• Proceedings of the Korean Fiber Society Conference
• /
• 2002.04a
• /
• pp.207-210
• /
• 2002

PVDF는 측쇄에 C=O기를 갖는 고분자인 PMMA와 PVAc와의 블렌드 및 주쇄에 C=O기를 갖는 poly(1,4-butylene adipate) (PBA)와의 블렌드에서 PVDF의 융점보다 상당히 높은 온도에서 LCST거동을 보이고 있음이 알려져 있다. 그런데 PVDF/PMMA와 PVDF/PVAC 블렌드계에서는 LCST가 고분자의 열분해온도와 유사하여 LCST거동을 실험적으로 관찰하기 어려웠다. 그런데 PVDF/PBA 블렌드계에서는 실험적으로 측정할 수 있을 정도로 LCST가 낮아지긴 하였지만 PBA의 열분해를 완전히 배제하기엔 아직도 높은 온도이다.[1] (중략)

• KSBB Journal
• /
• v.15 no.6
• /
• pp.548-555
• /
• 2000

A hydrogel, poly(N-isopropylacrylamide-co-N, N-dimethylaminopropylmethacrylamide), sensitive to both pH and temperature, was synthesized and characterized at $^13∼23{\circ}C$ and pH of 10.3∼12.3. The gel was more transparent and mechanically stronger at lower preparation temperature and pH. Large pores observed in scanning electron microscope seem to be responsible for the lower biomolecular separation efficiency. The lower critical solution temperature (LCST) decreased at a higher polymerization temperature. At $25^{\circ}C$, which is lower than the LCST, the gel was swollen regardless of the solution pH. At $40^{\circ}C$, however, the gel was swollen at neutral and acidic pHs even though the temperature was higher than the LCST. The gel collapse pH, defined as the point at which the gel made its largest volume decrease per unit pH increment, increased as the gel preparation temperature increased.

• Bulletin of the Korean Chemical Society
• /
• v.24 no.7
• /
• pp.901-905
• /
• 2003

The lower critical solution temperature (LCST) of thermosensitive poly(organophosphazenes) with methoxypoly(ethylene glycol) (MPEG) and amino acid esters as side groups was studied as a function of saccharide concentration in aqueous solutions of mono-, di-, and polysaccharides. Most of the saccharides decreased the LCST of the polymers, and the LCST decrease was more prominently observed by saccharides containing a galactose ring, such as D-galactose, D-galactosamine and D-lactose, and also the polysacccharide, 1-6-linked D-dextran effectively decreased the LCST of the polymers. Such an effect was discussed in terms of intramolecular hydrogen bonding of saccharides in polymer aqueous solution. The saccharide effect was found to be almost independent on the kinds of the amino acid esters and MPEG length of the polymers. Such a result implies that the polymer-saccharide interaction in aqueous solution is clearly influenced by the structure of sacchardes rather than by that of the polymers. The acid saccharides such as D-glucuronic and D-lactobionic acid increased the LCST, which seems to be due to their pH effect.

• Proceedings of the Korean Fiber Society Conference
• /
• 2002.04a
• /
• pp.351-351
• /
• 2002

새로운 LCST 형 블록 공중합체를 설계하기 위하여 LCST 블렌드 계를 선정하고, 이로부터 대응되는 블록 공중합체를 고안하였다 고안된 블록 공중합체의 분자 변수와 자기 집합에 의한 나노 미세 상 발현 거동과의 관계를 Cho의 압축성 random-phase approximation (RPA) 이론을 이용하여 구하였다. 본 연구의 대상 물질은 polystyrene (PS)과 poly(vinyl methyl ether) (PVME), PS 와 Poly(cyclo hexyl methacrylate) (PCHMA)의 블록 공중합체이다. (중략)

• Bulletin of the Korean Chemical Society
• /
• v.35 no.2
• /
• pp.501-504
• /
• 2014

A thermoresponsive polymer, poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), was successfully synthesized by atom transfer radical polymerization (ATRP). Different amounts of 1,3-propanesultone were used as quaternization agent to transit the PDMAEMA into partially modified poly(zwitterions), resulting in p[DMAEMA-co-3-dimethyl(methacryloyloxyethyl)ammonium propanesulfonate] (PDMAEMA-co-PDMAPS). Molecular weight, molecular weight distribution, and degree of quarternization were determined by gel permeation chromatography (GPC) and 1H NMR spectroscopy. The transmission spectra of the 1.0 wt % aqueous solutions of the resulting polymers at 650 nm were measured as a function of temperature. Results showed that the lower critical solution temperature (LCST) and the upper critical solution temperature (UCST) could be easily controlled by the different composition of dimethylamino and zwitterion groups. The effect of partial quaternization on thermoresponsive properties was also studied by dynamic light scattering (DLS) with the same aqueous concentration (1.0 wt %) as employed for turbidimetry studies. The LCST and UCST values measured by DLS correlated well with those determined by turbidimetry.

• Structural Engineering and Mechanics
• /
• v.78 no.2
• /
• pp.163-174
• /
• 2021

Track-bridge interaction has become an essential part in the design of bridges and rails in terms of modern railways. As a unique ballastless slab track, the longitudinal continuous slab track (LCST) or referred to as the China railway track system Type-II (CRTS II) slab track, demonstrates a complex force mechanism. Therefore, a comprehensive track-bridge interaction study between multi-span simply supported beam bridges and the LCST is presented in this work. In specific, we have developed an integrated finite element model to investigate the overall interaction effects of the LCST-bridge system subjected to the actions of temperature changes, traffic loads, and braking forces. In that place, the deformation patterns of the track and bridge, and the distributions of longitudinal forces and the interfacial shear stress are studied. Our results show that the additional rail stress has been reduced under various loads and the rail's deformation has become much smoother after the transition of the two continuous structural layers of the LCST. However, the influence of the temperature difference of bridges is significant and cannot be ignored as this action can bend the bridge like the traffic load. The uniform temperature change causes the tensile stress of the concrete track structure and further induce cracks in them. Additionally, the influences of the friction coefficient of the sliding layer and the interfacial bond characteristics on the LCST's performance are discussed. The systematic study presented in this work may have some potential impacts on the understanding of the overall mechanical behavior of the LCST-bridge system.

• Journal of the Korean Chemical Society
• /
• v.42 no.1
• /
• pp.84-91
• /
• 1998

Random copolymers of N-isopropyl acrylamide (NIPAAm) and acrylic acid (AAc) which exhibit temperature- and pH-responsive behavior were synthesized by free-radical polymerization. The copolymers were characterized by means of FT-IR spectrometry and titration. The influence of polyelectrolyte on the lower critical solution temperature (LCST) of pH/temperature-sensitive polymers was investigated in the pH range of 2-12. The LCSTs of PNIPAAm/water in poly(NIPAAm-co-AAc) were determined by cloud-point measurements. A polyelectrolyte complex was prepared by mixing poly(NIPAAm-co-AAc) with poly(allylamine) (PAA) or poly(L-lysine) (PLL) solutions as anionic and cationic polyelectrolytes, respectively. Back titration was performed to determine the content of AAc and to study the effect of comonomer ionization on the LCST. The LCSTs of PNIPAAm/water in the copolymers were strongly affected by pH, presence of polyelectrolyte, AAc content, and charge density on the polymer. The polyelectrolyte complexes were formed at neutral condition. The influence of more hydrophobic PLL as polyelectrolyte on the cloud-point of PNIPAAm/water in the copolymer was stronger than that of poly(allylamine) (PAA).

• KSBB Journal
• /
• v.14 no.1
• /
• pp.58-65
• /
• 1999

A hydrogel, poly(N-isopropylacrylamide-co-N,N'-dimethylaminopropyl methacrylamide), sensitive to both pH and temperature was synthesized and characterized for its welling behavior, lower critical solution temperature (LCST), and its appearance. The hydrogel with 5 mol% of N,N'-diemthylaminopropyl methacrylamide (DMAPMAAm) increased its volume phenomenonally in a lower pH range (ph 1~8) even at temperature ($37^{\circ}C$ and $40^{\circ}C$) higher than LCST. This behavior was unique compared to the temperature -sensitive hydrogel which did not exhibit any swelling in the same pH range. The hydrogel with 20 mol% of DMAPMAAm was swollen significantly at a higher pH of 12. With pH decrease from 12 to 2 water content in the gel increased from 38.8 wt% and 60.6 wt%, and 90.8 wt% for 5 mol% and 20 mol% gel, respectively. The transition pH that pH effect overwhelmed temperature effect occurred at a lower pH for a higher temperature ($40^{\circ}C$) and a lower mol% (5 mol%) of DMAPMAAm. Transparency and LCST of the gel increased with higher DMAPMAAm mol%.

• Polymer(Korea)
• /
• v.25 no.2
• /
• pp.263-269
• /
• 2001

MAPTAC-MMT was prepared by exchanging the mineral cation (sodium montmorillonite) with 3-(methacryloyl amino) propyltrimethyl ammonium chloride, thus rendering the mineral organophilic and forming polymerizable moieties directly bonded to the surface of montmorillonite (MMT). Thermoresponsive nanocomposites (PNIPAM-MMT) were synthesized by polymerization of N-isopropyl acrylamide in an aqueous suspension of MAPTAC-MMT at room temperature. Thermoresponsive nanocomposites exhibited a low critical solution temperature (LCST) similar to unmodified poly(N-isopropyl acrylamide) (PNIPAM). The LCST of thermoresponsive nanocomposites decreased in proportion to the amount of MAPTAC-MMT. TGA results showed that the thermal stability of thermoresponsive nanocomposites was improved compared to PNIPAM itself the thermoresponsive polymer.

• Bulletin of the Korean Chemical Society
• /
• v.23 no.4
• /
• pp.549-554
• /
• 2002

Thermosensitive poly(organophosphazenes) bearing methoxy-poly(ethylene glycol) (MPEG) and alkylamines as substituents have been synthesized and characterized by elemental analysis, NMR spectroscopy, GPC, and DSC. All the polymers exhibited crystallinity, which was probably induced by the MPEG side chain of the polymers. All the polymers exhibited the lower critical solution temperature (LCSTs) in the range of 28 to $94^{\circ}C$ depending on several factors such as mole ratio of the substituents, kinds of PEG and alkylamines. The higher content of MPEG and shorter chain length of alkylamines of the polymers afforded the higher LCST. The LCSTs of the polymers exhibited almost concentration-independent behavior in the range of 3-30 wt % of the polymers in aqueous solutions. The polymers showed the higher LCSTs in the acidic solutions than in the neutral and basic solutions. The ionic strength of the polymer solution affected the LCST, which decreased with increased NaCl concentration. The polymer bearing almost equimolar substitutuents with the -N-P-N- unit has shown the LCST more sensitive to NaCl and pH than that with the -N-P-O- unit. The polymers were found to degrade in acidic solution but be very stable in alkali solution as well as in the buffer solution of pH 7.4.