Reduced stress‐optical coefficient of polycarbonate by antiplasticization

We have investigated the effect of antiplasticization on the stress‐optical behavior of polycarbonate (PC) containing terphenyls (tPh) and di(2‐ethylhexyl)adipate (DEHA). Addition of the three tPhs (p‐, o‐, and m‐tPh) and DEHA at contents of 5–10 wt % increases the tensile storage modulus (E' ) of PC owing to the antiplasticization effect. In particular, p‐tPh increases E' more than the other additives, suggesting that the rod‐like shape matches the free volume of PC in the glassy state. The three tPh isomers improve the glassy birefringence of PC while DEHA does not change the glassy birefringence, which corresponds to the polarizability anisotropy. The stress‐optical coefficient, a ratio of stress and birefringence, of PC decreases with increasing additive content in order of p‐tPh ? o‐tPh > m‐tPh = DEHA. This result is agreement with a restricted rotational motion of additive molecule in PC, which is observed in dynamic mechanical and birefringence data. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 1837–1842     

Molecular motion of polycarbonate included in γ‐cyclodextrin

Molecular motions of single polycarbonate (PC) chains threaded into crystalline γ‐cyclodextrin (γ‐CD) channels were examined using solid‐state ¹³C NMR and molecular dynamics simulations. The location of PC within the channels was confirmed by spin diffusion from a PC ¹³C label to natural‐abundance ¹³C of the γ‐CD. Rotor‐encoded longitudinal magnetization (RELM) (under 7‐kHz magic‐angle sample‐spinning conditions) was combined with multiple‐pulse ¹H‐¹H dipolar decoupling to detect large‐amplitude phenyl‐ring motion in both bulk PC and polycarbonate γ‐cyclodextrin inclusion compound (PC‐γ‐CD). The RELM results indicate that the phenyl rings in PC‐γ‐CD undergo 180° flips faster than 10 kHz just as in bulk PC. The molecular dynamics simulations show that the frequency of the phenyl‐ring flips depends on the cooperative motions of PC atoms and neighboring atoms of the γ‐CD channel. The distribution of protonated aromatic‐carbon laboratory and rotating‐frame ¹³C spin‐lattice relaxation rates for bulk PC and PC‐γ‐CD are similar but not identical. The distributions for both systems arise from site heterogeneities. For bulk PC, the heterogeneity is attributed to variations in local chain packing, and for PC‐γ‐CD the heterogeneity arises from variations in the location of the PC phenyl rings in the γ‐CD channel. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1271–1282, 2007     

Phenylene motion in polycarbonate and polycarbonate/additive mixtures

Pulsed deuteron NMR line shapes have been analysed to characterize type and time scale of the phenylene group motion in glassy bisphenol-A polycarbonate. The motional mechanism involves-flips about theC ₁ C ₄ axis augmented by small angle fulctuations about the same axis, reaching a rms amplitude of ±35 at 380 K. The distribution of correlation times for the-flips is heterogeneous in nature and can be described either by a log-Gaussian or an asymmetric distribution with a more rapid decay at high correlation times comparable to the Williams-Watts distribution. From both distributions essentailly the same mean activation energy of 37 kJ/mol is obtained, whereas the temperature dependent width of the highly asymmetric distribution is somewhat smaller compared to the log-Gaussian distribution. Time scale and activation energy of the-flip motion are correlated to secondary mechanical relaxations. Low molecular mass additives, which suppress the mechanical relaxation, also hinder the phenylene motion for a substantial fraction of phenylene groups. The effect of additives is not only to shift the mean value of the distribution of correlation times to higher values but also to increase drastically the width of the distribution. The results of this work strongly suggest that the secondary mechanical relaxation and the large amplitude motions of the phenylene groups in polycarbonate are related.     

Hydrogen Adsorption and Diffusion in p‐tert‐Butylcalix[4]arene: An Experimental and Molecular Simulation Study

Experimental adsorption isotherms were measured and computer simulations were performed to determine the nature of the H₂ gas uptake in the low‐density p‐tert‐butylcalix[4]arene (tBC) phase. ¹H NMR peak intensity measurements for pressures up to 175 bar were used to determine the H₂ adsorption isotherm. Weak surface adsorption (up to ≈2 mass % H₂) and stronger adsorption (not exceeding 0.25 mass % or one H₂ per calixarene bowl) inside the calixarene phase were detected. The latter type of adsorbed H₂ molecule has restricted motion and shows a reversible gas adsorption/desorption cycle. Pulsed field gradient (PFG) NMR pressurization/depressurization measurements were performed to study the diffusion of H₂ in the calixarene phases. Direct adsorption isotherms by exposure of the calixarene phase to pressures of H₂ gas to ≈60 bar are also presented, and show a maximum H₂ adsorption of 0.4 H₂ per calixarene bowl. Adsorption isotherms of H₂ in bulk tBC have been simulated using grand canonical Monte Carlo calculations in a rigid tBC framework, and yield adsorptions of ≈1 H₂ per calixarene bowl at saturation. Classical molecular dynamics simulations with a fully flexible calixarene molecular force field are used to determine the guest distribution and inclusion energy of the H₂ in the solid with different loadings.     

Elastic excitations in polycarbonate membranes

Brillouin light scattering was used to probe acoustic waves propagating with both longitudinal and transverse polarizations in the surface and the bulk of self‐supported particle track‐etched polycarbonate membranes with 15‐ and 80‐nm nanopores. The recorded scattering line shape at gigahertz frequencies reveals changes in the surface waves of the membranes which are more pronounced for the 80‐nm nanopores despite the low porosity (0.7 and 0.05%). Because the measured elastic constants (1.2 and 6.2 GPa) were found to compare very well with the values for thick polycarbonate film, modifications of the elasto‐optical coefficients and/or the transparency might be the reason for the different scattering line shapes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3311–3317, 2004     

Crystallization of bisphenol‐A polycarbonate by a vacuum process

The surface of bisphenol‐A‐polycarbonate (BAPC) showing a stable amorphous state can be crystallized by the “vapor transportation method”. Crystallized BAPC was employed as the novel simple storage medium and bit patterns were recorded on its surface by laser irradiation. Copyright © 2004 John Wiley & Sons, Ltd.     

Slow Molecular Motions in Ionic Liquids Probed by Cross‐Relaxation of Nuclear Spins During Overhauser Dynamic Nuclear Polarization

Solution‐state Overhauser dynamic nuclear polarization (ODNP) at moderate fields, performed by saturating the electron spin resonance (ESR) of a free radical added to the sample of interest, is well known to lead to significant NMR signal enhancements in the steady state, owing to electron–nuclear cross‐relaxation. Here it is shown that under conditions which limit radical access to the molecules of interest, the time course of establishment of ODNP can provide a unique window into internuclear cross‐relaxation, and reflects relatively slow molecular motions. This behavior, modeled mathematically by a three‐spin version of the Solomon equations (one unpaired electron and two nuclear spins), is demonstrated experimentally on the ¹⁹F/¹H system in ionic liquids. Bulky radicals in these viscous environments turn out to be just the right setting to exploit these effects. Compared to standard nuclear Overhauser effect (NOE) work, the present experiment offers significant improvement in dynamic range and sensitivity, retains usable chemical shift information, and reports on molecular motions in the sub‐megahertz (MHz) to tens of MHz range—motions which are not accessed at high fields.     

Dynamic mechanical and gas transport properties of blends and random copolymers of bisphenol-A polycarbonate and tetramethyl bisphenol-A polycarbonate

Dynamic mechanical and gas transport properties for homogeneous homopolymer blends and random copolymers of bisphenol-A and tetramethyl bisphenol-A polycarbonates (PC-TMPC) were determined. The gas transport measurements were performed at 35°C for the gases He, H₂, O₂, Ar, N₂, CH₄, and CO₂. The results show that the copolymers have lower permeability, apparent diffusion, and solubility coefficients than the blends. Permeability coefficients for blends follow a semilogarithmic ideal mixing rule while copolymers exhibit negative deviations from this. Specific volume measurements show that the free volume available for gas transport is slightly larger in copolymers than in blends of the same composition. These apparently contradictory results may relate to the differences in local mode chain motions observed for the copolymer and blend series. The γ relaxation processes in PC and TMPC seem to operate independently in the blends (no intermolecular coupling) while there is clear evidence for intramolecular coupling in the copolymers. © 1992 John Wiley & Sons, Inc.     

Block copolymer materials from the organocatalytic ring‐opening polymerization of a pentaerythritol‐derived cyclic carbonate

9‐Phenyl‐2,4,8,10‐tetraoxaspiro[5,5]undecanone (PTO) was synthesized from pentaerythritol via the acid‐catalyzed acetal formation reaction with benzaldehyde and subsequent ring closure with ethyl chloroformate. The cyclic carbonate monomer was subsequently polymerized by ring‐opening polymerization (ROP) initiated from 1,4‐butanediol (1,4‐BDO) using the 1‐(3,5‐bis(trifluoromethyl)phenyl)‐3‐cyclohexylthiourea and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene dual organocatalytic system. It was found that the organocatalyst allowed for the synthesis of well‐defined polymers with minimal adverse side reactions and low dispersities. This system was then employed in the ROP of PTO initiated from an α,ω‐dihydroxy poly(caprolactone) (PCL) macroinitiator, with varying molecular weights, to yield a series of A‐B‐A block copolymers. These materials were characterized by ¹H NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis and tensile analysis. It was found that the chain extension from PCL with poly(PTO) (PPTO) blocks yielded a thermoplastic material with superior tensile properties (elongation and Young's modulus) to that of the PCL homopolymer. Furthermore, it was noted that the addition of PPTO could be employed to alter the crystallization properties (crystallization temperature (T_c), and percentage crystallization) of the central PCL block. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2279–2286     

High‐rate crystallization of polycarbonate in spincast thin film

Surface morphology of bisphenol‐A polycarbonate (BAPC) thin films, with thickness ranging from 30 to 1000 nm on silicon substrates was studied by atomic force microscopy. The films were prepared by spincasting from 1,2‐dichloroethane solutions of 0.25–5.0 wt % BAPC. Even though longer annealing than 250 h was necessary for complete crystallization for bulk BAPC, high crystallinity was observed for 30 nm thick film after annealing at 200 °C for 48 h in vacuum. Positron annihilation lifetime spectroscopy measurements showed that the free volume hole size in 30 nm thick film was larger than that of bulk at 200 °C. Comparison of the BAPC concentration in the precursor solution with the overlap concentration suggests that the high crystallinity of the 30 nm BAPC film is due to less entangled chains caused by rapid removal of the solvent from the dilute solution. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Site‐Resolved Backbone and Side‐Chain Intermediate Dynamics in a Carbohydrate‐Binding Module Protein Studied by Magic‐Angle Spinning NMR Spectroscopy

Magic‐angle spinning solid‐state NMR spectroscopy has been applied to study the dynamics of CBM3b–Cbh9A from Clostridium thermocellum (ctCBM3b), a cellulose binding module protein. This 146‐residue protein has a nine‐stranded β‐sandwich fold, in which 35 % of the residues are in the β‐sheet and the remainder are composed of loops and turns. Dynamically averaged ¹H‐¹³C dipolar coupling order parameters were extracted in a site‐specific manner by using a pseudo‐three‐dimensional constant‐time recoupled separated‐local‐field experiment (dipolar‐chemical shift correlation experiment; DIPSHIFT). The backbone‐Cα and Cβ order parameters indicate that the majority of the protein, including turns, is rigid despite having a high content of loops; this suggests that restricted motions of the turns stabilize the loops and create a rigid structure. Water molecules, located in the crystalline interface between protein units, induce an increased dynamics of the interface residues thereby lubricating crystal water‐mediated contacts, whereas other crystal contacts remain rigid.     

The effect of nanoparticle shape on polymer‐nanocomposite rheology and tensile strength

Nanoparticles can influence the properties of polymer materials by a variety of mechanisms. With fullerene, carbon nanotube, and clay or graphene sheet nanocomposites in mind, we investigate how particle shape influences the melt shear viscosity η and the tensile strength τ, which we determine via molecular dynamics simulations. Our simulations of compact (icosahedral), tube or rod‐like, and sheet‐like model nanoparticles, all at a volume fraction ? ≈ 0.05, indicate an order of magnitude increase in the viscosity η relative to the pure melt. This finding evidently can not be explained by continuum hydrodynamics and we provide evidence that the η increase in our model nanocomposites has its origin in chain bridging between the nanoparticles. We find that this increase is the largest for the rod‐like nanoparticles and least for the sheet‐like nanoparticles. Curiously, the enhancements of η and τ exhibit opposite trends with increasing chain length N and with particle shape anisotropy. Evidently, the concept of bridging chains alone cannot account for the increase in τ and we suggest that the deformability or flexibility of the sheet nanoparticles contributes to nanocomposite strength and toughness by reducing the relative value of the Poisson ratio of the composite. The molecular dynamics simulations in the present work focus on the reference case where the modification of the melt structure associated with glass‐formation and entanglement interactions should not be an issue. Since many applications require good particle dispersion, we also focus on the case where the polymer‐particle interactions favor nanoparticle dispersion. Our simulations point to a substantial contribution of nanoparticle shape to both mechanical and processing properties of polymer nanocomposites. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1882–1897, 2007     

Theoretical and experimental characterization of amino‐PEG‐phosphonate‐terminated Polyphosphorhydrazone dendrimers: Influence of size and PEG capping on cytotoxicity profiles

The synthesis of new series of PPH (poly(phosphorhydrazone)) dendrimers with amino‐PEG phosphonates or the corresponding amino‐PEG phosphonic acids as terminal groups is presented, from generations 1–3. The size of PEG‐terminated dendrimers is experimentally measured by diffusional NMR, and by means of dynamic light scattering. Classical molecular dynamics and well‐tempered metadynamics simulations are used to assess or confirm the formation of aggregates in some cases. The influence of PEG capping on the cytotoxicity profiles of the dendrimers is evaluated on human peripheral blood mononuclear cells by means of LIVE/DEAD assays, and confirms the importance of PEG capping to ensure low cytotoxicity. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 761–774     

Prediction of viscoelastic properties with coarse‐grained molecular dynamics and experimental validation for a benchmark polyurea system

To explore the relationship between microscopic structure and viscoelastic properties of polyurea, a coarse‐grained (CG) model is developed by a structure matching method and validated against experiments conducted on a controlled, benchmark material. Using the Green‐Kubo method, the relaxation function is computed from the autocorrelation of the stress tensor, sampled over equilibrium MD simulations, and mapped to a real time scale established by matching self‐diffusion rates of atomistic and CG models. Master curves computed from the predicted stress relaxation function are then compared with dynamic mechanical analysis experiments mapped to a wide frequency range by time–temperature superposition, as well as measurements of ultrasonic shear wave propagation. Computational simulations from monodisperse and polydisperse configurations, representative of the benchmark polyurea, show excellent agreement with the experimental measurements over a multidecade range of loading frequency. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 797–810     

Macrocycle Dynamics in a Branched [8]Catenane Controlled by Three Different Stimuli in Three Different Regions

A branched [8]catenane from an efficient one-pot synthesis (72 % HPLC yield, 59 % isolated yield) featuring the simultaneous use of three kinds of templates and cucurbit[6]uril-mediated azide–alkyne cycloaddition (CBAAC) for ring-closing is reported. Design and assembly of the [8]catenane precursors are unexpectedly complex that can involve cooperating, competing and non-influencing interactions. Due to the branched structure, dynamics of the [8]catenane can be modulated in different extent by rigidifying/loosening the mechanical bonds at different regions by using solvent polarity, acid-base and metal ions as the stimuli. This work not only highlights the importance of understanding the delicate interplay of the weak and non-obvious supramolecular interactions in the synthesis of high-order [n]catenane, but also demonstrates a complex control of dynamics and flexibility for exploiting [n]catenanes applications.     

Patterning of Tailored Polycarbonate Based Non‐Chemically Amplified Resists Using Extreme Ultraviolet Lithography

A series of high‐performance polycarbonates have been prepared with glass‐transition temperatures and decomposition temperatures that are tunable by varying the repeat‐unit chemical structure. Patterning of the polymers with extreme UV lithography has been achieved by taking advantage of direct photoinduced chain scission of the polymer chains, which results in a molecular‐weight based solubility switch. After selective development of the irradiated regions of the polymers, feature sizes as small as 28.6 nm have been printed and the importance of resist‐developer interactions for maximizing image quality has been demonstrated.

     

Synthesis,characterization, and mechanism studies on novel rare‐earth calixarene complexes initiating ring‐opening polymerization of 2,2‐dimethyltrimethylene carbonate

Rare‐earth (Nd, Y) p‐tert‐butylcalix[n]arene (n = 4, 6, and 8) complexes without coligands were synthesized from rare‐earth isopropoxides in toluene. The products were characterized as the following structures: [C4(OH)O₃ · CH₃C₆H₅]Nd ( 4 ), [C6(OH)₂O₄ · CH₃C₆H₅]₃Ln₄ [Ln = Nd ( 5 ), Y ( 6 )], and [C8(OH)₂O₆ · CH₃C₆H₅]Nd₂ ( 7 ). 2,2‐Dimethyl trimethylene carbonate (DTC) can be polymerized with complexes 4 – 7 alone as the initiator. PolyDTC (weight‐average molecular weight: 5700, polydispersity index: 1.11, measured by gel permeation chromatography) initiated by complex 5 was obtained with a conversion of 69.1% within 6 h in toluene at 80 °C. The thermal behavior of polyDTC has been compared with the published data. The DTC ring is opened via acyl‐oxygen bond cleavage with end‐group examination. NMR analyses of the polymerization reaction mixture indicated that the polymerization proceeds via a coordination‐insertion mechanism. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1390–1399, 2003     

Conformational Dynamics of apo‐GlnBP Revealed by Experimental and Computational Analysis

The glutamine binding protein (GlnBP) binds l ‐glutamine and cooperates with its cognate transporters during glutamine uptake. Crystal structure analysis has revealed an open and a closed conformation for apo‐ and holo‐GlnBP, respectively. However, the detailed conformational dynamics have remained unclear. Herein, we combined NMR spectroscopy, MD simulations, and single‐molecule FRET techniques to decipher the conformational dynamics of apo‐GlnBP. The NMR residual dipolar couplings of apo‐GlnBP were in good agreement with a MD‐derived structure ensemble consisting of four metastable states. The open and closed conformations are the two major states. This four‐state model was further validated by smFRET experiments and suggests the conformational selection mechanism in ligand recognition of GlnBP.