Preparation,characterization, and dilute solution properties of four-branched cage-shaped poly(ethylene oxide)

A four-branched cage-shaped poly(ethylene oxide) (4C-PEO) was prepared by a coupling reaction at very dilute condition between two kinds of end-functional four-armed star-shaped PEOs having amino and N-hydroxysuccinimide groups on their four ends, followed by purification using α-cyclodextrin (α-CD). The raw coupling reaction product shows multiple peaks including various high molecular weight multimeric products in size-exclusion chromatography measurements, while the product after α-CD purification shows a single peak eluted slightly earlier than the precursor star PEOs. Moreover, the final product obtained has about twice higher molecular weight than the star precursors. These results suggest that the targeted 4C-PEO polymer was successfully isolated through the α-CD purification. Small-angle neutron scattering (SANS) measurements of the final product in dilute solution were conducted, and its chain conformation was evaluated from the scattering profile in comparison with linear and star polymers. It has been found that the cage-shaped sample exhibits a distinct peak at lower q-region in the Kratky plot, which is in strong contrast with the linear counterpart. This result must be originated from the characteristic cage-shaped architecture, that is, having branched and closed-loop configurations, and hence having higher segmental density than simple linear and star molecules. In fact, the present experimental result is consistent with the recent Monte Carlo simulation reported by Uehara and Deguchi.     

Synthesis of cyclic and multicyclic polyisoprenes

Cyclic polyisoprenes have been synthesized by reaction of α,ω-dilithiopolyisoprenes with dichlorodimethylsilane or 1,2-bis(isopropenyl-4-phenyl) ethane (BIPE). Using the dihalide compound, the effect of the solvent polarity on the coupling reaction is more pronounced in the case of α,ω-dilithiopolyisoprene than with monofunctional polyisoprenyllithium. The yield in cyclic compound falls from 88% in pure hexane down to 53% in the presence of 15 vol% of tetrahydrofurane (THF). Using the nonconjugated diene (BIPE) as linking agent the addition of THF is required but the formed cycle retains its living character and allows the synthesis of cycles having two arms (after addition of isoprene) and of a bicyclic structure after a second cyclization reaction.     

Comparison of the rheological properties of linear and star-branched polyisoprenes in shear and elongational flows

The rheological properties of narrow-molecular-weight-distribution linear and star-branched polyisoprenes have been determined using both shearing and stretching deformations. At all strain rates studied the tensile stress measured under transient and steady-state conditions did not increase above the linear viscoelastic value. The absence of an enhanced tensile stress for the branched polymer is in contrast to what is observed for branched low-density polyethylene. An explanation for the difference is proposed. Additional remarks are made about the broad distribution of relaxation times observed for star-branched polyisoprenes and about the approach to steady state in constant-strain-rate and constant-stress tests.     

Synthesis and properties of amphiphilic star polysulfides

We here present the synthesis and characterisation of linear and star-shaped amphiphilic block copolymers based on hydrophobic polysulfides (poly(propylene sulfide), PPS) and hydrophilic polyethers (poly(ethylene glycol), PEG). We also discuss the proof of the principle of their responsiveness to oxidising conditions. In a water environment, these polymers aggregate in the form of sub-micron carriers that, due to the sensitivity to oxidation reactions typical of PPS, can be used for responsive drug delivery. In this first study we have focused on the study of large aggregates, which do not apparently show dramatic differences in behaviour when polymer chains with different degrees of branching are studied.     

Dilute solution properties of asymmetric six-arm star polystyrenes

Six-arm star polystyrenes having varying numbers of short and long arms attached to the same molecule have been synthesized by anionic polymerization. The molecules have been characterized by high resolution size exclusion chromatography using multiangle light scattering and viscosity detectors. This technique has allowed the radii of gyration and intrinsic viscosities to be measured for stars with each possible combination of arms. The branching parameters g and g′ are computed and compared with theoretical expectations. It is found that short arms add preferentially to the stars, because of reduced steric effects. The molecule with one long and five short arms exhibits behavior closest to that of a linear chain (largest branching ratios). The effect of arm polydispersity on solution properties of stars is discussed. © 1995 John Wiley & Sons, Inc.     

Effective interaction parameter of linear/star polymer blends and comparison with that of linear/linear and star/star blends

The authors present a detailed study of the microscopic parameters, which control the miscibility in binary linear/star polymer blends. The effective interactions of linear/star polymer blends are studied by means of Monte Carlo simulations and comparison is made with linear/linear and star/star blends, which they also determined. Using the bond fluctuation model on a simple cubic lattice, the authors are able to simulate symmetric linear/linear, star/star, and, for the first time, linear/star blends with a moderate number of arms. The simulations were performed at a volume fraction of occupied lattice sites phi=0.5, which corresponds to dense polymer mixtures for this algorithm. In particular, we study star/star blends with 4, 8, and 12 arms and the respective linear/linear blends as well as linear/star blends, all having the same total number of units equal to 73 and 121. The authors find that linear/star blends are more miscible than the corresponding linear/linear blends, which is in agreement with recent experimental and theoretical results. They find that linear/star mixtures are less miscible than star/star blends, a result which is also verified by theoretical findings.     

Hydrodynamic behavior of anionically prepared linear polyisoprenes and polystyrenes in carbon tetrachloride

Intrinsic viscosity, [η], weight-average molecular weight, M_w, relationships are reported for narrow molecular weight distribution linear polyisoprene and polystyrene samples in CCl₄ at 25°C. Molecular weight values cover a range nearly two orders in magnitude, extending as low as 3 × 10³. In the case of polystyrene there exists a molecular weight range (around M_w = 16,700) corresponding to a change in the Mark-Houwink-Sakurada (MHS) exponent from α = 0.71 to α = 0.54. Comparisons between the viscometric and hydrodynamic radii, from literature data, are made. For polyisoprene the MHS relationship is reported in CCl₄, for the first time. For this case α = 0.713 for the whole range of molecular weights studied. Values for the second virial coefficient from low-angle light-scattering measurements support the conclusions drawn from viscometry that CCl₄ is a good solvent for both polymers studied. The different behavior of the MHS exponent may be attributed to the difference in chain flexibility. © 1995 John Wiley & Sons, Inc.     

Viscoelastic properties and flow of narrow distribution polybutadienes and polyisoprenes

The dynamic shear modulus and the flow rate through capillaries under constant pressure and under constant velocity of the piston, have been measured for polybutadienes and polyisoprenes of narrow molecular weight distribution with molecular weights ranging, respectively, from 3.8 × 10⁴ to 5.8 × 10⁵ and from 1.06 × 10⁵ to 6.02 × 10⁵. The phenomena of the discontinuous increase of volume flow rate and self-oscillatory flow regime at critical rates of deformation have been considered in detail. It is proposed that these phenomena are due to the induced transition of the polymer from the fluid to the high-elastic state at higher deformation rates. As a result, an inference has been made that polybutadienes and polyisoprenes with a narrow molecular weight distribution in the high-elastic state, behave in certain respects as crosslinked polymers incapable of displaying fluidity. The quantitative relationships among the viscoelastic characteristics measured under dynamic regimes, the parameters determining the critical flow regimes, and the molecular weights of polybutadienes and polyisoprenes have been worked out.     

Synthesis and degradation of biomedical materials based on linear and star shaped polyglycidols

Linear and star shaped polyglycidols (synonym with polyglycerols) are prepared in a controlled ring opening polymerization of protected glycidols. Beside the molar mass and the polydispersity, the architecture of the polyglycidols is controlled by using mono‐ and multifunctional mono‐ and polydispers initiators. Copolymers of dissimilarly protected glycidols as well as copolymers with nonfunctional oxiranes were prepared by means of anionic polymerization while copolymers of protected glycidol with tetrahydrofuran were prepared by means of cationic polymerization. Polyethers with functional groups in the side chains (functional polyethers) with special emphasis on polyglycidols (containing hydroxymethyl groups in the side chains) were used to prepare multifunctional polymers and (hetero)grafted polymer brushes via chemical and enzyme catalyzed reaction. The potential of poly(glycidol‐graft‐ε‐caprolactone)‐co‐glycidol) prepared via enzyme catalyzed grafting of polyglycidols using ε‐caprolactone as a monomer and Lipase B from Candida antarctica as a catalyst is presented. Finally, comparative degradation studies of densely and loosely grafted polyglycidols are presented and discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3209–3231, 2009     

Synthesis,characterisation and properties of star polypseudorotaxanes with cucurbit[7]uril

New star polypseudorotaxanes that include 4,4′-dipyridyl-terminated 4-arm-poly(ethylene glycol) (PC1) and cucurbit[7]uril (CB[7]) were easily synthesised. The ¹H NMR, UV–vis and resonance light scattering (RLS) data show that the viologen units of the star polypseudorotaxanes could fall off from the hydrophobic cavity of CB[7] with the addition of 1-adamantylamine (ADA). The cyclic voltammograms results indicate that the star polypseudorotaxanes have the redox property with the addition of ADA compared with the non-redox property of the pure star polypseudorotaxanes. The biological toxicity experiment shows that the bactericidal activity of the star polypseudorotaxanes in Escherichia coli was aroused by adjusting CB[7] dethreading from the star polypseudorotaxanes with the addition of another competitive guest ADA, which has a very high affinity for CB[7].     

Synthesis, electrochemical, and optical properties of linear homo- and heterometallocene triads

The synthesis, electrochemical, and optical properties of homo- (5, 8, 9, and 12) and heterometallic (6, 7, 10, and 11) ferrocene-ruthenocene triads, are presented. Triferrocenyl derivatives 5 and 9 form the mixed-valence species 5*+ and 92+ by partial oxidation, which show intramolecular electro-transfer phenomena. Interestingly, spectroelectrochemical studies of compound 11, bearing two peripheral ferrocene units and one central ruthenocene moiety, revealed the presence of low-energy bands in the near-infrared (NIR) region, which indicate a rather unusual intramolecular charge-transfer between the ferrocene and ruthenocene units. The value of the electronic coupling parameter V(ab) = 150 cm(-1) calculated by deconvolution of the observed Fe(II)-Fe(III) IVCT transition in the mixed-valence compound 11*+, (d(Fe(II)-Fe(III)) = 18.617 A), indicates the ability of the ruthenocene system to promote a long distance intervalence electron-transfer. Moreover, the reported triads show selective cation sensing properties. Triads 5, 9, and 11 behave as dual redox and optical chemosensors for Zn(2+), Hg(2+), and Pb(2+). Their oxidation redox peaks are anodically shifted (up to 130 mV), and their low-energy (LE) bands of the absorption spectra are red-shifted (up to 115 nm) upon complexation with these metal cations. These changes in the absorption spectra are accompanied by dramatic color changes which allow the potential for "naked eye" detection.     

Synthesis and stability of linear and star polymers containing [C60] fullerene

Linear and symmetric star block copolymers of styrene and isoprene containing [C₆₀] fullerene were synthesized by anionic polymerization and appropriate linking postpolymerization chemistry. In all block copolymers, the C₆₀ was connected to the terminal polyisoprene (PI) block. The composition of the copolymers was kept constant (～30% wt PI), whereas the molecular weight of the diblock chains was varied. The polymers were characterized with a number of techniques, including size exclusion chromatography, membrane osmometry, and ¹H NMR spectroscopy. The combined characterization results showed that the synthetic procedures followed led to well‐defined materials. However, degradation of the fractionated star‐shaped copolymers was observed after storage for 2 months at 4 °C, whereas the nonfractionated material was stable. To further elucidate the reasons for this degradation, we prepared and studied a four‐arm star copolymer with the polystyrene part connected to C₆₀ and a six‐arm star homopolymer of styrene. These polymers as well as linear copolymers end‐capped, through ? N<, with C₆₀ were stable. Possible reasons are discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2494–2507, 2001     

Synthesis and solution properties of rodlike polyelectrolytes

The synthesis and the solution behavior of rigid, rodlike cationic polyelectrolytes having (i) poly(p-phenylene) backbones and (ii) main chains composed of 4,4“-bis(2,2′:6′,2”-terpyridine)2′,5′-dihexyl-p-terphenyl moieties and ruthenium(II) centers are presented. All these polymers are shown to have a homogeneous constitution and degrees of polymerization of up to P_n ≈ 70. Their solution properties were analyzed using viscosimetry, small-angle X-ray scattering (SAXS) and osmometry. Pronounced polyelectrolyte effects were found in salt-free solutions using viscosimetry. Small-angle X-ray scattering demonstrated directly the strong correlation of the counterions and the macroions. The osmotic coefficients measured in salt-free solution as function of polyelectrolyte concentration were found to be lower than predicted by the cell model.     

Cryogenic tensile stress–strain properties of cis- and trans-polybutadienes,polyisoprenes, and related copolymers

The low-strain-rate tensile stress–strain properties of cis- and trans-polybutadienes and -polyisoprenes, polybutadiene (cis/trans/vinyl), butyl rubber, and two SBR copolymers have been investigated from 77°K to up to 25°K below the glass transition temperature T_g. The energy E_p dissipated in a stress–strain test in the region of previously reported secondary glass transitions is found to be a function of both the free volume f? at the T_g and the damping A from 4°K to T_g ?25°K. The complex relationship between the impact strength, the free volume and the damping is briefly discussed. The effect of quenching through the T_g with liquid nitrogen was found to increase the value of E_p for all materials. In a number of cases this increase was associated with the presence of internal crazes. The surface-craze initiation stress is increased by the presence of surface residual compressive stresses caused by quenching. The internal tensile stresses balancing the surface compressive stresses together with the applied tensile stress cause internal dilatation and hence preferential initiation of internal crazing.     

Synthesis of linear and three-arm star tert-chlorine-telechelic polyisobutylenes by a two-step conventional laboratory process

A two-step conventional laboratory process was developed for the synthesis of mono- and difunctional linear and three-arm star tert-chlorine-telechelic polyisobutylenes (PIB) with desired molecular weights (MW) and narrow molecular weight distribution (MWD) by living carbocationic polymerization (LCCP). This polymerization method applies easy to handle operations and chemicals. LCCP of isobutylene (IB), was carried out in CH₂Cl₂ as solvent and with BCl₃ as coinitiator in the first step to obtain soluble low MW PIB prepolymer with narrow MWD. This was followed by addition of hexane, TiCl₄ and additional monomer in the second step to prepare PIBs with desired MW and narrow MWD in practically any suitable MW region. Comparison of the one-step and two-step processes is also described.     

Synthesis and properties of some linear oligobenzyls and polybenzyls

Properties of some linear oligobenzyls corresponding to polybenzyl, poly(2,5-dimethylbenzyl), and poly(2,3,5,6-tetramethyl-benzyl) systems are correlated to those of relative polymers. From infrared and x-ray diffraction data, evidence is found that oligomers tend to assume the same crystal structure of the polymer as early as teh tetramer or pentamer stage. Syntheses of oligomers are described. Linear, crystalline polymers, necessary for comparison with oligomers, have been prepared and characterized. Polymerization conditions have been explored to some extent; relevant data are tabulated and discussed.     

Synthesis and liquid crystal properties of phthalocyanine bearing a star polytetrahydrofuran moiety

A new polymeric ligand, 6-(3,4-dicyanophenylthio)-hexyl-2-polytetrahydrofuranacetate (2) and its liquid crystalline polymeric phthalocyanine, 2,9,16,23-tetrakis-{6-(polytetrahydrofuran-2-carboxylate)-hexylthio-phthalocyaninatocobalt(II) (3), {Co[Pc(S-C₆H₁₃OCO-poly-THF)₄]}(CoPcLC) have been synthesized. The ligand and the phthalocyanine, bearing polytetrahydrofuran moieties (poly-THF), were characterized using elemental analysis, FTIR, ¹H and ¹³C NMR, and UV–Vis techniques. CoPcLC (3) promotes a greater interaction between the mesogens, resulting in solution aggregations together with a red-shift in the Q-band in the presence of the soft Ag⁺ ion. The dielectric anisotropy and phase transition temperature values of CoPcLC doped with 4-cyano-4′-n-pentylbiphenyl (5CB) were found to be 7.17 and 40.5 °C, respectively. The dielectrical anisotropy behaviour of the liquid crystals changes from the positive to the negative type. The current–voltage characteristics of the liquid crystals show a non-linear behaviour.     

Synthesis,physical, and thermal properties of linear poly(dialkoxyphosphinyl-s-triazine)s

A novel class of linear poly(dialkoxyphosphinyl-s-triazine)s were prepared by interfacial or solution polycondensation reactions of various diamines such as ethylenediamine, hexamethy-lenediamine or bis(4-aminocyclohexyl)methane with 2-dialkoxyphosphinyl-4,6-dichloro-s-triazines. The latter were synthesized by reacting cyanuric chloride with an equimolar amount of trialkyl phosphite. The phosphorous-containing polymers were characterized by inherent viscosity measurements as well as by infrared (IR) and proton nuclear magnetic resonance (¹H-NMR) spectroscopy. The thermal properties of polymers were investigated by differential thermal analysis (DTA) and thermogravimetric analysis (TGA). Pyrolysis of all polymers was exothermic. Polymers were stable up to 150–200°C both in nitrogen and air atmosphere. They afforded 16–42% char yield at 700°C under anaerobic conditions.