Preparation via anionic polymerization

Fig. 16. Correlation of S in mL of sorbed liquid per gram of poly(Sty-Wock-DVB) (prepared via anion polymerization by Rempp [143] in 1970) with the corresponding calculated cube root of the number of backbone carbon atoms in the polystyrene segments between nodules of DVB...

After these initial considerations, the complete analysis of a number of diblock copolymers of styrene and methyl methacrylate shall be discussed in detail. The poly(styrene-ftlodc-methyl methacrylate)s under investigation were prepared via anionic polymerization of styrene and subsequent polymerization of methyl methacrylate, varying molar mass and composition (B1-B3). The polystyrene precursors (P1-P3) were isolated and characterized separately. As the PMMA block is the more polar block in the block copolymer, a polar (silica gel) column was chosen for establishing the critical point of PMMA. According to case (1) in Fig. 14, the PS block is then eluted in the SEC mode. The behavior of PMMA of different molar masses on silica gel Si-100 in eluents comprising methylethylketone and cyclohexane is shown in Fig. 15A [37]. 

Typically, the rates of initiation and propagation in an anionic polymerization are rapid, with the consequence that mixing of the initiator and monomer, or of the monomer-containing solution, may be detrimental to the resultant polymer product The most notable, and important, features of polymers prepared via anionic polymerization are their low polydispersity and stoichiometry. 

Amphiphilic miktoarm stars of the typ>e ABC, where A is polyethylene (PE), B is polyethylenoxide (PEO), and C is poly(perfluoropropylene oxide), were also prepared via anionic polymerization, using arm in-out methodology " (Scheme 16). At the first step of the synthetic process, anioni-cally prepared PBd was temunated with a heterobifunctional proteaed agent. The resulting hydroxyl end-functionalized PBd was then hydrogenated to an end-functionalized polyethylene (PE) block, which served as a macroinitiator (Ml) for anionic... 

A final arm-first method based on the preparation via anionic polymerization of star-shaped polymers will be mentioned. Here the anionic polymerization is only used to prepare a linear (D-fimctional polymer of controlled molar mass and functionality and not for the coupling reaction. In many cases, anionic polymerization is the only way to access these well-defined monofunctional precursor chains. In a second step, these functional polymers were reacted with plurifunctional compounds exhibiting antagonist functions. Some examples are given below. 

Functional polysiloxanes were also prepared via anionic polymerization of cycles with three or four SiO(CH3)R units, where R = CH2CH2CF3 [170], phenyl [171] or vinyl [172]. Similar kinetic features as for the anionic polymerization of D4 were... 

Detailed procedures for the synthesis ofa,o>-organofunctionally terminated siloxane oligomers with well defined structures have been given 50,66-67). Tables 6 and 7 provide the data on the synthesis and characteristics of aminopropyl and hydroxybutyl terminated polydimethylsiloxane oligomers prepared via anionic and cationic ringopening polymerization of octamethylcyclotetrasiloxane (D in the presence of appropriate disiloxanes, respectively. 

The synthesis of well-defined LCB polymers have progressed considerably beyond the original star polymers prepared by anionic polymerization between 1970 and 1980. Characterization of these new polymers has often been limited to NMR and SEC analysis. The physical properties of these polymers in dilute solution and in the bulk merit attention, especially in the case of completely new architectures such as the dendritic polymers. Many other branched polymers have been prepared, e.g. rigid polymers like nylon [123], polyimide [124] poly(aspartite) [125] and branched poly(thiophene) [126], There seems to be ample room for further development via the use of dendrimers and hyperbran-... 

Nylon 6 two-armed and three-armed systems prepared via anionic bulk polymerization had different characteristics than their linear counterparts. While little differences were found In IR and NMR spectra, changes In performance characteristics were discovered. 

Summary PDMS-6-PEO short-chain diblock copolymers were prepared via anionic ring-opening polymerization of cyclosiloxanes. Applying this method, various well-defined block copolymers with different compositions were synthesized and their phase behavior was investigated. The polymers predominantly showed lamellar phases in aqueous solutions. At small surfactant concentrations, vesicles were formed, as observed via cryogenic TEM. The aggregates of the diblock copolymers were used for the formation of lamellar thin films, applying the evaporation-induced self-assembly approach. 

Polypyrrole Apolymer of pyrrole, afive-membered heterocyclic substance with one nitrogen and four carbon atoms and with two double bonds. The polymer can be prepared via electrochemical polymerization. Polymers thus prepared are doped by electrolyte anion and are electrically conductive. Polypyrrole is used in lightweight secondary batteries, as electromagnetic interference shielding, anodic coatings, photoconductors, solar cells, and transistors. 

Cyclic ethers such as EO and other related monomers can be used in the synthesis of block copolymers via anionic polymerization as well. Block copolymers of EO and 2-alkyl oxazolines were prepared and their antielectrostatic properties were evaluated in their blends with Nylon 6 a,co-Ditosylated or... 

Iniferter polymerizations were also combined with anionic polymerization. The representative example involves the synthesis of PCL-l7-(PMMA-co-PSt)-l7-PCL. ° A polymeric thermal iniferter, PCL-substituted tetraphenylethane, was prepared by anionic polymerization of CL in the presence of aluminum triisopropoxide and benzopinacol. The benzopinacolate groups incorporated into the polymer chain initiated the polymerization of St and MMA via a controlled radical mechanism at 95 °C to yield the desired block copolymers (Scheme 47)... 

Halasa, A, (1997) Preparation and characterization of solution SIBR via anionic polymerization. Rubber Chem. TechnoL, 70, 295. 

It is also possible to prepare vinylpyridine-based (co)polymers in a controlled fashion with predetermined molecular weights and narrow molecular weight distributions. For example, the controlled pol5mierization of 16C and 18C is possible via anionic polymerization (197-201). 

Hydrogel preparation. pHEMA and its copolymers containing various anionic residues were prepared via radical polymerization as previously reported. [6] The formed gels were washed extensively with water to ensure the complete removal of unreacted monomers before they were used for mineralization and further physical characterizations. 

Use of polymers prepared with narrow molecular weight distributions, such as via anionic polymerization. 

In this section, we present the dispersion characteristics and rheology of end-functionalized polymers investigated by Zha et al. (2005). In their study, a PS and an SI diblock copolymer were synthesized via anionic polymerization. Then, the chain end of the PS was carboxylated to obtain end-fimctionalized PS-t-COOH, and the chain end of the PI block in the SI diblock copolymer was carboxylated to obtain end-functionalized SI-t-COOH. Subsequently, both PS-t-COOH and SI-t-COOH were neutralized using sodium hydroxide (NaOH) to obtain PS-t-COONa and SI-t-COONa. Each of the end-functionalized polymers was mixed with Cloisite 30B or Cloisite 20A to prepare nanocomposites. Table 12.2 gives sample codes of the eight organoclay nanocomposites prepared. 

Anionic polymerization is a well-established method for the synthesis of tailored block copolymers. The first anionic polymerizations of block copolymers were conducted as early as 1956 [6]. To prepare well-defined polymers, the technique is demanding, requiring high-purity starting reagents and the use of high-vacuum procedures to prevent accidental termination due to the presence of impurities. In the lab, it is possible to achieve polydispersities M /Mn < 1.05 via anionic polymerization. The method is also used industrially to prepare... 

PSt -co-PCMS copolymers were synthesized via the same procedure as shown in Scheme 3.44. The reactivity ratio of CMS St for the LFRP is evidently the same as for conventional radical polymerization, and the chlorine atoms are randomly distributed along the PSt backbone. The coupling reaction of PSt-co-PCMS with an excess of about 50% DPE-terminated polyisoprenylithium, which was prepared by anionic polymerization of isoprene with BuLi as initiator, followed by termination upon addition of DPE into the polymerization... 

---