PBS Segments Research Articles

Non-isothermal Crystallization Behaviors of Poly(p-dioxanone) and Poly(p-dioxanone)-b-poly(butylene succinate) Multiblock Copolymer from Amorphous State

A novel alternating multiblock copolymer poly(p-dioxanone)-b-poly(butylene succinate) (PPDOBS) was prepared through a two-step process including the initial ring-opening polymerization of p-dioxanone (PDO) initiated by poly(butylene succinate)-diol and the following chain extension, using hexamethylene diisocyanate (HDI) as a chain extender. The resulting PPDOBS was characterized by hydrogen nuclear magnetic resonance spectroscopy (1H NMR), wide angle X-ray diffraction (WAXD), and differential scanning calorimeter (DSC). The WAXD analysis showed that the introduction of PBS segments did not change the crystal structure of PPDO. The heating scans of DSC curves showed that the cold crystallization temperature was decreased after the introduction of PBS segments, which indicated that the ability of PPDO to crystallize was improved. The non-isothermal crystallization kinetics of PPDO and PPDOBS were evaluated by means of Avrami, Ozawa, and Mo methods. It was found that the Ozawa method was not suitable to describe the crystallization kinetics for both PPDO and PPDOBS. The results of Avrami and Mo methods showed that crystallization rate of PPDO were enhanced by introduction of PBS segments. In addition, the activation energies for non-isothermal crystallization calculated using the Kissinger method for PPDO and PPDOBS were 46 kJ/mol and 38 kJ/mol, respectively, indicating the crystallization ability of PPDO was improved after the introduction of PBS segments.

A novel biodegradable multiblock poly(ester urethane) containing poly(l-lactic acid) and poly(butylene succinate) blocks

A novel biodegradable multiblock poly(ester urethane) (PEU), consisting of poly(l-lactic acid) (PLLA) and poly(butylene succinate) (PBS) blocks, has been successfully synthesized via chain-extension reaction of dihydroxyl terminated PLLA (PLLA-OH) and PBS prepolymers (PBS-OH) using toluene-2,4-diisocyanate (TDI) as a chain extender. The chemical structures and molecular weights of PEUs, containing different block lengths and weight fractions of PLLA and PBS, were characterized by 1H NMR and GPC. The effects of the structures on the physical properties of PEUs were systematically studied by means of DSC, TGA, WAXD and tensile testing. The DSC results indicated that PLLA segment was compatible well with PBS segment in amorphous phase and the crystallization of PEU was predominantly caused by PBS segment, which was also confirmed by WAXD. The results of tensile testing showed that the extensibility of PLLA was largely improved by incorporating PBS segment. The PEU can be used as a potential substitute for some petroleum-based thermoplastics.

The Mechanic as Twentieth-Century Mona Lisa: Modernism’s Utopian Designs at the Corcoran Gallery

The Mechanic as Twentieth-Century Mona Lisa: Modernism’s Utopian Designs at the Corcoran Gallery John Paul Riquelme Modernism: Designing a New World 1914–1939. Corcoran Gallery of Art, Washington, D. C., 1703– 2907, 2007; conceived by and first shown at the Victoria and Albert Museum, London, 0604– 2307, 2006. Essential Modernism. Philip Brookman, Paul Greenhalgh, and Sarah Newman . London: V&A Publications, 2007. 100 illustrations, mostly color. Pp. viii + 88. $19.95 (cloth). Modernism: Designing a New World 1914–1939. Christopher Wilk , ed. London: V&A Publications, 2006. Pp. 447. 360 color plates, 60 black and white illustrations. $85.00 (cloth). The Mechanic[by Fernand Léger] of 1923 just struck me as being the twentieth century's Mona Lisa, you know? He's a confident boy. —Paul Greenhalgh, Director, Corcoran Gallery of Art Exhibiting and Interpreting the Utopian Machine Aesthetic The memorable exhibition of largely European modernist art and design at the Corcoran Gallery (originally at the V&A) is the most recent [End Page 755]of several ambitious, exceptionally interesting exhibitions concerning late-nineteenth-century and early-twentieth-century art and design that have traveled from the V&A to American museums. 1The objects and the argument of Modernismhave been presented with care in two beautifully designed books that provide important resources for anyone interested in modernism. The exhibition's range and diversity, a few exemplary objects and spaces, and the curatorial attitudes that shaped it are available in the streaming video of an eight-minute PBS segment from The Newshour with Jim Lehrer(19 April 2007). 2The segment includes a selective walk through, Jeffrey Brown's reportorial commentary, and excerpts from interviews with Paul Greenhalgh, Director of the Corcoran, and Christopher Wilk, Keeper of the Furniture, Textiles, and Fashion Department at the V&A and curator of Modernism. No brief report could communicate sufficiently Brown's accurate assertion that the exhibition was "huge." The books suggest more fully the show's monumental size and the stunning impact of many of the objects. The PBS interviews are revealing, particularly Greenhalgh's declaration concerning Fernand Léger that provides my epigraph. He continues: "He looks as though he knows what he's doing, and he looks in control of his life. And for me, it makes it this big, optimistic symbol." Greenhalgh and his coauthors put The Mechanicon the dust jacket of Essential Modernism. Wilk is equally declarative concerning modernist intentions: "When architects of this period got together, they tended to talk about three things, maybe four: housing—by which they meant public housing, social housing—housing, housing, and then how to build it. . . . the burning issue of the day was how to improve the plight of ordinary people by providing them with much better conditions." He points to Mies van der Rohe's influential sketch for the Friedrichstrasse Skyscraper Project(1921) as epitomizing with its glass sheathing the goal of "letting light in, and light is health-giving, and it's creating a sense of something higher." These claims about modernism's machine aesthetic, utopian aspirations, and Apollonian character articulate the exhibition's main directions and sharply defined focus. Although providing clarity for visitors is crucial, these claims beg many questions and leave the ostensible intentions of modernism largely uncriticized. Nietzsche, who was taken seriously in the period by Thomas Mann and others, had much to say about the limitations, delusions, and instability of cultural ideals that adopt the vocabulary of light, health, and the contrast of higher to lower. But we need not rely on Nietzsche's legacy to question Utopiaand its political implications. The term was widely understood to mean a Marxist-Leninist commitment to the establishment of communism by revolutionary means. It was not a universally admired term in debates concerning future social structures. This marvelous exhibition is conceptually weakened by not presenting more strenuously both the contemporary objections from the right to Utopia, a term with a contentious history, and the critique from the left that modernism was complicit with existing hierarchies of power. Understanding modernism depends on situating it in relation to these criticisms from its own time. Who sets the standards by...

A novel biodegradable polyester from chain-extension of poly( p-dioxanone) with poly(butylene succinate)

Prepolymers of both poly( p-dioxanone) (PPDO) and poly(butylene succinate) (PBS) reacted in the presence of toluene-2,4-di-iso-cyanate(TDI) as a chain extender to produce higher-molecular-weight chain-extended products (PPDOBS) in suitable reaction conditions. The novel biodegradable polymers were characterized by NMR, DSC, TG and WAXD. The results of thermal oxidative degradation show that chain-extended products have better thermal stability than PPDO. The thermal degradation of PPDOBS shows two stages, the first due to the degradation of PPDO segment of PPDOBS, and the second to the degradation of PBS segment. DSC measurement shows that the PPDOBS has only one T g, which means that PPDO has good compatibility with PBS. PPDOBS has two crystalline peaks during the cooling scan, but no crystalline peak during the heating scan. The diffraction peaks of PPDOBS appear at the same 2 θ angles as that of homopolymers, suggesting that the PPDO and PBS of the chain-extended products preserve their own crystal form. This kind of novel biodegradable polymer is expected to have potential applications in environmentally friendly materials.