Optical gradient materials produced via low‐temperature isothermal frontal polymerization

Using a newly developed low‐temperature frontal polymerization technique, poly(methyl methacrylate) (PMMA) matrices were prepared with nonuniform distributions of organic nonlinear optical dyes, with potential use as optical limiters. This technique affords lower temperature conditions than have been used before. A PMMA tube was filled with a dye, the initiator tert‐butyl peroxide, and methyl methacrylate (MMA). Curing at 4°C resulted in a radial gradient of dye. An axial dye gradient was observed when MMA was overlaid and polymerization effected from a dye‐doped PMMA seed using tricaprylmethyl ammonium persulfate as the initiator. In both cases, polymerization reactions were observed as a result of isothermal frontal polymerization with the subsequent formation of a nonlinear concentration distribution of the optical dye dopants. Low temperatures are desirable to eliminate thermal and photothermal degradation of temperature‐sensitive dyes during the polymerization. The preparation of long polymer rods with organic dye gradients on the scale of several centimeters can also be realized with the use of low‐temperature polymerization and the gradients controlled by the concentration of initiator. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 686–691, 2001     

Photoinduced cationic frontal polymerization of epoxy–carbon fibre composites

UV‐activated frontal polymerization was exploited for the preparation of epoxy–carbon fibre composites. The curing process was investigated showing the frontal behaviour, and the final properties of UV‐cured composites were compared with those of the same composites obtained by thermal curing in the presence of amine as hardener. The best curing formulations were designed, defining the photoinitiator‐to‐thermal initiator ratio, which was 1.5:1.5. It was observed that the presence of the carbon fibres induced an acceleration of the front velocity. By comparing the thermomechanical properties of the thermally cured composite and the same composite crosslinked using the frontal process, we could observe that the latter showed higher T_g value and lower σ_f. This was attributed to the formation of a different polymeric network structure. © 2019 Society of Chemical Industry     

Study on spatial–temporal kinetics of photo‐initiated frontal polymerization in stacked reaction cells

The spatial–temporal kinetics for photo‐initiated frontal polymerization(PFP) of isobornyl acrylate with 2,4,6‐trimethylbenzoyldiphenyl phosphine oxide (TPO) as photobleaching initiator was studied experimentally in stacked reaction cells. FTIR and NMR spectroscopy were employed to measure the polymerization conversion, which is dependent on the exposure time, sample depth, light intensity and photo‐initiator concentration. The experimental results are consistent with the theoretical model prediction and show that prolonged irradiation time, higher light intensity and lower photo‐initiator concentration are favorable in enhancing the advance of the polymerization front. The depth‐resolved GPC analysis shows that the average molecular weight of the PFP product dramatically increases with sample depth, while the molecular weight polydispersity reduces steadily with increase in sample depth. Copyright © 2006 Society of Chemical Industry     

前端聚合的研究进展

前端聚合因具有简易、节能、反应速度快和独特的产物形貌等优点而受到越来越广泛的关注。本论文将前端聚合按照聚合方法分为3类：热前端聚合,光前端聚合和等温前端聚合,讨论了前端聚合的组成,综述了前端聚合的应用,前端聚合在功能材料、有机无机纳米复合材料和工业生产上将会得到广泛的应用。     

Preparation of functionally gradient materials via frontal polymerization

Ascending frontal polymerization in a body with a moving boundary was accomplished experimentally. This process was shown to be a steady‐state process within a certain range of the parameters. Temperature profiles of the front were recorded. This new method gives an excellent opportunity to prepare functionally gradient materials because composition of a monomer feedstream can be varied in a programmable manner. Polymer samples with hyperbolic gradients of optical dye concentration were manufactured at ambient pressure and temperature. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2398–2404, 2000     

Frontal copolymerization of 2‐hydroxyethyl methacrylate and ethylene glycol dimethacrylate without porogen: comparison with suspension polymerization

Networked, crosslinked poly[(2‐hydroxyethyl methacrylate)‐co‐(ethylene glycol dimethacrylate)] (HEMA‐EGDM) was synthesized by frontal polymerization (FP) using azobisisobutyronitrile as initiator. HEMA‐EGDM copolymers of similar composition were also synthesized by suspension polymerization. The two sets of copolymers were characterized for functional groups (IR), pore volume (mercury intrusion porosimetry), surface area (nitrogen adsorption) and morphology (scanning electron microscopy). FP‐generated polymeric network structures had higher internal pore volumes and surface areas but their surface morphologies were inferior to those of copolymers synthesized by suspension polymerization. Copyright © 2004 Society of Chemical Industry     

Plasma‐induced,solid‐state polymerization of N‐isopropylacrylamide

The radio‐frequency plasma‐initiated polymerization of N‐isopropylacrylamide (NIPAM) in the solid state was performed. The isolated linear polymer was characterized by ¹³C‐NMR, ¹H‐NMR, and Fourier transform infrared spectroscopy, and the effects of selected operational plasma parameters (discharge power and time) on the conversion rates were studied. Reversible transitions at the volume‐phase‐transition temperatures of the swelled poly(N‐isopropylacrylamide) hydrogels were investigated by differential scanning calorimetry. The surface morphologies before and after plasma treatment were followed by scanning electron microscopy. With the obtained X‐ray diffraction results, we propose a solid‐state plasma polymerization mechanism for the NIPAM. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Cure‐on‐demand wood adhesive based on the frontal polymerization of acrylates

We demonstrated for the first time a cure‐on‐demand wood adhesive using thermal frontal polymerization with Southern Pine wood. Monomer structure, initiator loading, and filler loading all had an impact on the strength of the adhesive and the cure‐on‐demand ability. More flexible, ethoxylated monomers produced stronger adhesives; though, the ethoxylate groups reduce the ability of the system to be polymerized frontally. Addition of a highly reactive comonomer (acrylic acid) to increase molecular weight between crosslinks along with the ethoxylated triacrylate increased the propensity for frontal polymerization and made a tougher polymer. Increasing initiator loading could help ensure front propagation, but a maximum initiator loading was reached where the gaseous byproducts of the peroxide initiator made the network highly porous and thus lacking strength. Fillers such as kaolin and sawdust helped overcome decreases in strength at high initiator loadings. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44064.     

Solid‐state polymerization of bisphenol A polycarbonate with a spray‐crystallizing method

A novel crystallization method for the production of high‐molecular‐weight bisphenol A polycarbonate by solid‐state polymerization is suggested. In this method, a low‐molecular‐weight polycarbonate prepolymer is dissolved in a solvent and then partially crystallized with a novel spray‐crystallizing method to prepare crystallized polycarbonate particles having a very uniform and porous structure with a narrow melting region. As a result, during solid‐state polymerization, the phenol byproduct can be easily removed from the polymerizing porous polycarbonate particles, and the polymerization rate is dramatically increased. In particular, the effects of the crystallization methods on secondary crystallization during solid‐state polymerization and the melting behavior have been investigated with differential scanning calorimetry studies. The final product, a high‐molecular‐weight polycarbonate, displays a very narrow molecular weight distribution and uniform physical properties. A simultaneous process and an adequate reactor design for spray crystallization and solid‐state polymerization are also suggested. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Frontal polymerization preparation of poly(acrylamide‐co‐acrylic acid)/activated carbon composite hydrogels for dye removal

A series of poly(acrylic acid‐co‐acrylamide) (PAA)/activated carbon (AC) composite hydrogels were rapidly prepared via frontal polymerization (FP). It was found that an increase in the concentration of AC caused an increase in the front velocity (V_f) and the highest front temperature (T_max). It may be attributed to that AC particles could increase the liquid viscosity of reaction mixture and remain the reaction heat during FP. The Fourier transform infrared and scanning electron microscopy (SEM) confirmed that AC particles had entered the hydrogel network, and many spherical AC particles with an average diameter of 0.5–1 μm had been dispersed homogeneously in the PAA hydrogel matrix. The swelling behavior showed that the equilibrium swelling values of hydrogels increased when the concentration of AC particles increased. Adsorption studies showed that incorporation of AC particles into PAA hydrogel matrix could increase the sites of interaction between the hydrogels and crystal violet molecules and result in an increase of adsorption capacities of hydrogels toward dyes. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Polystyrene‐block‐polylactide obtained by the combination of atom transfer radical polymerization and ring‐opening polymerization with a commercial dual initiator

A polystyrene (PS)‐b‐polylactide (PLA) block copolymer was prepared from the combination of atom transfer radical polymerization and ring‐opening polymerization with commercially available 2,2,2‐tribromoethanol as a dual initiator in a sequential two‐step procedure. Hydroxyl‐terminated polystyrene (PS‐OH)s with various molecular weights were first prepared with polydispersity indices lower than 1.3; these provided valuable macroinitiators for the polymerization of D,L ‐lactide. A block copolymer with a composition allowing the formation of hexagonally packed PLA cylinders in a PS matrix was then obtained. The PS‐b‐PLA thin films revealed, after vapor solvent annealing, a hexagonally packed organization of the PLA cylinders, which was oriented perpendicularly to the surface of the film. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of accelerated ageing on methacrylate‐based denture resins heterogeneity as viewed by ESR‐spin‐probe method

The electron‐spin‐resonance (ESR) spin‐probe method, was used to study the heterogeneity of denture resins based on poly(methyl methacrylate). Results for three resins processed by microwave energy, conventional curing and cold curing (depending on the curing procedure and exposed to ageing in various environmental conditions) were compared. All three cured resins were stored over the same time (1200 h) in distilled water at ambient temperature and in artificial saliva at 348 K. The temperature‐dependent ESR spectra of a spin probe dispersed in the denture resins are analyzed in terms of line‐shapes and line‐widths. The appearance of two spectral components was taken as an indication of resin heterogeneity. The results reveal that the cold‐cured resin has a lower local density in comparison with microwave and conventionally cured resin. The amount of residual monomer also contributes to the local motion of polymer segments. The change of denture resins exposed to ageing is influenced both by the structure of the original resin and the ageing conditions. Restricted motion of a spin probe incorporated into the acrylic resins exposed to accelerated ageing suggests additional crosslinking of polymer chains. The differences are observed for all the investigated resins, but the highest change is observed with the cold‐cured resin. The ESR results are accompanied by T_g and T_m measurements. Copyright © 2005 Society of Chemical Industry     

Gas‐phase‐assisted surface polymerization of methyl methacrylate with Fe(0)/TsCl initiator system

To obtain a high polymer coated Fe(0) surface, gas‐phase‐assisted surface polymerization (GASP) of methyl methacrylate (MMA) was investigated using a zero‐valent iron (Fe(0))/p‐toluene sulfonylchloride (TsCl) initiator system, resulting in successful high polymer production on the solid surface. GASP was found to be initiated by radical species that might have been generated via redox reactions with Fe(0), Fe(II), Fe(III), and TsCl. From ¹H‐NMR analysis, the p‐toluene sulfonyl group was found at one end of the polymer chain. The molecular weight of obtained PMMA drastically decreased with increase in the composition ratio of Fe(0) in the initiator system, and increased with increase in polymer yield. From the results, it was assumed that the physically controlled polymerization of MMA proceeded by immobilized active species at gas–solid interfaces. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1879–1886, 2007     

Melt polymerization of bisphenol‐A and diphenyl carbonate in a semibatch reactor

The effect of thermodynamic phase equilibrium on the kinetics of semibatch melt polycondensation of bisphenol‐A and diphenyl carbonate was studied for the synthesis of polycarbonate. In the melt‐polymerization process, a partial loss of diphenyl carbonate occurs as the reaction by‐product phenol is removed from the reactor. To obtain a high molecular weight polymer under high temperature and low‐pressure conditions, a stoichiometric mol ratio of the two reactive end groups needs to be maintained during the polymerization. In this work, vapor–liquid equilibrium data for a binary mixture of phenol and diphenyl carbonate are reported and they are used in conjunction with the Wilson equation to calculate the exact amounts of diphenyl carbonate and phenol returned from a reflux column to the reactor. A good agreement between the reactor model simulations and the experimental polymerization data was obtained. It was also observed that diphenyl carbonate is quickly consumed during the early stage of polymerization and the fraction of evaporated diphenyl carbonate refluxed to the reactor is essentially constant during this period. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1253–1266, 2001     

Multi‐responsive microgel of a water‐soluble monomer via emulsion polymerization

Microgel of a water‐soluble monomer [2‐(N‐morpholino)ethyl methacrylate (MEMA)] was successfully prepared in aqueous media via emulsion polymerization by using a novel water‐soluble block copolymer as stabilizer. Characterization studies confirmed monodisperse spherical morphologies of microgels with a diameter of 280 nm at neutral pH. These microgels exhibited multi‐responsive behavior by responding solution pH, temperature, ionic strength, type of dispersing media, and magnetic particles. It swells well at low pH (<6.0) and at low temperature, but shrinks above pH 6.0, or even more shrinks with salt addition at neutral and basic conditions. In addition, the hydrodynamic diameter of PMEMA microgel was decreased gradually at basic and neutral pH when solution temperature was increased up to the lower critical solution temperature of PMEMA (LCST, 35°C), but microgel diameter did not change much above LCST. Multi‐responsive behavior of PMEMA microgel was investigated by using dynamic light scattering, UV‐Vis spectrophotometer and zeta potentiometer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42072.     

Synthesis of water‐soluble polyphenol‐graft‐poly(ethylene oxide) copolymers via enzymatic polymerization and anionic polymerization

Water‐soluble polyphenol‐graft‐poly(ethylene oxide) (PPH‐g‐PEO) copolymers were prepared using grafting‐through methodology. Polyphenol chains were synthesized via enzymatic polymerization of phenols, and the graft chains were synthesized via living anionic polymerization of ethylene oxides. The polymers were characterized using gel permeation chromatography, static light scattering and ¹H NMR, infrared and ultraviolet spectroscopies. The PPH‐g‐PEO graft copolymers are soluble in several common solvents, such as water, ethanol, N,N‐dimethylformamide, tetrahydrofuran and methylene dichloride. The solubility of the PPH‐g‐PEO graft copolymers is improved significantly compared with that of polyphenol. Copyright © 2009 Society of Chemical Industry     

Study on microemulsion polymerization of N‐butyl maleimide

By using sodium dodecyl sulfate (SDS) as an emulsifier, polymerization of N‐butyl maleimide (NBMI) was carried out in ternary oil‐in‐water microemulsion, initiated with potassium persulfate (KPS). The kinetics of microemulsion polymerization were measured by dilatometry. The effects of initiator concentration, polymerization temperature, monomer concentration, and emulsifier concentration on polymerization kinetics were investigated. On this basis, the polymerization kinetics were discussed. The experiment result showed that the microemulsion polymerization kinetics of N‐butyl maleimide were almost consistent with the prediction of the Smith‐Ewart theory in conventional emulsion polymerization, except that the emulsifier showed a special effect on polymerization. At the same time, the polymer was characterized by IR, ¹H‐NMR, DSC, and TGA. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 805–809, 2000     

Numerical simulation of the spin‐draw process of poly(ethylene terephthalate) fibers

Numerical simulation for the calculation of the profile developments of the spin‐draw process in the melt spinning of poly(ethylene terephthalate) was performed. Both spinning and drawing profiles were analyzed and included the structure development of birefringence and crystallinity in the draw line. By applying a simple model describing the continuous drawing process, we made it possible to simulate the spin‐draw process. The strain rate of the spinline had a broad distribution, and that of the draw line had a narrower peak. The calculated birefringence ranged from 0.176 to 0.192 and the crystallinity ranged from 0.37 to 0.44 with draw ratio. The birefringence profile had a similar pattern as the stress profile, and the crystallinity gently increased along the draw line more than the birefringence did. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2522–2527, 2007     

High‐temperature and high‐pressure ethylene polymerization using a cationic activated metallocene catalytic system

BACKGROUND: Normally, olefin polymerization via metallocene‐based catalysis occurs under mild conditions. However, most technology developed for polyolefin production is designed for more severe temperature and pressure processes. Attaining more thermally stable metallocene systems for industrial applications is an important challenge for researchers. RESULTS: A systematic study of ethylene homopolymerization at higher temperatures and pressures, employing the ternary system Ph₂C(Cp)(Flu)ZrCl₂/PhNHMe₂B(C₆F₅)₄/(i‐Bu)₃Al, is presented The optimal activity for this system is achieved with a Zr/B/Al molar ratio of 1/6/250 and a temperatures of around 130 °C. However, the amount of activator strongly affects the molecular weight and the polydispersity of the polymers produced. Polyethylene produced with Zr/B/Al molar ratios between 1/2/250 and 1/6/250 show no significant difference in their temperature of fusion (T_m) and their crystallinity (X_c). In contrast, in the presence of activator amounts higher than 1/6/250, both the temperature of fusion and polymer crystallinity undergo a steep decrease. All polymers presented lamellar morphology when the activator was present, and an amorphous aspect when the activator was not employed. CONCLUSION: The presence of the activator is essential for thermal stabilization of the catalytic system. Variation of the Zr/B/Al ratio leads to modifications of the catalytic activity as well as to the properties of the polymers synthesized. Copyright © 2008 Society of Chemical Industry     

Ring‐opening polymerization of ε‐caprolactone with a divalent samarium bis(phosphido) complex

The ring‐opening polymerization of ε‐caprolactone initiated with a divalent samarium bis(phosphido) complex [Sm(PPh₂)₂] is reported. The polymerization proceeded under mild reaction conditions and resulted in polyesters with number‐average molecular weights of 8.2 × 10³ to 12.5 × 10³. The yield and molecular weight of poly(ε‐caprolactone)s were dependent on the experimental parameters, such as the monomer/initiator molar ratio, the monomer concentration, the reaction temperature, and the polymerization time. The obtained polymers were characterized with Fourier transform infrared, NMR, gel permeation chromatography, and differential scanning calorimetry. On the basis of an end‐group analysis of low‐molecular‐weight polymers by NMR spectroscopy, a coordination–insertion mechanism is proposed for the polymerization. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1558–1564, 2005