Chain-extended structures

Annealing drawn PE hydrostatically at high pressure, generates a wide spectrum of crystal thicknesses varying from the common oriented chain folded to the chain-extended structures — where folds and ties tend to disappear63 —. This range of crystal thicknesses coupled with the chain axis orientation, offers a suitable model in... 

Diol Chain Extender Structure. The DSC results for PTMG 650-2900/M3 prepolymers chain extended with 1,4-BDO, 1,3-BDO, DMPD, EMPD, DEPD, and BEPD are shown in Table I. 

The specific inclusion of adamantyl groups in /3-cyclodextrin in aqueous environments has been used as binding interaction between adamantyl end-capped poly(ethylene oxide)263-264 or polyester and a cyclodextrin polymer. Even though the formation of linear chain extended structures was not specifically... 

NCO/OH ratio and chain extender structure on low temperature and elevated temperature properties, thermal stability during processing, and processability, in particular injection molding behavior. 

R. Adhikari, PA. Gunatillake, S.J. McCarthy, G.F. Meijs, Effect of chain extender structure on the properties and morphology of polyurethanes based on H12MD1 and mixed macrodiols (PDMS-PHMO), J. Appl. Polym. Sci. 74 (12) (1999) 2979-2989. 

The chain extender structure strongly influences the PUs mechanical performance. Modifying the ratio between the polyol and chain extender, PUs may result in a change from a hard, brittle material to a rubbery elastomer, as a result of the variation of the HS concentration (defined as the ratio of the mass of the non-polyol components to the total mass of the polymer) [2-4]. 

Fig. 3.7. Storage modulus as a means of observing the dependence of temperature stability upon chain-extender structure. PU type Capa 225/ CHDI/chain extender molar ratio 1 2 1 (from Barikanf 1986).

The influence of the diol chain-extender structure on the thermal stability of PU elastomers was also studied in a series of Capa 225/CHDI/chain extender-based polymers by using four different diols as chain extenders and a molar ratio of 1 2-6 1. Figure 3.9 displays storage modulus and tan d as a means of observing the dependence of temperature stability with respect to chain-extender structure. The maximum temperature to which storage modulus (log E ) values of PU elastomers remain constant is given... 

TRANSITION TEMPERATURES OF DIFFERENT CHAIN EXTENDER-BASED PU ELASTOMERS AS A MEANS OF OBSERVING THE EFFECT OF CHAIN-EXTENDER STRUCTURE ON THERMAL TRANSITION... 

Table 1.5 List of common chain extender structures used in resorbable polyurethanes...

Gisselfalt K, Helgee B. Effect of soft segment length and chain extender structure on phase separation and morphology in poly(urethane urea)s. Macromol Mater Eng 2003 288(3) 265-71. 

Tatai L, et al. Thermoplastic biodegradable polyurethanes the effect of chain extender structure on properties and in vitro degradation. Biomaterials 2007 28 5407-17. 

L. Tatai, T.G. Moore, R. Adhikari, F. Malherbe, R. Jayasekara, I. Griffiths, et al.. Thermoplastic biodegradable polyurethanes the effect of chain extender structure on properties and in-vitro degradation. Biomaterials 28 (December 2007) 5407-5417. 

Anneahng polyethylene at high temperatures ( 230-240°C) and high pressures ( 200 MPa) produces a chain-extended structure consisting of small domains where the crystal thicknesses are 2 pm, i.e. an aggregate of small, highly aligned units. This material can... 

The theoretical tensile modulus of polyethylene is 180-340 GPa. [165, 166] The extremely high tensile modulus of polyethylene is due to the small cross-sectional area of the chain, no side groups, and the planar zig-zag conformation in the orthorhombic crystal lattice. The theoretical tensile strength calculated from the C-C bond energy is in the order of 20-60 GPa. These theoretical values for polyethylene can happen if all the C-C bonds fracture simultaneously. This requires defect free, chain-extended structure, and infinite polymer chains which is a completely different situation from which is encountered [167]. 

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