摘要:

AbstractSingle‐chain Monte Carlo simulations of polynorbornene were carried out for three stereochemical isomers. These simulations employed custom force field parameters derived fromab initioand semi‐empirical quantum calculations. The scaling of intrinsic viscosity with molecular weight was determined from these simulations. An unusually large variation in this scaling was obtained, which is attributed to the large degree of steric hindrance inherent in this form of polynorbornene that retains the bicyclo‐heptane ring in the backbone. The same scaling was measured for three commercial samples of this polymer produced using three different catalysts. The simulation and experimental results were consistent and the former were used to estimate the stereochemical configuration of the commercial samples. The simulation results for a stereoregular isomer of polynorbornene were also consistent with previous RIS model results. These structure‐property relationships extracted from the simulations are potentially useful in the commercialization of polynorbornene for interlayer dielectric applications in electronic pa

ISSN:1022-1360    

DOI:10.1002/masy.19981330103

出版商:WILEY‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe infrared absorption spectra of poly(tetrafluoroethylene), PTFE, and poly(chlorotrifluoroethylene), PCTFE, are simulated using a method based on a combination of classical molecular simulations of the amorphous polymer phase with Kramers‐Kronig relations. The differences and the analogies between experimental and calculated spectra of the non‐stereoregular fluoride polymer, PTFE, are first reported. The isotactic and syndiotactic configurations of PCTFE are then investigated. The comparison between experimental and simulated spectra is established on a vibrational analysis. It reveals the preferred syndiotactic configuration adopted by the PCTFE ch

ISSN:1022-1360    

DOI:10.1002/masy.19981330104

出版商:WILEY‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe difference in the glass transition temperatures, Tg, of the iso‐ and syndiotactic forms of PMMA has been investigated through molecular dynamics simulations of short duration (110 ps) using an accurate force field,pcff.To correlate with the Gibbs‐DiMarzio theory, which specifies that conformational energy is a primary factor in determining Tg, an energetic analysis has been carried out. It is found that syndiotactic PMMA possesses lower intramolecular energy where the governing contribution is brought by the angle bending term; whereas the isotactic PMMA exhibits lower intermolecular energy. Such a behavior suggests that the chain packing greatly determines the difference in the

ISSN:1022-1360    

DOI:10.1002/masy.19981330105

出版商:WILEY‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe dynamics of polymer chains in the bulk state are discussed at three different temperature scales: (i) Well above the glass transition temperature where the basic step of motion is the rotameric transition of bonds. In this regime, the dynamics may conveniently be analyzed by the rotational isomeric state model, (ii) In the vicinity of glass transition where friction forces from the environment dominate. In this regime, the dynamics may be modeled according to the cooperative kinematics model, (iii) Well below glass transition. Here, an analogy with a native protein is made, and the mean‐squared fluctuations are analyzed by adopting the Gaussian Network Model, which recently proved successful in describing fluctuations in native protein

ISSN:1022-1360    

DOI:10.1002/masy.19981330106

出版商:WILEY‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractMonte Carlo simulations of bulk polyethylene were performed on a high‐coordination lattice. In this study, we investigated the effect of coarse‐grained short and long range interaction parameters on the dynamic properties of the bulk system. As a result of fine tuning of the simulation parameters, our coarse‐grained simulations were successful in mimicing the local and large‐scale dynamics of C44H90and C100H2

ISSN:1022-1360    

DOI:10.1002/masy.19981330107

出版商:WILEY‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe study of structure and properties of semi‐crystalline polymer inter‐phases is important to explain and extend polymer applications. In this region, polymer chains exist in three distinct populations: tie chains that bridge the two crystals, chain folds and chain ends. The distribution of these populations influences the properties of the interphase. We have developed off‐lattice Monte Carlo simulations of constrained interphases of semi‐crystalline polymers which utilize robust off‐lattice moves. A united atom model with polyethylene‐like interactions and with freely rotating bonds is used to mimic the prototypical flexible chain structure. These simulations capture the limiting distributions of tight and loose chain folds and of tie chains within the metastable phase. The dissipation in order and density between the crystal and amorphous regions has been studied, and results for freely rotating chains indicate that the characteristic decay of anisotropy occurs in a length scale of ca. 10 Å. Simulation results for the effect of system size and molecular weight for freely rotating chains have also been

ISSN:1022-1360    

DOI:10.1002/masy.19981330108

出版商:WILEY‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractWe hereby present i) a microscopic model for the self‐assembly of linear wormlike micelles for which scission/recombination processes and loop formation are allowed, and ii) a mesoscopic analytic description of such systems. Both approaches predict the extent of loop formation as function of the micellar concentration, the end‐cap energy and the flexibility of micelles. As a matter of fact, even if loop formation is unfavorable under many conditions, e.g., for stiff micelles and low end cap energies, they have to be treated correctly in any statistical approach to their behavior, since their presence can significantly affect the relaxation time spectrum, the rheological behavior and correlation function of various ty

ISSN:1022-1360    

DOI:10.1002/masy.19981330109

出版商:WILEY‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

ISSN:1022-1360    

DOI:10.1002/masy.19981330102

出版商:WILEY‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY