Synthesis, Morphology, and Field-Effect Transistor Characteristics of Crystalline Diblock Copolymers Consisted of Poly(3-hexylthiophene) and Syndiotactic Polypropylene

We report the synthesis, morphology, and the field effect transistor (FET) characteristics of the crystalline diblock copolymers of poly­(3-hexylthiophene) and syndiotactic polypropylene (P3HT-<i>b</i>-sPP). Four diblock copolymers with various sPP block lengths, P3HT_16K-<i>b-</i>sPP_3K (P1), P3HT_16K-<i>b-</i>sPP_6K(P2), P3HT_16K-<i>b-</i>sPP_9K(P3), and P3HT_16K-<i>b-</i>sPP_14K (P4), were prepared by the click coupling of N₃-capped sPP and ethynyl-capped P3HT. The stereoregular crystalline block sPP developed different types of molecular stacking structures and led the P3HT domains to pack lamellar edge-on structure with improved charge transporting characteristics, as evidenced by the grazing incidence wide-angle X-ray scattering (GIWAXS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The FET hole mobilities of P1–P3 thin films were 4.15 × 10^–3, 4.16 × 10^–2, and 3.95 × 10^–3 cm² V^–1 s^–1, respectively, which were up to 1 order of magnitude higher than that of the parent P3HT thin film (1.43 × 10^–3 cm² V^–1 s^–1). The crystalline-stereoregular crystalline diblock P3HT-<i>b</i>-sPP demonstrates that using the lattice matching concept could well clarify the molecular stacking structure of conjugated polymer segments in order to further improve the performance of organic electron devices

Crystallization of Isotactic Polypropylene under the Spatial Confinement Templated by Block Copolymer Microdomains

We investigate the crystallization behavior of isotactic polypropylene (iPP) under the influence of nanoscale confinement templated by the microphase-separated structure of an iPP-based diblock copolymer system, isotactic polypropylene-<i>block</i>-atactic polystyrene (iPP-<i>b</i>-aPS). Three types of iPP microdomains, i.e., lamellae, cylinder, and sphere, were generated by controlling the composition of the diblock. The effect of microdomain morphology on the nucleation mechanism, crystallization kinetics, self-nucleation behavior, the population of the helical sequence of iPP block in the melt state, and crystal orientation have been systematically studied. It was found that the crystallization rate of iPP was predominantly controlled by homogeneous nucleation when the crystallization process was largely confined within the individual cylindrical and spherical microdomains. Such a nucleation mechanism and the highly frustrated crystal growth in the isolated microdomains led to the absence of Domain II and atypical crystallization kinetics in Domain III in the self-nucleation study. The population of the longer helical sequence of iPP block revealed by infrared spectroscopy was found to be affected by temperature but not by the spatial confinement, chain stretching, and junction point constraint imposed by the microdomains. Finally, the orientation of α-form iPP crystals in the lamellae-forming iPP-<i>b</i>-aPS was identified over a broad range of crystallization temperatures (<i>T</i>_c). Different from other crystalline–amorphous diblocks, a lamellar branching of α-form iPP was observed in the lamellar microdomains at <i>T</i>_c lying between 15 and 80 °C, where the daughter lamellae developed from the perpendicularly orientated parent iPP crystals with a specific angle of 80° or 100°. Once the sample was crystallized at <i>T</i>_c ≤ 10 °C, the iPP crystals became randomly oriented

Stabilizing the Ordered Bicontinuous Double Diamond Structure of Diblock Copolymer by Configurational Regularity

We investigate the formation of the ordered bicontinuous structures in a stereoregular diblock copolymer, isotactic polypropylene-<i>block</i>-polystyrene (iPP-<i>b</i>-PS), in which the minority PP block possessed isotactic configuration. This diblock displayed the conventional ordered bicontinuous double gyroid (OBDG) morphology upon heating above the crystal melting point of the iPP block from the as-cast state. The OBDG phase remained stable in the heating process up to the order–disorder transition. In the subsequent cooling process from the nearly disordered state, the OBDG phase first developed, but when the temperature was sufficiently low, an order–order transition from OBDG to the ordered bicontinuous double diamond (OBDD) phase occurred, and OBDD eventually became the dominant structure. The results attested that OBDD and OBDG represented the thermodynamically stable structure at the lower and the higher temperature, respectively, and the OBDG morphology formed in the as-cast state was metastable. The present finding along with that of the syndiotactic polypropylene-<i>block</i>-polystyrene (sPP-<i>b</i>-PS) reported previously consolidated the role of configurational regularity in stabilizing the otherwise unstable OBDD phase for diblock copolymers. The stability of the OBDD structure was attributed to the cooperative effect of the relatively high polydispersity and the helical segment formation of the stereoregular minority block, as the conformational entropy loss arising from the packing frustration of the minority block in the network domain was effectively compensated by the release of enthalpy via the formation of helical segments and their associations

Order–Order Transition between Equilibrium Ordered Bicontinuous Nanostructures of Double Diamond and Double Gyroid in Stereoregular Block Copolymer

While ordered bicontinuous double diamond (OBDD) in block copolymers has always been considered as an unstable structure relative to ordered bicontinuous double gyroid (OBDG), here we report the existence of a thermodynamically stable OBDD structure in a diblock copolymer composed of a stereoregular block. A slightly asymmetric syndiotactic polypropylene-<i>block</i>-polystyrene (sPP-<i>b</i>-PS) as cast from xylene was found to display the OBDD morphology. When the OBDD-forming diblock was heated, this structure transformed to the OBDG phase at ca. 155 °C. Interestingly, OBDD was recovered upon cooling even in the temperature range above melting point of sPP, indicating that OBDD was a thermodynamically stable structure for sPP-<i>b</i>-PS melt, which was in contradiction to the conventional view. We propose that the larger free energy cost encountered in OBDD due to the larger packing frustration may be compensated sufficiently by the release of free energy due to local packing of the conformationally ordered segments of sPP blocks, which stabilizes the OBDD structure at the lower temperatures

Syndiotactic Polyallyltrimethylsilane-Based Stereoregular Diblock Copolymers: Syntheses and Self-Assembled Nanostructures

Structurally well-defined stereoregular diblock copolymers composed of syndiotactic polyallyltrimethylsilane (sPATMS) and poly­(methyl methacrylate) (PMMA) were prepared by using an α-bromoester-terminated sPATMS macroinitiator, which was chain extended by MMA using a cuprous halide-based atom transfer radical polymerization (ATRP) system. The α-bromoester-terminated sPATMS macroinitiator was prepared via the esterfication of hydroxyl-capped sPATMS with α-bromoisobutyryl bromide. The hydroxyl-capped sPATMS was generated via a selective chain transfer reaction to triethylaluminum (TEA) during the syndiospecific polymerization of allyltrimethylsilane (ATMS) conducted in the presence of syndiospecific <i>ansa</i>-metallocene catalysts. The proposed synthetic route not only offers the high-yield production of stereoregular sPATMS-<i>b</i>-PMMA but also provides the linking of the stereoregular block (sPATMS) with PMMA through a controlled/living radical polymerization process. Moreover, the proposed method offers effective control over the block chain length, the molecular weight distribution (<i>M</i>_w/<i>M</i>_n) and the stereoregularity of sPATMS block. Thus, the self-assembly of the resultant diblock copolymers produces well-ordered nanostructures from microphase separation, as evidenced by transmission electron microscopy and small-angle X-ray scattering results

Nanoporous Crystalline Templates from Double-Crystalline Block Copolymers by Control of Interactive Confinement

Single, double, and coincident crystallizations under hard or soft confinement are all carried out using a single type of syndiotactic poly­(<i>p</i>-methyl­styrene)-<i>block</i>-poly­(l-lactide) (<i>s</i>PPMS–PLLA) block copolymers. The single crystallization of <i>s</i>PPMS matrix can lead to the disordered arrangement of hexagonally packed PLLA cylinders under soft confinement. In contrast, the lamellar nanostructure remained unchanged regardless of the PLLA crystallization under hard or soft confinement. Crystallization-induced morphological transitions from the confined monosized lamella to the metastable dual-sized lamella and finally to the breakout morphology are evident by transmission electron microscopy and small-angle X-ray scattering. The dual-sized lamella is attributed to the thermodynamically and kinetically controlled nanocrystallite growth templating along the ordered microphase separation. Despite crystalline sequences, the double-crystallized morphologies are determined by the first-crystallized event even though the subsequent crystallization temperature is performed under soft confinement. By the control of interactive confinement, ordered crystalline nanosheets and cylindrical monoliths are obtained, providing a novel means for the fabrication of nanoporous crystalline templates

Interactive Crystallization Kinetics in Double-Crystalline Block Copolymer

The crystallization kinetics and crystallization-induced morphological formation of an asymmetric double-crystalline block copolymer, syndiotactic polypropylene-<i>block</i>-poly­(ε-caprolactone) (sPP-<i>b</i>-PCL), have been investigated by time-resolved simultaneous small-angle and wide-angle X-ray scattering (SAXS/WAXS). The sPP-<i>b</i>-PCL under study exhibited hexagonally packed cylinder morphology in the melt state, where the minority sPP block formed the cylindrical microdomains dispersed in the PCL matrix. The crystallization behavior was studied by imposing two types of crystallization histories: (1) two-stage crystallization, where the diblock was first cooled to the temperature <i>T</i>_c^sPP situating between the melting points of the two components (<i>T</i>_m^PCL < <i>T</i>_c^sPP < <i>T</i>_m^sPP) to allow sPP crystallization to saturation followed by cooling to <i>T</i>_c^PCL < <i>T</i>_m^PCL to induce PCL crystallization; (2) one-stage crystallization, where the system was cooled directly to <i>T</i>_c < <i>T</i>_m^PCL to allow the two components to crystallize competitively. In both cases, the crystallization of sPP block was in general able to disrupt the melt structure and transformed it into a crystalline lamellar morphology. For the two-stage crystallization process, the PCL block was found to exhibit a faster crystallization at a given <i>T</i>_c^PCL when the sPP block was precrystallized at higher <i>T</i>_c^sPP. This “interactive crystallization kinetics” was attributed to the mediation of the stretching of PCL blocks by the thickness of sPP crystalline domains which depended on <i>T</i>_c^sPP. In the one-stage process, the crystallization events of the two blocks became more competitive with decreasing <i>T</i>_c. The morphological perturbation induced by crystallization was also more hindered at lower <i>T</i>_c, such that a significant portion of sPP blocks remained confined within the cylindrical microdomains so as to suppress the sPP crystallinity