Carbocationic polymerization in supercritical carbon dioxide

Polymerization of isobutylene (IB) in supercritical carbon dioxide (SC·CO₂) at 32.5°C and 140 bar by the use of 2-chloro-2,4,4-trimethyl-pentane (TMPCl) initiator in conjunction with a mixture of TiCl₄/BCl₃ leads to well-defined polyisobutylenes (PIB) capped by a t-Bu head group and a t-Cl tail group (tBu-PIB-Cl^t) of M_n1800 g/mole and M_w/M_n=1.3. The TiCl₄/BCl₃ mixture may be viewed a new Friedel-Crafts Acid that effects rapid initiation, essentially chaintransferless propagation and reversible termination. The mechanism of IB polymerization of TiCl₄/BCl₃ mixtures is discussed.     

Complete devulcanization of sulfur‐cured butyl rubber by using supercritical carbon dioxide

Sulfur‐cured butyl rubber was devulcanized completely in supercritical CO₂ by using diphenyl disulfide (DD) as a devulcanizing reagent. The optimum devulcanizing conditions were studied and the sol fraction of the reclaimed rubber obtained was up to 98.5%. The possible devulcanizing mechanism was investigated. Then, the sol component of reclaimed rubber was characterized by gel permeation chromatography, ¹H‐NMR, and differential scanning calorimetry, and the reclaimed rubber was characterized by TGA. Because of the substitution of a large portion of allylic hydrogen by sulfurated functional groups during vulcanization, the signal of the olefinic proton shift. As a result of the numerous decreases in the active crosslinking sites and the remaining DD, reclaimed rubber could not be cured by sulfur. At last, the blends of virgin butyl rubber and different contents of reclaimed rubber were revulcanized and their mechanical properties investigated. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Ultrasonically initiated emulsion polymerization of n‐butyl acrylate

Ultrasonically initiated emulsion polymerization of n‐butyl acrylate (BA) without added initiator has been studied. The experimental results show that high conversion of BA can be reached in a short time by employing an ultrasonic irradiation technique with a high purge rate of N₂. The viscosity average molecular weight of poly(n‐butyl acrylate) (PBA) obtained reaches 5.24 × 10⁶ g mol^?1. The ultrasonically initiated emulsion polymerization is dynamic and complicated, with polymerization of monomer and degradation of polymer occurring simultaneously. An increase in ultrasound intensity leads to an increase in polymerization rate in the range of cavitation threshold and cavitation peak values. Lower monomer concentration favours enhancement of the polymerization rate. ¹H NMR, ¹³C NMR and FTIR spectroscopies reveal that there are some branches and slight crosslinking, and also carboxyl groups in PBA. Ultrasonically initiated emulsion polymerization offers a new route for the preparation of nanosized latex particles; the particle size of PBA prepared is around 50–200 nm as measured by transmission electron microscopy. © 2001 Society of Chemical Industry     

Dispersion polymerization of L-lactide in supercritical carbon dioxide

Triblock (A-B-A) oligomers of ε-caprolactone (ε-CL) (A) and poly(ethylene glycol) with an average molecular weight of 400 (PEG400) (B) were synthesized with three different molecular weight in the range of 2–6 kDa by changing the ratio of PEG400/ε-CL. These oligomers were then used in dispersion polymerization of L-lactide in supercritical carbon dioxide (scCO₂) as stabilizers. 5% stabilizer in the polymerization recipe allowed synthesis of poly(L-lactide) (PLLA) in scCO₂ in the powder form with a weight average molecular weight of around 60 kDa with polymerization yields around 80%. Interestingly, there was almost no effect of stabilizer molecular weight on polymerization. L-lactide polymerization in scCO₂ without any stabilizer was also possible but both the PLLA molecular weight and polymerization yield were lower, and the product was as aggregates instead of powders. A stabilizer concentration of 5% in the polymerization recipe was found adequate. Further increases in the stabilizer load resulted lower molecular weights and lower yields.     

Radical polymerization of n‐butyl methacrylate initiated by stibonium ylide

1,2,3,4‐Tetraphenylcyclopentadiene triphenyl stibonium ylide initiated radical polymerization of n‐butyl methacrylate (n‐BMA) in dioxane at (60 ± 0.2)°C for 90 min under nitrogen atmosphere has been carried out. The system follows nonideal kinetics, i.e., R_p α [ylide]^0.2 [n‐BMA]^1.8. The value of k/k_t and overall energy of activation have been computed as 0.133 × 10^?2 L mol^?1 s^?1, 33 kJ/mol, respectively. The FTIR spectrum shows a band at 1745 cm^?1 due to acrylate group of n‐BMA. The ¹H NMR spectrum shows a peak of two magnetically equivalent protons of methylene group at 2.1 δ ppm. The DSC curve shows glass transition temperature (T_g) as 41°C. The presence of six hyperfine lines in ESR spectrum indicates that the system follows free radical polymerization and the initiation is brought about by phenyl radical. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2457–2463, 2007     

Microemulsion polymerization of butyl acrylate initiated by γ rays

Radiation polymerization of butyl acrylate was carried out in a microemulsion stabilized with sodium 12-butinoyloxy-9-octadecenate (SBOA). The stable and reddish latex with high polymer content and low emulsifier content was successfully produced in this way. It was found that, for most cases, the polymerization rate shows three intervals: the increasing period, the plateau period, and the decreasing period. The length of the nucleation period becomes longer at a higher dose rate (D) and lower emulsifier content (E). The plateau region of polymerization rate is lengthened with the increase of monomer and emulsifier content and shortened with the increase of dose rate. It was shown that monomer content, emulsifier content, and dose rate have great effects on R_p (the polymerization rate in the plateau region, or the maximum polymerization rate during polymerization) and M_n (the molecular weight of the polymer). R_p ∞ [M^0.93D^1.27[E]^−1.07; M_n ∞ [M]^0.65D^0.28[E]^−1.66. The polymerization mechanism is discussed based on these results. © 1996 John Wiley & Sons, Inc.     

利用超临界二氧化碳流体脱硫再生丁基橡胶

研究了硫黄硫化的丁基橡胶在超临界二氧化碳流体辅助下的脱硫降解行为,讨论了脱硫工艺的条件,并通过凝胶渗透色谱、核磁共振、差示扫描量热等对丁基再生胶的结构和性能进行了考察。结果表明,在二氧化碳的超临界状态下丁基橡胶的脱硫降解更加充分。脱硫的最佳工艺条件为: 反应温度180 ℃,反应压力14. 1 MPa,脱硫剂二苯基二硫的用量为橡胶质量的8%; 经过120 min 脱硫反应后丁基再生胶中溶胶的质量分数为98. 5%。在有热降解和脱硫剂参与的脱硫反应的共同影响下,丁基再生胶中溶胶的数均分子量降至原胶的40%左右; 再生胶主链上接枝了部分脱硫剂的苯环; 硫化和脱硫过程中在接枝于主链上的极性基团的影响下,再生胶中溶胶主链双键氢的振动峰几乎消失,但再生胶的玻璃化转变温度并没有明显变化。     

Cross-linking polymerization of acrylic acid in supercritical carbon dioxide

Cross-linking polymerization of acrylic acid in supercritical carbon dioxide (scCO₂) was studied in a batch reactor at 50 °C and 207 bar with either triallyl pentaerythritol ether or tetraallyl pentaerythritol ether as the cross-linker and with 2,2′-azobis(2,4-dimethyl-valeronitrile) as the free radical initiator. All polymers were white, dry, fine powders. Scanning electron microscopy showed that the morphology of the polymer particles was not affected by cross-linking. As the cross-linker concentration was increased, the polymer glass transition temperature first decreased, then increased. Water-soluble and water-insoluble polymers were synthesized by adjusting the cross-linker concentration. Viscosity measurements showed that the polymer thickening effect strongly depended on the degree of cross-linking. Finally, cross-linking polymerization of acrylic acid in scCO₂ was carried out in a continuous stirred tank reactor. The use of cross-linker decreased the monomer conversion in this system.     

超临界CO2在聚合反应中的应用

对超临界CO2在溶液聚合、悬浮聚合、乳液聚合、沉淀聚合、分散聚合等聚合反应中的应用进行了综述。超临界CO2已广泛应用于萃取和生物工程等方面,由于其作为聚合反应介质具有无毒、无污染的特性．在聚合物制备中已得到越来越广泛的重视。     

Synthesis of conducting polyaniline‐montmorillonite nanocomposites via inverse emulsion polymerization in supercritical carbon dioxide

A new inverse emulsion polymerization and intercalation procedure in supercritical carbon dioxide (SCCO₂) was initially employed to synthesize polyaniline‐montmorillonite (PANI‐MMT) nanocomposites. The effect of chemical groups in MMT galleries on intercalation in SCCO₂ was investigated. The MMTs modified by different organic cationic surfactants were incorporated into the composite particles, and in unintercalated, partially delaminated or fully exfoliated state. The aminated MMT or fluorinated MMT were utilized to prepare conducting PANI‐MMT nanocomposites with highly concentrated (12–25 wt% loading to monomer), fully exfoliated MMT platelets in SCCO₂. The structure and morphology of PANI‐MMT nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray powder diffraction pattern (XRD), and transmission electron microscope (TEM). Thermogravimetry analysis (TGA) was performed to demonstrate the enhancement of thermal stability of the composites. SCCO₂ was shown to be more effective for impregnation, disaggregation and exfoliation of MMTs than isooctane, which indicates that SCCO₂ is an alternative solvent for synthesis of some intercalated composite materials, not only based on the environmental friendly characteristic of SCCO₂, but also owing to that SCCO₂ can play an important role in intercalative polymerization. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Detailed modelling of MMA dispersion polymerization in supercritical carbon dioxide

A comprehensive model of dispersion polymerization in supercritical media is presented. With respect to previous ones reported in the literature, this model accounts in detail for the interphase mass transport of the active polymer chains and specifically for its dependence on the chain length. All the model parameters have been evaluated from independent literature sources in the case of poly(methyl methacrylate) dispersion polymerization in supercritical carbon dioxide. The corresponding a priori predictions of the model have been validated with various sets of experimental data, covering a rather wide range of operating conditions, in terms of conversion, pressure and molecular weight distribution as a function of time. It has been found that the interphase mass transport of active chains plays a significant role in determining the number of reaction loci and consequently the final polymer properties and, in particular, the molecular weight distribution.     

Dispersion polymerization of methyl methacrylate in supercritical carbon dioxide using a silicone‐containing fluoroacrylate stabilizer

Free radical dispersion polymerization of methyl methacrylate (MMA) was carried out in supercritical carbon dioxide (scCO₂) using poly{(heptadecafluorodecyl acrylate)‐co‐3‐[tris(trimethylsilyloxy)silyl]propyl methacrylate} (p(HDFDA‐co‐SiMA)) as stabilizer. Dry, fine powdered spherical poly(methyl methacrylate) (pMMA) particles with well‐defined sizes were produced. The resulting high yield of spherical and relatively uniform micron‐size pMMA particles was formed utilizing various amounts of p(HDFDA‐co‐SiMA) random copolymer. The particle diameter was shown to be dependent on the weight percent of the stabilizer added to the system. The effects of varying the concentration of stabilizer (1–7 wt%), reaction time (4–12 h) and pressure (15–35 MPa) upon the polymerization yield, molar mass and morphology of pMMA were investigated. Copyright © 2005 Society of Chemical Industry     

Synthesis of poly(butyl acrylate‐co‐methyl methacrylate)/montmorillonite waterborne nanocomposite via semibatch emulsion polymerization

Poly(butyl acrylate‐co‐methyl methacrylate)‐montmorillonite (MMT) waterborne nanocomposites were successfully synthesized by semibatch emulsion polymerization. The syntheses of the nanocomposites were performed in presence of sodium montmorillonite (Na‐MMT) and organically modified montmorillonite (O‐MMT). O‐MMT was used directly after the modification of Na‐MMT with dimethyl dioctadecyl ammonium chloride. Both Na‐MMT and O‐MMT were sonified to obtain nanocomposites with 47 wt % solids and 3 wt % Na‐MMT or O‐MMT content. Average particle sizes of Na‐MMT nanocomposites were measured as 110–150 nm while O‐MMT nanocomposites were measured as 200–350 nm. Both Na‐MMT and O‐MMT increased thermal, mechanical, and barrier properties (water vapor and oxygen permeability) of the pristine copolymer explicitly. X‐ray diffraction and transmission electron microscope studies show that exfoliated morphology was obtained. The gloss values of O‐MMT nanocomposites were found to be higher than that of the pristine copolymer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42373.     

Influence of DMF on the polymerization of tert‐butyl acrylate initiated by 4‐oxo‐TEMPO‐capped polystyrene macroinitiator

BACKGROUND: In a number of studies it has been shown that 2,2,6,6‐tetramethylpiperidinooxy (TEMPO)‐mediated polymerization of acrylates is not facile. Therefore, the object of the study reported here was to prepare poly[styrene‐block‐(tert‐butyl acrylate)] (PS‐b‐PtBA) block copolymers using 4‐oxo‐TEMPO‐capped polystyrene macroinitiator as an initiator, in the presence of small amounts of N,N‐dimethylformamide (DMF). The kinetic analysis and the effect of DMF on the reaction mechanism are also discussed. RESULTS: PS‐b‐PtBA block copolymer was prepared through polymerization of tert‐butyl acrylate (tBA) initiated by 4‐oxo‐TEMPO‐capped polystyrene macroinitiator at 135 °C. The polymerization rate of tBA could be increased by adding a small amount of DMF, and the number average molecular weight of the PtBA block in PS‐b‐PtBA reached 10 000 g mol^?1 with narrow polydispersity. The activation rate constant k_act?tBA of alkoxyamine increased and the recombination rate constant k_rec?tBA decreased with increasing DMF concentration. CONCLUSION: DMF was shown to be a rate‐enhancing additive for the polymerization of tBA using a 4‐oxo‐TEMPO‐capped polystyrene macroinitiator. From the kinetic analysis, it was concluded that the improvement of polymerization with the addition of DMF was due to an increase in k_act?tBA and a decrease in k_rec?tBA. Copyright © 2008 Society of Chemical Industry     

Poly(ϵ‐caprolactone)‐functionalized carbon nanofibers by surface‐initiated ring‐opening polymerization

Carbon nanofibers (CNFs) were covalently functionalized with biodegradable poly(?‐caprolactone) (PCL) by in situ ring‐opening polymerization (ROP) of ?‐caprolactone in the presence of stannous octoate. Surface oxidation treatment of the pristine CNFs afforded carboxylic CNFs (CNF‐COOH). Reaction of CNF‐COOH with excess thionyl chloride (SOCl₂) and glycol produced hydroxyl‐functionalized CNFs (CNF‐OH). Using CNF‐OH as macroinitiator, PCL was covalently grafted from the surfaces of CNFs by ROP, in either the presence or absence of sacrificial initiator, butanol. The grafted PCL content was achieved as high as 64.2 wt %, and can be controlled to some extent by adjusting the feed ratio of monomer to CNF‐OH. The resulting products were characterized by FTIR, NMR, Raman spectroscopy, TGA, DSC, SEM, TEM, HRTEM, and XRD. Core–shell nanostructures were observed under HRTEM for the PCL‐functionalized CNFs because of the thorough grafting. The PCL‐grafted CNFs showed different melting and crystallization behaviors from the mechanical mixture of PCL and CNF‐OH. This approach to PCL‐functionalized CNFs opens an avenue for the synthesis, modification, and application of CNF‐based nanomaterials and biomaterials. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Redox initiated free radical polymerization of 4‐methylstyrene

Studies of the thermally initiated polymerization of 4‐methylstyrene using alkylperoxide in conjunction with cobalt and tertiary amine catalysts are reported. Addition of cobalt salts leads to a facile low temperature initiation of the polymerization process. The polymerization process was investigated using differential scanning calorimetry [DSC] and vibrating probe rheological measurements. Color changes which occur when the cobalt complex and peroxide are combined were studied using UV‐visible spectroscopy. The kinetics of polymerization was investigated using two different cobalt complexes. The initiation step in the polymerization is the conversion of the cobalt (II) to cobalt (III). The presence of the tertiary amine does not affect the oxidation state of the cobalt complex. The cobalt (III) complex gives a better rate of conversion than the cobalt (II) complex. The polymerization process is discussed in terms of redox reaction between the cobalt complex and the alkyperoxide. At low temperatures, the rate of conversion obeys simple Arrhenius kinetics. At higher temperatures the effects of gelation and catalysts inhibition influence the polymerization process. The polymerization process is sensitive to the level of available oxygen during the initiation step and inhibition by aldehyde is observed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Solubilities of sub‐ and supercritical carbon dioxide in polyester resins

In supercritical carbon dioxide (CO₂) assisted polymer processes the solubility of CO₂ in a polymer plays a vital role. The higher the amount of CO₂ dissolved in a polymer the higher is the viscosity reduction of the polymer. Solubilities of CO₂ in polyester resins based on propoxylated bisphenol (PPB) and ethoxylated bisphenol (PEB) have been measured using a magnetic suspension balance at temperatures ranging from 333 to 420 K and pressures up to 30 MPa. An optical cell has been used to independently determine the swelling of the polymers, which has been incorporated in the buoyancy correction. In both polyester resins, the solubility of CO₂ increases with increasing pressure and decreasing temperature as a result of variations in CO₂ density. The experimental solubility has been correlated to the Sanchez–Lacombe equation of state. POLYM. ENG. SCI. 46:643–649, 2006. © 2006 Society of Plastics Engineers     

Dispersion copolymerization of acrylonitrile‐vinyl acetate in supercritical carbon dioxide

Dispersion copolymerization of acrylonitrile‐vinyl acetate (AN‐VAc) had been successfully performed in supercritical carbon dioxide (ScCO₂) with 2,2‐azobisisobutyronitrile (AIBN) as a initiator and a series of lipophilic/CO₂‐philic diblock copolymers, such as poly(styrene‐r‐acrylonitrile)‐b‐poly(1,1,2,2‐tetrahydroperfluorooctyl methacrylate) (PSAN‐b‐PFOMA), as steric stabilizers. In dispersion copolymerization, poly(acrylonitrile‐r‐vinyl acetate) (PAVAc) was emulsified in ScCO₂ effectively using PSAN‐b‐PFOMA as a stabilizer. Compared with the precipitation polymerization (absence of stabilizer), the products prepared by dispersion polymerization possessed of higher yield and higher molecular weight. In addition, the particle morphology of precipitation polymerization was irregular, but the particle morphology of dispersion polymerization was uniform spherical particles. In this study, the effects of the initial concentrations of monomer and the stabilizer and the initiator, and the reaction pressure on the yield and the molecular weight and the resulting size and particle morphology of the colloidal particles were investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5640–5648, 2006     

Encapsulation of titanium dioxide in styrene/n‐butyl acrylate copolymer by miniemulsion polymerization

Miniemulsion copolymerization of styrene/n‐butyl acrylate was investigated as a means of encapsulating hydrophilic titanium dioxide (TiO₂) in a film‐forming polymer. Dispersion studies of the TiO₂ were first carried out to determine the choice of stabilizer, its concentration, and the dispersion process conditions for obtaining stable TiO₂ particles with minimum particle size. Through screening studies of various functional stabilizers and shelf‐life stability studies at both room and polymerization temperatures, Solsperse 32,000 was selected to give relatively small and stable TiO₂ particles at 1 wt % stabilizer and with 20–25 min sonification. The subsequent encapsulation of the dispersed TiO₂ particles in styrene/n‐butyl acrylate copolymer (St/BA) via miniemulsion polymerization was carried out and compared with a control study using styrene monomer alone. The lattices resulting from the miniemulsion encapsulation polymerizations were characterized in terms of the encapsulation efficiencies (via density gradient column separations; DGC) and particle size (via dynamic light scattering). Encapsulation efficiencies revealed that complete encapsulation of all of the TiO₂ by all of the polymer was not achieved. The maximum encapsulation efficiencies were 79.1% TiO₂ inside 61.7% polystyrene and 63.6% TiO₂ inside 38.5% St/BA copolymer. As the density of the particles collected from the DGC increased from one layer to another, both the average particle size and the number of the TiO₂ particles contained in each latex particle increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3479–3486, 2006     

Kinetics and mechanism of the charge‐transfer polymerization of methyl methacrylate initiated with n‐butyl amine and carbon tetrachloride catalyzed by palladium dichloride

We studied the kinetics and mechanism of the charge‐transfer polymerization of methyl methacrylate (MMA) initiated with n‐butyl amine (BA) and carbon tetrachloride (CCl₄) catalyzed by palladium dichloride (PdCl₂ or Pd^II) in a dimethyl sulfoxide medium by using a dilatometric technique at 60°C. The rate of polymerization (R_p) was a function of [MMA], [BA], [CCl₄], and [Pd^II]. The kinetic data indicated a mechanism involving the possible participation of the charge‐transfer complex formed between the {BA–Pd^II} complex and CCl₄ or monomer in the polymerization of MMA. In the absence of either CCl₄ or BA, no polymerization of MMA was observed under these experimental conditions. R_p was inhibited by hydroquinone; this suggested a free‐radical initiation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012