Styrene/4-vinyl pyridine block copolymer

Figure 6.17. The excess of styrene-2-vinyl pyridine block copolymer at a polystyrene/ poly(2-vinyl pyridine) interface, determined by forward recoil spectrometry. The degrees of polymerisation of the styrene and vinyl pyridine blocks were 391 and 68, respectively. The solid line is the prediction of self-consistent field theory, assuming a value for the Flory-Huggins interaction parameter %ps-pvp of 0.11. After Shull et al. (1990).

Figure 6.18. Interfacial tension between polystyrene and poly(vinyl pyridine) in the presence of styrene-2-vinyl pyridine block copolymer, as calculated by self-consistent field theory for the system whose interfacial excess is shown in figure 6.17. The value of the Flory-Huggins interaction parameter Xps-pvp was taken as 0.11, which provides a good fit to the adsorption isotherm below the CMC. After Shull et al. (1990).

Figure 7.4. Fracture energies of interfaces reinforced by block copolymers as a function of the effective areal density of chains crossing the interface. Triangles and squares are for polystyrene/poly(2-vinyl pyridine) interfaces reinforced with styrene-2-vinyl pyridine block copolymers (Creton et al. 1992) circles are for poly(xylenyl etherypoly(methyl methacrylate) interfaces reinforced with styrene-methyl methacrylate block copolymers (Brown 1991a, b). After Creton et al. (1992).

Figure 6.16. Segregation of a deuterium-labelled styrene-vinyl pyridine block copolymer to an interface between polystyrene and poly(vinyl pyridine), revealed by forward recoil spectrometry. The block copolymer was initially imiformly distributed in the upper, polystyrene film after annealing for 8 h at 178 °C an interfacial excess of 100 A has developed. After Shull etal. (1990).

Figure 7.9. Interfacial reinforcement of a polystyrene/poly(vinyl pyridine) interface by a high relative molecular mass deuterated styrene-vinyl pyridine block copolymer, with degrees of polymerisation of each block 800 and 870, respectively. Circles (right-hand axis) show the measured interfacial fracture energy as a function of the areal chain density of the block copolymer 2, whereas crosses show the fraction of dPS found on the polystyrene side of the interface after fiacture. The discontinuity in the curves at 2 = 0.03 nm is believed to reflect a transition from failure by chain scission to failure by crazing. After Kramer et al. (1994).

Figure 3.38. Force-displacement curves measured for interactions between a scanning force microscope s tip and a layer of styrene-4-vinyl pyridine block copolymer (the degrees of polymerisation of the styrene and 4-vinyl pyridine blocks were 200 and 20, respectively) in toluene. The solid curve is the prediction of self-consistent field theory. After Ovemey et al. (1996).

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]. 

As previously described, all microspheres discussed in this chapter were synthesized from AB type diblock copolymers. Precursor block copolymers, poly(styrene-b-4-vinyl pyridine) (P[S-b-4VP]) diblock copolymers, were synthesized using the additional anionic polymerization technique [13]. The basic properties of the block copolymers were determined elsewhere [24,25] and are listed... 

The poly(styrene-b-isoprene) (P(S-b-IP)) and poly(-styrene-b-2-vinyl pyridine) (P(S-b-2VP)) block copolymers with narrow molecular weight distributions for blending with the microspheres were also synthesized using the additional anionic polymerization technique. The number-average molecular weights (Mns) and PS contents are also shown in Table 1. 

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. 

C) Block Copolymers Without Polydiene Blocks 1) Copolymers of Styrene and Vinyl-2- or 4-Pyridine... 

Catalysts of the Ziegler-Natta type are applied widely to the anionic polymerization of olefins and dienes. Polar monomers deactivate the system and cannot be copolymerized with olefins. J. L. Jezl and coworkers discovered that the living chains from an anionic polymerization can be converted to free radicals by the reaction with organic peroxides and thus permit the formation of block copolymers with polar vinyl monomers. In this novel technique of combined anionic-free radical polymerization, they are able to produce block copolymers of most olefins, such as alkylene, propylene, styrene, or butadiene with polar vinyl monomers, such as acrylonitrile or vinyl pyridine. 

The following sections detail the literature reports pertaining to the synthesis of block copolymers using nitroxide-mediated polymerization techniques. The sections are organized according to monomer type and generally follow the historical development of the particular subsection. Most literature on nitroxide mediated preparation of block copolymers is found for the styrene-based monomers, and is summarized first. This is followed by acrylates and dienes, as they were the next monomers to be studied. These sections are followed by more recent work with vinyl pyridine, acrylamides, and maleic anhydride. The final section deals with methacrylates. This is presented last to stress the importance of developing new nitroxides that can successfully be used for the homopolymerization of methacrylate-based monomers. 

Due to the low solubility of poly(4-vinyl pyridine) in THF, a block copolymer of 4-vinyl pyridine with styrene has been used (Mn = 13,500). Living polyTHF (Mn = 3,300) has been grafted with efficiencies higher than 95 %. About 20 % of the pyridine units were consumed, yielding a graft copolymer with 80% polyTHF. No further data on this product were reported. 

The experimental results that will be examined consist of studies that look at the ability of a random copolymer to improve the properties of mixtures of the two homopolymers relative to the ability of a block copolymer. The three different systems that are examined include copolymers of poly(styrene-co-methyl methacrylate) (S/MMA), poly(styrene-co-2-vinyl pyridine) (S/2VP), and poly(styrene-co-ethylene) (S/E) in mixtures of the two homopolymers. The experiments that have been utilized to examine the ability of the copolymer to strengthen a polymer blend include the examination of the tensile properties of the compatibilized blend and the determination of the interfacial strength between the two homopolymers using asymmetric double cantilever beam (ADCB) experiments. 

Gallot has described the synthesis of poly(butadiene-b-vinyl naphthalene)while Szwarc has prepared p-xylylene block copolymers containing vinyl pyridine or styrene. These latter copolymers are prepared by producing p-xylylene vapor in the presence of "living" polystyrene or vinyl pyridine anions, or by the novel reaction of vinyl pyridine with p-xylylene radicals Block copolymers of ferrocenylmethyl methacrylate have also been prepared( 0). 

Early reports of the preparation of nano-objects from bulk assembly of block copolymers focused on the synthesis of spherical nanostmctures. The versatility of the technique toward polymers of varied compositions was demonstrated by Ishizu et al. through the use of several polymeric systems including poly(styrene)-btocfe-poly(4-vinyl pyridine). 

It has been shown by Angier and Watson [A8, W2] that if an elastomer is swollen with a vinyl monomer (styrene, chlorostyrene, acrylic acid, methyl acrylate, methacrylic acid, methyl methacrylate, vinyl pyridine, methyl vinyl ketone, etc.), mastication in the absence of oxygen can lead to the formation of block copolymers. This would seem to occur through the mechanism... 

This technique allows formation of many different types of block copolymers [437]. Lithium metal can be used to initiate polymerizations in solvents of varying polarity. Monomers, like styrene, a-methylstyrene, methyl methacrylate, butyl methacrylate, 2-vinylp3Tidine, 4-vinyl pyridine, acrylonitrile, and methyl acrylate, can be used. The mechanism of initiation depends upon formation of ion-radicals through reactions of lithium with the double bonds ... 

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