PS-PB bloCk copolymer

Fig. 6.37 Interfacial volume fraction profiles calculated for a ternary blend of a PS-PB block copolymer with PS and PB homopolymers in a good solvent (Noolandi and Hong 1982). The diblock has N — 600 and f = The homopolymers have infinite molecular weight. The solid lines are the volume fractions of homopolymer (A = PS) (B = PB), the dashed lines indicate the volume fractions of PS and PB blocks of the diblock. The dots correspond to the total volume fractions of the A and B components and the position is measured in units of a segment length a = 6.95 A.

Fig. 24 Logarithmic chain exchange kinetics of PS-PB block copolymer micelles (top) in DMF at 20° C (stars) and of inverted micelles (bottom) with swollen PS cores in n-hexadecane at 20°C (circles) and 30°C (triangles). Lines depict fits with a logarithmic time decay. Reprinted with permission from [101], Copyright (2006) by the American Physical Society...

Though our research has focused on PS-PI and PS-PB block copolymer thin films to form useful masks for patterning, their poor etch resistance under CF4 RIE limits the aspect ratio of fabricated features to no greater than 1. Future work will include the exploration of other block copolymer systems, such as those embedded with etch resistant metal clusters(J7) or silicon-containing block copolymers(J2). Etch resistant polymers or microdomains would enable the fabrication of features with larger aspect ratios which could be advantageous for filtration devices and memory storage. 

Fig. 36 DSC curves obtained at heating rate 20 K min for (a) homo PS (1) and PS blocks in the PS-PB block copolymers with the equal values for both blocks, 8 x 10 (2), 3.4 x 10 (3), and 1 X 10 (4) [181] and (b) homo PDMS and PDMS blocks in the PDMS-PI and PDMS-PPSSO block copolymers in the temperature region of PDMS glass transition. The activation energies Q obtained at respective temperatures are also indicated [25,129,182]...

A study of a PS-PB block copolymer showed variation in craze behavior as a result of rubber particles added to modify the otherwise brittle, glassy polymers. Such copolymers were studied under the high strain of physical laboratory testing where the polybutadiene in the copol)mier was stained with osmium tetroxide prior to microtomy [333]. The brittle behavior of the glassy polymers was shown by TEM and STEM to be modified by the rubber particles which provide toughening by control of the craze behavior. In a study of the craze behavior in isotactic polystyrene [146], films of polystyrene were drawn from dichlorobenzene solution and cast onto glass microscope slides, followed by... 

A possible strategr is shown in Figure 23(a), where the FIDs of the isolated rigid and mobile fraaions in a PS-polybutadiene (PS-PB) block copolymer were measured... 

Fig. 21 Formation of Janus micelles from PS-PB-PMMA copolymers. The copolymers are transformed into PS-PB-PMAA copolymers after hydrolysis of PMMA block. PS coronal blocks collapse in water and supermicelles are formed. A typical SEM picture of supermicelles is shown. Reprinted with permission from [55]. Copyright (2003) American Chemical Society... 

Macrophase separation after microphase separation has been observed in an AB block copolymer/homopolymer C blend (Hashimoto et al 1995). Blends of a PS-PB starblock copolymer (75wt% PS) and PVME homopolymer were prepared by solvent casting. Binary blends of PS and PVME exhibit a lower critical solution temperature (LCST), i.e. they demix at high temperatures. The initial structure of a 50% mixture of a PS-PB diblock and PVME shown in Fig. 6.20(a) consists of worm-like micelles. Heating led to macrophase separation as evident... 

Fig. 2a-d. Stress-strain response of four PS/PB diblock copolymers with rod morphology with a nominal weight fraction of PB rods of 0.23 but increasing molecular weight of block components, at two different strain rates (a) SB2, (b) SB5, (c) SB8, (d) SBIO. ( ) 1.3xl0 s- (O) 1.3x... 

Fig. 16 Experimental curves showing a realization of the KZAC/TR-S ANS technique applied to PS-PB block copol5imers dissolved in DMF, which is a selective solvent for PS. At time zero, fully deuterated d-PS-d-PB micelles are mixed with fully proteated h-PS-h-PB micelles in a isotopic h-DMF/d-DMF solvent mixture exactly matching the average scattering length density. As the block copolymer chains exchange, an overall decrease in the intensity is observed while the form factor and hence the structure remains constant...

Figure 9 Top cartoon representations of a spherical micelle, a wormlike micelle, and a vesicle. The red blocks represent the solvophilic blocks, and the blue blocks represent the solvophobic blocks. Bottom example TEM images showing diffa-ent micelle morphologies adopted by block copolymers in solution, (a) Spherical micelles formed from polyfethylene oxide)-f>-polycaprolactone (PEO-f>-PCL) copolymers.(b) Wormlike micelles, vesicles, and octupi formed by mixing PEO-fc-polybutadiene (PEO-fc-PB) block copolymers. (Reproduced from Ref. 32. American Chemical Society, 2004.) (c) Vesicles formed from PEO-f>-PCL copolymers. (Reproduced from Ref. 33. Royal Society of Chemistry, 2011.) (d) Multicompartment micelles formed from a triblock copolyma-. (Reproduced from Ref. 34. American Chemical Society, 2010.) (e) Stomatocytes formed using PEO-f>-polystyrene (PEO-f>-PS) copolyma-s. (Reproduced from Ref. 35. American Chemical Society, 2010.) (f) Toroidal micelles coexisting with cylindrical micelles and sphaical micelles formed from poly(acrylic acid)-f>-poly(methacrylic acid)-fc-PS (PAA-f>-PMA-f>-PS) triblock copolymers. (Reproduced from Ref. 36. Royal Society of Chemistry, 2009.)...

PS and PB homopolymers are immiscible. Any added PB-PS block copolymer in a PS-PB blend will have one sequence miscible in PS and one sequence miscible in PB, hence they will localise at the interface. As a consequence, the interfacial energy will decrease, greatly helping dispersion and providing phase adhesion, thus a transfer of mechanical properties. 

In a pure PB-PS block copolymer, both sequences are immiscible and the microstructure will be diphasic (at a supramolecular or nanoscopic level). If the ratio is such that PS particles are dispersed into a matrix of PB, below the Tg of PS, the system behaves like crosslinked PB, hence as an elastomer. However, above the Tg of PS, the system becomes viscous and can be processed like a thermoplastic. 

The term star-block copolymer is used for a star architecture in which each arm is a diblock. The influence of chain topology on mechanical and morphological properties was investigated for copolymers composed of PS and PB with a constant styrene content of = 0.74 by Michler s group (Fig. 32) [101,102], While hexagonally packed cylinders of PB in a PS matrix were observed in a symmetric PS-fo-PB-fr-PS triblock copolymer, an L phase... 

Fig. 32 Schematic representation of molecular structure and morphology observed in PS-fo-PB-fc-PS linear and star-block copolymers. Oblique lines between blocks for LN2 and ST2 indicate tapered transition of dissimilar blocks. From [102], Copyright 2003 Wiley...

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