Modification of Cross-Linked Rubber Particles by Free Radical Polymerization

The synthesis of polystyrene chains covalently bound to the surface of cross-linked rubber particles from recycled tires (ground tire rubber, GTR) was investigated via free radical polymerization in situ by using azobisisobutyronitrile (AIBN) and dibenzoyl peroxide (BPO) as initiators. Indeed, the graft polymerization provides a significant route to modify the physical and chemical properties of these particles allowing to improve their compatibility with other polymers. Polymerization reactions were carried out in bulk by changing the styrene/GTR ratio as well as the amount of free radical initiator. Appreciable amounts of polystyrene (PS) were grafted on GTR when BPO was used as confirmed by particle characterizations.     

Free radical ring‐opening polymerization of cyclic allylic sulfides: Liquid monomers with low polymerization volume shrinkage

The free radical polymerization of four methylated cyclic allylic sulfides was examined with reference to their polymerization volume shrinkage and the effect of ring size on reactivity. The compounds examined were 2‐methyl‐5‐methylene‐1,3‐dithiane ( 5 ) (solid), 2‐methyl‐6‐methylene‐1,4‐dithiepane ( 6 ) (liquid), 6‐methyl‐3‐methylene‐1,5‐dithiacyclooctane ( 7 ) (liquid), and 6,8‐dimethyl‐3‐methylene‐1,5‐dithiacyclooctane ( 8 ) (liquid). The monomers were stable materials not requiring any special handling or storage conditions. They were polymerized in bulk using thermal azobisisobutyronitrile (AIBN, VAZO88) and photochemical initiators (Ciba DAROCUR 1173) and in benzene solutions (AIBN, 70 °C). The six‐membered ring monomer 5 was unreactive whereas seven‐membered ring monomer 6 polymerized to high conversion in bulk. In addition, 6 did not polymerize in benzene solution at 70 °C at [ 6 ] = 1.25M. Eight‐membered ring monomers 7 and 8 polymerized in bulk to complete conversion with thermal and photochemical initiators to give lightly crosslinked materials. Near complete conversion to soluble polymers could be obtained in solution polymerizations in benzene. Soluble polymers were also obtained in photochemical initiated bulk polymerizations by lowering initiator concentrations or length of irradiation. The methyl substituent had no effect on which allylic carbon–sulfur bond fragmented in the ring‐opening step. The polymerization volume shrinkages of monomers 7 and 8 were 1.5 and 2.4% respectively and together with monomer 4 (1.5–2.0% shrinkage) are the best available liquid free radical ring‐opening monomers that can be polymerized in bulk at room temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 202–215, 2001     

2,3-二氰基-2,3-二苯基丁酸二乙酯引发苯乙烯的本体 聚合反应

在70～90℃对标题化合物外消旋异构体引发的苯乙烯本体聚合反应进行了研究,并与内消旋异构体、过氧化二苯甲酰和偶氮二异丁腈进行比较。结果表明,在本反应条件下,上述四种引发剂均能使聚合物分子量随反应时间的延续而增大,但C－C键引发剂对聚合物分子量及其链增长的影响远大于BPO和AIBN,这一现象应与α－氰基-α-乙氧甲酰基苄基自由基的结构特点有关。     

Surface Initiated Polymerization from Nanoparticle Surfaces

Abstract

The synthesis, characterization, and development of new nanoparticle materials have both scientific and technological significance. Surface initiated polymerization (SIP) from nanoparticle surfaces involves the growth of end‐tethered polymer brushes where the length or thickness can be more than twice the radius of gyration (Rg) compared to a free polymer in solution. Different mechanisms are possible on a variety of initiators, reaction conditions, monomers, and nanoparticles. Important differences to solution and bulk polymerization can be observed where the nanoparticles with grafted initiators behave as macroinitiators. In turn, the development of these materials will allow the preparation of thermodynamically and kinetically stable nanocomposites and colloids. Through the careful use of surface sensitive spectroscopic and microscopic techniques, much has been gained from the direct and in‐situ analysis of grafted polymers on the nanoparticles with regards to the kinetics and mechanism of the polymerization process. Parallels can be drawn to SIP on flat surfaces where surface sensitive spectroscopic and microscopic measurements are complementary to analysis methods for colloidal particles. Thus, this review surveys the different polymerization mechanisms and procedures towards forming core‐shell types of hybrid inorganic–organic polymer nanoscale materials.     

The role of initiation in the synthesis of silica/poly(methyl methacrylate) nanocomposite latex particles through emulsion polymerization

Silica/poly(methyl methacrylate) nanocomposite latex particles have been synthesized by emulsion polymerization of methyl methacrylate using a nonionic surfactant: nonylphenol poly(oxyethylene) and three different initiators, namely: 2,2′-azobis(2-amidinopropane) dihydrochloride (AIBA), potassium persulfate (KPS) and azobis(isobutyronitrile) (AIBN), being cationic, anionic and nonionic, respectively. A silica sol with an average diameter of 68 nm was used as the seed. The polymerization reaction was conducted under alkaline conditions in order to evaluate the role of the surface charge of the hydrophilic silica on the coating reaction. AIBA was found to be adsorbed on the silica surface owing to electrostatic interactions of the amidine function of the cationic initiator with the silanolate groups of the oxide surface, while the anionic and the nonionic initiators did not adsorb on silica under the same conditions. Nonetheless, whatever the nature of the initiator, polymerization took place on the silica particles as evidenced by transmission electron microscopy. The extent of interaction between the inorganic surface and the polymer particles was quantified by means of ultracentrifugation and a material balance. As much as 65% by weight of the total polymer formed was found to be present at the silica surface using AIBA, while only 40% for KPS and 25% for AIBN was found to cover the silica particles under alkaline conditions. We demonstrate that by using a cationic initiator and by controlling the pH of the suspension it is possible to significantly decrease the amount of free polymer. Coating of the silica particles took place through a kind of in situ heterocoagulation mechanism. Received: 8 December 2000 Accepted: 22 February 2001     

Synthesis of PS and PDMAEMA mixed polymer brushes on the surface of layered silicate and their application in pickering suspension polymerization

An ammonium free radical initiator was ion exchanged onto the surface of clay layers. Polystyrene (PS) and poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) mixed polymer brushes on the surface of clay layers were prepared by in situ free radical polymerization. PS colloid particles armored by clay layers with mixed polymer brushes were prepared by Pickering suspension polymerization. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the structure and morphology of the colloid particles. Clay layers on the surface of PS colloid particles can be observed. Because of the cationic nature of the PDMAEMA brushes the colloid particles have positive zeta potentials at low pH values. X‐ray photoelectron spectroscopy (XPS) was used to analyze the surface of the colloid particles. N_1s binding energy of PDMAEMA chains on the surface of clay layers was detected by XPS. The two peaks of the N_1s binding energy indicate two different nitrogen environments on the surface of clay layers. The peak with a lower binding energy is characteristic of neutral nitrogen on PDMAEMA chains, and the peak with a higher binding energy is attributed to protonated nitrogen on PDMAEMA chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5759–5769, 2007     

Synthesis of novel polymer containing selenium by radical addition polymerization of 1,4-benzenediselenol to 1,4-divinylbenzene

A novel addition polymerization of 1,4-benzenediselenol (BDSe) to 1,4-divinylbenzene (DVB) was carried out with various azo radical initiators [dimethyl 2,2′-azobisisobutyrate (DAIB), 1,1′-azobis(1-acetoxy-1-phenylethane) (AAPE), and AIBN] in toluene at 65 and 75°C under a nitrogen atmosphere. The polymerization proceded without an induction period, and pale-yellowish powder polymers were obtained in 89% yields for 75 h (DAIB), 89% yields for 24 h (AAPE), and 60% yields for 8 h (AIBN). The molecular weight (M_w) of the insoluble polymers in toluene was about 4000 (IBN) to 14,000 (DAIB or AAPE) by GPC. The polymer had an alternating structure of BDSe to DVB units by ¹H-NMR, IR analyses, and selenium contents, but the polymer contained the diselenide linkage by Raman spectroscopy. By AIBN initiator, the yield of the polymers did not increase over 60% and higher molecular weight polymer was hardly obtained. According to the model addition reaction of benzeneselenol to styrene by AIBN, it was found that AIBN was consumed by the side reaction between dimethyl-N-(2-cyano-2-propyl)ketenimine derivedAppl 11 from AIBN and benzeneselenol to give the adduct C, MH⁺ 295 by DCI MS. On the other hand, DAIB and AAPE initiators, which do not form a ketenimine intermediate, gave the polymers of higher molecular weight in a higher yield. The polymer film exhibited high refractive index (n²⁵_D = 1.81) and a reversible phase transition between a transparency and an opaque by thermal mode. © 1994 John Wiley & Sons, Inc.     

Synthesis of pH‐sensitive surfactants by the terpolymerization of methacrylic acid,methoxy poly(ethylene glycol) methacrylate,and lauryl methacrylate: Initiator effect and reactivity ratio study

For the development of pH‐sensitive surfactants to be used in water‐in‐oil fermentation, the free‐radical terpolymerization of methacrylic acid (MAA), methoxy poly(ethylene glycol) methacrylate (MPEGMA), and lauryl methacrylate (LMA), at a molar ratio of 1.0:0.04:0.76, was studied with two initiators, azobisisobutyronitrile (AIBN) and hydrogen peroxide, at different concentrations. The polymer synthesized with 0.45% AIBN as the initiator was the most promising, giving similar conversions of all three monomers throughout the 10‐h polymerization. The subsequent study on AIBN‐initiated systems indicated that MPEGMA caused an increase‐then‐decrease profile of the MAA conversion with a plateau around an ethylene glycol/MAA ratio of 1–2. This observation was fairly consistent with the well‐known type II template polymerization of poly(ethylene glycol) (PEG)–MAA systems. The reactivity ratios obtained in this study suggested that the polymer synthesized with AIBN as the initiator had a structure of alternating blocks of MAA and LMA, with isolated PEG grafts. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2950–2959, 2004     

Kinetics of emulsion copolymerization of methylmethacrylate and ethylacrylate: effect of type and concentration of initiator in unseeded polymerization system

The free radical emulsion copolymerization of methylmethacrylate (MMA) and ethylacrylate (EA) initiated by a water-soluble initiator (potassium persulphate, KPS) at 50 °C in the presence of anionic emulsifier above critical micelle concentration under constant stirring speed in an inert atmosphere is investigated. The effect of blend of KPS and oil-soluble initiators [KPS+2,2^′-azobisisobutyronitrile (AIBN)] is also examined. The order of the interval-II polymerization rate (R_p) is found to be 0.76±0.03 in KPS initiation alone and 0.72±0.04 in presence of fixed concentration of AIBN under similar experimental condition. On the other hand, interestingly, the rate of polymerization is found to be propotional to the 0.40th power of the AIBN concentration in presence of fixed concentration of KPS. The kinetic features of the present investigation indicate that probably the radical desorption is relatively facile and also the cage effect may be operative under high conversions (i.e. in polymer particles) in this MMA/EA emulsion copolymerization system. It is also found that the polydispersity index of polymer is being influenced by the type and concentration of initiators.     

Comparison of oil-soluble and water-soluble initiation of styrene polymerization in a three-component microemulsion

The polymerization of styrene in three-component oil-in-water microemulsions made with the cationic surfactant dodecyltrimethylammonium bromide is studied by dilatometry and quasielastic light scattering as a function of type and concentration of initiator. Fast polymerization rates, high conversions, and high molecular weight polymers are achieved with both oil-soluble (AIBN) and water-soluble (potassium persulfate) initiators. The rate of polymerization shows initiation and termination intervals, but no constant-rate interval is observed. Stable monodisperse microlatexes are obtained with both types of initiators. For both AIBN and potassium persulfate, polystyrene molecular weight is proportional to initiator concentration [I]^–0.4 and particle radii decrease as [I]^–0.2. Polymerization initiation occurs in or at the microemulsion droplets, and polymer particles grow by recruiting monomer and surfactant from uninitiated swollen micelles.     

Polymerization of allyl(vinyl phenyl) ethers and reactions of the resulting polymers

Solution polymerizations of allyl(o-vinyl phenyl)ether and allyl(p-vinyl phenyl)ether with cationic and radical initiators were investigated. Soluble polymers were formed in polymerizations with boron trifluoride etherate and with benzoyl peroxide. In polymerization with azobisisobutyronitrile the polymerization in dilute solution gave a soluble polymer, whereas that in concentrated solution gave a crosslinked, insoluble one. For informationon the polymerization behavior some infrared and ultraviolet spectroscopic investigations of the soluble polymers were made. From these results it appears that polymers with pendant allyl groups are formed in polymerization with boron trifluoride etherate at low temperature, and polymers containing pendant vinyl groups and allyl groups are obtained with the two types of radical initiator. Copolymerizations of these monomers with ethyl vinyl ether and styrene with the use of boron trifluoride etherate were sucessfully effected. Such reactions as Claisen rearrangement, crosslinking induced with radical initiators, and epoxidation with perbenzoic acid were examined for the polymers prepared in the polymerization with boron trifluoride etherate. Good results were obtained for the former two reactions. However, the latter was unsuccessful.     

Organometallic polymers. XXV. Preparation of polyvinylferrocene

The synthetic details of solution polymerization in benzene and bulk polymerization of vinylferrocene are reported. In benzene solutions, with azobisisobutyronitrile (AIBN) as the initiator, small yields of low-polydispersity low molecular weight (M?_n ? 5000) polyvinylferrocene is obtained. However, high yields can be obtained by continuous or multiple AIBN addition. Higher molecular weight polymers and binodal polymers can be obtained as the monomer concentration is increased. In bulk polymerizations, yields of 80% can be obtained. The molecular weight increases as temperature decreases from 80 to 60°C in bulk polymerizations, and an increasing amount of insoluble polymer results. The soluble portion is often binodal, the higher molecular weight node consisting of an increasingly branched structure. Lower molecular weight polymer was readily fractionated into narrow fractions from benzene–methanol systems, but higher molecular weight polymer proved impossible to fractionate into narrow fractions due to branching.     

Low Concentration Limitations of Catalyst and Conventional Free Radical Polymerization in ICAR ATRP of Butyl Methacrylate With PMDETA as the Ligand

Low concentration limitations of the catalyst and conventional free radical polymerization are investigated in the system of initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) of butyl methacrylate (BMA), in which 2,2-azobisisobutyronitrile (AIBN) is used as a reducing agent, pentamethyldiethylenetriamine (PMDETA) as a ligand, copper bromide (CuBr₂) as a catalyst and ethyl 2-bromoisobutyrate (EBiB) as an initiator. Results show that conventional radical polymerization happens in the early stage of the ICAR ATRP of BMA when the amounts of AIBN are 3～25 times of the catalyst. And with the increase of the conversion, the BMA polymerization solely conducts the controlled radical polymerization (CRP). The low concentration limitations (based on monomer) of the catalyst required in ICAR ATRP of BMA with good controllability are found to be closely related to the molar ratio of initiator to catalyst, which is determined by the stability of the catalyst/ligand complex. The smaller molar ratio of initiator to catalyst allows lower concentration limitations of the catalyst.     

甲基丙烯酸-β-羟基-γ-二烷氨基丙酯的合成及聚合

由甲基丙烯酸失水甘油酯与三烷基胺合成了甲基丙烯酸-2-羟基-3-二甲氨基丙酯(DMAHPMA)及甲基丙烯酸-2-羟基-3-二乙氨基丙酯(DEAHPMA),并进行了在各种自由基引发剂下的本体聚合。发现BPO不能使之聚合,其它过氧化物,如LPO,TBH,CHP,KPS等能引发聚合。测定了DEAHPMA在CHP,LPO,AIBN引发下的初期聚合速度Rp,并计算出它们的聚合活化能,据此,认为CHP,LPO以氧化还原机理引发DEAHPMA的聚合。 DMAHPMA在10％的盐水溶液中,不加悬浮稳定剂,即能成功地进行悬浮聚合。     

Homogeneous and heterogeneous free radical polymerizations in environmentally responsible supercritical carbon dioxide

Fluoropolymers are used in many technologically demanding applications because of their balance of high-performance properties. A significant impediment to the synthesis of variants of commercially available amorphous fluoropolymers is their general insolubility in most solvents except chlorofluorocarbons (CFCs). The environmental concerns about CFCs can be circumvented by preparing these technologically important materials in supercritical fluids (SCFs). The homogeneous solution homo- and copolymerization of highly fluorinated acrylic, styrenic and olefinic monomers in supercritical carbon dioxide using free radical methods will be discussed [Science, 257 , 945 (1992)]. Detailed decomposition rates and efficiency factors will be presented for azobisisobutyronitrile (AIBN) in supercritical carbon dioxide and will be compared to conventional liquid solvents [Macromolecules, 26 , 2663 (1993)]. Additionally, viscosities of polymer solutions in supercritical CO₂ have been measured using a high pressure, falling cylinder viscometer. The results show that the polymer solution viscosities in supercritical CO₂ are an order of magnitude lower than with the same polymers in conventional organic solvents. The results from these homogeneous solution polymerization studies has allowed us to also consider heterogeneous polymerizations in a carbon dioxide continuous phase. Conventional emulsion polymerizations of unsaturated monomers are performed in either aqueous or organic dispersion media with addition of surface active agents (surfactants) to stabilize the colloidal dispersion that forms. With free radical initiators that are preferentially soluble in the continuous phase, high rates of polymerization and high molar mass polymers can be obtained simultaneously. Herein we describe an environmentally responsible alternative to aqueous and organic dispersing media for emulsion polymerizations which utilizes supercritical carbon dioxide, in conjunction with molecularly engineered free radical initiators and amphiphilic molecules that are specifically designed to be interfacially active in CO₂. Conventional lipophilic monomers, exemplified by methyl methacrylate and styrene, can be polymerized heterogeneously using a fluorinated azo-initiator in supercritical CO₂ in the presence of added surfactant to form stable emulsions that result in submicron size particles. Detailed surfactant and initiator syntheses and phase behavior will also be discussed.     

Novel sol–gel methodology to produce LaCoO3 by acrylamide polymerization assisted by γ-irradiation

In this paper we report the synthesis of LaCoO₃ (LCO) nano-particles with two methodologies: the conventional sol–gel reaction of acrylamide (AA) polymerization using a cross-linking agent (methylenebisacrylamide or MBA) with the activation of the polymerization reaction by thermo-chemical initiator (azobisisobutyrnitrile or AIBN). The second was a novel sol–gel methodology in which the polymerization of AA monomers was done without MBA and the initiation was achieved by gamma radiation. With thermochemical initiator a xerogel with a foam and porous structure was obtained, while the gamma-irradiation of the mixture leads to the formation of a compact resin with entrapped cations. X-ray diffraction (XRD) shows that formation of the product begins around 500 °C and according to analysis of microscopy images of powders calcined in 700 °C the average sizes of particles are 20 nm and 42 nm for samples obtained using γ-irradiation and AIBN as initiators, respectively. TEM images also show differences in particle morphology. Those synthesized using AIBN as initiator are dispersed, while those with γ-irradiation are in aggregates.     

Polymerization of sodium acrylate in inverse-suspension stabilized by sorbitan fatty esters

This paper is devoted the synthesis of poly(sodium acrylate) by an inverse-suspension polymerization technique. Ammonium persulfate, ethylcellulose and toluene were used as initiator, suspending agent, and continuous organic phase, respectively. Two surfactants, sorbitan monooleate (SMO) and sorbitan monostearate, were used as the suspension stabilizers. The effect of the initiator concentration as well as the type and concentration of the surfactant on the polymer molecular weight and solution viscosity was investigated. Participation of the unsaturated surfactant (SMO) in the free radical polymerization was recognized to be the main reason of enhancement of the average molecular weight and viscosity of the products. A similar effect was observed when the polymerization reactions were run in the presence of air. In the latter conditions, however, an inhibition effect of atmospheric oxygen resulted in substantially decreased solution viscosity. Meanwhile, it was found that higher polymers were obtained when the as-synthesized beads were dewatered and hardened in methanol rather than in acetone.     

Chemo-enzymatic synthesis of comb polymers

The paper describes the synthesis and characterization of comb polymers by a two-step chemo-enzymatic process. In the first step macromonomers bearing unsaturation at the chain end were prepared by lipase catalyzed ring-opening polymerization (ROP) of ε-caprolactone (CL) and 1,5-dioxepane-2-one (DXO). The ROP was carried out in bulk at 60 °C under anhydrous conditions using 2-hydroxyethyl methacrylate (HEMA) as the initiator. The DP of the macromonomers was controlled by regulating the monomer: HEMA molar feed concentration. The macromonomers were then homo- or co-polymerized in the second step with alkyl methacrylate monomers (methyl methacrylate or HEMA) using AIBN initiated free radical polymerization. Characterization of the polymers was done by ¹H NMR, SEC and DSC techniques.     

Attapulgite grafted with polystyrene via a simultaneous reverse and normal initiation atom transfer radical polymerization

The surface grafting of attapulgite (ATP) with polystyrene (PS) was established via a simultaneous reverse and normal initiation atom transfer radical polymerization (SR&NIATRP). 4‐(chloromethyl)phenyltrimethoxysilane (CMPTMS) chemical bounded on the surface of ATP (ATP‐Cl, Cl‐I) was prepared via one‐step self‐assembly. SR&NI ATRP of styrene was conducted using CuCl₂ complex tris(2‐(dimethylamino)ethyl)amine (Me₆‐TREN) as the catalytic system, initiated by 2,2‐azobis(isobutyronitrile) (AIBN) and ATP‐Cl. FT‐IR, XRD, XPS, TGA and TEM data were consistent with the grafting of benzyl chloride groups and PS chains on ATP surface. The controllability of polymerization was investigated by the kinetics behavior under different molar ratio of AIBN and CuCl₂. The obtained polymer possessed a uniform distribution of molecular weights with a lower polydispersity index of 1.2～1.4. The relationship between polymerization on the surface of ATP and in solution was discussed in detail based on TGA data of hybrid particles and GPC trace of free polymer in solution. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1508–1516