Crosslinked polymers mechanical properties

The comparison of the mechaiucal properties of the UPy samples and the PEG controls demonstrates that the introduction of our biomimetic module into the network dramatically enhanced the polymer mechanical properties. As shown in the stress-strain curves (Fig. 10.8), the network containing the biomimetic crosslinker has significantly higher modulus, tensile strength, and toughness than the... 

With regard to the mechanical reactirai of a polymer network to a stress applied, it is important that loose ends of macromolecules in a network structure are as shmrt as possible and/or their concentration is low. As these ends mostly extend out of the lamellas of crystallites then, while crossUnking is taking place in an amorphous phase and with the simultaneous presence of crystallites, a network with small loose ends should be formed. The crosslink junctions stabilize the natural molecular network (entanglements and crystallites), and every chain in the system is potentially elastically operative and can contribute to the stress in a tensile experiment [33]. The stabilization effect of chemical crosslinks on entanglements and crystallites may be the direct cause of observed differences in the determination of the amount of chemical crosslinks from mechanical property measurements and sol-gel analysis of the cross-linked polymer. 

Minoura, Y. et ai (1978). Crosslinking and mechanical properties of liquid rubber. Part I Curative effect of aliphatic diols. J. Appl. Polym. ScL, 22, 1817 Part II Curative effect of aromatic diols. J. Appl. Polym. ScL, 22,3101 Minoura, Y. et al. (1979). Part III Curative effect of aralkyl and alicyclic diols. J. Appl. Polym. ScL, 23, 1137. 

Keywords Radiation, Medical polymers. Mechanical properties, Crosslinking, Scission, Aging,... 

Complex-forming POE/PAA interpenetrating polymer networks have been prepared by matrix polymerization of acrylic acid and ethylene diacrylate (a crosslinking agent) with a precrosslinked POE that was formed from hydroxyl-terminated POE and 2-isocyanatoethyl-2,6-diisocyanatohexanoate (131). At low degrees of POE crosslinking, dynamic mechanical properties in-... 

In the last three chapters we have examined the mechanical properties of bulk polymers. Although the structure of individual molecules has not been our primary concern, we have sought to understand the influence of molecular properties on the mechanical behavior of polymeric materials. We have seen, for example, how the viscosity of a liquid polymer depends on the substituents along the chain backbone, how the elasticity depends on crosslinking, and how the crystallinity depends on the stereoregularity of the polymer. In the preceding chapters we took the existence of these polymers for granted and focused attention on their bulk behavior. In the next three chapters these priorities are reversed Our main concern is some of the reactions which produce polymers and the structures of the products formed. 

An EB-curable struetural adhesive formulation usually eonsists of one or more crosslinkable oligomeric resins or prepolymers, along with such additives as reactive diluents, plasticizers, and wetting agents. The oligomer is an important component in terms of the development of mechanical properties. The adhesive and cohesive properties depend on the crosslink density, chemical group substitution, and molecular organization within the polymer matrix. Adhesion is achieved... 

Crosslinked polymers have two or more polymer chains linked together at one or more points other than their ends. The network formed improves the mechanical and physical properties of the polymer. 

As an organic polymer, poly(tetramethylene oxide) was also used for the preparation of ceramers. The mechanical properties in these cases were much improved in comparison with those for hybrids from polysiloxanes. In these poly (tetramethylene oxide)-silica hybrids, the effect of the number of functional triethoxysilyl groups was examined [13]. As shown in Fig. 2, more multifunctional organic polymer produced more crosslinked hybrid networks. This means that the more rigid the structure in the hybrids is, the higher the modulus and the lower swelling property. 

The mechanical properties of polymers also depend on the extent of crosslinking. Uncrosslinked or lightly crosslinked materials tend to be soft and reasonably flexible, particularly above the glass transition temperature. 

Again because of the crosslinks, such brittle behaviour occurs whatever the temperature unlike brittle materials based on linear polymers, there is no temperature at which molecular motion is suddenly freed. In other words, the Tg, if there is one, does not produce dramahc changes in mechanical properties so that the material is changed from one that undergoes brittle behaviour to one that exhibits so-called tough behaviour. 

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