PCEMA-PtBA

Liu and coworkers have investigated PI-PCEMA-PtBA triblock copolymers in which the central PCEMA block was cross-linked by UV irradi-... 

The first ABC triblock copolymer used by us to prepare nanotubes was polyzsoprene-fclock-poly(2-cinnamoyloxyethyl methacrylate)-fc/ock-poly(ferf-butyl acrylate) or PI-PCEMA-PtBA [19] ... 

Fig. 5 Steps invoked to prepare nanotubes from PI-PCEMA-PtBA...

Fig. 6 TEM image of PCEMA-PfBA nanotubes prepared from degradation of the PI core of PI-PCEMA-PtBA nanofibers...

The cylindrical nanoaggregate precursor approach has been used to prepare nanotubes from other triblock copolymers including PGMA-PCEMA-PtBA, where PGM A denotes poly(glyceryl methacrylate) [52]. 

Fig. 9 Structural comparison of a PHIC chain under a magnifying glass top left), a PS-PCEMA nanofiber top right), a PS-PCEMA-PtBA nanofiber bottom left), and a PS-PCEMA nanotube with a PAA-lined core bottom right)...

PCEMA nanofiber, a PS-PCEMA-PtBA nanofiber, and a PS-PCEMA nanotube with a PAA-lined core. 

In a PHIC chain, the backbone, covered by a corona of hexyl groups, consists of a Unear sequence of imide units. Their counterparts in the PS-PCEMA nanofiber are the cross-linked PCEMA cylindrical core and the PS chains as the corona. Other than the size difference, the PHIC molecule and the PS-PCEMA nanofiber bear a remarkable structural resemblance. If the PCEMA crosslinking density is high, the PtBA chains in a PS-PCEMA-PtBA nanofiber and the PAA chains in a PS-PCEMA-PAA nanotube become trapped inside the cores even if the solvent is good for both PtBA and PAA. Thus, the triblock copolymer nanofibers and nanotubes can be viewed as giant polymer chains as well [18]. 

For nanofibers and nanotubes, backbone modification refers to selective chemical transformation of one or more of the core blocks. In our preparation of nanotubes from the PI-PCEMA-PtBA and PS-PCEMA-PtBA triblock nanofibers, the core PI and PtBA blocks were sculpted away either fully or partially. These reactions are examples of nanofiber backbone modification. One can also consider inorganic reactions carried out inside one of the block copolymer phases to be a kind of backbone modification. These reactions lead to the formation of interesting polymer-inorganic hybrid nanostructures. This topic will be reviewed in the following paragraphs. 

Koh et al. utilized a bottom-up approach to build coreshell nanocylinders having distinctive chemical funaionalities throughout the internal domain and exposed at the end sites. These nanoscopic objects were fabricated via supramolecular assembly and intra-assembly cross-linking of polystyrene-b-poly(2-cinnamoyloxyethyl methacrylate)-b-poly(tert-butyl acrylate) (PS-b-PCEMA- -PtBA) ABC triblock terpolymers within a PS matrix. Functionalization of the end sites and chemical derivatization of the internal reactive groups were performed sequentially to afford these tmique regiochemically functionalized nanostmctures (Figure 32). 

Liu et al. prepared palladium nanoparticles in water-dispersible poly(acrylic acid) (PAA)-lined channels of diblock copolymer microspheres [47]. The diblock microspheres (mean diameter 0.5 pm) were prepared using an oil-in-water emulsion process. The diblock used was poly(t-butylacrylate)-Wock-poly(2-cinna-moyloxyethyl) methacrylate (PtBA-b-PCEMA). Synthesis of the nanoparticles inside the PAA-lined channels of the microspheres was achieved using hydrazine for the reduction of PdCl2, and the nanoparticle formation was confirmed from TEM analysis and electron diffraction study (Fig. 9.1). The Pd-loaded microspheres catalyzed the hydrogenation of methylacrylate to methyl-propionate. The catalytic reactions were carried out in methanol as solvent under dihydro-... 

PtBA-b-PCEMA poly(t-butyl acrylate)-block-poly(2-cinnamoyloxyethyl) methacrylate... 

Fig. 3 Structure of PtBA-PCEMA and TEM image after hydrolysis. Reproduced from [20]... 

The formation of cylindrical domains of one block in a matrix of another, in diblock copolymers, has also been exploited for the generation of nanochannels in thin film membranes [40, 41]. Using diblock copolymers of PtBA-b-PCEMA, but this time with a larger volume fraction (ca. 74 vol%) of the photo-crosslinkable PCEMA block, Liu et al, prepared thin polymer films containing a densely packed array of nanocylinders (diameter 22 nm) [40]. As expected, in these cases the PCEMA block forms the continuous phase with nanocylinders of the hydrolyzable PtBA blocks forming a densely packed array. Typically, thick films (or disks of ca. 

Fig. 1S.9. TEM image of a small area of 50 nm thick PAA-h-PCEMA film generated by crosslinking the PCEMA matrix followed by hydrolysis of the PtBA domain. (Reprinted with permission from Macromolecules, 1997, 30, 1851. 1997 American Chemical Society [40].)...

To prepare nanotubes from PGMA375-PCEMA 120-PtBA 120, the triblock was stirred for 3 to 5 days with water, which was selective for PGMA, to effect formation of cyUndrical nanoaggregates first. Such aggregates possessed a PtBA... 

The nanopartide S3mthesis process can be further modified through the use of additives during assembly. These additives vary from homopolymer of one of the block segments to surfactants and even metal oxides. Liu et al. demonstrated the assembly of a triblock copolymer of PS-b-PCEMA-b-PtBA in the presence of PS homopolymer.Adjustment of the volume fractions of the different blocks was achieved through modification of the triblock composition and the ratio of triblock and PS homopolymer and resulted in the formation of cylinders comprising a PtBA core surrounded by a PCEMA layer in a matrix of PS. The triblock and homopolymer mixture was cast from toluene the solvent was then allowed to evaporate slowly and the film was annealed. The nanocylinders were stabilized... 

Nanostructures like hollow tubes have attracted much attention mainly to meet the demand for smaller electronic devices. Tubes can be obtained using the sculpturing method. Liu and co-workers synthesized hollow nanotubes using triblock copolymers.The triblock copolymer poly(isoprene)-Z>/ocA -poly(2-cinnamoylethyl methacrylate)-Z)ZocA -poly(tert-bulyl aciylate) (PI-Z>-PCEMA-Z)-PtBA) containing 130 isoprene, 130 CEMA, and 800 fBA units formed self-assembled cylindrical micelles in methanol. 

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