Youngkwan Lee

Synthesis and characterization of linear and three-arm star radial poly(styrene-b-isobutylene-b-styrene) block copolymers using blocked dicumyl chloride or tricumyl chloride/TiCl4/pyridine initiating system

Abstract Linear and three-arm star styrene-b-isobutylene-b-styrene block copolymers were synthesized by living cationic polymerization using ring-substituted di- or tricumyl chloride, respectively, as initiator, TiCl4 as coinitiator, pyridine as an electron donor and 2,6-di-tert-butylpyridine as a proton trap in a 60 40 ( v v ) methylcyclohexane/methyl chloride solvent mixture at − 80°C. The polymers had equivalent compositions and segmental molecular weights allowing the effect of molecular geometry on sample morphology and physical properties to be determined. The samples exhibited a dual-phase morphology consisting of cylindrical polystyrene domains dispersed within a matrix of polyisobutylene; polymer geometry was found to have a significant effect on the tensile properties, with the three-arm star sample displaying a tensile strength twice that of the linear sample. In addition, the three-arm star block copolymer was found to have a higher rubbery plateau modulus than the linear block copolymer. Due to their perfectly saturated mid-block, polyisobutylene-based block copolymers were found to be much more thermally stable than the closely related styrene-b-(ethylene-co-l-butene)-b-styrene block copolymers (hydrogenated polybutadiene centre block).

Living Carbocationic Polymerization of Isobutylene Using Blocked Dicumyl Chloride or Tricumyl Chloride TiCl4 Pyridine Initiating System

Abstract Living polymerization of isobutylene was achieved using an initiation system based on either 1,3-di(1-chloro-l-methylethyl)-5-tert-butylbenzene (tert-butyl-dicumyl chloride) or 1,3,5-tris(l-chloro-l-methylethyl)benzene (tricumyl chloride) in conjunction with TiCl4, and pyridine in hexanes/methyl chloride (60/40, v/v) cosolvents. TiCl4/pyridine was found to yield narrow molecular weight distribution (MWD ≈ 1.1) and quantitative initiation efficiency (Ieff < 90%). The living nature of the polymerization system was demonstrated by the linearity of molecular weight vs conversion plots and first-order kinetic plots up to about 90% monomer conversion. If polymerization was allowed to proceed further, a departure from first-order kinetics and a broadening of the molecular weight distribution was observed to occur. The living polymerization was investigated as a function of temperature, reaction time, and the concentration of TiCl4/pyridine. Polymerization rates were observed to increase with decreasing ...

Investigation of the structure and properties of polyisobutylene-based telechelic ionomers of narrow molecular weight distribution. II. mechanical

Sulfonated polyisobutylene (PIB) telechelic ionomers with narrow molecular weight distribution (MWD) have been recently developed, providing additional control over the structure and properties of these novel polymers. A small angle X-ray scattering (SAXS) peak often associated with the aggregation of the ionic species in the bulk, and a secondary peak, were recently observed in the narrow MWD sulfonated PIB telechelics for the first time. SAXS evidence, given earlier as part I of this two-part series, suggests that compression-molded sulfonated PIB telechelic ionomers with a narrow MWD (M¯w/M¯n ≈ 1.15) may have a local secondary structure of ionic lamellae or cylinders, and no such structure is found in similar broad MWD (M¯w/M¯n ≈ 1.8) telechelics. It is shown that narrowing the MWD, which acts to promote locally continuous structure in the tri-arms, alters the character of the network, in that the modulus of the tri-arm telechelic systems increases and the elongation at break is lowered by narrowing the MWD or decreasing the M¯n. The tri-arms of the highest M¯n (49.5 kg/mol) exhibit strain hardening and the lowest modulus, highest-breaking stress, and highest elongation at break in the ionomers studied. The presence of local ionic structure is also indicated by stress relaxation experiments in which the long-term or near-equilibrium stress is seen to decrease when the MWD is broadened or M¯n increases. It is believed that the difunctional materials do not form extensive ionic networks at all, but principally chain-extend, as has also been found before. It is observed that the properties of a solution “blend” of narrow MWD ionomers that has the same counterion, M¯n, and polydispersity as a broad MWD system exhibits lower elongation to break, lower breaking stress, and modulus of narrow MWD systems relative to the broader MWD material. Dynamic mechanical data indicate that narrowing the MWD or decreasing M¯n increases the flow transition temperature and rubbery plateau modulus. The “blend” exhibits dynamic mechanical properties between the narrow and broad, having a higher flow transition temperature than the broad MWD, but lower than the narrow MWD, and a rubbery plateau modulus between the other two.

Sulfonation of chlorine-containing polymers: Sulfonation of various model tert-alkyl chlorides

Summarytert-Alkyl chlorides of the structure R-C(CH3)2Cl, where R-methyl, ethyl, tert-butyl, and neo-pentyl, were reacted with a stoichiometric quantity of acetyl sulfate at room temperature in methylene chloride diluent. Reaction conversion was monitored as a function of time using 1H NMR; structure of the sulfonated products was characterized using 1H and 13C NMR. Reactivity toward sulfonation increased with increasing size of the R group. In all cases the structure of the products was the same as would be expected from sulfonation of the olefin which results from dehydrochlorination of the tert-chloride. The observed behavior was consistent with a mechanism involving dehydrochlorination followed by addition of SO3 to yield a zwitterionic intermediate. Depending upon structure, the zwitterion may either eliminate a proton to form one or more isomeric β,γ-unsaturated sulfonic acids, or it may rearrange to form a five-membered γ-sultone. This chemistry, which is particularly useful in the synthesis of ionomers, represents a direct route to alkyl sulfonic acids when the alkyl halide is the natural starting point in the synthesis.