Investigation of Chain Dynamics in Poly(n‐alkyl methacrylate)s by Solid‐State NMR: Comparison with Poly(n‐alkyl acrylate)s

PnAMAs exhibit a local nanophase separation associated with intriguing chain dynamics (Macromol. Chem. Phys. 2005 , 206, 142). PnAMAs of high molar mass, as determined by SEC and MHKS parameters, were investigated in the melt with a recently‐developed solid‐state NMR method (NOE with dipolar filter; Solid State Nucl. Magn. Res. 2005 , 28, 160). The correlation times are assigned to the relaxation of the alkyl nanodomains, as coupled motions of the main chain and hindered local modes in the side chain. Comparison with poly(n‐alkyl acrylates) shows a higher anisotropy of the main chain motions and a better organized local nanophase separation in PnAMAs.

     

Investigation of Polymer‐Filler Interactions in TiO2‐Filled Poly(n‐alkyl methacrylates) by Low‐Field NMR Relaxometry

Low‐field NMR relaxometry is sensitive to molecular mobility within well‐defined time windows and can thus be applied to study interactions between polymers and inorganic filler particles in composite materials. Volume fraction and dispersion of the filler influence the polymer chain dynamics, which also modify the macroscopic properties of the polymer composites. As model systems, TiO₂‐filled poly(n‐alkyl methacrylates) with different side‐chain lengths and filler contents are prepared by melt mixing. Several ¹H NMR relaxation parameters, which are sensitive and selective toward polymer–filler interactions, are investigated at a Larmor frequency of 20 MHz as a function of temperature. Both physical and empirical models are used to analyze the NMR data, and the results are compared with the aim of an unambiguous detection of polymer–filler interactions.

     

Tuning of Sol–Gel Transition in the Mixed Polymer Micelle Solutions of Copolymer Mixtures Consisting of Enantiomeric Diblock and Triblock Copolymers of Polylactide and Poly(ethylene glycol)

Poly(ethylene glycol) (PEG) is partially furanylated with different feed ratios of furfuryl isocyanate and used as the macro initiator of ring‐opening polymerization of l ‐ and d ‐lactides to synthesize copolymer mixtures of furan‐terminated AB diblock and ABA triblock copolymers (poly(oxyethylene)–poly(l ‐lactide)/poly(l ‐lactide)–poly(oxyethylene)–poly(l ‐lactide) and poly(oxyethylene–poly(d ‐lactide)/poly(d ‐lactide)–poly(oxyethylene)–poly‐(d ‐lactide)) having different diblock/triblock ratios. The mixed micelle solutions of these enantiomeric copolymer mixtures undergo sol‐to‐gel or gel‐to‐sol transition depending on the diblock/triblock ratio of the copolymer mixtures. The rheological properties of the mixed micelle solutions could also be controlled by changing the diblock/triblock ratios or the initial furanylation ratio of PEG.

     

Effect of Mixed Sol‐Gel Precursors on the Metal‐Oxo Phase Within a UV‐Curable Silicone Hybrid Material

Summary: An inorganic hybrid material was produced using a polysiloxane binder and metal‐oxo‐clusters which were derived from sol‐gel precursors. The continuous phase is composed of an elastomeric polysiloxane functionalized with cycloaliphatic epoxide groups. Pendant alkoxy silane groups serve as a coupling agent to form a network between the metal‐oxo‐clusters and the crosslinked polysiloxane. Methyl, cyclopentyl, and cyclohexyl substituted polysiloxanes were formulated with a variety of sol‐gel precursors (tetraethylorthosilicate oligomers, titanium(IV) iso‐propoxide, zirconium(IV) propoxide, and zinc acetate). Phase‐modulated FT‐IR, X‐ray photoelectron spectroscopy, solid state ²⁹Si NMR, and solid state ¹³C NMR were used to investigate the internal structure of the mixed metal‐oxo/silicon‐oxo colloids prepared within the cured polysiloxane matrix. Results indicate that the cycloaliphatic groups inhibit the complete hydrolysis and condensation of the pendant triethoxysilane group and reaction of the sol‐gel precursors. Analysis also indicated that the metal‐oxo‐clusters were comprised of mixed species of sol‐gel precursors resulting in hetero‐bonded (Si? O? Metal) colloids.

Possible network compositions of the cured material (a) specific metal‐oxo‐clusters, (b) hetero‐bonded metal‐oxo‐clusters, and (c) core/shell type metal‐oxo‐cluster configuration.     

Molecular Dynamics of Poly(ethylene‐2,5‐furanoate) (PEF) as a Function of the Degree of Crystallinity by Dielectric Spectroscopy and Calorimetry

The segmental and local dynamics of the bio‐based polyester poly(ethylene‐2,5‐furanoate) (PEF) are investigated by dielectric spectroscopy (DS) at atmospheric pressure as a function of temperature and frequency for samples prepared with different degrees of crystallinity. Crystallization significantly alters the segmental process as this is manifested in the dielectric strength and the distribution of relaxation times. Enhanced crystallinity by the different annealing protocols increases the glass temperature of the mobile amorphous fraction. A two‐phase model is adequate in describing the dynamics associated with the β‐process within the glassy state. However, the same model fails in describing the segmental dynamics at and above the glass temperature. The combined differential scanning calorimetry and DS results provide evidence that for samples with a degree of crystallinity of ≈40%, approximately a third of segments are located within the restricted amorphous fraction.

     

Characteristic Sliding Frictional Behavior on the Surface of Nanocomposite Hydrogels Consisting of Organic‐Inorganic Network Structure

Summary: Sliding frictional behavior on the surface of novel nanocomposite hydrogels (NC gels), composed of poly(N‐isopropylacrylamide) and exfoliated clay, was investigated and compared with that of conventional chemically‐crosslinked hydrogels (OR gels). Since OR gels are so weak, the sliding test, in general, could not be carried out on their surfaces except when wet. On the contrary, NC gels can withstand sliding friction under high loading and it was found that the frictional forces are sensitive to the environmental surroundings (wet or in‐air), the gel composition (water, clay contents), and loading. In air, NC gels exhibit a characteristic force profile with a maximum static frictional force (max‐SFF) and subsequent constant dynamic frictional force. In contrast, NC gels exhibit very low frictional forces under wet conditions. The change in frictional force with surroundings was very distinctive for NC gels, particularly for those with low clay contents. Max‐SFF for NC1 gel decreased more than 100‐fold by changing the environment from in‐air to wet. The characteristic sliding frictional behaviors are explained on the basis of a unique organic/inorganic network structure of NC gels.

The model of sliding process on NC gel and effects of clay content of NC gels on the sliding frictional behavior.     

Effect of UV Curing on Electrical Properties of a UV‐Curable co‐Polyacrylate/Silica Nanocomposite as a Transparent Encapsulation Resin for Device Packaging

Electrical properties of UV‐curable co‐polyacrylate/silica nanocomposite resins prepared via sol‐gel process for device encapsulation were investigated. It was found that, by appropriate UV curing process and the formation of nanoscale silica particles finely dispersed in the resin matrix, the leakage current density of the nanocomposite resin films decreases from 235 to 1.3 nA · cm^?2 at the applied electrical field of 10 kV · cm^?1. The silica nanoparticles also restricted the motions of polar functional groups in organic matrix that the nanocomposite films with satisfactory dielectric properties [dielectric constant (ε) = 3.93 and tangent loss (tanδ = 0.0472) could be obtained. Chemical structure analyses revealed that excessive UV curing results in photooxidation and/or photodegradation in resin samples, leading to the polar groups and ionic/radical segments in organic matrix as well as the ? Si? O? Si? structure in the vicinity of silica nanoparticles. These organic/inorganic functional groups generated more permeation paths for charge carrier migration and hence deteriorated the electrical properties of the nanocomposite samples. Though post‐baking treatment at 80 °C for 1 h followed by UV curing improved the rigidity of the resin sample, it brought the polar functional groups closer to each other and similarly degraded electrical properties of the nanocomposite resins.

     

Synthesis and Dielectric Study of New Liquid‐crystalline Polysiloxanes Presenting a Thioether Spacer

Three new cyanobiphenyl polysiloxanes presenting long thioether spacers have been carried out. This type of spacer leads to very stable liquid‐crystalline polymers at room temperature and remove the crystallinity phenomenon. Dielectric analysis results show that the thioether spacer brings much more molecular flexibility to the system.

Example of an “interdigitated” structure observed by X‐ray analysis.     

Gel Formation and Molecular Characteristics of Poly(N‐isopropylacrylamide) Prepared by Free‐Radical Redox Polymerization in Aqueous Solution

The molecular characteristics of poly(N‐isopropylacrylamide) (PNIPA), prepared by free‐radical polymerization using an aqueous redox initiator and reaction conditions comparable to those used in the synthesis of nanocomposite gels, were investigated by altering the monomer concentration ([NIPA]) and the polymerization temperature (T_p) across the transition temperature (LCST). When T_p<LCST, there is a critical [NIPA] (=n*) above which PNIPA partially forms gels in the absence of a chemical crosslinker, and the gel fraction increases with increasing [NIPA] and decreasing T_p. In the range of n<n*, the molecular weight of soluble PNIPA correlated well with [NIPA]. When T_p>LCST, gels were not formed regardless of [NIPA]. The structure and mechanism of formation of self‐crosslinked PNIPA gels are discussed.

     

Confinement Effects on the Optical Properties and Chain Conformations of Poly(9,9‐di‐n‐octylfluorene‐alt‐benzothiadiazole) Nanotubes

Although many fabrication methods of conjugated polymer nanostructures have been developed, the effects of confinement on the morphologies, chain conformations, and optical properties of conjugated polymers are still not well understood. In this work, poly(9,9‐di‐n‐octylfluorene‐alt‐benzothiadiazole) (F8BT), a light‐emitting conjugated polymer, is used to fabricate nanotubes by a solution wetting method using anodic aluminum oxide templates. The property changes under the nanoscale confinement have been investigated. The morphologies of F8BT nanostructures are characterized by scanning electron microscope, transmission electron microscope, and laser scanning confocal microscope. The data show the hollow morphologies and no or low crystallinity of the nanostructures. The optical properties are also measured using UV–vis absorption, photoluminescence, and confocal Raman spectroscopy. The spectroscopy data indicate that F8BT polymer chains have less intermolecular interactions and coplanarity under the confinement effect.

     

Simultaneous Vapor‐Phase Polymerization of PEDOT and a Siloxane into Organic/Inorganic Hybrid Thin Films

The co‐vaporization and simultaneous polymerization of EDOT and APTES on a FTS‐coated substrate resulting in a homogeneous PEDOT/ASSQ thin film is described. The physicochemical properties of the film, including surface hardness, solvent mechanical wear resistance, and resistance to scratch, were much better than those of pure PEDOT. A PEDOT/ASSQ hybrid film with homogeneous morphology resulted, as judged by AFM topography scans, surface roughness calculations, and SEM images. The ASSQ proportion in the hybrid films, as investigated by XPS and EDS, was strongly dependent on the content of FTS on the substrate. In addition, the simultaneous polymerization of a PEDOT/ASSQ hybrid film onto selective micropatterns was demonstrated and analyzed.

     

Effect of Branched Side Chains on the Physicochemical and Photovoltaic Properties of Poly(3‐hexylthiophene) Isomers

Two P3HT isomers with branched alkyl side chains, P3EBT and P3MPT, are synthesized. The HOMO energy levels of P3EBT and P3MPT are ?5.35 and ?5.24 eV, respectively, which are significantly lower than that of P3HT with a linear side chain. The absorption edges of the two P3HT isomer films, especially those of P3EBT, are blue‐shifted in comparison with that of P3HT. A PSC based on P3EBT:IC₆₀BA (2:1 w/w) shows a high open‐circuit voltage of 0.98 V, which is the highest V_oc reported so far for polythiophene‐based PSCs. A PSC based on P3MPT:IC₇₀BA (2:1 w/w) exhibits a power conversion efficiency of 3.62% with a V_oc of 0.91 V. P3MPT is suitable for the application in tandem PSCs.     

Thermodynamics of Phase Behavior in PEO/P(EO‐b‐DMS) Homopolymer and Block Co‐Oligomer Mixtures under Pressure

The cloud‐point temperatures (T_cl's) of poly(ethylene oxide) (PEO) and poly(ethylene oxide)‐block‐polydimethylsiloxane (P(EO‐b‐DMS)) homopolymer and block‐oligomer mixtures were determined by turbidity measurements over a range of temperatures (105 to 130 °C), pressures (1 to 800 bar), and compositions (10–40 wt.‐% PEO). The system phase separates upon cooling and T_cl was found to decrease with an increase in pressure for a constant composition. In the absence of special effects, this finding indicates negative excess volumes. Special attention was paid to the demixing temperatures as a function of the pressure for the different polymer mixtures and the plots in the T‐? plane (where ? signifies volume fractions). The cloud‐point curves of the polymer mixture under pressures were observed for different compositions. The Sanchez‐Lacombe (SL) lattice fluid theory was used to calculate the spinodals, the binodals, the Flory‐Huggins (FH) interaction parameter, the enthalpy of mixing, and the volume changes of mixing. The calculated results show that modified P(EO‐b‐DMS) scaling parameters with the new combining rules can describe the thermodynamics of the PEO/P(EO‐b‐DMS) system well with the SL theory.

Cloud point curves for various PEO/P(EO‐b‐DMS) polymer mixtures at various pressures on the T‐?_PEO plane.     

Effect of the Structure of Reactor Poly(propylene‐co‐ethylene) Blends on the Diffusion Coefficient and Activation Energy of a Conventional Antioxidant

The diffusion of a thermal stabilizer, i.e., Irganox 1010, has been studied in three different reactor poly(propylene‐co‐ethylene) blends, namely HecoQ, ExpSS, and Super Soft. The diffusion experiments were carried out by using Roe's method based on a stack of several polymer films where each of them had 60–70 μm thickness. The concentration profile of the stabilizer in every film has been monitored by the absorbance at 282 nm of the recorded UV spectra. Under our experimental conditions, the diffusion of Irganox 1010 for all polymer materials can be correctly interpreted by using Fick's second law resolved under certain boundary conditions. Best‐fitting the experimental data with the equation model also allows calculation of the diffusion coefficient, D, for these polymer materials at 40, 70 and 80 °C. By applying an Arrhenius‐type equation to the calculated D coefficients, an estimation of activation energies of the diffusion process has been achieved. An interpretation, in terms of free volume theory, has been applied to explain the observed variation of D which depends mostly on the amount of amorphous phase of the blends.

Arrhenius plots of ln D versus 1/(RT) for the polymers given in legend.     

Effect of LiClO4 and LiCl Additives on the Kinetics of Anionic Polymerization of Methyl Methacrylate in Toluene‐Tetrahydrofuran Mixed Solvent

The kinetics of anionic polymerization of MMA has been studied at ?78 °C in toluene‐THF (9:1 v/v) using 1,1′‐diphenylhexyl lithium as initiator in the presence of lithium perchlorate and lithium chloride as Lewis acid additives. The control of the polymerization is lost in the absence of additives as evident from the non‐linear first‐order time‐conversion plot and polymers with broad multimodal molecular weight distribution. The presence of LiClO₄ and LiCl in 10:1 and 5:1 ratio, respectively, over the initiator brings about sufficient control, yielding polymers of narrow unimodal distribution throughout the polymerization. The reaction in the presence of the additives follows first‐order kinetics free of termination and transfer. Moreover, the order with respect to the active centers is found to be almost unity, which signifies a probable disaggregation of ion‐pairs to a single complexed propagating species.

GPC elugrams at different conversions for MMA polymerization in the presence of LiClO₄.     

Atom‐Transfer Radical Polymerization: A Strategy for the Synthesis of Halogen‐Free Amino‐Functionalized Poly(methyl methacrylate) in a One‐Pot Reaction

Summary: An initiator containing an alkyl bromide unit and a protected amine functional group is used with CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA), in a 1:2 molar ratio with respect to initiator concentration, in order to obtain amino‐group terminated as well as halogen‐free poly(methyl methacrylate) (PMMA) in a one‐pot atom‐transfer radical polymerization (ATRP). The terminal bromines are replaced by hydrogen atoms of the PMDETA ligand, which acts as a transfer agent. However, terminating side reactions like disproportionation or dehydrobromination occur from the beginning of the polymerization. Kinetic studies by in‐line Raman spectroscopy and off‐line ¹H NMR spectroscopy revealed that the controlled character of the ATRP is lost under these conditions. The measured molecular weights were consistently higher than the theoretical ones and the molecular weight distributions are relatively broad. Thermal analysis of the obtained poly(methyl methacrylate) shows two main degradation steps, one starting from unsaturated end groups (depolymerization), and one caused by main‐chain scission, a further proof for the occurrence of terminating side reactions.

Structural analysis of PMMA by matrix‐assisted laser desorption‐ionization mass spectrometry.     

Effect of Blend Composition on Scratch Behavior of Polystyrene/Poly(2,6‐dimethyl‐1,4‐phenyleneoxide) Blends

The relationship between the scratch behavior and molecular aggregation states of polystyrene (PS), poly(2,6‐dimethyl‐1,4‐phenyleneoxide) (PPO), and their blends, is investigated based on differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), polarized optical microscopy (POM), and indentation and scratch tests. DSC reveals that all the PS/PPO blends show the single glass transition temperature (T_g) and the T_g monotonically increase and T_g breadth exhibits a maximum, with an increase in PPO content. Furthermore, density and intermolecular chain distance obtained by WAXD exhibits maximum and minimum values at near 50 wt% of PPO, respectively. It is evident that densification occurs by blending PS and PPO. The scratch coefficient of friction (SCOF) value of PS is the largest and PS exhibits a fish‐scale pattern after scratch testing, while the SCOF value of PPO is much smaller than PS and PPO exhibits smooth groove formation. The PS50/PPO50 and PS20/PPO80 blends exhibit superior scratch and indentation resistance than PS and PPO. Damage morphology observation by POM and indentation tests reveals that molecular orientation is more restricted, and resistance against indentation increases for blends. This is due mainly to densification of the blend system.     

13C NMR Study of the Effect of Coordinating Solvents on Zirconocene‐Catalyzed Propene/1‐Hexene Copolymerization

The solvent effect observed in propene/1‐hexene copolymerizations performed with the isospecific catalyst rac‐Et(Ind)₂ZrCl₂/MAO is studied. A range of solvents with increasing donor character and steric hindrance has been tested, and their effect on copolymer yield, composition, and microstructure has been thoroughly analyzed. Our results demonstrate that the solvent can have a significant influence on the comonomer reactivities, even though the solvent polarity is not the relevant factor. At the same comonomer compositions in solution, polymerizations carried out in coordinating solvents (e. g., aromatic solvents), lead to the formation of products with considerably decreased content of 1‐hexene. The reduced incorporation of the higher α‐olefin is explained in terms of competition between the nucleophilic medium and the olefin monomer for coordination to the active polymerization site. These results give us valuable information regarding the mechanism of polymerization at the active centers.     

Effect of a Water‐Soluble Polymer on Polymer Interdiffusion in P(MMA‐co‐BA) Latex Films

We describe non‐radiative energy‐transfer experiments to measure the rates of polymer interdiffusion in P(MMA‐co‐BA) latex films formed in the presence of poly(vinyl alcohol) (PVOH). PVOH had relatively little effect on the initial efficiency of energy transfer, even when the amount of PVOH was large enough to form the continuous phase. Since Φ_ET(0) is a measure of the interfacial area between D‐ and A‐labeled cells in the film, we conclude that under these circumstances the dispersed P(MMA‐co‐BA) copolymer is in the form of clusters with many contacts between particles containing D and A labels. These large amounts of PVOH also reduce the amount of polymer diffusion that takes place when the films are annealed. When smaller amounts of PVOH are present, the effects are measurable but much smaller. In the presence of 2 to 17 wt.‐% PVOH, the polymer diffusion rate is retarded. The magnitude of the effect increases with the amount of PVOH present, and the effect is larger at 45 °C than at 63 °C. We show that the PVOH has its largest influence at the very early stages of polymer diffusion.

Schematic representation of an energy transfer experiment, which monitors polymer interdiffusion in a latex film.