Synthesis of thermosensitive gel by living free radical polymerization mediated by an alkoxyamine inimer

Thermosensitive gel is synthesized through controlled/“living” free radical copolymerization of styrene and DVB mediated by an alkoxyamine inimer, 2,2,6,6-tetramethyl-1-(1′-phenylethoxy)-4-(4′-vinylbenzyloxy)-piperidine (V-ET). The inimer plays the role of both incorporating “T-shaped” inter-chain linkages and mediating the polymerization. First order kinetics is observed for crosslinking polymerizations before gel point, indicating a constant concentration of propagating radicals. Monomer conversion at the gel point depends on the feed ratio of DVB to V-ET. Higher amount of V-ET results in later gel point due to smaller molecular weight of the primary chains that depends inversely on the concentration of nitroxide. The resulting gel contains permanent and labile crosslinking points formed by DVB units and alkoxyamine moieties, respectively. Therefore, the gels exhibit gel-sol transition within a narrow temperature range. The gel properties, such as the swelling ratio and gel-sol transition temperature, can be controlled by changing the feed ratio of DVB to V-ET. The microenvironments in different gels, or at different temperatures, are investigated by ESR spectroscopy.     

‘Living’ radical polymerization of styrene mediated by spiro ring-substituted piperidinyl-N-oxyl radicals. The effect of the spiro rings on the control of polymerization

The bulk radical polymerizations of styrene (St) at 80-120 °C in the presence of 6-aza-7,7-dimethyl-9-hydroxyspiro[4.5]decane-6-yloxyl (1) and 1-aza-2,2-dimethyl-4-hydroxy[5.5]undecane-1-yloxyl (2) were studied. At 100 and 120 °C, the polymerizations were well controlled by those nitroxides to give poly(St)s with narrow polydispersities. On the other hand, the polymerization mediated by 2 at 80 °C showed a good ‘livingness’ of polymerization, but 1 had a poor ability to control the polymerization to give poly(St) with a broad polydispersity of 1.52. The rate constants (k_act) for the homolysis of the NO-C bond of the alkoxyamines prepared from 1 and 2 were measured at 333-373 K, and the A_acts and E_acts values were determined to be 2.8×10¹³ s⁻¹ and 128 kJ mol⁻¹ (1) and 4.0×10¹³ s⁻¹ and 125 kJ mol⁻¹ (2), respectively, from the Arrhenius plots. These results are compared with those for the structurally related piperidinyl-N-yloxyl radicals including TEMPO.     

Polyamide 6/silica nanocomposites prepared by in situ polymerization

A polyamide 6 (PA 6)/silica nanocomposite was obtained through a novel method, in situ polymerization, by first suspending silica particles in ϵ-caproamide under stirring and then polymerizing this mixture at high temperature under a nitrogen atmosphere. The silicas were premodified with aminobutyric acid prior to the polymerization. The effects of the addition of unmodified and modified silicas on the dispersion, interfacial adhesion, isothermal crystallization, and mechanical properties of PA 6 nanocomposites were investigated by using scanning electron microscopy, dynamic mechanical analysis, differential scanning calorimetry, and mechanical tests, respectively. The results show that the silicas dispersed homogeneously in the PA 6 matrix. The addition of silicas increases the glass transition temperature and crystallization rate of PA 6. The mechanical properties such as impact strength, tensile strength, and elongation at break of the PA 6/modified silica nanocomposites showed a tendency to increase and decrease with increase of the silica content and have maximum values at 5% silica content, whereas those of the PA 6/unmodified silica system decreased gradually. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 355–361, 1998     

Graft polymerization of vinyl monomers initiated by peroxycarbonate groups introduced onto silica surface by Michael addition

The introduction of peroxycarbonate groups onto a silica surface and the graft polymerization of vinyl monomers initiated by peroxycarbonate groups introduced onto a silica surface were investigated. The introduction of peroxycarbonate groups onto a silica surface was achieved by Michael addition of amino groups introduced onto the silica surface to t‐butylperoxy‐2‐methacryloyloxyethylcarbonate (HEPO). The amount of peroxycarbonate groups was determined to be 0.17 mmol/g. The graft polymerization of various vinyl monomers such as styrene (St), N‐vinyl‐2‐pyrrolidinone (NVPD), and 2‐hydroxyethyl methacrylate (HEMA) was initiated by peroxycarbonate groups introduced onto the silica surface to give the corresponding polymer‐grafted silicas. The percentage of poly(St)‐grafting reached about 120% after 5 h. This means that 1.20 g of poly(St) is grafted onto 1.0 g of silica. The surface of poly(St)‐grafted silica shows a hydrophobic nature, but the surfaces of poly(NVPD) and poly(HEMA)‐grafted silica show a hydrophilic nature. Furthermore, the poly(St)‐grafted silica was found to give a stable colloidal dispersion in a good solvent for the grafted polymer. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1491–1497, 1999     

Architecture of colloidal crystals constructed by silica hybrid nanoparticles

Silica (SiO₂)‐crosslinked polystyrene (PS) particles possessing photofunctional N,N‐diethyldithiocarbamate (DC) groups on their surface were prepared by the free‐radical emulsion copolymerization of a mixture of SiO₂ (diameter D_n = 192 nm), styrene, divinyl benzene, 4‐vinylbenzyl N,N‐diethyldithiocarbamate (VBDC), and 2‐hydroxyethyl methacrylate with a radical initiator under UV irradiation. In this copolymerization, the inimer VBDC had the formation of a hyperbranched structure by a living radical mechanism. These particles had DC groups on their surface. Subsequently, poly(methyl methacrylate) brushes encapsulated SiO₂ particles were synthesized by the grafting from a photoinduced atom transfer radical polymerization (ATRP) approach of methyl methacrylate initiated by SiO₂‐crosslinked PS particles as a macroinitiator. We constructed the colloidal crystals using these photofunctional particles. Moreover, the SiO₂ particle array of colloidal crystals was locked by radical photopolymerization with vinyl monomer as a matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Reinforced chloroprene rubber by in situ generated silica particles: Evidence of bound rubber on the silica surface

Nano silica is generated in situ inside the uncrosslinked chloroprene rubber (CR) by the sol‐gel reaction of tetraethoxysilane (TEOS). This results in appreciable improvement in mechanical properties of the CR composites at relatively low filler content. Furthermore, exploitation of reactive organosilanes, γ‐aminopropyltrimethoxysilane (γ‐APS) in particular, in the silica synthesis process facilitates growing of spherical silica particles with a size distribution in the range of 20‐50 nm. The silica particles are found to be uniformly dispersed and they do not suffer from filler‐filler interaction. Additionally, it is observed that the silica particles are coated by silane and rubber chains together which are popularly known as bound rubber. The existence of the bound rubber on silica surface has been supported by the detailed investigations with transmission electron microscopy (TEM), energy filtered transmission electron microscopy (EFTEM) and energy dispersive X‐ray spectroscopy (EDAX). The interaction between rubber and silica, via bi‐functionality of the γ‐APS, has been explored by detailed FTIR studies. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43717.     

Effects of molecular weight on liquid-crystalline behavior of a mesogen-jacketed liquid crystal polymer synthesized by atom transfer radical polymerization

The synthesis of poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) with different molecular weight and low polydispersity was achieved by atom transfer radical polymerization in methoxybenzene solution using 1-bromoethylbenzene as an initiator and CuBr/sparteine complex as a catalyst. The concentration of the living centers throughout the polymerization was found to be constant. The liquid-crystalline behavior of the polymers with M_n ranging from 3800 to 17,400 g/mol was studied using DSC and POM. Only the polymers with M_n beyond 10,200 g/mol formed a liquid-crystalline phase, which was quite stable with a high clearing point (higher than the decomposition temperature of the polymer).     

Preparation of poly(methyl methacrylate)‐grafted attapulgite by surface‐Initiated radical polymerization

Poly(methyl methacrylate) (PMMA) was bonded on the surface of attapulgite (ATP) by using an ammonium persulfate amine redox initiation system via grafting from approach. ATP was modified with (3‐aminopropyl)triethoxysilane to anchor amine groups on the surface, and then the amine‐functionalized ATP was further treated with methacryloyl chloride and 4,4′‐azobis(4‐cyanovaleric acid) to give methacryl‐ and azo‐functionalized ATP, respectively. Subsequently, surface‐initiated graft polymerization of MMA in a soap‐free emulsion was performed to afford ATP/PMMA hybrids. Meanwhile, graft polymerizations on the surface of methacryl‐ and azo‐functionalized ATP were carried out for comparison. The grafting of PMMA on the surface of ATP was characterized by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and thermogravimetric analysis (TGA). The crystal structure of hybrids was characterized by X‐ray diffraction analysis. The morphology of hybrids was observed by scanning electron microscopy and transmission electron microscopy. The degree of grafting obtained from surface‐initiated graft polymerization in a soap‐free emulsion was found to be the greatest (29.4%) estimated from TGA. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41062.     

Effect of polymer chain length on the solubility of polystyrene grafted single‐walled carbon nanotubes in tetrahydrofuran

BACKGROUND: While carbon nanotubes are highly interesting materials for a variety of applications, their inherent insolubility limits widespread applications and solution‐phase processing. It is known that chemical functionalization can overcome this insolubility problem, and covalent grafting of polymers to the nanotube surface has been shown to be effective. In this study, the effect of polymer molecular weight on the solubility of polymer–nanotube conjugates was investigated. RESULTS: A series of nitroxide‐capped polystyrene polymers ranging in molecular weight from 2900 to 105 000 g mol^?1 were grafted to single‐walled carbon nanotubes (SWNTs). The resulting polystyrene–SWNT conjugates exhibited different degrees of solubility in tetrahydrofuran. Subsequent thermogravimetric and UV‐visible spectroscopy analyses indicated that carbon nanotube solubility reached a maximum when a polymer sample with a weight‐average molecular weight of 10 000 g mol^?1 was used. Higher and lower molecular weights resulted in reduced solubilities. CONCLUSION: Polymer chains of intermediate length maximize SWNT solubility, while lengths that are too low or too high seem to diminish the ability of the polymer–SWNT conjugates to remain in solution. Copyright © 2008 Society of Chemical Industry     

Preparation and characterization of polyaniline N‐grafted with poly(ethyl acrylate) synthesized via atom transfer radical polymerization

Polyaniline (PANI) N‐grafted with poly(ethyl acrylate) (PEA) was synthesized by the grafting of bromo‐terminated poly (ethyl acrylate) (PEA‐Br) onto the leucoemeraldine form of PANI. PEA‐Br was synthesized by the atom transfer radical polymerization of ethyl acrylate in the presence of methyl‐2‐bromopropionate and copper(I) chloride/bipyridine as the initiator and catalyst systems, respectively. The leucoemeraldine form of PANI was deprotonated by butyl lithium and then reacted with PEA‐Br to prepare PEA‐g‐PANI graft copolymers containing different amounts of PEA via an N‐grafting reaction. The graft copolymers were characterized by Fourier transform infrared spectroscopy, elemental analysis, and thermogravimetric analysis. Solubility testing showed that the solubility of PANI in chloroform was increased by the grafting of PEA onto PANI. The morphology of the PEA‐g‐PANI graft copolymer films was observed by scanning electron microscopy to be homogeneous. The electrical conductivity of the graft copolymers was measured by the four‐probe method. The results show that the conductivity of the PANI decreased significantly with increasing grafting density of PEA onto the PANI backbone up to 7 wt % and then remained almost constant with further increases in the grafting percentage of PEA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A comparative study on effects of two kinds of polymerization methods on grafting of polymer onto silica surface

In this article we present the result of a comparative study of two kinds of polymerization methods—solution polymerization (sol. poly.) and dispersion polymerization (dis. poly.) for grafting polymer onto silica. As a model for the grafting polymerization reaction, styrene was chosen as the monomer and azo diisobutyronitrile (AIBN) as the initiator. The study aims at supplying theoretical reference for better selecting polymerization method to graft polymer on the silica particle surface. First, monolayers of 3‐methacryloylpropyl trimethoxysilane were chemically bonded onto the surfaces of micrometer‐sized silica gel particles, and so double bonds were immobilized onto the silica surface. Second, the copolymerizations between the immobilized double bonds and the monomer styrene were carried out, homopolymerizations of styrene followed, and finally polystyrene was grafted to the silica surfaces. Two kinds of polymerization methods, sol. poly. and dis. poly., were adopted respectively, and the effects of polymerization methods on grafting process were examined mainly. At the same time, the effects of different polymerization conditions on the grafting degree were researched. It was found that in the dis. poly. system the grafting degree is obviously higher than that in the sol. poly. system under the same polymerization conditions, and the grafting degree can go up to 47%, i.e. 47g/100g. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5808–5817, 2006     

化学引发合成淀粉接枝共聚物的研究进展

淀粉与乙烯基单体接枝共聚是淀粉化学改性的重要方法 ,在利用农产品和开发新型功能材料方面有很好的发展前景。综述了近十年化学引发合成淀粉接枝共聚物的研究进展。     

TEMPO-mediated radical polymerization of styrene in aqueous miniemulsion: Macroinitiator concentration effects

The control/livingness in nitroxide-mediated polymerization of styrene (S) in aqueous miniemulsion at 125 °C employing a poly(S)-2,2,6,6-tetramethylpiperidinyl-1-oxy (PS-TEMPO) macroinitiator and the surfactant sodium dodecylbenzenesulfonate has been shown to depend strongly on the macroinitiator concentration for particles of approximate number-average diameter 65 nm. The control/livingness was relatively poor at [PS-TEMPO]₀ ≤ 0.02 M due to the combined effect of enhanced spontaneous initiation and the interface effect (whereby deactivation is suppressed due to interfacial activity of TEMPO). Satisfactory control/livingness was obtained at higher [PS-TEMPO]₀ as a result of the interface effect and enhanced spontaneous initiation exerting less pronounced influence per chain than at lower [PS-TEMPO]₀. Polymerizations using the sulfonate surfactant DOWFAX 8390 gave similar results, indicating that the present macroinitiator concentration effects are not specific to SDBS-based systems. The results also demonstrate that TEMPO-mediated polymerization of S in miniemulsion can proceed at a higher rate than in bulk with good control/livingness.     

Grafting of water‐soluble sulfonated monomers onto functionalized fumed silica nanoparticles via surface‐initiated redox polymerization in aqueous medium

Sulfonated polymer/fumed silica hybrid nanoparticles were prepared via surface‐initiated free radical polymerization of 2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid (PAMPS‐g‐FSN), styrene sulfonic acid sodium salt (PSSA‐g‐FSN) and vinyl sulfonic acid sodium salt (PVSA‐g‐FSN) from the surface of aminopropyl‐functionalized fumed silica nanoparticles (AFSNs) dispersed in aqueous medium. Cerium(IV) ammonium nitrate/nitric acid and sodium dodecyl sulfate were used as redox initiator and stabilizer respectively. AFSNs were prepared by covalently attaching 3‐aminopropyltriethoxysilane onto the surface of fumed silica nanoparticles. Sulfonated monomers (AMPS, SSA or VSA) were then grafted onto the AFSNs ultrasonically dispersed in water via redox initiation at 40 °C. Structure, thermal properties, particle size and morphology of the AFSNs and PAMPS‐g‐FSN, PSSA‐g‐FSN and PVSA‐g‐FSN hybrid nanoparticles were characterized by Fourier transform infrared spectroscopy, TGA, SEM, transmission electron microscopy (TEM) and dynamic light scattering (DLS). The results indicated that the sulfonated monomers were successfully grafted onto the fumed silica nanoparticles. Grafting amounts of the sulfonated polymers onto the fumed silica nanoparticle surface were estimated from TGA thermograms to be 59%, 13% and 29% for the PAMPS, PSSA and PVSA, respectively. From SEM, TEM and DLS analysis, polymer‐grafted fumed silica nanoparticles with an average diameter smaller than 70 nm and a (semi‐) spherical shape were observed. A significant bimodal particle size distribution was observed only for the PAMPS‐g‐FSN with average diameters of 39.6 nm (84.1% per number) and 106 nm (15.9% per number). The hydrophilic sulfonated polymer/grafted fumed silica obtained from the redox graft polymerization gave a stable colloidal dispersion in acidic aqueous medium. Copyright © 2012 Society of Chemical Industry     

Dispersion polymerization of methyl methacrylate with three types of comblike fluorinated stabilizers in supercritical carbon dioxide

Dispersion polymerizations of methyl methacrylate in supercritical carbon dioxide were conducted with three types of comblike fluorinate polymer stabilizers: poly(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10‐heptadecafluorodecyl methacrylate) (PHDFDMA), poly(3,3,4,4,5,5,6,6,7,7,8,8,8‐tridecafluorooctyl methacrylate) (PTDFOMA), and poly(2,2,3,3,3‐pentafluoropropyl methacrylate) (PPFPMA). The effect of the polymerization pressure was not significant on the mean diameters of the poly(methyl methacrylate) (PMMA) particles from 20 to 40 MPa. However, the coefficients of variation of the particle diameters produced at 20 MPa ( , where is the number‐basis mean particle diameter), where the heterogeneous phase was found before polymerization, were larger than those produced at 30 and 40 MPa, where the homogeneous phase was found. The mean size of the PMMA obtained with PTDFOMA and PPFPMA strongly depended on the stabilizer concentration compared with that obtained with PHDFDMA. Moreover, the mean size decreased as the carbon dioxide‐philic side chain length increased. As shown by the results of this study, the best stabilizer among the three types of stabilizers for producing PMMA particles was PHDFDMA. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43813.     

Ionomer covalent functionalization of single‐walled carbon nanotubes by radical polymerization of zirconium acrylate

A facile and efficient covalent functionalization of single‐walled carbon nanotubes (SWCNTs) via peroxide‐mediated free radical covalent attachment and polymerization of zirconium acrylate is reported. The resulting covalently functionalized SWCNTs exhibit improved solubility in organic solvents. The covalently functionalized SWCNTs are characterized by cross polarization magic angle spinning ¹³C NMR, differential scanning calorimetry, thermogravimetric analysis, x‐ray diffraction, Raman, and infrared spectroscopy. Infrared spectroscopy reveals that carboxylate groups of covalently attached ionomers chelate with zirconium ions and the participating carboxylate groups may be from different ionomer chains leading to cross‐linking the chains. The SWCNT topology, ionic clustering, and π‐electron clouds were explored by transmission electron microscopy. © 2014 American Institute of Chemical Engineers AIChE J, 60: 820–828, 2014     

Microwave‐assisted polymerization: Inert addition and surface coating of superabsorbent polymer for improved physical properties

Two different polymerization techniques, microwave‐assisted polymerization and free radical solution polymerization, were utilized in the syntheses of superabsorbent polymers with varying amounts of acrylic acid (31–50%). Degrees of neutralization were in the range of 68–80 mol %, and clay level was varied between 0 and 5%. The base polymer produced with microwave‐assisted polymerization had higher absorbency under low load (0.3 psi) than those with the free radical solution polymerization. To improve its absorbency under higher loads (0.6 and 0.9 psi), the surface coating step was implemented by using ethylene glycol diglycidyl ether as a surface crosslinking agent. Properties such as capacity, permeability, and absorbency under different loads were tested in 0.9% sodium chloride solution for the base and the surface‐coated polymers. In addition, extractables and residual acrylic acid were measured to determine the reaction's efficiency. In conclusion, surface coating improved polymer properties, and the incorporation of clay imparted permeability to the polymer. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43990.     

Surface‐initiated atom transfer radical polymerization (ATRP) of styrene from silica nanoparticles under UV irradiation

Diethyldithiocarbamyl‐modified silica nanoparticles were prepared and used as macroinitiator for the surface‐initiated atom transfer radical polymerization (SI‐ATRP) of styrene under UV irradiation. Well‐defined polymer chains were grown from the nanoparticle surfaces to yield particles composed of a silica core and a well‐defined, densely grafted outer PS layer with a mass ratio of styrene to silica, or percentage grafting, of 276.3% after an UV irradiation time of 5 h. Copyright © 2004 Society of Chemical Industry     

Differences in enthalpy recovery of gradient and random copolymers of similar overall composition: styrene/4-methylstyrene copolymers made by nitroxide-mediated controlled radical polymerization

Styrene/4-methylstyrene (S/MS) random and gradient copolymers were synthesized by nitroxide-mediated controlled radical polymerization (NM-CRP) and compared to random copolymers made by conventional free radical polymerization (ConvFRP). The gradient copolymers have molecular weight (MW) values approaching 85,000 g/mol, making these some of the higher MW gradient copolymers reported to date. Due to the proximity of the glass transition temperatures (T_g) of polystyrene (PS) and poly(4-methylstyrene) (PMS), there is no significant difference in T_g between the gradient and random copolymers, with both copolymer types yielding single T_gs that typically increase slightly with increasing MS content. While enthalpy relaxation studies demonstrate similarity in random copolymers made by NM-CRP and ConvFRP, they reveal significant differences between random and gradient copolymers. Gradient copolymers exhibit broad enthalpy recovery peaks, whereas random copolymers exhibit narrower enthalpy recovery peaks. The maxima in the enthalpy recovery peaks are at substantially lower temperature, as much as 17 °C, in the gradient copolymers as compared to random copolymers of equal overall composition. While random and gradient copolymers of a given overall composition exhibit similar enthalpy recovery values at a common physical aging time and quench depth relative to T_g, the major differences in the enthalpy recovery peaks indicate that differences in sequence distribution along the chain length can lead to unusual behavior in gradient copolymers relative to random copolymers.