Poly(styrene‐b‐tetrahydrofuran)/clay nanocomposites by mechanistic transformation

Synthesis of poly(styrene‐block‐tetrahydrofuran) (PSt‐b‐PTHF) block copolymer on the surfaces of intercalated and exfoliated silicate (clay) layers by mechanistic transformation was described. First, the polystyrene/montmorillonite (PSt/MMT) nanocomposite was synthesized by in situ atom transfer radical polymerization (ATRP) from initiator moieties immobilized within the silicate galleries of the clay particles. Transmission electron microscopy (TEM) analysis showed the existence of both intercalated and exfoliated structures in the nanocomposite. Then, the PSt‐b‐PTHF/MMT nanocomposite was prepared by mechanistic transformation from ATRP to cationic ring opening polymerization (CROP). The TGA thermogram of the PSt‐b‐PTHF/MMT nanocomposite has two decomposition stages corresponding to PTHF and PSt segments. All nanocomposites exhibit enhanced thermal stabilities compared with the virgin polymer segments. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2190–2197, 2009     

Gas barrier of polystyrene montmorillonite clay nanocomposites: Effect of mineral layer aggregation

Three polystyrene (PS)/clay hybrid systems have been prepared via in situ polymerization of styrene in the presence of unmodified sodium montmorillonite (Na‐MMT) clay, MMT modified with zwitterionic cationic surfactant octadecyldimethyl betaine (C18DMB) and MMT modified with polymerizable cationic surfactant vinylbenzyldimethyldodecylammonium chloride (VDAC). X‐ray diffraction and TEM were used to probe mineral layer organization and to expose the morphology of these systems. The PS/Na‐MMT composite was found to exhibit a conventional composite structure consisting of unintercalated micro and nanoclay particles homogeneously dispersed in the PS matrix. The PS/C18DMB‐MMT system exhibited an intercalated layered silicate nanocomposite structure consisting of intercalated tactoids dispersed in the PS matrix. Finally, the PS/VDAC‐MMT system exhibited features of both intercalated and exfoliated nanocomposites. Systematic statistical analysis of aggregate orientation, characteristic width, length, aspect ratio, and number of layers using multiple TEM micrographs enabled the development of representative morphological models for each of the nanocomposite structures. Oxygen barrier properties of all three PS/clay hybrid systems were measured as a function of mineral composition and analyzed in terms of traditional Nielsen and Cussler approaches. A modification of the Nielsen model has been proposed, which considers the effect of layer aggregation (layer stacking) on gas barrier. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1733–1753, 2007     

Synthesis of polybenzoxazine/clay nanocomposites by in situ thermal ring‐opening polymerization using intercalated monomer

A new class of polybenzoxazine/montmorillonite (PBz/MMT) nanocomposites has been prepared by the in situ polymerization of the typical fluid benzoxazine monomer, 3‐pentyl‐5‐ol‐3,4‐dihydro‐1,3‐benzoxazine, with intercalated benzoxazine MMT clay. A pyridine‐substituted benzoxazine was first synthesized and quaternized by 11‐bromo‐1‐undecanol and then used for ion exchange reaction with sodium ions in MMT to obtain intercalated benzoxazine clay. Finally, this organomodified clay was dispersed in the fluid benzoxazine monomers at different loading degrees to conduct the in situ thermal ring‐opening polymerization. Polymerization through the interlayer galleries of the clay led to the PBz/MMT nanocomposite formation. The morphologies of the nanocomposites were investigated by both X‐ray diffraction and transmission electron microscopic techniques, which suggested the partially exfoliated/intercalated structures in the PBz matrix. Results of thermogravimetric analysis confirmed that the thermal stability and char yield of PBz nanocomposites increased with the increase of clay content. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Long‐lived layered silicates‐immobilized 2,6‐bis(imino)pyridyl iron (II) catalysts for hybrid polyethylene nanocomposites by in situ polymerization: Effect of aryl ligand and silicate modification

Heterogeneous‐layered silicate‐immobilized 2,6‐bis(imino)pyridyl iron (II) dichloride/MMAO catalysts, in which the active polymerization species are intercalated within sodium‐ and organomodified‐layered silicate galleries, were prepared for producing hybrid exfoliated polyethylene (PE) nanocomposites by means of in situ polymerization. The inorganic filler was first treated with modified‐methylaluminoxane (MMAO) to produce a supported cocatalyst: MMAO reacts with silicates replacing most of the organic surfactant, thus modifying the original crystallographic clay order. MMAO anchored to the nanoclay was able to activate polymerization iron complexes initiating the polymer growth directly from the filler lamellae interlayer. The polymerization mechanism taking place in between the montmorillonite lamellae separates the layers, thus promoting deagglomeration and effective clay dispersion. Transmission electron microscopy revealed that in situ polymerization by catalytically active iron complexes intercalated within the lower organomodified clay led to fine dispersion and high exfoliation extent. The intercalated clay catalysts displayed a longer polymerization life‐time and brought about ethylene polymerization more efficiently than analogous homogeneous systems. PEs having higher molecular masses were obtained. These benefits resulted to be dependent more on the filler nature than on the ligand environment around the iron metal center and the experimental synthetic route. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 548–564, 2009     

Polymerization mechanism for in situ supported metallocene catalysts

The polymerization of ethylene was carried out with a novel in situ supported metallocene catalyst that eliminated the need for a supporting step before polymerization. In the absence of trimethyl aluminum (TMA), in situ supported Et[Ind]₂ZrCl₂ was not active, but the addition of TMA during polymerization activated the catalyst. Et[Ind]₂Zr(CH₃)₂ was active even in the absence of TMA, whereas the addition of TMA during polymerization enhanced the catalytic activity. The polymerization‐rate profiles of the in situ supported metallocene catalysts did not show rate decay as a function of time. A polymerization mechanism for the in situ supported metallocene catalysts is proposed for this behavior. During polymerization, the in situ supported metallocene catalysts may deactivate, but homogeneous metallocene species present in the reactor may form new active sites and compensate for deactivated sites. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 462–468, 2000     

In situ intercalative polymerization of conducting polypyrrole/montmorillonite nanocomposites

Conducting polypyrrole (PPy)‐montmorillonite (MMT) clay nanocomposites have been synthesized by the in situ intercalative polymerization method. The PPy‐MMT nanocomposites are characterized by field‐emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), ultraviolet–visible (UV–vis) spectroscopy, thermogravimetric analysis (TGA), and Fourier‐transform infrared (FTIR) spectroscopy. XRD patterns show that after polymerization by the in situ intercalative method with ammonium persulfate and 1 M HCl, an increase in the basal spacing from 1.2 to 1.9 nm was observed, signifying that PPy is synthesized between the interlayer spaces of MMT. TEM and SEM micrographs suggest that the coexistence of intercalated MMT layers with the PPy macromolecules. FTIR reveals that there might be possible interfacial interactions present between the MMT clay and PPy matrix. The study also shows that the introduction of MMT clay results in thermal stability improvement of the PPy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2279–2285, 2008     

Poly(dicyclopentadiene)‐montmorillonite nanocomposite formation via simultaneous intergallery‐surface initiation and chain crosslinking using ROMP

Exfoliated poly(dicyclopentadiene) (pDCPD)—montmorillonite (MMT) nanocomposites were synthesized via intergallery‐surface‐initiated ring opening metathesis polymerization (ROMP). This is the first example of in situ polymerization of pDCPD from clay intergallery surfaces using ROMP. Grubbs catalyst was immobilized on the surface of MMT clay modified with vinylbenzyl dimethyloctadecyl ammonium chloride (VOAC), and DCPD polymerized from the clay surface while simultaneously crosslinking to form a thermoset nanocomposite in a one‐pot reaction. X‐ray diffraction and transmission electron microscopy analysis indicated that the resultant nanocomposites exhibited exfoliated morphologies with heterogeneous clay platelet distribution. Conventional bulk‐initiated nanocomposites containing VOAC modified MMT were also synthesized as a comparison, and these resulted in nanocomposites with intercalated morphologies. The differences between the morphologies demonstrated that growing polymer chains from the initiator sites on the intergallery surface of the clay platelets pushed the platelets apart during the polymerization of the intergallery‐surface‐initiated nanocomposites, aiding in the exfoliation process. Compression testing indicated that the intergallery‐surface‐initiated nanocomposites led to improvements of up to 50% in the compressive Young's Modulus, while the bulk‐initiated nanocomposites at the same clay loadings did not exhibit improved properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Encapsulated clay particles in polystyrene by RAFT mediated miniemulsion polymerization

RAFT grafted montmorillonite (MMT) clays [i.e., N,N‐dimethyl‐N‐(4‐(((phenylcarbonothioyl)thio)methyl)benzyl)ethanammonium‐MMT (PCDBAB‐MMT) and N‐(4‐((((dodecylthio)carbonothioyl)thio)methyl)benzyl)‐N,N‐dimethylethanammo‐nium‐MMT (DCTBAB‐MMT)] of various loadings were dispersed in styrene (S) monomer and the resultant mixtures emulsified and sonicated in the presence of a hydrophobe (hexadecane) into miniemulsions. The stable miniemulsions thus obtained were polymerized to yield encapsulated polystyrene‐clay nanocomposites (PS‐CNs). The molar mass and polydispersity index (PDI) of the PS‐CNs depended on the amount of RAFT agent in the system, in accordance with the features of the RAFT process. The morphology of the PS‐CNs ranged from partially exfoliated to an intercalated morphology, depending on the percentage clay loading. The thermomechanical properties of the PS‐CNs were better than those of the neat PS polymer, and were dependent on the molar mass, PS‐CN morphology and clay loading. The similarities and differences of the PS‐CNs prepared here by miniemulsion polymerization were compared to those prepared using the same RAFT agents and polymer system by bulk polymerization (as reported by us in a previous article). © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7114–7126, 2008     

Characterization and thermal degradation studies on polyaniline‐intercalated montmorillonite nanocomposites prepared by a solvent‐free mechanochemical route

Polyaniline (PANI)‐montmorillonite (MMT) nanocomposites were prepared by direct intercalation of aniline molecules into MMT galleries, followed by in situ polymerization within the nano‐interlamellar spaces under solvent‐free conditions. The basal spacing of aniline‐intercalated MMT increased gradually up to 1.5 nm with increasing amounts of aniline loaded. This result suggests that aniline molecules were adsorbed by MMT clay and that intercalated aniline likely located perpendicular to the silicate sheets. After polymerization, X‐ray diffraction and Fourier transform infrared analyses confirmed the successful synthesis of PANI chains between the MMT nano‐interlayers. The scanning electron microscopy images indicated that the surface morphologies of PANI–MMTs were strongly different depending on the PANI content. The electrical conductivities of PANI nanocomposite particles in pressed pellets ranged in the order of between 10^?3 and 10^?2 S/cm. UV–vis spectroscopy and doping level measurement were further used to discuss the conductivities of nanocomposites. The thermal stabilities of PANI–MMT nanocomposites were examined by using thermogravimetric‐differential thermal analysis and derivative thermogravimetric analysis, and both analyses consequently demonstrated the improved thermal stabilities of the PANI chains in the nanocomposites as compared to pure PANI. The thermal stabilities of resulting nanocomposites were strongly related to the PANI content, which increased as the PANI content decreased in the nanocomposites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2705–2714, 2005     

Exploitation of introducing of catalytic centers into layer galleries of layered silicates and related epoxy nanocomposites. I. Epoxy nanocomposites derived from montmorillonite modified with catalytic surfactant‐bearing carboxyl groups

Montmorillonite (MMT) was modified with the acidified cocamidopropyl betaine (CAB) and the resulting organo‐montmorillonite (O‐MMT) was dispersed in an epoxy/methyl tetrahydrophthalic anhydride system to form epoxy nanocomposites. The intercalation and exfoliation behavior of the epoxy nanocomposites were examined by X‐ray diffraction and transmission electron microscopy. The curing behavior and thermal property were investigated by in situ Fourier transform infrared spectroscopy and DSC, respectively. The results showed that MMT could be highly intercalated by acidified CAB, and O‐MMT could be easily dispersed in epoxy resin to form intercalated/exfoliated epoxy nanocomposites. When the O‐MMT loading was lower than 8 phr (relative to 100 phr resin), exfoliated nanocomposites were achieved. The glass‐transition temperatures (T_g's) of the exfoliated nanocomposite were 20 °C higher than that of the neat resin. At higher O‐MMT loading, partial exfoliation was achieved, and those samples possessed moderately higher T_g's as compared with the neat resin. O‐MMT showed an obviously catalytic nature toward the curing of epoxy resin. The curing rate of the epoxy compound increased with O‐MMT loading. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1192–1198, 2004     

Non-isothermal crystallization kinetics of exfoliated and intercalated polyethylene/montmorillonite nanocomposites prepared by in situ polymerization

Polyethylene/montmorillonite (PE/MMT) nanocomposites, one intercalated sample with higher MMT content and one exfoliated sample with lower MMT content, were prepared by in situ polymerization using MMT-supported metallocene as catalyst. Non-isothermal crystallization behaviors of these two nanocomposites were investigated and compared. The exfoliated sample exhibits higher crystallization temperature (T_c) than the neat PE, showing nucleation effect of MMT. The intercalated sample has lower T_c than the neat PE due to the confinement of MMT. It is observed that the intercalated sample has longer induction period and faster overall crystallization rate, indicating co-existence of suppression and nucleation effects in this sample. The Avrami plots show that the crystal growth of PE in the intercalated sample is two-dimensional, while it is three-dimensional in the exfoliated sample. The crystallization activation energy of the intercalated sample is slightly smaller than that of the exfoliated sample.     

Dual bimodal polyethylene prepared by intercalated silicate with nickel diimine complex

The ethylene polymerization was catalyzed by the intercalated montmorillonite with the nickel complex, [ArN?C(Me)? C(Me)?NAr]NiBr₂ (Ar = 2,6‐C₆H₃ (i‐Pr)₂). Polymer with low melting point and high molecular weight was produced at the early stage of polymerization followed by formation of polymer with high melting point and low molecular weight. It is proposed that the gallery of silicate lowers the propagation rate of polymerization and frequency of “chain walking” process of nickel complex anchored inside the gallery, which produces polymer with low molecular weight and low branching, whereas the nickel complex immobilized on the surface of silicate generates polymer with high molecular weight and high branching. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5506–5511, 2005     

Synthesis,structure, and morphology of polymer–silica hybrid nanocomposites based on hydroxyethyl methacrylate

Two types of polymer–silica nanocomposites have been prepared by undergoing free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) either in the presence of HEMA-functionalized SiO₂ nanoparticles (Type 1) or during the simultaneous in situ growing of the silica phase through the acid-catalyzed sol–gel polymerization of tetraethoxysilane (TEOS) (Type 2). Relationships between synthesis conditions, chemical structure, and resulting morphology have been studied. Type 1 systems exhibit a classical particle-matrix morphology, but where particles tend to form aggregates. Type 2 systems possess a finer morphology characterized by a very open mass-fractal silicate structure, which is believed to be bicontinuous with the organic phase at a molecular level. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3172–3187, 1999     

Functional copolymer/organo‐MMT nanoarchitectures. XIX. Nanofabrication and characterization of poly(MA‐alt‐1‐octadecene)‐g‐PLA layered silicate nanocomposites with nanoporous core–shell morphology

Novel bioengineering functional copolymer‐g‐biopolymer‐based layered silicate nanocomposites were fabricated by catalytic interlamellar bulk graft copolymerization of L‐lactic acid (LA) monomer onto alternating copolymer of maleic anhydride (MA) with 1‐octadecene as a reactive matrix polymer in the presence of preintercalated LA…organo‐MMT clay (reactive ODA‐MMT and non‐reactive DMDA‐MMT) complexes as nanofillers and tin(oct)₂ as a catalyst under vacuum at 80°C. To characterize the functional copolymer layered silicate nanocomposites and understand the mechanism of in situ processing, interfacial interactions and nanostructure formation in these nanosystems, we have utilized a combination of variuous methods such as FT‐IR spectroscopy, X‐ray diffraction (XRD), dynamic mechanical (DMA), thermal (DSC and TGA‐DTG), SEM and TEM morphology. It was found that in situ graft copolymerization occurred through the following steps: (i) esterification of anhydride units of copolymer with LA; (ii) intercalation of LA between silicate galleries; (iii) intercalation of matrix copolymer into silicate layers through in situ amidization of anhydride units with octadecyl amine intercalant; and (iv) interlamellar graft copolymerization via in situ intercalating/exfoliating processing. The main properties and observed micro‐ and nanoporous surface and internal core–shell morphology of the nanocomposites significantly depend on the origin of MMT clays and type of in situ processing (ion exchanging, amidization reaction, strong H‐bonding and self‐organized hydrophobic/hydrophilic interfacial interactions). This developed approach can be applied to a wide range of anhydride‐containing copolymers such as random, alternating and graft copolymers of MA to synthesize new generation of polymer‐g‐biopolymer silicate layered nanocomposites and nanofibers for nanoengineering and nanomedicine applications. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of experimental conditions on ethylene polymerization with in‐situ‐supported metallocene catalyst

Ethylene polymerization was carried out with a novel in‐situ‐supported metallocene catalyst that eliminates the need for a supporting step before polymerization. The influence of the metallocene amount, aluminum to zirconium mole ratio, temperature, pressure, and cocatalyst type on polymerization kinetics and molecular weight distribution of the produced polyethylene was studied. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1803–1810, 2000     

Preparation of bimodal HDPEs with metallocene on Cr‐montmorillonite support

Previously described Cr‐montmorillonite (Cr‐MMT) was found to retain reactivity in the ethylene polymerization reaction regardless of which alkyl‐metal was used for workup in the preparation process, as long as alkylaluminium was used as a cocatalyst in the actual polymerization reaction. Introduction of hydrogen pressure was found to regulate the polymerization to give the product polymer with a narrower weight distribution, albeit with a somewhat smaller average molecular weight. Supporting metallocene onto Cr‐MMT produced a binuclear catalyst system which gave rise to bimodal polyethylene (PE). Polymer composition of the produced high density polyethylenes (HDPEs) could be controlled by changing factors such as the polymerization conditions and the identity of the metallocene compounds. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3722–3728, 2010     

Ethylene/1‐octene copolymerization studies with in situ supported metallocene catalysts: Effect of polymerization parameters on the catalyst activity and polymer microstructure

Ethylene and 1‐octene copolymerizations were carried out with an in situ supported rac‐[dimethylsilylbis(methylbenzoindenyl)] zirconium dichloride catalyst. In a previous study, it was found that some in situ supported metallocenes produced polyethylene/α‐olefin copolymers with broad and bimodal short chain branching distributions and narrow molecular weight distributions. The ability to produce polyolefins with multimodal microstructural distributions in a single metallocene and a single reactor is attractive for producing polymers with balanced properties with simpler reactor technology. In this study, a factorial experimental design was carried out to examine the effects of the polymerization temperature and ethylene pressure, the presence of hydrogen and an alkylaluminum activator, and the level of the comonomer in the feed on the catalyst activity, short chain branching distribution, and molecular weight distribution of the polymer. The temperature had the most remarkable effect on the polymer microstructure. At high 1‐octene levels, the short chain branching distribution of the copolymer broadened significantly with decreasing temperature. Several factor interactions, including the hydrogen and alkylaluminum concentrations, were also observed, demonstrating the sensitivity of the catalyst to the polymerization conditions. For this catalyst system, the responses to the polymerization conditions are not easily predicted from typical polymerization mechanisms, and several two‐factor interactions seem to play an important role. Given the multiple‐site nature of the catalyst, it has been shown that predicting the polymerization activity and the resulting microstructure of the polymer is a challenging task. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4426–4451, 2002     

Polymer–silicate nanocomposites produced by in situ atom transfer radical polymerization

Polymer–silicate nanocomposites were synthesized with atom transfer radical polymerization (ATRP). An ATRP initiator, consisting of a quaternary ammonium salt moiety and a 2‐bromo‐2‐methyl propionate moiety, was intercalated into the interlayer spacings of the layered silicate. Subsequent ATRP of styrene, methyl methacrylate, or n‐butyl acrylate with Cu(I)X/N,N‐bis(2‐pyridiylmethyl) octadecylamine, Cu(I)X/N,N,N′,N′,N″‐pentamethyldiethylenetriamine, or Cu(I)X/1,1,4,7,10,10‐hexamethyltriethylenetetramine (X = Br or Cl) catalysts with the initiator‐modified silicate afforded homopolymers with predictable molecular weights and low polydispersities, both characteristics of living radical polymerization. The polystyrene nanocomposites contained both intercalated and exfoliated silicate structures, whereas the poly(methyl methacrylate) nanocomposites were significantly exfoliated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 916–924, 2004     

Pendant cyclic carbonate‐polymer/Na‐smectite nanocomposites via in situ intercalative polymerization and solution intercalation

Nanocomposites of sodium smectite with polyether‐ and polystyrene‐containing pendant cyclic carbonates offer a novel approach to improving hydraulic barrier properties of Na‐smectite liners to saline leachates. The cyclic carbonate polyethers were prepared by cationic ring opening polymerization of a cyclic carbonate‐containing epoxide, whilst polystyrene polymers having pendant cyclic carbonate groups were obtained from radical photopolymerization of styrene. Na‐smectite nanocomposites of these polymers were formed via clay in situ polymerization and solution intercalation methods. X‐ray diffraction (XRD) and FT‐IR analysis confirmed that the polyether can be intercalated within the layers of smectite via in situ as well as solution intercalation of the pre‐formed polymer. The cyclic carbonate polyether nanocomposite was more resistant to leaching in 3M aqueous sodium chloride than its respective cyclic carbonate. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2421–2429     

Gas-Phase Polymerization with Transition Metal Catalysts Supported on Montmorillonite – A Particle Morphological Study

This investigation focuses on the mechanism of particle fragmentation and growth when clay-supported metallocene catalysts are used to polymerize ethylene in gas-phase reactors. We supported bis(cyclopentadienyl)-zirconium dichloride (Cp₂ZrCl₂) on montmorillonite (MMT) pretreated with triisobutylaluminum and 10-undecence-1-ol to produce in-situ polyethylene-clay nanocomposites. During gas phase polymerization, the MMT layers were exfoliated by the growing polymer chains, starting from the openings of the clay galleries. After microtoming, the cross-section of the fragmented MMT particles showed bundles of distorted silicate layer stacks, proving that exfoliation took place during polymerization, producing an in-situ polyethylene-clay nanocomposite. Calculations of d-spacing by transmission electron microscopy (TEM) matched those measured by X-ray diffraction (XRD) analysis.