order to recycle the valuable metal complexes after a first catalytic run. Weberskirch and coworkers [56] immobihzed an NHC—rhodium complex to a water-soluble block polymer (Scheme 2.164). The molecular defined rhodium complex was prepared by a two-step protocol. First, 1-methyhmidazol was alkylated with 2-bromoethanol to produce the imidazohum bromide. Following the protocol of Herrmann, 2 equiv of this salt was treated subsequently with [RhCl(COD)]2 and KOtBu in a mixture of methanol and THF (3 1) to produce the rhodium complex as yellow crystals [57]. 

In conclusion, the well-defined organometallic amphiphilic AB block copolymer of PFS-PDMAEMA and ABC block polymers of PFP-i-PFS- -PDMS were synthesized via anionic ROP approach. ... 

Albagli, D., G. C. Bazan, R. R. Schrock, and M. S. Wrighton. 1993. Surface attachment of well-defined redox-active polymers and block polymers via terminal functional-groups. (16) 7328-7334. 

By controlling the ligands and additives, these systems opened the way to the synthesis of a wide array of homo and block polymers of well-defined structures. Polymers with PDIs of less than 1.1 that contained a variety of functional groups were routinely prepared using these initiators. 

Based on work with aqueous mthenium-based metathesis systems, stable, active, and well-defined ruthenium metathesis catalysts were developed. As will be demonstrated, the early promise of broadly functional group-tolerant and water-tolerant initiators based on mthenium have been realized. The first complex, 10, was not particularly reactive, but would polymerize norbomene and its derivatives. These complexes were much more stable to functional groups, water, and oxygen than prior systems. It was demonstrated that these systems would give a living polymer with norbomene and could be used to form block polymers. ... 

---