The phase behaviors of side-chain liquid crystalline copolymers (SCLCPs) are governed by a delicate balance between molecular architecture, compositional variation, and intermolecular interactions. In this study, two series of random copolymers—A-r-B and A-r-C—were systematically investigated to elucidate the composition-dependent thermal transitions and self-organized structures arising from mesogenic groups positioned at different substituent sites. The synthesis was achieved through ring-opening metathesis polymerization (ROMP) using a Grubbs third-generation catalyst, yielding well-defined copolymers with controlled molar compositions ranging from 10% to 90% of monomer A.
Differential scanning calorimetry (DSC) revealed distinct thermal signatures across the copolymer series. For A-r-B copolymers, an exothermic peak during cooling and a corresponding endothermic peak during heating were observed near 169–173 °C, indicating a reversible liquid crystalline (LC)-to-isotropic transition. Notably, a smaller endothermic feature appeared at approximately 135 °C in A89-r-B11, suggesting an additional order-to-order phase transition preceding isotropization. This was confirmed by temperature-dependent SAXS, which showed a clear transformation from Colob/p2 diffraction peaks below 135 °C to characteristic lamellar reflections above that temperature, followed by complete loss of long-range order upon reaching the isotropic state.
Polarized optical microscopy (POM) provided visual confirmation of these transitions. Upon cooling from the isotropic phase, focal conic textures emerged in A89-r-B11, indicative of columnar ordering. As temperature decreased further, broken fan-like patterns developed, consistent with structural reorganization into a more disordered lamellar state. Similarly, A85-r-B15 displayed mosaic-like textures at low temperatures, reflecting the undulated lamellar morphology detected by GISAXS.
For the A-r-C system, comparable thermal responses were observed. DSC curves for A90-r-C10 and A77-r-C23 exhibited a LC-to-LC transition around 140–170 °C, followed by a Lam-to-isotropic transition near 157–170 °C. Temperature-dependent SAXS profiles demonstrated that both copolymers first enter a high-temperature lamellar phase before transitioning to isotropy. The persistence of (01), (02), and (03) lamellar peaks during heating, coupled with diminishing intensities of higher-order satellites, confirms that thermal motion reduces interfacial fluctuations while preserving the layered structure temporarily.
Grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM) further validated the structural evolution. Thin films of A89-r-B11 and A88-r-C12 displayed distinct 2D oblique lattice patterns in GISAXS, confirming parallel alignment of cylindrical aggregates within the plane.2089288-03-7 medchemexpress AFM height images revealed fingerprint-like topographies with periodic spacings (~16 nm), matching the calculated lattice parameter a = 16.110078-46-1 web 08 nm for A89-r-B11.PMID:22876374 In contrast, amorphous A10-r-B90 and lamellar A52-r-B48 films showed no regular surface features.
The phase diagrams constructed from these results illustrate a clear trend: as the molar fraction of A increases, both the LC-to-Lam and Lam-to-isotropic transition temperatures rise. This is attributed to increased volume fraction of aliphatic segments and enhanced steric frustration from branched mesogenic side chains, which promote curvature and drive the lamellar-to-columnar transition. The substitution position of the biphenyl group plays a critical role: despite identical chemical composition, the positional isomerism in B versus C leads to divergent phase sequences—A-r-B undergoes an amorphous-to-lamellar transition absent in A-r-C, highlighting the sensitivity of self-assembly to local molecular geometry.
In conclusion, this work demonstrates that precise control over mesogenic group positioning enables access to complex, multi-step phase transformations in SCLCPs. The emergence of intermediate undulated lamellar phases and the tunable thermal stability underscore the potential of such systems for applications requiring programmable structural response. These findings lay the foundation for future design of stimuli-responsive materials with hierarchical order and adaptive functionality.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com