Living free radical polymerization using cyclic trifunctional initiator

Free radical polymerization is a very robust route to produce polymers, however, it does not promote a control on the microstructure of the polymer: usually polymers with wide molecular weight distribution and polydispersity (PDI) greater than 1.5 are obtained. Ionic polymerization can be used to produce polymers with low PDI, however, this kind of route needs to be held with a high degree of purity. Living free radical polymerization (LFRP) is a promising technique to produce controlled polymers. In the literature, monofunctional conventional initiators have been used in LFRP process. In this study, the use of a cyclic trifunctional peroxide on controlled nitroxide mediated radical polymerization was investigated. The initiator used was Trigonox 301 (3,6,9‐triethyl‐3,6,9‐trimethyl‐1,4,7‐triperoxonane—41% solution in isoparaffinic hydrocarbons) and TEMPO (2,2,6,6‐tetramethyl‐1‐piperidin‐1‐oxyl) was used as controller agent. The results obtained show that it is possible to produce controlled polymers at certain operating conditions, when Trigonox 301 is used. It could be observed that the concentration of initiator and the ratio [TEMPO]/[Trigonox 301] have a huge effect on the polymer properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Evaluation of the confinement effect of nanoclay on the kinetics of styrene atom transfer radical polymerization

The grafting through method was employed to study the effect of nanoclay confinement on the atom transfer radical polymerization (ATRP) of styrene. An ammonium salt containing a double bond on its structure was used as a clay modifier. Employing ATRP to polymerize styrene in the presence of modified montmorillonite resulted in a finely well‐defined polystyrene nanocomposite. The gas chromatography (GC) results showed the linear increase of ln(M₀/M) versus time, which indicated the controlled behavior of the polymerization. Another confirmation of the living nature of the polymerization was the linear increase of molecular weight against monomer conversion concluded from the gel permeation chromatography (GPC) data. Nanoclay exerted acceleration on the polymerization of free polystyrene chains. The polydispersity indexes of polymer chains increased by the addition of nanoclay. In the case of clay‐attached polystyrene chains, number and weight‐average molecular weights were lower than that of freely dispersed polystyrene chains. The polydispersity index of the clay‐attached chains was higher in respect to the freely dispersed polystyrene chains. The living nature of polymer chains was more elucidated by Fourier transform infrared spectroscopy (FTIR). Exfoliation of the clay layers in the polymer matrix of polystyrene nanocomposite containing the lowest amount of nanoclay has proven by Transmission Electron Microscopy (TEM). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Solution styrene polymerizations performed with multifunctional initiators

This paper analyzes the performance of multifunctional initiators frequently used in the literature and in the industry for the production of polystyrene (PS). Polymerizations of styrene in ethylbenzene were conducted in batch at high temperatures (120°C) until conversions around 70%, as frequent in industrial sites. Polymerizations were conducted in glass test ampoules with different concentrations and types of initiators, parameterized in terms of the active oxygen concentration. The results showed that when used at similar active oxygen concentrations, the use of the tetrafunctional initiator tetrakis(tertbutylperoxy carbonate) can allow for the production of polymer resins with significant higher average molar masses with similar polymerization rates, which can be very useful at plant site for the modification of polymer grades. Besides, the results show that the decomposition of one peroxide group of the analyzed multifunctional initiators does not affect the rates of decomposition of the remaining ones significantly, as reaction proceeds as initiated by a monofunctional initiator. Finally, although described in previous styrene polymerization studies, the use of the trifunctional initiator 3,6,9‐triethyl 3,6,9‐trimethyl‐1,4,7 triperoxonane is difficult to justify in commercial units, given its very high half‐life time. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42609.     

Styrene–butadiene–styrene/montmorillonite nanocomposites synthesized by anionic polymerization

We successfully synthesized an exfoliated styrene–butadiene–styrene triblock copolymer (SBS)/montmorillonite nanocomposite by anionic polymerization. Gel permeation chromatography showed that the introduction of organophilic montmorillonite (OMMT) resulted in a small high‐molecular‐weight fraction of SBS in the composites, leading to a slight increase in the weight‐average and number‐average molecular weights as well as the polydispersity index. The results from ¹H‐NMR revealed that the introduction of OMMT almost did not affect the microstructure of the copolymer when the OMMT concentration was lower than 4 wt %. Transmission electron microscopy and X‐ray diffraction showed a completely exfoliated nanocomposite, in which both polystyrene and polybutadiene blocks entered the OMMT galleries, leading to the dispersion of OMMT layers on a nanoscale. The exfoliated nanocomposite exhibited higher thermal stability, glass‐transition temperature, elongation at break, and storage modulus than pure SBS. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Synthesis and photoconducting properties of C60‐bonded polystyrene initiated with C60Cln

C₆₀‐bonded polystyrene was produced with a novel initiator system, C₆₀Cl_n/CuCl/2,2′‐bipyridine (where the average value of n is 20). The molar ratio of styrene/C₆₀Cl_n/CuCl/bpy was 100:1/20:1:2, and the polymerization temperature was 130°C. Gel permeation chromatography detected with an ultraviolet detector demonstrated that C₆₀ was chemically bonded to polystyrene. The linear increase in the number‐average molecular weight (by gel permeation chromatography) with the conversion indicated that this novel initiator system had some characteristics of living polymerization. A possible polymerization mechanism was examined. The photoconducting properties of C₆₀‐bonded polystyrene were better than those of polystyrene initiated with CCl₄. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3001–3004, 2002     

Thermal polymerization of styrene in the presence of TEMPO

To investigate aspects of the contribution of (thermal) self-initiation in nitroxide-mediated radical polymerization (NMRP) of styrene, selective styrene polymerizations with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) in the absence of initiator were carried out at 120 and 130 °C. The results of these experiments (including conversion data, molecular weight averages, polydispersity and molecular weight distribution information) were compared with regular thermal polymerization of styrene and NMRP of styrene in the presence of a bimolecular initiator (benzoyl peroxide; BPO). It was observed that although the thermal polymerization of styrene can be controlled to some extent in the presence of TEMPO to provide polystyrene with low polydispersity, the polymerization was never as controlled as that obtained by a BPO-initiated NMRP.     

One‐step synthesis of triarm block copolymers via simultaneous reversible‐addition fragmentation chain transfer and ring‐opening polymerization

One‐step synthesis of star copolymers by reversible addition–fragmentation chain transfer (RAFT) and ring‐opening polymerization (ROP) by using a novel dual initiator is reported. Triarm block copolymers comprising one polystyrene (or polyacrylamide) arm and two poly(β‐butyrolactone) arms were synthesized in one‐step by simultaneous RAFT polymerization of styrene (St) (or acrylamide, designated as AAm) and ROP of β‐butyrolactone (BL) in the presence of a novel trifunctional initiator, 1,2‐propanediol ethyl xanthogenate (RAFT‐ROP agent). This dual initiator was obtained through the reaction of 3‐chloro‐1,2‐propanediol with the potassium salt of ethyl xanthogenate. The principal parameters such as monomer concentration, initiator concentration, and polymerization time that affect the one‐step polymerization reaction were evaluated. The characterization of the products was achieved using Fourier‐transform infrared spectroscopy (FTIR), ¹H‐nuclear magnetic resonance (¹H‐NMR), ¹³C‐nuclear magnetic resonance (¹³C‐NMR), Gas chromatography–mass spectrometry (GC–MS), gel‐permeation chromatography (GPC), thermogravimetric analysis (TGA), and fractional precipitation (γ) techniques. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

甲基丙烯酸二甲氨基乙酯的ATRP聚合

2-溴代异丁酸-Ⅳ-丁二酰亚胺酯（NHS—BIBA酯）由2-溴代异丁酸和,v-羟基丁二酰亚胺通过酯化反应制得。以它为引发剂,2,2＇-联吡啶（bpy）／CuBr为催化体系、水为溶剂,采用原子转移自由基聚合（ATRP）合成了带有功能基团的聚甲基丙烯酸二甲氨基乙酯（PDMAEMA）高分子。研究了引发剂、温度、反应时间、pH值和浓度对聚合产率的影响,利用凝胶渗透色谱（GPC）和核磁共振（1HNMR）测定了聚合物的分子量、多分散指数（PDI）和链结构。由GPC可知在最高产率下,Mn和Mw／Mn分别为8674和1．59,结果表明,NHS-BIBA酯引发的PDMAEMA实际数均分子量高于理论分子量,并具有低分散度,链结构上氢原子出峰符合特有的化学位移。     

Nanoclay‐encapsulated polystyrene microspheres by reverse atom transfer radical polymerization

Nanoclay‐encapsulated polystyrene microspheres were synthesized using reverse atom transfer radical polymerization in miniemulsion. Conversion and molecular weight were evaluated using gravimetry and gel permeation chromatography, respectively. Accordingly, conversion and molecular weight decrease by adding clay content. However, polydispersity index of the nanocomposites with higher clay content is higher. At high temperatures, thermal stability of the nanocomposites is relatively higher than the neat polystyrene, according to the thermogravimetric analysis results. Differential scanning calorimetry results show that glass transition temperature decreases by increasing clay content. Transmission electron microscopy result is in coincidence with X‐ray diffraction data and shows that clay layers are exfoliated in the matrix of PSNM 1. Scanning electron microscopy images display a homogeneous distribution of spherical particles with sizes in the range of ∼200 nm and also confirm dynamic light scattering (DLS) results. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Synthesis of polystyrene oligomers by nitroxide‐mediated radical polymerization using diethylketone triperoxide as a multifunctional radical initiator

Styrene oligomers (M_n, 2500–3000 g/mol) with low polydispersity index and containing peroxidic groups within their structure were synthesized using a novel trifunctional cyclic radical initiator, diethylketone triperoxide (DEKTP), through nitroxide‐mediated radical polymerization (NMRP), using OH‐TEMPO. During the synthesis of the polystyrene (PS) oligomers, camphorsulfonic acid (CSA) was used to inhibit the thermal autoinitiation of styrene at the evaluated temperatures (T = 120–130°C). The polymerization rate, which can be related to the slope of the plot of monomer conversion with reaction time, was monitored as a function of OH‐TEMPO, DEKTP, and CSA concentrations. The experimental results showed that all the synthesized polymers presented narrow molecular weight distributions, and the monomer conversion and the molecular weight of the polymers increased as a function of reaction time. Under the experimental conditions, T = 130°C, [DEKTP] = 10 mM, and [DEKTP]/[OH‐TEMPO] = 6.5, PS oligomers containing unreacted O? O sites in their inner structure were obtained. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Atom transfer radical polymerization of styrene initiated by bromoacetylated syndiotactic polystyrene macroinitiator

Atom transfer radical polymerization of styrene was conducted with bromoacetylated syndiotactic polystyrene as macroinitiator and copper bromide combined with N,N,N′,N′,N′‐pentamethyldiethylenetriamine as catalyst. A two‐stage process has been developed to synthesize the macroinitiator. First, syndiotactic polystyrene (sPS) was functionalized in the side phenyl rings with acetyl groups using the Friedel–Crafts reaction; second, the acetyl groups were converted to bromoacetyl groups by an acid‐catalyzed halogenation reaction. The initiator was found to be active in the polymerization of styrene, leading to the production of graft chains with well‐defined structure. The molecular weight and molecular weight distribution of the graft chains were determined using gel permeation chromatography after cleaving from the sPS backbone using peroxide acid oxidation followed by hydrazine‐catalyzed hydrolysis. The results indicated that the polymerization process was characteristic of a ‘living’ nature. Copyright © 2007 Society of Chemical Industry     

Synthesis of poly(octadecyl acrylate‐b‐styrene‐b‐octadecyl acrylate) triblock copolymer by atom transfer radical polymerization

The synthesis of triblock copolymer poly(octadecyl acrylate‐b‐styrene‐b‐octadecyl acrylate), using atom transfer radical polymerization (ATRP), is reported. The copolymers were prepared in two steps. First, polystyrene was synthesized by ATRP using α,α′‐dichloro‐p‐xylene/CuBr/bpy as the initiating system; Second, polystyrene was further used as macroinitiator for the ATRP of octadecyl acrylate to prepare ABA triblock copolymers in the presence of FeCl₂·4H₂O/PPh₃ in toluene. Polymers with controlled molecular weight (M_n = 17,000–23,400) and low polydispersity index value (1.33–1.44) were obtained. The relationship between molecular weight versus conversion showed a straight line. The effect of reaction temperature on polymerization was also investigated, showing a faster polymerization rate under higher temperature. The copolymers were characterized by FTIR, ¹H‐NMR, DSC, and GPC and the crystallization behavior of the copolymers was also studied. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1539–1545, 2004     

Synthesis of polydimethylsiloxane‐block‐polystyrene‐block‐polydimethylsiloxane via polysiloxane‐based macroinitiator in supercritical CO2

Polydimethylsiloxane‐block‐polystyrene‐block‐polydimethylsiloxane (PDMS‐b‐PS‐b‐PDMS) was synthesized by the radical polymerization of styrene using a polydimethylsiloxane‐based macroazoinitiator (PDMS MAI) in supercritical CO₂. PDMS MAI was synthesized by reacting hydroxy‐terminated PDMS and 4,4′‐azobis(4‐cyanopentanoyl chloride) (ACPC) having a thermodegradable azo‐linkage at room temperature. The polymerization of styrene initiated by PDMS MAI was investigated in a batch system using supercritical CO₂ as the reaction medium. PDMS MAI was found to behave as a polyazoinitiator for radical block copolymerization of styrene, but not as a surfactant. The response surface methodology was used to design the experiments. The parameters used were pressure, temperature, PDMS MAI concentration and reaction time. These parameters were investigated at three levels (?1, 0 and 1). The dependent variable was taken as the polymerization yield of styrene. PDMS MAI and PDMS‐b‐PS‐b‐PDMS copolymers obtained were characterized by proton nuclear magnetic resonance and infrared spectroscopy. The number‐ and weight‐average molecular weights of block copolymers were determined by gel permeation chromatography. Copyright © 2004 Society of Chemical Industry     

星状支化PS的合成与表征

利用原子转移自由基聚合方法,以α-溴代苯乙烷为引发剂,CuBr／2,2'-联二吡啶作为催化体系,合成星状支化聚苯乙烯(PS)。引发二苯甲烷双马来酰亚胺／苯乙烯电荷转移络合物体系就地优先生成多官能团引发剂,再引发苯乙烯聚合。采用核磁共振、凝胶渗透色谱、多角度激光散射和特性黏数等分析方法对聚合过程、聚合物结构、聚合物相对分子质量及其分布进行分析与表征。由多角度激光散射法测定的绝对重均分子量是由凝胶渗透色谱测定的4倍左右,相同相对分子质量的线型PS的特性黏数是星状PS的20倍,证实聚合产物确实具有支化结构。     

Coumarin end-capped polystyrene by ATRP and photodimerization reaction

Summary New coumarin-end-capped polystyrenes have been prepared using functional initiators by atom-transfer radical polymerization (ATRP). In the first case, the photosensitive initiator, 7-chloroacetoxy-4-methyl-coumarin, was prepared. Then the styrene was initiated by 7-chloroacetoxy-4-methyl-coumarin in the presence of a CuBr/bipyridine. The functionalization of the polymers was nearly quantitative, the molecular weight and structure were well controlled by adjusting the monomer/initiator molar ratio, polymerization temperature and time. At high monomer conversion, the polydispersity index of polymer was about 1.40. These coumarin-end-capped polystyrenes underwent [2+2] cycloaddition reaction under UV irradiation in film state. After irradiation the molecular weight and polydispersity index of polystyrene both increased, but the maximum molecular weight was less than the double of original one. It means that the photodimerization reaction was not complete throughly in film state for the diffusion of coumarin groups was blocked by polymeric chain entanglement.     

Radical styrene polymerization in the presence of trace levels of sulfonic acids

The bulk polymerization of styrene in the presence of the vinyl functional sulfonic acid 2‐sulfoethylmethacrylate (SEM) was found to have utility for making polystyrenes with narrow polydispersity, bimodal polydispersity, and ultrahigh molecular weight at fast polymerization rates. Narrow polydispersity polymers were made by the addition of SEM to nitroxide‐mediated polymerizations. Bimodal polydispersity polymers were made by the ultrahigh molecular weight component being made in the presence of SEM in the absence of an initiator and the low molecular weight component being made in the presence of an initiator and/or chain‐transfer agent. Ultrahigh molecular weight monomodal polystyrenes were prepared at much faster polymerization rates than possible via spontaneous polymerization in the absence of SEM. SEM was found to be more effective, by an order of magnitude, than camphor sulfonic acid on a weight basis and, because it is copolymerized into the polymer chain, should not lead to corrosion problems during fabrication of the polymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 869–875, 2003     

氢化钠/三异丁基铝体系合成星形聚苯乙烯的研究

采用阻滞阴离子调控技术,通过"先核后臂"法以NaH/三异丁基铝(i-Bu3Al)与苯乙烯、二乙烯基苯(DVB)反应制备的多钠引发剂为核,乙苯为溶剂,合成了星形聚苯乙烯(PS)(cs-PS);通过"先臂后核"法,以NaH/i-Bu3Al直接引发苯乙烯聚合,DVB为偶联剂,也合成了星形聚苯乙烯(as-PS)。采用气相色谱测定了聚苯乙烯钠与DVB中四种组分在100℃下的聚合反应速率,并用凝胶渗透色谱分析测试了聚合物的分子参数及平均臂数。结果表明:聚苯乙烯钠与DVB中四种组分的聚合反应速率与单体浓度呈假一级动力学关系;随着n(DVB)/n(NaH)的增加,cs-PS和as-PS的相对分子质量均逐渐增加,相对分子量分布均变宽,平均臂数也随之增大。     

Preparation of high molecular weight poly(N‐vinylcarbazole) in high yield by low‐temperature precipitation polymerization of N‐vinylcarbazole

To produce high molecular weight poly(N‐vinylcarbazole) (PVCZ) with high conversion, N‐vinylcarbazole (VCZ) was heterogeneously polymerized in methanol at 30, 40 and 50 °C using a low temperature initiator, 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN), and the effects of polymerization temperature and concentration of initiator and solvent on the polymerization behaviour and molecular parameters of PVCZ investigated. Globally, experimental results correspond to predicted ones. Low polymerization temperature using ADMVN and a heterogeneous system using methanol proved to be successful in obtaining poly(N‐vinylcarbazole) (PVCZ) of high molecular weight and high conversion with small temperature rise during polymerization, although free radical polymerization by azoinitiator was used. The polymerization rate of VCZ in methanol at 30 °C is proportional to the 0.88th power of ADMVN concentration. The molecular weight is higher and the molecular weight distribution is narrower with PVCZ polymerized at lower temperatures. For PVCZ produced in methanol at 30 °C using an ADMVN concentration of 0.0001 mol/mol of VCZ, a weight average molecular weight of 1 750 000 g mol⁻¹ is obtained, with a polydispersity index of 1.82 © 2000 Society of Chemical Industry     

A novel strategy to branched polyacrylonitrile via one‐pot RAFT copolymerization of acrylonitrile and an asymmetrical divinyl monomer

Branched polyacrylonitriles were prepared via the one‐pot radical copolymerization of acrylonitirle and an asymmetric divinyl monomer (allyl methacrylate) that possesses both a higher reactive methacrylate and a lower reactive allyl. RAFT technique was used to keep a low‐propagation chain concentration via a fast reversible chain transfer euilibration and thus the cross‐linking was prevented until a high level of monomer conversions. This novel strategy was demonstrated to engenerate a branched architecture with abundant pendant functional vinyl and nitrile groups, and controlled molecular weight as a behavior of controlled/living radical polymerization characteristics. The effect of the various experimental parameters, including temperature, brancher to monomer molar ratio, and chain transfer agent to initiator molar ratio, on the control of moleculer dimension (molecular weight and polydispersity indices) and the degree of branching were investigated in detail. Moreover, ¹H NMR and gel permeation chromatography confirm the branched architecture of the resultant polymer. The intrinsic viscosity of the copolymer is also lower than the linear counterpart.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis of hybrid free and nanoporous silica aerogel‐anchored polystyrene chains via in situ atom transfer radical polymerization

Polystyrene nanocomposite with mixed free and anchored chains was synthesized by atom transfer radical polymerization. Attachment of 3‐(trimethoxysilyl)propyl methacrylate with a double bond on the nanoporous silica aerogel surface results in a double bond grafted silica aerogel which could be incorporated into the polystyrene chains by a grafting‐through process. Conversion and molecular weight evaluation was carried out using gas chromatography and gel permeation chromatography, respectively. Double bond containing silica aerogel has an inconsiderable effect on conversion. There is no considerable discrepancy between the molecular weights of the free and anchored chains. Addition of silica aerogel with pendant CC bonds leads to increase of apparent rate constant of polymerization and also molecular weights. This is mainly because of initiator trapping in silica aerogel pores. Every percent of double bond containing silica aerogel with respect to styrene results in trapping of about 0.08 mol of ethyl alpha‐bromoisobutyrate among the silica pores. POLYM. COMPOS., 34:1648–1654, 2013. © 2013 Society of Plastics Engineers