Influence of molecular weight on the thermal and mechanical properties of polyurethane elastomers based on 4,4′‐diisocyanato dicyclohexylmethane

Hespe, H.; Zembrod, A.; Cama, Farhad J.; Lantman, C. W.; Seneker, S. D.

doi:10.1002/app.1992.070441118

Cited by 20 publications

(9 citation statements)

References 5 publications

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“…The hydrogen bonding between hard segments plays a major role in stabilizing the hard domains, which act as physical crosslinking sites, in PU. The soft segments, meanwhile, have a glass transition temperature that is well below room temperature and provide the long range elasticity necessary for thermoplastic elastomers 4–11. Generally, enhanced mechanical and thermal properties can be achieved with PUs having a higher degree of microphase separation.…”

Section: Introductionmentioning

confidence: 99%

Effect of molecular shape of diisocyanate units on the microscopic/macroscopic phase separation structure of polyurethanes

Park

Lim

et al. 2011

J Polym Sci B Polym Phys

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Three diisocyanate units having different linearity and planarity on the basis of the arrangement of constituent aromatic rings are used to synthesize three polyurethanes (PUs) and the effects of the molecular structure of the diisocyanate units on phase separated morphologies of PUs have been studied. The linear and planar diisocyanate unit allows good packing of the hard segments in the hard domain by extensive intersegmental hydrogen bonding, and it forms a well ordered, long hard domain. However, the nonlinear and noncoplanar diisocyanate unit shows a lesser degree of hydrogen bonding in the short hard domain. Strong preferential orientation of the rigid/long hard domains inside a macroscopic grain boundary has been observed with the polarizing optical microscope especially for the PU based on the rigid diisocyanate. It was concluded that the molecular structure of the diisocyanate unit in PU plays an important role in determining the interchain interaction, the detailed phase‐separated domain structure, and local domain orientation in each grain boundary. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

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Section: Introductionmentioning

confidence: 99%

Effect of molecular shape of diisocyanate units on the microscopic/macroscopic phase separation structure of polyurethanes

Park

Lim

et al. 2011

J Polym Sci B Polym Phys

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“…Polymers of high molecular weight are necessary to obtain materials with acceptable mechanical, physical and chemical properties. Other investigators have indicated the importance of the relationship between polymer molecular weight and properties of the polymer (24)(25)(26)(27), whereas other reports indicate that beyond a certain molecular weight, the molecular weight no longer influences the mechanical properties (28). In some of these references (24)(25)(26) the increase in molecular weight increased the efficiency of phase separation and therefore the creation of more distinct and ordered hard segments.…”

Section: Resultsmentioning

confidence: 92%

Synthesis of Poly(ether urethane amide) Segmented Elastomers

Penhasi¹,

Aronhime²,

Cohn³

1993

ACS Symposium Series

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A new series of polyurethane block copolymers was synthesized, based on the use of dicarboxylic acids as novel chain extenders. Poly(tetramethylene glycol) of molecular weight 2000 was used as the soft segment, which was reacted in a 1:2 ratio with hexamethylene diisocyanate. Amide groups were formed in the reaction of isocyanate groups with carboxylic groups. The effect of the type of diacid on the kinetics of the polymerization was determined by monitoring both the disappearance of isocyanate groups and the increase in intrinsic viscosity. The type of diacid had a pronounced effect on the kinetics, with the rate of reaction of diacid with isocyanate in the following order: oxalic acid > fumaric acid > sebacic acid. The kinetics of a model system comprising two moles of isocyanate and one mole of diacid were found to follow second order kinetics modified by the addition of an autocatalytic term. The polymer was characterized by elemental analysis, infrared spectroscopy, nuclear magnetic resonance spectroscopy, viscometry and thermal analysis. The time of the reaction was found to be important in determining the structure and properties of the segmented polymer, as observed by thermal analysis and viscometry. In addition, polymers prepared with oxalic and fumaric acids were of lower molecular weight when synthesized in THF as opposed to DMA, probably due to the lower compatibility of the polymers formed in THF.Thermoplastic polyurethane elastomers are one of the most important groups in the class of thermoplastic elastomers (2-5). A typical polyurethane elastomer is a block (or segmented) copolymer of the type (AB) n , which is composed of alternating hard and soft segments which are generally not compatible chemically. This incompatibility leads to phase separation and the creation of micro-domains, in which hard block domains are dispersed in the matrix of the soft segment. The hard segments serve as physical crosslinking sites due to their local order at normal use temperatures and impart strength and prevent flow. On the other hand, the soft segment glass transition temperature (Tg) is normally well below the use temperature, thus imparting flexibility to the system. The combination of physical crosslinks and flexibility allows for the very high elongations typical of these thermoplastic elastomers (d). One additional

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“…B ϭ 4 ϫ I 3.65 /I 3.36 (4) where I 3.65 and I 3.36 are the integral values of the peaks at ␦ ϭ 3.65 and 3.36 ppm, respectively (Fig. 2b).…”

Section: Determination Of Branch Valuementioning

confidence: 98%

“…It has been extensively studied that the morphology and properties of TPUEs were greatly affected by chemical structures, 1 stoichiometric ratio 2 of hard and soft segments, molecular weight and distribution of the macromolecules and the two segments, 3,4 and processing history 5,6 of the materials. As we know, the phase separation during processing of polyurethanes greatly influenced their mechanical properties.…”

Section: Introductionmentioning

confidence: 99%