Polymerization of vinyl chloride at reduced monomer accessibility. II. Polymerization at subsaturation pressure with emulsion PVC as seed

Vinyl chloride was polymerized at 59–92% of saturation pressure in a water-suspended system at 45–65°C with an emulsion poly(vinyl chloride) (PVC) latex as a seed. A water-soluble initiator was used in various concentrations. The monomer was continuously charged as vapor from a storage vessel kept at lower temperature. Characterization included determination of molecular-weight distribution and degree of long-chain branching by gel permeation chromatography (GPC) and viscometry, thermal dehydrochlorination, and microscopy. The polymerization rate decreases with decreasing pressure but is reasonable even at the lowest pressure. The molecular weight decreases with decreasing pressure and increasing initiator concentration and also with increasing polymerization temperature, if the initiator concentrations are chosen to give a constant initiator radical concentration. The degree of long-chain branching increases with increasing initiator concentration and decreasing monomer pressure but is unaffected by the polymerization temperature, if the initiator radical concentration is kept constant. The thermal stability decreases with decreasing M _n, while the degree of long-chain branching has only a minor influence. The most important factor in the system influencing the molecular parameter is the monomer accessibility.     

Polymerization of 1,P-Epoxides Initiated by Tetraalkyl Aluminates. I. Polymerization of Ethylene Oxide in the Presence of Sodium Tetrabutyl Aluminate

The polymerization of ethylene oxide (EO) initiated by NaA1Bu₄ is shown to proceed upon initial complex formation between monomer and initiator. In polymerization in toluene a high order of the kinetic equation with respect to initiator was found, indicating that chain propagation proceeds on dimers and trimers of the active center. An induction time of polymerization in THF is observed. It is necessary to reach a specific concentration of the NaAIBu₄.EO complexes which take part in the polymerization process. The wide molecular weight distribution, the high effectivity coefficient (initiation efficiency), and the polymerization rate increase with polymer yield are evidence of a polycentric polymerization mechanism.     

Preparation of water‐soluble,syndiotacticity‐rich,low molecular weight poly(vinyl alcohol) microfibrils in high yields with the low‐temperature polymerization of vinyl pivalate in tetrahydrofuran and saponification

To prepare water‐soluble, syndiotacticity‐rich poly(vinyl alcohol) (PVA) microfibrils for various industrial applications, we synthesized syndiotacticity‐rich, low molecular weight PVA by the solution polymerization of vinyl pivalate (VPi) in tetrahydrofuran (THF) at low temperatures with 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN) as an initiator and successive saponification of poly(vinyl pivalate) (PVPi). Effects of the initiator and monomer concentrations and the polymerization temperature were investigated in terms of the polymerization behaviors and molecular structures of PVPi and the corresponding syndiotacticity‐rich PVA. The polymerization rate of VPi in THF was proportional to the 0.91 power of the ADMVN concentration, indicating the heterogeneous nature of THF polymerization. The low‐temperature solution polymerization of VPi in THF with ADMVN proved to be successful in obtaining water‐soluble PVA with a number‐average degree of polymerization (P_n) of 300–900, a syndiotactic dyad content of 60–63%, and an ultimate conversion of VPi into PVPi of over 75%. Despite the low molecular weight of PVA with P_n = 800, water‐soluble PVA microfibrillar fibers were prepared because of the high level of syndiotacticity. In contrast, for PVA with P_n = 330, shapeless and globular morphologies were observed, indicating that molecular weight has an important role in the in situ fibrillation of syndiotacticity‐rich PVA. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1103–1111, 2002     

Synthesis and characterization of amino-terminated telechelic polybutadiene

Butadiene was polymerized with water-soluble 4,4′-azobis(amidinopropane)dihydrochloride initiator in an ethanol-water medium at 60°C. Important variables, such as the initiator concentration, monomer concentration, solvency, and polymerization time and temperature were studied. ¹³C-NMR studies showed that no observable chain transfer to ethanol occurred during the polymerization. The conversion of monomer to polymer was significantly increased while maintaining a relatively narrow molecular weight distribution by intermittent feed of the initiator. The amidino end-groups of the polymer were transformed into amino groups by reduction using lithium aluminum hydride in THF, so that amine-terminated polybutadiene was obtained. The amino functionality of the polybutadiene was determined by titration to be 2.0. © 1995 John Wiley & Sons, Inc.     

丁基锂引发的活性宽分布聚双烯烃的合成

<正> 用烷基锂引发的丁二烯“活性”聚合,通常只能得到分子量分布较窄的聚合物。这类聚合物的门尼粘度较高,不易加工,且易冷流。为了解决这些问题,一般是合成分子量分布较宽且有一定支化的聚合物。但在以往的合成宽分布聚合物的方法中,大多只能得到非“活性”聚双烯烃,因而无法进行“活性”高分子的一些典型反应,如嵌段、接枝及偶     

Characterization of hydrophilic networks synthesized by group transfer polymerization

Group transfer polymerization was used to synthesize several series of hydrophilic random and model networks. Cationic random networks were prepared both in bulk and in tetrahydrofuran (THF) using a monofunctional initiator and simultaneous polymerization of monomer and branch units, while a bifanctional initiator was employed in THF for the synthesis of model networks comprising basic or acidic chains. Upon polymerization of the monomer, the latter initiator gives linear polymer chains with two “living” ends, which are subsequently interconnected to a polymer network by the addition of a branch unit. Homopolymer network star polymers were also synthesized in THF by a one‐pot procedure. The synthesis involved the use of a monofunctional initiator and the four‐step addition of the following reagents: (i) monomer, to give linear homopolymers; (ii) branch unit, to form “arm‐first” star polymers; (iii) monomer, to form secondary arms and give “in‐out” star polymers; and, finally (iv) branch unit again, to interconnect the “in‐out” stars to networks. Different networks were prepared for which the degree of polymerization (DP) of the linear chains between junction points was varied systematically. For all networks synthesized, the linear segments, the “arm‐first” and the “in‐out” stars were characterized in terms of their molecular weight (MW) and molecular weight distribution (MWD) using gel permeation chromatography (GPC). The degrees of swelling of both the random and model networks in water were measured and the effects of DP, pH, and monomer type were investigated.     

双官能度引发剂引发苯乙烯聚合微观动力学

采用 2 ,5 二甲基 2 ,5 二己酰基过氧化己烷 (DMDEHPH)为引发剂 ,在 5 5～ 80℃下引发苯乙烯聚合 .通过研究影响聚合速率的各种因素 ,得出了聚合速率对单体浓度和引发剂浓度的级数分别为 1 0和 0 5次、聚合活化能为 92 0kJ mol、引发效率为 0 5 5± 0 0 3.温度一定 ,引发效率随引发剂浓度的增加而减小 .求得 6 0和70℃下DMDEHPH向引发剂的链转移常数分别为 0 0 37和 0 0 4 8、向单体的链转移常数分别为 0 5 9× 10 - 4和0 75× 10 - 4.     

Electrochemical polymerization to a controlled molecular weight distribution

Living polyanions were generated by the passage of electrolytic current through solutions in tetrahydrofuran (THF). The concentration of living polyanions was controlled by the current and could be increased by further electrolysis or decreased by electrolysis with reversal of polarity. Inasmuch as the living end (LE) concentration determines the molecular weight at a given monomer concentration it was possible to program a molecular weight distribution. Model distributions were attempted by (1) indirect methods in which an electrolytic formation of initiating dianions was followed by monomer addition, polymerization, current reversal and further polymerization and (2) direct methods in which monomer was present throughout the electrolysis. The molecular weight distributions were obtained by gel-permeation chromatography and corresponded closely to the values calculated from the simple kinetic model of anionic polymerization. For styrene a sharp low molecular weight fraction and a clear binodal high molecular weight fraction were obtained. The binodal character was attributed to the growth of active single-ended and double-ended polyanions. The yields of high and low molecular weight material, the ratios of molecular weights obtained, and the values of the molecular weights were in agreement with expectation. The direct electrochemical polymerization methods were employed for α-methylstyrene, but the high k_p for styrene thwarted efforts to apply the direct technique with this monomer.     

苯氧铜/正丁基锂体系引发MMA负离子聚合及其活性特征的研究

采用苯氧铜/正丁基锂(PhOCu/n-BuLi)体系引发MMA聚合, 通过GPC, ¹H NMR对聚合物进行了表征. 实验结果表明, 该体系聚合反应速度较快, 温度、引发体系组成是影响聚合物分子量及其分布、单体转化率、引发剂引发效率、聚合物的立构规整性的主要因素; －40 ℃时分子量分布比较窄, 但引发效率也比较低(大约15%). 低引发效率、宽分子量分布与引发剂的聚集状态有关. 分子量与单体浓度、引发剂浓度的关系说明, 该体系具有一定程度的活性聚合特点.     

Anionic polymerization of methacrylonitrile—I. Polymerization with n-butyllithium as initiator

The anionic polymerization of methacrylonitrile has been studied at ?75° in toluene and with n-butyllithium as initiator. The kinetics of the polymerization were investigated considering the consumption of both monomer and initiator. BuLi disappears relatively slowly and about 50–60% remains unreacted. A simple kinetic scheme cannot therefore be put forward. All possible side reactions have also been examined. The molecular weight study establishes the living character of this system and gives an initiator efficiency of about 0.2. The contribution of low molecular weight products, typical of the polymerization of polar monomers, is also taken into account. In order to obtain a better understanding of the mechanism of this polymerization, in which unreacted initiator is probably engaged in very stable and inactive mixed associated particles, small amounts of THF (known frequently to break down such aggregates) were added to the system. A rather unexpected slow but complete disappearance of the initiator occurs; the conversion at which the rate of monomer consumption levels off depends on the THF concentration.     

Living anionic polymerization of lauryl methacrylate and synthesis of block copolymers with methyl methacrylate

Anionic polymerization of lauryl methacrylate (LMA) with 1,1‐diphenylhexyl lithium in tetrahydrofuran (THF) at ?40 °C resulted in a multimodal and broad molecular weight distribution (MWD) with poor initiator efficiency. In the presence of additives such as dilithium salt of triethylene glycol (G₃Li₂), LiCl, and LiClO₄, the polymerization resulted in polymers with a narrow MWD (≤ 1.10). Diblock copolymers of methyl methacrylate (MMA) and LMA were synthesized by anionic polymerization using DPHLi as initiator in THF at ?40 °C with the sequential addition of monomers. The molecular weight distribution of the polymers was narrow and without homopolymer contamination when LMA was added to living PMMA chain ends. Diblock copolymers with broad/bimodal MWD were obtained with a reverse‐sequence monomer addition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 875–882, 2004     

含芳酰胺结构的新型甲壳型液晶高分子PMPACS的聚合反应动力学研究

采用称量法和GPC,研究了以二甲基乙酰胺为溶剂,偶氮二异丁腈为引发剂,自由基溶液聚合制备含芳酰胺结构的新型甲壳型液晶高分子聚[乙烯基对苯二甲酸二(4-甲氧基苯胺)](PMPACS)的聚合反应动力学.研究发现,(1)MPACS的聚合反应在60℃时主要为双基偶合终止,所以反应后期聚合物分子量明显增大,分子量分布变窄;(2)该反应的聚合反应速率方程为Rp=kp[M][I]1/2,表观活化能Eα=44 kJ/mol,在60℃时的聚合反应常数kp=1.04 L·mol-1·h-1;(3)相同聚合条件下,单体的转化率和数均分子量随单体初始浓度[M]0的增加而增大,当引发剂浓度[I]0增加时,聚合物的分子量随之降低,分子量分布增大;(4)该研究虽采用普通自由基聚合,所得聚合物的分子量分布却较窄,仅为1.1～1.4.     

Synthesis of polymethylmethacrylate in THF solution with phosphorous containing initiators

For the synthesis of polymethylmethacrylate, tetraphenyl biphosphine (TPhBP) with a thermally and photochemically unstable P‐P bond was employed. Under the influence of UV light, this bond split to two relatively stable biphenylphosphine radicals, which are able to react with the monomer. The resultant macroinitiators were isolated and were used for further polymerization with the same or another monomer to synthesize block‐copolymers. Controlled polymerization of methyl methacrylate with tetraphenyl biphosphine took place in the absence of oxygen by UV irradiation in THF solution. For MMA alone an insignificant portion photo‐ (0.3%) and thermal‐ (2%) polymerization were detected. Using selected quantity of the initiator, macroinitiators with predicted molecular weight as well as block‐copolymers were synthesized. The macroradicals were terminated by primary ‐PPh ₂ radicals, by chain transfer to initiator and by the combination of two macroradicals. We determined chain end groups by nuclear magnetic resonance spectroscopy (NMR) and the relative molecular weights of the polymers by gel permeation chromatography (GPC). The molecular weights were calculated using the ¹H NMR spectra from the ratio between the end groups signals and signals of the chain and were compared to GPC measurements. The calculated and observed molecular weights were in good agreement. At the lower concentration of initiator the molecular weight increased with conversion, while at the higher initiator concentration the molecular weight decreased with increasing conversion which could be ascribed to chain transfer to initiator. Copyright © 2001 John Wiley & Sons, Ltd.     

无乳化剂乳液聚合制备高分子量聚乙烯醇

通过无乳化剂乳液聚合方法, 采用氧化还原引发体系制备了超高分子量的聚醋酸乙烯酯(PVAc), 继而醇解为超高分子量的聚乙烯醇(PVA). 研究了聚合温度、引发剂浓度、单体转化率对PVA的分子量和分子结构的影响. 探讨了线性高分子量PVA结构的控制方法. 结果表明, 利用无乳化剂乳液聚合可以实现在室温(14~20 ℃)制备出聚合度为9899的高分子量的PVA, 聚合过程对PVA的分子量和结构均有显著的影响. 在无乳化剂乳液聚合恒速聚合区得到的聚合物分子量较高, 分子量分布窄, 且结构比较规整, 而在加速区, PVAc的支化和交联现象显著, 最终会对PVA的线性程度产生很大影响. 因此, 可以通过聚合过程来控制PVA的分子量和链结构.     

Monoaryloxo ytterbium(III) chlorides supported by β‐diketiminato ligands as novel initiators for the living ring‐opening polymerization of ε‐caprolactone

Ring‐opening polymerization of ε‐caprolactone (ε‐CL) was carried out using β‐diketiminato‐supported monoaryloxo ytterbium chlorides L¹Yb(OAr)Cl(THF) (1) [L¹ = N,N′‐bis(2,6‐dimethylphenyl)‐2,4‐pentanediiminato, OAr = 2,6‐di‐tert‐butylphenoxo‐], and L²Yb(OAr′)Cl(THF) (2) [L² = N,N′‐bis(2,6‐diisopropylphenyl)‐2,4‐pentanediiminato, OAr′ = 2,6‐di‐tert‐butyl‐4‐methylphenoxo‐], respectively, as single‐component initiator. The influence of reaction conditions, such as polymerization temperature, polymerization time, initiator, and initiator concentration, on the monomer conversion, molecular weight, and molecular weight distribution of the resulting polymers was investigated. Complex 1 was well characterized and its crystal structure was determined. Some features and kinetic behaviors of the CL polymerization initiated by these two complexes were studied. The polymerization rate is first order with respect to monomer. The M_n of the polymer increases linearly with the increase of the polymer yield, while polydispersity remained narrow and unchanged throughout the polymerization in a broad range of temperatures from 0 to 50 °C. The results indicated that the present system has a “living character”. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1147–1152, 2006     

Polymerization of Vinyl Chloride at Reduced Monomer Accessibility. I. Polymerization at Subsaturation Pressure with Suspension PVC as a Seed

Vinyl chloride was polymerized at 40–96% of saturation pressure in water suspended systems at 55°C with suspension PVC as a seed. The monomer was continuously charged as vapor from a storage vessel kept at lower temperature. Characterization included molecular weight distribution (MWD) and degree of long-chain branching (LCB) by GPC and viscometry, thermal dehydrochlorination, microscopy, and technical standard tests. A granular seed was necessary to obtain granular polymer and reasonable polymerization rate. In properly seeded systems with monomer-soluble initiator, crust formation is very low. With monomer-soluble initiator the polymerization reactions are restricted to the seed polymer, comprise its total structure, reducing its porosity. At pressure near saturation, molecular weight increased with conversion, and autoacceleration occurred. The changes in molecular weight are presumably due to the lack of a liquid monomer phase, which reduces the mobility of the radicals leading to decreased termination. At decreasing polymerization pressure the mobility is further reduced due to de-swelling of the gel. At low pressure the polymerization rate decreased, the amount of low molecular weight material increased, and considerable long-chain branching occurred as a result of monomer depletion. With water-soluble initiator (at pressure near saturation), new tiny particles were formed in the water phase at the boundary to the seed particles. The seed structure remained unchanged. The polymer formed showed broad MWD and high LCB. No marked reduction in polymerization rate was observed. The dehydrochlorinatlon measurements indicate that the end groups and not the branch points are responsible for the decrease in thermal stability noticed.     

丙烯腈的悬浮聚合

<正> 适用于普通溶液纺丝加工成形的聚丙烯腈(PAN)的分子量一般在5—8万范围内,近年来发展起来的冻胶纺丝方法使得(?)>4.0×10~5的超高分子量PAN也可以纺丝成形,成为制备高强高模PAN纤缎的有效方法之一。随着PAN材料应用领域的开拓,合成超高分子量的PAN是一个首要解决的问题。     

Synthesis and characterization of poly(ϵ-caprolactone)-poly(ethylene glycol) block copolymer

Poly(ϵ-caprolactone)–poly(ethylene glycol)–poly(ϵ-caprolactone) triblock copolymers (PECL) covering a wide range of poly(ethylene glycol) (PEG) lengths were synthesized with alkali metal alkoxide derivatives of poly(ethylene glycol). The effects of various factors, such as amount of the initiator, reaction time and temperature, polarity of solvent, length of PEG segment, and counterion on the polymerization were investigated. The copolymers were characterized by ¹H-NMR, IR, GPC, and DSC. It was found that THF system is superior to toluene system. The conversion of the monomer increased with increase of the initiator concentration. High molecular weight of the copolymer and high conversion of the monomer was obtained at below 30°C within 5 min. The polymerization process was studied by GPC and the coexistence of propagation and transesterification reaction was found, which leaded to relatively broad molecular weight distribution of the copolymers. © 1997 John Wiley & Sons, Inc.     

Anionic polymerization of acrylates. II. Polymerization of 2-ethylhexyl acrylate initiated by butyllithium/lithium-tert-butoxide system in tetrahydrofuran and its mixtures with toluene

The anionic polymerization of 2-ethylhexyl acrylate (EtHA) initiated with the complex butyllithium/lithium-tert-butoxide (BuLi/t-BuOLi) was investigated at ?60°C in a medium of various solvating power, i.e., in mixtures of toluene and tetrahydrofuran and in neat tetrahydrofuran. With increasing amount of THF in the mixture the attainable limiting conversion of polymerization decreases; the monomer can be polymerized quantitatively only in a toluene/THF mixture (9/1). Molecular weights of the polymers thus obtained, their distribution, and initiator efficiency are not appreciably affected by the polymerization medium. The molecular weight distribution of the products is medium-broad (M_w/M_n = 2–2.4), with a hint of bimodality. The ¹H-¹³C-NMR, and IR spectra suggest that during the polymerization there is neither any perceptible reesterification of the polymer with the alkoxide nor transmetalation of the monomer with the initiator. In a suitable medium, autotermination of propagation proceeds to a limited extent only, predominantly via intramolecular cyclization of propagating chains; in a medium with a higher content of polar THF, it prevails and terminates propagation before the polymerization of the monomer has been completed. © 1992 John Wiley & Sons, Inc.     

Atom Transfer Radical Polymerization of Styrene Using Multifunctional Iniferter Reagents as Initiators

Summary: Two multifunctional iniferters, 1,4-bis-(α-N,N-diethyldithiocarbamyl-isobutyryloxy)-benzene (BDCIB) and 1,3,5-tris-(α-N,N-diethyldithiocarbamyl-isobutyryloxy)-benzene (TDCIB), were successfully synthesized and used as initiators to initiate the polymerization of styrene in the presence of a CuBr/PMDETA complex. The polymerization results demonstrated that the kinetic plots in all cases were first-order to the monomer, the molecular weight of the polymers increased linearly with the monomer conversion; meanwhile, the molecular weight distribution of the polymer was kept to a very low value (M_w/M_n ≤ 1.35). Furthermore, the measured molecular weights were very close to the calculated values, which indicated the high efficiency of the initiator for the polymerization of styrene. The effect of catalyst concentration and initiator concentration was not obvious and the influence of polymerization temperature was apparent, and the polymerization rate increased with the polymerization temperature. The results of chain-extension and ¹H NMR analysis proved that the polymer obtained was capped with diethylthiocarbamoylthiy (DC) group.