Reactive and Functional Polymers (v.90, #C)

Challenging activated monomer ring-opening polymerization for direct synthesis of thiol end-functionalized polyesters by Maksym A. Kryuchkov; Ying Hua Qi; Iryna I. Perepichka; Carole Pelletier; Aurelie Regnaud; Zhengji Song; Sunil K. Varshney (1-6).
A direct, non-enzymatic procedure for the synthesis of thiol-functionalized polylactones was developed and optimized by using 2-mercaptoethanol, the simplest unprotected thiol-containing initiator for cationic ring-opening polymerization, catalyzed by HCl and methanesulfonic acid in dichloromethane solutions. Thiol-functionalized polylactones with a molecular weight of up to approximately 5000 Da were obtained in a controlled manner. It was observed that acid can play the dual role of activator and initiator, and for the first time, it was shown that abundant HCl and/or ambient temperature lead to the formation of undesired α-carboxy-ω-chloro-functionalized polylactones that form in parallel with the targeted thiol-functionalized ones. A plausible pathway towards the formation of chlorinated products is proposed based on an active-chain-end mechanism, and the procedure was optimized to eliminate its contribution to the polymerization process, thus allowing for the activated-monomer mechanism to prevail. Molecular weight characterization was performed using 1H NMR and size-exclusion chromatography. The results indicate that the polymers obtained under optimized conditions possess high SH functionality and moderate polydispersity, and that ring-opening polymerization proceeded in a controlled fashion. The proposed method allows for the preparation of metal free materials readily suitable for biomedical and/or electronic applications.
Keywords: Thiol-functionalized polyester; Chloro-functionalized polyester; Cationic ring-opening polymerization; Lactone; Mercaptoethanol;

Synthesis of conjugated polymers bearing pendant bipyridine ruthenium complexes by Yuxia Jin; Yingliang Liu; Wenbo Wu; Qiong Wu; Hongyan Gao; Chenxu Wang; Shengang Xu; Shaokui Cao (7-14).
Conjugated polymers bearing pendant bipyridine groups, PM1PT-x, were synthesized in high yield from a carefully designed dibromocarbazole monomer M1 using a Suzuki coupling reaction with a phenothiazine diborate monomer. PM1PT-x, where x is the mole percentage of M1 in the total feed of dibromo-monomers and varied to levels of 25%, 50%, 75% and 100%, was reacted with a ruthenium complex to yield conjugated polymers bearing pendant bipyridine ruthenium complexes, PM1PT-x-Ru. The introduction of ruthenium complexes extended the absorption of PM1PT-x-Ru to the visible light region. Furthermore, these polymers demonstrated sufficient stability and suitable energy levels to potentially be highly efficient photoactive materials for polymeric solar cells.
Keywords: Conjugated polymer; Ruthenium complex; Carbazole; Phenothiazine;

The potential of Kraft black liquor to produce bio-based emulsion-templated porous materials by Amandine Foulet; Marc Birot; Guido Sonnemann; Hervé Deleuze (15-20).
Emulsion-templated porous monoliths based on castor oil-in-black liquor and on 1,2-dichloroethane-in-black liquor medium internal phase emulsions have been prepared in order to evaluate a possible valorisation of that undervalued by-product of the paper mill Kraft process. The cross-linking behaviour of the different polymers originally contained in the black liquor was investigated. It appears that both lignin and hemicellulose fragments are involved. Characterisation of the monoliths by scanning electronic microscopy and mercury intrusion porosimetry showed that using either castor oil or 1,2-dichloroethane allowed to obtain macrocellular morphology along with a high porosity. However, higher concentration of the internal phase is possible in emulsions prepared with 1,2-dichloroethane than with castor oil, leading to more attractive materials from both chemical and environmental aspects.
Keywords: Emulsion template; PolyHIPE; Porous monolith; Black liquor;

Cross-linking of cellulose and poly(ethylene glycol) with citric acid by Pamela de Cuadro; Tiina Belt; Katri S. Kontturi; Mehedi Reza; Eero Kontturi; Tapani Vuorinen; Mark Hughes (21-24).
A novel approach to modifying native cellulosic fibres with poly(ethylene glycol) (PEG) impregnation and simultaneous cross-linking by citric acid (CA) was investigated. To understand the contributions of different components in the system, control references with just CA and cellulosic fibres (filter paper) were studied. The effect of sodium hypophosphite as a catalyst was also assessed. The results revealed that ester bonds are indeed formed in the cellulose–PEG–CA reaction system, as indicated by weight percentage gain (WPG) and FTIR analysis. The best results were achieved by using 5% CA and 10% PEG (calculated as weight-% from cellulose). In the reaction, the environmentally friendly CA prevents PEG from being leached out of cellulose during washing, resulting in promising future applications in dimensionally stabilized products based on cellulosic fibres.
Keywords: Cellulose esterification; Cellulosic fibres; FTIR; Hypophosphite catalyst; PEG impregnation;

Stimuli responsive conducting carbon nanocomposite hydrogels were synthesized from glycerol methacrylate, ethylene glycol methacrylate and diethylene glycol methacrylate by thermal polymerization techniques. Carbon nanoparticles of size <50 nm were incorporated into the polymer at a concentration of 0.005% (w/w) during synthesis. The hydrogels were characterized by Fourier Transform-Infrared Spectroscopy, thermogravimetric analysis, Scanning Electron Microscopy techniques and X-ray diffraction study. The hydrogels have excellent absorption properties in aqueous solvents which is sensitive to pH, temperature, ionic strength, etc. For instance, the pH sensitive swelling behavior of Polyglycerylmethacrylate-carbon nanocomposite increases from acidic medium (SR∼24, pH = 3) to basic medium (SR∼130, pH = 12). The hydrogels also showed significant swelling behavior in presence of different biological samples such as folic acid, uric acid, DNA and RNA. The electrical impedance value decreases to a large extent after the addition of carbon nanoparticles into the gels. It was observed that the conductivity rises to a maximum of about 1000 folds in the nanocomposite hydrogels. The increase in electrical conductivity is also verified by current–voltage measurements.
Keywords: Hydrosorbent; Nanocomposites; Swelling; Conducting hydrogels; Current–voltage study;

Influence of solvent characteristics in triaxial electrospun fiber formation by Abdurizzagh Khalf; Kumar Singarapu; Sundararajan V. Madihally (36-46).
Triaxial electrospinning is a novel method for fabrication of multilayered nano and microsize fibers with desirable features for particular applications. Since the effect of solvent volatilities in each layer and relative polymer molecular weights on uniform encapsulation of the core polymer process is not well understood, we evaluated (i) the role of solvent volatilities, and (ii) molecular weights using cellulose acetate (CA, 30 kDa), polycaprolactone (PCL, 45 kDa and 80 kDa), mineral oil, and polyvinyl alcohol (PVA, 30 kDa and 100 kDa). Different solvent mixtures were evaluated based on the boiling points determined using a simulator. Inner mineral oil was selectively removed to form Hollow fibers. Analysis of chemical compositions using FT-IR and DSC revealed the presence of each component. 24-h viability of human umbilical vein endothelial cells indicated the formed fibers were not toxic. Scanning electron micrographs indicated the formation of triaxial structured fiber of outer hydrophobic PCL/CA/Hollow, PCL/PVA/Hollow and outer hydrophilic CA/PCL/Hollow fibers. Tensile tests (both wet and dry) revealed that PCL/CA/Hollow fibers had increased stiffness and load carrying capacity than CA/PCL/Hollow fibers. Successful fiber formation was dependent on ensuring that the outer shell formed first i.e., the relative solvent volatility of encapsulating core polymer to lower than that of the shell polymer.
Keywords: Triaxial electrospinning; Multilayered structured fiber; Solvent volatility; Reinforced polymeric fiber;