Search results for "Polyester"
showing 10 items of 221 documents
(Photo)crosslinkable Smectic LC Main-Chain Polymers
2007
This paper presents the synthetic route to SmA LC main-chain polymers, that can be (photo)-crosslinked without solvent in the bulk phase. They are based on soluble polymalonates, in which higher ordered phases can be suppressed by copolymerization with a laterally brominated biphenyl. Two routes were developed to incorporate the crosslinkable groups into the polyester backbone. The first consists in the incorporation of phenols into the polyester. These phenols are not reactive enough to participate in the transesterification reaction used to build up the polymer, but they can be esterified afterwards with acrylates. Thermally or photochemically created radicals then start the crosslinking.…
Synthesis of Oxetane-Functional Aliphatic Polyesters via Enzymatic Polycondensation
2012
Synthesis, characterization, and thermal properties of a series of oxetane-functional aliphatic polyesters are investigated. The incorporation of the acid-sensitive 3,3-bis(hydroxymethyl)oxetane (BHMO) into polymers is achieved by using the enzyme CALB (Candida antarctica Lipase B) as a catalyst. This mild synthetic strategy provides well-defined, oxetane-functional polyesters. The enzymatic polycondensation allows for the synthesis of a series of aliphatic polyesters containing various ratios of the difunctional monomers sebacic acid, 1,8-octanediol, and BHMO with molecular weights between 5000–9800 g mol−1 and polydispersity indices (Mw/Mn) in the range of 1.25 and 1.92. Furthermore, cros…
Synthesis and phase behaviour of liquid-crystalline side group polyesters
1990
Abstract Several series of liquid-crystalline side group polymers with a polyester backbone structure have been synthesized using mesogenic diethylmalonate and 1,3-propanediol derivatives. The structures of the polymer backbone and the mesogenic units have been varied systematically. As shown by differential scanning calorimetry, polarizing microscopy and X-ray diffraction, the side group polyesters exhibit nematic and/or smectic mesophases. Polyesters synthesized from mesogenic diethylmalonate derivatives can tolerate long non-mesogenic segments in the polymer main chain without losing their liquid crystal properties. X-ray studies suggest that some of the smectic polymers exhibit interdig…
Synthesis, properties and processability of a new class of semirigid liquid crystalline copolyesteramides
1995
Abstract A new family of semirigid main chain liquid crystalline polymers (LCPs), referred to as SBAN, characterized by fairly good processability and mechanical properties, and improved thermal resistance, have been synthesized by the melt polycondensation of sebacic acid (S), 4,4′-dihyhxybiphenyl (B), 4-aminobenzoic acid (A), and 2-hydroxy-6-naphthoic acid (N), in a wide range of compositions. The molar concentration of the A ahd N units, in these LCPs must be kept lower than ca 40 and 60%, respectively, in order to avoid the formation of homopolymeric blocks, which impair spinnability. The presence of A units grants the formation of hydrogen bonds between neighboring macromolecules, and …
Tomographic and Topographic Investigation of Poly-D,L-Lactide-Co-Glycolide Microspheres Loaded with Prostaglandine E<sub>2</sub> for Exte…
2010
Polymeric, biodegradable microspheres represent a good reliable system to investigate the release of bioactive substances in both in vitro and in vivo applications. Common biomaterials for the synthesis of these microspheres are aliphatic polyesters of the poly(α-hydroxy)acids, especially poly-L-lactides (PLA) and polyglycolides (PGA) or their copolymers poly-D,L-lactide-co-glycolides (PLGA). In our own previous studies we have developed PLGA microspheres with integrated PGE2 as model substance for a wide range of biomedical applications, especially in angiogenesis, fracture healing and cartilage repair. The synthesis is based on a binary solvent in water emulsion approach, where two differ…
Effect of the Components Molar Mass and of the Mixing Conditions on the Compatibilization of PE/LCP Blends by PE-g-LCP Copolymers
1999
The rheology, morphology, and mechanical properties of blends of high-density polyethylene (HDPE) with a semiflexible liquid crystalline copolyester (SBH) were studied in order to assess the compatibilizing ability of added PE-g-SBH copolymers, and its dependence on the molar mass of the PE matrix, and on the technique used for blend preparation. The PE-g-SBH copolymers were synthesized as described in previous articles, either by the polycondensation of the SBH monomers in the presence of a functionalized PE sample containing free carboxyl groups, or by reactive blending of the latter polymer with preformed SBH. Two samples of HDPE having different molar masses, and two samples of SBH with…
Sanidics: A new class of mesophases, displayed by highly substituted rigid-rod polyesters and polyamides
1990
Abstract The structure of rigid-chain polyesters and polyamides which possess flexible side chains consisting of methylene or 1,4,7-trioxaoctyl oxide units have been investigated by means of X-ray scattering. The X-ray studies were performed on fibres and monodomains. Additional information was gained from calorimetric, dilatometric and microscopic studies. The investigations revealed that these polymers display mesophases and that the structures of the mesophases differ from those observed for discotic and calamitic phases. They are characterized by the fact that in the ordered and disordered phases board-like molecules are stacked parallel on top of each other and that these stacks of mol…
A Fractional-Order Model of Biopolyester Containing Naturally Occurring Compounds for Soil Stabilization
2019
Currently, the use of polymers and biopolymers as soil-stabilizer additives for control of the soil degradation, deterioration, and desertification and for improving the arid and semiarid soils has been expanded significantly in the agricultural sector. This research was conducted to determine the effect of naturally occurring compounds, such as quercetin (Q) and sodium montmorillonite (NaMMt) at different weight ratios, in biopolyester, such as polylactic acid (PLA), aiming to formulate ecosustainable materials to control the soil degradation and to protect the environment. As known, the use of sophisticated analytical tools to describe the material rheology and melting properties is nowad…
Characterization of a fiber reinforced semirigid liquid crystalline polymer
1997
In this work, samples of a semirigid Liquid crystalline polymer reinforced with carbon and glass fibers has been characterized. Semirigid liquid crystalline polymers (LCPs) show some advantages with respect to rigid LCPs: in particular lower processing temperatures, and better compatibility with flexible thermoplastics, but also some disadvantages: lower mechanical properties and poor thermomechanical resistance. Both properties can be improved by adding inorganic fillers. Although elastic modulus and tensile strength of the glass fiber filled LCP improve remarkably with increasing the filler content, the same properties for the carbon fiber-filled samples do not increase with increasing ti…
Macro-oriented network of liquid-crystalline polyesters: crosslinking induced by g-irradiation and thermally activated reaction.
2000
Abstract The synthesis of a macro-oriented network from liquid-crystalline polymers, bearing pendant groups with unsaturations, is reported. Virgin polymers are processable to obtain oriented samples, e.g. fibres, which may be crosslinked through thermal activation and/or exposure to γ-radiation. The liquid-crystalline state is “frozen” and the macroscopic anisotropy is preserved even at high temperatures. Compared to virgin fibres, irradiated samples show an enhancement of tensile performances, thus indicating that the main effect of irradiation is crosslinking without significant degradation phenomena.