Structure of poly(N‐butyl isocyanate)

Abstract

An x‐ray study of poly(N‐butyl isocyanate) (PBIC) was undertaken with the aim of providing the structural information required for the calculation of its ultraviolet absorption spectrum. Well defined diffraction patterns are obtained from powder samples and oriented films of the polymer cast from cyclohexane solution. All the reflections can be satisfactorily indexed in terms of a pseudo‐hexagonal unit cell with a = 13.3 Å and c = 15.4 Å. This indexing and the intensity distribution lead to the conclusion that PBIC has a helical structure with a translation of 1.94 Å and a rotation of 135° per monomeric unit (i.e., the c axis corresponds to 8 units in 3 helical turns). In the absence of single‐crystal data on closely similar model compounds, a range of possible bond lengths and angles was assumed. The atomic coordinates of the chromophoric group of PBIC were then computed using the restrictions imposed by the helical parameters. From an investigation of all the assumed range of bond lengths and angles, a few closely similar structures having no unacceptably short van der Waals contacts were found. A comparison of calculated and measured densities indicates that there are two molecules per unit cell. Construction of space‐filling models of PBIC supports this conclusion.

Synthesis and structure determination of helical polymers

“…This speculation is supported by the fact that st-PMMA can encapsulate fullerenes and it-PMMA within its helical cavity to form robust and peapod-like inclusion complexes 80 and a stereocomplex, 98 respectively. Recently, we found that a preferred-handed helical st-PMMA can be induced in toluene in the presence of optically active alcohols, such as (S)-or (R)-2-phenylethanol (38), resulting in an optically active gel, which showed a VCD in PMMA infrared regions. On addition of fullerenes, such as C 60 , helical st-PMMA traps fullerenes within its helical cavity to form an optically active peapod-like inclusion complex ( Figure 14).…”

“…47 This helical structure is comparable in structure with the corresponding helical polyisocyanate proposed by the fiber XRD method. 38 The single-X-ray crystallographic analysis of uniform oligomers has also been used to determine the helical structures of poly(2,3-quinoxaline)s 48 and N-substituted poly(p-benzamide)s, 49 which are considered to possess a one-handed helical conformation as evidenced by their intense Cotton effects. An optically and catalytic active pentamer of a diastereomerically pure oligo(2,3-quinoxaline) (16) was found to have a right-handed 5/2 helix in the solid state.…”

“…X-ray diffraction (XRD) is among the most convenient techniques for elucidating the structures of helical polymers as clearly demonstrated for biological polymers, such as polypeptides 36 and DNA. 37 In fact, on the basis of the XRD measurements of oriented films or fibers derived from liquid crystalline (LC) helical polyisocyanates such as poly (n-butyl isocyanate) (10), 38 and polysilanes, for instance, poly (di-n-pentylsilane) (11) 39 and poly(n-decyl-(S)-2-methylbutylsilane) (12), 40 their helical structures were elucidated to be the 8/3 helix and 7/3 helix, respectively (Chart 1). However, owing to the limited number of diffractions and difficulty in obtaining crystalline samples from most synthetic helical polymers, the XRD method seems to be laborious and cannot provide important structural information, in particular, on the helical sense.…”

Reversible conformation-driven order–order transition of peptide-mimic poly(n-alkyl isocyanate) in thin films via selective solvent-annealing

“…The obtained PHIC product was characterized using both proton and carbon nuclear magnetic resonance ( 1 H and 13 C NMR) spectroscopies with a JEOL NMR spectrometer (model JNM-LA300WB, JEOL Ltd, Tokyo, Japan) and using Fourier transform infrared (FT-IR) spectroscopy with a Perkin Elmer spectrometer (model 2000, Perkin Elmer, Waltham, MA, USA Figure S1). 13 The molecular weights of the polymers were determined using a multi-angle laser light scattering detector system and a size exclusion chromatography system (Interferometric Refractometry 478-009-690, Optilab DSP, Phoeix, AZ, USA and DAWN EOS Laser Photometer 113-E, Wyatt Technology, Santa Barbara, CA, USA) with four columns (HR 0.5, HR 1, HR 3 and HR 4, Waters Styragel columns run in series with column pore sizes of 50, 100, 500 and 1000 Å , respectively). THF with triethylamine (to prevent the adsorption of the hydrophilic polymer on the column) was used as the mobile phase at a flow rate of 1.0 ml per min.…”

“…For example, several helical conformations have been proposed, namely 2 1 , 5 1 and 8 3 in solution [9][10][11][12] and 8 3 , 8 5 and 12 5 in the solid state. [13][14][15] Furthermore, triclinic, monoclinic and pseudo-hexagonal lattices have all been proposed as possible molecular packing structures. 13,14,16 In the present work, we provide the first report on the formation of PHIC in thin films with both a helical conformation-based hexagonal packing order and a b-sheet conformation-based lamellar structure;…”