Solvent-induced microphase separation in diblock copolymer thin films with reversibly switchable morphology

We have studied the surface morphology of symmetric poly(styrene)-block-poly(methyl methacrylate) diblock copolymer thin films after solvent vapor treatment selective for poly(methyl methacrylate). Highly ordered nanoscale depressions or striped morphologies are obtained by varying the solvent annealing time. The resulting nanostructured films turn out to be sensitive to the surrounding medium, that is, their morphologies and surface properties can be reversibly switchable upon exposure to different block-selective solvents.

New titanium complexes with two beta-enaminoketonato chelate ligands: Syntheses, structures, and olefin polymerization activities

New titanium complexes with two nonsymmetric bidentate beta-enaminoketonato (N,O) ligands (4a-e), [(Ph)NC(R-2)C(H)C(R-1)O](2)TiCl2, have been synthesized. X-ray crystal structure reveals that complex 4a has a C-2-symmetric conformation with a distorted octahedral geometry around the titanium center. With modified methylaluminoxane (MMAO) as a cocatalyst, complexes 4a-e are active catalysts for ethylene polymerization at room temperature, producing high molecular weight polyethylenes bearing linear structures. The 4a,b/MMAO catalyst systems exhibit the characteristics of a quasi-living polymerization of ethylene, producing polyethylenes with narrow molecular weight distributions. Moreover, the 4a-d/MMAO catalyst systems are also capable of promoting the quasi-living copolymerization of ethylene with norbornene at room temperature, yielding high molecular weight alternating copolymers with narrow molecular weight distributions. The quasi-living nature of the catalysts allows the synthesis of new A-B polyethylene-block-poly(ethylene-conorbornene) diblock copolymer.

Study of the synthesis, crystallization, and morphology of poly(ethylene glycol)-poly(is an element of-caprolactone) diblock copolymers

Poly(ethylene glycol) -poly(epsilon-caprolactone) diblock copolymers PEG-PCL were synthesized by ring-opening polymerization of c-caprolactone using monomethoxy poly(ethylene glycol) as the macroinitiator and calcium ammoniate as the catalyst. Obvious mutual influence between PEG and PCL crystallization was studied by altering the relative block length. Fixing the length of the PEG block (M-n = 5000) and increasing the length of the PCL block, the crystallization temperature of the PCL block rose gradually from I to about 35 degreesC while that of the PEG block dropped from 36 to -6.6 degreesC. Meanwhile, the melting temperature of the PCL block went up from 30 to 60 degreesC, while that of the PEG block declined from 60 to 41 degreesC. If the PCL block was longer than the PEG block, the former would crystallize first when cooling from a molten state and led to obviously imperfect crystallization of PEG and vice versa. And they both crystallized at the same temperature, if their weight fractions were equal. We found that the PEG block could still crystallize at -6.6 degreesC even when its weight fraction is only 14%. A unique morphology of concentric spherulites was observed for PEG5000-PCL5000.

Fractionated crystallization of dispersed PA6 phase of PP/PP-g-MAH/PA6 blends

Fractionated crystallization behavior of dispersed PA6 phase in PP/PA6 blends compatibilized with PP-g-MAH was investigated by scanning electron microscopy (SEM), differential scanning calorimeter (DSC), polarized light microscopy (PLM), and wide-angle X-ray diffraction (WAXD) in this work. The lack of usual active heterogeneities in the dispersed droplet was the key factor for the fractionated crystallization of PA6. The crystals formed with less efficient nuclei might contain more defects in the crystal structures than those crystallized with the usual active nuclei. The lower the crystallization temperature, the lesser the perfection of the crystals and the lower crystallinity would be. The fractionated crystallization of PP droplets encapsulated by PA6 domains was also observed. The effect of existing PP-g-MAH-g-PA6 copolymer located at the interface on the fractionated crystallization could not be detected in this work.

Thermal and crystalline properties of random copolymer of CL and DTC prepared by La(OAr)(3)

Thermal and crystalline properties of random copolymer of epsilon-caprolactone (CL) and 2,2-dimethyl trimethylene carbonate (DTC) prepared by lanthanum tris(2,6-di-tert-butyl-4-methylphenolate) (La(OAr)(3)) have been investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and wide-angle X-ray diffraction (WAXD). Fox equation interprets the relationship between glass transition temperature (T-g) and copolymer compositions. T-g decreases from PDTC (16.7degreesC) to PCL (-65.1degreesC), reflecting the internal plasticizing effect of CL units on DTC units in the copolymers. The introduction of CL units to PDTC can effectively improve its heat resistance. Small amount of DTC (5% molar) in PCL chain improves the mechanical properties of the polymer, which had elongation of 1000, much higher than that of PCL (8.8).

Self-immobilized titanium and zirconium catalysts with phenoxy-imine ligands for ethylene polymerization. X-ray crystal structure of bis(N-(3-tert-butylsalicylidene)-4 '-allyloxyanilinato) zirconium(IV) dichloride

Four self-immobilized FI catalysts with allyl substituted phenoxy-imine ligands [{4-(CH2=CHCH2O)C6H5N=CH-C6H3(3-tert-C4H9)O}(2) MCl2] (1: M = Ti: 2: M = Zr), [{3-(CH2=CHCH2O)C6H5N=CH-C6H3(3-tert-C4H9)O}(2)MCl2] (3: M = Zr), [{4-(CH2=CHCH2-2,6-(iso-C3H7)(2))C6H5N=CH-C6H3(3,5-(NO2)(2))O}(2)MCl2] (4: M = Zr) have been synthesized and characterized. The molecular structure of 2 has been determined by X-ray crystallographic analysis. The results of ethylene polymerization showed that the self-immobilized titanium (IV) and zirconium (IV) catalysts 1-3 kept high activity for ethylene polymerization and 4 showed no activity. SEM showed the immobilization effect could greatly improve the morphology of polymer particles to afford micron-granula polyolefin as supported catalysts.

Radical co-polymerization of diiminedibromidenickel(II)-functionalized olefin with styrene: synthesis of polymer-incorporated nickel(II) alpha-diimine catalysts for ethylene polymerization

alpha-Diimine nickel catalyst hearing two allyl groups [ArN=C](2)C10H6NiBr2 (Ar = 4-allyl-2,6-(i-Pr)(2)C6H2)] (Cat-I) has been synthesized and characterized. The corresponding polymer-incorporated nickel catalysts PC and the SiO2-supported shell-core structure catalyst SC-1 were obtained by the co-polymerization of the olefin groups of Cat-1 with styrene in the presence of a radical initiator. Radical co-polymerizations with styrene in Solution were investigated in detail, and the compositions and molecular weight of the copolymers were determined. All three types of catalysts (Cat-1, PC and SC-1) have been investigated for ethylene polymerization. These catalysts were found to exhibit high activity in the presence of modified methylaluminoxane (MMAO) as a co-catalyst. Among them, the polymer-incorporated PC and SiO2 shell-core catalyst SC-1 displayed very high activity (similar to2.62 and similar to1.11 kg (mmol Ni)(-1) h(-1), respectively) with product molecular weights (M,) in the range 26 x 10(4) to 47 x 10(4) under 0.1 MPa ethylene pressure. The particle morphology of polyethylene produced by the shell-core structure catalyst SC-1 was improved.

Self-immobilized metallocene catalysts bearing an allyl group for ethylene polymerization, X-ray crystal structure of [(CH2=CHCH2)CH3Si(C13H8)(2)]ZrCl2

A series of ansa-metallocene complexes with an allyl substituted silane bridge [(CH =CHCH2)CH3Si(C5H4)(2)]TiCl2 (1), [(CH2=CHCH2)CH3Si(C9H6)(2)]MCl2 [M = Ti (2), Zr (3), Hf (4)] and [(CH2=CHCH2)CH3Si(C13H8)(2)]ZrCl2 (6) have been synthesized and characterized. The molecular structure of 6 has been determined by X-ray crystallographic analysis. Complexes 1-4, 6 bearing allyl groups have been investigated as self-immobilized catalysts for ethylene polymerization in the presence of MMAO. The results showed that the self-immobilized catalysts 1-4, 6 kept high ethylene polymerization activities of ca. 10(6) g PE mol(-1) M h(-1) and high molecular weight (M-w approximate to 10(5)) of polyethylene.

Morphology, tensile strength and thermal behavior of isotactic polypropylene/syndiotactic polystyrene blends compatibilized by SEBS copolymers

The effects of three triblock copolymers of poly [styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) of different molecular weight (MW) on the morphology, tensile strength and thermal behavior of isotactic polypropylene/syndiotactic polystyrene (iPP/sPS, 80/20) blend are investigated. Morphology observation shows that both the medium MW and the lower MW SEBS are more effective than the higher MW SEBS in compatibilizing the blends. Tensile tests revels both the medium and low MW compatibilizer lead to a significant improvement in tensile strength, while the higher MW compatibilizer is efficient in increasing the elongation at break of the blends. The localization of compatibilizers in the blends is observed by mean of SEM and the correlation between the distribution of the compatibilizers and mechanical properties of the blends is evaluated. The mechanical properties of the iPP/sPS blends depend on not only the interfacial activity of the compatibilizers but also the distribution of the compatibilizer in the blend. Addition of the compatibilizers to the blend causes a remarkable decrease in the magnitude of the crystallization peak of sPS at its usual T-c. Vicat softening points demonstrate that the heat resistance of iPP/sPS blend is much higher than that of the pure iPP.

Micellization and reversible pH-sensitive phase transfer of the hyperbranched multiarm PEI-PBLG copolymer

A novel, hyperbranched, amphiphilic multiarm biodegradable polyethylenimine-poly(gamma-benZyl-L-gluta- mate) (PEI-PBLG) copolymer was prepared by the ring-opening polymerization of gamma-benzyl-L-glutamate-N-car-boxyanhydride (BLG-NCA) with hyperbranched PEI as a macroinitiator. The copolymer could self-assemble into core-shell micelles in aqueous solution with highly hydrophobic micelle cores. As the PBLG content was increased, the size of the micelles increased and the critical micelle concentration (CMC) decreased. The surface of the micelles had a positive potential. The cationic micelles were capable of complexing with plasmid DNA (pDNA), which could be released subsequently by treatment with polyanions. The PEI-PBLG copolymer formed unimolecular micelles in chloroform solution. ne pH-sensitive phase-transfer behavior exhibited two critical pH points for triggering the encapsulation and release of guest molecules. Both the encapsulation and release processes were rapid and reversible. Under strong acidic or alkaline conditions, the release process became partially or completely irreversible.

Solvent-induced novel morphologies in diblock copolymer blend thin films

We report the morphology and phase behaviors of blend thin films containing two poly styrene-b-poly (methyl methacrylate) (PS-b-PMMA) diblock copolymers with different blending compositions induced by a selective solvent for the PMMA block, which were studied by transmission electron microscopy (TEM). The neat asymmetric PS-b-PMMA diblock copolymers employed in this study, respectively coded as a(1) and a(2), have similar molecular weights but different volume fractions of PS block (f(PS) = 0.273 and 0.722). Another symmetric PS-b-PMMA diblock copolymer, coded as s, which has a PS block length similar to that of a(1), was also used. For the asymmetric a(1)/a(2) blend thin films, circular multilayered structures were formed. For the asymmetric a(1)/symmetric s blend thin films, inverted phases with PMMA as the dispersed domains were observed, when the weight fraction of s was less than 50%. The origins of the morphology formation in the blend thin films via solvent treatment are discussed. Combined with the theoretical prediction by Birshtein et al. (Polymer 1992, 33, 2750), we interpret the formation of these special microstructures as due to the packing frustration induced by the difference in block lengths and the preferential interactions between the solvent and PMMA block.

Investigation of sol-gel transition in Pluronic F127/D2O solutions using a combination of small-angle neutron scattering and Monte Carlo simulation

Physical gelation in the concentrated Pluronic F127/D2O solution has been studied by a combination of small-angle neutron scattering (SANS) and Monte Carlo simulation. A 15% F127/D2O solution exhibits a sol-gel transition at low temperature and a gel-sol transition at the higher temperature, as evidenced by SANS and Monte Carlo simulation studies. Our SANS and simulation results also suggest that the sol-gel transition is dominated by the formation of a percolated polymer network, while the gel-sol transition is determined by the loss of bound solvent. Furthermore, different diffusion behaviors of different bound solvents and free solvent are observed. We expect that this approach can be further extended to study phase behaviors of other systems with similar sol-gel phase diagrams.