Search results for "elastomer"

Hyperbranched polymer architectures: From Flory's AB(f-1) polycondensates to controlled structures

2020

Abstract Celebrating the 100th anniversary of Staudinger's “macromolecular concept”, polymer scientists critically evaluate the past developments and future challenges of polymer science, asking: Quo vadis, Macromolecular Science? The main focus in Polymer Science has been on linear polymers or crosslinked systems (elastomers and thermosets) until the late 1980ies. The advent of dendritic polymers, i.e. dendrimers and hyperbranched polymers (HBPs) attracted wide-spread attention in the polymer community. This article gives a brief overview of the developments in the area of hyperbranched polymers and demonstrates that they have since become a novel class of polymer materials.

1996

Combined LC-polymers possess the structural properties of both LC main chain and LC side chain polymers. Beneath this structural speciality, their broad LC-phases and their polymorphism (different smectic phases and one nematic phase as a function of temperature) make them interesting. Crucial to an understanding of them is the fact that main chain and side chain mesogens orient parallel to each other and interact cooperatively to form the LC-phase. Due to this synergism the temperature range of the LC-phase is much broader than that of the corresponding LC main chain and LC side chain polymers. This interplay of main chain and side chain mesogens allows structures to be designed with prefe…

Processing and characterization of blends of fluoroelastomers with semirigid liquid crystal polymers

1996

Fluoroelastomers (FEs) usually have working temperatures above 150°C and a great resistance to aggressive agents such as oils, fuels, aliphatic and aromatic solvents, steam, moderate acid, and basic environments. Liquid crystal polymers (LCPs) can be effective processing aids and reinforcing agents for elastomers. These characteristics are very attractive to lower melt viscosity and to stiffen and strengthen the final product through a simple blending. Among the LCPs, the semirigid LCPs seem the most appealing for blending with flexible thermoplastics (FTs) because their processing temperatures can be arranged to be in the same processing temperature range of FTs and because the presence of…

Preparation of Soft Microactuators in a Continuous Flow Synthesis Using a Liquid-Crystalline Polymer Crosslinker

2012

We present the synthesis of a polymeric liquid crystalline (LC) crosslinker and its usage in the preparation of soft microactuators. The microactuators, composed of thermoresponsive liquid crystalline elastomers (LCE), are fabricated in a microfl uidic device in a continuous “on the fl y” process. The LC polymer crosslinker is miscible with the LC monomer and provides for a rapid polymerization and crosslinking. Most importantly, it promotes an enantiotropic mesophase of the mobile monomer phase, which is not provided by conventional nonmesogenic crosslinkers. This allows an isothermal handling inside the microfl uidic setup. Temperature-driven shape changes up to 65% could be achieved by j…

Mechanical performance of thermoplastic matrix natural-fibre composites

2008

Publisher Summary Natural-Fibre Composites (NFCs) are being considered as high-tech materials meant to replace conventional composites in high-performance applications. There are a number of advantages that natural fibres can offer compared with synthetic materials. Thermoplastic natural-fibre composites can be classified by the polymer used as a matrix as well as by the type of the fibre reinforcing the polymer. Currently, the main areas of application of thermoplastic NFCs are packaging, transportation and building industries. The packaging industry requires materials that possess specific properties, but that can also be easily discarded after use. This chapter discusses the mechanical p…

On the Improvement of the Processability of UHMW-HDPE by Adding a Liquid Crystalline Polymer and a Fluoroelastomer

2001

Ultra-high molecular weight polyethylene possesses many interesting properties but a very bad processability. This material is not usually processed in conventional devices but only by compression moulding and RAM extrusion. Low molecular weight polyethylene can be used to improve the processability. In this work small amounts of a fluoroelastomer and of a liquid crystalline polymer have been used as processing aids to improve the extrudability of this polymer. In fact, the die pressure decreases whereas the output flow rate slightly increases with increasing concentration of the processing aids. Solution viscosity data shows that reduction of the mechanical stress during extrusion decrease…

Liquid crystalline polymers and elastomers

2002

The results of experiments and theory correlate increasingly well in the investigation of liquid crystalline polymers. Current work focuses on rheology and the behavior of blends of thermotropic LC polymers, due to reemerging economic interest in these materials. Research on liquid crystalline elastomers concentrates on potential applications such as artificial muscles and lasing.

Emergence, evidence, and effect of junction clustering in supramolecular polymer materials

2021

A significant fraction of biomaterials consists of supramolecular polymers and networks formed by non-covalent interactions between associative motifs. They typically contain complex structures in which on top of binary associations, phase-separation and aggregation of associative junctions occur. Such hierarchical assemblies have significant influences on the dynamics as well as the physical and mechanical properties of the materials. Similar to supramolecular biomaterials, aggregation of associative junctions has also been frequently reported to occur in synthetic supramolecular polymers and networks. Engineering of such secondary structures in a sense to create and control the extent of …

1995

Supramolecular structures based on 4-(3,5-dioxo-1,2,4-triazolidin-4-yl) benzoic acid (U4A) units act as effective junction zones in functionalized polybutadienes, resulting in the formation of thermoplastic elastomers. The dynamics on a molecular scale of the phenyl rings have been probed by 2H-NMR. In the polymeric system, there are three spatially separated environments, which are reflected in the mobility of the polar units. Phenyl rings which are incorporated in the structures are either rigid or undergo 180° phenyl flips. The small fraction of free functional groups move isotropically and their mobility is coupled to the dynamics of the polybutadiene matrix. In two model compounds, whe…

Light-Fueled, Spatiotemporal Modulation of Mechanical Properties and Rapid Self-Healing of Graphene-Doped Supramolecular Elastomers

2017

Gaining spatially resolved control over the mechanical properties of materials in a remote, programmable, and fast-responding way is a great challenge toward the design of adaptive structural and functional materials. Reversible, temperature-sensitive systems, such as polymers equipped with supramolecular units, are a good model system to gain detailed information and target large-scale property changes by exploiting reversible crosslinking scenarios. Here, it is demonstrated that coassembled elastomers based on polyglycidols functionalized with complementary cyanuric acid and diaminotriazine hydrogen bonding couples can be remotely modulated in their mechanical properties by spatially conf…