Phase transitions in narrow-molar-mass samples of side-chain liquid-crystalline polymers: molar-mass dependence

Gedde, Ulf W.; Jonsson, H.; Hult, Anders; Percéc, Virgil

doi:10.1016/0032-3861(92)90279-6

Cited by 17 publications

(10 citation statements)

References 20 publications

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“…Quasi-elastic neutron scattering supports this interpretation [26]. For example, for some cyano-terminated polyacrylates the enthalpy of the smectic-isotropic transition decreases with increasing molar mass [28,29], in contrast to polysiloxanes where no such dependency is found [28]. Though distinct from these cyanoterminated polycrylates, whose phase behaviour is determined by dipolar frustration, we postulate for the present PABB-5 series the same type of conformational changes.…”

Section: Discussionsupporting

confidence: 68%

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et al. 2001

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The phase behaviour and structure are reported of a new type of frustrated side-chain liquid crystalline (LC) polymer, a polyacrylate with phenylbenzoate mesogenic side groups and a narrow polydispersity. At a high degree of polymerisation the LC polymers show a nematic, a smectic-A d , a re-entrant nematic and aC phase, for shorter chains only a nematic and aC phase. This constitutes a new example of nematic re-entrance for which the driving field is the length of the polymer chain. The smectic-A d layers consist of partially overlapped side groups while in theC phase the side chains are rearranged into chevron-like blocks of bilayers. We propose an explanation of the frustrated phase behaviour in terms of these two different competing length scales and their coupling to the backbone conformations. PACS. 64.70.Md Transitions in liquid crystals -78.70.Ck X-ray scattering -61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures

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Section: Discussionsupporting

confidence: 68%

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et al. 2001

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“…A second deviation from the conventional trend was observed in the case of a series of side chain liquid crystalline poly(vinyl ethers) . Therefore, the trends of both transition temperature and associated thermodynamic parameters on DP from Figure do not have a precedent.…”

Section: Resultsmentioning

confidence: 85%

“…This odd−even dependence shows an increase followed by a maximum before it reaches a plateau. A second deviation from the conventional trend was observed in the case of a series of side chain liquid crystalline poly(vinyl ethers) .…”

Section: Resultsmentioning

confidence: 93%

Mechanistic Investigations on the Formation of Supramolecular Cylindrical Shaped Oligomers and Polymers by Living Ring Opening Metathesis Polymerization of a 7-Oxanorbornene Monomer Substituted with Two Tapered Monodendrons

1997

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The synthesis of the monomer exo, exo-5,6-bis[[[(3,4,5-tris((4-(dodecyl-1-oxy)benzyl)oxy)]benzyl)oxy]carbonyl]-7-oxabicyclo[2.2.1]hept-2-ene (4), containing two tapered monodendrons and its living ring-opening metathesis polymerization initiated with RuCl2(dCHPh)(PCy3)2 are discussed. Oligomers and polymers with narrow molecular weight distribution (Mw/Mn ) 1.06-1.29) and degrees of polymerization (DP) from 6 to 120, which correspond to Mn from 12 600 to 252 800, were synthesized and characterized. The monomer (4) and the corresponding polymers (5) self-assemble into disklike and cylindrical shapes which produce an enantiotropic hexagonal columnar (Φh) liquid crystalline (LC) phase. The analysis of the Φh phase of the monomer, oligomers, and polymers as a function of the DP reveals four regions and mechanisms for the generation of the Φh phase, i.e., below the DP which forms a disklike molecule, below the DP which corresponds to the maximum length of a disklike molecule (DP ) 26), up to the DP which corresponds to the persistence length of the rodlike cylinder (DP ) 64), and above this value.

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“…For example for cyano terminated polyacrylates it was found that the enthalpy of the smectic-isotropic transition decreases with increasing molar weight. [37,38] This means that an extension of the backbone chain reduces stability of the smectic layering in polyacrylates. Other polymers, e.g.…”

Section: Discussionmentioning

confidence: 99%