• Macromolecular Research
• /
• v.16 no.2
• /
• pp.103-107
• /
• 2008

Carbon nanodots were prepared by the pyrolysis of a triblock copolymer. The triblock copolymer, poly(methyl methacrylate)-b-polystyrene-b-poly(methyl methacrylate) was synthesized by atom transfer radical polymerization using an initiator containing a diacetylene group. A polymer thin film on a mica substrate was prepared by spin-casting at 2,000 rpm from a 0.5 wt% toluene solution of the triblock copolymer. After drying, the cast film was vacuum-annealed for 48 h at $160^{\circ}C$. The annealed film formed a spherical morphology of polystyrene domains with a diameter of approximately 30 nm. The film was exposed to UV irradiation to induce a cross-linking reaction between diacetylene groups. In the subsequent pyrolysis at $800^{\circ}C$, the cross-linked polystyrene spheres were carbonized and the poly(methyl methacrylate) matrix was eliminated, resulting in carbon nanodots deposited on a substrate with a diameter of approximately 5 mn.

• Journal of Environmental Science International
• /
• v.15 no.6
• /
• pp.593-600
• /
• 2006

SIS triblock copolymers, one of the major raw materials of oil gelling agent, were synthesized by living anionic polymerization and the resultant copolymers formed with various shapes and sizes were used to examine their oil gelling capacities. Coupling method was adapted to form final triblock products from diblock living polymers. Prior to polymerization, the impurities in monomers and solvents were throughly removed by killing technique. We experimentally investigated the effects of operating parameters of synthesis and forming of SIS triblock copolymers on oil gelling capacity. The photocatalytic decomposition of SIS triblock copolymer under ultraviolet circumstance was also investigated and it is found that the addition of P-25 enhances the photocatalytic decomposition.

• Macromolecular Research
• /
• v.13 no.5
• /
• pp.373-384
• /
• 2005

Novel pH-sensitive moieties containing an s-triazine ring were synthesized with sulfonamide and secondary amino groups. The synthesized pH-sensitive moieties were used for the synthesis of a pH-sensitive amphiphilic ABA triblock copolymer. The pH-sensitive triblock copolymer was composed of diblock copolymers, methoxy poly(ethylene glycol)-poly ($\varepsilon$-caprolactone-co-D,L-lactide) (MPEG-PCLA), and pH-sensitive moiety. These copolymers could be dissolved molecularly in both acidic and basic aqueous media at room temperature due to secondary amino and sulfonamide groups. The synthesized s-triazine rings containing pH-sensitive compounds were characterized by ${^1}H-NMR,\;{^13}C-NMR$, and LC/MSD spectral data. The synthesized diblock and triblock copolymers were also characterized by ${^1}H-NMR$ and GPC analyses. The critical micelle concentrations at various pH conditions were determined by fluorescence technique using pyrene as a probe. Furthermore, the micellization and demicellization study of the triblock copolymer was done with pH-sensitive groups. The sensitivity towards pH change was further established by acid-base titration.

• Fibers and Polymers
• /
• v.3 no.1
• /
• pp.8-13
• /
• 2002

The effect of block sequence on the self-assembly of ABC-type triblock copolymers in the ordered state is investigated using an isothermal-isobaric molecular dynamics simulation. The block sequence has an important effect ,on the ]norphology of ABC triblock copolymers. Different morphologies are observed depending on the block sequence as well as the block composition. The triblock copolymers with the volume fraction of 1 : 1 : 1 ($f_A$=$f_B$=$f_C$= 0.33) show the three phase and four layered lamellar structures irrespective of the block sequence. The $A_{32}$$B_{16}$$C_{32}$triblock copolymer with $f_B$=0.2 shows a morphology In which cylinders of midblock B are formed at the interface between A and C lamellae, whereas the morphology of triblock copolymer $B_{16}$$C_{32}$ $A_{32}$ and $C_{32}$ $A_{32}$ $B_{16}$ show a cylindrical core-shell structure and a lamellar type morphology, respectively. The $A_{20}$$B_{40}$$C_{20}$the triblock copolymer with the block B as a major component shows a tricontinuous structure, whereas both $B_{40}$$C_{20}$$A_{20}$ and $C_{20}$$A_{20}$$B_{40}$ triblock coolymers exhibit the lamellar structures. When the block B has larger volrome fraction with $f_B$=0.75, the matrix is composed of block B, and other two blocks A and C form spherical domains.

• Macromolecular Research
• /
• v.10 no.6
• /
• pp.325-331
• /
• 2002

Phase behavior of a PEO-PPO-PEO (Pluronic P103) triblock copolymer in water is investigated using small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), dynamic light scattering (DLS) and rheology. Pluronic P103 shows apparent two gel states in different temperature regions. The first sol-to-gel transition at a lower temperature (i.e., the hard gel I state) turns out to be the hexagonal microphase as evidenced by the combined SANS and SAXS and the frequency dependence of both G′ and G" in rheology. In contrast to the hard gel I, the second sol-to-gel transition (i. e., the hard gel II state) at a higher temperature represents the block copolymer micelles in somewhat disordered state rather than the ordered state seen in the hard gel I. Moreover, turbidity change depending only on the temperature with four distinct regions is observed and the large aggregates with size larger than 5,000 nm are detected with DLS in the turbid solution region. Based upon the present study, two different gelation mechanisms for aqueous PEO-PPO-PEO triblock copolymer solutions are proposed.

• Macromolecular Research
• /
• v.17 no.5
• /
• pp.325-331
• /
• 2009

The synthesis and the characterization of crosslinked ABC triblock copolymer, i.e. polystyrene-b-poly (hydroxyethyl methacrylate)-b-poly(styrene sulfonic acid), (PS-b-PHEMA-b-PSSA) is reported. PS-b-PHEMA-b-PSSA triblock copolymer at 20:10:70 wt% was sequentially synthesized via atom transfer radical polymerization (ATRP). The middle block was crosslinked by sulfosuccinic acid (SA) via the esterification reaction between -OH of PHEMA and -COOH of SA, as demonstrated by FTIR spectroscopy. As increasing amounts of SA, ion exchange capacity (IEC) continuously increased from 2.13 to 2.82 meq/g but water uptake decreased from 181.8 to 82.7%, resulting from the competitive effect between crosslinked structure and the increasing concentration of sulfonic acid group. A maximum proton conductivity of crosslinked triblock copolymer membrane at room temperature reached up to 0.198 S/cm at 3.8 w% of SA, which was more than two-fold higher than that of Nafion 117(0.08 S/cm). Transmission electron microscopy (TEM) analysis clearly showed that the PS-b-PHEMA-b-PSSA triblock copolymer is microphase-separated with a nanometer range and well developed to provide the connectivity of ionic PSSA domains. The membranes exhibited the good thermal properties up to $250^{\circ}C$ presumably resulting from the microphase-separated and crosslinked structure of the membranes, as revealed by thermal gravimetric analysis (TGA).

• Macromolecular Research
• /
• v.9 no.2
• /
• pp.84-91
• /
• 2001

Both A-B-A triblock and multiblock copoly(ester-ether)s consisting of poly(L-Lactide) and poly(oxyethylene-co-oxypropylene) were prepared and characterized. The preparation of the triblock copolymer was done by ring-opening copolymerization of L-lactide with a commercially available telechelic copolyether, Pluronic$\^$TM/(PN) by catalysis of stannous octanoate. The molecular weight and unit composition of the produced copolymers were successfully controlled by changing the L-lactide/PN ratio in feed. However, a high molecular weight copolymer incorporating PN in large amount was not obtained because the molecular weight of the resulting copolymer was limited at a high L-lactide/PN composition. The multiblock copolymer was synthesized by the copolycondensation of oligo(L-lactic acid) prepared by thermal dehydration of L-lactic acid, PN, and dodecanedioic acid as carboxyl/hydroxyl adjusting agent. This polycondensation proceeded by catalysis of stannous oxide to give multiblock copolymers with high molecular weight and wide range of compositions.

• Macromolecular Research
• /
• v.17 no.10
• /
• pp.757-762
• /
• 2009

The micro domain structures and crystallization behavior of the binary blends of poly(methyl methacrylate)-b-poly(pentafluorostyrene)-b-poly(methyl methacrylate) (PMMA-PPFS-PMMA) triblock copolymer with a low molecular weight poly(vinylidene fluoride) (PVDF) were investigated by small-angle X-ray scattering (SAXS), small-angle light scattering (SALS), transmission electron microscopy (TEM), optical microscopy, and differential scanning calorimetry (DSC). A symmetric, PMMA-PPFS-PMMA triblock copolymer with a PPFS weight fraction of 33% was blended with PVDF in N,N-dimethylacetamide (DMAc). In the wide range of PVDF concentration between 10.0 and 30.0 wt%, PVDF was completely incorporated within the PMMA micro domains of PMMA-PPFS-PMMA without further phase separation on a micrometer scale. The addition of PVDF altered the phase morphology of PMMA-PPFS-PMMA from well-defined lamellar to disordered. The crystallization of PVDF significantly disturbed the domain structure of PMMA-PPFS-PMMA in the blends, resulting in a poorly-ordered morphology. PVDF displayed unique crystallization behavior as a result of the space constraints imposed by the domain structure of PMMA-PPFS-PMMA. The pre-existing microdomain structures restricted the lamellar orientation and favored a random arrangement of lamellar crystallites.

• Bulletin of the Korean Chemical Society
• /
• v.22 no.5
• /
• pp.467-475
• /
• 2001

A triblock copolymer based on $poly(\varepsilon-caprolactone)$ (PCL) as the hydrophobic part and poly(ethylene glycol) (PEG) as the hydrophilic portion was synthesized by a ring-opening mechanism of ${\varepsilon}-caprolactone$ with PEG containing a hydroxyl group at bot h ends as an initiator. The synthesized block copolymers of PCL/PEG/PCL (CEC) were confirmed and characterized using various analysis equipment such as 1H NMR, DSC, FT-IR, and WAXD. Core-shell type nanoparticles of CEC triblock copolymers were prepared using a dialysis technique to estimate their potential as a colloidal drug carrier using a hydrophobic drug. From the results of particle size analysis and transmission electron microscopy, the particle size of CEC core-shell type nanoparticles was determined to be about 20-60 nm with a spherical shape. Since CEC block copolymer nanoparticles have a core-shell type micellar structure and small particle size similar to polymeric micelles, CEC block copolymer can self-associate at certain concentrations and the critical association concentration (CAC) was able to be determined by fluorescence probe techniques. The CAC values of the CEC block copolymers were dependent on the PCL block length. In addition, drug loading contents were dependent on the PCL block length: the larger the PCL block length, the higher the drug loading content. Drug release from CEC core-shell type nanoparticles showed an initial burst release for the first 12 hrs followed by pseudo-zero order release kinetics for 2 or 3 days. CEC-2 block copolymer core-shell type nanoparticles were degraded very slowly, suggesting that the drug release kinetics were governed by a diffusion mechanism rather than a degradation mechanism irrelevant to the CEC block copolymer composition.

• Macromolecular Research
• /
• v.13 no.6
• /
• pp.529-532
• /
• 2005

A novel amphiphilic, symmetric rod-coil, triblock copolymer (denoted as PHEMA-b-PF-b-PHEMA) of poly(9,9-didodecylfluorene-2,7-diyl) (PF) and poly(hydroxyl ethyl methacrylate) (PHEMA) was synthesized. A $\pi$-conjugated poly(9,9-didodecylfluorene-2,7-diyl) (PF) was used as a rodlike midblock segment and connected with hydrophilic end blocks of poly(hydroxyl ethyl methacrylate) (PHEMA) by using an ATRP technique. The chemical structure of PHEMA-b-PF-b-PHEMA was confirmed by $^{1}H$-NMR and GPC, and its PL properties were investigated in selected solvents. Due to the dissimilarities in molecular conformation and solubility between PHEMA and PF blocks, both block segments were segregated to display a phase-separated morphology on a Si wafer.