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Homopolymer-Copolymer and Copolymer-Copolymer Blends
Published in Yuri S. Lipatov, Anatoly E. Nesterov, Thermodynamics of Polymer Blends, 2020
Yuri S. Lipatov, Anatoly E. Nesterov
Besides mixtures of homopolymer with copolymers and copolymer mixtures, the miscibility windows have been observed also for the mixtures of homopolymers with homologue series of polymers of various chemical nature.72,93,94 In particular, miscibility windows were found for the mixtures of hydroxy ethyl ether of bisphenol A with aliphatic polyethers,93 chlorinated PVC with polyesters.94 The miscibility windows in such systems are determined by the ratio CH2/COO groups in homologue series of the second polymer. To explain such behavior Paul and Barlow13 have used the same model of binary interaction, considering the homologue series as copolymers. In particular, polyesters may be presented as copolymer series containing CHx (2) and COO (3) units. The volume fractions of each of these units can be computed from the increments which each adds to the molar volume.95
Universal Calibration in Gel Permeation Chromatography of Oligomers
Published in Boris A. Rozenberg, Grigori M. Sigalov, Marina Z. Aldoshina, Yurii B. Scheck, Heterophase Network Polymers, 2020
Despite a number of advantages, GPC ensures only relative measurements. In order to determine MW and parameters of MWD, we have to obtain the calibration dependence between MW and retention volume by using some reference compounds with a well-known MW or very narrow MWD. For this reason, high precision and reproducibility of GPC measurements cannot often be realized because of insufficiently correct parameters of reference sample. In view of this, we suggested a procedure for plotting universal calibration curve for oligomers that requires no reference sample. Essentially, the procedure is based on separation of polymer homologues by their degree of polymerization, with a well-defined retention volume for each homologue [4]. The calibration procedure developed initially for oligomers of styrene and ethylene oxide was then successfully applied to oligomers of epichlorohydrin, butadiene, methyl methacrylate, propylene oxide, epoxy resins, and oligohydroquinones [1].
Hydrolytic Enzymes for the Synthesis of Pharmaceuticals
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
Sergio González-Granda, Vicente Gotor-Fernández
Levofloxacin is a potent fluoroquinolone antibacterial agent used in the treatment of pneumonia, sinusitis or urinary tract infections among others. Rhizomucor miehei lipase (RML) has been efficiently applied in the hydrolysis of racemic 1-(2,3-difluoro-6-nitrophenoxy)propan-2-yl acetate, (Scheme 9.8), leading to the formation of the enantiopure (R)-alcohol in 45% yield and the remaining (R)-acetate in 84% ee after 53 h at 30°C (López-Iglesias et al., 2015). Alternatively, the same alcohol and the homologue amine have been produced in higher-yielding processes starting from prochiral ketones through bioreduction or biotransamination experiments, respectively (Mourelle-Insua et al., 2016). RML-catalysed hydrolysis of a racemic ester for the production of a Levofloxacin precursor.
Introduction to the 51st Annual A&WMA Critical Review: PFOA and Cancer
Published in Journal of the Air & Waste Management Association, 2021
Michael T. Kleinman, Eric D. Stevenson
After some major producers phased out U.S. production of PFOA, PFOS, and their precursors, production shifted toward shorter-chain homologue replacements, including fluorotelomer-based products, per- and polyfluoroalkyl ether substances. However, these homologues are also environmentally persistent and bioaccumulate in food, water, and humans. Although the exact mechanisms are not fully understood, PFAS toxicity can cause increased oxidative stress, changes in gene expression, and immune suppression, all of which have been described as key characteristics of carcinogens that affect humans; thus, PFAS may pose significant risks as toxic contaminants and carcinogens.
The influence of the second core and the trifluoromethy terminal on the properties of multi-arm chenodeoxycholic acid-derived liquid crystals
Published in Liquid Crystals, 2022
Xin-Yi Wan, Yuan-Yuan Gao, Lu-Lu Guo, Ze-Long Feng, Kun-Li Liu, Hong-Yu Liu, Xiao-Yan Wang, Ying-Gang Jia, Mei Tian
What are the factors that affect the melting temperature? For homologues, the melting temperature decreases with the decrease of molecular weight. In addition, there are other factors that affect the melting temperature. It is known that melting is an equilibrium process in thermodynamics, which can be expressed by thermodynamic function:
The role of a terminal chain in promoting the twist-bend nematic phase: the synthesis and characterisation of the 1-(4-cyanobiphenyl-4′-yl)-6-(4-alkyloxyanilinebenzylidene-4′-oxy)hexanes
Published in Liquid Crystals, 2018
Daniel A. Paterson, Catriona A. Crawford, Damian Pociecha, Rebecca Walker, John M.D. Storey, Ewa Gorecka, Corrie T. Imrie
Figure 7 shows the dependence of the transition temperatures on the length of the terminal alkyloxy chain, m, for the CB6O.Om series. The melting point increases on passing from CB6O.O1 to CB6O.O2 and then decreases smoothly on further increasing m to CB6O.O7 appearing to approach a limiting value. However, the reduction in the melting point is more pronounced between CB6O.O7 and CB6O.O8. The melting point subsequently increases over the last three homologues. The N-I transition temperature, TNI, increases on passing from CB6O.O1 and CB6O.O2, and subsequently decreases on further increasing m. Superimposed on this decreasing trend is a weak alternation in which the even members show the higher values. The alternation attenuates on increasing m. The dependence of TNI on m is consistent with the behaviour observed for both conventional low molar mass mesogens having high values of TNI and liquid crystal dimers [50,51]. The effect of increasing the length of a terminal alkyl chain is two-fold; first, the anisotropic properties of the molecule are increased resulting in an increased TNI. For an alkyloxy chain, the shape anisotropy is enhanced to a greater extent by adding a methylene group to an odd-membered carbon chain giving an even-membered chain because the additional carbon atom lies more or less parallel to the major mesogenic unit axis. By contrast a methylene group added to an even-membered carbon chain to give an odd chain, lies at an angle to the major mesogenic unit axis and so a smaller increase in the anisotropic properties is seen. This alternation in the anisotropic properties of the molecule on varying m gives rise to the odd-even effect seen in TNI. The second effect of increasing the length of a terminal chain is the increased dilution of the interactions between the mesogenic units resulting in a decrease in the TNI. Thus, the overall effect of increasing the length of a terminal chain depends essentially on the interaction strength parameter of the cores. If the cores are, for example, two ring units then the increase in molecular anisotropy is noticeable resulting in an odd-even effect being observed on increasing m. If, however, the cores are large, for example three ring systems, then the dilution effect dominates and the transition temperatures simply fall with increasing chain length with little or no alternation. This latter case describes the behaviour of the CB6O.Om series. The entropy changes associated with the nematic-isotropic transition listed in Table 2 are small and rather similar within experimental error. This implies that the increase in the conformation entropy arising from increasing the terminal chain length makes only a small contribution to the overall entropy change.