α-Methoxyphenylmethylium hexachloroantimonate was used as a novel initiator for the polymerization of α,β-disubstituted oxiranes such as cyclohexene oxide (CHO) and 2-butene oxide (trans and cis) (2-BO) at ?78°C with dichloromethane or dichloromethane-toluene mixtures as solvents. The CHO polymerization mixture became turbid and the polymer precipitated in dichloromethane. The CHO polymerization proceed quantitatively in dichloromethane–toluene mixtures. The molecular weight distribution of polyCHO obtained was bimodal regardless of the solvent used. The polymerization of trans-2-BO was heterogeneous in both dichloromethane and dichloromethane–toluene mixture. The polymerization mixtures of cis-2-BO were transparent but reached a limit yield which was less than the polymer yield of trans-2-BO. Furthermore, the microstructure of the poly2-BOs were analyzed by Vandenberg's method and the results confirmed Vandenberg's finding that inversion of configuration occurs in the propagation step. 相似文献
Polymeric arylantimony(V) oxides [poly(ArSbO2), Ar = phenyl, p-chlorophenyl (CPh), and p-methylphenyl (Tol)] were employed as catalysts for the polymerization of oxirane [ethylene oxide (EO)] and also substituted oxiranes [propylene oxide (PO), 1,2-butylene oxide (BO), and epichlorohydrin (ECH)]. The polymerization of EO by ArSbO2s proceeded 3–60 times faster than that by the other organoantimony and -tin compounds such as triphenylstibine oxide (Ph3SbO) and arenestannoic acids (ArSnO2H), respectively. Apparent activation energy for the polymerization of EO was estimated as 13.7, 13.3, and 13.6 kcal/mol for PhSbO2, TolSbO2, and CPhSbO2, respectively. The results of the polymerization as well as 1H-, 13C-, and 17O-NMR spectroscopy suggested that the polymerization was initiated by ArSbO2 or Ar2Sb2O4 fragments, which was derived from a nucleophilc solvation of the polymeric ArSbO2 by oxiranes in situ. 相似文献
α-Methoxyphenylmethylium hexachloroantimonate was prepared from α-methoxybenzyl chloride and antimony pentachloride at 0°C and isolated for the first time, and its visible and 1H-NMR spectra were measured. This salt was used as a novel initiator for the polymerization of propylene oxide (PO) in the temperature range ?20 to 30°C with dichloromethane as solvent. PO polymerized spontaneously but a limit yield was observed. The microstructure of PO polymer is amorphous by 13C-NMR. The PO polymerization is thought to proceed in the conventional cationic mechanism on the basis of the polymerization behavior and the analyses of both the polymer structure and end groups attached to the PO polymer. 相似文献
A new type of single crystals was formed by a reaction between diethylzinc and DL-1-methoxy-2-propanol. The constituent unit of this single crystal was shown to be a two to two complex of zinc dialkoxide and ethylzinc alkoxide, [MeOCH2 CH(Me)OZnOCH(Me)CH2 OMe]2 · [EtZnOCH(Me)CH2 OMe]2, which has a chair type structure. The two to two complex was found to exhibit higher activity and stereospecificity in the PO polymerization compared with those of the one to six complex which were reported previously. Molecular level elucidation was made on the basis of NMR studies for polymerization system with a partly deuterated two to two complex as initiator. The excellent stereospecificity in isotactic propagation was ascribed to the highly chiral hole around the active site of the chair type complex. Another series of study revealed chemical behavior of cyclohexene oxide (CHO), which is different from that of PO, toward several organozinc compounds. The two to two complex was the only catalyst which showed high activity for both MO and CHO polymerizations. Three samples (I), (II) and (III) of poly-(CHO) were prepared with Et2Zn, EtZnOR and the two to two complex, respectively. After careful examinations of each of the three samples, it was concluded that most parts of the main chain of polymer (III) molecule were composed of syndiotactic triad, SS-RR-SS(or RR-SS-RR), while polymer (I) and (II) molecules contained syndiotactic and heterotactic triads in comparative amounts. In the CHO polymerization, the chiral hole of the two to two complex cannot recognize the mode of orientation of the achiral monomer, and the complex seems to serve as a simple bulky group which facilitates syndiotactic addition of CHO monomer molecule to the active site, strong steric effects being exerted from the penultimate unit of the growing chain during the propagation stage. 相似文献
A dinuclear Salph‐Al complex/bis(triphenylphosphine)iminium chloride catalyst system was synthesized and employed for cyclohexene oxide (CHO) and CO2 copolymerization. The catalyst system had an excellent selectivity of 99 % for carbonate linkages and the resultant poly(cyclohexene carbonate) (PCHC) had a high glass transition temperature (T g) of 123.8 °C and a thermal decomposition temperature (5 % weight loss; T d 5 %) of 265 °C. Furthermore, this catalyst system was active in the polymerization of phthalic anhydride (PA) and epoxides. Poly(CHO‐alt ‐PA) was completely alternating, and had improved thermal properties (T g=142.7 and T d 5 %=295 °C) compared with PCHC. The T g values of the polyesters could be adjusted by addition of PO to the CHO/PA reaction system. For the CHO/PO/PA terpolymerization, CHO and PO participated concurrently and proportionally in the chain growth and the obtained terpolyesters had tunable T g values from 62.8 to 142.7 °C depending on the CHO/PO feed ratio. 相似文献
Using supported multi-component zinc dicarboxylate catalyst,poly(1,2-propylene carbonate-co-1,2-cyclohexylene carbonate)(PPCHC) was successfully synthesized from carbon dioxide(CO2) with propylene oxide(PO) and cyclohexene oxide(CHO).The conversion of epoxides dramatically increased up to 89.7%(yield:384.2 g of polymer per g of Zn) with increasing reaction temperature from 60℃to 80℃.The optimized reaction temperature is 80℃.The chemical structure,the molecular weight,as well as thermal and mechanical properties of the resulting terpolymers were investigated extensively. When CHO feed content(mol%) is lower than 10%,the PPCHC terpolymers have number average molecular weight(Mn) ranging from 102×103 to 202×103 and molecular weight distribution(MWD) values ranging from 2.8 to 3.5.In contrast to poly(propylene carbonate)(PPC),the introduction of small amount of CHO leads to increase in the glass transition temperature from 38.0℃to 42.6℃.Similarly,the mechanical strength of the synthesized terpolymer is greatly enhanced due to the incorporation of CHO.These improvements in mechanical and thermal properties are of importance for the practical application of PPC. 相似文献
The dinuclear zinc complex reported by us is to date the most active zinc catalyst for the co‐polymerization of cyclohexene oxide (CHO) and carbon dioxide. However, co‐polymerization experiments with propylene oxide (PO) and CO2 revealed surprisingly low conversions. Within this work, we focused on clarification of this behavior through experimental results and quantum chemical studies. The combination of both results indicated the formation of an energetically highly stable intermediate in the presence of propylene oxide and carbon dioxide. A similar species in the case of cyclohexene oxide/CO2 co‐polymerization was not stable enough to deactivate the catalyst due to steric repulsion. 相似文献
Polymerization of MMA was carried out in presence of visible light (440 nm), quinoline-bromine charge-transfer complex being used as the photoinitiator. The initiator exponent was observed to be 0.5 up to 0.014 M initiator concentration; when chloroform was used as the solvent, the monomer exponent was found to be unity. The polymerization was inhibited in presence of hydroquinone but little inhibitory effect was observed in the presence of air. An average value of k2p/kt for this photopolymerization system was found to be (1.08 ± 0.22) × 10-2. Kinetic and other evidence indicates that the overall polymerization takes place by a radical mechanism. 相似文献
Summary: The possibility of transforming a living anionic polymerization into a stable radical‐mediated radical polymerization (SFRP) was demonstrated. For this purpose, 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) alcoholate, formed by a one‐electron redox reaction between potassium naphthalene and TEMPO, was used to initiate the living anionic polymerization of ethylene oxide (EO). Poly(ethylene oxide) obtained in this way possessed TEMPO terminal units and was subsequently used as an initiator for the SFRP of styrene to give block copolymers.
A one‐electron redox reaction gives rise to TEMPO alcoholate, which is able to initiate the living anionic polymerization of ethylene oxide (EO). 相似文献
Abstract ESR study on the primary radicals obtained by decomposition of azo-compounds showed that primary radicals with electron donating substituents were transformed to the corresponding cations in the presence of electron acceptors such as ph2I+PF?6. Accordingly, propagating radicals are transformed to the corresponding cations in the polymerization of p-methoxy-styrene (MOS), n-butyl vinyl ether (BVE), and N-vinylcarbazole (VCZ) with azoinitiators such as AIBN in the presence of electron acceptors such as Ph2I+PF?6. In the case of BVE, the polymer formation was caused by cationic species produced by the transformation of the initiating radical. The polymerizations of MOS and VCZ were ascribed to the transformation of the growing radical to the corresponding cation during the propagation step which was classified as the radical/cation transformation polymerization. Block copolymers of MOS/cyclohexene oxide (CHO) and VCZ/CHO were effectively prepared by the radical/cation transformation polymerization of the appropriate monomers in the presence of AIBN, electron acceptor and CHO. The formation of block copolymers was characterized by turbidimetry, thin-layer chromatography, and solubility tests. 相似文献
The polymerization of MMA was kinetically studied in the presence of visible light (using a 125-W high-pressure mercury vapor lamp with fluorescent coating, without a filter), a THF—bromine charge-transfer complex being used as the photoinitiator. The initiator exponent was 0.5 in bulk polymerization. The monomer exponent varied from about 1.2 to about 2.5, depending on the nature of the solvent used; the initiator exponent also varied in diluted systems, depending on the nature and proportion of the solvent, the variation being from a value of 0.5 in bulk system to zero or almost zero at about 25% (v/v) solvent concentration. Other kinetic parameters, viz., kp2/kt and the activation energy for polymerization, were determined and are reported. Kinetic and other evidence indicates that the photopolymerization takes place by a radical mechanism and termination is bimolecular in nature in bulk systems; in dilute systems, termination by initiator complex assumes predominance, particularly at high solvent concentrations (≥25% v/v). 相似文献
The metal‐free polymerization of propylene oxide (PO) using a special class of alkene—N‐heterocyclic olefins (NHOs)—as catalysts is described. Manipulation of the chemical structure of the NHO organocatalyst allows for the preparation of the poly(propylene oxide) in high yields with high turnover (TON>2000), which renders this the most active metal‐free system for the polymerization of PO reported to date. The resulting polyether displays predictable end groups, molar mass, and a low dispersity (?M<1.09). NHOs with an unsaturated backbone are essential for polymerization to occur, while substitution at the exocyclic carbon atom has an impact on the reaction pathway and ensures the suppression of side reactions. 相似文献