On the Formation of Narrowly Polydispersed PMMA by Surface Initiated Polymerization (SIP) from AIBN-Coated/Intercalated Clay Nanoparticle Platelets

Various free radical surface initiated polymerization (SIP) conditions were investigated on clay nanoparticles coated with monocationic 2,2‘-azobisisobutyronitrile (AIBN) type free radical initiators. Interesting differences in the mechanism of polymer nanocomposite product formation and the role of nanoparticle surface bound AIBN initiators were observed on three types of poly(methyl methacrylate) (PMMA) polymerization conditions:  bulk, suspension, and solution. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) measurements confirmed the attachment of the initiator on the clay particles without decomposition of the azo group. XRD and transmission electron microscopy (TEM) showed that a well-dispersed structure was accomplished only by bulk and solution SIP. The suspension SIP product consisted of a partially exfoliated structure as shown by XRD and clay particle aggregate formation as shown by TEM. In general, the molecular weights (MWs) of the surface bound polymers were found to be lower than those of the free polymer. Using the same clay loading and initiator concentrations, we observed that relatively higher MW polymers were obtained from suspension and bulk polymerizations in contrast to solution method. However, the most interesting observation is that the surface bound polymers (on all three conditions) showed much narrower polydispersity compared to that of a typical AIBN type free radical polymerization

Grafting of Polymers from Clay Nanoparticles via In Situ Free Radical Surface-Initiated Polymerization: Monocationic versus Bicationic Initiators

Surface-initiated polymerization (SIP) from clay nanoparticles was compared between surface-bound mono- and bicationic free radical initiators. Distinct properties in molecular weight (MW), extent of exfoliation, and particle morphology were observed as a consequence of using two different initiator architectures. X-ray diffraction (XRD) results showed that the clay intercalated with monocationic initiator has a larger d spacing and gave a more ordered structure. IR, X-ray photoelectron spectroscopy, and qualitative thermogravimetric analysis confirmed the attachment of both initiators. XRD further showed that the SIP product from the bicationic initiator retained some intercalated structure while a highly exfoliated structure is achieved by the SIP through the monocationic initiator. Consequently the monocationic initiator gave a higher MW polymer. We have found that well-dispersed intercalated clay particles and efficient monomer diffusion are crucial factors in performing a successful SIP and in achieving an exfoliated clay structure

A First Synthesis of Thiophene Dendrimers

Thiophene dendrons and dendrimers were designed and synthesized using a convergent approach. Metal-mediated coupling reactions were used in the synthesis. A rational approach allowed the formation of αα, ββ, and αβ linkages between the dendrons and thiophene units

Living Anionic Surface Initiated Polymerization (SIP) of Styrene from Clay Surfaces

Living Anionic Surface Initiated Polymerization (SIP) of Styrene from Clay Surface

Preparation of Capped Octahedral OsHC₆ Complexes by Sequential Carbon-Directed C–H Bond Activation Reactions

A synthetic procedure based on sequential C-directed C–H bond activation reactions is reported for the preparation of capped octahedral OsHC₆ complexes. Reactions of the dimer [OsCl₂(η⁶-<i>p</i>-cymene)]₂ (<b>1</b>) with PhMeLAgI (PhMeL = 1-phenyl-3-methyl-1<i>H</i>-benzimidazolyl­idene (PhMeBIm), 1-phenyl-3,5,6-trimethyl-1<i>H</i>-benzimidazolyl­idene (PhMeBIm*)) afford OsCl₂(η⁶-<i>p</i>-cymene)­(PhMeL) (L = BIm (<b>2</b>), BIm* (<b>3</b>)), which undergo cyclization to give OsCl­{κ²-C,C-(MeL-C₆H₄)}­(η⁶-<i>p</i>-cymene) (L = BIm (<b>4</b>), BIm* (<b>5</b>)) by stirring in dichloromethane suspensions of Al₂O₃. Complexes <b>4</b> and <b>5</b> exchange the anion with AgOTf (OTf = CF₃SO₃). In acetonitrile, at 75 °C, the resulting OTf derivatives Os­(OTf)­{κ²-C,C-(MeL-C₆H₄)}­(η⁶-<i>p</i>-cymene) (L = BIm (<b>6</b>), BIm* (<b>7</b>)) release the arene to yield the tetra­(solvento) compounds [Os­{κ²-C,C-(MeL-C₆H₄)­(CH₃CN)₄]­OTf (L = BIm (<b>8</b>), BIm* (<b>9</b>)). Complexes <b>8</b> and <b>9</b> react with PhMeLAgI to coordinate a second NHC ligand. The generated species Os­{κ²-C,C-(MeL-C₆H₄)­(PhMeL)­(CH₃CN)₃]­OTf (L = BIm (<b>10</b>), BIm* (<b>11</b>)), containing a C,C-chelate NHC-C₆H₄ ligand and a monodentate NHC group, exist as a mixture of <i>mer</i> (<b>a</b> and <b>b</b>) and <i>fac</i> (<b>c</b>) acetonitrile isomers. The X-ray diffraction structure of <b>10c</b> reveals aromatic–aromatic interactions between the <i>N</i>-phenyl substituent of the monodentate NHC group and aromatic rings of the chelate ligand. The π–π stacking has been analyzed by means of DFT calculations by using the AIM approach. Treatment of <b>10</b> and <b>11</b> with [PhMeLH]­I, in the presence of an excess of Et₃N, leads to the capped octahedral target compounds OsH­{κ²-C,C-(MeL-C₆H₄)}₃ (L = BIm (<b>12</b>), BIm* (<b>13</b>)), as a result of the coordination of a third NHC group and the orthometalation of the <i>N</i>-phenyl substituents of the second and third NHC ligands

Distinct Aggregation and Fluorescence Properties of a Water-Soluble Oligothiophene (6TN) Bolaform Amphiphile

Distinct Aggregation and Fluorescence Properties of a Water-Soluble Oligothiophene (6TN) Bolaform Amphiphil

Preparation of Capped Octahedral OsHC₆ Complexes by Sequential Carbon-Directed C–H Bond Activation Reactions

A synthetic procedure based on sequential C-directed C–H bond activation reactions is reported for the preparation of capped octahedral OsHC₆ complexes. Reactions of the dimer [OsCl₂(η⁶-<i>p</i>-cymene)]₂ (<b>1</b>) with PhMeLAgI (PhMeL = 1-phenyl-3-methyl-1<i>H</i>-benzimidazolyl­idene (PhMeBIm), 1-phenyl-3,5,6-trimethyl-1<i>H</i>-benzimidazolyl­idene (PhMeBIm*)) afford OsCl₂(η⁶-<i>p</i>-cymene)­(PhMeL) (L = BIm (<b>2</b>), BIm* (<b>3</b>)), which undergo cyclization to give OsCl­{κ²-C,C-(MeL-C₆H₄)}­(η⁶-<i>p</i>-cymene) (L = BIm (<b>4</b>), BIm* (<b>5</b>)) by stirring in dichloromethane suspensions of Al₂O₃. Complexes <b>4</b> and <b>5</b> exchange the anion with AgOTf (OTf = CF₃SO₃). In acetonitrile, at 75 °C, the resulting OTf derivatives Os­(OTf)­{κ²-C,C-(MeL-C₆H₄)}­(η⁶-<i>p</i>-cymene) (L = BIm (<b>6</b>), BIm* (<b>7</b>)) release the arene to yield the tetra­(solvento) compounds [Os­{κ²-C,C-(MeL-C₆H₄)­(CH₃CN)₄]­OTf (L = BIm (<b>8</b>), BIm* (<b>9</b>)). Complexes <b>8</b> and <b>9</b> react with PhMeLAgI to coordinate a second NHC ligand. The generated species Os­{κ²-C,C-(MeL-C₆H₄)­(PhMeL)­(CH₃CN)₃]­OTf (L = BIm (<b>10</b>), BIm* (<b>11</b>)), containing a C,C-chelate NHC-C₆H₄ ligand and a monodentate NHC group, exist as a mixture of <i>mer</i> (<b>a</b> and <b>b</b>) and <i>fac</i> (<b>c</b>) acetonitrile isomers. The X-ray diffraction structure of <b>10c</b> reveals aromatic–aromatic interactions between the <i>N</i>-phenyl substituent of the monodentate NHC group and aromatic rings of the chelate ligand. The π–π stacking has been analyzed by means of DFT calculations by using the AIM approach. Treatment of <b>10</b> and <b>11</b> with [PhMeLH]­I, in the presence of an excess of Et₃N, leads to the capped octahedral target compounds OsH­{κ²-C,C-(MeL-C₆H₄)}₃ (L = BIm (<b>12</b>), BIm* (<b>13</b>)), as a result of the coordination of a third NHC group and the orthometalation of the <i>N</i>-phenyl substituents of the second and third NHC ligands

Characterization, Supramolecular Assembly, and Nanostructures of Thiophene Dendrimers

We report the synthesis and characterization of dendritic thiophene derivatives with their unique supramolecular assembly into 2-D crystals, nanowires, and nanoparticle aggregates. The structure and size of the dendrons and dendrimers have been confirmed with various techniques, such as NMR, SEC, and MALDI-TOF-MS. The mass values were consistent with the mass observed by MALDI-TOF-MS, whereas SEC measurements also gave useful information on the hydrodynamic volume of the individual dendrimers. The interesting electrooptical properties were highlighted by very broad absorption spectra and narrower fluorescence consistent with their electrochemical behavior. The self-organization of the dendrimers on the solid substrate is dependent on the nature of the substrate, preparation methods, and the molecule−molecule and molecule−substrate interactions. Thus, 14T-1 and 30T both formed globular aggregates on mica surface, while 14T-1 also formed nanowires on graphite surface. On the other hand, the larger 30T was observed to form 2-D crystalline structures. By varying the alkyl chain length attached to 14T-1, we were also able to obtain 2-D crystals on graphite. This showed that the different symmetry of packing for 30T and 14T-1 is also dependent on several factors, such as the molecular shape, size, and the presence of noncovalent intermolecular interactions. The results demonstrated the unique ability of thiophene dendrimers to form nanostructures on surfaces

Distinct Aggregation and Fluorescence Properties of a Water-Soluble Oligothiophene (6TN) Bolaform Amphiphile

Distinct Aggregation and Fluorescence Properties of a Water-Soluble Oligothiophene (6TN) Bolaform Amphiphil

Preparation of Capped Octahedral OsHC₆ Complexes by Sequential Carbon-Directed C–H Bond Activation Reactions

A synthetic procedure based on sequential C-directed C–H bond activation reactions is reported for the preparation of capped octahedral OsHC₆ complexes. Reactions of the dimer [OsCl₂(η⁶-<i>p</i>-cymene)]₂ (<b>1</b>) with PhMeLAgI (PhMeL = 1-phenyl-3-methyl-1<i>H</i>-benzimidazolyl­idene (PhMeBIm), 1-phenyl-3,5,6-trimethyl-1<i>H</i>-benzimidazolyl­idene (PhMeBIm*)) afford OsCl₂(η⁶-<i>p</i>-cymene)­(PhMeL) (L = BIm (<b>2</b>), BIm* (<b>3</b>)), which undergo cyclization to give OsCl­{κ²-C,C-(MeL-C₆H₄)}­(η⁶-<i>p</i>-cymene) (L = BIm (<b>4</b>), BIm* (<b>5</b>)) by stirring in dichloromethane suspensions of Al₂O₃. Complexes <b>4</b> and <b>5</b> exchange the anion with AgOTf (OTf = CF₃SO₃). In acetonitrile, at 75 °C, the resulting OTf derivatives Os­(OTf)­{κ²-C,C-(MeL-C₆H₄)}­(η⁶-<i>p</i>-cymene) (L = BIm (<b>6</b>), BIm* (<b>7</b>)) release the arene to yield the tetra­(solvento) compounds [Os­{κ²-C,C-(MeL-C₆H₄)­(CH₃CN)₄]­OTf (L = BIm (<b>8</b>), BIm* (<b>9</b>)). Complexes <b>8</b> and <b>9</b> react with PhMeLAgI to coordinate a second NHC ligand. The generated species Os­{κ²-C,C-(MeL-C₆H₄)­(PhMeL)­(CH₃CN)₃]­OTf (L = BIm (<b>10</b>), BIm* (<b>11</b>)), containing a C,C-chelate NHC-C₆H₄ ligand and a monodentate NHC group, exist as a mixture of <i>mer</i> (<b>a</b> and <b>b</b>) and <i>fac</i> (<b>c</b>) acetonitrile isomers. The X-ray diffraction structure of <b>10c</b> reveals aromatic–aromatic interactions between the <i>N</i>-phenyl substituent of the monodentate NHC group and aromatic rings of the chelate ligand. The π–π stacking has been analyzed by means of DFT calculations by using the AIM approach. Treatment of <b>10</b> and <b>11</b> with [PhMeLH]­I, in the presence of an excess of Et₃N, leads to the capped octahedral target compounds OsH­{κ²-C,C-(MeL-C₆H₄)}₃ (L = BIm (<b>12</b>), BIm* (<b>13</b>)), as a result of the coordination of a third NHC group and the orthometalation of the <i>N</i>-phenyl substituents of the second and third NHC ligands