Methyl methacrylate/styrene block copolymer interfaces

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... 

To synthesize water-soluble or swellable copolymers, inverse heterophase polymerization processes are of special interest. The inverse macroemulsion polymerization is only reported for the copolymerization of two hydrophilic monomers. Hernandez-Barajas and Hunkeler [62] investigated the copolymerization of AAm with quaternary ammonium cationic monomers in the presence of block copoly-meric surfactants by batch and semi-batch inverse emulsion copolymerization. Glukhikh et al. [63] reported the copolymerization of AAm and methacrylic acid using an inverse emulsion system. Amphiphilic copolymers from inverse systems are also successfully obtained in microemulsion polymerization. For example, Vaskova et al. [64-66] copolymerized the hydrophilic AAm with more hydrophobic methyl methacrylate (MMA) or styrene in a water-in-oil microemulsion initiated by radical initiators with different solubilities in water. However, not only copolymer, but also homopolymer was formed. The total conversion of MMA was rather limited (<10%) and the composition of the copolymer was almost independent of the comonomer ratio. This was probably due to a constant molar ratio of the monomers in the water phase or at the interface as the possible locus of polymerization. Also, in the case of styrene copolymerizing with AAm, the molar fraction of AAm in homopolymer compared to copolymer is about 45-55 wt% [67], which is still too high for a meaningful technical application. 

The self-consistent field theory also allows one to calculate the segment density profiles of each homopol)maer and each block of the copolymer. Forward recoil spectrometry is unable to resolve the details of these concentration profiles — the apparent finite width of the copolymer layer shown in figure 6.6 is entirely due to the instrumental resolution - but from neutron reflectivity measurements on a series of differently labelled samples one is able to extract all four segment density profiles. Figure 6.20 shows an example of this, for a styrene/methyl methacrylate copolymer at an interface between polystyrene and poly(methyl methacrylate). 

From this extremely instructive data set we can draw a number of conclusions. Firstly, it is clear that the block copol5mier is localised at the interface between the two homopolymers and is organised with the styrene block at the polystyrene side of the interface and the methyl methacrylate block at the PMMA side. The joints between the two halves of the copolymer are localised to a relatively narrow region, while each half of the copolymer penetrates rather deeply into the corresponding homopolymer. The overall interface between all... 

Figure 6.20. Segment distributions of a styrene-(methyl methacrylate) block copolymer (relative molecular masses of each block were in the range 48 000-65 000) at an interface between polystyrene (relative molecular mass in the range 110000-127 000) and poly(methyl methacrylate) (relative molecular mass in the range 107000-146 000), revealed by a series of neutron reflection experiments in which various parts of the copolymer and/or one of the homopolymers was labelled with deuterium. The bold lines are the segment density profiles for all styrene and methyl methacrylate segments, summed over both the homopolymer and the copolymer the solid lines are the homopolymers, and the dotted lines are the styrene and methyl methacrylate blocks of the copolymer. After Russell et al. (1991).

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).

Winnik et al. [53] used time-resolved fluorescence spectroscopy (direct non-radi-ative energy transfer experiments) to determine the interface thickness in films of symmetric poly(styrene-fc-methyl methacrylate) (PS-PMMA) block copolymers labeled at their junctions with either a 9-phenanthryl or a 2-anthryl group. The corrected donor fluorescence decay profiles were fitted to simulated fluorescence decay curves in which the interface thickness 8 was the only adjustable parameter. The optimum value of the interface thickness obtained was 6 = 4.8 run. In similar studies [54—57], the same authors determined the interface thickness value 6 = 1.6 nm in mixtures of two symmetrical poly(isoprene-b-methyl methacrylate) (PI-PMMA) block copolymers of similar molar mass and composition [54] the interface thickness value 8 = 1.1 nm for the lamellar structures formed in films of symmetric PI-PMMA diblock copolymers bearing dyes at the junctions [55] a cylindrical interface thickness value of d slightly smaller than 1.0 nm in films consisting of mixtures of donor- and acceptor-labeled PI-PMMA (29vol% PI) that form a hexagonal phase in the bulk state [56] and the interface thickness 8 = 5 run on the diblock copolymer poly(styrene-l>-butyl methacrylate)(PS-h-PBMA) [57]. 

Rharbi, Y. and Winnik, M.A. (2001) Interface thickness of a styrene-methyl methacrylate block copolymer in the lamella phase by direct norrradiative energy... 

Utama et al. [46] recently proposed an alternative strategy for the preparation of nanocapsules using RAET polymerization in an inverse miniemulsion system. In this approach, dispersed aqueous droplets (with RAET-based active stabilizers at their interface) simply acted as templates, and chain extension (with hydrophobic monomers and crosslinkers contained in the surrounding continuous phase) yielded the nanocapsules. More specifically, methyl methacrylate (MMA) [46] or styrene [47], crosslinker (EGDMA or DVB, respectively), and initiator (AIBN) were dissolved in a toluene continuous phase. Water droplets containing sodium chloride as lipophobe were formed in these toluene solutions and stabilized with RAET-synthesized poly[M-2-(hydroxypropyl methacrylamide)]-h/oc -poly(methyl methacrylate) (PHPMA-h-PMMA) or PHPMA-h-PS block copolymers, where the PHPMA segment is hydrophilic. The subsequent polymerization was confined to... 

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