Multiple Ordering Transitions: Hierarchical Self‐Assembly of Rod–Coil Block Copolymers

Abstract

ExperimentalThe detailed experimental procedure is as follows: In and In 2 O 3 powders at a weight ratio of 1:4 were mechanically mixed and used as the source material. Heating was performed in a vertical induction furnace and a graphite inductor acted as a heating element. The powders were heated in a tube-like alumina crucible. The powders were put into the bottom of the crucible and heated to 1300 C and held at that temperature for 30 min. The heating was carried out under vacuum. After heating, a layer of gray±yellow powders was found on the upper part of the alumina crucible, where the temperature was » 700±800 C during heating. A field-emission scanning electron microscope (SEM, JSM-6700F) was used to observe the morphology of the products. X-ray diffraction (XRD) spectra of the prepared nanostructures were recorded on a RINT2200 X-ray diffractometer using standard Cu Ka radiation. Further structural characterization was performed on a JEM-3000F high-resolution field-emission transmission electron microscope (TEM) operating at 300 kV. Chemical composition of nanostructures was detected using an energy-dispersive spectrometer (EDS) attached to the TEM. [15,16,18] via directional solvent evaporation in a lyotropic nematic solution of a rod±coil diblock copolymer. Subsequent microphase separation and ordering of the rod-like chains yield an unprecedented hierarchical morphology consisting of crystals of rod block (unit cell~1 nm), block copolymer microdomains (layer periodicity~50 nm), and NØel domain walls (wall periodicity~1000 nm). The result is an example of combined dynamic and static self-assembly, [19] which creates an unconventional morphology with multiple length scales by a single step process.The first ordered state reached from the initial isotropic solution of rod-like polymers is typically a nematic phase. Oftentimes periodically spaced NØel domain walls arise when a flow, magnetic or electric field is applied in a direction orthogonal to the monodomain director. [15,16] In low viscosity nematic liquids, the walls are only transient, [17] whereas, in polymeric systems, passing below the glass transition by rapid cooling or by rapid evaporation of solvent can easily fix the structures.[20] NØel wall patterns have not yet been observed in block copolymer systems. Provided NØel domain walls form in the nematic polymer solution, further phase transitions to smectic, crystalline, or microphase separated states within the large scale defect pattern can yield a novel hierarchical morphology. The rod±coil block copolymer investigated consists of poly(3-(triethoxysilyl)propyl isocyanate) (PIC) and polystyrene (PS) blocks (Fig. 1d). [21] Polyisocyanates are stiff, helical, extended chain polymers and form lyotropic nematic liquidcrystalline solutions. [22,23] The molecular weight of the flexible coil PS block is 39 kg/mol and that of the PIC is 23 kg/mol, with a PIC weight fraction of 37 %. Conversion of polystyrene living anions to diphenylethyl anions and use of trioctyl aluminum in the isocyanate poly...

Preparation and characterization of organic-inorganic hybrid nanomaterials using polyurethane-b-poly[3-(trimethoxysilyl) propyl methacrylate] via RAFT polymerization

“…It may be ascribed to the deformation mechanism of PU [36]. In case of PU composed of hard and soft segment domains, the hard segment domain, sensitive to applied stress, can be tilted 22 Guo et al -eXPRESS Polymer Letters Vol.4, No.1 (2010) [17][18][19][20][21][22][23][24][25] Figure 5. TGA curves of PU and its nanocomposites Figure 6.…”

“…TPM with reactive trimethoxysilane groups is widely used in the preparation of organic-inorganic hybrid nanomaterials [15][16][17][18][19]. With a base catalyst, the R-Si(OCH 3 ) 3 groups can be easily hydrolyzed into R-Si(OH) 3 which can subsequently transform into cross-linked polysilsesquioxane nanocages by condensation, thus producing organic-inorganic hybrid nanoballs [7,20,21]. Recently, some research interests have sparked in the studies of self-assembly of copolymers based on poly [3-(trimethoxysilyl) propyl methacrylate] (PTPM).…”

“…The peak was also shifted gradually to higher molecular weight and the PDI became narrower with the increase of the feed ratio of TPM ( Table 1), indicating that the RAFT polymerization occurred and the well controlled copolymers were obtained. Polyurethane prepared by condensation polymerization, as 20 Guo et al -eXPRESS Polymer Letters Vol.4, No.1 (2010) [17][18][19][20][21][22][23][24][25] Figure 2. Gel permeation chromatograms of PU and PU-PTPM copolymer precursors known, has a high PDI.…”

“…">Experimental 2.1. MaterialsDibutyl tin dilaurate, 2-hydroxypropyl acrylate (HPA), methyl ethyl ketone (MEK), THF (purchased from Sinopharm Chemical Reagent Co., Ltd China), isophorone diisocyanate (IPDI, from Alfa 18 Guo et al -eXPRESS Polymer Letters Vol.4, No.1 (2010) [17][18][19][20][21][22][23][24][25] Aesar) and isophorone diamine (Fluka), 3-(trimethoxysilyl) propyl methacrylate (TPM, purchased from Acros Organics), 2,2′-Azobisisobutyronitrile (AIBN, purchased from Shanghai Shisihewei Chemical Co.) were used without further purification. Poly(diethylene adipate) (PDA, purchased from Jiangdu Longchuan Wear-Resistant Polymer Materials Co., Ltd China) was dried under vacuum at 80°C for 1 h before use.…”

Room temperature polymerization of alkyl isocyanates catalyzed by rare earth Schiff base complexes

“…Due to this dynamic helical conformation, polyisocyanates offer a lot of fascinating properties, such as light scattering, frictional, electrical and optical properties. Hence they have been studied for application as chiral recognition materials, optical switches and liquid crystal materials [1][2][3][4][5] . Usually, the polymerizations of isocyanates were carried out by anionic initiators such as NaCN, sodium naphthalene , and lithium amide of piperidine at very low temperatures (−78-98℃) [6][7][8][9] .…”