Search results for "Polymers"
showing 10 items of 3567 documents
The role of additives in the recycling of polymers
1998
The main problems in post-consumer plastics recycling are due to the degradation undergone by the polymers during processing steps and by the products during their lifetime and, for heterogeneous recycling, to the incompatibility of different polymers. To reduce the negative effects of the recycling steps, two main ways can be adopted for homogeneous materials: restabilization during the recycling to avoid or at least to slow the degradation and addition of fillers and modifiers capable of improving the performance of thermoplastic polymers without increasing the final cost of the secondary material. In the case of mixed plastics, compatibilization is the necessary step to obtain secondary …
Living Polymer Chains with Predictable Molecular Weight and Dispersity via Carbanionic Polymerization in Continuous Flow: Mixing Rate as a Key Parame…
2016
Aiming at systematic variation of the parameter dispersity, Đ (or “polydispersity”), living polymers with predictable dispersity (Đ = 1.15–2.20) and controlled molecular weights (Mn = 3200–18 500 g mol–1) were prepared via carbanionic polymerization. The approach relies on a continuous flow reactor equipped with a tangential four-way jet micromixing device. By varying the total flow rate, the mixing efficiency of the initiator (sec-BuLi) and the corresponding vinyl monomers is controlled, resulting in polymers with predefined dispersity, while the number-average molecular weight, Mn, is kept constant. In this manner living polystyrene (PS), poly(p-methylstyrene) (PpMeS), and poly(2-vinylpyr…
Polydispersity and Molecular Weight Distribution of Hyperbranched Graft Copolymers via “Hypergrafting” of ABm Monomers from Polydisperse Macroinitiat…
2013
The hypergrafting strategy designates the synthesis of hyperbranched graft copolymers (HGCs) in a grafting-from approach, using ABm monomers, from multifunctional, polydisperse macroinitiator cores by slow monomer addition. Hypergrafting leads to complex polymer topologies with defined molecular weight, degree of branching (DB), and polydispersity (PD). By a generating function formalism, a generally applicable equation for the PD of HGCs (PD = PDf + (m – 1)/f) is derived, where PDf is the polydispersity of the core and f its average functionality. In addition, the complete molecular weight distribution function has been calculated for varied m and f as well as for a given distribution of i…
Nanoscale Blends between Immiscible Polymers via Simultaneous Non-Interfering Polymerisation
2005
An important topic in polymer science seeks to improve the performances of polymer blends using nanoscale phase segregation. Here, blends between polystyrene and polycaprolactone are realised by a chemical route. The non-interfering character of the radical polymerisation of styrene and the lanthanide halide initiated ring-opening polymerisation of caprolactone is assessed. The molecular weights range from 2 000 to 3 500 for polycaprolactone and up to 140 000 for polystyrene, with reasonable polydispersity indexes. From calorimetry measurements, it is shown that polystyrene and low molecular weight polycaprolactone are immiscible. The morphology of the blends between the two immiscible poly…
Block Copolymers Build-up of Electron and Hole Transport Materials
2004
In this article we describe the synthesis of various monomers modified with triphenyl-1,3,5-triazine side groups as electron transport moieties. By nitroxide-mediated polymerization with a TEMPO unimer it was possible to obtain polymers with a narrow polydispersity. Furthermore, by living radical polymerization block copolymers were obtained from these monomers. Therefore, microphase separated structures are accessible which possess hole conducting moieties in one phase and electron conducting moieties in the other phase.
Functional Diblock Copolymers for the Integration of Triboluminescent Materials into Polymer Matrices
2008
This work describes the synthesis and use of new diblock copolymers to integrate functional inorganic particles into a polymer matrix. These diblock copolymers were synthesized by nitroxide-mediated polymerization (NMP) from styrene and two styrene-like monomers with protected functional groups for the later connection to the functional inorganic material. It was possible to keep the polydispersity of the block copolymers around or below 1.2 and to preset the length of the functional block to about 20 monomers or 10 mol-% of monomers. The groups for the surface functionalization (amino groups or chelating ligands) were obtained in their free form by polymer analogous reactions. As an exampl…
Correlation between polymer architecture, mesoscale structure and photovoltaic performance in side-chain-modified poly(p-arylene-ethynylene)-alt-poly…
2011
Abstract Recent investigations have shown that an anthracene containing poly( p -arylene-ethynylene)-alt-poly( p -arylene-vinylene) statistical copolymer consisting of a well defined conjugated backbone, along which linear and branched alkoxy side chains are attached in a random manner, yields, compared to its counterparts with regular side chain substitution, an improved performance in polymer [6,6]:-phenyl-C 61 -butyric acid methyl ester (PCBM) bulk-heterojunction solar cells. The microscopic origin for the improved power conversion efficiency ( η ≈ 3.8%) of the statistical copolymer – which is the best in its material class – has not been resolved. We conducted grazing incidence wide-an…
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…