Polystyrene/poly-4-vinylpyridine block polymer

So far, there have been only few reports about the synthesis of amphipolar polymer brushes, i.e. with amphiphilic block copolymer side chains. Gna-nou et al. [115] first reported the ROMP of norbornenoyl-endfunctionalized polystyrene-f -poly(ethylene oxide) macromonomers. Due to the low degree of polymerization, the polymacromonomer adopted a star-like rather than a cylindrical shape. Schmidt et al. [123] synthesized amphipolar cylindrical brushes with poly(2-vinylpyridine)-block-polystyrene side chains via radical polymerization of the corresponding block macromonomer. A similar polymer brush with poly(a-methylstyrene)-Wocfc-poly(2-vinylpyridine) side chains was also synthesized by Ishizu et al. via radical polymerization [124]. Using the grafting from approach, Muller et al. [121, 125] synthesized... 

The reactive end of a living polymer attacks a suitable group on a dead polymer Pji and grafts on Pjj as shown by Schreiber (15), who grafted living polystyrene on dead poly (methyl methacrylate). Such a procedure may lead to cross linking or to the formation of a loop, if both ends of the living polymer are active. Other block polymers prepared by this technique are polymers of styrene and ethylene oxide (14), polymers of styrene and dimethylsiloxanes (13), and polymers of styrene and vinylpyridine (16). 

The complexation of amphiphilic molecules with functionalized polymers forms layered smectic structures [94-97]. Polymeric complexes 41 consisting of poly(vinylpyridine) and an alkylphenol also form layered organized mesophases [94]. The incorporation of this structure into block copolymers with polystyrene results in the self-organization in two length scales, that is, block copolymer length and nanoscale length [95, 96]. 

The molecular weight of the reactive polymers, thus of the constitutive blocks of the compatibilizer, is also critical for efficient entanglements with the phases to be compa-tibilized. Indeed, good interfacial adhesion is essential for stress transfer from one phase to the other one to be efficient and for cracks initiated at the interface to be prevented from growth until catastrophic failure occurs. Kramer et al. studied the fracture mechanism of the polystyrene/poly(2-vinylpyridine) interface modified by the parent di-block copolymer. They found that the minimum degree of polymerization of PVP for entanglement (Npvp) was 255, below which the PVP block was pulled out in slow crack opening experiment [93, 94]. 

Polar monomers such as 2-vinylpyridine and methyl methacrylate are normally polymerized in polar solvents such as tetrahydrofuran and at low temperature (-78 °C). In addition, additives such as LiCl are often added to help lower the rates of termination reactions to levels insignificant in the time frame of the reaction. Block copolymers made with nonpolar and polar monomers start with the nonpolar monomer because of its greater reactivity. These active centers are then typically capped with 1,1-diphenylethylene to lower then-reactivity before the addition of the polar monomer. This helps eliminate side reactions resulting from addition of the active center to electrophilic sites in the polar monomers. The two polar polymers, polystyrene-2-vinylpyridine (PS-P2VP) and polystyrene-poly methyl methacrylate (PS-PMMA) have been extensively studied in thin films. 

Fig. 3 a-c. Summary of data from different laboratories, obtained by surface force measurement, on the average layer thickness L as a function of tethered chain length for flat, tethered layers constructed by adsorption of amphiphilic polymers on mica. Adapted from Ref. 21. (a) Data of reference 20 on poly-tert-butylstyrene chains anchored by adsorbing blocks of poly-2-vinylpyridine. (b) Data of references 11 and 12 on polystyrene chains anchored by adsorbing blocks of poly-2-vinylpyridine. (c) Data of references 13 and 14 on polystyrene chains anchored by adsorbing zwitterionic groups [13] or by small adsorbing blocks of polyethyleneoxide [14]... 

Another class of polymers capable of stabilizing Au NPs through physisorption is amphiphilic block copolymers. Initial reports describe the formation of Au NPs in the presence of different amounts of diblock copolymers like PS-P2VP (polystyrene-block -poly-2-vinylpyridine) [111] or PS-PEO (polystyrene-block-polyethyleneoxide) [112]. 

Similar polymers, slightly less perfect, are the umbrella star copolymers [101]. These polymers are based on a central polystyrene star with 25 arms. An average of five polybutadiene or poly(2-vinylpyridine) branches are grafted onto the end of each arm. Since these polymers are models for block copolymer micelles their properties have been studied in selective solvents. In particular, the PBd-PS umbrella-star copolymers are monomolecularly dissolved in non-solvents for the core-forming polystyrene. 

Self-assembled block copolymers are basically amphilic molecules which contain distinctively different polymers. This block copolymer contains two or more polymers quantitatively in the form of blocks. Some of the block copolymers are polyacrylic acid, polymethylacrylate, polystyrene polyethylene oxide, polybutadiene, polybutylene oxide, poly-2-methyloxazoline, polydimethyl sUoxane, poly-e-caprolactone, polypropylene sulfide, poly-A -isopropylacrylamide, poly-2-vinylpyridine, poly-2-diethylamino ethyl methacrylate, poly-2-(diisopropylamino) ethyl methacrylate, poly-2-(methacryloyloxy) ethyl phosphorylcholine, and polylactic acid. These copolymers contain more than polymers to form certain configurations like linear, branched, patterned. For example, if we take three polymers named A, B, and C, they can be combined to form arrangements AB, BA, AA, BAB, ABCAB, ABCABC, ABABAB, etc. in the form of branched configuration it forms (ABQa, (ABA)a, (AB)4, etc. Depending on the above-mentioned number of blocks, they are named as AB diblock copolymers, ABC triblock copolymers, ABC star block copolymers, etc. The covalent linkage between these different blocks of polymers makes macroscopic phase separation impossible, that is, in its place the phase separation... 

The IR spectra of all three polymers are recorded and compared with one another. The incorporation of monomeric tmits of 4-vinylpyridine can also be demonstrated by nitrogen analysis of the block copolymer. The solubility behavior is also determined. Poly(4-vinylpyridine) is soluble in pyridine, methanol, and chloroform, but insoluble in toluene and diethyl ether it swells considerably in water. On the other hand, the block copolymer, like polystyrene, is soluble in pyridine, chloroform, and toluene but unlike polystyrene, it swells significantly in methanol. 

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