Scheme 1 a a Conditions: (a) synthesis scheme of R-vinyl-ω-(phenyl) end-functionalized P3HT; (b) R-vinyl-ω-(phenyl) end-functionalized P3HT is activated by s-BuLi and forms 3, which subsequently serves as an anionic macroinitiator for the synthesis of P3HT-P2VP; dppp ) propane-1,3-diylbis-(diphenylphosphane).

A diblock copolymer of deuterated styrene and isoprene (dPS−PI) with a small volume fraction of isoprene was chemically modified to incorporate pendant fluorinated side chains (“fingers”). The composition distribution of the diblock copolymers within a high molecular weight polystyrene (PS) homopolymer was determined by forward recoil spectrometry. Surface segregation and interfacial segregation of the modified block copolymers from a polystyrene matrix are observed in as-spun films. Equilibrium segregation was achieved on annealing at 160 °C for several days. The segregation isotherms at the air−polymer interface are shown to be quantitatively described by a self-consistent mean field theory (SCMF), and these permit us to estimate an effective Flory parameter which describes the attraction of the fluorinated segments to the surface and their repulsion from the bulk. The change in the surface tension as a result of the adsorption of the block copolymers at the air−homopolymer interface was evaluated from the predictions of SCMF theory and compared with the changes in the water contact angle observed. Advancing water contact angle data are consistent with the presence of a nonuniform layer of PS, CF2, and CF3 segments on the surface of the segregated samples.

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A series of poly(diethylhexyloxy-p-phenylenevinylene-b-methyl methacrylate) (DEH-PPVb-PMMA) polymers with narrow polydispersity (PDI < 1.1) were synthesized using Siegrist polycondensation and anionic polymerizations followed by "click" chemistry. Alkyne-terminated DEH-PPV and azidoterminated PMMA were synthesized first, and then the two functionalized polymers underwent 1,3-cycloaddition reaction to obtain copolymers. Both the conversion of the end-functionalization of the homopolymers and the yield of the "click" reaction were higher than 98% as determined by 1 H nuclear magnetic resonance ( 1 H NMR) and gel permeation chromatography (GPC). Transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies reveal the details of copolymer morphology. The DEH-PPV-b-PMMA system presented here has higher block segregation strength than many previously studied rod-coil block copolymers yet still shows experimentally accessible phase transitions with respect to temperature. As a result, this molecule offers new insight into the competition between rod-rod and rod-coil interactions that occurs in the system. The DEH-PPV rods are organized as a monolayer that is inclined with the lamellar normal (smectic C) for the copolymers containing low volume fraction of PMMA coil (<54%). However, as the coil fraction increases, the strips containing DEH-PPV pack into hexagonal lattice. In contrast to previous work which demonstrated similar morphologies, the sequence of reversible liquid crystalline and microphase phase transitions is altered as a result of the increased block segregation. Upon heating, the low coil fraction copolymers exhibit a series of clear transitions of smectic-lamellar to amorphous-lamellar to disordered structures. In high coil fraction copolymers, the transitions between smectic-hexagonal to amorphous-hexagonal and smectic-hexagonal to disorder structures could not be clearly differentiated. The order-to-disorder temperature (ODT) decreases slowly with increasing coil fraction while the smectic-to-isotropic transition (SI) temperature stays relatively unchanged. The steady SI temperature suggests that the strong rod-rod interaction keeps the liquid crystalline rod in the nanodomain structure regardless of the amount of coil segment in the copolymers.

The fracture toughness Gc of an interface between the immiscible homopolymers polystyrene (PS) and poly(2-vinylpyridine) (PVP) reinforced with random copolymers, dPSf-r-

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We have measured the fracture toughness, G c, of an interface between polystyrene (PS) and poly (2-vinylpyridine) (PVP) reinforced with triblock copolymers (PVP-b-dPS-b-PVP) as a function of the areal chain density, Σ, of the copolymers at the interface. The failure mechanisms of the interface are studied by transmission electron microscopy and forward recoil spectrometry. For triblock copolymers with long PVP blocks (N PVP > N ePVP, where N ePVP is the entanglement polymerization index of PVP), a transition from chain scission at low Σ to crazing at high Σ* is observed. By comparing the areal chain density Σ* for the transition from chain scission to crazing for the triblock copolymers (Σ* = 0.015 chains/nm2) to that for the diblock copolymers, PVP−dPS (Σ* = 0.03 chains/nm2), we show that most of the triblock copolymers form a “staple” structure at the interface with the dPS block making a loop on the PS side of the interface and the PVP ends anchoring the “staple” in the PVP side. As a result of the “staple” structure, the saturation areal chain density of the triblock copolymer (Σsat) at the interface is half of that for the diblock copolymer of similar molecular weight. For Σ < Σsat in the crazing regime, the fracture toughness of the interface is controlled by the areal joint density, Σcross, where Σcross is the number density of the copolymer excursions across the interface. For Σ > Σsat, the triblock copolymers appear to reinforce the craze fibrils at the crack tip better than the corresponding diblock copolymers, leading to an interface fracture toughness approaching that of the PS homopolymer itself. For a triblock copolymer with short PVP blocks (N PVP < N ePVP), there is a transition in the fracture mechanism from pull out of the PVP block to crazing with increasing Σ. Short triblock copolymers can form two chain conformations:  one in which two PVP blocks anchor the copolymer on the homopolymer PVP side (staple structure) and one in which one PVP block anchors the copolymer on the PVP side (tail structure) of the interface. Comparison of G c between the triblock copolymer and the corresponding diblock copolymer is made. The larger G c values of the triblock copolymer reinforced interface in the crazing regime are observed as a result of enhancement in entanglements between the dPS loops of the triblock copolymer and the homopolymer PS.

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