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Mobile-amorphous-free crystals of a semiconducting polymer, poly(3-hexyl thiophene) (P3HT), were made via a flow induced crystallization technique to yield crystals that were microns long while the...

Extensive efforts have been employed to improve the power conversion efficiency of organic solar cells. One of the most successful approaches is the morphological control of the solar cells’ active...

The morphology of poly (3-hexylthiophene) (P3HT) in its liquid phase and its manipulation via flow-induced solution crystallization and its crystallization kinetics was studied to determine its mechanism. Shear flow-induced ordering of semiconducting P3HT, which generates more perfect crystal structures than quiescent methods, is elucidated using in situ rheo-SANS and rheo-SALS measurements, and an Avrami analysis is performed. Characteristic lengths of P3HT crystals were measured as a function of time, and 3-D networks of percolated P3HT fibril crystals were determined by measuring the apparent fractal, ∼2.6, by fitting the rheo-SANS data with a power law function. Additionally, UV–vis and DSC results revealed a process of P3HT crystal perfection determined by following the evolution of absorption peak characteristics of pi–pi stacking at 600 nm and the melting peaks as they shifted and narrowed with respect to increasing shear time. The Avrami exponent, m, reached a maximum value of 2 indicating homogeneous nucleation of P3HT macromolecules that allowed one-dimensional fibril crystal growth and was limited by contact time between the P3HT molecules rather than the diffusion of P3HT chains and this is attributed to the highly directional pi–pi stacking attractions of electron pi in the thiophene rings.

Tapered block polymers are an emerging class of macromolecules with unique and diverse self-assembly behavior and properties. Herein, we directly examine the manipulation of self-assembled interfaces in poly(isoprene-b-styrene) (I-S)-based block polymers (BPs) by synthesizing non-tapered (I-S), normal tapered (I-IS-S), and inverse tapered (I-SI-S) BPs with controlled monomer segment distributions. We provide the first direct measurements of interfacial mixing for these tapered polymers through X-ray reflectivity (XRR). The density profiles from XRR are compared to results from fluids density functional theory (fDFT) with good agreement. We find that our normal tapered BPs (30 vol % tapering) have similar interfacial mixing to diblock polymers, while our inverse tapered BPs (30 vol % tapering) have much wider interfaces. Additionally, differential scanning calorimetry (DSC) studies elucidate the influence of tapering on the glass transition temperature (Tg) and change of heat capacity (ΔCP) for each BP pha...

The rheological properties of poly(3-hexylthiophene) (P3HT) solutions were investigated in a nonvolatile solvent, 2-ethylnaphthalene, at various P3HT concentrations. A mild viscosity increase was noted during shear for lower concentration P3HT solutions over 24 h, yet the viscosity increase was greater than if the sample was not sheared at all over the same time period. In this case, crystalline fibrils with large aspect ratios were formed during shear. Crystallization was determined to be dictated by Brownian motion and mediated by shear, or in other words Brownian motion brought the molecules together while shear changed their conformation to allow crystallization. Higher concentration P3HT solutions produced a significant viscosity increase, up to 2 orders of magnitude, during shear. Again, if a similar solution was merely aged without shear, a much lower viscosity increase was noted. Simple calculations show that the fibril concentration was above the percolation threshold at the higher concentration ...

A series of organic/inorganic hybrid block and random copolymers were prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization using poly(ethylene glycol) methyl ether methacrylate (PEGMA) and 3-(3,5,7,9,11,13,15-heptaisobutylpentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane-1-yl)propyl methacrylate (MA-POSS) as monomers in order to study the effect of polymer morphology and POSS content on the properties of polymer electrolytes. Flexible and dimensionally stable free-standing films were made from the hybrid block and random copolymers mixed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) when the contents of MA-POSS unit were larger than 31 and 16 mol %, respectively. The ionic conductivity of the solid-state block copolymer (PBP) electrolyte was found to be 1 order of magnitude higher than that of the random copolymer (PRP) electrolyte when they had similar MA-POSS content, although their glass transition temperature values of their ion-conducting segments were quite clos...

Diels−Alder (DA) chemistry is increasing popular due to its simplicity and efficiency; however, one concept that has yet to be thoroughly explored is incorporation of DA linkages within materials f...

Polymeric nanoparticles can be manufactured by intramolecular cross-linking of benzocyclobutene (BCB)/styrene copolymers. We study this process by extensive molecular dynamics simulations of both atomistic and coarse-grained models. It is found that the rate of intramolecular cross-linking is close to quadratic in the number of unlinked cross-linkers, namely BCB monomeric units, while the completeness of the reaction is affected by the steric hindrance of the cross-linked polymer. An equation incorporating both of these processes yields a good agreement with simulation data. A rigidity effect is identified when the cross-linkers account for more than about 60% of a precursor BCB/styrene copolymer. Above this threshold, the radii of gyration of intramolecularly cross-linked BCB/styrene copolymers show little dependence on their cross-linker concentrations, and a relatively large number of BCB monomeric units are left unreacted in each polymer. In addition, a temperature series study is performed on the int...

A new synthetic approach to the preparation of intramolecularly collapsed nanoparticles under mild, room temperature conditions has been developed from commercially available vinyl monomers. Reaction of isocyanate functionalized linear copolymers with a diamine in dilute solution leads to the efficient formation of nanoparticles where the diameter of the nanoparticle can be varied by controlling both the molecular weight and mole percentage of isocyanate repeat units. Physical properties for the intramolecularly collapsed nanoparticles were fully consistent with a three-dimensional structure and analysis of the collapse reaction revealed that approximately 75% of the isocyanate groups along the backbone underwent crosslinking with 25% being available for further reaction with mono-functional amines. This stepwise consumption of the isocyanates allows the chemical and physical properties of the nanoparticles to be further tuned and significantly opens up the range of nanoparticles that can be prepared using this mild and highly efficient chemistry.

It is demonstrated that nanocomposites exhibiting reduced viscosity and multifunctional performance enhancements may be fabricated using simple processing procedures. These behaviors are elucidated by analysis of the effects of dispersed organic (fullerene) nanoparticles and inorganic (magnetite) nanoparticles on the behavior of polystyrene, demonstrating that simple spherical nanoparticles can induce a range of unexpected behavior due to nanoscale effects. In general, multifunctional performance improvements including enhanced mechanical, electrical, magnetic and thermal degradation properties as well as reduced viscosity are promoted when simple design guidelines are followed. These guidelines are tabulated.

Polymandelide, an aryl analogue of polylactide, was synthesized by the ring-opening polymerization of mandelide, the cyclic dimer of mandelic acid. The poor solubility of rac-mandelide limited the synthesis of polymandelide via solution polymerization, but polymerization of mandelide at 70 °C as a heterogeneous slurry in acetonitrile yielded first-order kinetic plots and polydispersities 150 °C exhibit properties that mimic those of polystyrene. Polymandelide is a glassy amorphous polymer with a Tg of 100 °C, with rheological properties comparable to polystyrene, and thermal gravimetric analyses under nitrogen show that the polymer is stable to ∼300 °C. Racemization during polymerization precluded formation of a crystalline polymer. Degradation of polymandelide in pH 7.4 buffer at 55 °C is consistent with a bulk erosion model and, due to its high Tg, proceeds at ∼1/100 the rate of polylactide under similar conditions.

The conformation of linear−dendrimer hybrid diblock copolymers in solution has been studied using both small-angle neutron scattering and dynamic light scattering. The diblock consisted of a fourth-generation benzyl ether dendrimer with different molecular weight polystyrene bonded to the focal point of the dendrimer; the total molecular weight ranged from 20 to 100 kDa. In agreement with previous studies, it was found that this dendron, without a linear chain attached, alters its size upon solvent change. The addition of a polystyrene chain to the focal point of a dendrimer was also found to have an effect on the dimensions and shape of the dendrimer block. A low-molecular-weight polystyrene chain swelled the dendrimer without perturbing its native spherelike conformation. However, at larger polystyrene molecular weights, the linear block manipulates a transition of the dendrimers' morphology form spherelike to an extended conformation. Control of this shape and size change has potential for these unique...

The effect of nanoscopic, shape persistent polystyrene (PS) nanoparticles on the rheological properties of linear PS is studied and a dramatic viscosity reduction is observed. This is an ideal blend which simplifies enthalpic interactions between the components and can be used to delineate the effect of particle size on the properties of the blends. Homogeneous blends are assured through small-angle neutron scattering (SANS) experiments which establish the absence of phase segregation (depletion flocculation) in the nanoparticle-polymer blend. We previously found that nanoparticles reduce the viscosity of high molecular mass linear PS when the interparticle gap is smaller than the linear polymer size. In the present study, we find that such confinement of entangled polymers is necessary for the viscosity reduction since lower concentrations provide a viscosity increase. Furthermore, the behavior is found to be dependent on the presence or absence of entanglements and confinement is seemingly not important for unentangled polymers. It is proposed that constraint release caused by the addition of nanoparticles is responsible for some of the observed changes in viscosity although it is suspected this is a very complicated phenomenon and introduction of free volume by the nanoparticles is certain to play a key role.

Hybrid copolymers with dendritic−linear blocks are shown to exhibit many of the classic microphase-separated structures of linear−linear block copolymers. Transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS) were used to evaluate the morphology of a sixth generation (G6) poly(benzyl ether) dendron covalently bonded to linear polystyrene (PS) at the dendron focal point. Increasing the fraction of the linear block, φPS, through an increase in the molecular weight of the PS block revealed morphologies evolving from disordered to ordered lamellar to hexagonally close-packed dendron cylinders. Significantly, the observed morphologies are distinct from those expected for analogous linear−linear blocks at equivalent volume fraction, although the direction of progression follows expectation. Quantitative analysis suggests substantial molecular deformation or shape change in the dendritic phase. The possible role of conformational entropy in determi...

The intrinsic viscosity of narrow molecular mass distribution polystyrene standards, poly(benzyl) ether dendrimers, and their hybrid block copolymers was measured in a variety of solvents. The relative change in the intrinsic viscosity for all these polymers was almost equivalent, indicating that poly(benzyl ether) dendrimers expand and contract quite readily with a change in solvent. The intrinsic viscosity maximum for all polymers was found to occur at essentially the same solvent solubility parameter demonstrating that the thermodynamic interaction with the selected range of solvents was also equivalent. The intrinsic viscosity for hybrid copolymers in a good solvent for both components was found to fall well below the intrinsic viscosity for neat polystyrene at intermediate molecular masses. Below and above this mass range the intrinsic viscosity was quite similar to polystyrene. Yet, the transition for intermediate to high molecular mass behavior was quite sharp as seen through a rapid intrinsic visc...

The zero shear melt viscosity, eta0, for a variety of dendritic poly(benzyl ether) macromolecules has been measured. The viscosity of low generation dendrimers exhibits a strong molecular mass, M, dependence, yet, direct proportionality between eta0 and M is observed at higher generations. The viscosity scales with M for mono- and tridendrons rather than generation number. Hypercore dendrimers continue this scaling although the viscosity is slightly greater. A large deviation from the master curve for the mono- and tridendrons is found for an end-substituted monodendron. The viscosity for the end-substituted monodendron is also much more temperature dependent than virgin dendrimers, and it is concluded that end groups have a much larger effect on the viscosity than the core. Reexamination of literature data for intrinsic viscosity and glass transition temperature is performed, and these quantities also scale with molecular mass. Comparison with free volume theory indicates that the theory is extremely robust although some question of its validity is made when applied to dendrimers.