PS-h-PMMA

Fig. 3 Schematic representation of control over block copolymer thin film orientation by applying an electric field to orient PS-h-PMMA cylinders perpendicular to the substrate (taken from [43])...

A similar technique was employed for the synthesis of miktoarm stars having PS, PEO, poly(e-caprolactone) (PCL) or PMMA branches [57]. A PS-h-PMMA diblock copolymer possessing a central DPE derivative, bearing a protected hydroxyl function was prepared. After deprotection and transformation of the hydroxyl group to an alkoxide the anionic ring opening polymerization of the third monomer (EO or e-CL) was initiated. Only limited characterization data were given in this communication. 

Block copolymer vesicles, or polymersomes, are of continued interest for their ability to encapsulate aqueous compartments within relatively robust polymer bilayer shells (Fig. 7) [66, 67]. Eisenberg and coworkers were the first to report the formation of block copolymer vesicles from the self-assembly of polystyrene-h-poly(acrylic acid) (PS-h-PAA) block copolymers. They also have described the formation of a wide range of vesicle architectures in solution from the self-assembly of five different block copolymers PS-h-PAA. PS-h-PMMA, PB-h-PAA, polystyrene-h-poly(4-vinyIpyridinium methyl iodide), and polystyrene-h-(4-vinylpyridinium decyl iodide) [68]. Small uniform vesicles, large polydisperse vesicles, entrapped vesicles, hollow concentric vesicles, onions, and vesicles with hollow tubes in the walls have been observed and the formation mechanism discussed. Since vesicles could be prepared with low glass transition polymers such as PB [69, 70] and PPO [71], it has been established than these structures are thermodynamically stable and not trapped by the glassy nature of the hydrophobic part. 

Piirma and Chou [22] synthesized triblock PMMA-h-PS-h-PMMA copolymers according to the following reaction ... 

The reaction was carried out at 25-60 °C in different solvents and leads to high molecular weights although with polydispersity indexes higher than 3 based on SEC determinations. Recently, Yamada et al. [75] studied initiators derived from the triphenylverdazyl radical. PS-h-PMMA copolymers are prepared although with low yields. 

The oxocarbenium perchlorate C(CH2OCH2CH2CO C1O4")4 was employed as a tetrafunctional initiator for the synthesis of PTHE 4-arm stars [146]. The living ends were subsequently reacted either with sodium bromoacetate or bromoisobutyryl chloride. The end-capping reaction was not efficient in the first case (lower than 45%). Therefore, the second procedure was the method of choice for the synthesis of the bromoisobutyryl star-shaped macroinitiators. In the presence of CuCl/bpy the ATRP of styrene was initiated in bulk, leading to the formation of (PTHP-fo-PS)4 star-block copolymers. Further addition of MMA provided the (PTHF-h-PS-h-PMMA)4 star-block terpolymers. Relatively narrow molecular weight distributions were obtained with this synthetic procedure. 

The same selective dissolution method can in fact be used even without an additive. When the minority component is selectively solvated then dried, the chains are left coating the matrix phase of the majority matrix, in an ultrathin film, the chains also migrate to cover the free surface on drying, leaving an empty pore in what was the center of the minority domain. Porous arrays up to around 30 nm thick based on PS-h-PMMA [72] (trifluorotoluene as selective PMMA solvent], PS-h-PVP [73] and PMMA-h-PVP [57] (ethanol as PVP solvent] have been created in this way. 

State reflected in poor ordering. In practice, Xu et aL found that standing cylindrical pores between 14 and 50 nm in diameter with center-to-center distances of 24 to 89 nm could be acheived in PS-h-PMMA templates by var5dng the molecular weight between 42 and 295 Kg mol" (Fig. 2.9). 

A linking reaction of the in-chain-SiOMP-functionalized living PS-h-PMMA with in-chain-BnBr-functionalized PS-b-PMMA. 

For the formation of solid copolymer nanoparticles without a liquid core, PS-h-PMMA was used as a model system. In order to be able to form nanoparticles, the block copolymer was dissolved in chloroform and the solution was miniemulsified in water by adding the SDS. In this case, homogeneous droplets were formed. After evaporation of the chloroform, nanoparticles consisting entirely of block copolymer... 

Tunca et al. [27, 28,38] reported in a series of papers on a multi-click approach for the preparation of brush copolymers. The backbone consisted of homopolymers, statistical polymers, or block copolymers from ONBEs with orthogonal side groups for Diels-Alder click reaction [27,28,38], azide/alkyne click reaction, [27, 28, 38] and nitroxide coupling [27]. In a grafting-to approach, maleimide-or ONBE-functionalized polymers (PEG, P BA, PMMA (56)) were attached by Diels-Alder click reaction with the anthracene groups pendant at the polymer backbone (55) (Scheme 9.8b). PCL chains were attached by an azide/alkyne click reaction, while a combination of Diels-Alder and azide/alkyne click reaction allowed the synthesis of graft copolymers with PS-/ -PEG-, PS-h-PMMA-, or PS-/ -P BA side chains. 

Most of the published research on directed assembly of block copolymers has focused on PS-h-PMMA, so we can use that as a baseline to which we can compare... 

Two recent publications provide additional examples of the CD control abilities of directed assembly of block copolymers, but also demonstrate for the first time the opportunity for resolution enhancement with block copolymer films directed to assemble on chemical patterns [81, 82]. In one case, cylinder-forming PS-h-PMMA was directed to assemble on a chemical pattern comprised of hexagonally arranged... 

It was found that the effective width of the interface between the PS and PMMA segments was 75 A, i.e., it was 50% broader than that found between the PS and PMMA homopolymers in the absence of the diblock copolymer (50 5 A [261]) and between the PS and PMMA lamellar microdomains of the pure PS-ft-PMMA in the bulk (50 4 A) [261,262]. The area occupied by the copolymer at the interface between the homopolymers is 30% larger than that of the copolymers in the bulk lamellar microstructure [39]. In that study, the amount of diblock copolymer at the interface was (approximately) equivalent ( 200 A) to half of the long period of the neat ordered copolymer. The same PS/PS-h-PMMA/PMMA system was subsequently investigated by a lattice-based self-consistent field model that was extended... 

This technique was first described in 1991 [153] and has since been reviewed [143,154]. It has been used to give molecular resolution images of electrically conductive polymers [155] and PS-h-PMMA block copolymers [156] in UHV. Because the technique is truly non-contact, it does not have the complexity of dual interaction paths (either repulsive or attractive) that are inherent to amplitude modulation IC-AFM. This makes the technique suitable for the study of metal-polymer bonding under controlled ambient conditions [157]. 

Figure 223 SEM micrograph of morphology of (a) 35/40/25 HDPE/PS/L-PMMA after extraction of L-PMMA by acetic acid, (b) 35/40/25 HDPE/PS/L-PMMA after extraction of PS by cyclohexane, (c) 35/40/25 HDPE/PS/H-PMMA (cryofracture), (d) 35/40/25 HDPE/PS/H-PMMA after extraction of PMMA by acetic acid, and (e) 35/40/25 HDPE/PS/H-PMMA after extraction of PS by cyclohexane. Ravati and Favis [14], Reproduced with permission of Elsevier.

Neutron reflectivity was used to investigate the segment density distribution of symmetric diblock copolymers of PS and PMMA [39] (molecular weights of about 100,000) at the interface between PS and PMMA homopolymers (molecular weights of about 100,000). Selective deuterium labeling of either a block of the PS-h-PMMA or of the PS or PMMA homopolymers provided the contrast necessary to isolate the distribution of the segments of the individual components at the interface. Results from a series of experiments were used simultaneously to yield the density profiles of the PS and PMMA segments of the homopolymers, and of the copolymer blocks at the interface (Fig. 22). 

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