Styrene-2-vinylpyridine block copolymer

The additional complexity present in block copolymer synthesis is the order of monomer polymerization and/or the requirement in some cases to modify the reactivity of the propagating center during the transition from one block to the next block. This is due to the requirement that the nucleophilicity of the initiating block be equal or greater than the resulting propagating chain end of the second block. Therefore the synthesis of block copolymers by sequential polymerization generally follows the order dienes/styrenics before vinylpyridines before meth(acrylates) before oxiranes/siloxanes. As a consequence, styrene-MMA block copolymers should be prepared by initial polymerization of styrene followed by MMA, while PEO-MMA block copolymers should be prepared by... 

Figure 19 Metastable cylindrical micelles from poly(styrene-i-2-vinylpyridine) block copolymer [222]...

It is important that a nucleus can undergo cross-linking in the case of styrene and 2-vinylpyridine block-copolymers (e.g. by 1,4-diiodobutane) [75]. The monodispersed microspheres formed have a lamellar morphology with a... 

Ramakrishnan, A., and Dhamodharan, R. (2000). A novel and simple method of preparation of poly(styrene-b-2-vinylpyridine) block copolymer of narrow molecular weight distribution living anionic polymerization followed by mechanism transfer to controlled/iivingc radical polymerization (ATRP). J. Macromol. ScL, Pure Appl. Chem., A37(6) 621-631. 

In an effort to create model surfaces to correlate the conformations of the polymers with the measured interactions, we have been examinming the interactions between layers of 2-vinylpyridine(PVP)-styrene(PS) block copolymers adsorbed onto mica substrates (in the surface force apparatus). " In these systems, we observed repulsive forces at distances many ( 10) times larger than the dimension of those polymers in solutions. In particular, we found that the distance at which the repulsive force becomes significant is a linear function of PS-block length. 

A number of methods such as ultrasonics (137), radiation (138), and chemical techniques (139—141), including the use of polymer radicals, polymer ions, and organometaUic initiators, have been used to prepare acrylonitrile block copolymers (142). Block comonomers include styrene, methyl acrylate, methyl methacrylate, vinyl chloride, vinyl acetate, 4-vinylpyridine, acryUc acid, and -butyl isocyanate. 

Application of amphiphilic block copolymers for nanoparticle formation has been developed by several research groups. R. Schrock et al. prepared nanoparticles in segregated block copolymers in the sohd state [39] A. Eisenberg et al. used ionomer block copolymers and prepared semiconductor particles (PdS, CdS) [40] M. Moller et al. studied gold colloidals in thin films of block copolymers [41]. M. Antonietti et al. studied noble metal nanoparticle stabilized in block copolymer micelles for the purpose of catalysis [36]. Initial studies were focused on the use of poly(styrene)-folock-poly(4-vinylpyridine) (PS-b-P4VP) copolymers prepared by anionic polymerization and its application for noble metal colloid formation and stabilization in solvents such as toluene, THF or cyclohexane (Fig. 6.4) [42]. 

To 5.3 g of 4-vinylpyridine is added to THE up to a volume of 50 ml 5 ml of this solution (containing 5 mmol 4-vinyl pyridine) are added in the same way to the above solution containing the "living" polystyrene, with vigorous agitation. After 15 min another 40 mmol of styrene are added, followed 15 min later by another 5 mmol of 4-vinylpyridine this operation is repeated once more. 15 min after the last addition of monomer the block copolymer is precipitated by dropping the solution into a mixture of 300 ml of diethyl ether and 300 ml of petroleum ether.The polymer is filtered, washed with ether,filtered again, and dried in vacuum at room temperature. 

Gold nanoparticles coated by short thiol end functional polystyrene homopolymers (PS-SH) can be incorporated into a poly(styrene-fo-2-vinylpyridine) diblock copolymer template (PS-NP2VP). It has been found that the surface density of PS chains on the gold particles is critical in controlling their location in block copolymer templates [95]. 

Au NPs have been synthesized in polymeric micelles composed of amphiphilic block copolymers. Poly(styrene)-block-poly(2-vinylpyridine) in toluene has been used as nanocompartments loaded with a defined amount of HAuCl4 and reduced with anhydrous hydrazine. The metal ions can be reduced in such a way that exactly one Au NP is formed in each micelle, where each particle is of equal size between 1 and 15 nm [113]. In another example, the addition of HAuCfi to the triblock copolymer (PS-b-P2VP-b-PEO) (polystyrene-block-poly-2-vinyl pyridine-block-polyethylene oxide) permits the synthesis of Au N Ps using two different routes, such as the reduction of AuC14 by electron irradiation during observation or by addition of an excess of aqueous NaBH4 solution [114]. 

Among copolymers containing isoprene, AB and ABA block copolymers of styrene and isoprene have been the most studied, but interesting results have also been obtained with copolymers of isoprene and vinylpyridine and of isoprene and methyl methacrylate. 

P(S VPD) P(S-b-BR) PSA PSBMA poly(styrene-co-4-vinylpyridine) styrene-butadiene rubber block copolymer poly(sodium acrylate) poly(sec-butyl methacrylate)... 

In similar approach it was possible to obtain cadmium sulfide nanocrystals in block copolymer micelles of poly(styrene-b-2-vinylpyridine) [240-242], Further approaches have been described recently by Antonietti [243],... 

In another report, a 50 nm thick poly(styrene-h-methylmethacrylate) block copolymer film with spherical domains was prepared on a sodium chloride monocrystal and coated by a thin layer of gold, replicating the domain pattern. Similar results were also obtained with poly(styrene-h-2-vinylpyridines) [113]. 

With the purpose of increasing the range of available block copolymers, comonomers other than methacrylates and acrylates can also be involved in sequential polymerization, provided that they are susceptible to anionic polymerization. Dienes, styrene derivatives, vinylpyridines , oxiranes and cyclosiloxanes are examples of such comonomers. The order of the sequential addition is, however, of critical importance for the synthesis to be successful. Indeed, the pX a of the conjugated acid of the living chain-end of the first block must be at least equal to or even larger than that of the second monomer. Translated to a nucleophilicity scale, this pK effect results in the following order of reactivity dienes styrenes > vinylpyridines > methacrylates and acrylates > oxiranes > siloxanes. 

Mesophases prepared by dissolution of the copolymer in a preferential solvent for the poly(vinylpyridine) block (acrylic acid, nitromethane, dfoxane, octanol, methylethyl ketone, ethyl acetate, vinyl acetate, styrene and methyl methaaylate) and dry copolymers obtained by slow evaporation of the solvent from the mesophases have been studied by low-angle X-r diffraction electron microscopy Copolymers of isoprene and vinylpyridine exhibit cylindrical hexagonal or lamellar structures dependii upon their comi siton.The influence of the nature, concentration, and polymerization of the solvent, molecular weight and composition of the copolymer, microstructure of the polyisoprene block, and position of the nitrogen atom in the vinylpyridine block on the values of the geometrical parameters of the periodic structures have been establidied ... 

The radical nature of nitroxide-mediated processes also allows novel types of block copolymers to be prepared in which copolymers, not homopolymer, are employed as one of the blocks. One of the simplest examples incorporate random copolymers124 and the novelty of these structures is based on the inability to prepare random copolymers by living anionic or cationic procedures. This is in direct contrast to the facile synthesis of well-defined random copolymers by nitroxide-mediated systems. While similar in concept, random block copolymers are more like traditional block copolymers than random copolymers in that there are two discrete blocks, the main difference being one or more of these blocks is composed of a random copolymer segment. For example, homopolystyrene starting blocks can be used to initiate the copolymerization of styrene and 4-vi-nylpyridine to give a block copolymer consisting of a polystyrene block and a random copolymer of styrene and 4-vinylpyridine as the second block.166... 

TEMPO, />substituted TEMPO based alkoxyamines 3, and compounds such as 4, 5, and 7 have been applied successfully for polymerizations of styrene, substituted styrenes, and 4-vinylpyridine, and some copolymerizations and block copolymerizations were reported. However, living and controlled radical polymerization of other monomers, especially acrylates, require the use of the more recently developed structures 6, 8, or 9. These also yield well-controlled and living block copolymers, but methacrylates have so far resisted all efforts to obtain large conversions. Undoubtedly, many failures are due to unfavorable rate constants or side reactions. 

---