Search results for "Plastics"
showing 10 items of 2724 documents
Mechanistic study on the metallocene-based tandem catalytic coordinative chain transfer polymerization for the synthesis of highly branched polyolefi…
2021
Abstract Creation and control of long-chain branches (LCBs) in coordination polymerization of olefins is an enduring focus of research in both academia and industry. We have recently introduced a tandem catalytic coordinative chain transfer polymerization reaction where upon the concerted function of the polymerization catalyst, the chain transfer agent (CTA), and the displacement catalyst, a highly branched microstructure can be formed. Here we introduce a new tandem catalytic system using Et(Ind)2ZrCl2 as the polymerization catalyst. Despite the optimal reaction temperature for the cooperative function of catalyst components is lower than the ideal temperature for the productivity of the …
Effect of irradiation temperature and dose rate on the mechanical tensile behaviour of low density polyethylene
1993
Abstract The effect of ageing due to gamma radiation, at various dose rates and temperatures, on the mechanical tensile behaviour of low density polyethylene is studied. In order to detect synergistic effects, tensile tests on samples subjected to thermal treatment corresponding to the same temperature for the same time as for the irradiation tests have also been performed. The results indicate a generalized decrease of the elongation at break, with brittleness of the material for the most severe ageing treatments. For modulus values, an increase is observed for particular experimental conditions. These results are related to morphological and structural modifications induced in the polymer…
Linear–dendritic block copolymers: The state of the art and exciting perspectives
2011
Concurrent with the rapid development of both dendrimers and hyperbranched polymers, a novel class of block copolymer architectures has emerged from the combination of these dendritic architectures with linear chains, the “linear–dendritic block copolymers” (LDBCs). This review gives a comprehensive summary of the state of the art in this rapidly developing field from pioneering early work to promising recent approaches.The different strategies leading to these hybrid architectures with either perfect dendrimer/dendron building blocks or imperfect, yet more conveniently accessible hyperbranched segments, are reviewed and compared. The consequences of the unusual polymer topology for supramo…
Hybrid materials from organic polymers and inorganic salts
1994
The prepaparation of amorphous, homogeneous blends of zwitterionic polymers and transition metal salts was investigated. Homogeneous miscibility was achieved in many cases up to equimolar amounts of salt, depending on the anion and cation chosen. Various analytical techniques point to a solid state solution of the inorganic ions in the polymer matrix.
Topology-Sensitive Microfluidic Filter for Polymers of Varying Stiffness
2017
The separation of polymers based on their size, rigidity, and topology is an essential but also highly challenging task for nanoscience and engineering. Using hybrid molecular dynamics simulations that correctly take into account hydrodynamics, we have designed microfluidic channels for separating linear from ring polymers in dilute solutions. We establish that the transport velocity of the polymers is independent of their topology and rigidity when the channel walls are smooth and repulsive. However, when the walls are decorated with attractive spots arranged on lines parallel to the flow, ring polymers exhibit an order of magnitude higher transport velocity compared to linear chains. The …
The glass transition in polymer melts
1994
This paper presents some results of a Monte Carlo simulation for the glass transition in two- and three-dimensional polymer melts. The melt was simulated by the bond-fluctuation model on a d-dimensional cubic lattice which was combined with a two-level hamiltonian favouring long bonds in order to generate a competition between the energetic and topological constraints in the system. This competition prevents crystallization and makes the melt freeze in an amorphous structure as soon as the internal relaxation times match the observation time of the simulation set by the cooling rate. The freezing point of the melt, i.e the glass transition temperature Tg, thus depends upon the cooling rate …
Influence of Hair Density and Hair Length on Interparticle Interactions of Spherical Polymer Brushes in a Homopolymer Matrix
2003
The dynamics of hairy spherical nanoparticles in a melt of linear polymer chains has been investigated by mechanical spectroscopy as a function of particle topology and concentration. Using a simple free volume approach for the data analysis of the structural relaxation time vs concentration and the well-known hard-sphere result as a reference, a semiquantitative measure for the interparticle interactions, that is particle deformability/softness, and the effective particle size compared to the size of a nonswollen spherical brush has been determined. For these studies, model particles of hairy nanoparticles differing in either hair length or grafting density have been prepared. In contrast …
Cylindrical polymer brushes – Anisotropic building blocks, unimolecular templates and particulate nanocarriers
2016
Abstract This article presents an overview of the latest key developments and research activities in the area of cylindrical polymer brushes (CPBs), also known as ‘molecular bottlebrushes’. CPBs consist of a polymer backbone containing polymer side chains that cause the backbone to extend and adopt a worm-like conformation. The extent of backbone stretching and the aspect ratio of CPBs is determined by the length and grafting density of the side chains. The latest developments in controlled/living polymerisation techniques led to novel and more efficient ways of producing delicate polymer architectures, such as block copolymer CPBs, and resulted in a considerable expansion of the field of a…
Determination of the conformation of polymers in the amorphous solid state and in concentrated solution by neutron diffraction
1975
Abstract From the coherent neutron scattering on dilute solid solutions of the ordinary polymer within the deuterated polymer, conformation parameters of polymer chains in amorphous solid states can be determined. In this way vitreous poly(methyl methacrylate) (PMMA) has been investigated. The chains form unperturbed coils and the radius of gyration is very near to the corresponding value in dilute solutions of the same polymer in the low molecular θ-solvent butyl chloride. The same principle of measurement has been applied to concentrated solutions of PMMA in D-acetone. The solutions contained 50% polymer, the main part of which (98% and more) was deuterated so that the system was opticall…
Equilibrium swelling and solvation studies on crosslinked polyacrylamides
2004
Polyacrylamide (PA) crosslinked with four different crosslinking agents, triethyleneglycol dimethacrylate (TEGDMA), N,N′-methylene bisacrylamide (NNMBA), hexanediol dimethacrylate (HDDMA) and divinylbenzene (DVB), with mole percents ranging from 5 to 20, was prepared by solution polymerization and subjected to swelling and solvation studies. Solubility parameters and cohesive energy density were determined from swelling studies. Molecular weight between crosslinks for these systems were determined by Flory–Rehner analysis. There is a discontinuous volume change for 10% NNMBA and HDDMA crosslinked PA, 15% TEGDMA crosslinked PA and 10 and 15% DVB crosslinked PA in solvent mixtures of acetic a…