Synthesis and characterization of multiarm star-branched polyisobutylenes: Effect of arm molecular weight

✍ Scribed by Robson F. Storey; Kelly A. Shoemake; Jimmy W. Mays; Steve Harville

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 242 KB
• Volume: 35
• Category: Article
• ISSN: 0887-624X
• DOI: 10.1002/(sici)1099-0518(199712)35:17<3767::aid-pola16>3.0.co;2-b

✦ Synopsis

A series of star-branched polyisobutylenes with varying arm molecular weights was synthesized using the 2-chloro-2,4,4-trimethylpentane/TiCl 4 /pyridine initiating system and divinylbenzene (DVB) as a core-forming comonomer (linking agent). The resulting star-branched polymers were characterized with regard to the weightaverage number of arms per star molecule ( N V w ) and dilute solution viscosity behavior. As the molecular weight of the arm ( M V w,arm ) was increased, dramatically longer star- forming reaction times were needed to produce fully developed star polymers. It was calculated that N V w varied from 50 to 5 as the M V 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 V 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 [ h] compared to the respective linear PIB arms, but a much lower [ h] compared to a hypothetical linear analog of an equivalent molecular weight. The dependence of [ h] on temperature for the stars and linear arms was very small over the temperature range 25 to 75ЊC, with only a very slight decrease with increasing temperature. [ h] star was also determined to increase with increasing M V w,arm , but decrease with increasing M V w,star . The branching coefficient, g, calculated for the stars at 25ЊC, in- creased as N V w decreased and agreed well with literature values for other star polymer systems.