Side-chain Crystal Research Articles

Iterative Exponential Growth Synthesis and Assembly of Uniform Diblock Copolymers.

Studies on the phase segregation of unimolecular block copolymers (BCPs) are limited by a lack of reliable, versatile methods for the synthesis of such polymers on the preparative scale. Herein, we describe an advancement of Iterative Exponential Growth (IEG) wherein chiral allyl-based IEG oligomers are subjected to thiol-ene reactions and converted into unimolecular BCPs. With this strategy we have synthesized uniform BCPs with molar masses up to 12.1 kDa on ∼1 g scale. BCPs composed of decane-based side chains and either triethyleneglycol- or thioglycerol-based side chains phase-segregate into hexagonal cylinder morphologies. The assembly is not driven by side-chain crystallization, but is instead the result of amorphous BCP assembly.

Effect of side chain length and degree of polymerization on the decomposition and crystallization behaviour of chlorinated poly(vinyl ester) oligomers

Four members of a homologous series of chlorinated poly(vinyl ester) oligomers CCl3–(CH2CH (OCO(CH2)mCH3))n–Cl with degrees of polymerization of 10 and 20 were prepared by telomerisation using carbon tetrachloride. The number of side chain carbon atoms ranges from 2 (poly(vinyl acetate) to 18 (poly(vinyl stearate)). The effect of the n-alkyl side chain length and of the degree of polymerization on the thermal stability and crystallization behaviour of the synthesized compounds was investigated.All oligomers degrade in two major steps by first losing HCl and side chains with subsequent breakdown of the backbone. The members with short side chains, up to poly(vinyl octanoate), are amorphous and show internal plasticization, whereas those with high number of side chain carbon atoms are semi-crystalline due to side-chain crystallization. A better packing for poly(vinyl stearate) is also noticeable. The glass transition and melting temperatures as well as the onset temperature of decomposition are influenced to a larger extent by the side chain length than by the degree of polymerization. Thermal stability is improved if both the size and number of side chains increase, but only a long side chain causes a significant increase of the resistance to degradation. This results in a stabilization of PVAc so that oligomers from poly(vinyl octanoate) on are stable under atmospheric conditions. Thus, the way to design stable, chlorinated PVEs oligomers is to use a long n-alkyl side chain.

Side-Chain-Induced Rigid Backbone Organization of Polymer Semiconductors through Semifluoroalkyl Side Chains.

While high-mobility p-type conjugated polymers have been widely reported, high-mobility n-type conjugated polymers are still rare. In the present work, we designed semifluorinated alkyl side chains and introduced them into naphthalene diimide-based polymers (PNDIF-T2 and PNDIF-TVT). We found that the strong self-organization of these side chains induced a high degree of order in the attached polymer backbones by forming a superstructure composed of "backbone crystals" and "side-chain crystals". This phenomenon was shown to greatly enhance the ordering along the backbone direction, and the resulting polymers thus exhibited unipolar n-channel transport in field-effect transistors with remarkably high electron mobility values of up to 6.50 cm(2) V(-1) s(-1) and with a high on-off current ratio of 10(5).

Self-assembly of amphiphilic macrocycles containing polymeric liquid crystal grafts in solution

Amphiphilic macrocycles containing polymeric liquid crystal side-chains are synthesized facilely, and the topological effects on their solution self-assembly behaviors are investigated, compared with their linear analogues.

Hydrogel-filled, semi-crystalline, nanoparticle-crosslinked, porous polymers from emulsion templating: Structure, properties, and shape memory

PolyHIPEs are porous polymers synthesized within high internal phase emulsions (HIPEs). This paper describes hydrogel-filled, shape-memory polyHIPEs (SMPHs) based upon a polyacrylate with crystallizable side-chains. These polyHIPEs had closed-cell-like voids with diameters ranging from 5 to 100 μm and a 200 nm thick hydrogel coating. The mechanical behavior was determined by the temperature and by the presence, and the state, of the hydrogel. The deformation during shape fixation, compression at 70 °C to 70% strain, depended on whether the polyHIPE was dry or hydrated. The hydrogel-filled SMPHs exhibited a partial “dual-lock” behavior. The crystalline element prevented recovery when below the melting point. The hydrogel element prevented full recovery in air above the melting point. A rapid, capillary-action-driven, full recovery could only be achieved through immersion in water at 80 °C, melting the crystalline element, plasticizing the hydrogel element, and allowing the elastomeric element to effect shape recovery.

Control of Fine Structure in "Polymer Nanosphere Multilayered Organization" and Enhancement of Its Optical Property.

This paper reports on a new functionality exhibited by "polymer nanosphere multilayered organization", a new type of molecular organization, and the relationship between their structure and function. The polymer nanosphere multilayered organization is a fine structural material formed by the accumulation of single-particle layers of a hydrophobic polymer at the air/water interface; these single-particle layers have uniform height along the c-axis. By employing the "alternate compression-relaxation method", high-density, low-defect particle layers are formed with a clear increase in their crystallite sizes. In the case of a ternary comb copolymer containing a carbazole ring, one particle is formed by the assembly of approximately 60 units of collapsed monolayer-like double layers. This structure is stabilized by the formation of side-chain crystals in the interlayer, with oriented π-π stacking of carbazole rings, resulting in enhanced fluorescence emission intensity.

Microphase Structure, Crystallization Behavior, and Wettability Properties of Novel Fluorinated Copolymers Poly(perfluoroalkyl acrylate-co-stearyl acrylate) Containing Short Perfluorohexyl Chains.

Novel fluorinated copolymers of stearyl acrylate (SA) and (perfluorohexyl)ethyl acrylate (C6A), (perfluorohexyl)ethyl methacrylate (C6MA), 2-[[[[2-(perfluorohexyl)]-sulfonyl]methyl] amino]ethyl acrylate (C6SA), and methacrylate (C6SMA) were synthesized via miniemulsion copolymerization. The extremely hydrophobic monomers perfluoroalkyl acrylate (FA) and SA acted as the reactive costabilizer in the miniemulsion system. The microstructure and surface wetting properties of the copolymers were characterized by (1)H NMR, FT-IR, and dynamic contact angle test. The crystallization behaviors and fine surface structures of the copolymer films were determined by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) analysis. The self-assembled aggregation and roughness of the copolymer films were investigated by atomic force microscopy (AFM). The results showed that the fluorinated side chains interrupted and impeded the crystallizable side chains of SA from forming complete crystals. And the Tm and ΔHf of the copolymers were decreased as a consequence of this effect. The fluorinated side chains in P(C6A/SA) and P(C6MA/SA) arranged between the crystallizable hydrocarbon side chains of SA, while the crystallization structure of fluorinated and nonfluorinated pendant groups existed all at once in copolymers P(C6SA/SA) and P(C6SMA/SA). The four copolymers exhibited very low surface free energy and excellent dynamic water repellency attributed to the restriction of perfluoroalkyl groups combined with crystallization of stearyl pendant groups.

Polymeric Flower-Like Microparticles from Self-Assembled Cellulose Stearoyl Esters.

Flower-like particles (FLPs) with hierarchical surface architectures have recently attracted considerable attention due to their potentially wide application range. Hitherto, nearly all FLPs were fabricated using inorganic compounds, while versatile organic polymers have not received sufficient attention yet. Herein, we show the construction of novel organic, polymeric FLPs with diameters of 2.5-5 μm using cellulose stearoyl esters (CSEs) by means of the crystallization of side chains. CSEs with degrees of substitution of approximately 3 were transformed into FLPs during the gradual precipitation of polymer chains from the mixture of their solutions in dichloromethane (DCM) and a nonsolvent, which is driven by the evaporation of DCM. Ordered petal-like nanostructures were formed on the particle surface through the crystallization of side chains. Finally, partially crystalline FLPs containing lamellar structures were obtained. Moreover, the formation process was strongly affected by the molecular weight of CSE, concentrations of CSE solutions and the volume ratio between DCM and nonsolvents.

Precise Synthesis and Surface Wettability of a Polymer with Liquid Crystalline Side Chains

Well-defined poly(methacrylate)s with liquid crystal side chains, designated as PPHM, were synthesized by a living anionic polymerization method. Introducing a short-length alkyl chain at the end of the side chain, the solubility of the polymer was improved, resulting in higher molecular weight polymers. While the highest weight-average molecular weight (Mw) of PPHM was 68k, it exceeded 100k for a slight-polydisperse PPHM. Wide-angle X-ray diffraction (WAXD) revealed that PPHM formed a smectic A phase with 2.7 nm layer spacing and that the layer structure is present even in the glassy state at room temperature. Molecular aggregation states of PPHM in surface regions of films were characterized by sum-frequency generation, grazing-incidence WAXD, and contact angle measurements. The results show that the PPHM with a larger Mw formed a layer structure parallel to the film plane. Although low Mw PPHM also maintained a layer structure, the structure became more random within internal regions. The surface reorg...

Effect of synthetic pathways on the phase transition and side-chain crystallization behavior of alkyl-substituted cellulose ethers

The influence of different synthetic pathways on the phase transition and side-chain crystallization behavior of cellulose ethers was systematically investigated by a combination of differential scanning calorimetry (DSC), small and wide-angle X-ray scattering (SAXS, WAXS) and Fourier transform infrared spectroscopy (FTIR) techniques. DSC investigation indicated that the melting temperature and crystallization temperature, respectively, of cellulose derivatives that were synthesized by homogeneous reactions in cellulose solutions differed from those of cellulose aggregates in a swollen state synthesized by heterogeneous reactions; this implies that the synthetic pathway had a strong effect on the side-chain crystallization behavior in comb-like polymers. WAXS results showed that the cellulose ethers prepared by homogeneous reaction packed into hexagonal crystals, while those prepared by heterogeneous reaction exhibited multiple crystals. These phenomena may be understood as a result of the effect of the regularity of the main chain and the difference in hydrogen bonding interactions in the two kinds of cellulose ethers. For the latter, the presence of free –OH groups at the C-6 position in the samples obtained via the heterogeneous reaction is considered to contribute critically to intermolecular hydrogen bonds that promote crystallization of the system.

Elucidation of Internal Fine Structure of "Polymer Nanosphere" in the Interfacial Particle Film

Transition behavior from a monolayer on the water surface to a single particle layer of a ternary comb copolymer with highly hydrophobic carbazole units and both hydrogenated and fluorinated side-chains have been investigated by surface pressure−area (π−A) isotherm and atomic force microscopic (AFM) observation. Moreover, we fabricated a polymer nanosphere multilayered organization consisting of such polymer nanoparticles by the Langmuir–Blodgett (LB) technique, and estimated the particle arrangement by performing out-of-plane X-ray diffraction (XRD) analysis. This polymer monolayer is able to form the polymer nanosheet with amorphous layers. The multiparticle layered organization of polymer nanosphere is fabricated from the single particle layer by the LB technique. These layer structures have highly regular arrangement along the c-axis. Further, we investigated molecular arrangement inside of polymer particles by performing in-plane XRD analysis and fluorescence spectroscopy. This copolymer formed side-chain crystals inside the particles. Fluorocarbon chains had a short spacing of 5.0 A for the two-dimensional side-chain lattice whereas hydrocarbon chains formed sub-cell at short spacing of 4.2 A. In addition, aggregated structure of carbazole rings is formed by π-π interaction.

Polyoctadecyl methacrylate brushes via surface‐initiated atom transfer radical polymerization

The synthesis of poly(octadecyl methacrylate) brushes on planar Si substrates using surface‐initiated atom transfer radical polymerization (SI‐ATRP) is reported. SI‐ATRP of octadecyl methacrylate from a silane initiator‐modified Si substrate yielded well‐defined homopolymer brushes of varying molar mass (5000–38 000 g mol−1) and film thickness from around 2 to 20 nm. Correlation of both free polymer molar mass and brush thicknesses confirmed controlled surface‐initiated ATRP from these modified surfaces. By optimization of brush molar mass, film thickness and thin‐film processing, we observed side chain crystallization of tethered poly(octadecyl methacrylate) chains, resulting in the formation of lamellar morphologies with high‐aspect‐ratio nanofibers. Copyright © 2013 John Wiley & Sons, Ltd.

Crystallization and Melting Behaviors of Cyclic and Linear Polypeptoids with Alkyl Side Chains

A series of cyclic and linear poly(N-alkyl glycine)s (a.k.a. polypeptoids) with various linear and branched alkyl side chains (n = 2, 4, 6, 8, 10, 12, and 14) were synthesized by N-heterocyclic carbene or benzylamine-initiated polymerizations of the corresponding N-alkyl N-carboxyanhydride (R-NCAs), respectively. DSC and WAXD studies revealed that cyclic and linear polypeptoids with long linear n-alkyl side chains (n = 4–14) are semicrystalline with two melting transitions attributed to the side chain and main chain crystallization. These crystallizations are strongly coupled: increasing side chain length promotes the side chain crystallization and weakens the main chain crystallization, as evidenced by the increased side chain melting temperature (enthalpy) and the decreased main chain melting temperature (enthalpy) with increasing side chain length. Cyclic and linear polypeptoids bearing alkyl side chains as short as 4 carbons exhibit side chain crystallization at low temperatures (−110 and −117 °C). However, if the side chain crystallization is completely suppressed as in the case of polypeptoids bearing short ethyl groups or asymmetrically branched rac-2-ethyl-1-hexyl groups, the main chain crystallization is also significantly inhibited, further supporting the coupling of the two crystallization events. It was also found that the cyclic polypeptoids exhibit higher main chain melting temperatures relative to the linear counterparts, whereas the side chain melting temperatures are not significantly affected by the polymer architecture. Furthermore, thermal history was shown to affect the polypeptoid crystallization. Annealing above the isotropic temperature followed by cooling significantly enhanced the polymer crystallization, whereas annealing between the two melting temperatures is not effective in promoting crystallization due to the coupling of the side chain and main chain crystallization.

Crystallization and melting of poly(glycerol adipate)‐based graft copolymers with single and double crystallizable side chains

ABSTRACTThe crystallization and melting behavior of a series of poly(glycerol adipate) (PGA) based graft copolymers with either poly(ε‐caprolactone) (PCL), poly(ethylene oxide) (PEO), or PCL‐b‐PEO diblock copolymer side chains (i.e., PGA‐g‐PCL, PGA‐g‐PEO, and PGA‐g‐(PCL‐b‐PEO)) was studied using polarized light optical microscopy (POM), differential scanning calorimetry (DSC), small‐angle X‐ray scattering (SAXS), and wide‐angle X‐ray diffraction (WAXD). These results were compared with the behavior of the corresponding linear analogs (PEO, PCL, and PCL‐b‐PEO). POM revealed that spherulitic morphology was retained after grafting. However, spherulite radius as well as radial growth rate was significantly smaller in the graft copolymers. Evaluation of isothermal crystallization kinetics by means of the Avrami theory revealed that the nucleation density was much higher in the graft copolymers. The DSC results indicated that the degree of crystallinity decreased strongly upon grafting while the melting temperatures of PGA‐g‐PCL and PGA‐g‐PEO were found to be close to the values of neat PCL and PEO, respectively. This was attributed to the absence of specific thermodynamic interactions, and, additionally, to lamella thicknesses being similar to those of the homopolymers. The latter point was confirmed by SAXS measurements. In case of PCL‐b‐PEO diblock copolymers and PGA‐g‐(PCL‐b‐PEO) graft copolymers, the crystallization behavior and thus the resulting lamellar morphology is more complex, and a suitable model was developed based on a combination of DSC, WAXD, and SAXS data. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1581–1591

Enzymatic esterification of tapioca maltodextrin fatty acid ester

In this work new types of hydrophobically modified maltodextrin were prepared by enzyme-catalyzed reaction of maltodextrin and three fatty acids: decanoic acid (C-10), lauric acid (C-12) and palmitic acid (C-16). Lipase obtained from Thermomyces lanuginosus was found to be a useful biocatalyst in the maltodextrin esterification. Esterified maltodextrin with a degree of substitution (DS) 0.015–0.084 was prepared at the optimum conditions of 60°C for 4h. The DS was found to be at its highest when maltodextrin and fatty acids were taken in the ratio 1:0.5. The functional properties of these esterified maltodextrin were investigated. All esterified maltodextrin did not completely dissolve in water. Esterified maltodextrin at a concentration of 25% (w/w) exhibited Newtonian flow behavior similar to that of native maltodextrin. Esterified maltodextrin had a higher viscosity compare to native maltodextrin. X-ray diffraction pattern of esterified maltodextrin indicated crystallization of the fatty acid side chains. The thermal stability of esterified maltodextrin was checked by differential scanning calorimetry (DSC). Esterified maltodextrin was then used as an emulsifier to make n-hexadecane O/W emulsions. The emulsions were characterized according to their oil droplet characteristics and emulsification index.

Synthesis and characterization of graft copolymers poly(ethylene oxide)-g-[poly(ethylene oxide)-b-poly(ε-caprolactone)] with double crystallizable side chains

Using a “grafting from” strategy, the graft copolymer poly(ethylene oxide)-g-[poly(ethylene oxide)-b-poly(e-caprolactone)] [PEO-g-(PEO-b-PCL)] with double crystallizable side chains was synthesized by a sequential ring-opening polymerization (ROP) mechanism. First, the ethoxyethyl glycidyl ether (EEGE) monomers containing a protected hydroxyl group were copolymerized with ethylene oxide (EO) monomers to form poly(ethylene oxide-co-ethoxyethyl glycidyl ether) [poly(EO-co-EEGE)], and the pendant hydroxyl groups were recovered by cleavage of the protecting groups for give poly(ethylene oxide-co-glycidyl) [poly(EO-co-Gly)]. Then, using poly(EO-co-Gly) with the pendant hydroxyl groups as a macroinitiator, the graft copolymer poly(ethylene oxide)-g-poly(ethylene oxide) (PEO-g-PEO) was obtained by ring-opening polymerization (ROP) of the EO monomers, and the graft copolymer PEO-g-(PEO-b-PCL) was obtained by sequential ROP of e-CL monomers. The target PEO-g-(PEO-b-PCL) and intermediates were all characterized in detail by size-exclusion chromatography (SEC) and Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR). The thermal stability and crystallization behaviors were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results showed that the graft structure and compositions had important effects on the thermal stability and crystallization behaviors, and the crystallizability of graft copolymers was predominantly controlled by the outer segments.

Fractionated Crystallization of Defect-Free Poly(3-hexylthiophene).

Fractionated crystallization (FC), a chain-sorting mechanism by length, is identified in well-defined, low molecular weight, and defect-free regioregular poly(3-hexylthiophene) by X-ray scattering and calorimetry of bulk samples. While wide-angle X-ray scattering (WAXS) qualitatively suggests that the degree of crystallinity is similar in all investigated samples, the melting enthalpies are largely different. We ascribe this to intricacies in the integration of the melting and crystallization peaks in calorimetric experiments, which is caused by FC occurring over a large temperature range. The extent of FC decreases with increasing molecular weight and increases with increasing polydispersity. The temperature-dependent investigation of the long period LP and the (100)-WAXS reflection of a sample in which FC is absent allows to disentangle effects from main-chain and side-chain crystallization.

Shape memory properties of polypeptide hydrogels having hydrophobic alkyl side chains

Polypeptide hydrogels were prepared by cross-linking of hydrophobically-modified poly[N5-(2-hydroxyethyl) l-glutamine] having alkyl side chains –CnH2n+1. Chain length of the alkyl group was n = 8, 16, and 18, and their mole fractions in the polypeptide were varied in the range of 0.05–0.16. Shape memory ability of the prepared polypeptide hydrogels was investigated. After deformation at 60 °C, the hydrogel was cooled in order to fix the temporary deformed shape. It was found that crystallization of the alkyl side chains did not occur, and the fixation ability of the hydrogel at 0 °C was low. In the subsequent heating process, the deformed temporary shape spontaneously recovered to the original shape gradually with increasing temperature, in other words, the shape recovery ratio varied with depending on the recovery temperature. From these observations, it was proposed that the shape fixation of the polypeptide hydrogel was achieved by strong segregation of the hydrophobic alkyl chains at low temperature, and the shape recovery of the deformed hydrogel was accompanied by the gradual decrease of the segregation strength with the temperature increase.

Spectroscopic study of side-chain melting and crystallization of regioregular poly(3-dodecylthiophene)

Regioregular poly(3-dodecylthiophene) was investigated by temperature-dependent FTIR. Clear turning points were observed at ∼80 °C in variations of vibrational bands associated with the alkyl side chains, indicating that the thermal transitions at this temperature are side-chain melting/crystallization. In contrast, no such turning points were found for poly(3-hexylthiophene).

Synthesis and properties of amphiphilic poly(ethylene oxide)-grafted cardo poly(aryl ether sulfone) copolymers

A series of comb-type amphiphilic copolymers (PES-g-PEO) with a stiff poly(aryl ether sulfone) backbone and flexible PEO side chains was synthesized via a “grafting onto” technique. By controlling the monomer feed ratios, high molecular weight copolymers with a range of PEO side chain content were prepared and used to form tough and flexible membranes. The PES-g-PEO membranes displayed high thermal stability ( T d > 230 °C) and good mechanical properties. The water contact angles of the PES-g-PEO membranes ranged from 60.5° to 66.7°, 20° lower than those of poly(aryl ether sulfone) membranes (82–86°), indicating that the PEO side chains improved the hydrophilicity of the membranes. Wide-angle X-ray diffraction results indicated that the PES-g-PEO membranes possessed an amorphous structure, that is, crystallization of the PEO side chains did not occur. The Li-ion conductivity reached 2.26 × 10 −4 S/cm at room temperature, much higher than that of the pure PEO-based system (10 −6 S/cm), due to the presence of the amorphous PEO side chains between the PES backbones, which provided an effective Li-ion transport pathway.