Search results for "Polyester"
showing 10 items of 221 documents
Torque rheometry investigation of model transreactions involving condensation polymers: I. Polyesters
2005
The chemical transformations taking place when poly(ethylene terephthalate) (PET) or poly(ethylene naphthalate) (PEN) are blended in the melt with different low molar mass substances containing hydroxyl, carboxyl, or amine functional groups have been investigated as models of the transreactions, undergone by the polyesters in reactive blending operations. The polyester molecular weight changes caused by the alcoholysis, acidolysis, aminolysis, and esterolysis reactions have been monitored by torque-rheometry, using a Brabender Plasticorder static mixer. The degradation of the polyesters by hydrolysis was also studied, under similar conditions, by the addition of a water-releasing substance …
Long-Chain Branched Poly(Lactide)s Based on Polycondensation of AB2 -type Macromonomers
2012
A series of long-chain branched poly(d-/l-lactide)s is synthesized in a two-step protocol by (1) ring-opening polymerization of lactide and (2) subsequent condensation of the preformed AB2 macromonomers promoted by different coupling reagents. The linear AB2 macromonomers are prepared by Sn(Oct)2-catalyzed ROP of D- and L-lactide with 2,2-bis(hydroxymethyl)butyric acid (BHB) as an initiator. Optimization of the polymerization conditions allows for the preparation of well-defined macromonomers (Mw/Mn = 1.09–1.30) with adjustable molecular weights (760–7200 g mol−1). The two-step approach of the synthesis comprises as well the coupling of these AB2 macromonomers and hence allows precise contr…
On the use of PET-LCP copolymers as compatibilizers for PET/LCP blends
1996
Copolyesters of poly[ethylene terephthalate) (PET) with a liquid crystalline polymer (LCP), SBH 1:1:2, have been synthesized by the polycondensation, carried out in the melt at temperatures up to 300 degrees C of sebacic acid (S), 4,4'-dihydroxybiphenyl (B), and 4-hydroxybenzoic acid (H) in the presence of PET. The PET-SBH copolyesters have been characterized by differential scanning calorimetry, scanning electron microscopy, X-ray diffraction, etc., and the relationships between properties and preparation conditions are discussed. The copolyesters show a biphasic nature, which is more evident for the products synthesized with a thermal profile comprising relatively lower temperatures (220-…
Water-soluble polyesters from long chain alkylesters of citric acid and poly(ethylene glycol)
2007
Abstract Long chain aliphatic alcohols have been used as model compounds to develop a preparative method for a water-soluble material, which could be a carrier for triacontanol, a highly hydrophobic plant growth regulator. New polyesters from long chain aliphatic (C = 12, 18 and 22) mono-1-alkyl citrates and poly(ethylene glycol) were synthesized and characterized by NMR spectroscopy. The polyester containing the triacontyl moiety was obtained from mono-1-triacontyl citrate, which was synthesized from the corresponding alcohol extracted from the Agave fourcroydes . The molecular weight M ¯ n of the polyesters depends on experimental conditions during synthesis such as reaction time, atmosph…
Kernspinlabel-Untersuchungen zur Struktur und Dynamik von flüssigkristallinen Hauptkettenpolymeren
1984
Thermotropic nematic polyesters, specifically deuterated at different positions of the polymer chain, were macroscopically aligned by strong magnetic fields and solid state extrusion. Analysis of the observed 2H NMR spectra was achieved, employing a dynamic NMR model, based on the stochastic Liouville equation. The model considers various double and multiple pulse sequences, recently employed in FT-NMR spectroscopy.
Genome Sequence of the Methanotrophic Poly-β-Hydroxybutyrate Producer Methylocystis parvus OBBP
2012
-- PAGS 2 5709-5710
Retentive strengths of cast gold crowns using glass ionomer, compomer, or resin cement
1998
The retention forces of a newly developed compomer cement (Dyract Cem), a glass ionomer cement (Ketac Cem Aplicap), and a resin cement (F21) were examined.Cemented cast gold crowns were removed along the path of insertion with a Zwick universal testing device. The impact of both a cured and a noncured additional bonding layer that were applied to the inner surface of the crowns was examined across the Dyract Cem group.The mean adhesive strength was measured at 2.36 +/- 0.69 N/mm2 in the Ketac Cem group, at 0.60 +/- 0.28 N/mm2 in the F21 group, and at 1.85 +/- 0.94 N/mm2 in the Dyract Cem group, respectively. The application of an additional bonding layer to the inner surface of the crowns d…
Hyaluronic acid and its derivatives in drug delivery and imaging: Recent advances and challenges.
2015
Hyaluronic acid (HA) is a biodegradable, biocompatible, nontoxic, and non-immunogenic glycosaminoglycan used for various biomedical applications. The interaction of HA with the CD44 receptor, whose expression is elevated on the surface of many types of tumor cells, makes this polymer a promising candidate for intracellular delivery of imaging and anticancer agents exploiting a receptor-mediated active targeting strategy. Therefore, HA and its derivatives have been most investigated for the development of several carrier systems intended for cancer diagnosis and therapy. Nonetheless, different and important delivery applications of the polysaccharide have also been described, including gene …
POLYASPARTAMIDE-POLYLACTIDE GRAFT COPOLYMERS WITH TUNABLE PROPERTIES FOR THE REALIZATION OF FLUORESCENT NANOPARTICLES FOR IMAGING
2015
Here, the synthesis and the characterization of novel amphiphilic graft copolymers with tunable properties, useful in obtaining polymeric fluorescent nanoparticles for application in imaging, are described. These copolymers are obtained by chemical conjugation of rhodamine B (RhB) moieties, polylactic acid (PLA), and O-(2-aminoethyl)-O'-methyl poly(ethylene glycol) (PEG) on α,β-poly(N-2-hydroxyethyl)-D,L-aspartamide (PHEA). In particular, PHEA is first functionalized with RhB to obtain PHEA-RhB with a derivatization degree in RhB (DDRhB ) equal to 0.55 mol%. By varying the reaction conditions, different amounts of PLA are grafted on PHEA-RhB to obtain PHEA-RhB-PLA with DDPLA equal to 1.9, 4…
Analysis of the crystallization behaviour of PBT-rich PBT/PET blends under processing conditions
2007
Among the high‐performance polyesters blends PBT/PET blends are expected to exhibit remarkable properties as far as the crystallization behaviour is concerned. The solidification behaviour of a 60/40 w/w PBT/PET blend was studied in a wide range of cooling conditions, according to a Continuous Cooling Transformation (CCT) procedure developed by the authors, aiming to emulate the typical conditions encountered in polymer processing. A set of several samples characterized by an homogeneous structure was prepared by solidification from the melt through spray cooling, and the resulting structure and properties were evaluated by density, Micro Hardness (MH), Wide Angle X‐ray Diffraction (WAXD) m…