Epoxide homopolymerization epoxides

Propylene oxide and other epoxides undergo homopolymerization to form polyethers. In industry the polymerization is started with multihinctional compounds to give a polyether stmcture having hydroxyl end groups. The hydroxyl end groups are utilized in a polyurethane forming reaction. This article is mainly concerned with propylene oxide (PO) and its various homopolymers that are used in the urethane industry. 

In the following sections, we describe the recent development of catalyst systems for epoxide polymerization, focusing on homopolymerization, (alternating) co-polymerization with CO or GO2 reported from 1993 to 2004. Although aluminum and zinc are not classified as transition metals, polymerization catalyst systems using those metals will be discussed since they greatly contribute to the field of epoxide polymerization. 

Other possible reactions, such as homopolymerization (epoxide+epoxide) and epox-ide+hydroxyl group (in the latter stages of cure), can be neglected when the ratio of epoxide to amine is stoichiometric and in the absence of catalyst or accelerator [194], For TGDDM/DDS resins, the homopolymerization reaction may be neglected at cure temperature below 180°C [84], At temperatures between 177°C and 300°C, dehydration and/or network oxidation occur, which results in formation of ether cross-linkings with loss of water. Decomposition of the epoxy-OH cure reaction can also take place, which results in propenal... 

The results of model compound studies with three different types of epoxides, obtained in the presence and absence of ammonium perchlorate are shown in Figures 4, 5, and 6. The epoxide DER-332 shows a uniform rate of disappearance for the acid and epoxide species in this reaction. In the presence of ammonium perchlorate, the rate is increased, and a minimum of side reactions occur. Similar data but faster reaction rates are obtained with Epon X-801, but the consumption of epoxide species by side reactions is increased, particularly in the presence of ammonium perchlorate. On the other hand, the epoxide ERLA-0510 (Table IV), which contains a basic nitrogen, shows a reaction rate which is an order of magnitude greater than that for DER-332, accompanied by a substantial increase in side reactions. In the presence of ammonium perchlorate, the side reactions of ERLA-0510 predominate. In all probability, the side reactions of the multifunctional epoxides studied are homopolymerization. 

The nature of the cure reactions in these epoxies can be confirmed by monitoring the epoxide consumption via near infra-red spectroscopy for a series of epoxide-amine mixtures containing a range of amine contents. A plot of % epoxide consumption vs. amine concentration for DGEBA-T403 epoxies is illustrated in Fig. 2. This plot confirms that the DGEBA-T403 epoxy system forms exclusively from epoxide-amine addition reactions, because (i) 100% epoxide consumption is attained at the stoichiometric amine concentration associated with exclusive epoxide-amine addition cure reactions and (ii) extrapolation of this plot to zero amine content indicates there is no epoxide consumption i.e. there are no epoxide homopolymerization reactions. 

The homopolymerization reactions of impure TGDDM (MY720) in the presence and absence of a BF3 NH2C2H5 catalyst and, also, pure TGDDM were monitored by FTIR as a function of cure temperature from 177 to 300 °C. The intensities of the epoxide, hydroxyl, ether and carbonyl bands at 906, 3500, 1120 and 1720 cm-1 respectively were determined from spectral differences and are plotted as a function in cure conditions in Figs. 10,11,12 and 13 respectively. The 906,1120 and 1720 cm-1 band intensities were normalized to the 805 cm-1 band and the 3500 cm-1 to the 1615 cm 1 band. The 805 and 1615 cm-1 bands are associated with the phenyl group which is assumed to chemically unmodified during the homopolymerization reactions. 

In the 177-300 °C temperature range studied, epoxide isomerization, oxidation and homopolymerization can occur followed by complex degradation reactions. There have been numerous studies on the homopolymerization of epoxides including the effects of catalysts, alcohols, cure temperature and epoxide-amine ratio on the... 

This reaction is in fact the homopolymerization of the epoxide. The reactivity of the secondary hydroxy group with respect to the epoxy group is intermediate between that of tertiary and primary hydroxy group 26). 

In contrast to the non-catalyzed reaction, the base-initiated copolymerization was found to be a specific reaction 35,36,39 -45) and the consumption of both monomers, epoxide and anhydride, is the same. The initiator not only affects the rate of copolymerization but also suppresses the undesirable homopolymerization of the epoxide. At equimolar ratio, epoxide and anhydride are strictly bifunctional. 

Equation (31) allows the determination of the ratio of propagation rate constants k3/k2 by correlation of the experimental results obtained in copolymerization using equimolar ratios of monomers with the results obtained at non-equimolar monomer ratio and excess of anhydride (an excess of epoxide should not be used because of homopolymerization of the monomers at high degree of conversion). A value of k3,/k2 equal to 0.2 0.1 was found for the system 2-hydroxy-4-(2,3-epoxypropoxy) benzophenone-phthalic anhydride in nitrobenzene initiated by hexadecyltrimethyl-ammonium bromide 56). 

Aluminum-porphyrin complexes, in epoxide homopolymerization, 11, 599 Aluminum(III)-sulfur bonds, mixed covalent and non-covalent systems, 9, 258... 

Aluminum—tetradentate ligand catalyst system, in epoxide homopolymerization, 11, 601 Aluminum(I) tetrahedra, synthesis, 9, 262 Aluminum(III)-tin exchange, process, 9, 265 Aluminum-transition metal bonds, characteristics, 9, 264 Amavadine, for alkane carboxylations, 10, 234—235 Ambruticin S, via ring-closing diene metathesis, 11, 218 Amide-allenes, cyclizations, 10, 718 Amide ether complexes, with Zr(IV) and Hf(IV), 4, 783 Amide hybrid ligands, in organometallic synthesis, 1, 64 Amides... 

Cationic alkyltin species, characteristics, 3, 820 Cationic aluminum catalyst system, in epoxide homopolymerization, 11, 603 Cationic aluminum compounds... 

Homopolymerization, epoxides aluminate-Lewis acid catalyst system, 11, 602 via aluminum-porphyrin-Lewis acid catalysts, 11, 599 aluminum-tetradentate ligand catalyst system, 11, 601 anionic polymerization, 11, 598 cationic aluminum catalyst system, 11, 603 cationic polymerization, 11, 598 characteristics, 11, 597 zinc-based catalyst system, 11, 605 Homopolymers, cyclic olefins, 11, 716... 

Ferulic acid, a phenolic acid that can be found in rapeseed cake, has been used in the synthesis of monomers for ADMET homo- and copolymerization with fatty acid-based a,co-dienes [139]. Homopolymerizations were performed in the presence of several ruthenium-based olefin metathesis catalysts (1 mol% and 80°C), although only C5, the Zhan catalyst, and catalyst M5i of the company Umicore were able to produce oligomers with Tgs around 7°C. The comonomers were prepared by epoxidation of methyl oleate and erucate followed by simultaneous ring opening and transesterification with allyl alcohol. Best results for the copolymerizations were obtained with the erucic acid-derived monomer, reaching a crystalline polymer (Tm — 24.9°C) with molecular weight over 13 kDa. 

As discussed above, monomer molecules are capable of functioning either as it-electron donors and n-electron acceptors (e.g. C=C double bond containing compounds), respectively, or as n-electron donors (e.g. epoxides). Therefore, their ground or excited states can interact with donor or acceptor molecules, which are unable to polymerize. For that interaction the general Scheme 3 holds, too. Clearly, in these cases only a homopolymerization of the monomer used takes place. The mechanism of that reaction depends on the electronic properties existing (e.g. monomer acts as donor or acceptor), and on the structural conditions in both molecules. Again, in some cases a proton transfer reaction could occur. 

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