Cationic Ring-Opening Polymerization of Epichlorohydrin in the Presence of Ethylene Glycol

Abstract

Cationic ring-opening polymerization of epichlorohydrin, using triethyloxonium hexafluorophosphate initiator in the presence of ethylene glycol to produce a low molecu lar weight polyepichlorohydrin glycol, was examined. A new polymerization mechanism was postulated that: polymerization initiates at the hydroxyl groups in the ethylene glycol, and the polymer chain propagates simul taneously at both ends through the addition of the monomer. In this polymerization system, the polymer molecular weight increases directly with the polymer conversion, and it can be controlled by the molar ratio of epichlorohydrin and ethylene glycol.The obtained polyepichlorohydrin glycols possess predominantly secon dary hydroxyl groups, narrow molecular weight distribu tion, and a hydroxyl functionality of 2.Byproducts formed in polyepichlorohydrin glycol are identified as non-functional cyclic oligomers, mainly epichlorohydrin cyclopentamer and cyclohexamer.It is well known that the low molecular weight polyether glycols such as poly(tetramethylene ether) glycol have been utilized in many polyurethane foams, rubbers, and castable elastomers. Recently halogen containing polyether glycols such as polyepichlorohydrin glycol attracted interest for flame resistance polyurethane applica tion. Among the several methods to prepare such polyether glycol, a cationic ring-opening polymerization of epichlorohydrin (ECH) using water and ethylene glycol seems to be a promising metHod (1-2). Recently employing a similar method, poly(3,3-disubstituted trimethylene ether) glycols have been prepared using borontrifluoride initiator in the presence of alkanediols for an application in high energetic polyurethane binders for rocket propellants (3). In order to prepare polyether glycols possessing the desired molecular weight and hydroxyl functionality, research has been conducted to examine the role of using water and alkanediols in the cationic ring-opening polymerization of oxetane and tetrahydrofuran (3-5). To extend the investigation of the preparation of low molecular weight polyether

Synthesis and Characterization of Glycidyl Azide Polymers Using Isotactic and Chiral Poly(epichlorohydrin)s

“…The microstructure of PECH is controlled by the polymerization conditions, and especially by the type of initiator employed: cationic or organometallic initiators are generally used. Cationic initiators such as Lewis acids or tertiary oxonium salts, often complexed with water, alcohol, or ether, lead to an atactic low molecular weight polymer (<4000 g/mol) with hydroxyl end groups. , Telechelic polymers of molecular weight up to 15 000 g/mol can also be obtained with the use of 1,4-butanediyl ditriflate as the initiator using organometallic initiators, which yields a polymer of high molecular weight that is often fractionated into its atactic and isotactic components; the degree of isotacticity of PECH is generally determined by 13 C nuclear magnetic resonance spectroscopy. ,

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Chlorinated Solvent-Free Living Cationic Ring-Opening Polymerization of Epichlorohydrin Using BF3•OEt2 as Co-Initiator: Toward Perfectly Functionalized Poly(epichlorohydrin) Diols

“…Clearly, PECH s synthesized by catalytic or anionic means are not ideal tools for the preparation of GAP, principally because of the lack of desired functionality. In stark contrast, the cationic ROP of ECH in conjunction with a molecular diol as an initiator results systematically in dihydroxy-terminated PECH. − Two different mechanisms, i.e., activated chain end (ACE) and activated monomer (AM) mechanisms, simultaneously operate during the ROP of ECH, depending on the reaction conditions (Scheme ). In the ACE mechanism, the active propagating species are oxonium ions located at the chain ends and propagation occurs through the addition of neutral monomer molecules to these oxonium ions (Scheme a).…”

“…The cationic ROP of ECH was already largely described in the literature, using catalytic systems based on Lewis acids such as BF 3 •Et 2 O, − SnCl 4 , Et 3 O + PF 6 – , and…”

“…29 Triethyloxonium hexafluorophosphate (Et 3 O + PF 6 − ) in conjunction with ethylene glycol allowed to synthesize welldefined PECH diol (Đ ≈ 1.3) of low molar masses (M n < 1000 g mol −1 ). 28 The comparison of efficiency of BF 3 •Et 2 O and SnCl 4 in the cationic ROP of ECH revealed that BF 3 •Et 2 O afforded PECH with higher functionality in chain-end hydroxyl groups and lower dispersity, even if the corresponding polymerizations were performed at slightly different ECH/1,4-butanediol (BD) ratios. 27 The best control of the synthesis of PECH diols free of cycles with controlled molar mass (M n ≤ 2500 g mol −1 ) and low dispersity (Đ < 1.20) was published by Penczek et al in 1991.…”

“…ECH can be polymerized via coordinative, − anionic, ,− and cationic − mechanisms. Catalytic ring-opening polymerization (ROP) of ECH was originally discovered by Vandenberg. ,, Vandenberg’s catalyst is prepared by mixing 1 equiv of trialkyl aluminum with 0.5 equiv of H 2 O and 0.5 equiv of acetylacetone to generate, as it was proposed recently, a bis­(μ-oxo)­dialkylaluminum active species .…”