Umit Tunca

Constructing star polymersvia modular ligation strategies

Branched polymers result in a more compact structure in comparison to linear polymers of identical molecular weight, due to their high segment density which affects the crystalline, mechanical, and viscoelastic properties of the polymer. Star polymers constitute the simplest form of branched macromolecules where all of the chains—or arm segments—of one macromolecule are linked to a centre defined as the core. Over recent years, modular ligation reactions—some of which adhere to click criteria—have enabled the synthesis of a variety of star polymersvia efficient polymer–polymer conjugations. While the modified Huisgen [3 + 2] dipolar copper catalyzed azide and alkyne cycloaddition (CuAAC) has been widely employed for macromolecular star synthesis, Diels–Alder and hetero Diels–Alder reactions offer alternative pathways which allow for similarly efficient macromolecular conjugations. Moreover, combinations of these protocols afford the synthesis of more complex star polymer structures which previously had not been achievable.

Double click reaction strategies for polymer conjugation and post-functionalization of polymers

Double click reaction strategies, which are a combination of different type of click reactions, allow the preparation of polymers with various topologies and the post-functionalization of polymers, which cannot be easily achieved by using only one click reaction. The most studied click reaction combinations may be listed as the Cu(I) catalyzed azide-alkyne cycloaddition (CuAAC)–Diels–Alder, and the CuAAC–nitroxide radical coupling reactions for polymer–polymer conjugation and the CuAAC–Diels–Alder, or the CuAAC–thiol-ene reactions for post-modification of polymers.

Polymerization of acrylamide initiated by the redox system Ce(IV)-4,4′-azobis (4-cyano pentanol)

SummaryAcrylamide was polymerized by eeric ion Ce (IV)-4,4′-azobis(4-cyano pentanol)(ACP) redox pair in aqueous nitric acid under nitrogen atmosphere. The rate of polymerization is proportional to [M]2,[ACP] and [Ce(IV)]−1. Termination mechanism which was exclusively linear offered one azo group per polymeric chain. The obtained polyacrylamide can be used as a water soluble initiator for vinyl polymerization.

Aqueous polymerization of acrylamide initiated by redox pair: Ce(IV)—Azo compounds with methylol functional groups

Abstract The polymerization of acrylamide (AAm) initiated by redox pair: the cerie ammonium nitrate[Ce(IV)]-hydroxy containing thermolabile azo compounds (R) has been investigated in aqueous nitric acid at 20 °C. It was determined that how the rate of polymerization depends on [AAm], [R] ( 1 or 2 ) and [Ce(IV)], respectively. The relationships between degree of polymerization and AAm-, R-, and Ce(IV)-concentrations were also evaluated.

Well-defined polyethylene-based graft terpolymers by combining nitroxide-mediated radical polymerization, polyhomologation and azide/alkyne “click” chemistry

Novel well-defined polyethylene-based graft terpolymers were synthesized via the “grafting onto” strategy by combining nitroxide-mediated radical polymerization (NMP), polyhomologation and copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) “click” chemistry. Three steps were involved in this approach: (i) synthesis of alkyne-terminated polyethylene-b-poly(e-caprolactone) (PE-b-PCL-alkyne) block copolymers (branches) by esterification of PE-b-PCL-OH with 4-pentynoic acid; the PE-b-PCL-OH was obtained by polyhomologation of dimethylsulfoxonium methylide to afford PE-OH, followed by ring opening polymerization of e-caprolactone using PE-OH as a macroinitiator, (ii) synthesis of random copolymers of styrene (St) and 4-chloromethylstyrene (4-CMS) with various CMS contents, by nitroxide-mediated radical copolymerization (NMP), and conversion of chloride to azide groups by reaction with sodium azide (NaN3) (backbone) and (iii) “click” linking reaction to afford the PE-based graft terpolymers. All intermediates and final products were characterized by high-temperature size exclusion chromatography (HT-SEC), Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (1H NMR) and differential scanning calorimetry (DSC).

1,3-Dipolar and Diels–Alder cycloaddition reactions on polyester backbones possessing internal electron-deficient alkyne moieties

In this study we prepared a series of polyesters containing electron deficient internal alkyne units derived from acetylene dicarboxylic acid in the main backbone. Next, one of the polyesters was employed as a polymeric platform in copper free cycloaddition reactions like, Huisgen type 1,3-dipolar and Diels–Alder cycloaddition reactions in the presence of various dipoles and dienes, respectively. The 1,3-dipolar cycloaddition reactions were performed at mild temperatures (rt and 40 °C) in 1,4-dioxane for 16 h and had moderately high efficiencies (80–100%). However, the Diels–Alder cycloaddition reactions were carried out at higher temperatures (60 to 120 °C) in 1,4-dioxane for 16 h with reasonable efficiencies (45–97%). Moreover, the polyester was successfully used in one-pot 1,3-dipolar, sequential 1,3-dipolar/Diels–Alder, and sequential 1,3-dipolar cycloaddition/retro-Diels–Alder reactions.

Novel multiarm star block copolymer ionomers as proton conductive membranes

A series of well-defined novel multiarm star block copolymer ionomers with an average of 6, 11 and 15 arms, sulfonated polystyrene-block-poly(2,2,3,3,3-pentafluoropropyl methacrylate) (SPS-b-PFPMA), were prepared via a combination of atom transfer radical polymerization (ATRP), Diels–Alder click reaction and postsulfonation reaction. First, multiarm star polymer with anthracene functionality as reactive periphery groups was prepared by a cross-linking reaction of divinyl benzene using α-anthracene end functionalized PS (PS-anthracene) as a macroinitiator. Thus, obtained multiarm star polymer was reacted with furan protected maleimide-end functionalized PFPMA (PFPMA-MI) resulting in the corresponding fluorinated multiarm star block copolymers via Diels–Alder click reaction. The third step involves the sulfonation reaction of phenyl ring of polystyrene block with acetyl sulfate at 20 °C. The structures, molecular characterization and thermal properties of the multiarm star block copolymers were characterized by 1H nuclear magnetic resonance (1H NMR) and infrared (IR) spectroscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Thermal analysis indicated separate glass transitions of the PFPMA and PS phases. Both the membranes from sulfonated multiarm star block copolymer and its sulfonated poly(phenylene oxide) (SPPO) blends were prepared by solution casting method. All of the multiarm star block ionomers were readily soluble in N,N-dimethyl acetamide. The influence of star functionality and ion exchange capacity (IEC) of star ionomers on the flexibility and the proton conductivity of ionomer membranes were examined. 6-arm star block copolymer ionomer membrane with 1.00 mmol g−1 IEC exhibited conductivity (19.37 mS cm−1) higher than that of SPPO with 1.34 mmol g−1 IEC (3.82 mS cm−1) measured at 80 °C and relative humidity of 100%. The morphology of dry membranes was investigated by scanning electron microscopy (SEM). This work showed that it is possible to tailor and prepare proton exchange membrane with well-defined architecture by employing star block copolymers with a sulfonated core bearing hydrophobic fluorinated periphery.

Synthesis of polymers containing crown ether and ferrocene units

Abstract Polyketone containing crown ether and ferrocene moieties was obtained by means of the reaction of 1,1′-ferrocenedicarboxylic acid with dibenzo-18-crown-6 in Eatons reagent at room temperature. The structure of the polymer was confirmed by various methods.

Synthesis of Poly(vitamin C) through ADMET

l-Ascorbic acid, commonly known as vitamin C and one of the most important biological compounds, is converted to a α,ω-diene monomer and subsequently polymerized for the first time by acyclic diene metathesis. Various experimental conditions such as polymerization medium, catalyst type, temperature, and monomer/catalyst ratio are studied. The moderate molecular weight polymers are achieved when the polymerizations are conducted under bulk conditions employing the Grubbs first generation (G1) or Hoveyda-Grubbs second generation catalyst (HG-2). In the solution case, on the other hand, low molecular weight polymers are obtained regardless of the catalyst type. Moreover, when the catalyst performances are compared, it is found that G1 produces the higher molecular weight as well as higher yield polymers with respect to the HG-2.

A new strategy for the preparation of multiarm star-shaped polystyrene via a combination of atom transfer radical polymerization and cationic ring-opening polymerization

A multiarm star-shaped polystyrene (PS) was prepared from polystyrene-block-poly(glycidyl methacrylate) (PS-b-PGMA) by combination of atom transfer radical polymerization (ATRP) and cationic-ring opening polymerization (CROP). First, ATRP of styrene was carried out using ethyl 2-bromoisobutyrate (EIBr) as the initiator and copper halide (CuBr) with N,N,N′, N″, N″-pentamethyldiethylenetriamine (PMDETA) as the catalyst system in bulk at 110°C. Then, previously obtained PS was used as a macroinitiator for ATRP of glycidyl methcrylate (GMA) using CuCl/PMDETA as the catalyst system in anisole at 60°C. This produced an AB-type di-block co-polymer (PS-b-PGMA) with a controlled molecular weight and low polydispersity (M w/M n = 1.15). As a third step, CROP of pendant oxirane rings of PS-b-PGMA di-block co-polymer led to a multiarm star-shaped PS in a novel approach. The obtained polymers were characterized by gel-permeation chromatography and 1H-NMR.