Surface Functionalization of Electrospun Poly(butylene terephthalate) Fibers by Surface‐Initiated Radical Polymerization

A facile surface modification procedure for electrospun poly(butylene terephthalate) (PBT) fibers by surface‐initiated atom transfer radical polymerization (SI‐ATRP) is reported. Initiators are introduced through aminolysis and chemical vapor adsorption. SI‐ATRP is subsequently carried out to prepare a polymer‐grafted layer at the PBT fiber surface without altering the fiber geometry. After modification with a zwitterionic poly(sulfobetaine), poly(3‐(N‐2‐methacryloyloxyethyl‐N,N‐dimethyl) ammonatopropanesulfonate), the surface is superhydrophilic. The surface properties are thermally stable due to the high melting temperature of the PBT crystallites and are maintained for a prolonged period.

     

Surface Functionalization of Polypropylene Film via UV‐Induced Photografting of N‐Vinylpyrrolidone/Maleic Anhydride Binary Monomers

Summary: A polymeric surface with desirable wettability and versatile reactivity was facilely fabricated by UV‐induced surface photografting of N‐vinylpyrrolidone (NVP)/maleic anhydride (MAn) binary monomers, with polypropylene (PP) film as a model substrate. It was found that the photografting process of NVP/MAn is much faster than that of individual NVP or MAn; both the grafting efficiency (E_g) and grafting yield (Y_g) reach a maximum at around 1:1 molar feed ratio of NVP to MAn. These results indicate that the electron donor‐acceptor monomers can synergistically promote surface photografting by a known charge‐transfer‐complex (CTC) mechanism. Moreover, the grafted NVP and MAn units cooperatively enhance the surface hydrophilicity; the water contact angle of the modified surface drastically decreases from the original 99.4° to less than 36° within 30 s of irradiation time. Subsequently, we demonstrated that the surface‐grafted succinic anhydride groups could readily perform a variety of organic reactions such as acidic/alkaline hydrolysis and esterification, which is expected to facilitate further surface functionalizations. Besides, the complexing reaction of surface pyrrolidone groups with iodine was investigated, which was followed by UV‐vis spectroscopy. The antimicrobial activity against Escherichia coli, Staphylococcus aureus and Candida albicans show that this unique iodine‐complexated surface has desirable antimicrobial property.

Surface photografting of NVP/MAn and post reactions of surface‐grafted anhydride groups and pyrrolidone groups.     

One‐Step Spontaneous Formation of Dual Wrinkling on Uniform‐Sized Microparticles Induced by Surface

This study demonstrates the wrinkle formation on biodegradable polymer‐blend microparticles prepared from an emulsion‐solvent evaporation method and investigates the formed patterns. A labyrinthine pattern is obtained for uniform‐sized microparticles, owing to the considerable size reduction during solvent evaporation. Changing the radius of the organic droplets dispersed in the aqueous solution switches the wrinkle pattern from labyrinth to bi‐phase. For the first time, the dual wrinkling structure is prepared; both labyrinthine texture and hexagonal dimple structures are spontaneously formed on the same microparticle surface. The former pattern is due to the surface instability from blends of hydrophobic polymer and amphiphilic block copolymer, while the latter is due to a mechanism similar that of the breath figure formed with organic phase change materials during solidification of microparticles. The general applicability of this approach is demonstrated on other pairs of polymer blends.     

Controlled Thiol‐Ene Functionalization of Polyferrocenylsilane‐block‐Polyvinylsiloxane Copolymers

A general route for the controlled functionalization of polyferrocenylsilane‐block‐polyvinylsiloxane copolymers, which should be transferable to other silicone‐based materials, is developed utilizing the photoinitiated thiol‐ene reaction. Poly(ferrocenyldimethylsilane)₅₄‐block‐poly(methylvinylsiloxane)₅₁₀ (PFDMS₅₄‐b‐PMVS₅₁₀) is synthesized via sequential living anionic polymerization and quantitatively functionalized with a range of thiols, with the aim of tuning the solubility of the resulting materials for self‐assembly studies or incorporating more complex functionality for subsequent applications. When functionalization is attempted using a deficit of thiol, the photoinitiator 2,2‐dimethoxy‐2‐phenylacetophenone, used to accelerate the radical reaction, is found to cause significant cross‐linking of the polysiloxane chain. Reproducible percentage thiol‐ene functionalization of the polysiloxane block can be achieved by the use of PFDMS₅₃‐b‐PMVS₅₈/PDMS₄₄₄ (PDMS = polydimethylsiloxane), prepared by the copolymerization of cyclic siloxane monomers, [Me(CH?CH₂)SiO]₃ and [Me₂SiO]₃, to tune the vinyl group incorporation pre‐functionalization.

     

Synthesis of Diene‐Functionalized Macromonomers via Functionalization with Hexa‐1,3,5‐triene

The reaction of poly(styryl)lithium (PSLi) with hexa‐1,3,5‐triene (HXT) was studied as a route to diene‐functionalized macromonomers. When PSLi was reacted with 1.5 molar equivalents of HXT for 2.5 h at ?10 °C in toluene, it was found that the diene‐functionalized macromonomer was obtained in high yield; however, oligomerization of the HXT was observed by matrix‐assisted laser absorption ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS). Oligomerization was eliminated by running the reaction with only 1.2 molar equivalents of HXT to PSLi and allowing the reaction to run for 15 min at ?10 °C in toluene. The resulting polymer exhibited high diene chain‐end functionality and no oligomerization was observed by MALDI‐TOF MS. ¹³C NMR spectroscopy and the attached‐proton test (APT), along with calculated chemical shifts, showed the presence of both the 1,2‐ and 1,4‐addition chain‐end structures. Further analysis by the reaction of the functional polymer with maleic anhydride indicated that 18 wt.‐% of the product was unreactive, either because of a 1,4‐addition chain‐end structure or a nonfunctional polymer. The structure of the maleic anhydride‐modified polymer was determined by MALDI‐TOF MS and ¹³C NMR spectroscopy. Preliminary work on the reactivity of the diene‐functionalized macromonomers was performed by the addition of a large excess of PSLi to a solution of macromonomer followed by characterization by size‐exclusion chromatography (SEC).

The formation of hexa‐1,3,5‐triene‐functionalized polystyrenes and their reaction with maleic anhydride.     

Photosulfonation of Low‐Density Polyethylene Films

Summary: Photosulfonation of low‐density polyethylene (LDPE) films by UV irradiation in the presence of gaseous sulfur dioxide (SO₂) and oxygen (O₂) was studied by attenuated total reflectance (ATR) infrared spectroscopy and X‐ray photoelectron spectroscopy (XPS). The ATR and XPS analysis and chemical modification of UV‐irradiated LDPE films demonstrated the generation of C?C double bonds and sultones in the reaction. These results indicated the possibility that sulfur trioxide (SO₃) was produced during the photosulfonation. New pathways for the SO₃ reaction with LDPE films, resulting in the formation of sulfonic acid groups, were proposed.

Overview of the mechanism proposed for the photosulfonation of low‐density polyethylene by SO₃ (produced upon UV‐irradiation of gaseous SO₂ and O₂).     

Thickening Processes of Lamellar Crystal Monolayers of a Low‐Molecular‐Weight PEO Fraction on a Solid Surface

Using hot‐stage atomic force microscopy, the thickening processes of monolayer crystals of PEO ( = 5 000 g · mol^?1 and = 1.008) from one‐folded (FC1) to extended‐chain (EC) lamellae are experimentally monitored at three temperatures: 50, 52, and 58 °C. At 50 °C some small areas in large FC1 crystals spontaneously thicken into EC crystals. At 52 °C the spontaneously thickened area further expands so as to inductively thicken the entire FC1 lamella into EC lamella. At 58 °C EC crystals first force the adjacent FC1 crystals to melt and then absorb the melted molecules to grow laterally into large EC lamellae till all FC1 lamellae vanish. The three thickening steps express the main thickening process of lamellar crystals from a metastable state to another metastable (or equilibrium) state. The possible mechanisms are discussed in the text.

     

Azido Platform Surfaces for Post‐Functionalization with Aromatic Groups Using the Huisgen Reaction to Obtain High Water Adhesion

In this work, platform post‐modifications using the Huisgen reaction are reported. Various platform surfaces are developed and post‐functionalized with aryl side chains. The development of different conducting polymer platforms allows the study of the impact of the starting surface on the modified surface properties. Also in this work, different aryl side chains are investigated (with one, two, three, or four aromatic rings) in order to investigate the impact of the side chain on the final surface feature. All the combinations (surface vs aryl side chain) are investigated for their wettability. Highly hydrophobic features are observed with apparent contact angles θ higher than 140° and extremely high water adhesion. Surface morphologies are also investigated and important changes in morphology are observed after surface post‐functionalization. The reported strategy to develop various highly hydrophobic surfaces with high water adhesion feature can be a powerful strategy for water trap elaboration.

     

Polylactide‐Based Nanoparticles with Tailor‐Made Functionalization

Biocompatible polymer nanoparticles are of high interest in chemical, biological, and medical research as potential drug delivery systems. These nanoparticles must be nontoxic and metabolizable. Poly(lactic acid) (PLA) meets these requirements and therefore is widely used for biomedical applications. The miniemulsion/solvent evaporation procedure is a very efficient approach to produce PLA nanoparticles with controlled size and morphology using preformed polymer. In this paper, the synthesis of PLA‐based nanoparticles functionalized with either carboxyl groups or fluorescent molecules is presented. Both functionalities are covalently attached to the particle, thus any physical desorption and leakage of the dye upon storage or experiments performed under physiological conditions, for example during uptake by living cells, can be avoided. The fluorescence properties and stability of the obtained nanoparticles in aqueous solutions with different ionic strength are studied by fluorescence correlation spectroscopy and dynamic light scattering.

     

Photoreactive Functionalization of Poly(ethylene terephthalate) Track‐Etched Pore Surfaces with “Smart” Polymer Systems

Summary: Poly(ethylene terephthalate) (PET) track‐etched membranes with a pore diameter of ca. 700 nm, optionally surface‐functionalized to create a “carboxyl” or “amino” surface, were used for heterogeneous graft copolymerizations. Grafted poly(acrylic acid) acted as a pH responsive, “smart” polymer. To evaluate the surface‐specific initiation of graft copolymerizations unmodified and primary functionalized membranes were systematically combined with three differently charged benzophenone derivatives as photoinitiators, which were adsorbed on the PET surface prior to the reaction. The functionalized membranes thus obtained were characterized for chemical structure and permeability as a function of pH. The pore structure with a narrow size distribution and the resulting high sensitivity of the membrane permeability to the grafting functionalizations made the track‐etched PET membranes a very useful tool for analyzing structure and function of responsive grafted polymer layers. The primary functionalization of the base polymer with a molecular layer of a multifunctional alkylamine (“amino” surface) enhanced the efficiency of the subsequent graft copolymerization via photoinitiated hydrogen abstraction considerably because a high density of well accessible reactive groups had been introduced. The preadsorption of the photoinitiator on the base polymer surface was significantly improved by ionic interactions between the respective functional groups of the surface and the photoinitiator. Such a photoinitiator preadsorption, especially when combined with a reactive layer from the primary functionalization, enabled a very efficient and surface selective functionalization because a better control of grafting density and a reduction of photoinitiated side reactions along with a more efficient use of the photoinitiator were possible.

Water permeabilities (pH 2 and pH 7) of unmodified and functionalized PET membranes for identification of optimal synthesis and evaluation conditions.     

Functionalization of Shortened Single‐Walled Carbon Nanotubes with Poly(p‐dioxanone) by “Grafting‐From” Approach

Summary: It has been a real challenge to form carbon nanotube (CNT)/polymer composites where CNTs are well‐dispersed in the polymer matrix and the interactions between CNTs and polymers are effectively strong. In this paper, we applied surface‐initiated, ring‐opening polymerization (SI‐ROP) of p‐dioxanone (PDX) to shortened single‐walled carbon nanotubes (s‐SWCNTs) and successfully formed s‐SWCNT/PPDX composites (see Figure). Due to intimate interactions between s‐SWCNTs and PPDX, we observed dramatic changes in PPDX properties upon the formation of the composites: 10%‐weight‐loss‐temperature of PPDX increased by 20 °C (measured by thermogravimetric analysis) and the patterns of T_g and T_m were greatly altered. We did not observe any noticeable peaks from the composite up to 120 °C in differential scanning calorimetry (DSC), while DSC data of PPDX itself showed T_g and T_m at ?13.4 and 103 °C respectively.

Schematic representation of the procedure for formation of s‐SWCNT/PPDX composites.     

Synthesis and Characterization of Surface Functional Polymer Nanoparticles by a Bottom‐Up Approach from Tailor‐Made Amphiphilic Block Copolymers

Core‐crosslinked nanoparticles presenting secondary amine functional groups in the hydrophilic shell are synthesized by a bottom‐up approach. The route utilizes polymerization of 2‐oxazolines to prepare tailor‐made block copolymers with a primary or secondary amine end group in the hydrophilic block and alkynyl moieties in the hydrophobic part of the polymer. Upon solubilization in the aqueous media, these block copolymers form micelles that are photocrosslinked by a radical polymerization process to afford two types of core‐crosslinked nanoparticles, either with secondary amines, NP1, or primary amines, NP2, on the surface. The dimensions and stability of the core‐crosslinked nanoparticles are characterized by dynamic light scattering and fluorescence spectroscopy. The availability and reactivity of the amine groups in the hydrophilic shell are demonstrated by reaction with different aromatic model compounds resulting in a degree of surface functionalization of 4–47% for NP1 nanoparticles with secondary amino groups and a 20–95% degree of surface functionalization for NP2 with primary amine groups, as determined by UV–vis spectroscopy.

     

One‐Pot Formation of ZnO‐graft‐Poly(d,l‐Lactide) Hybrid Systems via Microwave‐Assisted Polymerization of d,l‐Lactide in the Presence of ZnO Nanoparticles

The surface modification of inorganic nanoparticles by polymer grafting is generally required for obtaining well dispersed polymer‐based (bio)nanocomposites, and the in situ polymerization of corresponding monomers is considered to be a versatile approach to this purpose. In this work, the microwave‐assisted ring‐opening polymerization of d ,l ‐lactide in the presence of zinc oxide (ZnO) nanoparticles affords an original and straightforward method for generating ZnO‐graft‐poly(d ,l ‐lactide) hybrid systems. The influence of ZnO particle size and concentration on polymerization kinetics and molar masses of free poly(d ,l ‐lactide) (PLA) chains is analyzed. Several physico‐chemical techniques, including proton nuclear magnetic resonance (¹H NMR), Fourier‐transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and thermogravimetric analysis, are used to characterize intermediates and/or reaction products. Taking into account the kinetic and spectroscopic investigation, competitive chemical pathways based on grafting from and grafting onto reactions are proposed for the one‐pot formation of PLA‐grafted ZnO nanoparticles.

     

Selectable and Releasable Noncovalent Functionalization of Semiconducting SWCNTs by Biethynyl‐2,5‐bis(dodecoxy)benzene Unit‐Containing Conjugated Copolymers

A rigid structural unit diethynyl‐2,5‐bis(dodecoxy)benzene (DDB) is proposed to functionalize single‐walled carbon nanotubes (SWCNTs) with the assistance of pyrimidine ring. The effectiveness of conjugated polymer extraction of semiconducting SWCNTs is demonstrated by absorption and Raman spectroscopy. The protonated pyrimidine ring by the trifluoroacetic acid is used to reduce the interaction between polymer and SWCNTs that the bound wrapping polymer can be removed from the sorted SWCNTs, and molecular dynamics simulations of the binding ability of DDB and pyrimidine units to SWCNTs are conducted to further illustrate the strong binding ability of DDB units to SWCNTs. Therefore, this work provides an effective structural and theoretical reference for polymer separation or modification of semiconducting SWCNTs.     

Synergist Immobilization Method for Photo‐Grafting: Factors Affecting Surface Selectivity

The surface‐selectivity of photo‐grafting has been used as a crucial parameter to evaluate the ‘grafting‐from’ efficiency of the synergist immobilization method developed in our recent work. The factors that affect surface‐selectivity of photo‐grafting have been further investigated. It was shown that the competition of solvent with the membrane surface towards the generation of starter radicals led to a decrease in the degree of grafting and surface‐selectivity of photo‐grafting. High UV intensity made the functionalization mechanism more complicated, due to the generation of a new type of starter radical at the membrane surface with immobilized synergist in the absence of BP and because it could lead to cross‐linking in the grafted layer. An appropriately low photo‐initiator concentration was also required in order to achieve the ideal surface‐selectivity of photo‐grafting. In addition, this method has been successfully applied to the track‐etched PET membranes. Pore size distributions as well as ethanol and water permeability of the membranes were used to retrieve information about the effective thickness of the grafted polymer layers.

     

Nitro‐Group Functionalization of Dopamine and its Contribution to the Viscoelastic Properties of Catechol‐Containing Nanocomposite Hydrogels

Linear polyacrylamide (PAAm) is modified with dopamine or nitrodopamine (PAAm‐D and PAAm‐ND, respectively) to evaluate the effect of nitro‐group modification on the interfacial binding properties of polymer‐bound catechol. Nanocomposite hydrogels are prepared by mixing PAAm‐based polymers with Laponite and the viscoelastic properties of these materials are determined using oscillatory rheometry. The incorporation of a small amount of catechol (≈0.1 wt% in swollen hydrogel) drastically increases the shear moduli by 1–2 orders of magnitude over those of the catechol‐free control. Additionally, PAAm‐ND exhibits higher shear moduli values than PAAm‐D across the whole pH range tested (pH 3.0–9.0). Based on the calculated effective crosslinking density, effective functionality, and molecular weight between crosslinks, nitro‐group functionalization of dopamine results in a polymer network with increased crosslinking density and crosslinking points with higher functionality. Nitro‐functionalization enhances the interfacial binding property of dopamine and increases its resistant to oxidation, which results in nanocomposite hydrogels with enhanced stiffness and a viscous dissipation property.

     

Controlled Grafting‐From of Polystyrene on Polybutadiene: Mechanism and Spectroscopic Evidence of the Functionalization of Polybutadiene with 4‐Oxo‐TEMPO

Polybutadienes functionalized with nitroxide (multifunctional macroalkoxyamines) were synthesized by heating PB in the presence of a nitroxide radical (N) and a radical initiator (I). Another functional PB was prepared by using only nitroxide. These functionalized polymers were characterized by FT‐IR, GPC, and NMR and as a result it was possible to elucidate the resulting structure of the macroalkoxyamines, to propose likely functionalization mechanisms, and to estimate functionalization characteristics. One of these polymers was heated in the presence of styrene to obtain PB grafted with polystyrene, which was characterized in detail in order to investigate its structure and level of grafting control.

     

Preparation of Head‐to‐Tail Regioregular 6‐(1‐Alkenyl)‐Functionalized Poly(pyridine‐2,5‐diyl) and its Post‐Functionalization via Hydroboration

In this work, the preparation of head‐to‐tail regioregular poly(6‐(1‐tridecenyl)‐pyridine‐2,5‐diyl) ( PPy ) and its post‐functionalization via hydroboration is described. PPy has been prepared via Kumada‐coupling polycondensation with different catalytic systems. Number‐average molecular weights of up to M_n = 14.7 kDa (PDI = 2.0, DP_n = 60) can be obtained, as determined by gel permeation chromatography relative to polystyrene standards. PPy has been characterized by MALDI‐TOF MS, optical spectroscopy, and cyclic voltammetry. The regioregularity of the material is confirmed by comparison with a head‐to‐head‐tail‐to‐tail regioregular polybipyridine ( PBPy , M_n = 14.0 kDa, PDI = 1.5, DP_n = 29). The 1‐alkenyl‐substituents in PPy have been introduced to provide functional groups for post‐functionalization. Herein, it is also demonstrated that these internal double‐bonds are sufficiently reactive to allow for hydroboration with 9H‐borabicyclo[3.3.1]nonane (9H‐BBN), to furnish an intermediate borylated polymer ( PPyHB ). Treatment of PPyHB with strong acids, and characterization of the deborylated polymer PPyH₂ proves quantitative conversion of the precursor polymer.