| The living coupling reaction of living polyisobutylene (PIB), prepared by the 2-chloro-2,4,4-trimethylpentane/TiCl4/2,6-di-tert -butylpyridine/hexane:CH3Cl (60:40, v:v)/--80°C system, has been studied using 1,3-bis(1-phenylethenyl)benzene (MDDPE), 2,2-bis[4-(1-phenylethenyl)phenyl]propane (BDPEP), and 2,2-bis[4-(1-tolylethenyl)phenyl] propane (BDTEP) as coupling agents. The reaction of living PIB with MDDPE yielded the monoadduct due to the decreased reactivity of the second double bond upon monoaddition. Using BDPEP and BDTEP, which have two 1,1-diphenylethylene (DPE) units separated by an electron-donating spacer group, rapid and quantitative coupling was achieved. Kinetic studies by 1H NMR spectroscopy indicated the coupling reaction of living PIB by BDPEP is a consecutive reaction where the second addition is faster than the first one. By kinetic treatment of the experimental results, it was found that the second addition is about 5 times faster than the first one.;On the basis of this living coupling reaction, amphiphilic A2B2 star-block copolymers (A = PIB and B = poly(methyl vinyl ether)) have been prepared. The living coupling reaction of living PIB was carried out using BDTEP as a living coupling agent, and this was followed by the chain-ramification polymerization of methyl vinyl ether (MeVE) at the junction of the living coupled PIB. By fractionation of the crude A2 B2 star-block copolymer, the purity of the crude A2 B2 star-block copolymer was calculated to be ∼94%. Two Tgs (-60 and -20°C) were observed for the star-block copolymer by DSC indicating the presence of the microphase separation. An A2B2 star-block copolymer with 80 wt% PMeVE composition ((IB45)2-s-(MeVE170) 2) exhibited a critical micelle concentration (cmc) of 4.25 x 10-4 M in water, which is an order of magnitude higher than cmcs obtained with linear-diblock copolymers with same total Mn and composition (IB90-b-MeVE 340) or with same segmental lengths (IB45-b-MeVE 170). This suggests that block copolymers with star architectures exhibit less tendency to micellization than their corresponding linear diblock copolymers. Average particle sizes in aqueous solution above the cmcs were measured to be from 41 to 177 nm, depending on the architecture and/or the molecular weight.;Taking advantage of the monoaddition reaction of living PIB to double-DPEs, such as MDDPE or 1,4-bis(1-phenylethenyl)benzene (PDDPE), PIB macromonomers with terminal-DPE functionality have been prepared. The addition reaction of living PIB to 2 equiv of MDDPE resulted in the predominant formation of the monoadduct with negligible but detectable amounts (∼3%) of the diadduct. When 4 equiv of MDDPE was used, the diadduct was virtually absent and the product exhibited ∼100% DPE functionality. The addition reaction of living PIB to 2 equiv of PDDPE resulted in a rapid and quantitative formation of PIB-DPE macromonomer without the formation of the coupled product. Kinetic studies using fiber-optic visible spectroscopy indicated that PDDPE is ∼2.5 times more reactive than MDDPE towards living PIB. |
