Styrenes orientation control

Inclusion of crosslinkable benzocyclobutene monomer with the random copolymerization of styrene and methyl methacrylate initiated from unfrmctionalized TEMPO the benzocyclobutene component crosslinks with heat, rendering heated films insoluble. An advantage to this method is that bond formation to the substrate is not required therefore this technique can be extended to substrates other than silicon oxide. Use of photolithographic techniques to pattern gold on top of this solvent-resistant neutral layer gives selective orientation control with resolution demonstrated to 6 jm. °... 

Other NAD microspheres are composed of styrene, MMA, hydroxyethyl acrylate, acrylic acid and acrylonitrile and are blended with acrylic copolymers and melamine/formaldehyde resins [341,342]. Particles of this polymer are used as rheology modifiers to prevent sagging in automotive coatings and for controlling the orientation of metal flake pigments. 

Phenyl azide undergoes stereospecific addition to (Z)- and ( )-methyl-styrene as shown in Scheme 28.2 7,144 Although the reaction is sensitive to steric effects, as evidenced by the failure of phenyl azide to add to tetra-methylethylene,40 the orientation is controlled by electronic rather than steric factors.27,34,40... 

Zambelli et al. reported on the mechanism of styrene polymerization [36]. They showed that the main chain of the syndiotactic polymer has a statistically trans-trans conformation. It was established then the double-bond opening mechanism in the syndiospecific polymerization of styrene involves a cis opening. The details in the control of the monomer coordination for this polymerization mechanism were examined by Newman and Malanga using detailed, 3C NMR. It was shown through the analysis of tacticity error (rmrr) that the tacticity in the polymer is chain-end controlled and that the last monomer added directs the orientation and coordination of the incoming monomer unit prior to insertion [37]. 

The effect of going from styrene to phenylacetylene is therefore to lower the HOMO and the LUMO by about, say, 0-5 eV. This makes what was clearly a dipole-LU-con-trolled reaction into one which is affected by both interactions (Fig. 4-64). Since dipole-HO control leads to the opposite regioselectivity, it is not so surprising that both orientations are now observed. 

Other LC-based copolymers incorporating styrene-based monomers were prepared by Ober et al. [149] who chain extended pAcOSt-TEMPO (Mn=7000, Mw/Mn=1.18) with [(4 -methoxyphenyl)4-oxybenzoate]-6-hexyl (4-vinylbenzoate) (MPVB, Fig. 10). The reactions were controlled, with molecular weights ranging from Mn=12,600-23,000 and Mw/Mn=1.19-1.44. The content of pMPVB in the copolymer determined by XH NMR increased as the molar ratio of the MPVB to pAcOSt-TEMPO increased [149]. For two out of the three copolymers prepared a smectic-isotropic transition was observed however, it was at a value lower than expected based on the composition of the copolymer, even after annealing. X-Ray diffraction patterning indicated that the copolymer was oriented in a lamellar morphology and that the smectic layers were perpendicular to the block copolymer lamellae [149]. 

SCORIM shear controlled orientation of re- SIR styrene-isoprene... 

Film thickness constraints can also be exploited to control the orientation of the nanodomains. More specifically, when the thickness of the film approaches the lattice constant of the block copolymer, the orientation of the nanodomains is sometimes altered with respect to the substrate. Simply stated, the stress generated by the incommensurate film thickness can be relieved by a change in domain orientation. This is further illustrated by an example in Fig. 14. A styrene-ferrocenyldimethylsilane block copolymer (PS-fo-PFS), consisting of a styrene fraction of 0.73 forms a cylindrical structure in the bulk [6]. Within a thin film, the pattern that is formed by the block copolymer also depends on the film thic ess [80]. 

Control of macroscopic orientation of the microphase-segregated structures leads to efficient anisotropic conduction of proton and ions [132-139], Proton conductive supramolecular materials have been prepared by using microphase segregation of supramolecular block polymers 42 consisting of poly(styrene)- tock-(4-vinylpyridine), toluene sulfonic acid, and 3-pentadecyl phenol (Figure 31) [137]. Ionic conductive side-chain polymers have been obtained by complexation of oligo(ethylene oxide)sulfonic acid with poIy(styrene)-fe/ock-(4-vinylpyridine) [139]. 

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