DIBLOCK COPOLYMER Subject

Block copolymers subjected to large shear fields in the bulk state have been of interest since the first studies by Keller et al. [280]. They oriented a cylindrical S-B-S triblock terpolymer of polystyrene (S) and polybutadiene (B) by extrusion. The cylindrical domains of the polystyrene blocks were found to orient parallel to the direction of shear flow. Then several years passed before the influence of shear on the alignment and phase behavior of block copolymers became the subject of further scientific investigations. The experimental and theoretical works on diblock copolymers subjected to shear have been reviewed recently [96,97]. 

Micellar structure has been a subject of much discussion [104]. Early proposals for spherical [159] and lamellar [160] micelles may both have merit. A schematic of a spherical micelle and a unilamellar vesicle is shown in Fig. Xni-11. In addition to the most common spherical micelles, scattering and microscopy experiments have shown the existence of rodlike [161, 162], disklike [163], threadlike [132] and even quadmple-helix [164] structures. Lattice models (see Fig. XIII-12) by Leermakers and Scheutjens have confirmed and characterized the properties of spherical and membrane like micelles [165]. Similar analyses exist for micelles formed by diblock copolymers in a selective solvent [166]. Other shapes proposed include ellipsoidal [167] and a sphere-to-cylinder transition [168]. Fluorescence depolarization and NMR studies both point to a rather fluid micellar core consistent with the disorder implied by Fig. Xm-12. 

The effect of blending an AB diblock copolymer with an A-type homopolymer has been the subject of many research activities. On a theoretical basis the subject was investigated e.g. by Whitmore and Noolandi [172] and Mat-sen [173]. If a diblock exhibiting lamellae morphology is blended with a homopolymer of high molecular weight, macrophase separation between the... 

Another intriguing feature emerged when we examined PFS-PDMS diblock copolymers having a longer soluble block as well as an increased block ratio (1 12 and 1 18). Samples of the two polymers were prepared by the same protocol, i.e., subjected to the same thermal history. Dilute solutions in decane were heated for 30 min at 61 °C, cooled to room temperature over two hours and allowed to age for 24 hours. We have already shown, in Fig. la, that under these conditions, PFS50-PDMS300 formed dense rod-like structures in hexane. However, as... 

Block—graft copolymers, having a PS—PB diblock as a backbone and PS, PI, PB and PS-b-PI branches, were prepared by anionic polymerization and hydro-silylation reactions.156 The diblock copolymer backbone was prepared by sequential addition of styrene and butadiene. The polymerization of butadiene took place in the presence of dipiperidinoethane, resulting in high 1,2-content. The backbone was then subjected to hydrosilylation in order to incorporate the desired amount of SiCl groups on the PB block. These groups were then used as branching sites, where PSLi, PILi,... 

Qi and Wang also observed a transient undulated HEX state during the melting of the HEX phase to the disordered state. This is consistent with the experimental observation in the shear cessation experiments of Bates and co-workers (Bates et al., 1994a Almdal et al., 1996). In these experiments, an initially disordered phase of the asymmetric poly(ethylenepropylene-b-ethylethylene) (PEP-PEE) diblock copolymer close to the order-disorder boundary is subjected to a steady shear which induces a transition to the HEX phase. The shear is then suddenly stopped and a transient modulated state is observed as the system relaxes back to the DIS. Insofar as a HEX... 

By sequential copolymerization of styrene and propylene using a modified Ziegler-Natta catalyst, MgCl2/TiCl4/NdClc(OR) //Al(iBu)3, which was developed in our laboratory, a styrene-propylene block copolymer is obtained. After fractionation by successive solvent extraction with suitable solvents, the copolymer was subjected to extensive molecular and morphological characterization using 13C-NMR, DSC, DMTA, and TEM. The results indicate that the copolymer is a crystalline diblock copolymer of iPS and iPP (iPS-fo-iPP). The diblock copolymer contains 40% iPS as determined by Fourier transform infrared spectroscopy and elemental analysis. 

Here Q is the partition function of a single diblock copolymer molecule subject to the coA(r) and a>s(r) fields ... 

ADMET depolymerization has been explored in a variety of ways [174]. In its simplest form, an unsaturated polymer subjected to metathesis conditions in the presence of ethylene will undergo a retro-ADMET reaction, resulting from CM with ethylene. This concept had been explored with classical catalyst systems [le]. Schrock s catalyst was used to depolymerize PBD, poly-tr s-isoprene, polynor-bornene, andKraton (a butadiene/styrene diblock copolymer) [175] in the presence of ethylene (ethenolysis), and a mixture of products comprising the monomer and some oligomers were produced. 

The NSCFT microphase diagram of conformationally symmetric, diblock copolymers has been presented in Figure 3 and discussed in Section II. In this section, we present a number of other diagrams for different systems, exploring the effects of conformational asymmetry and architectures. We focus on two-species copolymers, which have been the subject of most calculations. 

While the compatibilizing efficacy of ABR random copolymers in ternary ABR/ hA/hB blends has been the subject of investigation, we consider only binary blends consisting of an AB diblock copolymer and an ABR random copolymer in this section. Unlike miscible AB/hA blends in which the hA chain can be solubilized within the A microdomains of the AB copolymer or miscible (AB)j(/(AB)p blends in which the A and B blocks of each copolymer reside in their respective microphases, the bicomponent ABR chain caimot be readily... 

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