We studied the mechanism of the chain-growth polymerization of 2-bromo-5-chloromagnesio-3-hexylthiophene (1) with Ni(dppp)Cl2 dppp = 1,3-bis(diphenylphosphino)propane, in which head-to-tail ...poly(3-hexylthiophene) (HT-P3HT) with a low polydispersity is obtained and the M n is controlled by the feed ratio of the monomer to the Ni catalyst. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra showed that the HT-P3HT uniformly had a hydrogen atom at one end of each molecule and a bromine atom at the other. The reaction of the polymer with aryl Grignard reagent gave HT-P3HT with aryl groups at both ends, which indicates that the H-end was derived from the propagating Ni complex. The degree of polymerization and the absolute molecular weight of the polymer could be evaluated from the 1H NMR spectra of the Ar/Ar-ended HT-P3HT, and it was found that one Ni catalyst molecule forms one polymer chain. Furthermore, by reaction of 1 with 50 mol % Ni(dppp)Cl2, the chain initiator was found to be a bithiophene−Ni complex, formed by a coupling reaction of 1 followed by insertion of the Ni(0) catalyst into the C−Br bond of the dimer. On the basis of these results, we propose that this chain-growth polymerization involves the coupling reaction of 1 with the polymer via the Ni catalyst, which is transferred intramolecularly to the terminal C−Br bond of the elongated molecule. We call this mechanism “catalyst-transfer polycondensation”.
The development and applications of chain-growth condensation polymerization are reviewed. Well-defined aromatic polyamides, polyesters, and polyethers have been synthesized via substituent ...effect-assisted chain-growth condensation polymerization, in which the polymer propagating ends are more reactive than the monomers due to resonance or inductive effects between the functional groups of the terminal monomer units. Chain-growth condensation polymerization for the synthesis of aromatic polyamides has been applied to the construction of well-defined block copolymers and star-shaped polymers. Nickel-catalyzed condensation polymerization of 5-metalated 2-halothiophene has been found to proceed in a chain-growth polymerization manner. Detailed investigations revealed that this polymerization is a catalyst-transfer condensation polymerization, in which the chain-growth nature is attributable to intramolecular catalyst transfer. Phase-transfer polymerization in a solid−solution biphasic system, in which the monomers are stored in an unpolymerizable solid phase, has been applied to the chain-growth condensation polymerization of potassium 4-bromomethyl-2-octyloxybenzoate.
Catalyst-transfer Suzuki−Miyaura coupling polymerization of 2,5-bis(hexyloxy)-4-iodophenylboronic acid (1b) with t Bu3PPd(Ph)Br (2) was investigated. When 1b was polymerized with 2 at 0 °C in the ...presence of 4 equiv of CsF, 8 equiv of 18-crown-6, and a small amount of water (to dissolve CsF), poly(p-phenylene) (poly1b) with a narrow molecular weight distribution was obtained. The conversion-number average molecular weight (M n) and feed ratio−M n relationships indicate that this polymerization proceeded in a chain-growth polymerization manner. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra showed that poly1b with moderate molecular weight uniformly had a phenyl group, derived from 2, at one end of each polymer chain and a hydrogen atom at the other, indicating involvement of a catalyst-transfer mechanism. However, the molecular weight distribution of the polymer gradually became broader with increase of the feed ratio of 1b to 2, and polymer chains with other end groups were formed. Successive catalyst-transfer Suzuki−Miyaura coupling polymerization of 2-(7-bromo-9,9-dioctyl-9H-fluoren-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3) and then 1b yielded a well-defined block copolymer of polyfluorene and poly(p-phenylene).
Synthesis of B–A–B type triblock copolymers of aliphatic polyester (PEs) and polystyrene (PSt) was investigated by using cyclic unsaturated PEs prepared by conventional polycondensation of ...4-octene-1,8-diol and sebacoyl chloride. The obtained cyclic PEs underwent cross-metathesis with PSt containing a carbon–carbon double bond (CC) at the central position, which was obtained by atom transfer radical polymerization (ATRP) of styrene with a bifunctional initiator containing a CC bond. PSt with a longer methylene spacer between the CC bond and PSt successfully afforded the PSt-b-PEs-b-PSt triblock copolymer. As another approach to obtain the triblock copolymer, cross-metathesis of cyclic PEs with 2-butene-1,4-diol or 4-octene-1,8-diol bis(2-bromoisobutyrylate)s was conducted to afford linear PEs having ATRP initiation sites at both ends, followed by ATRP of styrene. The unsaturated PEs segment in the triblock copolymer obtained by the second approach was converted into a saturated PEs segment by treatment with tosyl hydrazide and tributylamine. DSC analysis of the triblock copolymer containing the saturated PEs segment showed crystallinity when the PEs content was ≥14 mol %.
We show that reversible polycondensation through an alkoxide-catalyzed ester-ester exchange reaction is an effective strategy for the synthesis of telechelic polymers free from contamination with ...cyclic polymers in the polycondensation of difunctional nucleophilic monomers and difunctional electrophilic monomers (A
2
+ B
2
polycondensation). Polycondensation of excess diol formate
1
and 1.0 equiv. of dimethyl dicarboxylate
2
at high monomer concentrations afforded polyesters with a hydroxyl group at both ends, uncontaminated with cyclic polymers. On the other hand, the polycondensation of 1.0 equiv. of
1
and excess
2
selectively afforded polymers with a methyl ester moiety at both ends, even at lower monomer concentrations. Under the same conditions, the irreversible polycondensation of a diol and diacid chloride invariably afforded cyclic polymers, as well as telechelic polymers end-capped with the excess monomer. These results indicated that cyclic polymers, formed during reversible polycondensation, are converted into telechelic polymers by an ester-ester exchange reaction of the cyclic polymers with the excess monomer. Furthermore, the polycondensation of equimolar
1
and
2
in the presence of a symmetrical ester molecule having two functional groups as an exchange reagent (ExR) afforded a variety of telechelic polyesters with the functional groups derived from the ExR at both ends. Notably, when bispoly(ethylene glycol) (PEG) isophthalate was used as the ExR, a PEG-
b
-polyester-
b
-PEG triblock copolymer was obtained.
Reversible unstoichiometric polycondensation of a diol formate and dicarboxylic acid ester through an ester-ester exchange reaction is an effective strategy for the synthesis of telechelic polymers free from contamination with cyclic polymers.
tBu3 PPd(Ph)Br (1)‐catalyzed Suzuki‐Miyaura coupling polymerization of 2‐(4‐hexyl‐5‐iodo‐2‐thienyl)‐4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolane (2) was investigated. Monomer 2 was polymerized with 1 at 0 ...°C in the presence of CsF and 18‐crown‐6 in THF containing a small amount of water to yield P3HT with a narrow molecular weight distribution and almost perfect head‐to‐tail regioregularity. The $\overline {M} _{{\rm n}} $ values increased up to 11 400 g · mol−1 in proportion to the feed ratio of 2 to 1. The MALDI‐TOF mass spectra showed that P3HT with moderate molecular weight uniformly had a phenyl group at one end and a hydrogen atom at the other, indicating involvement of a catalyst‐transfer mechanism. Successive 1‐catalyzed polymerization of fluorene monomer 3 and then 2 yielded a well‐defined block copolymer of polyfluorene and P3HT.
Suzuki‐Miyaura coupling polymerization of 2‐(4‐hexyl‐5‐iodo‐2‐thienyl)‐4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolane (2) with tBu3PPd(Ph)Br (1) proceeds at 0°C in the presence of CsF and 18‐crown‐6 to yield P3HT with controlled molecular weight up to 11400 g·mol−1 and almost perfect head‐to‐tail regioregularity. Successive 1 ‐catalyzed polymerization of fluorene monomer 3 and then 2 yielded well‐defined block copolymer of polyfluorene and P3HT.
We describe the synthesis of polycarbonate by means of the polycondensation of diol formate and dialkyl carbonate through an ester-carbonate exchange reaction. The reaction of dodecane-1,12-diol ...formate (1a) and dipropyl carbonate (2e) in the presence of 5 mol%, compared to 1a, potassium tert-butoxide (tBuOK) in diglyme at 120 °C under reduced pressure (90–100 Torr) afforded high-molar-mass polycarbonate (PC). When polycondensation of 1a and diethyl carbonate (2d) was conducted in the presence of poly(1,12-dodecamethylene isophthalate) (PEs) in toluene at 60 °C under reduced pressure, both the synthesis of PC and the exchange reaction between the PC and PEs backbones proceeded simultaneously, and a statistical copolymer of PC and PEs was obtained. The composition of PC and PEs in the copolymer could be arbitrarily altered by changing the feed ratio of the monomers to PEs. The crystallization temperature (Tc) of the copolymer increased linearly with increasing PC content in the copolymer from −10.8 °C (100% PEs) to 47.3 °C (100% PC).We describe the synthesis of polycarbonate (PC) by means of the polycondensation of diol formate and dialkyl carbonate through an ester-carbonate exchange reaction. Furthermore, the polycondensation of diol formate and diethyl carbonate in the presence of polyester (PEs) under reduced pressure affords a statistical copolymer of PC and PEs. The composition of PC and PEs in the copolymer can be arbitrarily altered by changing the feed ratio of the monomers to PEs.
Suzuki–Miyaura polycondensation of an excess of linearly extended, conjugated dibromo monomer with meta -phenylenediboronate and of an excess of the extensively conjugated, kinked dibromo monomer ...with para -phenylenediboronate in the presence of t Bu 3 PPd(0) precatalyst, which has a strong propensity for intramolecular π-face transfer, afforded cyclic polymers with M n 12 400–6400, although unstoichiometric polycondensation generally affords linear polymers.
The Suzuki-Miyaura catalyst-transfer condensation polymerization (CTCP) of fluorene-thiophene biaryl monomers was investigated for the synthesis of well-defined poly(fluorene-
alt
-thiophene). Model ...reactions of α,ω-dibromo(fluorene-thiophene) with arylboronic acid esters showed that
t
-Bu
3
PPd and di-
tert
-butyl(4-dimethylaminophenyl)phosphine (AmPhos) Pd catalysts undergo intramolecular catalyst transfer from fluorene to thiophene, irrespective of the use of phenyl- or thiopheneboronate. Based on the results of the model reactions, PinB-fluorene-thiophene-Br (PinB = pinacol boronate) monomers were synthesized. The polymerization of the monomer containing the 3-octyl-5-bromothiophene-2-yl unit was accompanied by disproportionation, whereas the polymerization of the monomer containing the 4-octyl-5-bromothiophene-2-yl unit with an AmPhos Pd initiator proceeded according to the CTCP mechanism: the
M
n
values of the obtained polymers increased in proportion to monomer conversion and to the feed ratio of the monomer to initiator. Moreover, successive CTCP using the fluorene-thiophene monomer, dioctylfluorene monomer, and 3-hexylthiophene monomer with the AmPhos Pd initiator yielded a variety of all-conjugated di- and triblock copolymers.
The Suzuki-Miyaura coupling polymerization of
PinB-F8T(3)-Br
was accompanied by disproportionation, whereas that of
PinB-F8T(4)-Br
proceeded in a chain-growth polymerization manner to afford a well-defined fluorene-thiophene alternating copolymer.
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