四官能度过氧化物JWEB50引发的PS-b-PMMA合成与表征

引言嵌段共聚物是具有两种或两种以上不同链段的聚合物,不同链段间存在的化学键限制了聚合物的相分离程度,易形成微相分离结构[1],而嵌段共聚物能作为聚合物共混体系的相容剂,只需加入少量     

Multicomponent vapor deposition polymerization of poly(methyl methacrylate) in an axisymmetric vacuum reactor

An axisymmetric, multicomponent initiated chemical vapor deposition (i-CVD) apparatus was designed to study the vapor-phase growth of glassy poly(methyl methacrylate) (PMMA) films. Preheated monomer (methyl methacrylate) and initiator (t-butyl peroxide) vapors were metered into a pressure-controlled reaction chamber. Inside the chamber, gases pass through a high-temperature hot-zone where primary free radicals are formed. The gas mixture then condenses and polymerizes on a back-cooled target substrate. Key reactor operating parameters were systematically varied to understand film growth kinetics. These include the hot-zone temperature, reactor base-pressure, substrate temperature, and the monomer/initiator molar feed ratio. Polymer deposition requires good thermal contact between feed gases and the hot-zone. Packed with glass beads, the hot-zone reactor resulted in more efficient initiation and film growth. Experiments also show that polymer deposition rate is limited by thermal initiation of primary free radicals, transport of primary free radicals to the target substrate, and by monomer adsorption. Size exclusion chromatography of deposited polymers is used to relate molecular weight to the monomer-to-initiator feed ratio. The addition of a third vapor component, 1-butanol, was also found to affect polymer molecular weight.     

Observation for mechanical property variations of single polymer particles

Monodisperse polymer particles were prepared via conventional microsuspension polymerization or one‐step seeded polymerization, using 1,6‐hexanedioldiacrylate or its mixture with ethylene glycol dimethacrylate (EGDMA) as crosslinking monomer and poly(methyl methacrylate) synthesized by soap‐free polymerization as seed particles. For the study, the effects of the ratio of the absorbed monomer or monomer mixture to the seed polymer particles (swelling ratio), the ratio of EGDMA in absorbed monomer mixture, the dosage of initiator, polymer particle structure, and the electroless Ni plating on the mechanical properties of polymer particles, such as recovery rate, K‐values, breaking strength, and breaking displacement were investigated using micro compression test. It was observed that monomer swelling ratio influenced only on breaking strength, whereas EGDMA ratio in monomer mixture, dosage of initiator, polymer structure and electroless Ni plating did on both K‐values and breaking strength. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis of chitosan‐modified poly(methyl methacrylate) by emulsion polymerization

Emulsion polymerization of methyl methacrylate (MMA) in the presence of chitosan was studied and a reaction mechanism was proposed. It was proved in the companion article that potassium persulfate (KPS) free radicals can degrade chitosan chains into chain free radicals. Therefore, it is possible to produce a chitosan copolymer when the monomer and the KPS initiator are added into the chitosan solution. According to the proposed mechanism, concentrations of different species such as the initiator, total free radicals, and degraded chitosan chain were calculated with the reaction time. All the results agreed with the experimental observation. The results showed that the polymerization rate varied with 0.83‐ and 0.82‐order of the total free‐radical concentration and chitosan repeating unit concentration, respectively. It was also verified that chitosan played multiple roles in the reaction system. If the monomer was added into the chitosan solution before the addition of KPS, chitosan served mainly as a surfactant. Consequently, the polymer particle number was increased with the chitosan addition and so was the polymerization rate. However, if the monomer was added into the solution where the chitosan was already degraded by KPS, the polymerization rate was decreased with the predegradation time of chitosan. In both cases, the final polymer particles consisted of the poly(methyl methacrylate) (PMMA) homopolymer and the chitosan‐PMMA copolymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3047–3056, 2002     

Chain transfer of vegetable oil macromonomers in acrylic solution copolymerization

The use of vegetable oil macromonomers (VOMMs) as comonomers in emulsion polymerization enables good film coalescence without the use of solvents that constitute volatile organic compounds (VOCs). VOMMs are derived from renewable resources and offer the potential of post‐application crosslinking via auto‐oxidation. However, chain transfer reactions of VOMMs with initiator and/or polymer radicals during emulsion polymerization reduce the amount of allylic hydrogen atoms available for primary auto‐oxidation during drying. Vegetable oils and derivatives were reacted with butyl acrylate and methyl methacrylate via solution polymerization, and the polymerization was monitored using in situ infrared spectroscopy to determine the extent of chain transfer. ¹H NMR spectroscopy was used to determine the loci of chain transfer and the molecular weight characteristics of the polymers were characterized by SEC. Solution polymerization was utilized because this limited temperature fluctuations and insolubility of the polymer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Crosslinking kinetics in emulsion polymerization

Network formation in free-radical polymerization is investigated both from experimental and theoretical points of view. In a bulk free-radical crosslinking copolymerization, the radical concentration increases significantly due to a decrease in the bimolecular termination rate. Some fraction of radicals is trapped during the course of network formation, and the reactivity of the radicals in liquid state is completely different from that in solid state (trapped radicals) in terms of both propagation and termination. In emulsion crosslinking polymerization, the crosslinking density tends to be fairly high even from the start of the polymerization. The crosslinking density development is substantially different from that in bulk and solution polymerizations, in which the crosslinking density increases with time, at least in the earlier stages of polymerization. Due to the elastic contribution of free energy change, the monomer concentration in the polymer particles is lower than for linear emulsion polymerizations as long as the monomer droplets exist, resulting in an enhanced tendency toward crosslinking reactions.     

E.s.r. study of radical polymerization of pentaerythrityl monoacetal dimethacrylate in polystyrene matrix at high pressure

The e.s.r. spectrum of free radicals formed during polymerization of a bifunctional monomer of pentaerythrityl monoacetal dimethacrylate by thermal decomposition of benzoyl peroxide in a polystyrene matrix at 700 MPa is studied. Formation of propagating radicals of cyclopolymerization and crosslinking polymerization is discussed.     

Mechanistic investigation of the simultaneous addition and free-radical polymerization in batch miniemulsion droplets: Monte Carlo simulation versus experimental data in polyurethane/acrylic systems

A detailed kinetic Monte Carlo simulation was used to predict the characteristics of the batch miniemulsion polymerization of an isocyanate and an acrylic monomer mixture that contains a hydroxyl functional monomer (HEMA). The simulation takes into account the simultaneous polyaddition of the polyurethane prepolymer with the hydroxyl group of HEMA and the free radical polymerization of the acrylic monomers and all reactions in aqueous and polymer particle phases. The model has been assessed by batch miniemulsion polymerizations carried out using an aliphatic isocyanate prepolymer, n-butyl acrylate, 2-hydroxyethyl methacrylate monomers and potassium persulfate as an initiator. It was found that partitioning of water had a significant effect on both kinetics and microstructure of the resulting polymer. Evolution of different species of PU prepolymer produced in the reaction and the sol and gel fractions revealed that the terminal pendent double bond of the HEMA in polymer chains has significantly lower reactivity than that of the HEMA free monomer. Detailed information on gel microstructure has been derived in the model by both distribution of molecular weight between crosslinking points in acrylic chains and distribution of chain extension of PU prepolymers. These crosslinking density distributions can be related to mechanical and adhesive properties of the polymer.     

Experimental study of emulsion polymerization with crosslinking

Herein is reported the results of an extensive experimental investigation of the kinetics of emulsion polymerization as affected by crosslinking in the polymer particles. The model monomer system, methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA), was chosen for this study due to its earlier comprehensive investigation in bulk polymerization. Standard recipes with sodium dodecylsulfate (SDS) as anionic emulsifier and potassium persulfate (KPS) as initiator were used for the batch emulsion polymerizations. Results, which clearly show the effect of crosslinking on the kinetics, are discussed in detail. These include swellability of polymer particles by monomer; polymer particle nucleation rates, below and above the critical micelle concentration (CMC); average number of radicals per particle; and gel-sol levels. It was found advantageous to use electron spin resonance (ESR) to follow radical concentrations during crosslinking in polymer particles. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 935–957, 1997     

Polymerization of methyl methacrylate at high temperature with 1‐butanethiol as chain transfer agent

The free‐radical polymerization of methyl methacrylate (MMA) at high temperature (120 to 180°C) has been studied in the presence of di‐tertiobutyle peroxide as an initiator and 1‐butanethiol as a chain transfer agent. No solvent was used, and the polymerization was run to high monomer conversion. Based on the experimental data collected with a dilatometric reactor, the features of the reaction have been pointed out. Working at high temperature with a chain transfer agent proved efficient to reduce the intensity of the gel effect and control the molecular weight obtained. At a temperature up to 170°C, however, the burn‐out of the initiator limits the final conversion, and the increase of the polymerization rate during the gel effect has been more difficult to detect and quantify. An empirical expression of the termination rate constant has been adopted to describe the autoacceleration and predict the conversion versus time curves and the average molecular weight of the polymer obtained. The mathematical model includes two adjustable parameters that have been determined as a function of the temperature and the initial concentration of the chain transfer agent. The agreement between the predicted and experimental data on conversion and molecular weight was good, while the polydispersity index was often underestimated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1589–1599, 1999     

Kinetics of radical polymerization of glycidyl methacrylate initiated by multi‐site phase transfer catalyst–potassium peroxydisulfate in two‐phase system

The kinetics of radical polymerization of glycidyl methacrylate, initiated by the free radicals formed in situ in the multi‐site phase transfer catalyst (PTC), 1,1,2,2‐tetramethyl‐1‐benzyl‐2‐n‐propylethylene‐1,2‐diammonium bromide chloride–potassium peroxydisulfate system was studied in an aqueous–organic two‐phase media at 60°C ± 1°C under inert and unstirred condition. The rate of polymerization (R_p) was determined at various concentrations of the monomer, initiator, catalyst, and volume fraction of aqueous phase. The effect of acid, ionic strength, and water‐immiscible organic solvents on the R_p was examined. The temperature dependence of the rate was studied, and activation parameters were calculated. R_p increased with an increase in the concentrations of monomer, initiator, multi‐site PTC, and increase in the polarity of solvent and temperature. The order with respect to monomer, initiator, and multi‐site PTC was found to be 0.50. A feasible free‐radical mechanism consistent with the experimental data has been proposed, and its significance was discussed. The synthesized polymer was confirmed by Fourier transform infrared spectral analysis. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

PVC modification through polymerization of a monomer absorbed in porous suspension‐type PVC particles

In‐situ polymerization is the polymerization of one monomer in the presence of another polymer. It can be performed by sequential emulsion polymerization, or by reactions in the melt, in the solid phase, or in solution. The current report describes two methods to obtain poly(vinyl chloride) (PVC) modification through polymerization of a monomer absorbed in commercial porous suspension‐type PVC particles. The generated modified PVC products differ significantly in their structure and properties. The first approach includes absorption of a monomer/peroxide solution within porous suspension‐type PVC particles, followed by polymerization/crosslinking in the solid state at 80°C in an aqueous stabilizer‐free dispersion. The monomer/crosslinker pairs selected are styrene/DVB (divinyl benzene), methylmethacrylate/EGDMA (ethylene glycol dimethacrylate), butyl acrylate/EGDMA, and ethylhexyl acrylate/EGDMA. The influence of composition and nature of the polymerizing/crosslinking constituents on the modified PVC particle structure was studied by microscopy methods, porosity measurements, and dynamic mechanical behavior (DMTA). The level of molecular grafting between PVC and the modifying polymer was determined by solvent extraction experiments. This work shows that the different monomers used represent distinct courses of monomer transport through the PVC particles. The characteristics of the modified PVC particle indicate that the polymerization/crosslinking process occurs in both the PVC bulk, i.e., within the walls constituting a particle, and in the PVC pores. No indication of chemical intermolecular interaction within the modified PVC particles was found. In the second approach, a solution of monomer, initiator, and a crosslinking agent is absorbed in commercial suspension‐type porous PVC particles, thus forming a dry blend. This dry blend is subsequently reactively polymerized in a twin‐screw extruder at an elevated temperature, 180°C, in the molten state. The properties of the reactively extruded PVC/PMMA blends are compared with those of physical blends at similar compositions. Owing to the high polymerization temperature, short‐chain polymers are formed in the reactive polymerization process. Reactively extruded PVC/PMMA blends are transparent, form single‐phase morphology, have a single T_g, and show mechanical properties comparable with those of the neat PVC. The resulting reactively extruded PVC/PMMA blends have high compatibility. J. Vinyl Addit. Technol. 10:109–120, 2004. © 2004 Society of Plastics Engineers.     

Structural control in radical polymerization with 1,1 diphenylethylene: 2. Behavior of MMA-DPE copolymer in radical polymerization

Copolymers of 1,1-diphenylethylene (DPE) behave in a very special way in radical polymerization. Particularly, the behavior of MMA-DPE copolymers in radical polymerization is investigated. The results reveal that the semiquinoid structure of the precursor polymer identified in a previous contribution is activated by the attack of free radicals and thus, in a second stage polymerization with a second monomer, block copolymers are formed. The block copolymer yield depends strongly on the ratio between the amount of DPE-containing precursor polymer and the initiator and monomer concentration used in the second stage. The mechanism proposed is able to explain at least qualitatively all experimental results including the restriction of this mode of control of radical polymerization to the formation of diblock copolymers only.     

Preparation of polystyrene/poly(methyl methacrylate) core‐shell composite particles by suspension‐emulsion combined polymerization

Suspension‐emulsion combined polymerization process, in which methyl methacrylate (MMA) emulsion polymerization constituents (EPC) were drop wise added to styrene (St) suspension polymerization system, was applied to prepare polystyrene/poly(methyl methacrylate) (PS/PMMA) composite particles. The influences of the feeding condition and the composition of EPC on the particle feature of the resulting composite polymer particles were investigated. It was found that PS/PMMA core‐shell composite particles with a narrow particle size distribution and a great size would be formed when the EPC was added at the viscous energy dominated particle formation stage of St suspension polymerization with a suitable feeding rate, whereas St‐MMA copolymer particles or PS/PMMA composite particles with imperfect core‐shell structure would be formed when the EPC was added at the earlier or later stage of St suspension polymerization, respectively. It was also showed that the EPC composition affected the composite particles formation process. The individual latex particles would exist in the final product when the concentrations of MMA monomer, sodium dodecyl sulfate emulsifier, and potassium persulfate initiator were great in the EPC. Considering the feature of St suspension polymerization and the morphology of PS/PMMA composite particles, the formation mechanism of PS/PMMA particles with core‐shell structure was proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Bulk polymerization of methyl methacrylate initiated by high intensity ultrasonic irradiation and ESR study

High‐intensity ultrasound was used to initiate the bulk polymerization of methyl methacrylate. The polymerization rate varied with the sonication time, the intensity of the ultrasound, and the initiator concentration of poly (methyl methacrylate) in the monomer. Electron spin resonance (ESR) spectra, obtained by the spin trapping technique, testified that free radicals were produced during the sonication process, and the concentration of radicals also changed with the sonication condition. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1731–1735, 2002     

Atom transfer radical polymerization of methyl methacrylate induced by an initiator derived from an ionic liquid

An ionic liquid, 1‐(2‐bromoisobutyryloxyethyl)‐3‐methylimidazolium hexafluorophosphate, was synthesized to act as the initiator of the atom transfer radical polymerization of methyl methacrylate (MMA). By a combination with CuBr and pentamethyldiethylenetriamine, the ionic liquid initiated the free radical polymerization of MMA to proceed in a controlled way over a wide temperature range of 0 to 60 °C. The number‐average molecular weight of the poly(methyl methacrylate) (PMMA) increased with monomer conversion and the polydispersity was relatively narrow. End‐group analysis by proton NMR indicated the presence of the initiator fragments at the ends of the polymer main chain. Lowering the reaction temperature had the result of increasing the content of rr triads. The glass transition temperature was higher for PMMA obtained at lower temperature than at higher temperature. The solubility of the PMMA in methanol increased with the incorporation of imidazolium groups in the polymer. Copyright © 2006 Society of Chemical Industry     

Synthesis and properties of oil absorption resins filled with polybutadiene

Polybutadiene (PB) is used to fill an oil absorption resin as a physical crosslinker to construct a kind of 3‐dimensional network with a high degree crosslinking and low crosslink density. A series of acrylic resin particles with various compositions are prepared by suspension polymerization, using benzoyl peroxide (BPO) as an initiator and ethylene glycol dimethacrylate (EGDMA) as a chemical crosslinker. The effects of the polymerization temperature, initiator concentration, monomer feed ratio, and chemical and physical crosslinker concentrations on the oil absorbency and gel fraction (degree of crosslinking) are studied. The recipe and operation conditions are optimized as follows: a mass ratio of 3:1 for styrene (St)/dodecyl methacrylate or St/butyl acrylate, 0.5 wt % BPO, and 80°C for 7–8 h. The effect of the physical crosslinker (PB) concentration is complex. The oil absorbency increases with increasing PB at lower EGDMA concentrations. However, under this same condition, particles cannot be formed if the PB concentration is higher than a certain value. By contrast, there is an optimum PB concentration when the EGDMA concentration is higher. The oil absorption speed is also investigated. The presence of PB can speed up absorption. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3309–3314, 2003     

Studies on the graft polymerizations of styrene and methyl methacrylate to hydroxyl terminated polybutadiene

Hydroxyl terminated Polybutadiene (HTPB) was grafted with styrene (St) or methyl methacrylate (MMA) by free radical solution polymerization. The graft copolymerizations were conducted in benzene at 70 °C. The initiators used were benzoyl peroxide (BPO) and azobis-isobutyronitrile (AIBN). The microstructures of theobtained graft copolymers were characterized by¹³C NMR measurement and the DEPT technique, as well as by IR spectrometer. The mechanism of grafting reactions was determined from the microstructures of derived graft copolymers. It showed that graft copolymer resulted when BPO was used as initiator of the vinyl monomer polymerization, but not with AIBN. It appeared that the reaction leading to graft formation was direct attack of oligomeric styrene radicals or double bonds of the HTPB. Whereas the graft copolymerization of MMA to HTPB was the same as that suggested in the literature i.e., by a hydrogen abstract reaction.     

Block copolymers obtained by free-radical mechanism. I. Methyl methacrylate and styrene

Block copolymers were synthesized using styrene and methyl methacrylate as the monomers and a multifunctional initiator, di-t-butyl 4,4′-azobis(4-cyanoperoxyvalerate). The unique feature of this sequential initiator is the fact that the formation of the free radicals can be achieved thermally and/or by a redox system at different stages. The polymerizations for the formation of the block copolymer were carried out in two stages. First, a polymeric initiator was synthesized, which was then used in the second stage to initiate the polymerization of the second monomer. Styrene and methyl methacrylate were used as the comonomers. Selective solvent fractionation was used for the separation of the block from the homopolymers. The separation technique was found to be efficient, giving pure block copolymers which could subsequently be characterized by GPC, NMR, IR, and EM techniques.     

Radical thermo‐ and sonopolymerization of methyl methacrylate initiated by iodobenzene 1,1‐diacetate

The efficiency of iodobenzene 1,1‐diacetate or (diacetoxyiodo)benzene (DAIB) as a thermo‐ and sono‐initiator of methyl methacrylate (MMA) in radical bulk polymerization is tested. The polymerization kinetics and molecular‐mass characteristics support an assumption for a combined polymerization mechanism including a classical bimolecular termination with chain transfer reaction and iniferter quasi‐living polymerization. In addition to the equilibrium formation and degradation of the ‘dormant’ polymer ends, other possible decomposition reactions of the hypervalent iodine bond are the probable reason for the deviation of this polymerization from the iniferter polymerization mechanism. These reactions bear some similarity to the two‐step addition–fragmentation chain transfer mechanism of controlled radical polymerization. The application of the poly(MMA) obtained as a macroinitiator is evidence of ‘dormant’ chain end formation. © 2001 Society of Chemical Industry