Ring‐opening polymerization with kinetically controlled enhancement of macrocyclic oligomers or linear macromolecules

In the polymerization of c-caprolactone (tCL) initiated with (CH,CH,),AlOCH,, (CH,CH,),-A10CH2CH=CH2, or [(CH,),CHCH,],AlOCH, and carried out in THF solvent at 20 or 25 O C linear poly(cCL) with 1.03 < Mw/Mn < 1.13 and free of macrocyclics was obtained. Comparison of Mn, calculated and measured, indicated that each initiator molecule starts one macromolecule and that during polymerization transfer reactions, including cyclization, are practically absent. 'H and 13C NMR studies of the end-group structures revealed that only alkoxy groups (OR') from initiator (R2A10R) were directly involved in initiation. The described polymerization of tCL can be considered as the living process, yielding linear polyesters free from cyclics within the polymerization time required to reach 99% of monomer conversion. Cyclics are produced after much longer time from the linear polymer already formed. The ratios of propagation rate constant (k,(l)) to the rate constants of back-biting, leading to the cyclic dimer (kb(2)), have been used as a measure of kinetic enhancement in linear polymer. For cCL polymerizations carried out in THF at 20 O C and initiated with (CH,CH2),A10CH, and [(CH,)2CHCH2]2A10CH, kp(1)/kb(2) = 4.6 X lo4 and 7.7 X lo4 Lsmol-', respectively. These values are substantially higher than for the anionic polymerization of cCL with Na+ counterion (kp(1)/kb(2) = 1.55 X lo3 Lsmol-').

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“…(d,2 Hc), 5.72 (m, 1 Hd),5.05 (d,1 He), 4.96 (d,1 Hf); Ja_b = 8.Hz, Jd_t = 10.20 Hz, <7e_f = 1.35 Hz. Anal.…”

mentioning

confidence: 99%

Living pseudoanionic polymerization of iε-caprolactone. Poly(iε-caprolactone) free of cyclics and with controlled end groups

Duda¹,

Florjańczyk²,

Hofman³

et al. 1990

Macromolecules

182

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“…[1][2][3] However, if polymerization is carried out in the presence of hydroxyl group containing compounds, such as diols, cyclization can be eliminated or at least be reduced. Cyclic oligomers are formed by the back-biting reaction of oxygen atom in linear units with the active species positioned at the end of growing chain.…”

Section: Introductionmentioning

confidence: 99%

“…Cyclic oligomers are formed by the backbiting reaction of oxygen atoms in linear units with the active species positioned at the end of growing chain. [1][2][3] However, if polymerization is carried out in the presence of hydroxyl group containing compounds, such as diols, cyclization can be eliminated or at least be reduced. 4 For example, Penczek et al reported in the cationic ring-opening polymerization (CROP) of propylene oxide (PO), the proportion of cyclic oligomer could drop from 50% to 0.95%, and in the case of epichlorohydrin (ECH), polyepichlorohydrin is nearly free of cyclic oligomers.…”

Section: Introductionmentioning

confidence: 99%

Preparation of a P(THF-co-PO)-b-PB-b-P(THF-co-PO) triblock copolymer via cationic ring-opening polymerization and its use as a thermoset polymer

et al. 2015

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The triblock copolymer poly(tetrahydrofuran-co-propylene oxide)-b-polybutadiene-b-poly(tetrahydrofuran-co-propylene oxide) [P(THF-co-PO)-b-PB-b-P(THF-co-PO)] was synthesized via the cationic ring-opening copolymerization of tetrahydrofuran (THF) and propylene oxide (PO) in the presence of hydroxyl-terminated polybutadiene (HTPB). The copolymerization mechanism was studied using Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), and size-exclusion chromatography coupled with multi-angle laser light scattering (SEC-MALLS). The results showed both active chain end (ACE) and activated monomer (AM) mechanisms contribute to the chain propagation process to different extents, and the copolyether segments in triblock copolymer had a gradient microstructure accordingly. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and viscosity testing results showed that the triblock copolymer had lower Tg than HTPB, low crystallization tendency and viscosity, and excellent thermal stability. To explore its potential applications, the triblock copolymer was used to prepare elastomer by thermosetting process. Dynamic thermomechanical analysis (DMA) and tensile test results indicated that the triblock copolymer based elastomer had lower Tg, as well as dramatically higher tan δ value and elongation at break, than HTPB based elastomer because of the introduction of copolyether segments.

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“…Recently, we reported a new synthetic route that allows “living” and/or controlled cationic ring-opening polymerization oxetane (Ox) in 1,4-dioxane (1,4-D) (cyclic ether which has no homopolymerizability) solvent. , In this system (Scheme c), the solvent is used to end-cap the strain tertiary 1-oxoniacyclobutane ions A1 (rate constant k d ), producing a less reactive terminal tertiary 1-oxonia-4-oxacyclohexane group T1. As T1 is less reactive, then there is greater discrimination between the more nucleophilic oxygen atom in Ox (rate constants k a(exo) and k a(endo) ) and in 1,4-D (rate constant k s ) than the less nucleophilic polymer chain ether oxygen atoms (see Figure ), , suspending reversible transfer, backbiting, and intermolecular transfer reactions as it occurs in normal polymerization of Ox in non-nucleophilic dipolar aprotic solvent (Scheme a). ,,,,,− Using phenoxypropyl-1-oxonia-4-oxacylohexane hexafluoroantimonate (structure equivalent to T1) as initiator yielding fast and instant initiation (i.e., k i ≥ k a(exo) > k a(endo) ), poly(oxetane- co -1,4-dioxane) (which possess 2% of 1,4-D fragment) with predictable number-average molecular weight (up to 160 000 g mol −1 ) and narrow PDI (∼1.2−1.3) was produced successfully. , The use in 1,4-D of initiator (e.g., (BF 3 ·CH 3 OH) 1,4-D ) yielding growing α-(hydroxyl)polyoxetane oxonium ions (Scheme b) was found to not be beneficial for the control of the polymerization as a subsystem of cyclic oligomers formation can also proceed from those growing chains failing to reach the sufficient length to entropically , disfavor the end-to-end ring closure reaction. Further investigations in dichloromethane (DCM) showed that cyclic oligomers formation by initiated end-biting reaction can be enhanced against chain growth by using diphenyl ether (i.e., less nucleophilic than polymer chain ether oxygen atoms) as end-capping agent.…”

Section: Introductionmentioning

confidence: 99%

“…Order of basicity of oxygen atoms − present during the cationic ring-opening polymerization of oxetane.…”

Section: Introductionmentioning

confidence: 99%

Pseudoperiodic “Living” and/or Controlled Cationic Ring-Opening Copolymerization of Oxetane with Tetrahydropyran: Microstructure of Polymers vs Kinetics of Chain Growth

et al. 2009

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The "living" and/or controlled cationic ring-opening bulk copolymerization of oxetane (Ox) with tetrahydropyran (THP) (cyclic ether with no homopolymerizability) at 35 °C was examined using ethoxymethyl-1-oxoniacyclohexane hexafluoroantimonate (EMOA) and (BF 3 3 CH 3 OH) THP as fast and slow initiator, respectively, yielding living and nonliving polymers with pseudoperiodic sequences (i.e., each pentamethylene oxide fragment inserted into the polymer is flanked by two trimethylene oxide fragments). Good control over number-average molecular weight (M n up to 150 000 g mol -1 ) with molecular weight distribution (MWD ∼ 1.4-1.5) broader than predicted by the Poison distribution (MWDs > 1þ1/DP n ) was attained using EMOA as initiating system, i.e., C 2 H 5 OCH 2 Cl with 1.1 equiv of AgSbF 6 as a stable catalyst and 1.1 equiv of 2,6-di-tert-butylpyridine used as a non-nucleophilic proton trap. With (BF 3 3 CH 3 OH) THP , a drift of the linear dependence M n(GPC) vs M n(theory) to lower molecular weight was observed together with the production of cyclic oligomers, ∼3-5% of the Ox consumed in THP against ∼30% in dichloromethane. Structural and kinetics studies highlighted a mechanism of chains growth where the rate of mutual conversion between "strain ACE species" (chain terminated by a tertiary 1-oxoniacyclobutane ion, A1) and "strain-free ACE species" (chain terminated by a tertiary 1-oxoniacyclohexane ion, T1) depends on the rate at which Ox converts the stable species T1 (kind of "dormant" species) into a living "propagating" center A1 (i.e., k a app [Ox]). The role of the THP solvent associated with the suspension of irreversible and reversible transfer reactions to polymer, when the polymerization is initiated with EMOA, was predicted by our kinetic considerations. The activation-deactivation pseudoequilibrium coefficient (Q t ) was then calculated in a pure theoretical basis. From the measured apparent rate constant of Ox (k Ox app ) and THP (k THP app = k a(endo) app ) consumption, Q t and reactivity ratio (k p /k d , k a(endo) /k a(exo) , and k s /k a(endo) ) were calculated, which then allow the determination of the transition rate constant of elementary step reactions that governs the increase of M n with conversion.

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Ring‐opening polymerization with kinetically controlled enhancement of macrocyclic oligomers or linear macromolecules

Cited by 21 publications

References 29 publications

Living pseudoanionic polymerization of iε-caprolactone. Poly(iε-caprolactone) free of cyclics and with controlled end groups

Living pseudoanionic polymerization of iε-caprolactone. Poly(iε-caprolactone) free of cyclics and with controlled end groups

Preparation of a P(THF-co-PO)-b-PB-b-P(THF-co-PO) triblock copolymer via cationic ring-opening polymerization and its use as a thermoset polymer

Pseudoperiodic “Living” and/or Controlled Cationic Ring-Opening Copolymerization of Oxetane with Tetrahydropyran: Microstructure of Polymers vs Kinetics of Chain Growth

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