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High-resolution small angle X-ray scattering (SAXS) measurements were performed on two series of poly(ethylene-alt-propylene)-b-poly(D,L-lactide) (PEP-PLA) diblock copolymer materials exhibiting differences in the widths of the poly(D,L-lactide) block molecular mass distributions as measured by their polydispersity indices (PDIPLA). At symmetric compositions of PEP-PLA (fPLA ≈ 0.5), all SAXS data were successfully fit to an established model describing the small angle scattering from lamellar mesostructures. According to this model, the increase in the PDIPLA negligibly affected the amount of lattice disorder. The apparent asymmetry of the poly(ethylene-alt-propylene)-block lamellae (ϕ), also determined by the fitting procedure, were more substantially affected; increasing the PDIPLA resulted in a decrease in ϕ. At asymmetric compositions of PEP-PLA (fPLA ≈ 0.67), only the data at the highest values of the PDIPLA could be reasonably fit to this model. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3386–3393, 2007
Block copolymers containing polystyrene and polycyclooctene were synthesized with a ring-opening metathesis polymerization/chain-transfer approach. Polystyrene, containing appropriately placed olefins, was prepared by anionic polymerization and served as a macromolecular chain-transfer agent for the ring-opening metathesis polymerization of cyclooctene. These unsaturated polymers were subsequently converted to the corresponding saturated triblock copolymers with a simple heterogeneous catalytic hydrogenation step. The molecular and morphological characterization of the block copolymers was consistent with the absence of significant branching in the central polycyclooctene and polyethylene blocks [high melting temperatures (114–127 °C) and levels of crystallinity (17–42%)]. A dramatic improvement in both the long-range order and the mechanical properties of a microphase-separated, symmetric polystyrene–polycyclooctene–polystyrene block copolymer sample was observed after fractionation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 361–373, 2007
Funktionelle Gruppen am Ende: Unter Rh-Katalyse ist käufliches lineares Niederdruckpolyethylen (LLDPE) mit Borreagentien selektiv funktionalisierbar. Die anschließende Oxidation sowie weitere Umwandlungen der borhaltigen Polymere führen eine Vielfalt polarer Funktionen (z. B. Hydroxy-, Amino- oder Formylgruppen) an den Enden und Seitenketten ein (siehe Schema).
A versatile coupling reaction for the preparation of polybutadiene–poly-(hexafluoropropylene oxide) (BF) diblock copolymers is described. Six diblock copolymers with different block lengths were characterized by nuclear magnetic resonance spectroscopy and size exclusion chromatography; all six had total molecular weights below 15,000. Microphase separation of the block copolymers in the bulk state was established by small-angle X-ray scattering (SAXS) and differential scanning calorimetry. SAXS data suggest that the diblocks are characterized by an unusually large Flory-Huggins interaction parameter, χ, on the order of 10. However, extraction of χ from the order–disorder transition gave large (order 1) but significantly different values, thereby suggesting that these copolymers are too small and too strongly interacting to be described by block copolymer mean-field theory. Dynamic light scattering was used to analyze dilute solutions of the title block copolymers in four selective organic solvents; the sizes of the micelles formed were solvent dependent. The micellar aggregates were large and nonspherical, and this is also attributed to the high degree of incompatibility between the two immiscible blocks. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3685–3694, 2005
We report the preparation of novel fluorinated block copolymers using a two-step modification sequence. We first prepared model polyisoprene-poly-tert-butylmethacrylate block copolymers by anionic polymerization. Exposing these materials to difluorocarbene (generated by the thermolysis of hexafluoropropylene oxide) resulted in modification of the polyisoprene block to the corresponding difluorocyclopropane repeating unit without compromising the integrity of the poly-tert-butylmethacrylate block. Hydrolysis of the difluorocarbene-modified materials gave the corresponding difluorocarbene-modified polyisoprene-polymethacrylic acid diblock copolymers. These amphiphilic materials are expected to exhibit interesting self-assembly behavior in aqueous solution.
Two sets of styrene-based semifluorinated block copolymers, one with a perfluoroether pendant group and another with a perfluoroalkyl group, were synthesized by atom transfer radical polymerization. Microphase separation of the block copolymers was established by small-angle X-ray scattering and differential scanning calorimetry (DSC). DSC measurements also showed that the perfluoroether-based polymer had a low glass-transition temperature (−44 °C). Contact-angle measurements indicated that the semifluorinated block copolymers had low surface energies (ca. 13 mJ/m2). These materials hold promise as low-surface-energy additives or surfactants for supercritical CO2 applications. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 853–861, 2004
Melt blending of polylactide and linear low-density polyethylene (LLDPE) was performed in an effort to toughen polylactide. In addition, two model polylactide-polyethylene (PLLA-PE) block copolymers were investigated as compatibilizers. The LLDPE particle size and the impact resistance of binary and ternary blends were measured to determine the extent of compatibilization. For the amorphous polylactide (PLA), toughening was achieved only when a PLLA-PE block copolymer was used as a compatibilizer. For the semicrystalline polylactide (PLLA), toughening was achieved in the absence of block copolymer. To decrease the variability in the impact resistance of the PLLA/LLDPE binary blend, as little as 0.5 wt % of a PLLA–;PE block copolymer was effective. The differences that were seen between the PLA and PLLA binary blends were investigated with adhesion testing. The semicrystalline PLLA did show significantly better adhesion to the LLDPE. We propose that tacticty effects on the entanglement molecular weight or miscibility of polylactide allow for the improved adhesion between the PLLA and LLDPE. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3757–3768, 2003
Fluorinated block copolymers combine the unique properties of fluoropolymers and the intriguing self-assembly of hybrid macromolecules. The preparation of the title molecules by selective fluorination procedures and the effect of fluorine incorporation on the material thermodynamics are presented. We highlight two fluorination schemes developed in our laboratory, difluorocarbene and perfluoroalkyliodide additions to polydienes, that allow for the selective and tunable incorporation of different fluorinated groups into model block copolymers. The fluorination changes the physical properties of the parent materials and leads to interesting changes in the component incompatibilities. The role of fluorination in determining block copolymer thermodynamics in both the solid state and in solution and in ultimately exploiting fluorination to produce novel, higher order structures is central to our research efforts. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 1–8, 2002
A set of well-defined poly(ethylene-alt-propylene)-b-polylactide (PEP-PLA) diblock copolymers containing volume fractions of PLA (fPLA) ranging between 0.08 and 0.91 were synthesized by a combination of living anionic polymerization, catalytic hydrogenation, and controlled coordination-insertion ring-opening polymerization. The morphological behavior of these relatively low-molecular-weight PEP-PLA diblock copolymers was investigated with a combination of rheology, small-angle X-ray scattering, and differential scanning calorimetry. The ordered microstructures observed were lamellae (L), hexagonally packed cylinders (C), spheres (S), and gyroid (G), a bicontinous cubic morphology having Ia3d space group symmetry. The G morphology existed in only a small region between the L-C morphologies in close proximity to the order–disorder transition (ODT). Transformations from L to G were observed upon heating in several samples. The efficacy of the reverse G to L transition in one sample was cooling rate dependent. The PEP-PLA Flory–Huggins interaction parameter as a function of temperature χPEP-PLA(T) was estimated from TODT's by mean-field theory and subsequently used in the construction of the experimental PEP-PLA morphology diagram (χN versus fPLA). The resultant morphology diagram was symmetric there were the well-defined L-C morphology boundaries. The low molecular weight of the materials imparted no significant deviation from previously documented diblock systems. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2364–2376, 2002
In quest of new, single-site catalysts for cyclic ester polymerizations, a series of mononuclear yttrium(III) complexes of N,N′-bis(trimethylsilyl)benzamidinate ([LTMS]−) and hindered N,N′-bis-(2,6-dialkylaryl)toluamidinates ([LEt]−, aryl = Et2C6H3, and [LiPr]−, aryl = iPr2C6H3) were synthesized and characterized by X-ray diffraction: LY(μ-Cl)2Li(TMEDA) (1), LY(OC6H2tBu2Me) (2), LY(OC6H3Me2)2Li(THF)4 (3), LY(μ-OtBu)2Li(THF) (4), LiPrY[N(SiMe2H)2]2(THF) (5), LY(THF)(Cl)(μ-Cl)Li(THF)3 (6), and LY[N(SiMe2H)2] (7). Coordination numbers ranging from five to seven were observed, and they appeared to be controlled by the steric bulk of the supporting amidinate and alkoxide, phenoxide, or amide coligands. Complexes 2–5 and 7 are active catalysts for the polymerization of D,L-lactide (e.g., with 2 and added benzyl alcohol, 1000 equiv of D,L-lactide were polymerized at room temperature in less than 1 h, with polydispersities less than 1.5). The neutral complexes 2, 5, and 7 were more effective than the anionic complexes 3 and 4. In addition, the presence of the more hindered amidinate ligands [LEt]− and [LiPr]− on yttrium-amides slowed the polymerizations (7 < 5 < Y[N(SiMe2H)2]3). © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 284–293, 2001
A model polyethylene-poly(L-lactide) diblock copolymer (PE-b-PLLA) was synthesized using hydroxyl-terminated PE (PE-OH) as a macroinitiator for the ring-opening polymerization of L-lactide. Binary blends, which contained poly(L-lactide) (PLLA) and very low-density polyethylene (LDPE), and ternary blends, which contained PLLA, LDPE, and PE-b-PLLA, were prepared by solution blending followed by precipitation and compression molding. Particle size analysis and scanning electron microscopy results showed that the particle size and distribution of the LDPE dispersed in the PLLA matrix was sharply decreased upon the addition of PE-b-PLLA. The tensile and Izod impact testing results on the ternary blends showed significantly improved toughness as compared to the PLLA homopolymer or the corresponding PLLA/LDPE binary blends. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2755–2766, 2001
A nucleation efficiency scale for isotactic poly(L-lactide) (PLLA) was obtained with self-nucleation and nonisothermal differential scanning calorimetry experiments. The maximum nucleation efficiency occurred at the highest concentration of self-nucleating sites, and the minimum efficiency occurred in the absence of these sites (pure PLLA polymer melt). Blends of PLLA and isotactic poly(D-lactide) (PDLA) led to the formation of a 1/1 stereocomplex. In comparison with the homopolymer (PLLA), the stereocomplex had a higher melting temperature and crystallized at higher temperatures from the melt. Small stereocomplex crystallites were formed in PLLA/PDLA blends containing low concentrations of PDLA. These crystallites acted as heterogeneous nucleation sites for subsequent PLLA crystallization. Using the PLLA nucleation efficiency scale, we evaluated a series of PLLA/PDLA blends (0.25–15 wt % PDLA). A maximum nucleation efficiency of 66% was observed at 15 wt % PDLA. The nucleation efficiency was largely dependent on the thermal treatment of the sample. The nucleating ability of the stereocomplex was most efficient when it was formed well before PLLA crystallization. According to the efficiency scale, the stereocomplex was far superior to talc, a common nucleating agent for PLLA, in its ability to enhance the rate of PLLA crystallization. In comparison with the PLLA homopolymer, the addition of PDLA led to reduced spherulite sizes and a reduction in the overall extent of PLLA crystallization. The decreased extent of crystallization was attributed to the hindered mobility of the PLLA chains due to tethering by the stereocomplex. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 300–313, 2001
Anionic polymerization of isoprene initiated by an alkyl lithium containing a silyl ether protected hydroxyl functionality followed by termination with ethylene oxide gave α,ω-functionalized polyisoprene with narrow molecular weight distribution and prescribed molecular weight in high yield. Deprotection resulted in α,ω-hydroxyl polyisoprene (HO-PI-OH) that was reacted with triethylaluminium to form the corresponding aluminium alkoxide macroinitiator. The macroinitiator was used for the controlled polymerization of lactide to yield polylactide-block-polyisoprene-block-polylactide triblock copolymers with narrow molecular weight distributions and free of homopolymer (HO-PI-OH) contamination. Microphase separation in these novel triblock copolymers was confirmed by SAXS and DSC.
