We investigated the single chain motions of monodisperse polyisobutylene chains in the melt by neutron spin echo spectroscopy. Thereby a wide range in momentum space over a large dynamic range was covered. Motional processes from the center of mass diffusion, the Rouse dynamics to the more local relaxation processes which limit the validity of the standard Rouse model, were elucidated. The observed dynamic structure factors were analyzed in terms of relevant theoretical approaches addressing the limiting factors of the Rouse model. We found that other than claimed in the literature effects of local chain stiffness-they were treated in terms of the all rotational states model and a bending force model-cannot account for the experimental observations. It appears that additional damping effects related to an internal viscosity of the chain have to be involved, in order to explain the experimental results.

The living cationic polymerization of isobutylene (IB) was studied using the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl4/2,6-di-tert-butylpyridine (DTBP) system in hexane (Hex)/methyl chloride (MeCl) (60/40 and 40/60, v/v) solvent mixtures at various temperatures ranging from -25 to -80°C. From the Arrhenius plots of the apparent rate constants for propagation, negative apparent activation energies were observed and calculated to be -8.5 and -6.9 kcal/mol using Hex/MeCl, 60/40, v/v and 40/60, v/v solvent mixtures, respectively. At temperatures e -60°C, linear first-order plots and linear Mn versus conversion plots were obtained, suggesting the absence of termination and chain transfer. Irreversible termination was conspicuously observed from the curved ln([M]0/[M]) versus time plots when the polymerizations were carried out at temperatures g -40°C in both solvent mixtures. Mn versus conversion plots, however, exhibited linear growth of Mn, on the theoretical line, with increased conversion indicating the absence of chain transfer to monomer. Structural analysis of products obtained at -40°C using 1 H NMR spectroscopy revealed the presence of olefinic end groups, increasing in content with increased conversion. On the basis of these results, it is concluded that termination at higher temperature involves terminative chain transfer, that is, -proton elimination from the living chain ends with the eliminated proton being instantaneously entrapped by a proton trap, DTBP. By a kinetic treatment of the terminative chain transfer, the spontaneous chain-transfer constants (k tr/kp's), zero order in monomer,

Amphiphilic A2B2 star−block copolymers (A = polyisobutylene (PIB) and B = poly(methyl vinyl ether) (PMeVE)) have been prepared via the living coupling reaction of living PIB, using 2,2-bis[4-(1-tolylethenyl)phenyl]propane (BDTEP) as a living coupling agent, followed by the chain ramification reaction of methyl vinyl ether (MeVE) at the junction of the living coupled PIB. Model reactions for the synthesis of A2B2 star−block copolymers indicated that the fine-tuning of Lewis acidity to the reactivity of MeVE is a crucial step for the structural integrity of the resulting A2B2 star−block copolymers. Side products were negligible using a [Ti(OEt)4]/[TiCl4] ratio of 0.7 and the minimum tuning time (∼5 min). Fractionation of the crude A2B2 star−block copolymer was carried out on a silica gel column, and on the basis of the weights of fractions, the purity of the crude A2B2 star−block copolymer was calculated to be ≥93.5%. Two T gs (−60 °C for PIB and −20 °C for PMeVE) were observed for the star−block copolymer by DSC indicating the presence of two microphases. An A2B2 star−block copolymer with 80 wt % PMeVE composition ((IB45)2-s-(MeVE170)2) exhibited a critical micelle concentration (cmc) of 4.25 × 10-4 M in water, which is an order of magnitude higher than cmcs obtained with linear diblock copolymers with same total M n and composition (IB90-b-MeVE340) or with same segmental lengths (IB45-b-MeVE170). 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 cmc were measured to be from 41 to 177 nm, depending on the architecture and/or the molecular weight.

The living coupling reaction of living polyisobutylene (PIB), prepared by the 2,4,4-trimethyl-2-chloropentane/TiCl4/hexane:methyl chloride (60:40, v:v)/-80 °C system, has been studied using 1,3bis(1-phenylethenyl)benzene (MDDPE), 2,2-bis[4-(1-phenylethenyl)phenyl]propane (BDPEP), and 2,2bis[4-(1-tolylethenyl)phenyl]propane (BDTEP) as coupling agents. The reaction of living PIB with MDDPE yielded the monoadduct, possibly due to delocalization of positive charge over the meta-substituted benzene ring upon monoaddition and thereby decreased reactivity of the second double bond. Using BDPEP and BDTEP which have two diphenylethylene (DPE) moieties separated by an electron-donating spacer group, rapid and quantitative coupling was achieved independently of the chain length of the original PIB. The coupled product exhibited doubled molecular weight and narrowed molecular weight distribution. Direct evidence of the quantitative coupling reaction was also obtained by comparison of the 1 H NMR spectra of the samples before and after the coupling reaction. Kinetic studies by 1 H 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. As a result, high coupling efficiency was also observed when excess BDPEP was used.

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