Development of crystallinity in a semiflexible thermotropic polyurethane. 2. Structure and dynamics

Pollack, Steven K.; Smyth, Gerald E.; Papadimitrakopoulos, Fotis; Stenhouse, Peter; Hsu, Shaw Ling; MacKnight, William J.

doi:10.1021/ma00035a014

Cited by 32 publications

(18 citation statements)

References 14 publications

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“…In this study it is also noticeable, when the CO absorption is fitted with two peaks, that the width of the hydrogen-bonded CO peak is explained by the variability of the strength in the hydrogen bonds. When in certain systems a third peak was noticed, , two peaks were then explicitly assigned to hydrogen bonding, one of them being “disordered” and the other “ordered”, as already done for the urea groups.…”

Section: Resultsmentioning

confidence: 99%

Hydrogen Bonding in Copoly(ether−urea)s and Its Relationship with the Physical Properties

et al. 1997

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The evolution of hydrogen bonding with temperature in three copoly(ether-urea)s with no phase separation has been studied by Fourier transform infrared spectroscopy (FT-IR) in the region of the carbonyl absorption of the urea groups. Assignment of the bands was made by supposing the existence of chains of urea groups linked by bifurcated hydrogen bonds. Quantum mechanical calculations of these chains fitted qualitatively with the experimental results. Dynamic mechanical and calorimetric experiments showed that the apparition of the band related to the "internal" urea groups of the chains produces a decrease in the glass transition of the polyether moiety of the copolymer and that prior to it a transition that we related to the glass transition of the bis(ureaphenyl)methane units takes place.X

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Section: Resultsmentioning

confidence: 99%

Hydrogen Bonding in Copoly(ether−urea)s and Its Relationship with the Physical Properties

et al. 1997

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“…A number of papers concerning the preparation and physical properties of thermotropic polyurethanes have been reported, − since thermotropic polyurethanes were first reported by Iimura and co-workers − …”

Section: Introductionmentioning

confidence: 99%

Liquid Crystallinity of Thermotropic Para-Type Homo- and Copolyurethanes Containing Biphenylene Mesogen and Their Blends

Lee

Koide

et al. 1998

Macromolecules

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High-molecular-weight para-type homopolyurethanes prepared by polyaddition of 2,5-tolylene diisocyanate with 4,4‘-bis(ω-hydroxyalkoxy)biphenyls showed monotropic liquid crystallinity, when measurements were performed under shearing. For example, a polyurethane PU6T having [η] 0.82 which was obtained from 4,4‘-bis(6-hydroxyhexyloxy)biphenyl showed T I - LC of 201 °C and T LC - K of 181 °C. In addition, thermotropic liquid-crystalline para-type copolyurethanes PUmnT (m and n denoting carbon number in alkylene moiety: 2, 6, 8, and 11) were synthesized by polyaddition of the diisocyanate with two 4,4‘-bis(ω-hydroxyalkoxy)biphenyls having different alkylene lengths. For example, PU68T(75/25) had T I - LC of 188 °C and T LC - K of 173 °C. Blends of two para-type homopolyurethanes also exhibited monotropic liquid crystallinity. The liquid crystallinity was examined by differential scanning calorimetry measurement, polarized optical microscope observation, and X-ray diffractometry.

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“…In the carbonyl stretching region there are three principal absorptions corresponding to different interaction strengths of the hydrogen bonded polymers (Ref. 12). At room temperature, the absorption at ca.…”

Section: Resultsmentioning

confidence: 99%

“…Polyurethanes are a class of liquid crystalline (LC) polymers (Refs. [6][7][8][9][10][11][12][13] in which extensive hydrogen bonding can easily occur between the urethane -NHCOOmoieties (Ref. 12) and can affect substantially the LC behavior.…”

Section: Introductionmentioning

confidence: 99%

The effects of hydrogen bonding on the liquid crystalline behavior of semiflexible poly(urethaneester)s

Laus

Angeloni

Francescangeli

et al. 1997

Macromolecular Symposia

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The peculiar liquid crystalline behavior of two poly(urethane-ester)s TDI-C6C4 and TDI-C6C8 is reported. Evidence is provided of the formation of two nematic mesophases, a cybotactic nematic and a conventional nematic mesophase, in TDI-C6C8 and of one cybotactic nematic mesophase in TDLC6C4. IR spectroscopy indicates that different hydrogen bonded and non-bonded structum occur with varying temperature.The transition from the nematic cybotactic mesophase to the nematic mesophase, or to the isotropic phase, is accompanied by a substantial decrease of the strength of the hydrogen bonds. This is also reflected in the dynamic-mechanical behavior of these poly(urethane-ester)s which is similar to the one of slightly crosslinked thennoreversible networks.

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Development of crystallinity in a semiflexible thermotropic polyurethane. 2. Structure and dynamics

Cited by 32 publications

References 14 publications

Hydrogen Bonding in Copoly(ether−urea)s and Its Relationship with the Physical Properties

Hydrogen Bonding in Copoly(ether−urea)s and Its Relationship with the Physical Properties

Liquid Crystallinity of Thermotropic Para-Type Homo- and Copolyurethanes Containing Biphenylene Mesogen and Their Blends

The effects of hydrogen bonding on the liquid crystalline behavior of semiflexible poly(urethaneester)s

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