Synthesis and Characterization of Multiarm Star-Branched Polyisobutylenes: Effect of Arm Molecular Weight

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Polymers and High Performance Materials


A series of star-branched polyisobutylenes with varying arm molecular weights was synthesized using the 2-chloro-2,4,4-trimethylpentane/TiCl4/pyridine initiating system and divinylbenzene (DVB) as a core-forming comonomer( linking agent). The resulting star-branched polymers were characterized with regard to the weight-average number of arms per star molecule ((N) over bar(w)) and dilute solution viscosity behavior. As the molecular weight of the arm ((M) over bar(w,arm)) was increased, dramatically longer star-forming reaction times were needed to produce fully developed star polymers. It was calculated that (N) over bar(w) varied from 50 to 5 as the (M) over bar(w,arm) was increased from 13,000 to 54,000 g/mol. The radius of gyration, R-g, of the star polymers was observed to increase as (M) over bar(w,arm) was increased. The solution properties of the star polymers were evaluated in heptane using dilute solution viscometry. It was determined that the stars had a much higher [eta] compared to the respective linear PIB arms, but a much lower [eta] compared to a hypothetical linear analog of an equivalent molecular weight. The dependence of [ri] on temperature for the stars and linear arms was very small over the temperature range 25 to 75 degrees C, with only a very slight decrease with increasing temperature. [eta](star) was also determined to increase with increasing (M) over bar(w,arm), but decrease with increasing (M) over bar(w,star). The branching coefficient, g', calculated for the stars at 25 degrees C, increased as (N) over bar(w) decreased and agreed well with literature values for other star polymer systems. (C) 1997 John Wiley & Sons, Inc.

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Journal of Polymer Science Part A: Polymer Chemistry





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