Polyester Segments (polyester + segment)

Distribution by Scientific Domains

Selected Abstracts

Synthesis of rosin-based flexible anhydride-type curing agents and properties of the cured epoxy

Honghua Wang
Abstract BACKGROUND: Although rosin acid derivatives have received attention in polymer synthesis in recent years, to the best of our knowledge, they have rarely been employed as epoxy curing agents. The objective of the study reported here was to synthesize rosin-based flexible anhydride-type curing agents and demonstrate that the flexibility of a cured epoxy resin can be manipulated by selection of rosin-based anhydride-type curing agents with appropriate molecular rigidity/flexibility. RESULTS: Maleopimarate-terminated low molecular weight polycaprolactones (PCLs) were synthesized and studied as anhydride-type curing agents for epoxy curing. The chemical structures of the products were confirmed using 1H NMR spectroscopy and Fourier transform infrared spectroscopy. Mechanical and thermal properties of the cured epoxy resins were studied. The results indicate that both the epoxy/anhydride equivalent ratio and the molecular weight of PCL diol play important roles in the properties of cured resins. CONCLUSION: Rosin-based anhydride-terminated polyesters could be used as bio-based epoxy curing agents. A broad spectrum of mechanical and thermal properties of the cured epoxy resins can be obtained by varying the molecular length of the polyester segment and the epoxy/curing agent ratio. Copyright 2009 Society of Chemical Industry [source]

Comparison of micelles formed by amphiphilic star block copolymers prepared in the presence of a nonmetallic monomer activator

Hoon Hyun
Abstract In this article, we describe the synthesis of PEG- b -polyester star block copolymers via ring-opening polymerization (ROP) of ester monomers initiated at the hydroxyl end group of the core poly(ethylene glycol) (PEG) using HCl Et2O as a monomer activator. The ROP of ,-caprolactone (CL), trimethylene carbonate (TMC), or 1,4-dioxan-2-one (DO) was performed to synthesize PEG- b -polyester star block copolymers with one, two, four, and eight arms. The PEG- b -polyester star block copolymers were obtained in quantitative yield, had molecular weights close to the theoretical values calculated from the molar ratio of ester monomers to PEG, and exhibited monomodal GPC curves. The crystallinity of the PEG- b -polyester star block copolymers was determined by differential scanning calorimetry and X-ray diffraction. Copolymers with a higher arm number had a higher tendency toward crystallization. The crystallinity of the PEG- b -polyester star block copolymers also depended on the nature of the polyester block. The CMCs of the PEG- b -PCL star block copolymers, determined from fluorescence measurements, increased with increasing arm number. The CMCs of the four-arm star block copolymers with different polyester segments increased in the order 4a-PEG- b -PCL < 4a-PEG- b -PDO < 4a-PEG- b -PLGA < 4a-PEG- b -PTMC, suggesting a relationship between CMC and star block copolymer crystallinity. The partition equilibrium constant, Kv, which is an indicator of the hydrophobicity of the micelles of the PEG-polyester star block copolymers in aqueous media, increased with decreasing arm number and increasing crystallinity. A key aspect of the present work is that we successfully prepared PEG- b -polyester star block copolymers by a metal-free method. Thus, unlike copolymers synthesized by ROP using a metal as the monomer activator, our copolymers do not contain traces of metals and hence are more suitable for biomedical applications. Moreover, we confirmed that the PEG- b -polyester star block copolymers form micelles and hence may be potential hydrophobic drug delivery vehicles. 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2084,2096, 2008 [source]

Synthesis and characterization of semifluorinated polymers and block copolymers

Doris Pospiech
Abstract The goal of the investigation presented here was to evaluate the influence of semifluorinated side chains on the bulk structure and the surface properties of polysulfones with different chain structure. Thus, segmented block copolymers consisting of polysulfone and semifluorinated aromatic polyester segments as well as polysulfones having semifluorinated side chains randomly distributed over the polymer backbone were synthesized and characterized. Oxydecylperfluorodecyl side chains were used because of their strong tendency for self-organization. The influence of the chain architecture on the self-organization as well as on the surface properties, particularly the wetting behavior, was examined. It could be shown that despite of the higher self-organizing tendency of block copolymers the surface properties of both polymer types are comparable and depend only on the concentration of side chains. [source]

Preparation and properties of transparent thermoplastic segmented polyurethanes derived from different polyols

Da-Kong Lee
Various segmented polyurethanes of different soft segment structure with hard segment content of about 50 wt% were prepared from 4,4,-diphenylmethane diisocyanate (MDI), 1,4-butanediol and different polyols with a Mn of 2000 by a one-shot, hand-cast bulk polymerization method. The polyols used were a poly(tetramethylene ether)glycol, a poly(tetramethylene adipate)glycol, a polycaprolactonediol and two polycarbonatediols. The segmented polyurethanes were characterized by gel permeation chromatography (GPC), UV-visible spectrometry, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X-ray diffraction, and their tensile properties and Shore A hardness were determined. The DSC and DMA data indicate that the miscibility between the soft segments and the hard segments of the segmented polyurethanes is dependent on the type of the soft segment, and follows the order: polycarbonate segments > polyester segments > polyether segments. The miscibility between the soft segments and the hard segments plays an important role in determining the transparency of the segmented polyurethanes. As the miscibility increases, the transparency of the segmented polyurethanes increases accordingly. The segmented polyurethanes exhibit high elongation and show ductile behavior. The tensile properties are also affected by the type of the soft segment to some extent. POLYM. ENG. SCI., 47:695,701, 2007. 2007 Society of Plastics Engineers. [source]