New Poly(propylene glycol)‐ and Poly(ethylene glycol)‐Based Polymer Gelators with L‐Lysine

Summary: New polymer gelators consisting of poly(propylene glycol) or poly(ethylene glycol) and L ‐lysine‐based low‐molecular‐weight gelators have been developed. These polymer gelators were synthesized according to a simple procedure with high reaction yield, and formed organogels in many organic solvents. The organogelation mechanism was proposed from the transmission electron microscopy and FTIR spectroscopy studies.

Structures of the polymer gelators synthesized here.     

Nature of the Ring‐Banded Spherulites in Blends of Aromatic Poly(ether ketone)s

Summary: The ring‐banded spherulites in liquid crystalline poly(aryl ether ketone) (LC‐PAEK) and poly(aryl ether ether ketone) (PEEK) blends with a higher content (>50%) of LC‐PAEK are investigated by polarizing light microscopy (PLM) and atomic force microscopy (AFM) techniques. The results indicate that the light core and rings of the ring‐banded spherulites under PLM are mainly composed of an LC‐PAEK phase, while the dark rings consist of coexisting phases of PEEK and a small amount of LC‐PAEK. The formation of the ring‐banded spherulites is attributable to structural discontinuity caused by a rhythmic radial growth.

PLM image of ring‐banded spherulites in a 70:30 LC‐PAEK/PEEK blend caused by rhythmic growth.     

Synthesis of Folic Acid Functionalized PLLA‐b‐PPEGMA Nanoparticles for Cancer Cell Targeting

Poly(L ‐lactic acid)‐block‐poly(poly(ethylene glycol) monomethacrylate) (PLLA‐b‐PPEGMA) has been prepared by the ring‐opening polymerization of lactide with a double‐headed initiator, 2‐hydroxyethyl 2′‐methyl‐2′‐bromopropionate (HMBP), followed by atom transfer radical polymerization (ATRP) of poly(ethylene glycol) monomethacrylate (PEGMA). PLLA‐b‐PPEGMA nanoparticles with encapsulated Fe₃O₄ are prepared by a solvent evaporation/extraction technique, and then further functionalized with folic acid, a cancer targeting ligand. Our results show that such functionalized PLLA‐b‐PPEGMA nanoparticles have good potential as carriers for targeted drug delivery in cancer treatment.

     

Annular Multi‐Shelled Spherulites in Interiors of Bulk‐Form Poly(nonamethylene terephthalate)

Morphology of crystallized spherulites in poly(nonamethylene terephthalate) (PNT) in bulk forms, instead of thin‐film forms, was investigated using scanning electron microscopy (SEM), polarized‐optical microscopy (POM), and transmission electron microscopy (TEM). Ring textures were found to exist on the fractured surfaces or microtomed films from bulk PNT samples. By further SEM and TEM examinations, the fracture surfaces and microtomed films from the interior of the bulk display similar ring‐banded patterns as those in thin films cast on glass slides. Although the cast PNT thin films in two‐dimensional growth are known to display both Type‐1 ring bands as majority and Type‐2 ring bands as minority, this study further shows that the interior of PNT bulk exhibits mainly Type‐1 (single rings with narrower spacing than Type‐2) ring bands, and Type‐2 spherulites exist sporadically in three‐dimensional forms. From these analyses on the ring bands in the interiors of bulk‐form PNT crystallized at several specific temperatures, it can be proposed that the growth of spherulites in three dimensions is layer‐by‐layer, packing into a multi‐shells structure in three‐dimensional ring‐banded spheres.

     

Microscopic Fourier Transform Infrared Characterization on Two Types of Spherulite with Polymorphic Crystals in Poly(heptamethylene terephthalate)

FTIR microspectrometry with in situ temperature variation and IR‐peak‐mapping capability, and POM characterization were used to study the crystal distribution in dual spherulites in poly(heptamethylene terephthalate). By tracing the crystalline IR bands of the α‐crystal and β‐crystal to get the crystal distribution, the techniques resolve that the ringed and ringless spherulites comprise α‐ and β‐crystals, respectively. In addition, temperature‐dependent IR analyses on the spots related to the two crystals also reveal the α‐ and β‐crystals melt at 98 and 104 °C, respectively. The ringed and ringless spherulites were proven to be correlated with the α‐ and β‐crystal forms, respectively.

     

Silyl‐Substituted Poly(thienylenevinylene) via Heteroaromatic Dehydrohalogenation Polymerization

A long alkylsilyl group was attached to a thiophene ring system to overcome the instability of 2,5‐bis(halomethyl)thiophene monomers, by imparting steric hindrance and electronic delocalization. The resulting stable monomer could be used directly to prepare low‐band‐gap poly(thienylenevinylene) (1.57 eV) through heteroaromatic dehydrohalogenation polymerization.

     

Ring‐Opening Polymerization of ε‐Caprolactone by Poly(ethylene glycol) by an Activated Monomer Mechanism

Summary: The polymerization of ε‐caprolactone (CL) in the presence of HCl · Et₂O by an activated monomer mechanism was performed to synthesize diblock or triblock copolymers composed of poly(ethylene glycol) (PEG) and poly(ε‐caprolactone) (PCL). The obtained PCLs had molecular weights close to the theoretical values calculated from the CL to PEG molar ratios and exibited monomodal GPC curves. We successfully prepared PEG and PCL block copolymers by a metal‐free method.

The non‐metal catalyzed living ring‐opening polymerisation of ε‐caprolactone by PEG.     

Photoinduced Controlled Radical Polymerization

Well‐controlled radical polymerization of methyl methacrylate can be achieved by in situ photochemical generation of copper (I) complex from air‐stable copper (II) species without using any reducing agent at room temperature. The living character of this polymerization was confirmed by both the linear tendency of molecular weight evolution with conversion and a chain extension experiment.

     

Supercritical Carbon Dioxide‐Treated Electrospun Poly(vinylidene fluoride) Nanofibrous Membranes: Morphology,Structures and Properties as an Ionic‐Liquid Host

A reverse‐barrier technique is used to enable the treatment of electrospun poly(vinylidene fluoride) nanofibrous membranes with supercritical carbon dioxide. The treatment induces the formation of nanopores and extended‐chain β crystallites of small lateral dimensions in the nanofibers. It also creates interfiber junctions, resulting in a remarkable improvement in mechanical properties of the membranes. The treated membranes are able to retain their shape very well after loading with an ionic liquid (IL). The ionic conductivity of the IL‐loaded membrane is very close to that of the neat IL.

     

Novel C60‐Anchored Two‐Armed Poly(tert‐butyl acrylate): Synthesis and Characterization

Summary: A multistep synthetic procedure for preparing novel C₆₀‐anchored two‐armed poly(tert‐butyl acrylate) was developed. First, two‐armed poly(tert‐butyl acrylate) bearing a malonate ester core with well‐controlled molecular weight was synthesized through atom transfer radical polymerization. The effective Bingel reaction between C₆₀ and the well‐defined polymer was then carried out to yield C₆₀‐anchored polymer. GPC, ¹H NMR, and UV‐vis spectroscopy indicated that the C₆₀‐anchored polymer was a monosubstituted and ‘closed’ 6,6‐ring‐bridged methanofullerene derivative.

Schematic of a novel C₆₀‐anchored two‐armed polymer.     

Fabrication of Highly Photoluminescent TiO2/PPV Hybrid Nanoparticle‐Polymer Fibers by Electrospinning

In this study, we have synthesized highly photoluminescent TiO₂/poly (phenylene vinylene) (PPV) hybrid nanoparticle‐polymer fibers by electrospinning a PPV precursor added to a TiO₂ sol‐gel solution. The diameters of the hybrid fibers ranged from 100–300 nm and the average size of TiO₂ nanoparticles within the fibers was 10–60 nm. FT‐IR analysis indicated that a new band around 1 632 cm⁻¹ assigned to the Ti O C vibration appeared, which resulted in the stronger luminance of the fluorescence of the TiO₂/PPV hybrid fibers compared to free standing PPV nanofibers.

     

A Facile Approach to Single‐Wall Carbon Nanotube/Poly(allylamine) Nanocomposites

A facile approach to polymer nanocomposites with single‐wall carbon nanotubes and cationic polymers is reported. The composite material was synthesized by producing carboxylic acid groups at the nanotube termini followed by a reaction with poly(allylamine) in water. Fourier transform infrared spectral and thermogravimetric analyses corroborate that the poly(allylamine) chains were wrapped on the surface of the carbon nanotubes. The scanning electron microscopic (SEM) image shows that the nanotubes were dispersed with little aggregation, thus, strongly suggesting that the poly(allylamine) chains have covered the single‐wall carbon nanotubes, which was further evidenced by transmission electron microscopy. The composites are soluble in water, and this solubilization process opens up new opportunities in the solution chemistry on pristine nanotubes.

     

Poly(cyclic imino ether)s Beyond 2‐Substituted‐2‐oxazolines

2‐Oxazolines (2‐OZO) are 5‐membered cyclic imino ethers whose cationic ring‐opening polymerization (CROP) mechanism and resulting polymer properties are extensively studied. However, also 6‐ and 7‐membered cyclic imino ethers can be polymerized via CROP. Together with the much less studied 4‐ and 5‐substituted main‐chain chiral poly(2‐oxazoline)s (P‐2‐OZO), these compounds are interesting monomers to enhance the versatility of (co)poly(cyclic imino ether)s. To emphasize the potential of such alternative cyclic imino ether monomers, we provide an overview on the polymerizations of 2‐oxazine (2‐OZI) and chiral 4‐ and 5‐substituted 2‐OZO as well as of selected properties of the resulting polymers. In addition, the hydrolysis of these polymers into the corresponding poly(alkylene imine)s will be addressed.

     

A New Crystal Form,Polymorphism, and Multi‐Morphology in Biodegradable Poly(3‐hydroxypropionate)

Summary: A new crystal morphology (δ form) of poly(3‐hydroxypropionate) (PHP) is found in cast and melt‐crystallized PHPs with low molecular weight, in which the PHP chains possibly adopt a 2₁ helix rather than the trans conformation found in the β or γ form. The fusion temperature‐ and the crystallization temperature‐dependent polymorphism are responsible for the dual morphologies and the unique growth kinetics of spherulites in the melt‐crystallized PHPs.

a) A dual‐morphology developed at 70 °C in PHP films after melting at 117 °C and b) that formed during cooling at a rate of 1 °C · min⁻¹ from 130 °C.     

Homogeneously Dispersed Poly(propylene)/SiO2 Nanocomposites with Unprecedented Transparency

Summary: Physico‐chemical interactions between hydrophobic polyolefin materials and hydrophilic inorganic nanoparticles such as surface‐hydroxylated SiO₂ have not been well understood so far. In this study, the effects of particle size and content of SiO₂ nanoparticles on isothermal growth rate of PP spherulites in various PP/SiO₂ nanocomposites were investigated by polarized optical microscopy. It was unexpected to find that hydrophilic SiO₂ nanoparticles can be homogeneously dispersed in a PP matrix. Spherulite growth rates of PP in PP/SiO₂ nanocomposites decrease significantly with increasing SiO₂ content and decreasing particle size. Most interestingly, the spherulite growth rate was zero for PP/16 nm‐SiO₂ nanocomposites with SiO₂ content above 2.5 wt.‐% resulting in a highly transparent film.

Photographs of 200 µm‐thick PP and PP/16 nm‐SiO₂ (5 wt.‐%) sheets in front of a graphic pattern.     

Photo‐Induced Solid‐State Crosslinking of Electrospun Poly(vinyl alcohol) Fibers

Summary: Poly(vinyl alcohol) (PVA) was derivatized by polymer analogous reaction with thienyl acryloyl chloride and processed to submicrometer fibers by electrospinning from aqueous solution. Water solubility of otherwise water‐soluble PVA fibers was reduced considerably by UV crosslinking of thienyl acrylate modified PVA fibers in the solid state. Water stability of these crosslinked fibers was proven by water steam test at 95 °C.

UV/Vis spectrum of PVA‐Thio fibers irradiated for different periods at 300 nm.     

Microwave Accelerated Polymerization of 2‐Phenyl‐2‐oxazoline: Microwave or Temperature Effects?

Summary: Investigations regarding the cationic ring‐opening polymerization of 2‐phenyl‐2‐oxazoline under microwave irradiation and conventional heating are reported. This study was inspired by contradictory reports of the (non‐)existence of non‐thermal microwave effects that might accelerate the cationic ring‐opening of 2‐oxazolines. The polymerization of 2‐phenyl‐2‐oxazoline was investigated under pressure in acetonitrile and under reflux (or at the boiling point of butyronitrile in a closed vessel) in butyronitrile utilizing a single‐mode microwave reactor and automated synthesis robots with conventional heating.

     

Synthesis and Fluorescent Properties of Biodegradable Hyperbranched Poly(amido amine)s

Disulfide‐functionalized hyperbranched poly(amido amine)s (HPAMAMs) were synthesized by Michael addition polymerization of N,N'‐cystaminebisacrylamide and 1‐(2‐aminoethyl)piperazine. The novel HPAMAMs displayed bright fluorescence, and the emissions bands cover nearly the whole visible wavelength range. When polymer solutions were excited at 330–385, 460–490, and 510–550 nm, blue, green, and red solutions were observed, respectively. The HPAMAMs are biodegradable and they can be easily cleaved by 2‐mercaptoethanol or glutathione, leading to a decrease in the fluorescence intensity. Studies of applications of the biocompatible and biodegradable HPAMAMs in fluorescence imaging technology and biological science are in progress.

     

Cross‐Linking and Degradation Properties of Plasma Enhanced Chemical Vapor Deposited Poly(2‐hydroxyethyl methacrylate)

Plasma Enhanced Chemical Vapor Deposition (PECVD) of poly‐2‐hydroxyethyl methacrylate (pHEMA) biocompatible, biodegradable polymer films were produced alone and cross‐linked with ethylene glycol diacrylate (EGDA). Degree of cross‐linking was controlled via manipulation of the EGDA flow rate, which influenced the amount of swelling and the extent of degradation of the films in an aqueous solution over time. Noncross‐linked pHEMA films swelled 10% more than cross‐linked films after 24 h of incubation in an aqueous environment. Increasing degree of film cross‐linking decreased degradation over time. Thus, PECVD pHEMA films with variable cross‐linking properties enable tuning of gel formation and degradation properties, making these films useful in a variety of biologically significant applications.

     

PMMA/Zinc Oxide Nanocomposites Prepared by In‐Situ Bulk Polymerization

Summary: Dispersing surface‐modified zinc oxide nanoparticles (ZnO) in methyl methacrylate (MMA) improves the free radical bulk polymerization process as well as the thermal stability of the formed polymer. Hydroxy groups available on the ZnO surface may induce a degenerative transfer. This suppresses the gel effect, which leads to a better control of the heat evolution during the late stages of polymerization. The formation of chains having vinylidene end groups and head‐to‐head links is suppressed, which shifts the onset of thermal decomposition to the regime where decomposition occurs by random chain scission.

Thermal degradation profiles of PMMA and its composite with ZnO at 11 wt.‐%.