Styrene/Butadiene Gradient Block Copolymers:  Molecular and Mesoscopic Structures

Abstract

Rubbery−glassy block copolymer dispersions are an attractive solution for toughening rigid thermoplastics like polystyrene without affecting optical transparency. An interesting facet of the copolymers used is molecular disorder, artificially introduced during anionic synthesis through composition gradients along the copolymer chain and/or blending and partial coupling of different copolymers. In particular, this level of disorder is apparently a key to achieve the desired PS/copolymer blend morphologies and properties in short processing times. In this work, we investigate the role of these “synthesis imperfections” on self-assembly of styrene-rich asymmetric gradient triblock copolymers, denoted S1−G−S2, where Si are pure polystyrene blocks and G is a gradient copolymer of styrene and butadiene. Kinetic modeling of conversion data is used to predict gradient composition profiles for the anionic copolymerization conditions used. Self-assembly, dynamic viscoelastic behavior, and experimentally determined mesoscopic composition profiles across microdomains are discussed in light of the particular copolymer structure.

Controlling Macroscopic Properties by Tailoring Nanoscopic Interfaces in Tapered Copolymers

“…The copolymer materials were prepared by batch living anionic polymerization in cyclohexane (99.9% purity), similar to the method described by Leibler and co-workers. 23 The discrete block (DB) and tapered block (TB) copolymers were synthesized first by the addition of butadiene (Airgas, polymerization grade), followed by copolymerization of equal weights of styrene (Fischer, certified grade), and only the tapered block would have polar modifier tetrahydrofuran (THF, Fischer) and n-butyllithium (Rockwood Lithium Inc., 2 wt % in cyclohexane) added in a molar ratio of THF/Li = 2.6, to incorporate a transition region. The inverse tapered block (ITB) copolymer follows a similar preparation to the tapered block, with the exception of starting with the styrene component and ending with butadiene, while using the same THF/Li = 2.6 molar ratio addition.…”

Gradient and block side-chain liquid crystalline polyethers

“…In dramatic contrast, the gradient copolymer generally exhibits a very broad liquid crystalline phase transition. For the gradient copolymers of short gradient lengths, E 28 -g-B 14 and E 35 -g-B 34 , the phase transitions are more obvious as shown in the first two DSC curves on the bottom of Fig. 4b.…”

“…5 shows 1D SAXS profiles of the gradient copolymers with growth of the polymer chains. As illustrated in the profiles of E 28 -g-B 14 and E 35 -g-B 34 samples in the bottom of the figure, there solely appears a diffraction peak at q ~ 1.38 nm -1 , which results from the reflection of layered liquid crystalline structure. As the gradient length further increases, for example, to E 49 -g-B 63 , a distinct peak located at q ~ 0.53 nm -1 emerges, indicating the occurrence of phase separation.…”

“…[4][5][6][7][8][9][10][11] Gradient polymers can also serve as a constituting section in different positions of a polymer chain, for instance, to form the so-called tapered-block copolymer. [12][13][14][15][16][17] Largely widened double gyroid phase regime of diblock copolymer has been predicted when a taper is incorporated into the junction portion of the chain, which has been attributed to the relieved packing frustration due to the gradient nature of the polymer chains. 17 Recently, extensive experimental works on gradient polymers have been reported in literature.…”

Block Copolymers in External Fields: Rheology, Flow‐Induced Phenomena, and Applications

“…Moreover they do not have to be pure homopolymers. Many block copolymers used in applications are gradient or tapered block copolymers whose composition varies gradually along the chain or the blocks from A-rich at one end to B-rich at the other end [12][13][14][15][16][17]. It is nearly impossible to list the huge variety of block copolymers that have been synthesized and investigated.…”