Synthesis and characterization of poly(2‐methacryloyloxyethyl phosphorylcholine) onto graphene oxide

The polyzwitterionic brushes comprised of poly(2‐methacryloyloxyethyl phosphorylcholine) (pMPC) segments, which are used for surface modification of polymers and biocompatible coatings, were investigated. In this work, reverse surface‐initiated atom transfer radical polymerization (RATRP) of zwitterionic 2‐methacryloyloxyethyl phosphorylcholine (MPC) is employed to tailor the functionality of graphene oxide (GeneO) in a well‐controlled manner and produce a series of well‐defined hemocompatible hybrids (termed as GeneO‐g‐pMPC). The complexes were characterized by FT‐IR, XRD, and Raman. Results show that MPC has been coordinated on the graphene oxide sheet. Thermal stability of the nanocomposites in comparison with the neat copolymer is revealed by thermogravimetric analysis and differential thermal analysis. Scanning electron microscopy and transmission electron microscope images of the nanoconposite displays pMPC chains were capable of existing on GeneO sheet by RATRP. The biocompatibility properties were measured by plasma recalcification profile tests, hemolysis test, and MTT assays, respectively. The results confirm that the pMPC grafting can substantially enhance the hemocompatibility of the GeneO particles, and the GeneO‐g‐pMPC hybrids can be used as biomaterials without causing any hemolysis. With the versatility of RATRP and the excellent hemocompatibility of zwitterionic polymer chains, the GeneO‐g‐pMPC nanoparticles with desirable blood properties can be readily tailored to cater to various biomedical applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Donor–acceptor (donor) polymers with differently conjugated side groups at the acceptor units for photovoltaics

Four new donor–acceptor (donor) [D–A(D)], PBDT‐PTQ, PBDT‐PTTQ, PBDT‐TQ, and PBDT‐TTQ, bearing the same backbone of alternative benzodithiophene (BDT) and quinoxaline units but with phenylene thienyl, phenylene di‐thienyl, thienyl and di‐thienyl groups (other donors), respectively, at the acceptor quinoxaline units, were designed and synthesized to investigate the impacts of the conjugated side chains at the acceptor units on the photovoltaic properties of polymers. The power conversion efficiencies (PCEs) of the polymer solar cells (PSCs) based on PBDT‐TQ:[6,6]‐phenyl‐C‐70‐butyric acid methyl ester (PC70BM) and PBDT‐PTQ:PC70BM reach to 4.39 and 3.58%, respectively, which are 43 and 17% higher, respectively, than that of a reported alkylphenyl substituted polymer with the same main chain. However, the PCEs based on PBDT‐TTQ and PBDT‐PTTQ, in which an additional thiophene is added at a side chain of PBDT‐TQ and PBDT‐PTQ, respectively, decline. The mechanism how the conjugated side chains affect the performance of the PSCs is also discussed. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Tuning the frontier molecular orbital energy levels of n‐type conjugated copolymers by using angular‐shaped naphthalene tetracarboxylic diimides,and their use in all‐polymer solar cells with high open‐circuit voltages

An angular‐shaped naphthalene tetracarboxylic diimide (NDI) was designed and synthesized as a new building block for n‐type conjugated polymers to tune their energy levels. Three n‐type copolymers incorporating this angular‐shaped NDI as the acceptor moiety were obtained by Stille coupling reactions and had number average molecular weights of 18.7–73.0 kDa. All‐polymer bulk‐heterojunction solar cells made from blends of these polymers with poly(3‐hexylthiophene) gave a power conversion efficiency up to 0.32% and exhibited an open‐circuit voltage (V_oc) up to 0.94 V due to their relative high‐lying lowest unoccupied molecular orbital energy levels. The high V_oc of 0.94 V is higher than that of solar cells based on linear‐shaped NDI‐containing polymers (<0.6 V). The results indicate that the angular‐shaped NDI is a promising building block for constructing nonfullerene polymer acceptors for solar cells with high open‐circuit voltages. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Solvent replacement to thermo‐responsive nanoparticles from long‐subchain hyperbranched PSt grafted with PNIPAM for encapsulation

Long‐subchain hyperbranched polystyrene (lsc‐hp PSt) with uniform subchain length was obtained through copper‐catalyzed azide‐alkyne cycloaddition click chemistry from seesaw macromonomer of PSt having one alkynyl group anchored at the chain centre and two azido group attached to both chain ends [alkynyl‐(PSt‐N₃)₂]. After precipitation fraction, different portions of lsc‐hp PSt having narrow overall molecular weight distribution were obtained for further grafting with alkynyl‐capped poly(N‐isopropylacrylamide) (alkynyl‐PNIPAM), which was obtained via single‐electron transfer living radical polymerization of NIPAM with propargyl 2‐bromoisobutyrate as the initiator and grafted onto the peripheral azido groups of lsc‐hp PSt via click chemistry. Thus, amphiphilic lsc‐hp PSt grafted with PNIPAM chains (lsc‐hp PSt‐g‐PNIPAM) was obtained and would have star‐like conformation in tetrahydrofuran (THF). By replacing THF with water, lsc‐hp PSt‐g‐PNIPAM was dissolved at molecular level in aqueous solution due to the hydrophilicity of PNIPAM and exhibited thermal induced shrinkage of PNIPAM arms. The water‐insoluble lsc‐hp PSt would collapse densely and could be served as a reservoir to absorb hydrophobic chemicals in aqueous solution. The influence of overall molecular weight of lsc‐hp PSt on the absorption of pyrene was studied. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis of highly monodisperse quantum dot‐loaded polymer beads by impregnation and precipitation techniques

A novel approach to the synthesis of highly monodisperse quantum dot‐loaded polymer beads by combining impregnation and precipitation techniques was reported. The monodisperse poly(glycidyl methacrylate) (PGMA) beads were first synthesized by dispersion polymerization. Then, the PGMA beads were chemically modified to generate carboxyl groups, and impregnation of cadmium ions (Cd²⁺) inside the beads. Subsequently, the cadmium ions were reacted with thioacetamide to form cadmium sulfide (CdS) quantum dots within the polymer beads. The morphology, structure, and properties of CdS quantum dot‐loaded polymer beads were studied by field emission scanning electron microscope (SEM), transmission electron microscope, fluorescence spectrophotometer, fluorescence microscope, Fourier transform infrared spectroscopy, powder X‐ray diffraction, and thermogravimetric analysis. The results indicated that the CdS quantum dot‐loaded polymer beads had an average size of 1.4 μm, and were highly monodisperse. More interestingly, the CdS quantum dots distributed evenly within the polymer beads, which provide very strong fluorescence intensity. The existence of carboxyl groups on the quantum dot‐loaded polymer beads was measured quantitatively, and was found to be 0.2 mmol/g. These CdS quantum dot‐loaded polymer beads involving functional carboxyl groups would have potential applications in biological immunoassay and photoelectronic fields. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis and properties of amphoteric copolymer of 5‐vinyltetrazole and vinylbenzyl phosphonic acid

Amphoteric polymers have been studied for various applications such as separation of low molecular weight organic molecules from inorganic salt mixtures, selective ion transport, drug delivery through membranes of biological interest, separation of ionic drugs and proteins, and separation of alcohol and water. Typical amphoteric polymers consist of weak base and weak acid groups. In present study, the copolymerization of 5‐vinyltetrazole (VT) and diisopropyl‐p‐vinylbenzyl phosphate (DIPVBP) via free radical polymerization is studied. The reactivity ratio of VT and DIPVBP, which is calculated from Kelen‐Tudos plot, is 0.251 and 0.345, respectively. The amphoteric copolymer of VT and diisopropyl‐p‐vinylbenzyl phosphonic acid (poly(VT‐co‐VBPA)) is obtained from hydrolysis of the copolymer of VT and DIPVBP (poly(VT‐co‐DIPVBP)). Poly(VT‐co‐VBPA) is thermally stable under 190 °C. The anhydrous proton conductivity of amphoteric poly(VT‐co‐VBPA) can reach 1.54 × 10^‐4 S cm^?1 at 170 °C with an activation energy of 114.7 kJ mol^?1. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3486–3493     

Quantification of ATRP initiator density on polymer latex particles by fluorescence labeling technique using copper‐catalyzed azide‐alkyne cycloaddition

We developed a novel fluorescence labeling technique for quantification of surface densities of atom transfer radical polymerization (ATRP) initiators on polymer particles. The cationic P(St‐CPEM‐C₄DMAEMA) and anionic P(St‐CPEM) polymer latex particles carrying ATRP‐initiating chlorine groups were prepared by emulsifier‐free emulsion polymerization of styrene (St), 2‐(2‐chloropropionyloxy)ethyl methacrylate (CPEM), and N‐n‐butyl‐N,N‐dimethyl‐N‐(2‐methacryloyloxy)ethylammonium bromide (C₄DMAEMA). ATRP initiators on the surface of polymer particles were converted into azide groups by sodium azide, followed by fluorescent labeling with 5‐(N,N‐dimethylamino)‐N′‐(prop‐2‐yn‐1‐yl)naphthalene‐1‐sulfonamide (Dansyl‐alkyne) by copper‐catalyzed azide‐alkyne cycloaddition (CuAAC). The reaction time required for both azidation of ATRP‐initiating groups and successive fluorescence labeling of azide groups with Dansyl‐alkyne by CuAAC were investigated in detail by FTIR and fluorescence spectral measurement, respectively. The ATRP initiator densities on the cationic P(St‐CPEM‐C₄DMAEMA) and anionic P(St‐CPEM) particle surfaces were estimated to be 0.21 and 0.15 molecules nm^?2, respectively, which gave close agreement with values previously determined by a conductometric titration method. The fluorescence labeling through click chemistry proposed herein is a versatile technique to quantify the surface ATRP initiator density both on anionic and cationic polymer particles. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4042–4051     

Time‐resolved spectroscopy study of donor–acceptor‐type copolymers in a monodisperse system: The effect of ratio between the acceptor and the donor

The photoexcitation processes of two donor–acceptor‐type copolymers PCFBT with different ratios between the donor and the acceptor ( PCFBT_0.5 and PCFBT_0.1 ) in the solution system are systematically studied. If the number of the donor is equal to that of the acceptor in one repeat unit (such as PCFBT_0.5 ), intrachain charge transfer (ICT) can occur and participate in the relaxation of the excited state after photoexcitation. When the number of donors is much larger than that of acceptors (such as PCFBT_0.1 ) in one repeat unit, the ICT character can disappear, and the localized exciton decay process is dominant in the relaxation of the copolymer, which also involves an excitation intensity‐independent vibrational thermal relaxation process at the initial time. The results further the understanding of the basic structure‐property relationship. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 992–996     

Enhanced mobility and environmental stability in all organic field‐effect transistors: The role of high dipole moment solvent

Low‐operating voltage, high mobility, and stable organic field‐effect transistors (OFETs) using polymeric dielectrics such as pristine poly(4‐vinyl phenol) (PVP) and poly(methyl methacrylate) (PMMA), dissolved in solvents of high dipole moment, have been achieved. High dipole moment solvents such as propylene carbonate and dimethyl sulfoxide used for dissolving the polymer dielectric enhance the charge carrier mobilities by three orders of magnitude in pentacene OFETs compared with low dipole moment solvents. Fast switching circuits with patterned gate PVP‐based pentacene OFETs demonstrated a switching frequency of 75 kHz at input voltages of |5 V|. The frequency response of the OFETs is attributed to a high degree of dipolar‐order in dielectric films obtained from high‐polarity solvents and the resulting energetically ordered landscape for transport. Remarkably, these pentacene‐based OFETs exhibited high stability under bias stress and in air with negligible shifts in the threshold voltage. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1533–1542