. European Polymer Journal [Internet]. 2016;83:148-160.
We present a strategy for the synthesis of a well-defined rod-coil block copolymers of regioregular poly(3hexylthiophene) and polystyrene (P3HT-b-PS), carrying pendant fullerenes (C60) at precise positions along the PS block. The synthesis is achieved by combining ‘living’ anionic polymerization, Kumada catalyst-transfer polycondensation, and click chemistry. Azide terminated polystyrene was synthesized via anionic polymerization, while C60 moieties were grafted along the coil block with a [4+2] Diels-Alder cycloaddition reaction. The regioregular poly(3-hexylthiophene) rod donor block was end-capped with alkyne and was coupled with the azide terminated polystyrene via a copper catalyzed alkyne-azide cycloaddition. Size exclusion chromatography (SEC), NMR, and FTIR spectroscopies were employed to confirm the synthesis of the diblock copolymers. Furthermore, the end-capping of the ‘living’ polystyrene (PS) with the diphenylethylene cyclobutene (DPE-CB) end-group was confirmed by matrixassisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS). Thermogravimetric analysis (TGA) was employed for the estimation of the C60 content in the block copolymer. The C60 content at the coil block was 22 wt% and a strong quenching of photoluminescence (PL) was observed as the result of the aggregation and percolation structure of the C60 within the PS phase. This behavior indicates that the bonding of C60 across the PS block may offer new routes to engineering stable morphologies, where the degree of aggregation/crystallization of the acceptor material is of paramount importance for stable and efficient electron transport.
The frequency ω dependent storage G′(ω) and loss G″(ω) moduli of star-shaped polystyrene (SPS) molecules of a range of functionalities f and molecular weights per arm Ma were measured under small amplitude oscillatory shear conditions. Star-shaped macromolecules are composed of an inner region, core, where the chain segments are stretched and the “packing” density is higher than that of the outer region, corona. The frequency dependencies of G′(ω) and G″(ω) for low functionality molecules (f<8) with long arms Ma are well described by the model of Milner and McLeish, indicating that the translational dynamics are facilitated by an arm retraction mechanism. With increasing values of f and decreasing Ma the model failsthe arm retraction process is no longer validdue largely to the increasing size of the core in relation to the overall size of the molecule. The molecules exhibit evidence of spatial structural order due to entropic, intermolecular interactions, and the translational dynamics of these molecules occur via a cooperative process, akin to that of soft colloids, for suﬃciently large values of f and small Ma. The overall dynamics may be summarized in a diagram delineating diﬀerent mechanisms that facilitate ﬂow as a function of f and Ma.
We report on the eﬀect of interfacial energy on the glass temperature, Tg, of several amorphous polymers with various glass temperatures and polymer/substrate interactions conﬁned within self-ordered nanoporous alumina (AAO). The polymers studied include poly(phenylmethylsiloxane) (PMPS), poly(vinyl acetate) (PVAc), 1,4-polybutadiene (PB), oligostyrene (PS), and poly(dimethylsiloxane) (PDMS). The segmental dynamics and associated Tg’s are studied by means of dielectric spectroscopy. The interfacial energy for the polymer/substrate interface, γSL, is calculated with Young’s equation whereas the AAO membrane surface energy is obtained by measuring contact angles for several reference liquids. We ﬁnd that interfacial energy plays a signiﬁcant role in the segmental dynamics of polymers under conﬁnement within AAO. There is a trend for a decreasing glass temperature relative to the bulk with increasing interfacial energy. PDMS exhibits the highest interfacial energy and the highest reduction in glass temperature within AAO. Other eﬀects that may also contribute to changes in Tg are discussed.
We investigated the phase behavior of thin film, thickness h 100 nm, mixtures of a polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymer with star-shaped polystyrene (SPS) molecules of varying functionalities f, where 4 < f < 64, and molecular weights per arm Marm. The miscibility of the system and the surface composition varied appreciably with Marm and f. For large values of Marm, regardless of f, the miscibility of the system was qualitatively similar to that of linear chain PS/PS-b-P2VP mixtures – the copolymer chains aggregate to form micelles, each composed of an inner P2VP core and PS corona, which preferentially segregate to the free surface. On the other hand, for large f and small Marm, SPS molecules preferentially resided at the free surface. Moreover, blends containing SPS molecules with the highest values of f and lowest values of Marm were phase separated. These observations are rationalized in terms of competing entropic interactions and the dependence of the surface tension of the star shaped molecules on Marm and f.
A novel hydrocarbon-soluble trifunctional organolithium initiator, with no polar-additive requirements, has been synthesized for use in anionic polymerization. The complete synthesis of the unsaturated tri-diphenylethylene compound, 4,4,4-(ethane-1,1,1-triyl)tris(((3-(1-phenylvinyl)benzyl)oxy)benzene) (I), is described and the eﬃciency of the new initiator is evaluated using 1H NMR and Nano-assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (NALDI-TOF MS). Activation of precursor I, was performed in situ using stoichiometric amounts of sec-BuLi in benzene. Three-arm polystyrene and polyisoprene stars with narrow molecular weight distributions were obtained in the case of relatively high total anion concentration, [sec-BuLi]0 > 3.8 × 10−3 mol L−1 (3 × [I]0). At low total anion concentrations, uncontrolled molecular weight and broad/bimodal distributions were obtained, plausibly attributed to the presence of partially solvated aggregation dynamics complicating the propagation. The ‘living’ nature of the polymerization was conﬁrmed by the sequential polymerization of styrene, and isoprene. The viscometric branching factor g’ values of the ﬁnal branched polymers were measured and compared to g’ values of three-arm stars reported in the literature.
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