The authors show that a photovoltaic device composed of a -donor-bridge–acceptor-bridge- type block copolymer thin film exhibits a significant performance improvement over its corresponding donor/acceptor blend (Voc increased from 0.14to1.10V and Jsc increased from 0.017 to 0.058mA∕cm2) under identical conditions, where donor is an alkyl derivatized poly-p-phenylenevinylene (PPV) conjugated block, acceptor is a sulfone-alkyl derivatized PPV conjugated block, and bridge is a nonconjugated and flexible unit. The authors attribute such improvement to the block copolymer intrinsic nanophase separation and molecular self-assembly that results in the reduction of the exciton and carrier losses.

A novel class of light harvesting conjugated block copolymers, with electron-donating conjugated blocks (D) connected to electron-accepting conjugated blocks (A) via non conjugated and flexible bridge chains (B), has been designed, synthesized, and characterized. Specifically, D is a decyloxy-substituted polyphenylenevinylene (C10−PPV). A 1 and A 2 are PPVs with sulfone (SO2) acceptor moieties substituted on every other phenylene unit. A 1 carries two decyloxy groups on every phenylene unit, while in A 2 , half of the phenylene units are unsubstituted. The optical energy gaps are 2.24 eV for the donor block (D), 2.33 and 2.45 eV for A 1 and A 2 acceptor blocks. LUMO level offsets are 0.24 and 0.16 eV for D/A 1 and D/A 2 pairs, respectively. Comparing the photoluminescence from both films and solutions, very large red shifts (71 and 74 nm for A 1 and A 2 respectively) were observed in the two acceptor polymers. These red shifts in the emission spectra were more than twice as much as that observed for D (31 nm). The (DBA 1 B) n and (DBA 2 B) n block copolymer films exhibited improved processability and optoelectronic properties when compared with the corresponding films composed of donor/acceptor blends. Atomic force microscopic (AFM) studies of D, A 1 , and A 2 films were also undertaken to observe the degree of aggregation in the films. The results indicate the tendency of intermolecular aggregation increases as A 2 > D > A 1 . AFM topological images revealed that large aggregates of several hundreds of nanometers formed in donor/acceptor blend films, while in block copolymer films, domain sizes were similar to individual block sizes which are 1 order of magnitude smaller than in the blend.

Phase transitions in sphere-forming polystyrene-block-polyisoprene-block-polystyrene (SIS triblock) copolymer and its blends with polystyrene (PS) were investigated using oscillatory shear rheometry, transmission electron microscopy, and small-angle X-ray scattering (SAXS). For the investigation, a commercial grade of high-molecular-weight SIS triblock copolymer (Vector 4113, Dexco Polymers) and a low-molecular-weight SIS triblock copolymer (SIS-100) synthesized in our laboratory were used. It is found from oscillatory shear rheometry and SAXS that both Vector 4113 and SIS-100 undergo order−disorder transition (ODT) having a characteristic feature of lattice disordering/ordering transition (LDOT) of spheres, giving rise to a phase consisting of micelles with short-range liquidlike order at thermal equilibrium above ODT and demicellization/micellization transition (DMT), as a pseudo phase transition, giving rise to a micelle-free phase with only thermal composition fluctuations. The LDOT temperature (T LDOT) of Vector 4113 is found to be ca. 205 °C, and the DMT temperature (T DMT) is much higher than 220 °C, the highest experimental temperature employed to avoid thermal degradation/cross-linking reactions. The addition of various amounts of low-molecular-weight PS enabled us to estimate, via extrapolation, the T DMT of Vector 4113 to be ca. 260 °C. On the other hand, SIS-100 is found to have T LDOT of 85 °C and T DMT of 105 °C. Transmission electron microscopy confirmed the existence of disordered micelles in both Vector 4113 and SIS-100 between T LDOT and T DMT. Phase diagrams for (SIS-100)/PS blends were constructed using T LDOT, T DMT, and cloud point measurements.

The effects of triblock copolymer architecture (ABA-type vs ABC-type) and the degree of functionalization on the organoclay dispersion in nanocomposites were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), and linear dynamic viscoelasticity. For the study, a lamella-forming polystyrene-block-polyisoprene-block-polystyrene (SIS triblock) copolymer and a homogeneous polyisoprene-block-polystyrene-block-polybutadiene (ISB triblock) copolymer were synthesized via sequential anionic polymerization. Subsequently, the polyisoprene block of the SIS triblock copolymer was hydroxylated yielding an SIOHS triblock copolymer, and the polybutadiene block of the ISB triblock copolymer was hydroxylated yielding an ISBOH triblock copolymer. The degree of hydroxylation in both SIOHS and ISBOH triblock copolymers was varied. Both the unfunctionalized (SIS and ISB) and functionalized (SIOHS and ISBOH) triblock copolymers were used to prepare nanocomposites with two different types of organoclays:  one (Cloisite 30B) treated with a surfactant having hydroxyl groups and the other (Cloisite 15A) treated with a surfactant having no hydroxyl groups. It was found from TEM that Cloisite 30B aggregates had a very high degree of dispersion in the ISBOH triblock copolymer, while Cloisite 15A aggregates had a low degree of dispersion in both ISBOH and SIOHS triblock copolymers. A very unusual temperature dependence of linear dynamic viscoelasticity of the ISBOH/Cloisite 30B nanocomposites was observed. An optimum degree of hydroxylation in the ISBOH triblock copolymer existed such that it gave rise to the highest degree of dispersion of Cloisite 30B aggregates. These observations are supported by XRD patterns. In situ Fourier transform infrared spectroscopy confirms the presence of hydrogen bonds in ISBOH/Cloisite 30B nanocomposites and not in ISBOH/Cloisite 15A nanocomposites.

The molecular weight dependence of zero-shear viscosity (η0) of polystyrene-block-polyisoprene (SI diblock) copolymer in the disordered state was investigated. For the investigation, a series of lamella-forming, nearly monodisperse SI diblock copolymers were synthesized via sequential anionic polymerization, and order-disorder transition temperatures (T ODT) of the block copolymers were determined from isochronal dynamic temperature sweep experiments at an angular frequency (ω) of 0.01 rad/s and also from dynamic frequency sweep experiments over a wide range of temperatures. The η0 of the SI diblock copolymers in the disordered state (at T > TODT) was determined from η0,r ) limωf0[|η r / (ω)|], for which logarithmic plots of reduced complex viscosity |η r / (ω)| vs aTω with aT being temperature-dependent shift factor were first prepared, where |η r / (ω)| is defined by |η r / (ω)| ) |η*(ω)|(TrFr/TF)/aT in which |η*(ω)| is the complex viscosity at ω, T is the measurement temperature, Tr is a reference temperature defined by Tr ) Tg,PS + 104 °C with Tg,PS being the glass transition temperature of the polystyrene phase, and F and Fr are the densities at T and Tr, respectively. The molecular weight (M) dependence of η0 for the SI diblock copolymers in the disordered state is found to follow the relationship η0 ∝ M 1.15(0.09 for M < Mc and η0 ∝ M 4.69(0.18 for M g Mc, where Mc is the viscosity critical molecular weight at which the slope of η0 vs log M plot changes abruptly. Also investigated, for comparison, was the molecular weight dependence of η0 for nearly monodisperse homopolystyrenes, which were synthesized via anionic polymerization, and it is found that η0 ∝ M 1.21(0.23 for M < Mc and η0 ∝ M 3.37(0.21 for M g Mc, which is in excellent agreement with the literature. Further, the molecular dependence of steady-state recoverable compliance (J e o ) of SI block copolymer in the disordered state was determined from J e o ) limωf0J′(ω) for which logarithmic plots of dynamic storage compliance J′(ω) vs aTω were first prepared, where J′(ω) is defined byfor the SI diblock copolymers in the disordered state is found to follow the relationship J e o ∝ M 1.63(0.17 for M < Mc, and J e o ∝ M 5.22(0.78 for M g Mc. The much stronger molecular weight dependence of η0 and J e o for the disordered SI diblock copolymers than that for homopolystyrenes observed in this study is attributable to the styrene-isoprene junction effect that originates from the difference in the monomeric friction coefficients between polystyrene and polyisoprene blocks.

Phase transition in polystyrene-block-polyisoprene-block-polystyrene (SIS triblock) copolymers end-capped with carboxylic acid group (−COOH) or sodium carboxylate group (−COONa) was investigated using oscillatory shear rheometry and transmission electron microscopy (TEM). For the study, three SIS triblock copolymers having almost an equal block length ratio, but varying molecular weights, were synthesized via sequential anionic polymerization. The number-average molecular weights of the three block copolymers synthesized were 1.8 × 104 g/mol (SIS1), 2.3 × 104 g/mol (SIS2), and 3.4 × 104 g/mol (SIS3). It was found that both SIS1 and SIS2 were homogeneous block copolymers, while SIS3 had lamellar microdomains, and it had an order−disorder transition temperature (T ODT) of 180 °C. Each of the triblock copolymers was end-capped with a −COOH group to obtain SIS−COOH using high-purity, gaseous carbon dioxide. Subsequently, part of the SIS−COOH was neutralized with sodium hydroxide to obtain SIS−COONa. It was found that SIS1−COOH, SIS1−COONa, and SIS2−COOH remained homogeneous, while SIS2−COONa microphase-separated into a lamella-forming triblock copolymer, as determined from TEM, which has a T ODT of 123 °C as determined from oscillatory shear rheometry. The T ODT of lamella-forming SIS3 was found to increase from 180 to 182 °C after it was end-capped with a −COOH group and to 228 °C after it was end-capped with a −COONa group. Cloud point measurements show that (i) the upper critical solution temperature (UCST) of the mixtures composed of polyisoprene (PI) and polystyrene (PS) end-capped with a −COONa group, PI/(PS−COONa) mixtures, is much higher than that of the mixtures composed of PI and PS end-capped with a −COOH group, PI/(PS−COOH) mixtures, and PI/PS mixtures, and (ii) the UCST of PI/(PS−COOH) mixtures is only slightly higher than that of PI/PS mixtures. It is concluded that the formation of lamellar microdomains in SIS2−COONa from homogeneous SIS2 after it was end-capped with a −COONa group and a very high T ODT observed for SIS3−COONa are attributable to strong ionic associations and significantly increased repulsive segment−segment interactions between the PI and PS−COONa phases in the block copolymers.

The dispersion characteristics of organoclay in nanocomposites based on end-functionalized polystyrene (PS) and end-functionalized polystyrene-block-polyisoprene (SI diblock) copolymer were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), and oscillatory shear rheometry. For the study, a low-molecular-weight polystyrene (PSLMW), having molecular weight (M) lower than the viscosity critical molecular weight (M c), and a high-molecular-weight polystyrene (PSHMW), having M > M c, were synthesized via anionic polymerization. Each polystyrene (PS) was terminated by carboxylic acid (−COOH) group via carbonation, yielding PSLMW-t-COOH or PSHMW-t-COOH, which were then neutralized, yielding PSLMW-t-COONa or PSHMW-t-COONa. Further, two SI diblock copolymers were synthesized via anionic polymerization. In so doing, the PS block or PI block were end-functionalized via carbonation to yield IS-t-COOH or SI-t-COOH, which were then neutralized to obtain IS-t-COONa or SI-t-COONa. Each of the end-functionalized polymers was mixed in a cosolvent of tetrahydrofuran and water with an organoclay (Southern Clay Products) to prepare nanocomposites. It has been found via XRD and TEM that the polymers terminated by sodium carboxylate (−COONa) group are much more effective in dispersing organoclay aggregates than the polymers terminated by −COOH group. The ionic interaction between the negatively charged carboxylic ion (−COO-) at the polymer chain end and positively charged N+ ion in the surfactant residing at the surface of organoclay is believed to be the driving force that has enhanced the dispersion of organoclay aggregates, giving rise to a very high degree of dispersion. The rheological measurements at elevated temperatures, via oscillatory rheometry, indicate that the storage modulus of the nanocomposites based on end-functionalized polymers is considerably higher than that of neat end-functionalized polymers. This observation is attributed to ionic interactions between the negatively charged anion at polymer chain end and the positively charged ion in the surfactant residing at the surface of organoclay.

The effect of saturation of polydienes with varying microstructures on the phase behavior of poly(vinylcyclohexane) (PVCH)/poly(ethylene-co-1-butene) (PEB) and PVCH/poly(ethylene-alt-propylene) (PEP) blends was investigated. For the study, a series of polyisoprenes (PI) and polybutadienes (PB) with varying microstructures and molecular weights and polystyrenes (PS) with varying molecular weights were synthesized via anionic polymerization. Subsequently, they were saturated, yielding PVCH, PEB, and PEP, respectively. Binary blends of PVCH and PEB and binary blends of PVCH and PEP with blend compositions varying from 10 to 90 wt % were prepared from solvent casting in toluene. Laser light scattering was used to take cloud point measurements, which were then used to construct phase diagrams. For comparison, the phase behavior of PS/PI and PS/PB blends was also investigated. It was found that the PVCH/PEB and PVCH/PEP blends exhibit upper critical solution temperature, similar to the PS/PI and PS/PB blends. The interaction parameter for each polymer pair chosen was determined by curvefitting the experimental phase diagram to a theoretical phase diagram predicted from the Flory-Huggins theory. The interaction parameters thus obtained were used to predict, via the currently held mean-field theory, the order-disorder transition temperature (T ODT) of the PVCH-block-PEB and PVCH-block-PEP copolymers reported in the literature. It has been found that the predicted TODT of the PVCH-block-PEP and PVCH-block-PEB copolymers is higher than that of the unsaturated precursors having PI or PB blocks with predominantly 1,4-addition. These findings are in agreement with the experimental results reported in the literature. It is concluded that the experimentally observed increase in TODT after complete saturation of SI or SB diblock copolymers having PI or PB blocks with predominantly 1,4-addition is due to the substantial increase in the repulsive segment-segment interactions between PVCH and PEP and between PVCH and PEB.