Influence of Alkyl Chain Spacer Length on the Charge Carrier Mobility of Isotactic Poly(N-carbazolylalkyl acrylates)

In the search for semiconducting polymer alternatives to conjugated polymers, stereoregular nonconjugated pendant electroactive polymers (NCPEPs) have recently shown competitive hole mobilities with conjugated polymers and a dramatic increase in mobility relative to atactic analogues. Here we investigate one of the key structural variables of NCPEPs: the flexible alkyl spacer that separates the electroactive pendant from the backbone. We investigate a straightforward postpolymerization functionalization synthetic method to synthesize such polymers with high isotacticity using poly(N-carbazolylalkyl acrylate) as a model system, where the alkyl chain spacer in the NCPEPs is varied from 2 to 12 carbons. We observed that the hole mobility increased from the two-carbon spacer, resulting in the highest mobility upon thermal annealing with a four-carbon spacer for 75% isotactic polymers and with a six-carbon spacer for 87% isotactic polymers. As such, we have demonstrated an important role of the spacer chain in influencing mobility. For all spacer lengths, higher mobilities were measured with the more isotactic polymer. While physical characterization of the largely amorphous polymers yielded little insight into the structure-function relationships, DFT and MD simulations indicated helical structures for the polymers where intermolecular short-range π-stacking is observed and is affected by spacer chain length. This work demonstrates that both the degree of stereoregularity and the spacer chain length play a role in determining the hole mobility in NCPEPs.

Structures and properties of side-chain liquid crystalline polynorbornenes containing an amide group: hydrogen bonding interactions and spacer length effects

Side-chain liquid crystalline polynorbornenes based on benzanilide mesogens exhibit rich self-organization behaviours and enhanced mechanical properties owing to the lateral hydrogen bond interaction that can be tuned by the spacer length.

Monodisperse Liquid Crystal Network Particles Synthesized via Precipitation Polymerization

The production of liquid crystalline (LC) polymer particles with a narrow size distribution on a large scale remains a challenge. Here, we report the preparation of monodisperse, cross-linked liquid crystalline particles via precipitation polymerization. This versatile and scalable method yields polymer particles with a smectic liquid crystal order. Although the LC monomers are randomly dissolved in solution, the oligomers self-align and LC order is induced. For the polymerization, a smectic LC monomer mixture consisting of cross-linkers and benzoic acid hydrogen-bonded dimers is used. The average diameter of the particles increases at higher polymerization temperatures and in better solvents, whereas the monomer and initiator concentration have only minor impact on the particle size. After deprotonating of the benzoic acid groups, the particles show rapid absorption of a common cationic dye, methylene blue. The methylene blue in the particles can be subsequently released with the addition of Ca²⁺, while monovalent ions fail to trigger the release. These results reveal that precipitation polymerization is an attractive method to prepare functional LC polymer particles of a narrow size distribution and on a large scale.

In situ characterization of strain-induced crystallization of natural rubber by synchrotron radiation wide-angle X-ray diffraction: construction of a crystal network at low temperatures

Strain-induced crystallization (SIC) of natural rubber (NR) at descending temperatures as low as -60 °C is systematically investigated by in situ synchrotron radiation wide-angle X-ray diffraction (SR-WAXD) measurement. The detailed structural evolution of NR during SIC is studied in the strain-temperature space, where up to four regions are defined depending on the SR-WAXD results. In region I, the molecular chains begin to be oriented under tensile loading. The onset of crystallization happens in the very beginning of region II, and the NR crystal acts as a new physical cross-linking point to form a crystal network, namely the series model. The further increment of crystallinity (> ca. 8%) leads to the transition of the crystal network from the series model to the parallel model in region III. The crystal network is finally accomplished in region IV, where the crystallinity remains almost constant. Interestingly, regions III and IV exist only in the intermediate-temperature zone II (-40 °C to -10 °C), which are missing in zones I (-10 °C to 25 °C) and III (-60 °C to -40 °C). This suggests that sufficient crystallinity (χ_II-III > ca. 8%) is required to form the parallel model. The new crystal network provides a deep understanding of SIC of NR considering the microscopic features, i.e. oriented amorphous component, the onset of crystallization and crystallinity evolution and its correlation with the macroscopic stress-strain curve.

Self-organization of cholesterol-side-chain liquid crystalline polymers by tailoring the main chain structure and flexible spacer length

Liquid crystal polymers with cholesterol side-chains formed different smectic A phases under the influence of the main-chain structure and flexible spacer length.

Phase Separation Driven On-Demand Debondable Waterborne Pressure-Sensitive Adhesives

A waterborne pressure-sensitive adhesive (PSA) that shows high adhesive performance and easy debondability on demand without leaving residues on the substrate (adhesive failure) has been developed. A key component of the PSA is a semicrystalline phase that is beneficial for the adhesive properties and that becomes fluid when heated above the melting temperature. Migration of this liquid-like polymer to the substrate-adhesive interface and hardening upon cooling results in a hard non-tacky interface that facilitates debonding. The effect of the particle morphology on the debonding ability is discussed.

Self-organization behaviours of hemiphasmidic side-chain liquid-crystalline polymers with different spacer lengths

The influence of flexible spacers on unusual self-organization behaviours of side-chain liquid-crystalline polymers containing biphenyl hemiphasmidic mesogens.