Study of poly(ethylene oxide) melting by temperature-modulated DSC

Result of temperature-modulated DSC study of poly(ethyleneglycol) with molecular weight 3000

Phase equilibrium in aqueous solutions of octablock copolymer of poly(propylene oxide)/poly(ethylene oxide)

The phase diagram of the associating octablock star copolymer of polyethylene oxide/polypropylene oxide in water was constructed on the basis of visual observations and DSC measurements

The study of crystallization and melting of polymers by temperature modulated DSC

Melting behaviour of poly(N-methyldodekaco lactam) was studied by the temperature modulated DSC. Non-linear behaviour observed is given by melting kinetics and strong temperature dependence of c.sub.p./sub. in the melting region

Character of transitions in frozen sucrose solutions

The classical DSC methods was employed to study aqueous solutions of sucrose in the whole concentration range and the temperature interval of -120 to 30 °C

Crystallization of poly(N-methyldodecano-12-lactam) in blends with poly(styrene-stat-acrylic acid)

Crystallization behaviour of blends of poly(N-methyldodecano-12-lactam) (PMDL) with statistical copolymer poly(styrene-stat-acrylic acid) (PSAA) has been studied by the DSC and WAXD methods. The blend films prepared from dioxane solutions were crystallized at laboratory temperature for five days. Approximate crystallinities of as-prepared neat lower-PMDL 5 and higher-molecular weight PMDL 45 were 28% and 19%, respectively. With increasing PSAA content in the blends the crystallinities decreased sharply. The melting point of the primary crystalline structure of PMDL showed a decreasing dependence on PSAA content in the blends, confirming miscibility of the PMDL-PSAA pair. Recrystallization was strongly suppressed in the blends. The lower-melting endotherm appearing at about 10-15 degrees C above the crystallization temperature was attributed to melting to I ess perfect structures formed during secondary crystallization. In neat PMDL, the extent of secondary crystallization was approximately 5-10%. In the blends containing 20% PSAA approximate relative proportion of secondary crystallites on total crystallinity was 40% and 60% for the blends with PMDL 5 and PMDL 45, respectively. WAXD measurements did not reveal any change in crystal modification on blending. Increased T-g in blends of flexible PMDL cannot play a significant role in suppression of primary in favour of secondary crystallization. This was attributed to low mobility of PMDL chains due to dilution effect and specific interactions with the amorphous copolymer component.. and. in case of the higher-molecular-weight PMDL, a greater involvement of entanglements. Higher T-g of blends was involved in retardation of non-isothermal crystallization on cooling and subsequent cold crystallization. (C) 2007 Elsevier Ltd. All rights reserved.106/02/1248, GACR, Grantová Agentura České Republik

Long-term X-ray stimulated crystallization of poly(N-methyldodecano-12-lactam) in blend with poly(styrene-stat-acrylic acid)

The effect of X-ray irradiation on crystallization of the blend of poly(N-methyldodecano-12-lactam) (PMDL) with 29.5% of statistical copolymer poly(styrene-stat-acrylic acid) (PSAA) was studied using DSC, WAXD, and solid-state C-13 NMR methods. Significant acceleration of crystallization was found in the as-prepared X-ray irradiated (XI), that is, WAXD-measured, samples compared with the nonirradiated (NI) ones. In the XI blend, the incubation period was shortened and crystallization proceeded at significantly higher rate. In the asymptote, after 100-120 days, both NI and XI samples reached the same final crystallinity of about 18%. The second DSC runs indicated that the stimulating effect of X-ray irradiation was eliminated by heating the sample during the first run. The C-13 NMR studies have shown that PMDL chains crystallize exclusively in cis conformation on the C-N bond. Both in neat PMDL and in the blend with PSAA, the XI samples contained a significantly higher proportion of cis conformers in amorphous phase than the NI samples. It is suggested that energy absorbed by the sample during the standard WAXD measurement helps overcome the barrier of the trans/cis transition in the PMDL molecules. This opens the way to the formation of a higher number of critical equilibrium nuclei and, finally, results in accelerated crystallization of the XI samples. No irreversible changes were found in the XI samples. (C) 2007 Wiley Periodicals, Inc

Interfacial activity of styrene-butadiene block copolymers in low-density polyethylene/polystyrene blends

The. effect of molecular structure of styrene-butadiene (SB) block copolymers on their interfacial activity in low-density polyethylene/polystyrene (LDPE/PS) (4/1) blends was studied. It was found that addition of some SB copolymers, which are localized in brittle PS particles, leads to a decrease in the blend impact strength in spite of the fact that these SB improve the toughness of both the blend components. Comparison with our previous results showed that the distribution of SB copolymers between the interface and bulk phases and their supermolecular structure in LDPE/PS (4/1) blends strongly differs from those in LDPE/PS (1/4) blends

Glass transition study of blends of poly(N-methyldodecano-12-lactam) with poly(styrene-co-acrylic acid)

The blends of poly(N-methyldodecano-12-lactam) (MPA) with poly(styrene-co-acrylic acid) (PSAA) prepared from dioxane solutions were studied by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The experimental DSC data of glass transition temperature T, as a function of composition of amorphous phase were fitted for the as-prepared and re-scanned samples using theoretical approaches. The as-prepared blends show monotonic single-T-g dependence. The values of the Gordon-Taylor coefficient not far from unity suggest miscibility of the blend system in amorphous phase in the whole concentration range. As documented by FTIR, this miscibility is associated with hydrogen bonds between COOH groups of the acrylic acid units in PSAA molecules acting as the H-bond donor and CO groups of MPA acting as the H-bond acceptor. The T-g-dependencies obtained form the second runs have a profound sigmoid character. The Schneider treatment induced an idea of partial limited miscibility in the MPA/PSAA blends caused by prevalence of homogeneous contacts. The difference in T-g between the first and second run can partly be attributed to higher crystallinities in the former. (c) 2005 Elsevier Ltd. All rights reserved

Polymer blends II. Preparation and development of phase structure

Práce podává přehled metod přípravy polymerních směsí a diskutuje jejich výhody a nevýhody při aplikaci v laboratorním měřítku a především v průmyslové praxi. Jsou zde shrnuty výsledky studia vývoje fázové struktury polymerních směsí při jejich míchání a zpracování v tavenině. Tyto výsledky jsou diskutovány s ohledem na možnost řízení fázové struktury konečných materiálů a výrobků.The paper provides survey of the methods of polymer blends preparation and discusses their advantages and disadvantages at application in laboratory scale and especially in industry. The results of studies of the phase structure development of polymer blends at their mixing and processing in melt are summarized. The results are discussed with respect of the control of the phase structure of final materials