Polymeric nanocomposites containing polyhedral oligomeric silsesquioxanes prepared via frontal polymerization

Frontal polymerization (FP) has been successfully applied, for the first time, to obtain polymeric nanocomposites containing polyhedral oligomeric silsesquioxanes (POSS) in an amine‐cured epoxy matrix. Variations of maximum temperature (T_max) and front velocity (V_f) have been studied. A comparison of these products with the corresponding materials, obtained by the classical batch polymerization technique, demonstrated that FP allows a higher degree of conversion than batch polymerization. The products have been characterized in terms of their thermal behavior with DSC analysis. SEM and X‐ray analyses revealed the morphology and the structures of the nanocomposites. The nanocomposites obtained by FP have the same characteristics of those synthesized, in much longer times, by batch polymerization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4514–4521, 2007     

Novel dinitroxide mediating agent for stable free‐radical polymerization

A novel dinitroxide mediating agent that was suitable for stable free‐radical polymerization was synthesized and used in the block copolymerization of styrene and t‐butyl styrene. Quantitative yields of a novel dinitroxide based on 1,6‐hexamethylene diisocyanate and 4‐hydroxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy were obtained. Various experimental parameters, including the nitroxide‐to‐initiator molar ratio, were examined, and it was determined that the polymerization was most controlled under conditions similar to those of conventional 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐mediated stable free‐radical polymerization. Moreover, the dinitroxide mediator proved to be a viable route for the facile two‐step synthesis of triblock copolymers of styrene and t‐butyl styrene. However, the dinitroxide mediation process resulted in a higher than expected level of nitroxide decomposition, which resulted in polymers possessing a terminal alkoxyamine and an adjacent hydroxylamine rather than a preferred internal bisalkoxyamine. This decomposition resulted in the formation of diblock copolymer species during the triblock copolymer synthesis. Gel permeation chromatography was used to monitor the chain‐end decomposition kinetics, and the determined observed rate constant (5.89 × 10^?5 s^?1) for decomposition agreed well with previous studies for other dinitroxide mediating agents. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1547–1556, 2004     

Atom transfer radical polymerization of 2-methoxy ethyl acrylate and its block copolymerization with acrylonitrile

2-Methoxy ethyl acrylate (MEA), a functional monomer was homopolymerized using atom transfer radical polymerization (ATRP) technique with methyl 2-bromopropionate (MBP) as initiator and CuBr/N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA) as catalyst system; polymerization was conducted in bulk at 60 °C and livingness was established by chain extension reaction. The kinetics as well as molecular weight distribution data indicated towards the controlled nature of polymerization. The initiator efficiency and the effect of initiator concentration on the rate of polymerization were investigated. The polymerization remained well-controlled even at low catalyst concentration of 10% relative to initiator. The influence of different solvents, viz. ethylene carbonate and toluene on the polymerization was investigated. End-group analysis for the determination of high degree of functionality of PMEA was determined with the help of ¹³C{¹H} NMR spectra. Chain extension experiment was conducted with PMEA macroinitiator for ATRP of acrylonitrile (AN) in ethylene carbonate at 70 °C using CuCl/bpy as catalyst system. The composition of individual blocks in PMEA-b-PAN copolymers was determined using ¹H NMR spectra.     

Copper(0)-mediated radical polymerization of styrene at room temperature

The “living’/controlled radical polymerization (LRP) of styrene (St) at room temperature is rarely reported. In this work, copper(0) (Cu(0))-mediated radical polymerization of St at room temperature was investigated in detail. Dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF) as well as a binary solvent, tetrahydrofuran/1,1,1,3,3,3-hexafluoro-2-propanol were used as the solvents, respectively. Methyl-2-bromopropionate and ethyl 2-bromoisobutyrate were used as the initiators, respectively. The polymerization proceeded smoothly with moderate conversions at room temperature. It was found that DMF was a good solvent with the essential features of LRP, while DMSO was a poor solvent with uncontrollable molecular weights. Besides, the match among the initiator, solvent and molar ratios of reactants can modulate the livingness of the polymerization, and the proper selection of ligand was also crucial to a controlled process. This work provided a first example of Cu(0)-mediated radical polymerization of St at room temperature, which would enrich and strength the LRP technique.     

Novel well-defined star homopolymers and star-block copolymers of poly(n-hexyl isocyanate) by anionic polymerization

Anionic polymerization high-vacuum techniques and appropriate multifunctional initiators/additives were employed for the synthesis of novel star structures of poly(n-hexyl isocyanate) (PHIC). A new trifunctional initiator prepared by the reaction of tris(4-isocyanatophenyl)methane with benzyl sodium was used for the synthesis of three-arm star PHIC. Divinyl benzene and the core-first or the arm-first/core-first (in-out) approach were utilized for the synthesis of multiarm star homopolymers, (PHIC)_n, star-block copolymers, (PHIC-b-PI)_n, and miktoarm star copolymers, (PS)_n(PHIC)_n, where PS is polystyrene. The molecular characteristics obtained by size-exclusion chromatography, equipped with refractive index and two-angle light scattering detectors, nuclear magnetic resonance, spectroscopy, and dilute solution viscometry showed that well-defined structures were synthesized in this study. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2387–2399, 2007     

Some novel accelerating agents for nitroxide‐mediated living free‐radical polymerization

Malononitrile (MN), trifluoroacetic acid anhydride, acetylacetone, acetoacetic ester, and diethyl malonate have been identified as novel rate‐accelerating additives for nitroxide‐mediated living free‐radical polymerization. Among these additives, MN has the greatest accelerating effect. Adding MN at an MN/2,2,6,6‐tetramethylpiperidine‐oxyl (TEMPO) molar ratio of 4.0 results in a nearly 20 times higher rate of polymerization of styrene (St), and adding MN at an MN/TEMPO molar ratio of 2.5 results in a nearly 15 times higher rate of copolymerization of St and methyl methacrylate. The polymerization of St proceeds in a living fashion, as indicated by the increase in the molecular weight with time and conversion and the relatively low polydispersity. The polymerization rate of St is so quick that the conversion reaches 70% within 1 h at 125 °C when the molar ratio of MN to TEMPO is 4:1. Moreover, the reaction temperature can be reduced to 110 °C. A possible explanation for this effect is that the formation of hydrogen bonds between the MN and TEMPO moiety weakens the C? ON bond at the end of the polymer chain. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5246–5256, 2005     

Hybrid atom transfer radical polymerization system for balanced polymerization rate and polymer molecular weight control

A hybrid polymerization system that combines the fast reaction kinetics of conventional free radical polymerization and the control of molecular weight and distribution afforded by ATRP has been developed. High‐free radical initiator concentrations in the range of 0.1–0.2 M were used in combination with a low concentration of ATRP catalyst. Conversions higher than 90% were achieved with ATRP catalyst concentrations of less than 20 ppm within 2 h for the hybrid ATRP system as compared with ATRPs where achieving such conversions would take up to 24 h. These reaction conditions lead to living polymerizations where polymer molecular weight increases linearly with monomer conversion. As in living polymerization and despite the fast rates and low ATRP catalyst concentrations, the polydispersity of the produced polymer remained below 1.30. Chain extension experiments from a synthesized macroinitiator were successful, which demonstrate the living characteristics of the hybrid ATRP process. Catalyst concentrations as low as 16 ppm were found to effectively mediate the growth of over 100 polymer chains per catalytic center, whereas at the same time negating the need for post polymerization purification given the low‐catalyst concentration. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2294–2301, 2010     

Synthesis of well‐defined glycidyl methacrylate based block copolymers with self‐activation and self‐initiation behaviors via ambient temperature atom transfer radical polymerization

Well‐defined glycidyl methacrylate (GMA) based di‐ and triblock copolymers, with self‐activation and self‐initiation behaviors by incorporation of 2‐(diethylamino) ethyl methacrylate (DEA) blocks, were synthesized via ambient temperature atom transfer radical polymerization (ATRP). The stability of the GMA pendant oxirane rings in tertiary amine environments at ambient temperature was investigated. More importantly, both self‐activation behavior in oxirane ring opening addition reaction and self‐initiation behavior in post‐cure oxirane ring opening crosslinking of these block copolymers were evidenced by ¹H NMR studies. The results demonstrated that the reactivity of pendent oxirane rings was strongly dependant on the nucleophilicity and steric hindrance of tertiary amine moieties and temperature. This facilitated the synthesis of well‐defined block copolymers of GMA and DEA via sequential monomer addition ATRP, particularly for polymerization of GMA monomer at ambient temperature. Moreover, these one‐component GMA based block polymers have novel self‐activation and self‐initiation properties, rendering some potential applications in both enzyme immobilization and GMA‐based thermosetting materials. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2947–2958, 2007     

Ligand‐free Cu(0)‐mediated controlled radical polymerization of methyl methacrylate at ambient temperature

For the first time, ligand‐free Cu(0)‐mediated polymerization of methyl methacrylate (MMA) was realized by the selection of ethyl‐2‐bromo‐2‐phenylacetate as initiator at ambient temperature. The polymerization can reach up to 90% conversion within 5 h with dimethyl sulfoxide (DMSO) as solvent, while keeping manners of the controlled radical polymerization. Extensive investigation of this system revealed that for a well‐controlled Cu(0)‐mediated polymerization of MMA, the initiator should be selected with the structure as alkyl 2‐bromo‐2‐phenylacetate, and the solvent should be DMSO or N,N‐dimethylformamide. The selectivity for solvents indicated a typical single‐electron transfer‐living radical polymerization process. Scanning for other monomers indicated that under equal conditions, the polymerizations of other alkyl (meth)acrylates were uncontrollable. Based on these results, plausible reasons were discussed. The ligand‐free Cu(0)‐mediated polymerization showed its superiority with economical components and needless removal of Cu species from the resultant products. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Fundamental kinetic aspects of living radical polymerization and the use of gel permeation chromatography to shed light on them

The control achievable by living radical polymerization (LRP) is based on a kinetic balance of the activation–deactivation reversible reactions, which are specific to LRP, with conventional elementary reactions such as initiation, propagation, and termination. This work describes, as plainly as possible, how chains grow and how their polydispersity evolves as they experience activation–deactivation cycles and how these processes can be quantitatively analyzed by gel permeation chromatography. A comprehensive probability theory on the polydispersity indices of LRP polymers is presented. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4743–4755, 2004     

凝胶渗透色谱-高效液相色谱-串联质谱法同时测定烟草中3种抑芽剂残留

建立了用凝胶渗透色谱净化-液相色谱-串联质谱分析烟草中3种抑芽剂残留的方法。卷烟中的待测抑芽剂组分用V(乙酸乙酯)∶V(环己烷)=1∶1超声提取后通过凝胶渗透色谱净化;凝胶色谱柱为Biobeads S-X3玻璃柱(50 g,400 mm×25 mm),流动相为V(乙酸乙酯)∶V(环己烷)=1∶1溶液,流速5 mL/min;收集第10~25 min流出的液体用液相色谱色谱-三重四极杆串联质谱仪测定。在0.5~100 ng/mL的质量浓度范围内,各种抑芽剂标准溶液的线性相关系数均大于0.99。在样品中添加3种抑芽剂(添加水平为5,20,100μg/kg)的混合标准溶液,平均回收率在86.2%~108.4%之间,3种抑芽剂的RSD在1.1%~7.5%之间;方法的检测限在0.01~0.06μg/kg之间。     

Atom transfer radical copolymerizationof acrylonitrile/n‐butyl acrylate: Microstructure determination by two‐dimensional nuclearmagnetic resonance spectroscopy

Atom transfer radical polymerization conditions were optimized and standardized with different initiator and catalyst systems. Acrylonitrile/n‐butyl acrylate copolymers were synthesized with 2‐bromopropionitrile as the initiator and CuCl/Cu(0)/2,2′‐bipyridine as the catalyst system. Variations of the feed composition led to copolymers with different compositions. The number‐average molecular weight and the polydispersity index were determined by gel permeation chromatography. Quantitative ¹³C{¹H} NMR was employed to determine the copolymer composition. The reactivity ratios calculated with a methodology based on the Mao–Huglin terminal model were r_A = 1.30 and r_B = 0.68 for acrylonitrile and n‐butyl acrylate, respectively. The reactivity ratios determined by the modified Kelen–Tudos method were r_A = 1.29 ± 0.01 and r_B = 0.67 ± 0.01. ¹³C{¹H} NMR and distortionless enhancement by polarization transfer (DEPT‐45, 90, and 135) were used to distinguish methyl, methylene, methine, and quaternary carbon resonance signals. The overlapping and broad signals of the copolymers were assigned completely to various compositional and configurational sequences by the correlation of one‐dimensional (¹H, ¹³C{¹H}, and DEPT) and two‐dimensional (heteronuclear single quantum coherence, total correlation spectroscopy, and heteronuclear multibond correlation) NMR spectral data. The complete spectral assignments of carbonyl and nitrile carbons were performed with the help of heteronuclear multibond correlation spectra. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2810–2825, 2005     

凝胶渗透色谱净化-气质联用法测定土壤中三嗪类除草剂

建立了以超声波提取、凝胶渗透色谱净化(GPC)、HP-5 MS石英毛细管柱分离、E1离子源质谱法测定土壤中13种三嗪类除草剂的多残留检测方法.三嗪类除草剂的添加水平为0.010～0.100 mg/kg时,平均回收率为72.1%～118.3%,相对标准偏差为2.6%～19.8%(n=4);方法的检出限为0.30～2.50μg/kg.     

Effects of hydration and hydrophilicity on Na‐Clay‐supported aqueous‐phase catalysis for atom transfer radical polymerization

Hydrated sodium montmorillonite (Na‐clay) has been used as a catalyst support for the heterogeneous atom transfer radical polymerization of benzyl methacrylate in the presence of various concentrations of water, reducing agent, and CuBr₂ in anisole at ambient temperature. The polymerization was promoted via reduction of Cu^II to Cu^I through the addition of sodium ascorbate (NaAsc) as a reducing agent in aqueous solution. The polymerizaton proceeded in a controlled manner and produced poly(benzyl methacylate) with moderately narrow molecular weight distribution (MWD) when performed under optimum conditions of hydration (10 wt % ≤ H₂O/Na‐clay ≤ 21 wt %) and reducing agent (0.15 ≤ [NaAsc]/[I] ≤ 0.23). The polymerization was uncontrolled if hydration and NaAsc exceed above their optimum range of concentrations. Apparent rate of the polymerization (k_app) increased in the presence of decane–anisole (1/3, v/v) mixture solvent. Selective adsorption of decane at the interfaces of the hydrated clay was attributed for the rate enhancement due to increased polymer and hydrophobic interface interaction. The polymerization progressed in a controlled manner as confirmed by the first‐order time‐conversion plot, linear increase in molecular weights, and moderately narrow MWDs over conversion. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of diblock copolymers by combining stable free radical polymerization and atom transfer radical polymerization

A stable nitroxyl radical functionalized with an initiating group for atom transfer radical polymerization (ATRP), 4‐(2‐bromo‐2‐methylpropionyloxy)‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy (Br‐TEMPO), was synthesized by the reaction of 4‐hydroxyl‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy with 2‐bromo‐2‐methylpropionyl bromide. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br‐TEMPO. The obtained polystyrene had an active bromine atom for ATRP at the ω‐end of the chain and was used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare block copolymers. The molecular weights of the resulting block copolymers at different monomer conversions shifted to higher molecular weights and increased with monomer conversion. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2468–2475, 2006     

Synthesis of poly(dimethylsiloxane)‐containing diblock and triblock copolymers by the combination of anionic ring‐opening polymerization of hexamethylcyclotrisiloxane and nitroxide‐mediated radical polymerization of methyl acrylate,isoprene, and styrene

Poly(dimethylsiloxane)‐containing diblock and triblock copolymers were prepared by the combination of anionic ring‐opening polymerization (AROP) of hexamethylcyclotrisiloxane (D₃) and nitroxide‐mediated radical polymerization (NMRP) of methyl acrylate (MA), isoprene (IP), and styrene (St). The first step was the preparation of a TIPNO‐based alkoxyamine carrying a 4‐bromophenyl group. The alkoxyamine was then treated with Li powder in ether, and AROP of D₃ was carried out using the resulting lithiophenyl alkoxyamine at room temperature, giving functional poly(D₃) with M_w/M_n of 1.09–1.16. NMRPs of MA, St, and IP from the poly(D₃) at 120 °C gave poly(D₃‐b‐MA), poly(D₃‐b‐St), and poly(D₃‐b‐IP) diblock copolymers, and subsequent NMRPs of St from poly(D₃‐b‐MA) and poly(D₃‐b‐IP) at 120 °C gave poly(D₃‐b‐MA‐b‐St) and poly(D₃‐b‐IP‐b‐St) triblock copolymers. The poly(dimethylsiloxane)‐containing diblock and triblock copolymers were analyzed by ¹H NMR and size exclusion chromatography. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6153–6165, 2005     

Facile and quick synthesis of poly(N‐methylolacrylamide)/polyhedral oligomeric silsesquioxane graft copolymer hybrids via frontal polymerization

We report on a new strategy for fabricating well‐defined POSS‐based polymeric materials with and without solvent by frontal polymerization (FP) at ambient pressure. First, we functionalize polyhedral oligomeric silsesquioxane (POSS) with isophorone diisocyanate (IPDI). With these functionalized POSS‐containing isocyanate groups, POSS can be easily incorporated into a poly(N‐methylolacrylamide) (PNMA) matrix via FP in situ. Constant velocity FP is observed without significant bulk polymerization. The morphology and thermal properties of POSS‐based hybrid polymers prepared via FP are comparatively investigated on the basis of scanning electronic microscopy (SEM) and thermogravimetric analysis (TGA). Results show that the as‐prepared POSS‐based polymeric materials exhibit a higher glass transition temperature than that of pure PNMA, ascribing to modified POSS well‐dispersed in these hybrid polymers. Also, the products with different microstructures display different thermal properties. The pure PNMA exhibits a featureless morphology, whereas a hierarchical morphology is obtained for the POSS‐based polymeric materials. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1136–1147, 2009     

Synthesis of AB2 miktoarm star-shaped copolymers by combining stable free radical polymerization and atom transfer radical polymerization

A stable nitroxyl radical functionalized with two initiating groups for atom transfer radical polymerization (ATRP), 4-(2,2-bis-(methyl 2-bromo isobutyrate)-propionyloxy)-2,2,6,6-tetramethyl-1-piperidinyloxy (Br₂-TEMPO), was synthesized by reacting 4-hydroxyl-2,2,6,6-tetramethyl-1-piperidinyloxy with 2,2-bis-(methyl 2-bromo isobutyrate) propanoic acid. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br₂-TEMPO. The obtained polystyrene had two active bromine atoms for ATRP at the ω-end of the chain and was further used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare AB₂-type miktoarm star-shaped copolymers. The molecular weights of the resulting miktoarm star-shaped copolymers at different monomer conversions shifted to higher molecular weights without any trace of the macroinitiator, and increased with monomer conversion.     

Bulk atom transfer radical polymerization of allyl methacrylate

A detailed investigation of the polymerization of allyl methacrylate, a typical unsymmetrical divinyl compound containing two types of vinyl groups, methacryloyl and allyl, with quite different reactivities, was performed with atom transfer radical polymerization (ATRP). Homopolymerizations were carried out in bulk, with ethyl‐2‐bromoisobutyrate as the initiator and with copper halide (CuX, where X is Cl or Br) with N,N,N′,N″,N″‐pentamethyldiethylenetriamine as the catalyst system. Kinetic studies demonstrated that during the early stages of the polymerization, the ATRP process proceeded in a living manner with a low and constant radical concentration. However, as the reaction continued, the increased diffusion resistance restricted the mobility of the catalyst system and interrupted the equilibrium between the growing radicals and dormant species. The obtained poly(allyl methacrylate)s (PAMAs) were characterized with Fourier transform infrared, ¹H NMR, and size exclusion chromatography techniques. The dependence of both the gel point conversion and molecular characteristics of the PAMA prepolymers on different experimental parameters, such as the initiator concentration, polymerization temperature, and type of halide used as the catalyst, was analyzed. These real gel points were compared with the ones calculated according to Gordon's equation under the tentative assumption of equal reactivity for the two types of vinyl groups. Moreover, the microstructure of the prepolymers was the same as that exhibited by those homopolymers prepared by conventional free‐radical polymerization; the fraction of syndiotactic arrangements increased as the reaction temperature was lowered. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2395–2406, 2005     

在线凝胶渗透色谱-二维气相色谱/质谱法测定鲫鱼样品中的14种农药残留

建立了在线凝胶渗透色谱-二维气相色谱/质谱(GPC-MDGC/MS)测定鲫鱼样品中14种农药残留的方法。样品用环己烷/乙酸乙酯(1：1,v/v)提取两次,合并提取液。提取液冷冻、过膜后,经在线凝胶渗透色谱净化后直接进行MDGC/MS分析,通过中心切割的方式将农药组分选择性切割进入二维色谱柱进行进一步分离分析,采用内标法进行定量。实验结果表明：14种农药在0.01~0.9 mg/L范围内具有较好的线性关系,相关系数均大于0.99。14种农药在3个添加水平(0.01、0.05、0.1 mg/kg)的加标回收率为83.0%~112.9%,相对标准偏差为3.2%~12.0%。该方法前处理简单,实现了在线GPC和MDGC的有效结合,准确度好、精密度高,具有很好的推广性。