摘要:

AbstractThe mean‐square radius of gyration of poly(1,1‐disubstituted ethylene)s is calculated according to a method already developed for poly(methyl methacrylate), poly(α‐methylstyrene) and polyitaconate. During the derivation both the effect of side groups and the masses of skeletal atoms were taken into account. A hypothetical polymer chain was introduced, in which the mass of the substituents on every Cαwas considered to be concentrated in their center of mass, and the virtual side bond vector runs from Cαto this center. The mean‐square radius of gyration of poly(1,1‐disubstituted ethylene)s consists of two parts, one of which is the mean‐square radius of gyration of the hypothetical molecule described before and the other is related to the geometrical characteristics of the side groups. Numerical calculations indicated that the dependence of the mean‐square radius of gyration of poly(1,1‐disubstituted ethylene)s on the molecular weight is analogous to that of vinyl polymers, 〈S2〉 =aMb, whereaandbare constants charact

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040111

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe conformational disorder compatible with the highly extended chains found in mesomorphic poly(ethylene terephthalate) has been studied by Monte Carlo calculations on model oligomers confined inside cylindrical tubes. The distribution of torsional angles for such extended chains is characterized by OCCO bonds being always in thetransdomain, while the COCC bonds show an approximately similar probability of being found intransandgauchestates, the probability maxima being centered at 90° and −90° in the latter cases. At variance with the torsional angles of the OCCO and the ester bonds, always very close to 180°, the distributions for all other torsional angles show flat and broad probability maxima, indicating the possibility of substantial deviations from the average value inside each domain. This is also true for the fictitious OC˙˙˙CO bonds across the phenylene rings, for which a nearlytransgeometry is prefer

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040112

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA simple and general algorithm, convenient for computer implementation, for calculation of the copolymer molecular weight distribution (MWD), its moments, copolymer composition, etc. from standard data has been developed describing copolymerization as a Markovian process. The algorithm is applicable for simulations of multimonomer copolymerization with monomolecular, bimolecular and mixed termination. It can be used for calculating the MWD of copolymers prepared under non‐stationary conditions. Explicit formulae have been derived for the above parameters. They are exact even for low‐molecular‐weight oligomers. The calculation procedure involves nothing but plain matrix operations as matrix multiplication and inversion. For high‐molecular‐weight copolymers, even simpler dependencies that resemble those used for homopolymers can be used. A very simple numerical test has been proposed for checking their co

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040113

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractFree radical addition reactions in the presence of cobaloximes and related compounds have been modelled. Several mechanisms are presented and similarities with the “persistent radical effect” noted by Daikh and Finke are discussed. Cobaloximes and salophenSystem. name:N‐acetyl‐p‐aminophenyl salicylate.derivatives are widely used in organic synthesis to build carbon‐carbon bonds, whereas in polymer synthesis they are used as catalytic chain transfer agents in the production of oligomers. This work shows that these reactions are closely related and also demonstrates the influence that an external radical source has on the overall reacti

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040114

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractDissociation energies (ED) of different components of repeating units of heteropolymers (HPs) have been calculated by the semiempirical PM‐3 method. Comparison ofEDvalues of heterocycles (HCs) and of single bonds contained in phenyl‐substituted benzoheterocycles have shown that for polybenzazoles and HPs with carbonyl‐containing HCs the initial degradation in the absence of weak links (uncyclized units, structural defects, etc.) preferably starts with HC homolytic decomposition. For these two groups of HCs the relationship between theEDof HCs and the initial degradation temperature of corresponding HPs is, on the whole, similar to the one found upon calculation of benzoheterocycles. In HPs based on quinoline and quinoxaline the single bond between HC and phenyl (Ph) group is less stable than the HC, and the breaking of that single bond can accompany the initial HP degradation. An analysis of relative stabilities of X‐Ph bonds of Ph‐X‐Ph fragments of HPs with X = O, S, CH2, CO and of the relationship between their stabilities and those of other fragments of the HP repeating unit has been performed by using both calculatedEDvalues and those obtained from thermochemical data.EDvalues for Ph‐X‐Ph decompositions turned out to be close to tho

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040115

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractMolecular orbital studies were carried out to compare the easiness of ring‐opening in the radical polymerization of spiro‐orthocarbonates bearingexo‐methylene groups at α‐position of the ether oxygen, spiro[2,4‐benzodioxepine‐4′‐methylene‐3,2′‐[1,3]‐dioxolane](1), and at β‐position of the ether oxygen, spiro[2,4‐benzodioxepine‐5′‐methylene‐3,2′‐[1,3]‐dioxane](2). The formation energy suggests that1would show a degree of ring‐opening larger than2, contrary to the experimental result. Therefore, a reverse relation in activation energy was suggested, i. e., the kinetic factor surpasses the thermodynamic factor in the ring‐opening reaction of1and2. Although the calculation of the activation energy of the radical ring‐opening reaction was not successful, the result extracted from the perturbation energy calculations of vinyl polymerizations of1and2agree well with their radical vinyl polymerizability. Namely,1was confirmed to have a larger vinyl polymerizability than2, which agrees well with the smaller ring‐opening polymerizability of1compared with2. The real HOMO and LUMO (highest occupied and lowest unoccupied molecular orbitals) of1, 2and their intermediates for the radical addition were confirmed not to correspond to the apparent HOMO and LUMO from the detailed analysis of their coefficients of atomic orbitals (AOs). The frontier electron density of1and2agrees well with the fact that the β‐carbon of theirexo‐methylene group has a hi

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040116

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040117

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY