Search results for "BOND"
showing 10 items of 3527 documents
Penetrant diffusion in frozen polymer matrices: A finite-size scaling study of free volume percolation
1996
The diffusion of penetrant particles in frozen polymer matrices is investigated by means of Monte Carlo simulations of the bond fluctuation model. By applying finite-size scaling to data obtained from very large systems it is demonstrated that the diffusion process takes place on a percolating free volume cluster describable by a correlated site percolation model which falls into the same universality class as random percolation. The diverging correlation length entails a pronounced dependence of the diffusion constant on the size of the simulated system. It is shown that this dependence is appreciable for a wide range of parameters around the transition. \textcopyright{} 1996 The American …
Simulation of Dense Polymer Systems in Two and Three Dimensions
1991
Dense polymer systems are modeled by self- and mutually avoiding walks on lattices. Both simple models where the step length is one lattice spacing and more complicated models where the step length is distinctly longer and may fluctuate (“bond fluctuation model”) are discussed, and it is shown that the computer simulation of such models gives useful insight to understand the thermodynamic phase behavior and the relaxational dynamics of dense polymer solutions and polymer melts. The huge demands in computing power needed for a successful simulation of such systems can be covered by parallel computers such as the multitransputer facility of the University of Mainz.
Cooperative self-assembling in statistical copolymers: a new approach to high-temperature thermoplastic elastomers
1994
Based on previous work, where it was shown that 4-urazoylbenzoic acid (U4A) groups, which are attached statistically to polybutadiene, form ordered supramolecular arrays in the unpolar polymer matrix, the present work describes the synthesis of a new molecular building block capable of self-assembling in the unpolar polymer matrix. 5-Urazoylisophthalic acid (U35A) groups attached to 1,4-polybutadiene chains cause the formation of a thermoplastic elastomer of improved properties. The clusters of functional groups show an endothermic transition. The melting temperature increases for low levels of modification from 130°C up to 190°C. The mechanical properties (stress–strain and dynamic mechani…
Polymerization of mono- and multilayer forming diacetylenes
1977
Heptadeca-2,4-diine-1-ol and Heptadeca-2,4-diine-1-acid were synthesized and their polymerization behaviour in the solid state was investigated. Both compounds polymerize thermally below the melting point and photochemically under the action of uv-light to form polymers via 1,4-addition to the conjugated triple bonds with a backbone of conjugated double-and triple-bonds. The photoresponse spectra resemble the absorption spectra exhibiting maxima of photoreactivity in the absorption band of the conjugated triple bonds of the monomers.
Some monomers, oligomers and polymers with conjugated triple bonds
1991
In the first part new monoaminodiacetylenes with different numbers of CH2-groups, the formation of Perowskit-type Mn complexes and their polymerizability are described. Symmetrical diaminodiacetylenes and some derivatives therefrom have also been prepared. The second part deals with different types of polymers with diacetylene units in the backbone. Under irradiation color formation and crosslinking take place. Well-defined low molecular weight model compounds of polydiacetylenes is the subject of the third part. Finally rod-like but soluble polymers with alternating p-phenylene and acetylene units are described.
Modelling the hydrogen-bonding interactions in a copolymer/biodegradable homopolymer blend through excess functions
2008
A recent theoretical approach based on the coupling of both the Flory-Huggins (FH) and the Association Equilibria thermodynamic (AET) theories was modified and adapted to study the miscibility properties of a multi- component system formed by two polymers (a proton-donor and a proton-acceptor) and a proton-acceptor solvent, named copolymer(A)/solvent(B)/polymer(C). Compatibility between polymers was mainly attained by hydrogen- bonding between the hydroxyl group on the phenol unit of the poly(styrene-co-vinyl phenol) (PSVPh) and the car- bonyl group of the biodegradable and environmentally friendly poly(3-hydroxybutyrate) (PHB). However, the self- association of PSVPh and specific interacti…
Dynamics of entangled supramolecular polymer networks in presence of high-order associations of strong hydrogen bonding groups
2017
Dynamics of entangled polymer chains in the melt state are deliberately excluded in most of the studies on supramolecular polymer networks by utilizing nonentangled precursor chains. Relaxation of the system mainly depends on the dissociation of the associative groups in latter case and nonentangled chains deliver nothing to resist afterward. Conversely, in an entangled system, relaxation of polymer chains and dissociation of associative groups can occurred parallel. Supramolecular networks based on an entangled precursor polymer with different levels of strong associating ureidopyrimidinone (UPy) groups are synthesized to screen the corresponding effects on the dynamics of the system. Bina…
Acylsemicarbazide Moieties with Dynamic Reversibility and Multiple Hydrogen Bonding for Transparent, High Modulus, and Malleable Polymers
2020
The realization of covalent adaptable networks with excellent mechanical and dynamic properties remains a major challenge. Herein, the acylsemicarbazide (ASC) moieties with dynamic reversibility and multiple hydrogen bonding were disclosed and used to prepare transparent, high modulus, and malleable polymer networks. It was found that the ASC moiety can reversibly generate isocyanate and hydrazide at elevated temperatures, that is, exhibiting dynamic reversibility. ASC can also produce the disordered multiple hydrogen bonds that contribute to superior mechanical strength for dynamic polymers. The hydrogen bonding in ASC moieties can diminish the energy barrier for the cleavage of dynamic co…
Molecular Mobility in Oriented and Unoriented Membranes Based on Poly[2-(Aziridin-1-yl)ethanol]
2021
Unoriented and oriented membranes based on dendronized polymers and copolymers obtained by chemical modification of poly[2-(aziridin-1-yl) ethanol] (PAZE) with the dendron 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoate were considered. DSC, XRD, CP-MAS NMR and DETA, contribute to characterize the tendency to crystallize, the molecular mobility of the benzyloxy substituent, the dendritic liquid crystalline group and the clearing transition. The orientation of the mesogenic chain somewhat hindered this molecular motion, especially in the full substituted PAZE. The fragility, free volume and thermal expansion coefficients of these membranes near the glass transition are related to the orie…
Synthesis strategies and properties of smart amphiphilic networks
1996
This paper briefly surveys recent developments in the field of amphiphilic networks (APN) which are a new class of crosslinked polymer systems consisting of covalently bonded hydrophobic and hydrophilic chain segments. The covalent bonds between immiscible hydrophobic and hydrophilic polymer chains prevent demixing and yield polymer networks with unique structure and properties. Telechelic macromonomers provide the basis for the first generation of APNs obtained by copolymerization of the macromonomer with selected low molecular weight monomers. Synthesis of a variety of APNs using methacrylate-telechelic polyisobutylene (PIB) macromonomers prepared by living carbocationic polymerization (L…