Diols as chain extenders

The influence of the diol chain-extender structure on the thermal stability of PU elastomers was also studied in a series of Capa 225/CHDI/chain extender-based polymers by using four different diols as chain extenders and a molar ratio of 1 2-6 1. Figure 3.9 displays storage modulus and tan d as a means of observing the dependence of temperature stability with respect to chain-extender structure. The maximum temperature to which storage modulus (log E ) values of PU elastomers remain constant is given... 

COMPARISON OF THE THERMAL STABILITY EFFECTS OF A DIAMINE WITH DIOLS (AS CHAIN EXTENDERS) IN POLYURETHANE ELASTOMERS (MOLAR RATIO 1 3 2)... 

Mixed Aliphatic Diols as Chain Extenders (CHDM and BDO)... 

In general, polyurethane urea are always created when diamines are used instead of diols as chain extenders during the synthesis of polyurethanes. This measure changes the hard segment of the resulting polymer molecule. The result is polyurethane urea instead of PUR. If aliphatic diisocyanates, macrodiols, and diamines are also involved, aliphatic polyurethane urea is created. If an aliphatic polyester (M = 1000 to 4000 mol) is used as the macrodiol, we speak of aliphatic polyester-polyurethane ureas [953]. 

In recent years, aromatic amine chain extenders have been introduced that have largely replaced the diols as chain extenders. The most widely used amine is an 80/20 mixture of two isomers 2,4- and 2,6-diamino-3,5-diethyltoluene. 

PUMAs were obtained by two-step bulk polymerization, using a polycarbonate diol (PHCD) as macroglycol, an aliphatic diisomaleic acid butane diol as chain extenders. The reagents were used in the stoichiometric ratio PHCD diisocyanate chain extender = 1 2 1. Dibutyl-tin-dilaurate or staimous octanoate were used as catalysts. All of them were purified from residual catalyst, and solvent-cast from DMA solutions. 

Chain extenders Diols and diamines are generally used as chain extenders in PU industry and choice of chain extender influences elastomer properties considerably. The standard diol chain extender used for the synthesis of PU elastomer is 1,4-butane diol (BDO). Compared with a diol, better physical properties usually result when a diamine is employed as an extender. This is probably due to the introduction of urea linkages which enter into strong hydrogen bonded interactions. A diamine is usually chosen as the chain extender when a relatively unsymmetrical diisocyanate is employed. Diamines also function as efficient catalysts in addition to chain extenders. 

The two main groups used as chain extenders are diamines and hydroxyl compounds. Triols are also used where some cross-linking is required. The choice of chain extender depends on the properties required and the process conditions. Diols are the most commonly used hydroxyl compound. In the normal course of events, diols provide good properties and processing speed with MDI-based prepolymers and diamines with TDI-terminated prepolymers. 

Preparation of Microcellular Foams. The major polyols for microcellular elastomers include aliphatic polyester diols having a molecular weight of about 1,000 to 3,000, and poly-epsilon-caprolactones. Poly(oxytetramethylene) glycols (PTMEG) can also be used. The polyisocyanates to be used for microcellular elastomers are TDI-prepolymers and liquid MDI, i.e., carbodiimide-modified MDI or urethane-modified MDI. Low-molecular-weight, active-hydrogen compounds such as chain extenders (difunctional compounds) and... 

Short-chain diols are used as chain extenders, especially when both hydroxyl groups are primary. Secondary hydroxyl groups react more slowly with isocyanates but first can be capped with ethylene oxide (EO) to give the primary hydroxy-terminated derivatives. 

A special aromatic aminic polyol was obtained by propoxylation or ethoxylation of aniline [7]. These diols were used sometimes as chain extenders in elastomers and in coatings. The disadvantage of these aniline-based diols is the fact that at a ratio of 2 mols of alkylene oxide (PO, especially EO) they become solid at room temperature, by crystallisation ... 

Bisphenol A propoxylated or ethoxylated with 2-10 mols of alkylene oxides/mol of bisphenol A are used as chain extenders for PU elastomers and as aromatic diols for isocyanuric and urethane isocyanuric foams [30] (structure 15.30). 

The principal components of commercially available urethane coatings are di- or polyisocyanates and di- or polyhydroxy compounds. Active hydrogen-containing compounds, especially diols and diamines, as well as alkanolaraines, are also employed as chain extenders. In addition, various cross-linking agents such as neutral or tertiary amine based triols or tetrols are also used. 

Chain Extenders and Cross-linkers. In addition to the two principal components of most urethane coatings, isocyanate and polyol components, a number of di- or polyfunctional, active hydrogen components may be used as chain extenders or cross-linkers. The most important classes of compounds for this use are diols or polyols (monomers or oligomers), diamines, and alkanolamines. Typical examples of diols are ethylene, dlethylene, dlpropylene glycol, 1,4-butanedio1, 1,5-hexanediol, neopentyl glycol,... 

In this work, MDI-terminated polyester prepolymer based on ethylene adipate polyol (Baytec MS-242) was used to prepare cast poly(ester urethane) materials. The HER-TG materials, HER-HP and HQEE were used as chain extenders. As discussed in section 8.4, technical grade HER materials contain various levels of high MW diols as reactive impurities. Therefore, as with poly(ether urethanes), the high MW diols are expected to play a major role in the performance of poly(ester urethanes) made with these materials. 

Bis-acyllactams have also been investigated for use as chain extenders, including terephthaloyl-bis-laurolactam or -caprolactam [199], and species synthesised from terephthaloyl chloride, caprolactam and either aliphatic diols or diamines [188]. The latter, due to the alkylene spacer group contribution of the aliphatic species, would tend to provide more flexible linkages. It was also noted that such species are thermally stable up to at least 260 °C. 

A systematic study of PUs with HS of variable crystallinity was made by us [60, 61, 127, 135]. Two diisocyanates were considered the frequently employed MDI, and its close relation DBDI, that is of special interest because of its tendency to crystallize on cooling from the melt in the presence of some chain extenders [135]. The family of model PUs was synthesized for this work in the authors Romanian laboratory. They were all three-component systems combined in stoichiometric proportions, and consisting of (1) a diisocyanate—either MDI or DBDI (2) a SS macrodiol—PEA, PTHF, or PBA and (3) a small molecule diol as chain... 

Chan-Chan LH, Vargas-Coronado RF, Cervantes-Uc JM, Cauich-Rodriguez JV, Rath R, Phelps EA, et al. Platelet adhesion and human umbilical vein endothelial cell cytocom-patibility of biodegradable segmented polyurethanes prepared with 4,4 -methylene bis(-cyclohexyl isocyanate), poly(caprolactone) diol and butanediol or dithioerythritol as chain extenders. J Biomater Appl 2013 28(2) 270-7. 

Zhou et al. described the synthesis of pH-sensitive biodegradable PUs. They used a novel pH-sensitive macrodiol containing acid-cleavable hydrazone linkers, poly(E-caprolactone)-hydrazone-poly(ethylene glycol)-hydiazone- ly(E-caprolactone) diol (PCL-Hyd-PEG-Hyd-PCL). The macrodiol was used with L-lysine ethyl ester diisocyanate (LDI) and L-lysine-derived tripeptide as chain extender [47]. These PUs could self-assemble into micelles in aqneons solutions. Later, the same research group synthesized pH-sensitive polymers nsing 1,4-bntanediol as chain extenders and suggested its use as antitumor drug carriers [41]. 

Folic acid-conjngated PUs were reported, using LDI, PEG diol, and PEG amine as chain extender [108]. 

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