Correlation of Model Compounds and Laterally Attached Side-Chain Liquid-Crystalline Polynorbornenes with an 11-Carbon Spacer

Poly{5-[[[11‘-[2‘‘,5‘‘-bis[2-(3‘-fluoro-4‘-n-alkoxyphenyl)ethynyl]phenyl]undecyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-ene}s exhibit an enantiotropic nematic mesophase when n = 2−12. In contrast to the corresponding reference polymers with a 1-carbon spacer, none of these polymers with an 11-carbon spacer crystallize if their molecular weight is sufficiently high. Although the corresponding 1,4-bis[(3‘-fluoro-4‘-n-alkoxyphenyl)ethynyl]-2-undecylbenzenes exhibit only a monotropic nematic mesophase when n = 2, 4, 6−11, their isotropization temperatures are nearly identical to those of the polynorbornenes, and they are therefore appropriate models of the polymers. The polymers (DPn = 14−158, pdi = 1.14−1.37) were prepared by ring-opening metathesis polymerization of 5-{[[11‘-[2‘‘,5‘‘-bis[2-(3‘-fluoro-4‘-n-alkoxyphenyl)ethynyl]phenyl]undecyl]oxy]carbonyl}bicyclo[2.2.1]hept-2-enes in THF using Mo(CHCMe2Ph)(N-2,6-iPr2Ph)(OtBu)2 as the initiator. Their thermotropic behavior becomes independent of molecular weight at approximately 30 repeat units

Nanopattern Formation from Tethered PS-<i>b</i>-PMMA Brushes upon Treatment with Selective Solvents

Nanopattern Formation from Tethered PS-b-PMMA Brushes upon Treatment with Selective Solvent

Patternable Conjugated Polymers with Latent Hydrogen-Bonding on the Main Chain

Conjugated polymers with latent hydrogen-bonding on the main chain were synthesized using Suzuki coupling reaction. The resulting polymers with latent hydrogen-bonding can be converted to the actual hydrogen-bonded polymers by thermal annealing or UV irradiation. As the hydrogen-bonding sites are fused with π-conjugated units on the polymer backbone, the intermolecular interactions between the polymer chains will be strongly enhanced when the hydrogen-bonds are formed. By removing the protection group and forming hydrogen-bonding, the polymers exhibited a bathochromic shift over those with latent hydrogen-bonding, indicating a hydrogen-bonding-mediated enhancement of π–π stacking. In addition, the fused hydrogen-bond sites and π-conjugated units led to closely packed polymer chains, resulting in insoluble pigment-like polymers. This drastic solubility change from polymers with latent hydrogen-bonding to hydrogen-bonded polymers can be used to pattern conjugated polymers directly. The photolithography of the conjugated polymer with latent hydrogen-bonding was demonstrated, and the patterned electrochromic devices were fabricated and tested

Formation of Nanostructured Materials via Coalescence of Amphiphilic Hollow Particles

A new, simplified route to amphiphilic core−shell nanotubes, microfibers, and microrods has been developed that does not involve the traditional utilization of well-defined block copolymers. Thus, amphiphilic graft copolymers (PEI-g-PMMA) are prepared by an aqueous free radical polymerization that self-assemble in situ to form uniform core−shell nanoparticles. The hydrophobic homopolymer (PMMA) that is also formed is incorporated in the cores. Slight cross-linking of the shells followed by extraction of the homopolymer results in hollow nanoparticles that coalesce to form nanotubes. When the shells are not cross-linked, the hollow particles coalesce to form microrods and microfibers. The sizes and shapes of the micromaterials can be controlled by varying the experimental conditions

Solvent Dependence of the Morphology of Spin-Coated Thin Films of Polydimethylsiloxane-Rich Polystyrene-<i>block</i>-Polydimethylsiloxane Copolymers

The as-spun, thin film morphologies of a series polydimethylsiloxane-rich cylinder and lamellar-forming polystyrene-<i>block</i>-polydimethylsiloxane (PS<i>-<i>b</i>-</i>PDMS) copolymers with constant PDMS molecular weight and varying PS volume fraction were studied with a range of solvents of varying solubility parameter. It was found that PDMS occupies the surface of the thin films regardless of the choice of solvent used in spin-coating due to its extremely low surface tension. The morphology shifted from parallel cylinders to hexagonally perforated lamellar to parallel lamellar as the solvent was varied from PDMS to PS selective solvents (increasing solvent solubility parameter). The transition points between each morphology were also dependent on the volume fraction of the block copolymer where the transitions were observed at lower solubility parameter with increasing PS volume fraction of the polymer. The morphology variations are attributed to selective swelling effects of the individual blocks even under good solvent conditions. These results are discussed in the context of current theories of solvent evaporation induced ordering of block copolymer thin films

Patternable Conjugated Polymers with Latent Hydrogen-Bonding on the Main Chain

Conjugated polymers with latent hydrogen-bonding on the main chain were synthesized using Suzuki coupling reaction. The resulting polymers with latent hydrogen-bonding can be converted to the actual hydrogen-bonded polymers by thermal annealing or UV irradiation. As the hydrogen-bonding sites are fused with π-conjugated units on the polymer backbone, the intermolecular interactions between the polymer chains will be strongly enhanced when the hydrogen-bonds are formed. By removing the protection group and forming hydrogen-bonding, the polymers exhibited a bathochromic shift over those with latent hydrogen-bonding, indicating a hydrogen-bonding-mediated enhancement of π–π stacking. In addition, the fused hydrogen-bond sites and π-conjugated units led to closely packed polymer chains, resulting in insoluble pigment-like polymers. This drastic solubility change from polymers with latent hydrogen-bonding to hydrogen-bonded polymers can be used to pattern conjugated polymers directly. The photolithography of the conjugated polymer with latent hydrogen-bonding was demonstrated, and the patterned electrochromic devices were fabricated and tested

Determination of the Extent of Lateral Spread and Density of Secondary Nucleation in Polymer Single Crystal Growth

As illustrated in an earlier work (Macromolecules 2006, 39, 1008), isotactic poly(vinylcyclohexane) (PVCH) single crystals display twinned growth sectors. Mapping of the twinned domains is possible via dark-field electron microscopy imaging. Each twinned domain results from a growth twin on the lateral growth face of the single crystal. The width of the twinned domain provides a measure of the so-called lateral spread extent, a fundamental parameter of classical theories of nucleation and growth for which only indirect estimates are available. The extent of lateral spread (and, as a corollary, the secondary nucleation density) (both average values and distribution), are determined for single crystals of PVCH produced in squalane over a wide range of crystallization temperatures (120−240 °C). These observations provide the first direct experimental data on these elementary processes in polymer crystal growth

Induction of Smectic Layering in Nematic Liquid Crystals Using Immiscible Components. 2. Laterally Attached Side-Chain Liquid-Crystalline Poly(norbornene)s and Their Low-Molar-Mass Analogues with Hydrocarbon/Oligodimethylsiloxane Substituents

In contrast to their hydrocarbon analogues which exhibit only nematic mesophases, poly{5-[[[2‘,5‘-bis[(4‘‘-(n-(dimethylsiloxyl)alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-ene}s and their low-molar-mass model compounds exhibit smectic C mesophases. Since nematic liquid crystals can be forced into layers by terminating their hydrocarbon substituents not only with fluorocarbon segments but also with flexible siloxane segments, this supports the hypothesis that the smectic mesomorphism of amphiphilic molecules containing linear fluorocarbon segments is due primarily to the immiscibility of the hydrocarbon and fluorocarbon segments, rather than to a shape persistence of “mesogenic perfluoroalkyl rods”. The 2,5-bis[(4‘-(n-(oligodimethylsiloxyl)alkoxy)benzoyl)oxy]toluenes mimic both the phases formed by the polymers and the general temperatures of their transitions and are thereforeexcellent models of the polymers. The 5-{[[2‘,5‘-bis[(4‘‘-(n-(oligodimethylsiloxyl)alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl}bicyclo[2.2.1]hept-2-enes were polymerized by ring-opening metathesis polymerization in THF at room temperature using Mo(CHCMe2Ph)(N-2,6-iPr2Ph)(OtBu)2 as the initiator

Cooperative Soft-Cluster Glass in Giant Molecular Clusters

Three-dimensional giant molecular clusters, OPOSS16 and OPOSS24, have been designed and precisely synthesized. They have 16 or 24 octyl polyhedral oligomeric silsesquioxane (OPOSS) building blocks chemically linked by short, flexible chains. Despite the small difference in their molecular weight, 25 and 38 kg/mol respectively, they show different dynamics above the conventional glass transition temperature (Tg). OPOSS16 in the bulk quickly turns to viscous. In contrast, OPOSS24 shows a long-lasting elastic plateau even far above the Tg, corresponding to confinements on individual OPOSS. To achieve any confinements, clusters have to be immobile, although individual OPOSS possesses mobility. It directly confirms that in the bulk giant molecular clusters possess a cooperative soft-cluster glass in addition to conventional glass if they are larger than the critical diameter. This critical diameter is close to the estimated diameter of cooperative rearranging regions during glass transition. Giant molecular clusters present unique dynamics different from colloidal caging in solution or polymer entanglements

Self-Assembly of Porphyrin and Fullerene Supramolecular Complex into Highly Ordered Nanostructure by Simple Thermal Annealing

Self-Assembly of Porphyrin and Fullerene Supramolecular Complex into Highly Ordered Nanostructure by Simple Thermal Annealin