Showing papers in "Journal of Polymer Science in 2011"

Biomedical applications of biodegradable polymers

Abstract: Utilization of polymers as biomaterials has greatly impacted the advancement of modern medicine. Specifically, polymeric biomaterials that are biodegradable provide the significant advantage of being able to be broken down and removed after they have served their function. Applications are wide ranging with degradable polymers being used clinically as surgical sutures and implants. To fit functional demand, materials with desired physical, chemical, biological, biomechanical, and degradation properties must be selected. Fortunately, a wide range of natural and synthetic degradable polymers has been investigated for biomedical applications with novel materials constantly being developed to meet new challenges. This review summarizes the most recent advances in the field over the past 4 years, specifically highlighting new and interesting discoveries in tissue engineering and drug delivery applications.

Natural underwater adhesives

Abstract: The general topic of this review is protein-based underwater adhesives produced by aquatic organisms. The focus is on mechanisms of interfacial adhesion to native surfa- ces and controlled underwater solidification of natural water- borne adhesives. Four genera that exemplify the broad range of function, general mechanistic features, and unique adaptations are discussed in detail: blue mussels, acorn barnacles, sandcas- tle worms, and freshwater caddisfly larva. Aquatic surfaces in nature are charged and in equilibrium with their environment, populated by an electrical double layer of ions as well as adsorbed natural polyelectrolytes and microbial biofilms. Surface adsorption of underwater bioadhesives likely occurs by exchange of surface bound ligands by amino acid sidechains, driven primarily by relative affinities and effective concentra- tions of polymeric functional groups. Most aquatic organisms exploit modified amino acid sidechains, in particular phospho- rylated serines and hydroxylated tyrosines (dopa), with high- surface affinity that form coordinative surface complexes. After delivery to the surfaces as a fluid, permanent natural adhesives solidify to bear sustained loads. Mussel plaques are assembled in a manner superficially reminiscent of in vitro layer-by-layer strategies, with sequentially delivered layers associated through Fe(dopa)3 coordination bonds. The adhesives of sandcastle worms, caddisfly larva, and barnacles may be delivered in a form somewhat similar to in vitro complex coacervation. Marine adhesives are secreted, or excreted, into seawater that has a significantly higher pH and ionic strength than the internal envi- ronment. Empirical evidence suggests these environment trig- gers could provide minimalistic, fail-safe timing mechanisms to prevent premature solidification (insolubilization) of the glue within the secretory system, yet allow rapid solidification after secretion. Underwater bioadhesives are further strengthened by secondary covalent curing. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 757-771, 2011

Tuning the mechanical properties in model nanocomposites: Influence of the polymer-filler interfacial interactions Part B Polymer physics

Abstract: This article presents a study of the polymer-filler interfacial effects on filler dispersion and mechanical reinforcement in Polystyrene (PS)/silica nanocomposites by direct comparison of two model systems: ungrafted and PS-grafted silica dispersed in PS matrix. The structure of nanoparticles has been investigated by combining small angle neutron scattering measurements and transmission electronic microscopic images. The mechanical properties were studied over a wide range of deformation by plate-plate rheology and uni-axial stretching. At low silica volume fraction, the particles arrange, for both systems, in small finite size nonconnected aggregates and the materials exhibit a solid-like behavior independent of the local polymer-fillers interactions suggesting that reinforcement is dominated by additional long range effects. At high silica volume fraction, a continuous connected network is created leading to a fast increase of reinforcement whose amplitude is then directly dependent on the strength of the local particle-particle interactions and lower with grafting likely due to deformation of grafted polymer.

Synthesis of raspberry-like organic-inorganic hybrid nanocapsules via pickering miniemulsion polymerization: Colloidal stability and morphology Part A Polymer chemistry

Abstract: Raspberry-like hybrid nanocapsules with a hydrophobic liquid core were successfully prepared via the copolymerization of styrene, divinylbenzene (DVB), and 4-vinyl pyridine (4-VP) in Pickering-stabilized miniemulsions by using silica particles as the sole emulsifier and hexadecane (HD) as liquid template. When compared with conventional Pickering miniemulsions and Pickering suspensions, the colloidal stability of the current systems is much more sensitive to the variation of reaction parameters such as pH, size, amount of silica particles, and content of 4-VP. The systems without coagulum were only obtained in a narrow pH range at around 9.5 and by using 12 nm silica particles as emulsifier. The formation of well-defined raspberry-like capsules was confirmed by transmission electron microscopy (TEM) and high-resolution scanning electron microscopy (HRSEM). The stable attachment of silica particles on the surface of hybrid particles was verified by centrifugation and subsequent characterizations, such as Fourier transform infrared spectroscopy, TEM, and HRSEM. The influence of pH and weight content of HD, DVB, and 4-VP on the particle morphology was extensively investigated. Interestingly, the particle morphology strongly depends on the particle size. When compared with the organic surface-active surfactant, the formation of capsule morphology could be promoted by the application of silica particles taking advantage of their surface inactivity. The formation mechanisms of capsules/solid particles are discussed.

Versatile functionalization of polyester hydrogels with electroactive aniline oligomers Part A Polymer chemistry

Abstract: Functionalizing aliphatic polyester hydrogels with an aniline oligomer is a means of achieving electrically conductive and degradable hydrogels. To lower the aniline oligomer content while maintaining a high conductivity and to overcome the acidic degradation product from polylactide reported in our previous work, a series of electroactive and degradable hydrogels based on polycaprolactone (PCL) hydrogels and carboxyl-capped aniline pentamer (CCAP) were synthesized by a simple coupling reaction at room temperature. The reaction was carried out between the hydroxyl groups of hydroxyethylmethacrylate in a photopolymerized glycidyl methacrylate (GMA)-functionalized PCL-poly(ethylene glycol)-PCL degradable network and carboxyl group of CCAP, using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide as water-condensing agent and 4-dimethylaminopyridine as catalyst. The electroactivity of the hydrogels was verified by cyclic voltammetry, which showed three pairs of redox peaks. The electrical conductivities and swelling ratios of these hydrogels were controlled by the CCAP content, the poly(ethylene glycol) molecular weight in the macromer, and the crosslinking density of the hydrogels.

Synthesis, two-photon absorption, and optical power limiting of new linear and hyperbranched conjugated polyynes based on bithiazole and triphenylamine Part A Polymer chemistry

Abstract: Two new linear and hyperbranched conjugated polymers P1 and P2 have been synthesized by Sonogashira coupling reaction, in which the main chain consists of bithiazole moieties as electron acceptors and triphenylamino groups as donors. The conjugated polymers were characterized by TGA, UV-vis absorption, fluorescence emission, electrochemical cyclic voltammetry, and two-photon absorption measurements. They exhibited excellent solubility in organic solvents and high thermal stability (5% of weight loss at 299 °C). The two-photon absorption cross sections (σ) measured by the open aperture Z-scan technique using 140 femtosecond (fs) pulse were determined to be 1014 and 552 GM per repeating unit for P1 and P2, respectively. This result shows that the σ of linear conjugated P1 is higher than that of hyperbranched P2, indicating that the linear polymer offers better intramolecular charge transfer ability. In THF, P1 and P2 exhibit intense frequency up-converted fluorescence under the excitation of 140 fs pulses at 800 nm with the peaks located at 580 and 548 nm, respectively. Meanwhile, the optical limiting behaviors for the polymers were studied by using a focused 800 nm laser beam of 140 fs duration. It was found that these polymers also exhibit good optical-limiting properties and make them potential candidates for optical limiters in the photonic fields.

Solution processable high band gap hosts based on carbazole functionalized cyclic phosphazene cores for application in organic light-emitting diodes Part B Polymer physics

Abstract: A new class of solution processable dendrimers based on cyclic phosphazene (CP) cores have been prepared and used as host materials for blue and green organic light emitting diodes (OLEDs). The dendrimers are prepared in high yield from minimal step reactions, are soluble in common solvents for solution processing, are amorphous, and have excellent thermal properties necessary for application in OLEDs. OLED efficiencies of 10.3 cd/A (4.2 lm/W) and 35.3 cd/A (33.5 lm/W) were achieved using commercially available FIrpic and Ir(mppy)₃ as blue and green phosphorescent emitters, respectively. These efficiencies were 2× higher than control devices prepared using poly(N-vinylcarbazole), the most commonly used host material in solution processed phosphorescent OLEDs.

Alternating copolymers incorporating cyclopenta[2,1-b:3,4-b′]dithiophene unit and organic dyes for photovoltaic applications Part A Polymer chemistry

Abstract: We have synthesized six p-type copolymers, CPDT-co-TPADCN, CPDT-co-TPADTA, CPDT-co-TPATCN, CPDT-co-DFADCN, CPDT-co-DFADTA, and CPDT-co-DFATCN, consisting of a cyclopenta[2,1-b:3,4-b′]dithiophene (CPDT) unit and an organic dye in an alternating arrangement. Triphenylamine (TPA) or difluorenylphenyl amine (DFA) units serve as the electron donors, whereas dicyanovinyl (DCN), 1,3-diethyl-2-thiobarbituric acid, or tricyanovinyl (TCN) units act as the electron acceptors in the dyes. The target polymers were prepared via Stille coupling, followed by postfunctionalization to introduce the electron acceptors to the side chains. Because of the strongest withdrawing ability of TCN acceptor to induce efficient intramolecular charge transfer, CPDT-co-TPATCN and CPDT-co-DFATCN exhibit the broader absorption spectra covering from 400 to 900 nm and the narrower optical band gaps of 1.34 eV. However, the CPDT-co-TPATCN:PC₇₁BM and CPDT-co-DFATCN:PC₇₁BM based solar cells showed the power conversion efficiencies (PCEs) of 0.22 and 0.31%, respectively, due to the inefficient exciton dissociation. The DFA-based polymers possess deeper-lying HOMO energy levels than the TPA-based polymer analogues, leading to the higher Voc values and better efficiencies. The device based on CPDT-co-DFADTA:PC₇₁BM blend achieved the best PCE of 1.38% with a Voc of 0.7 V, a Jsc of 4.57 mA/cm², and a fill factor of 0.43.

Multicomponent supramolecular thermoplastic elastomer with peptide-modified nanofibers Part A Polymer chemistry

Abstract: Bioactive nanofibers present a promising synthetic niche for in vivo applications due to their morphological and functional resemblance to the extracellular matrix. Potentially interesting nanofibers are constructed from the hard-segment regimes in well-defined thermoplastic elastomers (TPEs). The supramolecular interactions between these hard segments cause physical crosslinking by the formation of nanofibers and provide excellent mechanical properties. Here, we make use of a new class of biocompatible supramolecular TPEs, in which both the formation of the main chain and the hard block is based on multiple hydrogen-bonding interactions. A self-assembly process is explored to arrive at well-defined peptide-modified nanofibers embedded in a biocompatible soft matrix. Crucial for the success in the synthetic design is the use of an exact match between the molecular recognition units of the peptide and the supramolecular unit that takes care of forming the supramolecular nanofibers of the TPE. Evidence for the strong anchoring of the modified peptides in the hard-segment nanofibers of the supramolecular TPE is provided by simple extraction experiments.

Cocrystallization of ethylene/1-octene copolymer blends during crystallization analysis fractionation and crystallization elution fractionation

Abstract: Blending of ethylene/1-octene copolymers can be used to achieve a well-controlled broad chemical composition distribution (CCD) required in several polyolefin applications. The CCD of copolymer blends can be estimated using crystallization analysis fractionation (CRYSTAF) or crystallization elution fractionation (CEF). Unfortunately, both techniques may be affected by the cocrystallization of chains with different compositions, leading to profiles that do not truly reflect the actual CCD of the polymer. Therefore, understanding how the polymer microstructure and the analytical conditions influence copolymer cocrystallization is critical for the proper interpretation of CRYSTAF and CEF curves. In this investigation, we studied the effect of chain crystallizabilities, blend compositions, and cooling rates on cocrystallization during CEF and CRYSTAF analysis. Cocrystallization is more prevalent when the copolymer blend has components with similar crystallizabilities, one of the components is present in much higher amount, and fast cooling rates are used. CEF was found to provide better CCD estimates than CRYSTAF in a much shorter analysis time.

Versatile synthesis of asymmetrical dendron-like/dendron-like poly(ε-caprolactone)-b-poly(γ-benzyl-L-glutamate) block copolymers Part A Polymer chemistry

Abstract: Dendron-like/dendron-like poly(e-caprolactone)-b-poly(γ-benzyl-L-glutamate) block copolymers with asymmetrical topology (PCL 208-b-PBLGn, both the subscript and the superscript denote the degree of polymerization and the branch number, respectively; n = 1, 2, and 4) were synthesized by combining ring-opening polymerization (ROP) and click chemistry. The dendron-like propargyl focal point PCL 208 precursor with eight branches was synthesized from the controlled ROP of e-caprolactone, and then click conjugated with azido focal point poly(amido amine) dendrons to generate the PCL 208-dendrons with multiple primary amine groups. The PCL 208-dendrons were further used as macroinitiators for the ROP of γ-benzyl-L-glutamate N-carboxyanhydride to produce the targeted asymmetrical block copolymers. Their molecular structures and physicochemical properties were thoroughly characterized by means of FT-IR, ¹H NMR, gel permeation chromatography, differential scanning calorimetry, and wide angle X-ray diffraction. Both the maximal melting temperature and the degree of crystallinity of PCL block within copolymers decreased with increasing the PBLG branches and/or the chain length, demonstrating that the crystallinity of PCL block was progressively suppressed by PBLG block. Meanwhile, the PBLG block within copolymers progressively transformed from β-sheet to α-helical conformation with increasing the PBLG chain length. Consequently, this provides a versatile strategy for the synthesis of biodegradable and biomimetic block copolymers with asymmetrical dendritic topology.

Synthesis of poly(naphthalenecarboxamide)s with low polydispersity by chain-growth condensation polymerization Part A Polymer chemistry

Abstract: Condensation polymerization of 6-(N-substituted-amino)-2-naphthoic acid esters (1) was investigated as an extension of chain-growth condensation polymerization (CGCP). Methyl 6-(3,7-dimethyloctylamino)-2-naphthoate (1b) was polymerized at −10 °C in the presence of phenyl 4-methylbenzoate (2) as an initiator and lithium 1,1,1,3,3,3-hexamethyldisilazide (LiHMDS) as a base. When the feed ratio [1a]₀/[2]₀ was 10 or 20, poly(naphthalenecarboxamide) with defined molecular weight and low polydispersity was obtained, together with a small amount of cyclic trimer. However, polymer was precipitated during polymerization under similar conditions in [1a]₀/[2]₀ = 34. To increase the solubility of the polymer, monomers 1c and 1d with a tri(ethylene glycol) (TEG) monomethyl ether side chain instead of the 3,7-dimethyloctyl side chain were synthesized. Polymerization of the methyl ester monomer 1c did not proceed well, affording only oligomer and unreacted 1c, whereas polymerization of the phenyl ester monomer 1d afforded well-defined poly(naphthalenecarboxamide) together with small amounts of cyclic oligomers in [1d]₀/[2]₀ = 10 and 29. The polymerization at high feed ratio ([1d]₀/[2]₀ = 32.6) was accompanied with self-condensation to give polyamide with a lower molecular weight than the calculated value. Such undesirable self-condensation would result from insufficient deactivation of the electrophilic ester moiety by the electron-donating resonance effect of the amide anion.

Synthesis of repeating sequence copolymers of lactic, glycolic, and caprolactic acids Part A Polymer chemistry

Abstract: Repeating sequence copolymers of poly(lactic-co-caprolactic acid) (PLCA), poly(glycolic-co-caprolactic acid) (PGCA), and poly(lactic-co-glycolic-co-caprolactic acid) (PLGCA) have been synthesized by polymerizing segmers with a known sequence in yields of 50-85% with Mns ranging from 18-49 kDa. The copolymers exhibited well-resolved NMR resonances indicating that the sequence encoded in the segmers used in their preparation is retained and that transesterification is minimal. The exact sequences allowed for unambiguous assignment of the NMR spectra, and these standards were compared with the data previously reported for random copolymers. The glass transition temperatures (Tgs) of the PLCA and PGCA copolymers were found to depend primarily on monomer ratio rather than sequence. Sequence dependent Tgs were, however, noted for the PLGCA polymers with 1:1:1 L:G:C ratios; poly LGC and poly GLC exhibited Tgs that differed by nearly 8 °C.

The NSN link as electron accepting moiety for stable, solution‐processable conjugated oligomers Part A Polymer chemistry

Abstract: New conjugated oligomers, oligo(9,9‐didodecylfluorene‐bis‐sulphurdiimide), consisting of 9,9‐didodecylfluorene separated by NSN moieties, are reported. These oligomers are stable purple solids under ambient conditions with absorption covering a broad spectral window in the UV‐vis range and a main broad peak centered at 555 nm with onset extending to 700 nm. These oligomers show an obviously longer conjugation length than its dimeric analogue, bis‐9,9‐didodecyl‐fluorene‐2‐sulfurdiimide that shows a band‐edge absorption centered at 484 nm with onset at 590 nm. The dimer and oligomers are soluble in a variety of organic solvents. Moreover, we found that the oligomer with an average repeating‐unit number of six could significantly quench the photoluminescence (PL) of poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylene vinylene] (MEH‐PPV) or poly(3‐hexylthiophene) (P3HT) in the solid state. More importantly, the composites of this oligomer with P3HT showed a nearly 10‐fold enhancement of the photocurrent, compared with that of P3HT itself. In addition, the PL of this oligomer could be quenched by the presence of phenyl‐C₆₁‐butyric acid methyl ester (PCBM) in toluene. These results suggest the presence of photoinduced charge transfer in composites of these oligomers blended with an electronic partner that either donates or accepts electrons.

Dual thermo- and pH-sensitive network-grafted hydrogels formed by macrocrosslinker as drug delivery system Part A Polymer chemistry

Abstract: Dual thermo- and pH-sensitive network-grafted hydrogels made of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) network and poly(N-isopropylacrylamide) (PNIPAM) grafting chains were successfully synthesized by the combination of atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and click chemistry. PNIPAM having two azide groups at one chain end [PNIPAM-(N₃)₂] was prepared with an azide-capped ATRP initiator of N,N-di(β-azidoethyl) 2-chloropropionylamide. Alkyne-pending poly(N,N-dimethylaminoethyl methacrylate-co-propargyl acrylate) [P(DMAEMA-co-ProA)] was obtained through RAFT copolymerization using dibenzyltrithiocarbonate as chain transfer agent. The subsequent click reaction led to the formation of the network-grafted hydrogels. The influences of the chemical composition of P(DMAEMA-co-ProA) on the properties of the hydrogels were investigated in terms of morphology and swelling/deswelling kinetics. The dual stimulus-sensitive hydrogels exhibited fast response, high swelling ratio, and reproducible swelling/deswelling cycles under different temperatures and pH values. The uptake and release of ceftriaxone sodium by these hydrogels showed both thermal and pH dependence, suggesting the feasibility of these hydrogels as thermo- and pH-dependent drug release devices.

Synthesis of nonsymmetric chain end functionalized polyisobutylenes Part A Polymer chemistry

Abstract: We present the synthesis of nonsymmetric α-ω-functionalized polyisobutylenes (PIBs) bearing different functional moieties on their chain ends. Thus, on one chain end either, a short tri-ethylene oxide chain (TEO) or a phosphine oxide ligand is attached, whereas the other chain end is substituted by hydrogen bonding moieties (thymine/2,6-diaminotriazine). The nonsymmetric PIBs were synthesized via living cationic polymerization using methyl-styrene epoxide as initiator, followed by quenching reaction with 3-bromopropyl-benzene. Subsequent bromide/azide exchange and the use of the azide/alkyne click reaction allowed the synthesis of (a) (α)-TEO-(ω)-thymine-telechelic PIB (7a), (b) (α)-triethyleneoxide-(ω)-triazine telechelic PIB (7b), and (c) (α)-phosphinoxide-(ω)-thymine-telechelic PIB (13) with molecular weights Mn ∼ 4000 g mol⁻¹ and low polydispersities (Mw/Mn = 1.3). The chemical identity of the final structures was proven by extensive ¹H NMR investigations and matrix-assisted laser desorption/ionization-mass spectroscopy (MALDI). The presented method for the first time offers a simple and highly versatile approach toward supramolecular nonsymmetric α-ω-functionalized PIB.

Synthesis, micellar structures, and multifunctional sensory properties of poly(3-hexylthiophene)-block-poly(2-(dimethylamino)ethyl methacrylate) rod-coil diblock copolymers Part A Polymer chemistry

Abstract: We report the synthesis, micellar structures, and multifunctional sensory properties of new conjugated rod-coil block copolymers, poly(3-hexylthiophene)-block-poly(2-(di methylamino)ethylmethacrylate)(P3HT-b-PDMAEMA). The new copolymers, synthesized by atom transfer radical polymerization of P3HT macroinitiator, consisted PDMAEMA coil lengths of 43, 65, and 124 repeating units. All the P3HT-b-PDMAEMA copolymers exhibit a similar low critical solution temperature in water around 33 °C. The micellar structures of the synthesized polymers were characterized by AFM, TEM, and dynamic light scattering, by varying temperature, pH, and water/THF composition. The micelles of P3HT₂₀-b-PDMAEMA₄₃ in water had a reversible size change from 75 ± 5 nm to 132 ± 5 nm on heating from 25 to 55 °C and reduced to the original size during cooling. In addition, the micellar size also showed a significant pH dependence, changing from 67 ± 8 nm (pH = 12) to 222 ± 6 nm (pH = 4), depending on the protonation of the PDMAEMA blocks and their electrostatic repulsion. The micellar structure of three P3HT-b-PDMAEMA copolymers changed from spheres, to vesicles, and finally to larger sphere micelles as the solvent composition varied from 0 to 100 wt % water in the mixed solvent. The different micellar structures of P3HT₂₀-b-PDMAEMA₄₃ solution led to a red-shift on the absorption or photoluminescence spectra and exhibited the emission colors of yellow, orange, red, and dark red with increasing the water content. This study suggested that new copolymers had potential applications as multifunctional sensory materials toward temperature, pH, and solvent.

Supercapacitive energy storage based on ion-conducting channels in hydrophilized organic network Part B Polymer physics

Abstract: Conventional electrode materials for supercapacitors are based on nanoscaled structures with large surface areas or porosities. This work presents a new electrode material, the so-called hydrophilized polymer network. The network has two unique features: 1) it allows for high capacitance (up to 400 F/g) energy storage in a simple film configuration without the need of high-surface-area nanostructures; 2) it is unstable in water, but becomes extremely stable in electrolyte with high ionic strength. The above features are related to the hydrophilizing groups in the network which not only generate hydrated ionic conduction channels, but also enable the cross-linking of the network in electrolyte. Because of its practical advantages such as easy preparation and intrinsic stability in electrolyte, the hydrophilized network may provide a new route to high-performance supercapacitive energy storage.

SET-LRP of N-isopropylacrylamide in the presence of chain transfer agent Part A Polymer chemistry

Abstract: In this study, single electron transfer-living radical polymerization (SET-LRP) of N-isopropylacrylamide (NIPAM) in the presence of 2-mercaptoethylamine chain transfer agent (CTA) was carried out by Cu(0) generated in situ from the disproportionation of CuBr/2,2′-bipyridine (2,2′-bpy) in N,N-dimethylformamide (DMF) at 90 °C. Analysis of polymerization kinetics in the presence of CTA showed that the premature termination of growing polymer chains leads to retardation. The apparent rate constant of polymerization (k papp) decreased from 4.49 × 10⁻⁴ to 2.59 × 10⁻⁴ min⁻¹ with increasing CTA concentration. The initiator efficiency (Ieff) and the chain transfer constant (Cs) were found to be 0.524 and 0.286, respectively. The molecular weights of poly(N-isopropylacrylamide) [poly(NIPAM)] produced were significantly higher than the predicted values, and the polydispersities were less than 1.22.

Synthesis of aromatic oxazolyl- and carboxyl-functionalized polymers: Atom transfer radical polymerization of styrene initiated by 2-[(4-bromomethyl)phenyl]-4,5-dihydro-4,4-dimethyloxazole Part A Polymer chemistry

Abstract: The synthesis of a new compound, 2-[(4-bromomethyl)phenyl]-4,5-dihydro-4,4-dimethyloxazole (1), and its utility in the synthesis of oxazoline-functionalized polystyrene by atom transfer radical polymerization (ATRP) methods are described. Aromatic oxazolyl-functionalized polymers were prepared by the ATRP of styrene, initiated by (1) in the presence of copper(I) bromide/2,2′-bipyridyl catalyst system, to afford the corresponding α-oxazolyl-functionalized polystyrene (2). The polymerization proceeded via a controlled free radical polymerization process to produce the corresponding α-oxazolyl-functionalized polymers with predictable number-average molecular weights, narrow molecular weight distributions in high-initiator efficiency reactions. Post-ATRP chain end modification of α-oxazolyl-functionalized polystyrene (2) to form the corresponding α-carboxyl-functionalized polystyrene (3) was achieved by successive acid-catalyzed hydrolysis and saponification reactions. The polymerization processes were monitored by gas chromatography analyses. The unimolecular-functionalized initiator and functionalized polymers were characterized by thin layer chromatography, spectroscopy, size exclusion chromatography, and nonaqueous titration analysis.

Theoretical study of spectroscopic properties of insulated molecular wires formed by substituted oligothiophenes and cross-linked α-cyclodextrin Part B Polymer physics

Abstract: The inclusion compound formed between cross-linked α-cyclodextrin dimer and substituted oligothiophene, was investigated using density functional theory (DFT). Energy gap, spectroscopy (IR, UV-vis, ¹³C NMR, and ¹H NMR) and first hyperpolarizability data were analyzed for the free species and inclusion compound, pp-PT@(αCD-αCD). The semiconducting property of the included pp-PT was not substantially affected on inclusion, with the energy gap increasing by only 10% after interaction with αCD-αCD. On the other hand, the nonlinear optical (NLO) response was significantly decreased, with the first hyperpolarizability, β, predicted to be just more than 60% lower for the [2]rotaxane than for free pp-PT, but still having considerable magnitude. This was explained by the two-state model based on the charge-transfer contribution to the electronic transitions. The sensitivity of electronic spectra might also be useful for the inclusion complex characterization. The IR spectrum was slightly sensitive to the host-guest interaction and the calculated ¹³C NMR and ¹H NMR chemical shifts for the pp-PT guest showed appreciable variations of 5-10 and 1-1.5 ppm, respectively, and so can be used for the characterization of inclusion compounds. We concluded that the formation of inclusion complexes with CDs, seems indeed very promising and the use of encapsulating conducting material should be experimentally pursued.

Alternating copolymerization of bis(hexafluoroisopropyl) fumarate with styrene and vinyl pentafluorobenzoate: Transparent and low refractive index polymers Part A Polymer chemistry

Abstract: Bis(hexafluoroisopropyl) fumarate (BHFIPF) did not homopolymerize with free radical initiators. However, BHFIPF yielded alternating copolymers with styrene in bulk with Azobisisobutyronitrile (AIBN) as a radical initiator. The monomer reactivity ratios of BHFIPF (M₁) and styrene (M₂) were calculated as r₁ = 0.00 and r₂ = 0.02. BHFIPF also copolymerized with vinyl pentafluorobenzoate (VPFB) in bulk and in pentafluoroisopropanol solution to produce an alternating copolymer. The reactivity ratios of BHFIPF (M₁) with VPFB (M₂) were r₁ = 0.00 and r₂ = 0.05 in bulk and r₁ = 0.01 and r₂ = 0.11 in pentafluoroisopropanol, respectively. The glass transition temperatures (Tg) of the BHFIPF-styrene and BHFIPF-VPFB copolymers were 107 and 86 °C, respectively. The BHFIPF-styrene copolymer was thermally stable, and the thermal degradation temperature (Td) was 400 °C, whereas the Td of BHFIPF-VPFB copolymer was 240 °C. The films obtained by casting from tetrahydrofuran (THF) solutions of these copolymers were flexible and transparent. Their refractive indices were 1.4048 for the BHFIPF-styrene copolymer, and 1.3980 for the BHFIPF-VPFB copolymer at 633 nm, respectively.

Synthesis of polyacrylonitrile by single-electron transfer-living radical polymerization using Fe(0) as catalyst and its adsorption properties after modification Part A Polymer chemistry

Abstract: Fe(0) was firstly used as single-electron transfer-living radical polymerization catalyst for acrylonitrile polymerization using carbon tetrachloride as initiator, hexamethylenetetramine as N-ligand, and N,N-dimethylformamide as the solvent at 65 °C. First-order kinetic studies indicated that this polymerization proceeded in a “living”/controlled manner. The living nature of the polymerization was also confirmed by chain extension of methyl methacrylate with polyacrylonitrile (PAN) as macroinitiator. Furthermore, PAN was modified with NH₂OH·HCl to generate amidoxime groups for extraction of heavy metal ions (Hg²⁺) from aqueous solutions. Fourier transformed infrared spectroscopy was performed to characterize chemical composition and structure. The adsorption property of Hg²⁺ was investigated at different pH values of aqueous solutions and distilled water. The maximal saturated adsorption capacity of Hg²⁺ was 4.8 mmol g⁻¹.