Enzymatic Polymerization towards Biodegradable Polyester Nanoparticles

The direct enzymatic polymerization of miniemulsions consisting of lactone nanodroplets represents a new and convenient pathway for the synthesis of biodegradable polymer nanoparticles, where the chemical composition and molecular weight can be varied in a certain range. Oligoesters completely end‐capped with an alkene or diene group can also be prepared by this technique. These building blocks extend polyester application as they allow to impart improved biodegradability to both siloxane and resin chemistry.

TEM image of the polyester particles obtained by enzymatic polymerization in miniemulsion.     

Novel in situ NMR Measurement System for Evaluating Molecular Mobility during Drawing from Highly Entangled Polyethylene Melts

A novel in situ measurement system for evaluating molecular mobility during uniaxial drawing of polymeric materials was established by introducing drawing and stress‐detecting devices into a ¹H pulse nuclear magnetic resonance spectrometer. In this study, we analyze the changes in molecular motion of amorphous chains during melt‐drawing of ultra‐high molecular weight polyethylenes (UHMW‐PEs) with different molecular weight distributions. In the initial stage of drawing, a three‐component resolution was possible for the relaxation decay curve, which includes “rigid”, “intermediate”, and “mobile” amorphous components. The quality and quantity changes in these components demonstrated that this intermediate amorphous component could be regarded as the index of the change in molecular entanglement characteristics during the orientation of PE chains.

     

Facile and Controlled Fabrication of Functional Gold Nanoparticle‐coated Polystyrene Composite Particle

Gold nanoparticles‐coated polystyrene (AuNPs‐coated PS) composite particles with raspberry‐like morphology are successfully prepared with the aid of a unique thermodynamically driving effect. It is of considerable interest that the AuNPs generate and self‐assemble with raw, ordinary PS microspheres that preexist in the oxidation–reduction systems. The synthesized AuNPs‐coated PS composite particles have been extensively characterized using scanning electron microscope, transmission electron microscope, and UV–Vis‐NIR spectroscopy. The results indicate that the morphology of the resultant composite particles is governed by simply changing the amount and type of reductants and the concentration of PS microspheres. The AuNPs‐coated PS composite particles also exhibit the good surface‐enhanced Raman scattering and catalytic performances.

     

Initiator‐Grafted Silica Particles for Controlled Free Radical Polymerization: Influence of the Initiator Structure on the Grafting Density

A series of organic‐inorganic hybrid particles were synthesized by a self‐assembled layer of different initiators, immobilized on silica particles and used for controlled radical polymerization. We use three different initiator systems for atom‐transfer radical polymerization (ATRP), unimolecular nitroxide mediated polymerization (NMP), and bimolecular NMP, for the development of the hybrid inorganic/organic particles. After preliminary qualitative characterization by X‐ray spectroscopy (XPS) and Fourier‐transformed infrared (FT‐IR) measurements, the hybrid nanoparticles were studied by thermogravimetric analysis (TGA) to determine and discuss the initiator graft density in terms of steric hindrance.

The coupling agents employed for the various approaches used here: a) NMP1‐bimolecular system, b) NMP2‐unimolecular system, and c) ATRP.     

Aggregation Behavior of Homo‐PS/PS‐b‐P2VP Blends at the Air/Water Interface

The mixed Langmuir monolayers and Langmuir–Blodgett (LB) films of homo‐polystyrene (h‐PS) and the diblock copolymer polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) have been characterized by the Langmuir monolayer technique and tapping mode atomic force microscopy (AFM), respectively. When the content of h‐PS is below 80 wt.‐%, the mixed LB films of h‐PS/PS‐b‐P2VP mainly exhibit isolated circular nanoaggregates. With a further increase of the h‐PS content (80–95%), however, highly uniform and stable necklace‐network structures are observed in the mixed LB films.

     

New Strategy Targeting Well‐Defined Polymethylene‐block‐Polystyrene Copolymers: The Combination of Living Polymerization of Ylides and Atom Transfer Radical Polymerization

Well‐defined polymethylene‐block‐polystyrene (PM‐b‐PS) diblock copolymers were synthesized via a combination of living polymerization of ylides and atom transfer radical polymerization (ATRP) of styrene. A series of hydroxyl‐terminated polymethylenes (PM‐OHs) with different molecular weight and narrow molecular weight distribution were prepared using living polymerization of ylides following efficient oxidation in a quantitive functionality. Then, the macroinitiators (PM‐MIs ( = 1 900–15 000; PDI = 1.12–1.23)) transformed from PM‐OHs in ≈ 100% conversion initiated ATRPs of styrene to construct PM‐b‐PS copolymers. The GPC traces indicated the successful extension of PS segment ( of PM‐b‐PS = 5 000–41 800; PDI = 1.08–1.23). Such copolymers were characterized by ¹H NMR and DSC.

     

Shape of Micelles Formed From Strongly Adsorbed Grafted Polymers in Poor Solvents

Summary: We consider the shape of strongly adsorbed polymer chains in poor solvents. Using both SCF theory and Monte Carlo simulations, we find these chains undergo an instability which is driven, surprisingly, by polymer entropy. This instability occurs above some critical grafting separation and the intermediate segregation regime. An analytical calculation also suggests that this instability occurs for strongly adsorbed polymer chains. We proceed to study multi‐chain systems and observe a number of novel morphological structures including circular polymer droplets, lamellae and a polymer layer with a solvent‐filled hole.

Shape of strongly adsorbed multi‐chain polymer globules.     

Fabrication of Superhydrophobic and Superoleophilic Polystyrene Surfaces by a Facile One‐Step Method

A facile one‐step method has been developed to prepare both superhydrophobic and superoleophilic surfaces of polystyrene (PS) without any chemical modification. A rough film consisting of micro‐bead and nano‐fiber mixed structures is formed by spraying a PS solution onto a large area and any type of substrate. The mixed structures with such unique wettability properties can be used in oil/water separation and as oil sorbents.

     

Structured Hybrid Nanoparticles via Surface‐Initiated ATRP of Methyl Methacrylate from Ordered Mesoporous Silica

Structured hybrid nanoparticles were synthesized via surface‐initiated atom transfer radical polymerization of MMA from ordered mesoporous silica (OMS) nanoparticles with various morphologies. The design of the OMS particles was adjusted to target either spherical core‐shell or cylindrical morphologies with a mean diameter below 400 nm. The polymer growth via ATRP from the silica surface was well‐controlled as demonstrated by the macromolecular characteristics of the grafted chains. Original hybrid multilayered nanoparticles composed of either a dense silica core or hollow core; an inner OMS shell showing radial orientation of the mesopores and an outer PMMA shell with controlled thickness were successfully prepared.

     

Enhancement of Biomolecular Recognition of DTIC Based on Functional Monodisperse Polystyrene Spheres

Summary: Monodisperse carboxy polystyrene (PS) spheres were synthesized and utilized as an interface to increase the detection sensitivity of some biomolecules. The binding behavior of dacarbazine (DTIC), an anticancer drug, with DNA bases in the absence and presence of the PS spheres was investigated. The results indicated a remarkable effect of PS on the binding behavior of DTIC to DNA bases and significantly enhanced detection sensitivity for the relative biomolecular recognition.

Electrochemical detection of DTIC on a GCE surface in the absence and presence of polystyrene spheres.     

Mechanism of Conjugated Polymer Organization on SWNT Surfaces

Summary: The interactions between poly{(2,6‐pyridinylenevinylene)‐co‐[(2,5‐dioctyloxy‐p‐phenylene)vinylene]} (PPyPV) and SWNTs have been investigated using UV‐Vis absorption spectroscopy. The SWNTs promoted polymer organization. PPyPV is a Lewis base and can be doped by strong and weak Lewis acids. The basicity strength of the PPyPV depended on the polymer interchain interactions, which were enhanced by the presence of SWNTs. As the SWNT concentration was increased, an increment in the K_b of PPyPV was observed.

     

Enhancement of Photostability in Blue‐Light‐Emitting Polymers Doped with Gold Nanoparticles

A dramatic increase in the photostability of a blue‐light‐emitting polymer, poly(9,9‐dioctylfluorene), was achieved by the addition of 5–10 nm gold nanoparticles. The optical absorption band of the gold nanoparticles was tuned to resonate the triplet exciton ground state bandgap energy of the polymer. Photo‐oxidation rate of poly(9,9‐dioctylfluorene) was effectively reduced by doping the polymer with very small amounts (≈10⁻⁶–10⁻⁵ volume fraction) of the gold nanoparticles.

Retarded photo‐oxidation in PDOF nanocomposite films with various doped gold nanoparticles.     

Polystyrene Microspheres and Nanospheres Produced by Electrospray

Summary: Polystyrene (PS) micro‐ and nanospheres with uniform dimensions and smooth surfaces have been produced by electrospray. The effect of PS molecular weight on beads morphology and the fundamental role of concentration have been investigated. Moreover, a new apparatus was designed to collect the polymer spheres during the process and to prevent the coalescence among the spheres.

PS micro‐ and nanospheres produced by electrospray     

Combinatorial Methods and Informatics Provide Insight into Physical Properties and Structure Relationships during IPN Formation

Combinatorial methods and informatics are applied to the study of complex property‐structure‐processing relationships during interpenetrating polymer network formation in an epoxy/acrylate system. Principal component analysis of a dataset that covers different compositions and process sequences successfully identifies the most unique samples as well as relationships between material properties. The relationships between material properties can be exploited in future investigations by allowing high throughput screening and as a guide for engineering materials. The use of combinatorial methods, high throughput screening, and informatics will lead to accelerated material design.

     

Selective and Sequential Re‐Assembly of Patterned Block Copolymer Thin Film for Fabricating Polymeric,Inorganic, and Their Composite Nanostructured Arrays

We report that the nanostructures of poly(styrene‐block‐4‐vinylpyridine) block copolymer (PS‐b‐P4VP) thin film on a wafer substrate can be re‐assembled by sequential vapor treatment using selected solvents. Metal or other inorganic nanoparticles that were randomly pre‐loaded inside or on the surface of PS‐b‐P4VP thin film could be pulled to the rim of PS and P4VP along with the movements of PS and P4VP blocks during the treatment. As a result, the patterned polymeric or inorganic/polymer composite nanoisland and nanoring arrays were fabricated.

     

Selectivity in Polystyryllithium Chain Coupling Induced by Monobromoalkane Additives

Summary: The end coupling of living PSLi chains in hydrocarbon media by the addition of monoalkylbromides has been examined. A very selective PS–PS coupling reaction was obtained with neo‐pentylbromide (94%) at a ratio of PSLi/alkylbromide equal to 1 while the secondary and tertiary bromine derivatives yield only very limited coupling. The coupling mechanism is likely to involve a lithium‐bromine interchange at the PS chain end, generating polystyryl‐bromide which then reacts selectively with the remaining polystyryllithium chains.

     

Hairy PEO‐Silica Nanoparticles through Surface‐Initiated Polymerization of Ethylene Oxide

Summary: The grafting of poly(ethylene oxide) (PEO) onto silica nanoparticles was performed in situ by the ring‐opening polymerization of the oxirane monomer initiated from the mineral surface using aluminium isopropoxide as an initiator/heterogeneous catalyst. Alcohol groups were first introduced onto silica by reacting the surfacic silanols with prehydrolyzed 3‐glycidoxypropyl trimethoxysilane. The alcohol‐grafted silica played the role of a coinitiator/chain‐transfer agent in the polymerization reaction and enabled the formation of irreversibly bonded polymer chains. Silica nanoparticles containing up to 40 wt.‐% of a hairy layer of grafted PEO chains were successfully produced by this technique.

The grafting of poly(ethylene oxide) (PEO) onto silica nanoparticles by in‐situ ring‐opening polymerization of the oxirane monomer.     

Tandem RAFT Polymerization and Click Chemistry: An Efficient Approach to Surface Modification

PS grafted silica nanoparticles have been prepared by a tandem process that simultaneously employs RAFT polymerization and click chemistry. In a single pot procedure, azide‐modified silica, an alkyne functionalized RAFT agent and styrene are combined to produce the desired product. As deduced by thermal gravimetric and elemental analysis, the grafting density of PS on the silica in the tandem process is intermediate between analogous “grafting to” and “grafting from” techniques for preparing PS brushes on silica. Relative rates of RAFT polymerization and click reaction can be altered to control grafting density.

     

Synthesis of POSS‐Functionalized Polyisobutylene via Direct Initiation

POSS‐functionalized polyisobutylenes (PIBs) were synthesized by carbocationic polymerization using an epoxy‐POSS/TiCl₄ initiating system in hexane/methyl chloride (60:40 v/v) solvent mixture at −80 °C. ¹H NMR spectroscopy verified the incorporation of one epoxy‐POSS per polymer chain. Light scattering and TEM analysis demonstrated the formation of 50–100 nm sized aggregates and micron‐sized clusters.