End-capped Copolymers Research Articles

Controlled Hydrolytic Degradation of Polyglycolide–Caprolactone-Based Bioabsorbable Copolymer

Polyglycolide–caprolactone (PGCL)-based copolymer was synthesized from glycolide and caprolactone by ring opening polymerization in the presence of stannous octoate catalyst and diethylene glycol initiator. The effects of prepolymerization time, monomer ratio, monomer-to-catalyst and monomer-to-initiator ratios on per cent weight conversion were optimized. The end-capped copolymer was synthesized to make absorbable sutures having controlled bioabsorbability at different pH levels. It was observed that endcapped absorbable copolymer was more stable at pH 10.0 compared to uncapped absorbable material. End-capped copolymer also retained higher tensile strength compared to uncapped copolymer after 21 days. This phenomenon of controlled hydrolytic degradation of PGCL-based bioabsorbable polymer having terminal group end-capping can be attributed to less availability of hydrophilic end groups facilitating hydrolytic degradation of polymers.

End Capping Does Matter: Enhanced Order and Charge Transport in Conjugated Donor–Acceptor Polymers

Optimized microstructure through control of both intra- and intermolecular interactions in organic semiconductors is critical for enhancing and optimizing charge transport for the realization of next-generation low-cost, mechanically flexible, and easy to process high performance, organic field effect transistors (OFETs). Herein, we report donor–acceptor alternating copolymers of dithienogermole (DTG) with 2,1,3-benzothiadiazole (BTD) and probe the importance of end groups on the control of molecular order and microstructure as it relates to the enhancement of charge carrier transport. Partial end-capping reactions, confirmed by 1H NMR and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analyses, on the DTG–BTD copolymer provided significant improvement in grazing incidence wide angle X-Ray scattering (GIWAXS) determined polymer ordering in thin films. Consequently, OFETs exhibited charge-carrier mobilities up to 0.60 cm2/(Vs) for the end-capped copolymer, which are an order of ma...

Synthesis and photovoltaic properties of phthalocyanine end-capped copolymers with conjugated dithienylbenzothiadiazole–vinylene side chains

Two phthalocyanine end-capped copolymers with conjugated dithienylbenzothiadiazole–vinylene side chains, PHY1 and PHY2, have been synthesized according to the Stille–Coupling polymerization method. The structures, thermostability, optical and electrochemical properties of the copolymers were characterized via NMR, GPC, TGA, DSC, UV–vis, photoluminescence (PL) spectroscopy, and cyclic voltammetry (CV), respectively. The two copolymers exhibit excellent film-forming ability and good thermostability in a wide temperature range. PHY1 and PHY2 end-capped with different phthalocyanines showed broad absorption bands ranging from the ultraviolet to the red/near-infrared (IR) region of the solar spectrum and deep HOMO energy levels. Bulk heterojunction polymer solar cells were fabricated based on PHY1 and PHY2 with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as the electron acceptor and showed power conversion efficiencies (PCE) of 1.56% and 1.26%, respectively, under the illumination of AM 1.5, 100mW/100cm2.

Acrylate End-Capped Poly(ester-carbonate) and Poly(ether-ester)s for Polymer-on-Multielectrode Array Devices: Synthesis, Photocuring, and Biocompatibility

Polymeric materials based on epsilon-caprolactone (CL), 1,5-dioxepan-2-one (DXO), and trimethylene carbonate (TMC) were prepared and evaluated as possible candidates for polymer-on-multielectrode (PoM) applications. CL was copolymerized with either DXO or TMC in the presence of the diol initiator 1,4-benzenedimethanol (BDM). The ring-opening polymerization experiments, carried out in bulk and using tin(II) catalysis, yielded the desired low molecular weight random copolymer diols, as evidenced by NMR, IR, MALDI-ToF MS, and DSC techniques. Upon reaction with acryloyl chloride, the corresponding diacrylate end-capped copolymers were obtained. The latter were characterized by NMR and IR spectroscopy, and their photocross-linking (in the presence of a UV initiator) was followed by ATR-FTIR spectroscopy. Transparent and soft thin films of the copoly(ether-ester) and copoly(ester-carbonate) diacrylates were prepared and cured under UV irradiation. The resulting polymeric films showed good biocompatibility properties as far as in vitro neural stem cells proliferation and differentiation to neurons and astrocytes are concerned. Noteworthy are the beneficial effects obtained upon preconditioning the copolymers by means of the cell-culture medium and the excellent properties shown particularly by the CL-TMC copolymer. Moreover, preliminary results show that microchannel formation by photocuring is possible with the synthesized polymers.

Synthesis and characterization of controlled molecular weight disulfonated poly(arylene ether sulfone) copolymers and their applications to proton exchange membranes

tert-Butylphenyl terminated disulfonated poly(arylene ether sulfone) copolymers with controlled molecular weights ( M n), 20–50 kg mol −1, were successfully prepared by direct copolymerization of the two activated halides, biphenol and the endcapper, 4- tert-butylphenol. The high molecular weight copolymer (molecular weight over 80 kg mol −1) was also synthesized with 1:1 stoichiometry without an endcapping reagent. The chemical compositions and the molecular weights of the endcapped copolymers were characterized by their 1H NMR spectra utilizing the 18 unique protons at the chain ends. Modified intrinsic viscosity measurements in 0.05 M LiBr/NMP solution further correlated well with NMR results. Combining the endcapping chemistry with proton NMR end group analysis and intrinsic viscosity measurements, one can demonstrate a powerful tool for characterizing molecular weight of sulfonated poly(arylene ether sulfone) random copolymers. This enables one to further investigate the influence of molecular weight on several critical parameters important for proton exchange membranes, including water uptake, in-plane protonic conductivity and selected mechanical properties. These are briefly discussed herein and will be more fully described in subsequent publications.

Thermally responsive polymeric micellar nanoparticles self-assembled from cholesteryl end-capped random poly( N-isopropylacrylamide- co- N,N-dimethylacrylamide): synthesis, temperature-sensitivity, and morphologies

Cholesteryl end-capped thermally responsive amphiphilic polymers with two different hydrophobic/hydrophilic chain-length ratios were synthesized from the hydroxyl-terminated random poly( N-isopropylacrylamide- co- N,N-dimethylacrylamide) and cholesteryl chloroformate. The hydroxyl-terminated precursor polymers with narrow molecular weight distributions were synthesized by free-radical polymerization using 2-hydroxyethanethiol as a chain-transfer agent. The aqueous solutions of the cholesteryl end-capped copolymers exhibited reversible phase transitions at temperatures slightly above human body temperature, with the lower critical solution temperature values being 37.7 and 38.2 °C, respectively. The critical micelle concentration values of the two cholesteryl end-capped polymers were 9 and 25 mg/L, respectively. Polymeric micellar nanoparticles were prepared from the amphiphilic polymers using a dialysis method as well as a direct dissolution method. Transmission electron microscope studies showed that the micellar nanoparticles existed in different morphologies, including spherical, star-like, and cuboid shapes. Pyrene as a model hydrophobic compound could be readily encapsulated in these polymeric nanoparticles, at loading levels of 1.0 and 0.8 mg/g for the two cholesteryl end-capped polymers, respectively. The temperature sensitivity and unusual morphology of these novel polymeric nanoparticles would make an interesting drug delivery system.

Synthesis and Dilute Solution Properties of Styrene−Isoprene Diblock Copolymers with Mesogenic−Zwitterionic End Groups

Diblock copolymers of styrene and isoprene with an ionic-liquid crystalline end group were synthesized by anionic polymerization high-vacuum techniques. Using (3-dimethylamino)propyllithium as initiator, the dimethylamino group was introduced at either chain end. This group was converted to a zwitterionic-liquid crystalline end group by reaction with 2-{6-[4-(4-methoxyphenylazo)phenoxy]hexyloxy}-2-oxo-1,3,2λ5-phospholane. The dilute solution properties of the diblock copolymers, containing ∼30 wt % PS, were studied in CCl4, a nonpolar equally good solvent for both the polymeric blocks, by means of static and dynamic light scattering and viscometry. Static light scattering experiments indicate that dimers are formed in most cases, except for copolymers with Mw ≤ 12 000. The estimated aggregation numbers were found to be lower than in the case of sulfozwitterionic end-capped copolymers. It seems that the lower polarity of the nitrogen−phosphorus zwitterion and the increased steric hindrance of the mesogenic...

Fluorinated functional materials possessing biological activities: gel formation of novel fluoroalkylated end-capped 2-acrylamido-2-methylpropanesulfonic acid polymers under non-crosslinked conditions

New fluoroalkylated end-capped 2-acrylamido-2-methylpropanesulfonic acid homopolymers were prepared by reaction of fluoroalkanoyl peroxides with 2-acrylamido-2-methylpropanesulfonic acid (AMPS). Similarly, fluoroalkylated end-capped copolymers were prepared by reaction of fluoroalkanoyl peroxides with AMPS and the comonomers such as trimethylvinylsilane and methyl methacrylate. These thus-obtained fluoroalkylated end-capped AMPS polymers were found to form gels not only in water but also in organic polar solvents such as methanol, ethanol,N,N-dimethylformamide and dimethyl sulfoxide under non-crosslinked conditions. On the other hand, AMPS polymer containing fluoroalkylene units {[-RF-(AMPS)q]p-} could cause no gelation under similar conditions. This suggests that fluoroalkylated end-capped AMPS polymers can cause gelation where strong aggregation of the end-capped fluoroalkyl segments is involved sterically in establishing the physical gel network in these media. Interestingly, these fluoroalkylated end-capped AMPS polymer hydrogels had a strong metal ion binding power. Moreover, it was demonstrated that these fluoroalkylated gelling polymers are potent and selective inhibitors of HIV-1 replication in cell culture. In addition, one of these gelling polymers was found to possess antibacterial activity againstStaphylococcus aureus. Therefore, these fluorinated gelling polymers are suggested to have high potential for new functional materials through their gelling ability and biological activity.