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Published in Eric J. Goethals, Telechelic Polymers: Synthesis and Applications, 2018
However, a number of systems may exhibit such a poor compatibility that the system is already phase separated at the reaction temperature. This is, for instance, the case of hydroxyl-terminated polybutadienes with 1,4-butane diol as chain extender.115,116 A distinct two-phase structure was found in these systems. The concentration of the functional groups in these regions was apparently not the same. Also, experiments with hydroxyl-terminated polybutadienes cross-linked with low molecular weight triols — trimethylolpropane, triethanola-mine, or glycerol — showed that the final system was not homogeneous and that the cross-linking density determined from the equilibrium modulus was not proportional to the concentration of the cross-linker, and the rheoptical investigations gave indication of nonhom-ogeneity.114
The Chemistry of Polyurethane Copolymers
Published in Nina M. K. Lamba, Kimberly A. Woodhouse, Stuart L. Cooper, Polyurethanes in Biomedical Applications, 2017
Nina M. K. Lamba, Kimberly A. Woodhouse, Stuart L. Cooper
Chain extenders can be categorized into two general classes of aromatic diols and diamines, and the corresponding aliphatic diols and diamines. In general, aliphatic chain extenders yield softer materials than aromatic chain extenders. Commonly used chain extenders are shown in Figure 16. Chain extenders are used to extend the length of the hard segment, and increase the hydrogen-bond density and the molecular weight of the polyurethane. Trifunctional or higher chain extenders also act as branching or crosslinking agents. The reaction of equimolar quantities of macroglycol and diisocyanate generally results in a polymer that may not exhibit microphase separation and may possess poor physical properties. Common commercial chain extenders include 1,4-butanediol (BD), ethylene diamine (ED), 4,4′ methylene bis (2-chloroaniline) (MOCA), ethylene glycol (EG), and hexanediol (HD). MOCA is not used in polyurethanes for biomedical applications, as it has been shown to be carcinogenic in rats.
Organic Phase Change Materials
Published in Asit Baran Samui, Smart Polymers, 2022
Swati Sundararajan, Asit Baran Samui
Cross-linked polyurethanes (PU) are considered a suitable container for the PCMs with the aim of obstructing the migration of the PCM with repeated use and giving way to a synergistic phase change effect, allowing a wider transition range. The solid-solid PCM with the urethane linkage is prepared by synthesizing the prepolymer from PEG and methylene diphenyl diisocyanate (MDI), which is further reacted with glucose. The reaction mixture is then blended with extra PEG and cured with heat over an extended period to obtain form-stable PCM.50 The synthesized polymeric PCM exhibits a solid-solid phase change and a synergistic effect is observed due to the presence of PEG in the cross-linked polymeric chain as well as in the blend. An improvement in enthalpy of 21.3% over the polymeric PCM can be achieved. An environmentally friendly, cost-effective method is adopted to prepare polyurethane/paraffin composites by avoiding the use of toxic organic solvents.51 This method allows the maximum encapsulation of a series of paraffin waxes in the hard PU segment made with PEG 10,000. Fusion enthalpy of 141 J g−1 and transition temperatures ranging from 20 to 65°C, exhibited by this combination, are suitable for multiple energy storage applications. In these polyurethane composites, the chain extender is a vital component that is responsible for increasing the phase separation that enhances the crystallization of soft segments.52 However, with PU-based graphene composites of SSPCMs without a chain extender, higher heat of fusions, higher thermal stability, and better thermal reliability have been observed.53
Novel copper complexes-polyurethane composites that mimics anti-inflammatory response
Published in Journal of Biomaterials Science, Polymer Edition, 2023
Guido Antonio Zapata-Catzin, Gualberto Antonio Zumbardo-Bacelis, Rossana Vargas-Coronado, Jorge Xool-Tamayo, Victor Ermilo Arana-Argáez, Juan Valerio Cauich-Rodríguez
DP, LP, LC or GR can be used as chain extenders for polyurethane/urea synthesis as demonstrated by FTIR and Raman spectroscopy. Furthermore, copper can be incorporated in these polyurethane matrices by using the same chain extender improving their miscibility with the amorphous phase. Even when polyurethanes prepared with DPCu exhibited the best mechanical properties derived from their PCL crystalline phase this chain extender rendered pro-inflammatory polymers. However, when using LC and GR along with copper complexes an anti-inflammatory behavior was observed. LC and Glutathione copper complexes also provide anti-inflammatory benefits to commercial polyurethanes such as Tecoflex SG 80A™. Taking all these properties (anti-inflammatory and potential copper release) these polyurethanes composites are suggested as coating for cardiovascular devices such as stents.
Characterization of recycled polycarbonate/polybutylene terephthalate blends
Published in Journal of the Chinese Institute of Engineers, 2019
Hsien-Tang Chiu, Jen-Kai Huang, Jen-How Huang
The chain extender is capable of capturing molecule fragments of the broken polymeric molecule chains and then re-connecting them to the backbone chains (Wang et al. 2016; John et al. 2016). However, the experimental results indicated that only adding a chain extender (1.5% w/w) cannot improve the stress value and strain of CB20 significantly (treatment CB20/ChE(99/1.5), Figure 6). Adding a chain extender alone probably led to the CB20 backbone chain tangling. Styrene maleic anhydride is frequently taken to support solubilization of different components in a polymer blend (Cha and White 2002). However, the modification based on virgin PC and PBT, chain extender and SMA failed because of the low-stress value (5.10 kgf mm–2), although the strain increased largely to 140.2% (treatment CB20/PC/PBT/SMA/ChE(69/14/14/2/1.5), Figure 6). The largely improved strain but scarcely bettered stress value of the modified CB20 was hypothesized here as resulting from the weak interactions of SMA and chain extender with PC and PBT molecules. PC and PBT possess only a few functional groups at the same time mostly with low polarity (Demongeot et al. 2017; Aden, Roesner, and Olowinsky 2010), leading to not only weak binding but also the low compatibility of SMA and chain extender with PC and PBT. To summarise, the successful modification of CB20 is only possible by adding virgin PC together with PBT (Figure 6, Table 1).
Polyurethane asphalt binder: a promising candidate for steel bridge deck-paving material
Published in International Journal of Pavement Engineering, 2022
Meng Jia, Aimin Sha, Jinghui Lin, Zengping Zhang, Bing Qi, Dongdong Yuan
Both chain extenders and cross-linkers are generally low molecular weight substances that establish a connection between PU pre-polymers, producing polymer chain PU with markedly better properties than the corresponding individual pre-polymers (Cong et al. 2019a, Zhao et al. 2020). Chain extenders are di-functional in nature and they typically contain diols, diamines and ethanolamine, promoting the formation of thermoplastic linear PU; in contrast, cross-linkers, i.e. curing agents, such as triols and tetraols have high functionality (at least 3), which can endow PU with a cross-linked network structure and thermosetting properties (Liu 2012, Xie et al. 2019).