首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
In the polymerization of α-methylstyrene (α-MeSt) in dichloromethane in the temperature interval between ?60 and ?20°C the polymer yield decreased with increasing temperature depending on the initiating system used (I-IV) in the series II > I > IV > III, where I was a freshly prepared solution of 2,5-dichloro-2,5-dimethylhexane (DDH) with BCl3 in dichloromethane, was the same solution as in the preceding case, but stored at room temperature one month and then used, III was a freshly prepared BCl3 solution in dichloromethane, and IV was the initiation system “H2O”/BCl3. The polymer samples synthesized at ≤ ?30°C had a bimodal molecular weight distribution (MWD), which was attributed to the different participation of ionic pairs and free ions in the propagation reaction. The stereoregularity of the polymer observed (ca. 85% syndiotactic and ca. 15% heterotactic triads) determined from the 1H-NMR spectra was not affected by the difference in the initiation system. MWD of the polymer samples was investigated by the GPC method  相似文献   

2.
The synthesis of α,ω-di-t-chloropolyisobutylene has been accomplished by living polymerization using aliphatic and aromatic tert-diacetate initiators in conjunction with BCl3 coinitiator in various solvents in the ?20 to ?70°C range. The living nature of the polymerizations was demonstrated with the instantaneous initiators 2,4,4,6-tetramethyl-heptane-2,6-diacetate and 1,4-di(2-propyl-2-acetate)benzene by linear [Mbar]n versus amount of PIB formed (W PIB) plots starting at the origin. The formation of undesirable indanyl structures that arise with the aromatic initiator can be suppressed by decreasing the temperature and the polarity of the polymerization medium (i.e., by using CH3Cl/n-C6H14 mixtures). Living polymerization of isobutylene can also be obtained with noninstantaneous initiators, e.g., 2,5-dimethylhexane-2,5-diacetate, 2,5-dimethylhexyne-2,5-diacetate. However, with these systems the initiator efficiency is less than 100%.  相似文献   

3.
The polymerization of p-chlorostyrene (pClSt) under carbocationic conditions has been investigated. The use of binifers 1,4-di(2-chloro-2-propyl) benzene (pDCC) and 1,3-di(2-chloro-2-propyl)-5-tert-butylbenzene (m-tBuDCC) in conjunction with BCl3 coinitiator in CH3Cl diluent at ?60 and ?35°C give α,ω-di-benzylic chlorine-capped polymer sCl? PpClSt? Cls. According to kinetic investigations the inifer mechanism is operative and both binifers are efficient in controlling the end structures, molecular weights, and to a certain extent molecular weight distributions (MWD). Strong circumstantial evidences have been generated to demonstrate the satisfactory synthesis of sCl? PpClSt? Cls and the absence of indanyl end-groups, i.e., structural considerations, linearity of inifer plots, quantitative Cl end-group microanalysis, FTIR spectroscopy, and blocking experiments. The latter involved the blocking of THF from the sec-benzylic chlorine end-groups by AgPF6 and thus led to the synthesis of a new triblock copolymer PTHF-b-PpClSt-b-PTHF. Interestingly, the isotactic content (mm triads and mmmm pentads) of PpClSt is significantly higher than that of polymer prepared by free-radical induced polymerization. The Tg of a PpClSt of M?n = 5700 g/mol was 123°C.  相似文献   

4.
Asymmetric telechelic polyisobutylene, α-PIB-ω), carrying the olefinic head group α = (CH3)2 C[dbnd]CHCH2- and tertiary chlorine endgroup ω = -C(CH3)2Cl has been synthesized by the use of the (CH3)2C[dbnd]CHCH2Cl/BCl3 initiating system. Highest yields were obtained by using methylene chloride diluent at about ?50°C. The presence and position of the olefinic head-group was proven by epoxidation/titration and epoxidation/cleavage. The presence and position of a tertiary chlorine endgroup was proven by initiating block polymerization of a second monomer, such as styrene or α-methylstyrene, by using the asymmetric telechelic polyisobutylene prepolymer in conjunction with Et2AlCl coinitiator. According to I/DP versus 1/[M] plots obtained in model block copolymerization experiments, with the use of the tert-BuCl/Et2AlCl initiating system at ?30°C, significant chain transfer to monomer occurs during blocking of styrene; however, monomer transfer is negligible during blocking of α-methylstyrene. Thus, under suitable conditions head-functionalized block copolymers (CH3)2C[dbnd]CHCH2-PIB-b-PαMeSt virtually free of homopolymer contaminants can be obtained.  相似文献   

5.
The new α,ω-[boryl(organyl)]phosphane o-Ph2PC6H4CH2B (NMe2)2 ( 10 ) was obtained in good yields from the reaction of CIB(NMe2)2 with o-Ph2PC6H4CH2Li(tmeda). Five derivatives of 10 were obtained by substituting the boron-bound amino groups by reactions with MeOH, BCl3, HCl, and LiAlH4, respectively, in particular, o-Ph2(HCl)PC6H4CH2BCl2 (HNMe2) ( 10 e ) which shows a unique P? H? Cl? H? N unit. Compound 10 and its derivatives were characterized by multinuclear NMR methods, mass spectra, and elemental analyses. In addition, the structure of 10 e · 1.5 C6H6 was determined by single crystal X-ray diffraction.  相似文献   

6.
Complexes of boron trichloride, boron tribromide, and ethylaluminumdichloride with various acetates were directly observed by 1H-NMR. Complexes of secondary and tertiary acetates which model macromolecular active species in polymerization of styrene and isobutene are stable at ?75°C, but decompose at temperatures above ?30°C to yield corresponding chlorides or bromides. The stability of complexes depends on the Lewis acid, the alkyl group in the ester, and the structure of acetate. Rates of the bimolecular exchange of complexes with excess acetate were calculated from dynamic NMR to be kex = 2 × 101 L mol?1 s?1 (?65°C) and kex = 5 × 104 L mol?1 s?1 (?75°C) for 1-phenylethyl acetate with BCl3 and EtAlCl2, respectively.  相似文献   

7.
The polymerization of isobutylene by 3-chloro-1-butene/trivinylaluminum (V3Al) and t-butyl chloride/V3Al initiator systems with methyl chloride and methylene chloride as solvents has been investigated in the range from ?30 to ?72?C. The rate of polymerization increases with decreasing temperatures from ?30 to ?50°C and then decreases when the temperature is further lowered, for example, to ?72°C. Mayo plots and a determination of the number of polymer molecules n? formed per molecule of initiator employed suggests a transfer-less, i.e., termination-dominated system. A critical analysis shows that for systems containing both free ions and ion pairs, the Mayo equation is meaningful only when the degree of dissociation α remains constant over the whole [M] range investigated. This condition is achieved in RCl/V3Al-initiated systems by using an initiator (t-BuCl) for which the rate of catalyst destruction is insignificant compared to rate of initiation, Ri, i.e., initiation efficiency, f ≈ 1 and Ri independent of [M]. Polyisobutylene, containing, 1.8 ± 0.1 terminal unsaturation, has been synthesized by the use of 3-chloro-1-butene initiator in conjunction with V3Al coinitiator, and avenues for further efficient synthesis of α,ω-diene-polyisobutylenes have been outlined.  相似文献   

8.
Unlike the α,ω-dihalogenopolydimethylsiloxanes, the α,ω-dichloropolydimethyl-N-methylsilazanes show a net preference for cyclic species with respect to linear structures at equilibrium. The aim of this study is to evaluate the perturbations in the molecular constitution of these α,ω-dihalogenopolydimethyl-N-methylsilazanes resulting from the substitution of the terminal chlorine atoms by fluorine atoms. This polymeric family was prepared by reacting (CH3)2SiF2 with nonamethylsilazane [(CH3)2SiNCH3]3. The redistribution of the fluorine atoms with the bridging methylimino groups reached an equilibrium after about 5 months' heating at 150°C for all the samples prepared. The relative abundance of the various molecular species and fragments at equilibrium was deduced from the quantitative analysis of the proton nuclear magnetic resonance (NMR) spectra. The molecular constitution at equilibrium is described by two constants. The first, K = [neso] [middles in chains]/[terminal moieties]2 = (2.8 ± 0.8) 10?2, shows that the presence of terminal fluorine atoms is unfavorable to the formation of short chains. On the other hand, the trimeric cyclic species [(CH3)2SiNCH3]3 are found to be highly favored (K°3 = 550 ± 100 mole/liter). These observations further confirm that the equilibrium constants which control the noncyclic part of polymeric families depend little on the functionality of the substituents exchanged [for example, on changing from ? N(CH3)2 to ? NCH3? ] when the reorganization heat order is one.  相似文献   

9.
The polymerization of the complex of methyl methacrylate with stannic chloride, aluminum trichloride, or boron trifluoride was carried out in toluene solution at several temperatures in the range of 60° to ?78°C by initiation of α,α′-azobisisobutyronicrile or by irradiation with ultraviolet rays. The tacticities of the resulting polymers were determined by NMR spectroscopy. Both the 1:1 and the 2:1 methyl methacrylate–SnCl4 complexes gave polymers with similar tacticities at the polymerization temperatures above ?60°C. With decreasing temperature below ?60°C, the isotacticity was more favored for the 2:1 complex, whereas the tacticities did not change for the 1:1 complex. On the ESR spectroscopy of the polymerization solution under the irradiation of ultraviolet rays at ?120°C, the 1:1 SnCl4 complex gave a quintet, while the 2:1 SnCl4 complex gave both a quintet and a sextet. The sextet became weaker with increasing temperature and disappeared at ?60°C. This behavior of the sextet corresponds to the change of the tacticities of polymer for the 2:1 SnCl4 complex. An intra–intercomplex addition was suggested for the polymerization of the 2:1 complex, which took a cis-configuration on the basis of its infrared spectra. The sextet can be ascribed to the radical formed by the intracomplex addition reaction, while the quintet can correspond to that formed by the intercomplex addition reaction. The proportion of the intracomplex reaction was estimated to be about 0.25 at ?75°C, and the calculated value of the probability of isotactic diad addition of the intracomplex reaction was found to be almost unity.  相似文献   

10.
Abstract

The living carbocationic polymerization and copolymerization of indene (Ind) and p-methylstyrene (pMeSt) have been investigated by the use of the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl4 and the 2-chloro-2-propylbenzene (cumyl chloride, CumCl)/BCl3 initiating systems in the presence of triethylamine (Et3N) as electron donor and CH3Cl or CH3Cl/QH14 mixed solvents at ?80°C. The TMPCl/TiCl4 initiating system gives essentially living copolymerization with slow initiation up to M n ≈ 20,000. The CumCl/BCl3 initiating system also induces living Ind homopolymerization up to at least M n ≈ 13,000. The homopolymerization of pMeSt with the latter initiating system, however, is not living as it shows evidence for a large amount of chain transfer. Thus, with the CumCl/BCl3 combination a small amount of chain transfer has apparently been observed in the presence of 50% of pMeSt in the charge. Reactivity ratio studies, fractionation, 1H- and 13C-NMR spectroscopy, and glass transition temperature (Tg ) investigations indicate that virtually random Ind-co-pMeSt copolymers of M n ≈ 20,000 can be obtained under suitable conditions. The Tg of the copolymers can be controlled between ≈115°C (the Tg of PpMeSt) and ≈194°C (the Tg of PInd) by the relative composition of the two monomers in the charge.  相似文献   

11.
Phosphaneimine and Phosphoraneiminato Complexes of Boron. Synthesis and Crystal Structures of [BF3(Me3SiNPEt3)], [BCl2(NPPh3)]2, [BCl2(NPEt3)]2, [B2Cl3(NPEt3)2]+BCl4?, and [B2Cl2(NPiPr3)3]+BCl4? The title compounds have been prepared from the corresponding silylated phosphaneimines and boron trifluoride etherate and boron trichloride, respectively. The compounds form white moisture sensitive crystals, which were characterized by 11B-nmr-spectroscopy, IR-spectroscopy and by crystal structure determinations. [BF3(Me3SiNPEt3)] : Space group P21/c, Z = 4, R = 0.032 for reflections with I > 2σ(I). Lattice dimensions at ?70°C: a = 1361.0, b = 819.56, c = 1422.5 pm, β = 109.86°. The donor acceptor complex forms monomeric molecules with a B? N bond length of 157.8 pm. [BCl2(NPPh3)]2 · 2 CH2Cl2 : Space group P21/c, Z = 2, R = 0.049 for reflections with I > 2σ(I). Lattice dimensions at ?50°C: a = 1184.6, b = 2086.4, c = 843.0 pm, β = 96.86°. The compound forms centrosymmetric dimeric molecules in which the boron atoms are linked to B2N2 four-membered rings with B? N distances of 152.7 pm via μ2-N bridges of the NPPh3 groups. [BCl2(NPEt3)]2 : Space group Pbca, Z = 4, R = 0.029 for reflections with I > 2σ(I). Lattice dimensions at ?90°C: a = 1269.5, b = 1138.7, c = 1470.3 pm. The compound has a molecular structure corresponding to the phenyl compound with B? N ring distances of 151.0 pm. [B2Cl3(NPEt3)2]+BCl4? : Space group Pbca, Z = 8, R = 0.034 for reflections with I > 2σ(I). Lattice dimensions at ?70°C: a = 1309.3, b = 1619.8, c = 2410.7 pm. Within the cations the boron atoms are linked to planar, asymmetrical B2N2 four-membered rings with B? N distances of 155.1 and 143.1 pm via the μ2-N atoms of the NPEt3 groups. [B2Cl2(NPiPr3)3]+BCl4? · CH2Cl2: Space group Pna2, Z = 4, R = 0.033 for reflections with I > 2σ(I). Lattice dimensions at ?70°C: a = 1976.5, b = 860.2, c = 2612.7 pm. Within the cations the boron atoms are linked to planar, asymmetrical B2N2 four-membered rings with B? N distances of 153.7 and 150.5 pm via the μ2-N atoms of two of the NPiPr3 groups. The third NPiPr3 group is terminally connected to the sp2-hybridized boron atom with a B? N distance of 133.5 pm and with a B? N? P bond angle of 165.3°.  相似文献   

12.
Detailed understanding of the mechanism of initiation and chain transfer in BCl3-coinitiated isobutylene polymerization led to the efficient synthesis of symmetric telechelic polyisobutylenes carrying ~CH2C(CH3)2Cl groups at either end of the molecule Cl-PIB-Cl. The synthesis is based on the use of inifers, i.e., bifunctional initiator-transfer agents that effect controlled initiation and propagation in the absence of chain transfer to a monomer. Specifically, the synthesis of Cl-PIB-Cl was achieved by the p-dicumyl chloride/BCl3/isobutylene/CH2Cl2 system. According to the inifer mechanism each Cl-PIB-Cl contains two terminal tertiary chlorines and one phenyl group at the interior of the chains. The structure of this new symmetric telechelic polymer has been established by detailed characterization studies including a sensitive new gel permeation chromatography (UV plus RI) analysis method, 1H-NMR, kinetic experiments, and chemical derivatization. The Cl-PIB-Cl molecule is a key intermediate for the synthesis of hosts of new materials, e.g., triblock copolymers, α,ω-diolefins, and α,ω-difunctional polymers.  相似文献   

13.
The polymerization of styrene with BF3, BCI3, and BBr3 coinitiators and CH2Cl2 solvent has been investigated. The effects of temperature, monomer concentration, and the nature of the boron halide on molecular weights, molecular weight distribution, and conversion were determined. Molecular weights were found to decrease in the order BCl3 >BF3 >BBr3. This sequence was discussed in terms of system ionicity and counterion stability. The overall energies of activation for polymerization (ΔE) were ?1.6 ± 0.3, ?1.9 ± 0.8, and ?0.9 ± 0.5 kcal/mole for BF3, BCI3, and BBr3, respectively, which indicated similar overall polymerization mechanisms in the range of ?20 to ?80°C. The predominant molecular-weight-governing event in polymerizations with BCl3, and BBr3 was chain transfer to monomer, whereas with BF3 chain transfer and termination were nearly equal. Chain termination in BCl3-coinitiated polymerizations involves chlorination of the growing polystyryl cation by BCl3OH? and leads to benzylic chlorine termini.  相似文献   

14.
The polymerization of L - and DL -alanine NCA initiated with n-butylamine was carried out in acetonitrile which is a nonsolvent for polypeptide. The initiation reaction was completed within 60 min.; there was about 10% of conversion of monomer. The number-average degree of polymerization of the polymer obtained increased with the reaction period, and it was found to agree with value of W/I, where W is the weight of the monomer consumed by the polymerization and I is the weight of the initiator used. The initiation reaction of the polymerization was concluded as an attack of n-butylamine on the C5 carbonyl carbon of NCA. The initiation, was followed by a propagation reaction, in which there was attack by an amino endgroup of the polymer on the C5 carbonyl carbon of NCA. The rate of polymerization was observed by measuring the CO2 evolved, and the activation energy was estimated as follows: 6.66 kcal./mole above 30°C. and 1.83 kcal./mole below 30°C. for L -alanine NCA; 15.43 kcal./mole above 30°C., 2.77 kcal./mole below 30°C. for DL -alanine NCA. The activation entropy was about ?43 cal./mole-°K. above 30°C. and ?59 cal./mole-°K. below 30°C. for L -alanine NCA; it was about ?14 cal./mole-°K. above 30°C. and ?56 cal./mole-°K. below 30°C. for DL -alanine NCA. From the polymerization parameters, x-ray diffraction diagrams, infrared spectra, and solubility in water of the polymer, the poly-DL -alanine obtained here at a low temperature was assumed to have a block copolymer structure rather than being a random copolymer of D - and L -alanine.  相似文献   

15.
The oxidative polycondensation of 4-[(pyridin-3-ylimino)methyl]phenol (4-PIMP) with O2, H2O2, and NaOCl was studied in an aqueous alkaline medium between 50°C and 90°C. Oligo-4-[(pyridin-3-ylimino)methyl]phenol (O-4-PIMP) prepared was characterized by 1H-NMR, 13C-NMR, FT-IR, UV-VIS, size-exclusion chromatography, and elemental and thermal analyses techniques. At the optimum reaction conditions, the yield of O-4-PIMP was 18.9%, 39.4%, and 46.8% using H2O2, O2, and NaOCl oxidant, respectively. According to the TG analysis, the initial degradation temperature of O-4-PIMP was 218°C, which was by 50°C higher than that of 4-PIMP. Thermal analyses of 4-PIMP and O-4-PIMP were carried out in N2 atmosphere at 15–1000°C. The highest occupied molecular orbital, the lowest unoccupied molecular orbital, and electrochemical energy gaps of 4-PIMP and O-4-PIMP were determined from the onset potentials for n-doping and p-doping, respectively. Also, optical band gaps of 4-PIMP and O-4-PIMP were determined according to UV-VIS measurements.  相似文献   

16.
Bis-ε-aminocaproylaminocaproylhexamethylenediamine ( I ) was synthesized as an analog of 6-nylon pentamer diamine, and its incorporation into block copolymers was studied with the use of α,ω-dihydroxyl, α,ω-bisdimethylchlorosilyl, and α,ω-diepoxy polystyrene. In the course of the experiments, the stability and the reactivity of 4,4′-diphenylmethane diisocyanate and tetramethylene diisocyanate in aprotic dipolar solvents were examined by infrared spectroscopy. The only usable solvent, N-methylpyrrolidone, was found still inadequate for the synthesis involving I, diisocyanate, and α,ω-dihydroxyl polystyrene. A block copolymer having M n = 18,000 was obtained by the reaction of I and α,ω-diepoxy polystyrene. All Tg values of the block copolymers were above 90°C, higher than for polystyrenes with corresponding molecular weight.  相似文献   

17.
The kinetics of anionic polymerization of α-methylstyrene with Na+ as counterion have been studied in mixed solvents of tetrahydrofuran (THF) and toluene in various compositions at ?25 to 5°C. The ion-pair rate constant k(±) increases by about a factor of 50 at ?10°C, whereas the activation energy decreases from 5.1 to ?2.2 kcal/mole, when THF in the mixed solvent increases from 30 to 100 vol-%. The plot of log k(±) against (D ? 1)/(2D + 1) is a curve, where D is the dielectric constant of the medium. This deviation from linearity is explained in terms of propagation by two types of ion-pairs.  相似文献   

18.
Alternating—i.e., -(A-B)n- type—block copolymers of polyisobutylene (PIB) and aromatic polyether sulfone (PSU) have been prepared by phase transfer catalyzed Williamson polyetherification of α,ω-di(phenol)PIB with α,ω-di(chloroallyl)- or -(bromobenzyl)PSU. Block copolymers of the two prepolymers were also synthesized by the phase transfer catalyzed polyetherification of methylene chloride with α,ω-di(phenol)PIB and α,ω-di(phenol)PSU (bisphenol-A-terminated PSU). This method leads to -[(A)x-(B)y]n- block copolymers with formal linkages between segments. At sufficiently high segment lengths, both types of block copolymers exhibit two distinct Tgs, indicating phase separation into rubbery PIB and glassy PSU domains.  相似文献   

19.
New fluorinated poly(ether sulfone)s were prepared from bisphenols and α,ωbis(4-fluorophenylsulfonyl)perfluoroalkanes. The fluorinated sulfone monomers were synthesized by reaction of 4-fluorobenzenethiol salts with perfluoroalkylene diiodides, followed by oxidation. Sodium carbonate mediated polymerization gave high molecular weight polymers in excellent yield. The polymers are generally soluble in chlorinated hydrocarbons and some dipolar solvents, are amorphous with Tg's in the range of 120–160°C and are stable to 400°C. They form clear, colorless films by solution casting. Cast films have dielectric constants and dissipation factors somewhat below those of typical poly(ether sulfone)s, and show good permeability and selectivity for O2/N2 gas separations.  相似文献   

20.
A new synthetic pathway of A–B–A tri-block copolyether which is composed of a hydrophilic poly(oxyethylene) unit as an A part and a hydrophobic poly(oxy-2-methyl-trimethylene) unit as a B part is proposed. Telechelic α-tosyl-ω-tosyloxypoly(oxy-2-methyl-trimethylene) derived from tosylation of poly(oxy-2-methyl-trimethylene glycol) (PMTG) was allowed to react with poly(ethylene glycol) (PEG) in the presence of sodium hydroxide. Tg of the resulting A–B–A tri-block copolyether (PEMG) (M?n = 1600) was ?72°C and its specific gravity [D415] was 1.055.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号