Four-arm Poly Research Articles

In-Situ Grazing Incidence Small-Angle X-ray Scattering Studies on Nanopore Evolution in Low-k Organosilicate Dielectric Thin Films

The first in-situ two-dimensional grazing incidence small-angle X-ray scattering (2D GISAXS) study on the evolution of nanopores during the thin film formation of porous dielectrics from composite films is reported. A soluble poly(methylsilsesquioxane) (PMSSQ) precursor and a four-armed poly(e-caprolactone) (PCL4) were chosen as the model matrix and porogen components within the composite film. The measured 2D GISAXS data were analyzed quantitatively using a GISAXS formula derived under the distorted wave Born approximation. It is shown that in-situ GISAXS is a powerful tool for monitoring the evolution of nanopores in dielectric thin films, providing structural characteristics such as size, size distribution, shape, electron density, and porosity, all as a function of temperature and time. In addition, the mechanism for forming imprinted nanopores in the dielectric films by sacrificial thermal degradation of the porogen was determined by in-situ GISAXS analysis. Phase separation of the PCL4 porogen was i...

Comparison of Tethering of Linear and Four-Arm Poly(ethylene oxide)

Comparison of Tethering of Linear and Four-Arm Poly(ethylene oxide)

Synthesis and Properties of Asymmetric Heteroarm PEOn-b-PSm Star Polymers with End Functionalities

We report on the “core-first” synthesis of asymmetric three- and four-arm poly(ethylene oxide) (PEO)−polystyrene (PS) star polymers with functional terminal groups of a general formula PEOn-b-PSm with n = 0, 1, and 2 and n + m ≤ 4. The synthesis was conducted by anionic polymerization of ethylene oxide and followed by atom transfer radical polymerization (ATRP) of styrene. The properties of asymmetric star-shaped macromolecules with different numbers of arms (n = 1; m = 2 and 3) and similar lengths of the PEO arm were compared with homoarm star polymers (PEO4 and PS4) and corresponding linear polymers. All star polymers obtained here possessed well-defined architecture with a relatively narrow molecular weight distribution as confirmed by NMR, FTIR, and arm-disassembling techniques. Star polymers showed suppression of melting temperature and lower crystallinity PEO phase due to the presence of a junction point. Preliminary studies demonstrated surface activities of these block copolymers with a rich polymorphism of micellar surface structures expected for amphiphilic block copolymers despite the presence of the bulky terminal functionalized groups.

Synthesis of four-armed poly(ε-caprolactone)-block -poly(ethylene oxide) by diethylzinc catalyst

Biodegradable, amphiphilic, four-armed poly(epsilon-caprolactone)-block-poly(ethylene oxide) (PCL-b-PEO) copolymers were synthesized by ring-opening polymerization of ethylene oxide in the presence of four-armed poly(epsilon-caprolactone) (PCL) with terminal OH groups with diethylzinc (ZnEt2) as a catalyst. The chemical structure of PCL-b-PEO copolymer was confirmed by H-1 NMR and C-13 NMR. The hydroxyl end groups of the four-armed PC L were successfully substituted by PEO blocks in the copolymer. The monomodal profile of molecular weight distribution by gel permeation chromatography provided further evidence for the four-armed architecture of the copolymer. Physicochemical properties of the four-armed block copolymers differed from their starting four-armed PCL precursor. The melting points were between those of PCL precursor and linear poly(ethylene glycol). The length of the outer PEO blocks exhibited an obvious effect on the crystallizability of the block copolymer. The degree of swelling of the four-armed block copolymer increased with PEO length and PEO content.

Interpolymer Complexes through Hydrophobic Interactions: C60-End-Capped Linear or Four-Arm Poly(ethylene oxide)/Poly(acrylic acid) Complexes

Complexation between C60-end-capped linear or four-arm poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) was studied. The introduction of hydrophobic [60]fullerene (C60) in PEO has a dramatic effect on the complex formation of the PEO/PAA system. Interestingly, the yields of C60-end-capped four-arm PEO/PAA complexes are lower than those of C60-end-capped linear PEO/PAA complexes. The result indicates a competition between the hydrophobic effect and the steric effect originated from C60. Similar to the PEO/PAA system, there are hydrogen-bonding interactions between the carboxylic acid groups of PAA and the ether oxygen in C60-end-capped PEOs.

Star Polymer Synthesis from ε-Caprolactone Utilizing Polyol/Protonic Acid Initiator

Three- and four-armed star-shaped poly(ε-caprolactone)s were synthesized from trimethylolpropane and pentaerythritol as initiators using fumaric acid as an activator of the monomer, respectively. Star-shaped poly(ε-caprolactone)s could be satisfactorily obtained, which was confirmed by size exclusion chromatography equipped with low-angle laser light scattering and viscometer detectors. Comparing the melting points among the polymers with similar molecular weights, the order was as follows: linear poly(ε-caprolactone) > three-armed poly(ε-caprolactone) > four-armed poly(ε-caprolactone). On the other hand, poly(ε-caprolactone)s with similar arm length showed similar melting points irrespective of the arm numbers. Thermal decomposition temperature of poly(ε-caprolactone)s increased with the arm number.

Synthesis and characterization of four-armed poly(1,3-dioxepane) tetraol

A new four-armed poly(1,3-dioxepane) tetraol was prepared by cationic ring-opening polymerization of 1,3-dioxepane (DOP) in the presence of 6,6-bis(5-hydroxyl-2-oxapentyl)-4,8-dioxaundecanediol1,11 (THA) with triflic acid(I) as initiator. The structure of the poly(DOP) tetraol obtained was characterized by 1 H and 13 C NMR spectra. The molecular weights of the obtained tetraols were controlled by the mole ratio of DOP consumed to initial THA, and it was found that each macromolecule contains only one THA unit on the average. GPC studies showed that the cyclic oligomers in the products were negligible.

Isothermal Thickening and Thinning Processes in Low-Molecular-Weight Poly(ethylene oxide) Fractions Crystallized from the Melt. 8. Molecular Shape Dependence

Three- and four-arm poly(ethylene oxide) (PEOs) fractions have been synthesized to investigate the molecular shape dependence on polymer crystallization, melting, and annealing behaviors. Each arm in these star PEOs has a molecular weight (MW) of 2220 (Ma = 2220) and has been coupled using 1,3,5-benzene tricarbonyl trichloride and 1,2,4,5-benzene tetracarboxylic acid. Molecular parameters have been characterized via vapor pressure osmometry, gel permeation chromatography, light scattering, and Fourier transfer infrared spectroscopy. The coupling agents containing phenylene groups act as chemical defects at the center of the molecule. Diffusion in the melt of these star PEOs as measured by nuclear magnetic resonance shows that at constant temperature the self-diffusion slows down with an increase in the number of arms. Wide-angle X-ray diffraction (WAXD) experiments indicate that these star PEOs possess monoclinic crystal structures identical to those of linear PEOs, implying that the coupling agents are rejected from the crystals. The overall crystallization rate of the star PEOs decreases with increasing crystallization temperature (Tc) and number of arms. On the basis of synchrotron small-angle X-ray scattering (SAXS) experiments, it has been found that during the initial isothermal crystallization at low undercoolings (ΔT's) the long period gradually decreases with increasing time before reaching a thickness corresponding to the summation of the thicknesses of the crystals with an extended arm length and two layers consisting of the coupling agent and the uncrystallized PEO arm. The final crystals possess the regular overall molecular conformations. At high ΔT's, the long period remains constant both during and after crystallization with no observed thinning process. Only irregular overall molecular conformations in these crystals can be expected. The dependence of the final long period on Tc, as determined by SAXS, is remarkably similar to the melting temperature response to Tc obtained via differential scanning calorimetry (DSC). The annealing effect has been examined for samples crystallized at 32 °C, subsequently heated to 50 °C, and isothermally annealed for various periods of time. A partial melting upon heating and recrystallization during annealing can be identified based on the combined experimental results obtained from DSC, WAXD, and SAXS methods.