Incorporation of Styrene into a Model Polyolefin for Enhanced Compatibility with Polyisoprene

Abstract

Polyisoprene (PI) and hydrogenated medium-vinyl polybutadiene (hPB), a polydiene–polyolefin pair, are expected to show limited compatibility (with a high interaction energy density, X, proportional to the Flory interaction parameter, χ). The regular mixing model suggests that styrene (S) units can boost the interblock compatibility when incorporated in small amounts into the hPB chain via random copolymerization. The mixing thermodynamics in symmetric polydiene–polyolefin “block–random” copolymers composed of PI and a random copolymer of styrene and hydrogenated medium-vinyl butadiene (hSBR) were investigated, through measurements of the order–disorder transition temperature. Block and block–random copolymers were prepared by anionic polymerization, followed by selective saturation of the butadiene units. More than a 2-fold decrease in X was achieved on incorporating ∼20 wt % S in the random block, with a further decrease observed at ∼30 wt % S incorporation, indicating a strong enhancement in compatibility. At higher styrene contents, X varied parabolically as qualitatively predicted by the regular mixing model, but better quantitative agreement was obtained with the copolymer equation model.

Synthesis, characterization and self-assembly of linear and miktoarm star copolymers of exclusively immiscible polydienes

“…It should be noted that this type of copolymers cannot be studied with small angle X-ray scattering (SAXS) due to the similar and almost identical electron density of the two polydiene segments involved. 33,43 The sample preparation used to investigate the morphology of all final copolymers in bulk is a crucial and important procedure. The casting was performed in a non-selective solvent for several days to promote the formation of equilibrium morphologies.…”

“…In this case, it would be interesting to prepare binary blends of the diblock copolymers, with either homopolymer PB 1,4 or homopolymer PI 3,4 in order to explore whether the double gyroid morphology will appear in the volume fraction regime 0.25-0.32. If not, then the specific studied system indicates a major discrepancy with the microphase separation of the well-studied PS-b-PI [42][43][44][45] diblock copolymer system.…”

Blends of Polyisoprene with Model Styrene–Olefin Copolymers: Mixing Energetics in Blends versus Block Copolymers

“…In addition, blends of PI with hPB and with PS homopolymers were also studied. In all the SBRs synthesized, TMEDA was added as a polar modifier 25 to randomize the styrene−butadiene sequence as shown by Halasa and coworkers. 57,58 The butadiene units can be preferentially saturated over the styrene units using a variety of catalysts.…”

“…Figure 6 shows a comparison between X blend and the PI−hSBR block copolymer X for each styrene content in the hSBR. Except for PI−hPB and PS−PI, for which block copolymer interaction energy data are available across a range of temperatures, all the other block copolymer data are shown at a single temperature (T ODT of the corresponding PI−hSBR block copolymer 25 ).…”

“…52 A detailed description of the NMR peak assignments for PI/hSBR systems has been presented earlier. 25 Selective Hydrogenation of SBR to hSBR. The SBRs were selectively hydrogenated using a colloidal lithium−cobalt (Li/Co) catalyst, 53,54 which saturates the butadiene units completely with undetectable saturation of the styrene units (>99% butadiene saturation and <1% styrene saturation, corresponding to the 1 H NMR detectability limit).…”