Synthesis and Characterization of Novel Multiarm-Star Polyisobutylene-Polystyrene Thermoplastic Elastomers

Abstract New multiarm-star block copolymers of polyisobutylene (PIB) and polystyrene (PS) were synthesized by living carbocationic polymerization using a novel hexafunctional initiator in conjunction with TiCl4. The new initiator, hexaepoxy squalane (HES) was prepared by a simple epoxidation (RT, 5 min) of commercial squalene. The homopolymerization of isobutylene (IB) initiated by HES is living, demonstrated by linear ln([M]o/[M]t) vs time and Mn vs conversion plots and relatively narrow molecular weight distributions (MWD=1.2). The branched nature of the PIBs was proven directly by diphenyl ethylene end capping, and indirectly by kinetic analysis and size exclusion chromatography (SEC). Subsequent blocking of PIB with PS was demonstrated by triple detection SEC: refractive index (RI), multiangle laser light scatering (MALLS) and ultraviolet (UV). A new multiarm-star and a conventionally prepared linear triblock copolymer sample were subjected to supercritical fluid (SCF) fractionation and the fractions were analyzed by SEC and 1H NMR. Analysis of the fractions indicated living conditions for the PS blocking in the star-block. Interestingly, the linear triblock showed bimodal distribution in terms of PS content and molecular weight.

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Relationships between Molecular Weights and Rheological Properties of Asphalts

Transportation Research Record Journal of the Transportation Research Board ◽

10.1177/0361198196153500102 ◽

1996 ◽

Vol 1535 (1) ◽

pp. 10-14 ◽

Cited By ~ 2

Author(s):

Jan F. B ranthaver ◽

Raymond E. Robertson ◽

John J. Duvall

Keyword(s):

Molecular Weight ◽

Rheological Properties ◽

Size Exclusion Chromatography ◽

Size Exclusion ◽

Molecular Weights ◽

Molecular Weight Distributions ◽

Molecular Associations ◽

Weight Distributions ◽

Exclusion Chromatography ◽

Microstructural Model

It is known that the rheological properties of mixtures of organic compounds are functions of molecular weight distributions. However, with respect to asphalts, which are composed of many different compounds and compound types, molecular weights are difficult to measure. This difficulty occurs because the molecular associations that form are held together by forces of varying strengths and are partly broken up by heat and solvents. In theory, the strongest molecular associations in asphalts should have the greatest influence on the rheological properties of asphalts. These associations would be expected to be the major contributors to the asphalt's behaving as if it were a relatively high molecular weight material. Asphalt molecular associations should be isolatable by means of size exclusion chromatography. Several fractions of varying molecular weights (measured by membrane osmometry and vapor phase osmometry) were isolated from Strategic Highway Research Program (SHRP) asphalt AAD-1 by preparative size exclusion chromatography. Molecular weights of these fractions ranged from approximately 2,000 daltons to over 40,000 daltons. When these fractions were independently mixed with asphalt AAD-1 solvent moiety, mixtures were obtained whose rheological properties were a function of the molecular weights and concentrations of the associated materials. These results support the microstructural model of asphalt proposed during SHRP. The results also suggest that the unusual rheological properties of some asphalts may be explained by measuring molecular weight distributions. This type of information may be useful for modification of asphalts to achieve desirable rheological properties.

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