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Flow Synthesis: A Better Way to Conjugated Polymers?
Published in John R. Reynolds, Barry C. Thompson, Terje A. Skotheim, Conjugated Polymers, 2019
James H. Bannock, Martin J. Heeney, John C. de Mello
Under the chosen reaction conditions, the THF formed stable ~0.5 μL droplets that passed along the PTFE tubing at a uniform speed of ~1 cm/s without coalescing (see Figure 16.21c). The polymerization proceeded rapidly, with the color of the droplets changing progressively from a pale yellow/orange to pink/red as they spiraled through the oil bath. Importantly, the product and reactants remained fully compartmentalized within the THF droplets, with no signs of deposition on the reactor wall at any point. Operating the reactor for a period of 16.6 hours yielded a final (purified) solid product of 0.9 g, corresponding to a yield of 44% (compared with a theoretical maximum yield of ~80% for the chosen GRIM route) and a conversion efficiency of ~55%. The average molecular weight of the material could be readily controlled by changing the temperature, reaction time, catalyst loading, or monomer concentration (e.g. Figure 16.22), with Mn values from ~10 to ~40 kg/mol being obtained depending on the reaction conditions selected. Bulk heterojunction solar cells based on the droplet-synthesized P3HT and PC61BM yielded power conversion efficiencies of 4.0 ± 0.1%, comparable to some of the best efficiencies reported for P3HT: PC61BM devices elsewhere in the literature [69].
Structure and Properties of Polymer Matrix
Published in Noureddine Ramdani, Polymer and Ceramic Composite Materials, 2019
The molecular weight of polymers is one of the most relevant parameters that determines their properties. Several mechanical properties increase with the increasing of molecular weight, whereas their processing will be very difficult due to the increase of their viscosities. The second key parameter is degree of polymerization (DP), which determines the number of mers (basic unit) in any polymer. The molecular weight (MW) and the DP are linked by relationship below: Mw=Dpx(Mw)u
Functional Polymers by Living Ionic Polymerization
Published in Eli Ruckenstein, Hangquan Li, Chong Cheng, Solution and Surface Polymerization, 2019
Eli Ruckenstein, Hangquan Li, Chong Cheng
Living polymerizations can exert superior control to macromolecular structures as compared to conventional chain polymerizations. With the absence or greatly suppressed chain-breaking reactions, living polymerizations with fast propagation relative to initiation generally lead to well-defined polymers with predetermined number-average molecular weight (Mn) and narrow polydispersity index (PDI; also called molecular weight dispersity, Ð). Polymers with complexed structures, such as block copolymers and graft copolymers, can also be prepared by living polymerizations.
Enhancing adhesion of thermosetting urea-formaldehyde resins by preventing the formation of H-bonds with multi-reactive melamine
Published in The Journal of Adhesion, 2022
Eko Setio Wibowo, Byung-Dae Park
Figure 1a shows that the Mw significantly increases from 515 to 814 g/mol as the melamine content increases from 0 to 20%, which is proportional to the increment in viscosity. In addition, the PDI represents the ratio of the Mw to Mn. It measures the broadness of molecular weight distribution (MWD). The larger the PDI (>1), the broader the molecular weight, and the polymer is referred to as a poly-dispersed polymer.[36] However, if PDI equal to one, the polymer is called a mono-dispersed polymer, meaning that all polymer chains have the same length or weight. Figure 1a shows that the PDI increases as the melamine content increases from 0 to 15% but begins to decrease after a 20% melamine content is attained. Neat UF resins have the lowest Mw and PDI due to the presence of linear molecules, as described in a previous study .[12] As the melamine content increased to 15%, the PDI increased due to an increase in the Mw, resulting in the formation of heterogeneous structures due to a considerable variation in chain length, weight, and polymer branching. However, the PDI decreased afterward, likely due to the formation of identical branched structures with high molecular weight. In other words, the linear polymers were completely converted into branched structures when 20% melamine was added.
Enhancing the performance of low molar ratio urea–formaldehyde resin adhesives via in-situ modification with intercalated nanoclay
Published in The Journal of Adhesion, 2021
Muhammad Adly Rahandi Lubis, Byung-Dae Park
The GPC chromatograms of ODA−BNT/UF resins for different ODA−BNT nanoclay content showed different patterns regarding molecular weight distribution (MWD) (Figure 5). The MWD of modified UF resins became increasingly wider as the ODA−BNT nanoclay content increased. An increase in the ODA−BNT content resulted in a greater portion of high molecular weights for UF resins. The highest Mw and Mn values of ODA−BNT/UF resins were obtained for the 5% ODA−BNT nanoclay, i.e., 580 g/mole and 342 g/mole, respectively. The lowest was detected for neat UF resins at 425 g/mole and 289 g/mole. As a result, the PDI values also increased alongside an increase in ODA−BNT content, from 1.47 to 1.69. PDI is a measure of molecular weight distribution; the greater the PDI is, the broader the molecular weights is.[39] A PDI increase with an increase in the ODA-BNT level suggests that the modified UF resins contain more branched molecules than that of neat UF resins because the GPC detects the hydrodynamic size of a molecule in a mobile phase.
Acid and enzymatic extraction of collagen from Atlantic cod (Gadus Morhua) swim bladders envisaging health-related applications
Published in Journal of Biomaterials Science, Polymer Edition, 2020
Rita O. Sousa, Ana L. Alves, Duarte Nuno Carvalho, Eva Martins, Catarina Oliveira, Tiago H. Silva, Rui L. Reis
A polymeric solution contains at least hundreds of polymer chains. These chains are not homogenous in nature. They probably differ in several physicochemical properties, the molecular weight being one of them [40]. The GPC-RALS method allows the determination of the Number Average Molecular Weight (Mn) and Weight Average Molecular Weight (Mw), as well as the polydispersity (Mw/Mn) [41]. The Mn can be defined as Total mass of material divided by the total number of molecules, meanwhile the Mw can be described as the total mass of material multiplied by the molecules mass. The molecular weight of a substance, particularly a polymer, is a key chemical characteristic that can dramatically influence the material mechanical performance, particularly the viscosity and rheological behavior [42]. The results show that the higher molecular masses correspond to ASCsb (Table 2). This is confirmed by the elution times showed in the chromatograms, where high molecular weight molecules will elute first. These chromatograms are wide, indicating broad molar mass distribution. This is in concordance with the PDI values obtained. Although not manifested in its PDI, PSCsb has probably a subtle tendency to form aggregates. This particularity can be deduced from the form of its RI curve, which presents a lump in its left hillside (Figure 6). The ASCsb result is in agreement with the SDS-PAGE profile but the same is not observed in the result of PSCsb, possibly due to the conformation of the molecule.