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1.
Abstract

A two-stage process was developed for the living polymerization of isobutylene (IB) employing di-tert-alcohol initiators in conjunction with BCl3 coinitiator in the first or initiation stage, followed by TiCl4 coinitiator in the second or propagation stage; the process was shown to yield high molecular weight (up to M n 20,000), narrow molecular weight distribution (MWD) M w/M n = 1.1–1.2) di-tert-chlorine telechelic polyisobutylenes (tCl-PIB-Clt). The initiation stage involves the homogeneous solution living polymerization of IB induced by the di-tert-alcohol/BCl3 combination in the presence of an electron donor such as N,N-dimethylacetamide in CH3Cl solvent at ?80°C and proceeds up to M n < 5000; this is followed by the propagation stage in which TiCl4 and the bulk of IB plus a sufficient amount of n-C6H14 are added to the charge to bring the solvent composition to CH3Cl/n-C6H14 60/40 v/v and the living polymerization is continued until high M n product is obtained. This two-stage process was developed because 1) it employs very inexpensive chemicals; 2) di-tert-alcohol/BCl3 combinations initiate living IB polymerization in CH3Cl but the product after reaching M n ≤ 5000 precipitates out of the CH3Cl solution, and di-tert-alcohol/BCl4 combinations do not initiate IB polymerization; and 3) di-tert-alcohol/BCl3 systems do not initiate (or only very slowly) the living polymerization of IB in CH3Cl/n-C6H14 mixtures, whereas similar TiCl4-based systems do. The polymerization remains living during both stages although the propagating species and solvent polarity are profoundly altered. The livingness of the system has been analyzed by kinetic experiments and the structure of the tCl-PIB-Clt product by routine spectroscopic means.  相似文献   

2.
The kinetics of the anionic polymerization of octamethylcyclotetrasiloxane (D4) initiated by α-methylstyrene living polymer in tetrahydrofuran was studied. The following kinetic scheme was postulated: Initiation: Propagation: where S- and M represent the initiator and D4, respectively. At a living end concentration of 0.0377 mole/l. and a monomer concentration of 1.5 mole/l. in tetrahydrofuran at 25°C. the following kinetic data were obtained: k1 = 2.3 × 10?4 l./mole-sec., k2 < 2.3 × 10?5 sec.?1, k3 = 2.75 × 10?2l./mole-sec. k4 ≈ 1.17 × 10?2 sec.?1, K1 > 10 l./mole and K2 ≈ 2.35 l./mole. The rate constants k1 and k3 were found to be dependent on the concentration of anions. This is attributed to the dissociation of ion pairs to free ions at lower concentration. Under the experimental conditions studied the majority of the anions were present in the form of ion pairs. The reactivity of the free ions is about 100 times greater than that of ion pairs. There is no temperature effect on K2, indicating zero ΔH and positive ΔS in the propagation reaction.  相似文献   

3.
The effect of common anion producing salt, tetrabutylammonium chloride (n-Bu4NCl), on the livingness and kinetics of styrene (St), p-chlorostyrene (pClSt), and p-methylstyrene (pMeSt) polymerization initiated by the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl4 system has been investigated. Uncontrolled (conventional) carbocationic polymerization of St and p MeSt can be converted to living polymerization by the use of n-Bu4NCl. Under similar conditions the polymerization of p ClSt is living even in the absence of n-Bu4NCl, although the molecular weight distribution (MWD) of the polymer becomes narrower in the presence of this salt. The apparent rates of polymerizations decrease in the presence of n-Bu4NCl in proportion with the concentration of the salt. The rate of living polymerization of p ClSt is noticeably lower than that of St, while that of p MeSt is higher. The apparent rate constants, kpA, of these polymerizations have been determined, and the effects of the electron donating p Me- and electron withdrawing p Cl-substituents relative to the rate of St polymerization have been analyzed. [For part LXI, see J. Si and J. P. Kennedy, Polym. Bull., 33 , 651 (1994)]. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3341–3347, 1997  相似文献   

4.
Abstract

A novel scheme was developed for the synthesis of pure polyisobutylene-poly(p-methylstyrene) block copolymers by sequential monomer addition. The synthesis involves the living polymerization of isobutylene by the TiCl4/methyl chloride:methylcyclohexane or hexanes 40:60 v:v/ -80°C system in the presence of di-tert-butylpyridine. When the polymerization of isobutylene is complete, the living polyisobutylene chain end is transformed to the corresponding diphenyl alkyl end by capping with 1,1-diphenylethylene. Subsequently, titanium(IV) isopropoxide or titanium(IV) butoxide is added to decrease the Lewis acidity followed by the addition of p-methylstyrene. The success of the method was demonstrated by p-methylstyrene homopolymerization experiments initiated by 2-chloro-2,4,4-trimethylpentane that resulted in ~ 100% initiator efficiencies when the TiCl4/titanium(IV) isopropoxide or -butoxide ratio was less than 25/7, as well as by the clean synthesis of polyisobutylenepoly(p-methylstyrene) diblock copolymers.  相似文献   

5.
Abstract

The living polymerization of styrene was achieved with the 2,4,4-trimethyl-2-pentyl chloride/TiCl4/MeCl:methylcyclohexane 40:60 v:v/?80°C polymerization system in the presence of di-tert-butylpyridine in concentrations comparable to the concentration of protic impurities. It was determined that the living nature of the polymerization is not due to carbocation stabilization. The polymerization is second order in TiCl4. Side reactions, namely polymerization by direct initiation and intermolecular alkylation, are operational, and a careful selection of experimental conditions is necessary to minimize their effect and obtain apparently living behavior. Polymerization by direct initiation can be minimized by increasing the initiator concentration, and intermolecular alkylation can be reduced by quenching the polymerization system when the conversion reaches close to 100%.  相似文献   

6.
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   

7.
Abstract

Living copolymerization of the isobutylene (IB)-p-methylstyrene (pMeSt) monomer pair in combination with the constant copolymer composition (CCC) technique produces high molecular weight ( M n ≈ 100,000 g·mol?1) and narrow molecular weight distribution ( M w/ M n ≈ 1.45) compositionally uniform IB/pMeSt copolymer molecules in the industrially important IB/pMeSt = 97–99/3–1 mol% composition range. Syntheses were carried out with TiCl4 coinitiator in n-butyl chloride homogeneous solution at ?85°C by the use of the Leidenfrost reactor (i.e., by direct cooling of the charge with liquid nitrogen). In order to carry out the CCC technique it was necessary to obtain reliable copolymerization reactivity ratios. These investigations led to rIB = 0.5 ± 0.1 and r pMeSt = 10 ± 4. The attainment of CCC and living copolymerization conditions has been quantitatively demonstrated by dedicated diagnostic plots. Specifically, the attainment of CCC conditions was proven by the analysis of composite rate plots (comonomers input and corresponding copolymer formed versus time) and composition plots (comonomer composition in feed and copolymer formed versus weight of copolymer formed, W p), and living copolymerization was proven by linearly ascending number-average molecular weight of copolymer ( M n) versus W p plots starting at the origin.  相似文献   

8.
The aim of this research was to develop a quantitative treatment of the consequences of relatively slow initiation on M n and N (the number of molecules formed, Wp/M n , where Wp =weight of polymer formed) in living carbocationic polymerizations, particularly for the case of the incremental monomer addition (IMA) technique. This has been achieved by analysis of the effect of initiator efficiency (Ieff (%) = 100N/[I 0], where [I 0] = initiator input) on M n versus Wp , and N versus Wp plots. Three types of systems have been discerned: 1) Ieff equal to 100%; 2) Ieff constant but less than 100%; and 3) Ieff less than 100% but increasing with increasing number of monomer increments j by the IMA technique. Thus conditions can be found under which slowly initiating systems yield close to “ideal” product, i.e., one with M n = [M0 ]/[I0 ] and narrow molecular weight distribution (M w /M n ≈ 1.1). The corresponding equations and plots can be used to diagnose the mechanism. Subsequently, this quantitative analysis was used to describe a novel living system, trans‐2,5‐diacetoxy‐2,5‐dimethyl‐3‐hexene (DiOAcDMH6)/BCI3/isobutylene/CH3CI. This system produces linear t‐chlorine‐telechelic polyisobutylenes under homogeneous conditions. Surprisingly, cationation seems to be rate determining. This conclusion is illustrated by chemical equations.  相似文献   

9.
The propagation kinetics of anionic polymerization of styrene initiated by dicarbanionic oligostyrylbarium (PS=Ba++) in THF are described. The apparent propagation rate constant kp increases drastically with the degree of polymerization (DP) of living chains and tends at 20°C, for the highest molecular weight (DP ? 5000), to the value determined for monocarbanionic polystyrylbarium(PS?)2Ba++. At given DP, the propagation step follows usual first-order kinetics with respect to monomer, and kp is inversely proportional to carbanion concentration; as observed for (PS?)2Ba++. Similar behavior is observed in the temperature range from ?60 to +20°C. The activation energy of the propagation is 4–5 kcal/mole (16.7–21 kJ/mole). It is shown that kp may be considered as directly proportional to the dissociation constant Kd of ion pairs (~S?Ba++?S~ is considered as an ion pair ~(SBa)+S?~). The striking variation of kp with the DP living chains is interpreted in terms of cyclic living chains, in which both carbanionic ends are bound to the same cation. Values of the intramolecular dissociation constant Kd of ion pairs included in such a model are computed as a function of DP, and their variation is found to fit rather well with experimental data.  相似文献   

10.
Abstract

Using elementary analysis, NMR on 3 1P and 1H nuclei, and electroconductivity methods, the acrylonitrile, methacrylonitrile, formaldehyde, and β-propiolactone anionic polymerization in the presence of triethylphosphine is shown to follow the macrozwitterion mechanism: quartary phosphonium being on one end of a polymer chain and the growing anion on the other. The number of covalent bonds through the whole polymer chain between charges forming the active center increases with the propagation reaction. The active centers stationary concentration in the system is low when connected with both the slow initiation reaction and with the fast active centers termination reaction. Thus the ion interaction of different growing polymer chains can be ignored. The active centers parts occurring in the form of ion pairs (the ends are near and form the “cyclic”) and of free ions (the ends are separated) are determined by the monomolecular equilibrium, and its constant depends upon the macro-zwitterion polymerization degree Kd (n) = Kd (I)n3/2. Such constant depends upon the chain length affords the macrozwitterion self-accelerated propagation with its length, as the free ion reactivity is more than that of ion pairs. The self-accelerated chain propagation effect shows up as an increase of polymerization initial rate order and polymer molecular weight in the monomer concentration. This effect can be avoided by the introduction of electrolyte into the system, which dissociates into ions and transforms all cyclic ion pairs into the linear form, the latter dissociating independently of chain length. The strict mathematical analysis of stationary and nonstationary polymerization kinetics made it possible to determine all the elementary constants separately: Ki = 5.6 × 10?4 liters/ (mole) (min); K- = 2.5 × 104 liter/ (mole) (min); K± = 2.0 liters/ (mole) (min); Kt = 0.84/min; Kt 1 = 4/min; Kd (I) = 10?4; K3 = 0.07 × 10?4 mole/liter.  相似文献   

11.
This paper will compare the mechanism and kinetics of living carbocationic polymerization of isobutylene (IB) and styrene (St), initiated by the 2-chloro-2,4,4-trimethyl-pentane (TMPCl) / TiCl4) system in 60/40 (v/v) methylcyclohexane / methyl chloride mixed solvent at −80 and −75 °C. The rate of initiation was found to be first order in TiCl4 in both systems. While initiation is instantaneous in IB polymerization at [TiCl4]0 ⩾ [TMPCl]0, it is slow in St polymerization. Kinetic derivation showed that initiating efficiency is dependent on [M] in this latter system, which was also demonstrated experimentally. The apparent initiation rate constant was determined from initiator consumption rate data and was found to be ki,app = 1.39 l2/mol2sec. The rate of St consumption measured using a real time fibre-optic mid-FTIR monitoring technique compared well with gravimetric data and was found to be closer to first order in TiCl4 at [TiCl4]0 < [TMPCl]0. However, the rate followed a close to second order in TiCl4 at [TiCl4]0 ⩾ [TMPCl]0. The mechanistic model proposed earlier for living carbocationic IB polymerization, which yielded good agreement with experimental data, seems to apply to carbocationic St polymerization as well. This model reconciles the discrepancy between rate constants published for carbocationic IB and St polymerizations, and accounts for shifting TiCl4 orders. However, independent investigations are necessary to verify the proposed mechanistic model. Optimized conditions led to living carbocationic St polymerization producing high molecular weight PS with 100% initiating efficiency.  相似文献   

12.
This article is a critical analysis of kinetic dataavailable on carbocationic polymerizations. A survey of published propagation rate constant (kp) data revealed several orders of magnitude differences. In this article, an explanation of this apparent discrepancy is offered with a case study involving the carbocationic polymerization of 2,4,6‐trimethylstyrene (TMS). With the polymerization mechanism originally proposed for this system, kp = 1.35 × 104 L mol?1 s?1 was extracted from experimental data with the Predici polyreaction package. The alternative mechanism yielded kp = 1.01 × 107 L mol?1 s?1, close to that predicted by Mayr's Linear Free Energy Relationship (LFER). We propose that true rate constants can only be obtained from direct competition experiments or from kinetic interpretation based on independently proven mechanisms. The second part of this review discusses critical analysis of the temperature and concentration dependence of various living IB systems. Comparison of the temperature dependence in systems initiated with 2‐ chloro‐2,4, 4‐ trimethylpentane (TMPCl)/TiCl4 from various laboratories yielded of ΔH ~?25 and ?34.5 kJ/mol for high and low TMPCl/TiCl4 ratios, respectively. Aromatic (cumyl‐type) initiators show ΔH ~ ?40 kJ/mol, whereas H2O/TiCl4 in the presence of the strong electron‐ pair donor dimethylacetamide gave ΔH = ?12 kJ/mol. The significant differences indicate different underlying mechanisms with complex elementary reactions. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5394–5413, 2005  相似文献   

13.
Abstract

Living polymerization of isobutylene was achieved using an initiation system based on either 1,3-di(1-chloro-l-methylethyl)-5-tert-butylbenzene (tert-butyl-dicumyl chloride) or 1,3,5-tris(l-chloro-l-methylethyl)benzene (tricumyl chloride) in conjunction with TiCl4, and pyridine in hexanes/methyl chloride (60/40, v/v) cosolvents. TiCl4/pyridine was found to yield narrow molecular weight distribution (MWD ≈ 1.1) and quantitative initiation efficiency (Ieff < 90%). The living nature of the polymerization system was demonstrated by the linearity of molecular weight vs conversion plots and first-order kinetic plots up to about 90% monomer conversion. If polymerization was allowed to proceed further, a departure from first-order kinetics and a broadening of the molecular weight distribution was observed to occur. The living polymerization was investigated as a function of temperature, reaction time, and the concentration of TiCl4/pyridine. Polymerization rates were observed to increase with decreasing temperature and/or increasing concentration of TiCl4/pyridine. Number-average molecular weights of the polyisobutylenes ranged from 5,000 to 100,000 under the conditions employed.  相似文献   

14.
The active center concentration C_p, the rate constant k_p, and the activation energy of chain propagation E_p in the polymerization of propylene with complex-type TiCl_3-(C_2H_5)_2AlCl catalyst system were studied. The Mn was corrected by (?) value determined by GPC. The values thus obtained for C_p, k_p, and E_p at 50℃were 3.01 mol/mol Ti, 6.27 1/mol·sec, and 5.10 Kcal/mol respectively.The kinetic parameters were compared with those obtained from conventional TiCl_3·AlCl_2 catalyst, showing that the higher activity of the complex-type catalyst over the conventional catalyst is not only due to the higher C_p of the former, but to a greater extent due to the increase of the k_p value.  相似文献   

15.
Abstract

Novel thermoplastic elastomers (TPEs) consisting of a central rubbery polyisobutylene (PIB) segment flanked by two glassy outer segments comprising indene (Ind)-co-p-methylstyrene (pMeSt) random copolymers have been prepared. The synthesis was effected by sequential monomer addition in one reactor: The process starts by the biliving homopolymerization of isobutylene (IB) and yields the living dication +PIB+; the latter, upon the introduction of Ind/pMeSt mixtures, induces the living copolymerization of these monomers and yields the target TPE P(Ind-co-pMeSt)-b-PIB-b-P(Ind-co-pMeSt) triblock. The length of the rubbery midblock and the composition of the Ind-co-pMeSt random copolymer outer blocks (i.e., the overall composition of the triblocks) can be readily controlled. The glass transition temperature (Tg ) of the outer blocks can be fine-tuned by controlling the relative Ind/ pMeSt composition. The triblocks are excellent TPEs; for example, a P(Ind-co-pMeSt)-b-PIB-b-P(Ind-co-pMeSt) of M n ≈ 115,000 g/mol containing a PIB midblock of M n ≈ 70,200 g/mol and glassy copolymer outer blocks of P(Ind-co-pMeSt) [Ind/pMeSt = 41/59 (w/w)] exhibited 23.4 MPa tensile strength and 460% elongation. Tensile strengths and 300% moduli increase with the relative amount of the glassy segment present. Hardness increases with increasing Ind content.  相似文献   

16.
Abstract

Gamma ray induced polymerization of N,N'-methylenebisacrylamide (MBA) in aqueous solution has been studied. Rates of polymerization have been determined as a function of dose, dose rate, and monomer concentration. Polymerization mechanism was found to be free radical with chain propagation step involving ring formation. About 90% conversion was achieved in 25 minutes of irradiation (dose rate 1.54 × 1018 eV dm?3 s?1) of MBA solution (36 mmol). The polymerization rates were found to vary from 1.9 × 10 4 to 5.6 × 10?4 mol dm?3 s?1 when the monomer concentrations were varied between 80–164 mmols. The value of the constant kp/kt 1/2 was calculated to be 9.85 for the dose rate of 1.54 × 1018 eV dm?3 s?1. The precipitated polymer showed mono disperse particles of diameter of about 170 nm. The polymer was found to be highly crosslinked and insoluble in any solvent.  相似文献   

17.
The kinetic parameters have been measured for octene-1 solution polymerization at 120°C catalyzed by zirconocene with the cocatalyst methylaluminoxane. The polymerizations were performed in an attenuated total reflectance (ATR) reaction cell. The progress of the reactions were followed by observing the disappearance of octene-1 using the 910 cm?1 band measured by FT-IR spectroscopy. The dependence of the reaction rate, Rp, on catalyst concentration and cocatalyst/catalyst ratio was examined. The catalyst deactivation mechanism was studied by fitting the experimental data to mathematical models involving second-order propagation and either first or second order catalyst deactivation. Second-order catalyst deactivation provided a much better fit. The calculated deactivation rate constant, kd, is 21 (Ms)?1. This model is used to determine the propagation rate constant for Al/Zr = 4 × 103 as kp = 19.9 (M s)?1. A decrease in Al/Zr = 3 × 102 lowered the propagation rate constant, kp, to 9.6 (M s)?1 indicating that less than 50% of the initial Zr is active at this Al/Zr ratio.  相似文献   

18.
The polymerization of 2,4,6-trimethylstyrene (vinyl mesitylene) has been investigated, and quasiliving polymerizations have been achieved under a comfortably wide experimental condition range. This monomer is particularly suitable for quasiliving polymerizations because the methyl groups in the 2 and 6 positions prevent chain transfer to monomer involving indanyl-skeleton formation. Quasiliving polymerizations readily occurred by the use of cumyl chloride/TiCl4 or BCl3 initiating systems in various n-C6H14/CH2Cl2 mixtures at -50°C. Because indanyl-skeleton formation is impossible, the rate of monomer addition can be safely decreased to very low values without risking chain transfer by intramolecular alkylation.  相似文献   

19.
Abstract

The synthesis of novel asymmetric telechelic polyisobutylenes (PIB) carrying a CH3OCO— headgroup and a —CH2C(CH3)2C1 tailgroup by the use of novel initiators mediating the living carbocationic polymerization (LC+Pzn) of isobutylene (IB) is described. Subsequently, the parent headgroup has been quantitatively converted into a HOCO— group, and the parent tailgroup into a —pC6H4OH group. Scheme 1 summarizes the synthesis routes to the initiators, as well as the polymerizations and functionalizations leading to various asymmetric telechelic PIBs. The CH3OCO— headgroup of the initiator most likely functions as an internal electron donor during the LC+Pzn of IB.  相似文献   

20.
Abstract

Methyl methacrylate (MMA) was found to be effectively polymerized with bis(cyclopentadienyl)titanium dichloride (CP2TiCl2) in a water-methanol mixture (1:1, v/v). The polymerization proceeded heterogeneously because the resulting poly(MMA) was insoluble in the system. The rate (R p) of the heterogenous polymerization was apparently expressed by R p = k[Cp2TiCl2]2[MMA]2˙5 (at 40°C). The resulting poly(MMA) was observed to consist of tetrahydrofuran (THF)-soluble and insoluble parts. In contrast with the usual radical poly(MMA), the THF-insoluble part was soluble in benzene, toluene, and chloroform but insoluble in polar solvents such as ethyl acetate, acetone, acetonitrile, dimethylformamide, and dimethylsulfoxide. The polymerization was found to be profoundly accelerated by irradiation with a fluorescent room lamp (15 W). The results of copolymerization of MMA and acrylonitrile indicated that the present polymerization proceeds through a radical mechanism.  相似文献   

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