Conformation of comb‐like liquid crystal polymers in isotropic solution probed by small‐angle neutron scattering

Abstract

AbstractThe conformational characteristics of a comb‐like side‐chain liquid crystal polysiloxane (SCLCP), dissolved in deuterated chloroform, were evaluated by small‐angle neutron scattering (SANS) measurements over a wide q range. SANS studies were carried out on specimens with constant backbone length (DP = 198) and variable spacer length (n = 3, 5, and 11), and with constant spacer length (n = 5) and variable DP (45, 72, 127, and 198). The form factor P(q) at high q was analyzed using the wormlike chain model with finite cross‐sectional thickness (Rc) and taking into account the molecular weight polydispersity. The analysis generated values of persistence length in the range lp = 28–32 Å, considerably larger than that of the unsubstituted polysiloxane chain (lp = 5.8 Å), with contour lengths per monomer comparable to the fully‐extended polysiloxane backbone (lm = 2.9 Å). This indicates a relatively rigid SCLCP chain due to the influence of the densely attached mesogenic groups. The SCLCP with n = 11 is more flexible (lp = 28 Å) than those with n = 3 and n = 5 (lp = 32 Å). The cross‐sectional thickness increases with spacer length, Rc ∼ n0.21±0.02 (3 ≤ n ≤ 11), and the contour length per monomer decreases with increasing spacer length, lm ∼ n−0.35±0.01. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2412–2424, 2006