The ability to precisely control the self-assembly behavior of liquid crystalline polymers hinges on the strategic design of molecular architecture. In this study, two series of polynorbornene-based random copolymers—A-r-B and A-r-C—were synthesized with biphenyl mesogenic side groups positioned at different substituent sites, enabling a detailed investigation into how subtle structural variations influence phase stability and morphological evolution. The homopolymers exhibit distinct native structures: polymer A forms an oblique columnar (Colob/p2) phase with a lattice parameter exceeding 16 nm, polymer C adopts a lamellar structure, while polymer B remains amorphous. By systematically varying the molar ratio of monomer A relative to comonomers B or C, a rich sequence of phase transformations was observed.
Small-angle X-ray scattering (SAXS) analysis revealed that in the A-r-B system, increasing the molar content of A (xA) drives a transition from amorphous (xA = 10%) through lamellar (xA = 23%), undulated lamellar (xA = 80%), and finally to a well-ordered Colob/p2 structure (xA ≥ 89%). This progression is attributed to increasing volume fraction of aliphatic segments and enhanced steric frustration from the disubstituted mesogenic units. The presence of two biphenyl groups in A introduces branching-like effects, where one mesogen aligns parallel to the layer normal while the other must orient nearly within the plane, inducing curvature at the aromatic-aliphatic interface and promoting cylindrical aggregation.75706-12-6 supplier
In contrast, the A-r-C system follows a different pathway: starting from a lamellar structure at xA = 50%, it transitions through undulated lamellar (xA = 77%) to Colob/p2 (xA ≥ 82%).70-25-7 Molecular Weight Notably, the undulated lamellar phase appears at lower xA values in A-r-C compared to A-r-B, indicating that the position of the mesogenic group significantly influences the onset of structural instability. This sensitivity arises from differences in molecular packing efficiency and interfacial energy, as the substituent location alters the preferred orientation and alignment of the mesogenic units.
Grazing-incidence small-angle X-ray scattering (GISAXS) confirmed the orientation and symmetry of these phases in thin films.PMID:29999671 For A89-r-B11 and A88-r-C12, clear 2D oblique lattice patterns were observed, confirming parallel alignment of cylindrical domains with the a-axis aligned along the substrate. AFM height images showed fingerprint-like topographies with periodic spacings of ~16 nm, consistent with the calculated lattice parameter a = 16.08 nm for A89-r-B11. Films of A52-r-B48 exhibited flat-on lamellae with no surface features, while A80-r-B20 and A85-r-B15 displayed stripe-like undulations, indicating lateral deformation of the lamellar plane.
Thermal analysis by differential scanning calorimetry (DSC) revealed that both systems exhibit increased transition temperatures with higher xA. The LC-to-isotropic transition temperature rises from ~158 °C (A75-r-B25) to ~173 °C (A89-r-B11), reflecting enhanced thermal stability due to stronger intermolecular interactions and more ordered packing. Moreover, a secondary endothermic peak near 135 °C in A89-r-B11 indicates an order-to-order transition from Colob/p2 to a high-temperature lamellar phase, confirmed by temperature-dependent SAXS showing the reappearance of lamellar reflections before isotropization.
These findings demonstrate that the substituent position of mesogenic groups plays a decisive role in determining not only the final phase but also the kinetic pathway and intermediate states during self-assembly. The emergence of an undulated lamellar intermediate—a rare feature in SCLCPs—mirrors phenomena seen in block copolymer systems, highlighting the convergence of soft matter principles across different architectures. This work establishes a framework for designing SCLCPs with tunable mesophase stability, hierarchical organization, and responsive behavior through precise control of side-chain substitution.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
