• Title, Summary, Keyword: block copolymers

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Thermal and Dynamic Mechanical Properties of Ethylene-Propylene Copolymers -Structure-Property Relationship- (에틸렌-프로필렌 공중합체의 열적 및 동탄성적 성질 -구조와 성질과의 관계-)

  • 박영환
    • Textile Science and Engineering
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    • v.27 no.3
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    • pp.69-78
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    • 1990
  • ABA type block copolymers of ethylene and propylene, where the central B block is a random copolymer of ethylene and propylene and the A blocks are isotactic polypropylene, are prepared in addition to ethylene-propylene random copolymers. A dry catalyst system of TiCl3(AA)-Et2AlCl and a gas-phase polymerization technique were used for the preparation of copolymers. Thermal and dynamic mechanical behavior of ethylene-propylene block copolymers are described with respect to the relationships between structure and property. The results from thermal analysis and dynamic mechanical analysis demonstrated that the EP random copolymers developed the 'blocky'nature. The block architecture as well as monomer composition was demonstrated as an important factor in determining the physical and mechanical properties of ABA type ethylene-propylene block copolymers.

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Synthesis and Biodegradability of Block Copolymer Comprising Poly(L-lactic acid) and Poly(oxypropylene) for Medical Suture (의료용 봉합사로서 Poly(L-lactic acid)/Poly(oxypropylene)을 포함한 블록 공중합체의 합성 및 생분해성)

  • 이찬우;오세화
    • Textile Science and Engineering
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    • v.35 no.1
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    • pp.1-7
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    • 1998
  • The A-B-A block copolymers were prepared by the ring opening polymerization of L-lactide by the polypropylene glycol (PPG; Mw/Mn=1.1, Mn=4000) with $Me_3Al-H_2O$ as the catalyst. When the feed ratios of PPG were over 5 and 10 wt% relative to L-lactide, the polymerization of L-lactide took place from the PPG hydroxyl terminals to give the desired A-B-A block copolymers in high yields. The resulting molecular weights were in good agreement with the values estimated from the monomer conversions and the feed ratios of PPG. At the lower feed ratios of PPG, the poly(L-lactic acid) (PLLA) homopolymer was formed along with the block copolymers. The block copolymers were melt-spun by the conventional method and the fibers obtained were extended by drawing at $60^{\circ}C$. At the same draw ratio, the modulus of the fibers was decreased with increasing PPG content in the block copolymers. The fibers of the PLLA-PPG-PLLA block copolymers with different contents of PPG were subjected to degradation in vitro. Upon immersion in a phosphate buffer solution (pH=7.4), the fibers showed a time-dependent decrease in tensile strength with accompanying surface erosion. The degradation rate of this fiber was much higher than that of PLLA fiber. It was therefore suggested that the block copolymers comprising PLLA and PPG, have high potential as the biodegradable suture with improved flexibility and biodegradability.

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Synthesis of Poly(ethylene oxide-b-acrylonitrile) Block Copolymers with Higher Polyacrylonitrile Content Using Controlled Radical Polymerization Techniques (조절 라디칼 중합법을 이용한 PAN 함량이 많은 PEO-b-PAN 블록 공중합체의 합성)

  • Kim, Tae-Young;Kwark, Young-Je
    • Textile Science and Engineering
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    • v.52 no.1
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    • pp.20-25
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    • 2015
  • Poly(ethylene oxide-b-acrylonitrile) (PEO-b-PAN) block copolymers were prepared as precursors to mesoporous carbons. Redox-initiated radical polymerization and controlled radical polymerization techniques, such as reversible addition-fragmentation chain transfer (RAFT) and activators regenerated by electron transfer atom-transfer radical polymerization (ARGET ATRP), were successfully applied to prepare PEO-b-PAN block copolymers with high PAN content. Radical polymerization of acrylonitrile (AN) using ceric ion as redox initiator gave block copolymers with PEO:PAN ratio of up to 1:38.4, but their high molecular weight and polydispersity index (PDI) indicated that the structure was not controlled. Therefore, in order to achieve better control on the structure of the PAN block, controlled radical polymerization techniques were used. Poly(ethylene oxide) with trithiocarbonate (PEO-CTA) and bromide (PEO-Br) end groups were synthesized as polymeric chain transfer agent for the RAFT process and as initiator for the ATRP process, respectively. The RAFT process of AN using PEO-CTA gave block copolymers with PAN block length 0.53-3.58 times that of the PEO block. Moreover, ARGET ATRP allowed to prepare block copolymers with a very high molecular weight of 72,000, while maintaining a PDI value as low as 1.20.

Self-Assembled Block Copolymers: Bulk to Thin Film

  • Kim, Jin-Kon;Lee, Jeong-In;Lee, Dong-Hyun
    • Macromolecular research
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    • v.16 no.4
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    • pp.267-292
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    • 2008
  • Block copolymers that two or more polymer chains are covalently linked have drawn much attention due to self-assembly into nanometer-sized morphology such as lamellae, cylinders, spheres, and gyroids. In this article, we first summarize the phase behavior of block copolymers in bulk and thin films and some applications for new functional nanomaterials. Then, future perspectives on block copolymers are described.

New Characterization Methods for Block Copolymers and their Phase Behaviors

  • Park, Hae-Woong;Jung, Ju-Eun;Chang, Tai-Hyun
    • Macromolecular research
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    • v.17 no.6
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    • pp.365-377
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    • 2009
  • In this feature article, we briefly review the new methods we have utilized recently in the investigation of morphology and phase behavior of block copolymers. We first describe the chromatographic fractionation method to purify block copolymers from their side products of mainly homopolymers or block copolymer precursors inadvertently terminated upon addition of the next monomer in the sequential anionic polymerization. The chromatographic method is extended to the fractionation of the individual block of diblock copolymers which can yield the diblock copolymer fractions of different composition and molecular weight, which also have narrower distributions in both molecular weight and composition. A more detailed phase diagram could be constructed from the set of block copolymer fractions without the need of acquiring many block copolymers each prepared by anionic polymerization. The fractions with narrow distribution in both molecular weight and composition exhibit better long-range ordering and sharper phase transition. Next, epitaxial relationships between two ordered structures in block copolymer thin film is discussed. We employed the direct visualization method, transmission electron microtomography(TEMT) to scrutinize the grain boundary structure.

Hydrophilic Modification of PET by Using Block Copolymer -Molecular Structure and Hydrophilicity of PET-PEG Block Copolymers- (블록 공중합체를 이용한 PET의 친수화 연구 - PET-PEG 블록공중합체의 구조에 따른 친수성의 비교 -)

  • 우상원;조창기
    • Textile Science and Engineering
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    • v.36 no.3
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    • pp.211-218
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    • 1999
  • Multi-block copolymers of poly(ethylene terephthalate) (PET) and poly(ethylene glycol) (PEG) were synthesized. Similarly, triblock copolymers of PET and poly(ethylene glycol) methyl ether (MPEG) were synthesized. PEG and MPEG of various molecular weights were used. Obtained block copolymers were made into film, and conditioned at 65% RH at $25^{\circ}C$ after vacuum drying. Water contact angle measurement indicated the enrichment of PET domain on the film surface after vacuum drying, and the enrichment of PEG domain on the film surface after conditioning. The hydrophilicity of the film increased as the molecular weight of PEG block increased. Also, the surface energy increased as the molecular weight of PEG increased, and this increase was mainly due to the increase in the polar component of surface energy. In spite of lower PEG contents, triblock copolymers showed relatively good hydrophilicity.

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Synthesis of New pH-Sensitive Amphiphilic Block Copolymers and Study for the Micellization Using a Fluorescence Probe

  • Kim, Kyung-Min;Choi, Song-Yee;Jeon, Hee-Jeong;Lee, Jae-Yeol;Choo, Dong-Joon;Kim, Jung-Ahn;Kang, Yong-Soo;Yoo, Hyun-Oh
    • Macromolecular research
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    • v.16 no.2
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    • pp.169-177
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    • 2008
  • This paper reports a facile synthesis of new water-soluble poly(ethylene oxide) (PEO)-based amphiphilic block copolymers showing pH sensitive phase transition behaviors. The copolymers were prepared by atom transfer radical polymerization (ATRP) of methacrylamide type of monomers carrying a sulfonamide group using a PEO-based macroinitiator and a Cu(I)Br/$Me_6TREN$ catalytic system in aqueous media. The resulting polymers were characterized by a combination of $^1H$-NMR, size exclusion chromatography, and UV/Visible spectrophotometeric analysis. The micellization of the block copolymers as a drug-loading mechanism in aqueous media using fluorescein salt was examined as a function of pH. The stable micelle formation and its loading efficacy suggest that the block copolymers can be used as precursors for drug-nanocontainers.

Isothermal Crystallization Behavior of PCL-PPG-PCL Triblock Copolymers (PCL-PPG-PCL 3블록 공중합체의 등온결정화 거동)

  • 김영호;장진성
    • Textile Science and Engineering
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    • v.34 no.11
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    • pp.784-792
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    • 1997
  • A new method for the estimation of the initial portion of the crystallization exotherm, normally obscured due to the response time of the DSC in the case of fast crystallization, was developed. This method allowed a more accurate analysis of the DSC isothermal crystallization data. Poly(propylene glycol)(PPG)-poly($\varepsilon$-caprolactam) (PCL)-PPG triblock copolymers with various PPG contents were synthesized via anionic copolymerization of $\varepsilon$-cairo-lactam and the macroactivators which contain PPG units. Isothermal crystallization behaviors of the synthesized block copolymers were allalyzed with Avrami equation by using above-mentinned non-linear curve fitting program and conventional Avraml plot. At PPG contents greater than 10%, the overall crystallization rate decreased because of the uncrystallizable PPG unit. The induction time for crystallization increased, and the ratio of primary crystallization to overall crystallization increased at the same degree of undercooling. On the other hand, crystal growth rate increased with PPG content. The presence of PPG unit in the block copolymer has two opposing effects on crystallization. First, as the amount of PPG unit increases it interferes with nucleation. As a result the induction time for crystallization increases and the crystallization rate decreases. Secondly, it increases the mobility of the block copolymers because of the ether linkage and allows faster diffion of the copolymer chain to the crystal surface. Consequently the crystal growth rate after nucleation increases. Between the two effects the first one seems to be dominating and the overall crystallization rate decreases with increasing PPG content in block copolymers. Furthermore there are some different crystallization behaviors between the block copolymers and PCL homo polymer. Nucleation of block copolymers of PPG content up to 10% occurs faster than in the case of homo PCL because small amounts of PPG unit may act as heterogeneous nuclei. Also the chain mobility increased with the introduction of PPG unit, therefore the overall crystallization rate was faster than homo PCL. But if the PPG content exceeds 10% the overall crystallization rate of the block copolymers becomes slower than homo PCL.

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Synthesis and Degradation Behaviors of PEO/PL/PEO tri-block Copolymers

  • Lee, Soo-Hong;Kim, Soo-Hyun;Kim, Young-Ha;Han, Yang-Kyoo
    • Macromolecular research
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    • v.10 no.2
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    • pp.85-90
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    • 2002
  • Poly (ethylene oxide)/polylatide/poly(ethylene oxide) (PEO/PL/PEO) tri-block copolymers, which each block is connected by ester bond, were synthesized by coupling reaction of PL with PEO in the presence of pyridine. PL/PEO/PL tri-block copolymer was synthesized by ring opening polymerization of L-lactide initiated by PEO in the presence of stannous octoate. Degradation behavior of the copolymers was investigated in a pH 7.4 phosphate buffer saline (PBS) at 37$\pm$1 $^{\circ}C$. Gel permeation chromatography (GPC) and $^1$H-nuclear magnetic resonance (NMR) were used to monitor the change of mass loss, molecular weight and composition of copolymers. In hydrolytic degradation, the PEO/PL/PEO tri-block copolymer with high PEO contents affected the increase of its mass loss, and resulted in the decrease of its molecular weight as well as PEO composition. However, when PL/PEO/PL and PEO/PL/PEO tri-block copolymers had similar PEO contents, PEO/PL/PEO decreased faster in molecular weight and PEO composition than PL/PEO/PL.

Nanostructuring of Semi-conducting Block Copolymers: Optimized Synthesis and Processing for Efficient Optoelectronic Devices

  • Hadziioannou, Georges
    • Proceedings of the Polymer Society of Korea Conference
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    • pp.74-75
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    • 2006
  • In organic opto-electronic applications, such as light emitting diodes (LEDs) and photovoltaic devices (PVDs), the morphology of the active layer is of crucial importance. To control the morphology of the active layer the self-assembling properties of block copolymers was used. Several rod-coil semiconducting diblock copolymers consisting of a conjugated block and a second coil block functionalized with electron transporting and/or accepting materials (such as $C_{60}$) were synthesized. The conjugated block acting as light absorbing, electron donating and hole transporting material. The donor/acceptor photovoltaic devices performance with active layer the above mentioned semiconducting block copolymers will be presented.

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