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Commercial polylactide (PLA) was converted and endowed with shape-memory properties by synthesizing ionic hybrids based on blends of PLA with imidazolium-terminated PLA and poly[ε-caprolactone-co-d, l-lactide] (P[CL-co-LA]) and surface-modified silica nanoparticles. The electrostatic interactions assist with the silica nanoparticle dispersion in the polymer matrix. Since nanoparticle dispersion in polymers is a perennial challenge and has prevented nanocomposites from reaching their full potential in terms of performance we expect this new design will be exploited in other polymers systems to synthesize well-dispersed nanocomposites. Rheological measurements of the ionic hybrids are consistent with the formation of a network. The ionic hybrids are also much more deformable compared to the neat PLA. More importantly, they exhibit shape-memory behavior with fixity ratio Rf ≈ 100% and recovery ratio Rr = 79%, for the blend containing 25 wt % im-PLA and 25 wt % im-P[CL-co-LA] and 5 wt % of SiO2-SO3Na. Dielectric spectroscopy and dynamic mechanical analysis show a second, low-frequency relaxation attributed to strongly immobilized polymer chains on silica due to electrostatic interactions. Creep compliance tests further suggest that the ionic interactions prevent permanent slippage in the hybrids which is most likely responsible for the significant shape-memory behavior observed. [ABSTRACT FROM AUTHOR]

Different P3HT chain lengths have been synthesized, functionalized at both chain ends with aldehyde moieties and finally cyclized following the McMurry reaction in a pseudo high dilution process. The confirmation of the high yielded intramolecular coupling came from the decrease of the hydrodynamic radius observed by SEC, correlated to the conservation of the mass distribution by MALDI-ToF and by the very low content of residual linear precursor estimated by NMR. Different aggregation behaviors between linear and cyclic and between short and long systems have been pointed out by DSC and UV-vis absorption spectroscopy. We estimate that long cyclic structures present similar aggregation behavior than long linear ones mainly due to the folding of those chains. [ABSTRACT FROM AUTHOR]

Poly(butylene succinate-ran-butylene azelate) random copolyesters (PBS-ran PBAz) were studied using broadband dielectric spectroscopy (BDS) and differential scanning calorimetry (DSC). These copolymers are characterized by being isodimorphic and by displaying a eutectic behavior. Depending on their composition, the PBS-rich phase, the PBAz-rich phase, or both phases can crystallize. The complex development of the amorphous phase, especially at compositions around the eutectic point was demonstrated by BDS results. The comonomer fraction included in the amorphous phase was quantified from the relaxation strength of the dielectric β relaxations, and thus the crystalline fraction can be calculated. The good agreement between the values determined from BDS and the crystallinity obtained from DSC experiments demonstrates that the degree of comonomer exclusion in these random copolymers during crystallization is far larger than comonomer inclusion. However, the glass transition temperatures determined from the dielectric α relaxation behavior are lower in most of the copolymers than those measured by DSC, whereas they are about the same in the homopolymers. This result is probably caused by a significant amount of amorphous phase in the copolymers that is not influenced by crystallinity. Furthermore, the crystallization behavior of these copolymers at different cooling protocols showed that the α relaxation depends not only on the crystalline fraction but also on the details of the crystallization process in these complex multiphasic copolymers. [ABSTRACT FROM AUTHOR]

This work deals with the synthesis and characterization of new diblock copolymers based on π-conjugated and depolymerizable units. These diblock copolymers are based on a regioregular poly(3-hexylthiophene) sequence associated with a sacrificial block, namely polyphthalaldehyde. The conjugated polymer was obtained by Grignard metathesis polymerization and end-capped by an alkynyl group while the depolymerizable segment was synthesized by an anionic cyclopolymerization from an azide moiety. Diblock copolymers with different molecular weights were then successfully synthesized via an alkyne-azide coupling reaction. Under specific conditions, these copolymers self-assemble intofibrillar nanostructures in thin films. The elimination of polyphthalaldehyde was carried out by thermal treatment, generating nanoporous poly(3-hexylthiophene) films. The use of a dry treatment to remove the polyphthalaldehyde block strongly reduces the morphological damages that would occur with a "wet" processing route. These nanoporous poly(3-hexylthiophene) films could be useful for controlling the morphology of the heterojunction in organic photovoltaic devices after successful filling with an electron-acceptor material. [ABSTRACT FROM AUTHOR]

Thestructure, morphology, and thermal properties of biobased andbiodegradable poly(butylene succinate-ran-butyleneazelate) random copolyesters with a wide composition range were studied.These PBS-ran-PBAz copolymers can crystallize inthe entire composition range despite being random, displaying a eutecticpoint when their melting point is plotted as a function of composition.Wide angle X-ray scattering (WAXS) studies confirmed isodimorphicbehavior where PBS-rich copolymers crystallize with PBS type unitcells with some PBAz repeating unit inclusions and vice versa forPBAz-rich copolymers. Away from eutectic compositions the copolymersexhibit only one crystalline phase (PBS-rich or PBAz-rich crystallinephases) while at the eutectic point both phases can crystallize. Theonly double crystalline copolymer among those prepared had a compositionclose to the eutectic point of 45 mol % PBS (and 55 mol % PBAz). Thecrystallization of the two phases occurred in the same temperaturerange upon cooling from the melt at 10 °C/min in a DSC (i.e.,coincident crystallization). Self-nucleation (SN) studies of the PBS-richphase were performed. After SN, the separate crystallization of eachphase was clearly observed during cooling from the self-nucleationtemperature (i.e., PBS and PBAz-rich phases). Small angle X-ray scattering(SAXS) experiments were performed for the first time for these typesof isodimorphic copolymers. The results show that the lamellar longperiod is a strong function of composition. While limited inclusionsof PBAz units within the crystal lattice only cause a slight expansionof the PBS component unit cell, the increase of comonomer contentproduces an unexpected synergistic increase in long periods and lamellarthickness values. In the case of the only double crystalline copolymerexamined, the PBS-rich phase forms space filling spherulites (observedby polarized light optical microscopy, PLOM) at higher temperaturesthat template the superstructural morphology of the copolymer. ThesePBS-rich phase spherulites contain radial lamellar stacks whose longperiod was determined by SAXS. Upon further cooling, the PBAz-richphase crystallizes in the intraspherulitic amorphous regions withnewly formed lamellae that have their own distinct long period accordingto SAXS results. AFM observations of the PBS-rich crystalline lamellaeconfirmed the lamellar thickness and long spacings determined by SAXS.A schematic morphological model of the mixed spherulites producedby this double crystalline diblock copolymer is proposed based onthe experimental evidence collected by SAXS, PLOM, and AFM. [ABSTRACT FROM AUTHOR]

Identifyingsolvent- and catalyst-free conditions for polymerizationsof engineering thermoplastics is of increasing interest due to newpolymer processing technologies such as 3-D printing. We report theselective formation of linear poly(aryl ether sulfone)s (PESs) fromthe polycondensation of trimethylsilyl-protected bisphenol A (TMS-BPA)with nitro-substituted diaryl fluorides without added solvent or catalyst.DFT calculations show that nitro groups strategically placed in the ortho-position to the fluoride leaving group form a stableMeisenheimer complex during polyether synthesis. This strategy representsa route to linear PESs that employs anionic conditions, destabilizingpropagating phenoxide chain ends preventing backbiting while simultaneouslystabilizing the Meisenheimer complex intermediate. Thermodynamic overkinetic control in the polycondensation minimizes cyclic PES formationand promotes the formation of pure linear PESs. [ABSTRACT FROM AUTHOR]

Shapememory properties of polymers represent one of the most expandingfields in polymer science related to numerous smart applications.Recently, multiple-shape memory polymers (multiple-SMPs) have attractedsignificant attention and can be achieved with complex polymer architectures.Here, miscible PLLA/PMMA blends with broad glass transitions are investigatedas an alternative platform to design multiple-SMPs. Dual-shape memoryexperiments were first conducted at different stretching temperaturesto identify the so-called “temperature memory effect”.The switch temperature of the symmetric 50% PLLA/50% PMMA blend smoothlyshifted from 70 to 90 °C for stretching temperatures increasingfrom 65 to 94 °C, attesting for a significant “temperaturememory effect”. Asymmetric formulations with 30% and 80% PMMAalso present a “temperature memory effect”, but thesymmetric blend clearly appeared as the most efficient formulationfor multiple-shape memory applications. A programming step designedwith two successive stretchings within the broad glass transitionconsequently afforded high triple-shape memory performances with tunableintermediate shapes, demonstrating that the symmetric blend couldrepresent an interesting candidate for future developments. Advancedshape recovery processes are consistent with a selective activationof specific “soft domains” or nanodomains arising fromthe broad glass transition and the large distribution of relaxationtime observed by DSC and dielectric spectroscopy. Polarized IR measurementspointed out that the composition of activated/oriented “softdomains” could vary with stretching temperature, giving riseto the “temperature-memory effect”. Consequently, froma polymer physics standpoint, nanoscale compositional heterogeneitieswithin the symmetric blend could be suspected and discussed on thebasis of available models for miscible blends and for multiple-SMPs. [ABSTRACT FROM AUTHOR]

Wereport the use of an organic catalyst system capable of switchingbetween active and dormant propagating states during the ROP of cyclicmonomers. While the ROP of both ε-caprolactone and trimethylenecarbonate proceeds under nitrogen, the simple addition of CO2results in a dormant “off” state. Cycling betweenatmospheres provides the ability to regulate the molecular weightsof the resulting polymers without appreciable loss of catalytic activityfor several “on/off” cycles. [ABSTRACT FROM AUTHOR]

Polyelectrolytes are promising electronicallyinsulating layers for low-voltage organic field effect transistors.However, the polyelectrolyte–semiconductor interface is difficultto manufacture due to challenges in wettability. We introduce an amphiphilicsemiconducting copolymer which, when spread as a thin film, can changeits surface from hydrophobic to hydrophilic upon exposure to water.This peculiar wettability is exploited in the fabrication of polyelectrolyte-gatedfield-effect transistors operating below 0.5 V. The prepared amphiphilicsemiconducting copolymer is based on a hydrophobic regioregular poly(3-hexylthiophene)(P3HT) covalently linked to a hydrophilic poly(sulfonated)-based randomblock. Such a copolymer is obtained in a three-step strategy combiningGrignard metathesis (GRIM), atom transfer radical polymerization (ATRP)processes, and a postmodification method. The structure of the diblockcopolymer was characterized using FT-IR, 1H NMR spectroscopy,and gel permeation chromatography (GPC). [ABSTRACT FROM AUTHOR]