Styrene−Butadiene Gradient Block Copolymers for Transparent Impact Polystyrene

Abstract

The mechanical behavior of styrene/butadiene triblock copolymers and their blends with high molecular weight polystyrene (PS) homopolymer was studied. Symmetric triblock copolymers with two PS end blocks of equal length (SBS) were compared with asymmetric triblocks with end blocks of different lengths (S1BS2) and with asymmetric triblocks comprising a styrene/butadiene composition gradient in the middle block (S1GS2). The precise molecular architecture of these copolymers and its role on morphology and properties were described elsewhere (Macromolecules2007402432.). Here, immiscible blends of these copolymers with long PS chains are discussed. While solvent casting yields the expected phase separation, melt extrusion produces tough and transparent blends with metastable submicrometer scale dispersions of soft microdomains highly controlled by processing. The particular molecular architecture of gradient asymmetric triblocks significantly improves ductility of these nanostructured blends. The volume fraction of soft microdomains extracted from dynamic mechanical data is identified as a universal parameter that controls tensile behavior of the different blends studied.

Positron annihilation lifetime spectroscopy for miscibility investigations of styrene–butadiene–styrene copolymer/polystyrene blends

“…It is a consensus that the phase morphology and miscibility are the critical factors affecting the properties of blends. Therefore, the microstructures and miscibility of SBS/PS blends are deeply investigated via the various characterization methods, such as DMA, DSC, TEM, AFM, NMR, SAXS, and so on . DSC and DMA are sensitive to heterogeneities larger than approximately 50 nm in domain size.…”

Morphology re‐entry in asymmetric PS‐PI‐PS' triblock copolymer and PS homopolymer blends

“…Much less attention has been paid to asymmetric ABA' triblock copolymers, where A and A' have same chemical constitution but different lengths. Since ABA' systems are expected to exhibit different phase behavior than corresponding ABA triblocks in neat form or in blends with another homopolymer, 5,6,[11][12][13][14] the relative length of the A and A' blocks could represent a useful formulation design variable in applications where mechanical strength is not a primary concern. symmetric ABA triblock copolymers have nearly symmetric phase diagrams about 0.5 in the volume fraction of A blocks, denoted as f A .…”

“…By further introducing dissimilar length end blocks, the ABA' architecture can exhibit much more pronounced compositional asymmetry than ABA, both in the envelope of the order-disorder transition (ODT) boundary and in significant deflection of order-order transition (OOT) boundaries. 5,[11][12][13][14] Specifically, Matsen predicts that the ordered nanostructures with discrete A domains persist to relatively high volume fraction of A (f A ) at specific values of the block length asymmetry parameters ¼ N 0 =ðN A þ N A 0 Þ, where N A and N A' are the lengths of the A and A' blocks. 5 Diluting a relatively expensive block copolymer by blending with a homopolymer provides a strategy to continuously tune physical properties while simultaneously lowering cost.…”

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

“…In practice, the development of a specific TPE must satisfy several requirements to adapt the temperature of microphase separation to the processing conditions, to control the morphology of the phase-separated microdomains, and ultimately to obtain the properties that are desired. In some instances, this has led chemists and engineers to design and produce commercially a variety of block copolymers that associate complex architectures with the existence of gradients of composition [7,13,31].…”

“…They are intended for use whenever enhanced UV resistance, high service temperature, and processing stability are essential. The recent years have seen the development of 7.1 INTRODUCTION styrenic-based copolymers made of more than three blocks, with the motivation to optimize the linear and nonlinear mechanical properties of the final materials [31,32]. Polyolefin-based thermoplastics are also widely used with the advantage of having a better chemical stability than the styrenic products [3].…”