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Introduction to Chain Molecules
Published in Timothy P. Lodge, Paul C. Hiemenz, Polymer Chemistry, 2020
Timothy P. Lodge, Paul C. Hiemenz
In contrast, for condensation polymers: The polymer repeat unit arises from reacting together two different functional groups, which usually originate on different monomers. In this case, the repeat unit is different from either of the monomers. In addition, small molecules are often eliminated during the condensation reaction. Note the words usual and often in the previous statements; exceptions to both statements are readily found.The mechanistic aspect of these reactions can be summarized by saying that the reactions occur in steps. Thus, the formation of an ester linkage between two small molecules is not essentially different from that between a polyester and a monomer.The product molecules have the functional groups formed by the condensation reactions interspersed regularly along the backbone of the polymer molecule:–C–C–Y–C–C–Y–
The structure of solids
Published in Peter Domone, John Illston, Construction Materials, 2018
The backbone of the chain normally consists of covalently-bonded carbon atoms (although some silicon-based polymers, known collectively as silicones, are made). The monomer molecule typically contains a double bond between carbon atoms, which reduces to a single bond on polymerisation. The monomer therefore provides the repeat unit in the chain; two examples, polyethylene and polyvinyl chloride (PVC), are shown in Fig. 3.14. Polymerising a mixture of more that one type of monomer produces a copolymer.
Biodegradation Properties
Published in Chih-Chang Chu, J. Anthony von Fraunhofer, Howard P. Greisler, Wound Closure Biomaterials and Devices, 2018
In conclusion, Pratt and Chu85 found that the rate of ester hydrolysis has been found to be greatly affected by halogen substituents due primarily to charge delocalization, a substituents on the acyl portion of the ester favor the formation of the tetrahedral intermediate but retard the rate-determining alkoxide elimination step. Interpretation of the β and γ substituent effects is less straightforward, as differences apparently arise from a combination of relatively small inductive, steric, and conformational effects. Halogen substituents on the alkyl fragment have only a slight effect on the enthalpy of hydroxide attack, but greatly accelerate the elimination step by stabilization of the forming alkoxide ion. This effect falls off rather slowly with distance from the carbonyl group, and is still significant in the γ position. Therefore, the polymer degradation rate can be modified by altering both the number of methylene groups in the repeat unit, and the position of the heteroatoms. Rapid degradation could be achieved with chlorine substitution in the alkyl portion of the ester, adjacent to the carbonyl group, while a fluorine substitution in the acyl fragment would slow the rate-determining step, if the number of methylene groups was sufficiently large to avoid the inductive effects in the alkyl portion of the polyester.
Water-soluble polycarbodiimides and their cytotoxic and antifungal properties
Published in Journal of Biomaterials Science, Polymer Edition, 2021
Enosha Harshani De Silva, Narges Salamat, Li Zhang, Jie Zheng, Bruce M. Novak
As discussed, water-soluble macromolecules can be ionic or neutral. There have been a number of studies carried out to investigate the properties of ionic polycarbodiimides; however, comparatively less effort has been made to investigate the properties of neutral water-soluble carbodiimide materials. The general synthesis of water-soluble carbodiimide polymers is shown in Schemes 1 and 2. The polymers are made water-soluble by including polar functional groups such as dimethyl amine, piperazine, and morpholine to each repeat unit of the polymer backbone. The functionalized hydrophilic monomers were polymerized with both S-BINOL-Ti(IV) isopropoxide and R-BINOL-Ti(IV) isopropoxide enantiomeric catalysts to obtain single screw-sense chirality. These polymers are soluble in polar solvents like water and various buffer solutions. Because of their amphiphilic nature, all these polymers displayed a wide range of solubilities in different polar and nonpolar organic solvents.
Preparation of a cellulose-polyphenylacetylene-polyaniline composite
Published in The Journal of The Textile Institute, 2021
Figure 2 shows the infrared absorption spectroscopy measurement results of cellulose, Cell/PPA, and Cell/PPA/PANI. An intense absorption at 3340 cm−1 is assigned to the OH stretching vibration of the cellulose unit. The absorption peak of alkyl groups is observed at 2900 cm−1 (νCH2, νCH3). The stretching vibration of C–O–C is observed at 1029 cm−1. The CH out-of-plane vibration (γCH) peak is observed at 588 cm−1. Cell/PPA shows the same absorption as that of pure cellulose because the absorption peak owing to the side chain phenylene group overlaps with the absorption peak of cellulose at 1641 cm−1. Other fundamental absorption peaks of PPA on the cellulose fiber overlap those of cellulose. Cell/PPA/PANI has an absorption band at 1579 cm−1 owing to the quinonoid structure of monomer repeat unit of PANI deposited on the surface of PPA. The benzenoid structure of monomer repeat unit of polyaniline is observable as a small signal at 1565 cm−1. These IR measurements confirm the formation of the triple-layer composite.
Recent progress at the interface between nanomaterial chirality and liquid crystals
Published in Liquid Crystals Reviews, 2021
Diana P. N. Gonçalves, Marianne E. Prévôt, Şenay Üstünel, Timothy Ogolla, Ahlam Nemati, Sasan Shadpour, Torsten Hegmann
Finally, we will consider how multidomain cholesteric emitting layers can combine semiconducting and photonic functionalities to make OLEDs emitting CP electroluminescence (CPE). OLEDs can emit circularly polarized electroluminescence (CPEL) when the emitting organic material is chiral and of one handedness only. Friend and team exploited a chiral and enantiomerically pure substituted polyfluorene copolymer poly(fluorene-alt-benzothiadiazole) (c-PFBT) used as emitting layer in the OLEDs (Figure 20) [151]. The polymer contained a fluorene-benzothiadiazole donor–acceptor repeat unit forming the conjugated backbone, with chiral centres attached to the fluorene moiety. Thermal annealing led to the self-assembly of the polymer into a multidomain N*-LC film. CPEL with up to 40% excess of right-handed polarization was reached under pulsed voltage bias operation ( = − 0.8) and 30% ( = − 0.6) under constant voltage bias. CPEL originated from circular selective scattering and birefringence in such multidomain films (Figure 20b).