Poly interface with polystyrene, diblock copolymers

The interfacial properties of an amphiphilic block copolymer have also attracted much attention for potential functions as polymer compatibilizers, adhesives, colloid stabilizers, and so on. However, only a few studies have dealt with the monolayers o well - defined amphiphilic block copolymers formed at the air - water interface. Ikada et al. [124] have studied monolayers of poly(vinyl alcohol)- polystyrene graft and block copolymers at the air - water interface. Bringuier et al. [125] have studied a block copolymer of poly (methyl methacrylate) and poly (vinyl-4-pyridinium bromide) in order to demonstrate the charge effect on the surface monolayer- forming properties. Niwa et al. [126] and Yoshikawa et al. [127] have reported that the poly (styrene-co-oxyethylene) diblock copolymer forms a monolayer at the air - water... 

Three homopolymer (diblock copolymer) phase boundary systems have been studied extensively the system of polystyrene (PS) and poly(2-vinylpyridine) (PVP) reinforced with diblock copolymers ofPS-PVP [22,25,28,31-33], the system of poly(methyl methacrylate) (PMMA) and PS reinforced with diblock copolymers of PMMA-PS [17,24,34,35] and the system of PMMA and poly(phe-nylene oxide) (PPO) reinforced by diblock copolymers of PMMA-PS [ 14,36,37]. Phase boundaries between PS and a crosslinked epoxy (XEp) were reinforced with carboxy-terminated PS chains whose -COOH ends reacted with either excess amines or epoxy to form a grafted brush at the interface [38,39]. In a similar manner, interfaces between rubber-modified PS (HIPS) and XEp reinforced with grafted PS-COOH chains have been investigated [40]. 

First experiments which focused on the variation of the conformational properties have been performed by Brown et al. [240], who studied the role of the interactions between matrix and brush polymers (enthalpy driven brush swelling, see Eq. 59). They used a series of polystyrene (PS)-poly(methyl methacrylate) (PMMA) symmetric diblock copolymers with different blocks labeled by deuterium, placed at the interface between PMMA and poly(2,6-dimethylphenylene oxide) (PPO) homopolymers. A double brush layer was created with PMMA blocks dangling into (neutral) PMMA homopolymer and PS blocks immersed in favorably interacting PPO melt (x=Xps/ppo<0)- The SIMS profiles obtained showed that the PS side of the block copolymer is stretched by at least a factor of 2 with respect to the PMMA side. 

The first set of experiments that will be considered has examined the ability of random copolymers of styrene and methyl methacrylate to improve the interfacial strength between polystyrene and poly(methyl methacrylate). Using the asymmetric double cantilever beam technique, the researchers have found that a diblock copolymer (50/50 composition, Mw = 282,000) creates an interface with strength of400 J/m2. When utilizing a random copolymer however, it was found that the strongest interface (70% styrene, Mw =... 

Since this fluorescent labeling methodology is a living functionalization reaction, the resulting living fluorescent-labeled polymers can be used to initiate the polymerization of a second monomer to produce a block copolymer with the label at the block interface as discussed previously. For example, this procedure has been used to prepare polystyrene-Wock-poly(ethylene oxide) copolymers with both pyrene (60) (see Scheme 23) and naphthalene fluorescent groups at the interface between the two blocks [180-182]. Lithium was used as the counterion to prepare well-defined, quantitatively-ethylene oxide-functionalized polystyrenes in benzene solution [183]. However, under these conditions, it is not possible to polymerize ethylene oxide [183]. Therefore, it was necessary to add either dimethylsulfoxide [180, 181] or a potassium alkoxide [182] to promote ethylene oxide block formation as shown in Scheme 23. These diblock copolymers were fractionated to obtain pure diblock copolymer... 

Figure 42 SFM height Images of topographical features that appear in ordered symmetric polystyrene-b/oc/r-poly(methyl methacrylate) diblock copolymer thin films on silicon substrates as a function of proportionality of the film thickness (h) to the lamellae periodicity (/.). n is an integer. Adapted and reprinted with permission from Green, P. F. Limary, R. Adv. Colloid Interface Sci. 2001, 94,53-81...

Figure 2 Phase selectivity in polymer-templated self-assembly, (a) Schematic of a diblock copolymer mixture and a nanopartide similar to those of the experiments in References 87 and 88 and simulations in Reference 89. (b) Schematic of nanopartides that prefer to be in the center of the BCP domain, (c) TEM image of nanopartides coated entirely with polystyrene (PS) in a PS-poly(vinylpyridine) (PVP) BCP film, where nanopartides prefer to be at the center of the PS domain, and (d) the associated histogram of the nanopartides location within the BCP. (e) Schematic of nanopartides that prefer the domain interface, (f) TEM image of nanopartides coated with a 20% PVP 80% PS in a PS-PVP BCP film that prefer the domain interface and (g) the associated histogram of nanopartides location. The nanopartide surface coating dictates the behavior seen in parts (b)-(g). Reprinted with permission from Chiu, J. J. Kim, B. J. Kramer, E. J. Pine, D. J. J. Am. Chem. Soc. 2005, 127 (14), 5036-5037. Copyright 2005 American Chemical Society.

A well studied example is given by the poly(oxyethylene-Z locfc-styrene). In case of atactic sequences of polystyrene, only the poly(oxyethylene), POE, can crystallize. A typical morphology of the POE is shown in Fig. 5.55. Single crystals of the copolymer can be grown from a common solvent which keeps both components mobile up to the time of crystallization of the POE-component. Figure 7.53 illustrates a growth spiral out of poly(oxyethylene-fclocfe-styrene), grown at 293 K from a solution of ethylbenzene (AB diblock, 28 wt-% oxyethylene block with a molar mass of about 10,000 Da). The crystal is comparable to the lamellar crystals of Fig. 5.55, i.e., the poly(oxyethylene) crystals are chain-folded with about 2.5 nm amorphous polystyrene layers at the interfaces. 

Styrene has also been polymerized under dispersion conditions in CO2. However, the poly(FOA) homopolymer and the PDMS macromonomer were not the best stabilizers for this monomer. Polystyrene (PS) was polymerized efficiently under dispersion conditions using a PS/poly(FOA) diblock stabilizer (48). The PS segment anchored to the growing PS particle, while the poly(FOA) block provided steric stabilization in CO2. Indeed, it has been shown that the block copolymer reduces the interfacial tension at the PS-CO2 interface (49). As was shown previously, added stabilizer increased both the yield and molecular weight of the PS when compared with polymerizations without stabilizer. The mean particle diameter and the particle size dispersity decreased as the length of both the PS and the poly(FOA) blocks increased. Poly(FOA) homopolymer did offer some stabilization to the dispersion polymerization of PS when compared with no added stabilizer, but the presence of the PS block greatly enhanced the stabilization of the PS particles. 

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