“…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. , …”
Section: Introductionmentioning
confidence: 99%
“…1,2 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. 3 However, most of the industrial elastomeric PECH is produced by the Vandenberg process 4 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. 5,6 PECH has already been used as a precursor of some liquid crystalline polymers [7][8][9] and various other polymers.…”
Isotactic and chiral glycidyl azide polymers (GAPs) have been
synthesized by the reaction
of isotactic and chiral poly(epichlorohydrin)s (PECHs) with sodium
azide in dimethylformamide at 95
°C. The azidation does not affect the isotacticity of the
chains, but the polymer backbone is degraded in
the process; a GAP of high molecular weight (100 kg/mol) is
nevertheless obtained. Despite the high
isotacticity of the polymer chains, the GAPs are not crystalline.
Long reaction times favor the branching
and/or the cross-linking of the polymer. The isotactic and chiral
PECHs used as starting materials for
the GAP syntheses have been prepared by the Vandenberg process using
racemic or chiral monomers,
leading thus to partially ((RS)-PECH) or completely
((R)- or (S)-PECH) isotactic polymers,
respectively.
They have been split into a soluble and an insoluble fraction by
acetone extraction. The fractionation of
chiral PECH withdraws from the polymer the incompletely isotactic
chains coming from the presence of
monomers of opposite configuration in the chiral epichlorohydrin or
from a defective polymerization
process. The population of crystals remaining in the insoluble
chiral PECH fraction is thus more
homogeneous, leading to an improved crystallinity and a higher melting
temperature.
“…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. , …”
Section: Introductionmentioning
confidence: 99%
“…1,2 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. 3 However, most of the industrial elastomeric PECH is produced by the Vandenberg process 4 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. 5,6 PECH has already been used as a precursor of some liquid crystalline polymers [7][8][9] and various other polymers.…”
Isotactic and chiral glycidyl azide polymers (GAPs) have been
synthesized by the reaction
of isotactic and chiral poly(epichlorohydrin)s (PECHs) with sodium
azide in dimethylformamide at 95
°C. The azidation does not affect the isotacticity of the
chains, but the polymer backbone is degraded in
the process; a GAP of high molecular weight (100 kg/mol) is
nevertheless obtained. Despite the high
isotacticity of the polymer chains, the GAPs are not crystalline.
Long reaction times favor the branching
and/or the cross-linking of the polymer. The isotactic and chiral
PECHs used as starting materials for
the GAP syntheses have been prepared by the Vandenberg process using
racemic or chiral monomers,
leading thus to partially ((RS)-PECH) or completely
((R)- or (S)-PECH) isotactic polymers,
respectively.
They have been split into a soluble and an insoluble fraction by
acetone extraction. The fractionation of
chiral PECH withdraws from the polymer the incompletely isotactic
chains coming from the presence of
monomers of opposite configuration in the chiral epichlorohydrin or
from a defective polymerization
process. The population of crystals remaining in the insoluble
chiral PECH fraction is thus more
homogeneous, leading to an improved crystallinity and a higher melting
temperature.
“…1,4-butanediyl ditriflate and some acidic clays . The ROP of ECH in the presence of acidic clays was done in bulk, so that the resulting polymer was characterized by low M n , broad multimodal molar mass distribution, and contains a large fraction of cyclic by-products .…”
Section: Introductionmentioning
confidence: 99%
“…The ROP of ECH in the presence of acidic clays was done in bulk, so that the resulting polymer was characterized by low M n , broad multimodal molar mass distribution, and contains a large fraction of cyclic by-products . 1,4-Butanediyl ditriflate initiates slow polymerization of ECH to afford the expected PECH diol with M n from 3400 to 15,000 g mol –1 and relatively high dispersity (Đ ≈ 1.5) at moderate yields (20–50%) . Triethyloxonium hexafluorophosphate (Et 3 O + PF 6 – ) in conjunction with ethylene glycol allowed to synthesize well-defined PECH diol (Đ ≈ 1.3) of low molar masses ( M n < 1000 g mol –1 ) …”
The cationic ring-opening polymerization of epichlorohydrin co-initiated by BF 3 •Et 2 O has been investigated here. Fast synthesis of pure poly(epichlorohydrin) diols (F n (OH) ≈ 2.0) with controlled molar mass (M n up to 4000 g mol −1 ) and low dispersity (Đ < 1.25) was performed both in toluene and in bulk. An original approach was developed here, consisting of first generating in situ the initiator through the BF 3 •Et 2 O-catalyzed reaction of ECH with water, leading to a mixture of oligomers with better solubility in the reaction medium than conventional initiators previously used. Then, through a second monomer starved-feed step, polymerization proceeds exclusively through the activated monomer mechanism, allowing perfect control of the polymer growth. The developed procedure was successfully upscaled to 100 g of polymer to validate a future industrial production of PECH, as well as its derivative glycidyl azide polymer (GAP), the most important energetic binder for solid propellants. Additionally, a separate study was performed to elucidate the reasons for coloration of the polymer observed in the course of polymerization and/or under storage.
“…The terminated hydroxyls could react with di-or tri-isocyanates to give linear or cross-linked polyurethane materials, 1 while the nucleophilic substitution of -Cl by azide (-N 3 ) would result in the formation of glycidylazide polymer, which could be used as an energetic binder. 2 For most of the disclosed catalysts, like Lewis acids of BF 3 etherate, 3 SnCl 4 , 4 or SbCl 5 , 5 inorganic acid of sulfuric acid, 6 trialkyl oxonium salt of triethyloxonium tetrauoroborate, 7 and super acid esters of CF 3 SO 3 R or FSO 3 R, 8 generally, a protic compound co-initiator is essentially required. These co-initiators could be water, alcohol and organic carbonic acid, which were responsible for the generation of the end hydroxyl groups.…”
This work describes the first regio-selective synthesis of poly(epichlorohydrin) diol via a simple one-pot bulk polymerization with a heterogeneous catalyst.
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