Reactive and Functional Polymers (v.72, #4)

Functionalized polylactides (PLAs) containing acryloyl, methacryloyl or propargyl end groups have been obtained by cationic ring-opening polymerization performed in the presence of appropriate alcohols (HEMA, HEA, propargyl alcohol) as initiators and triflic acid as a catalyst. 1H NMR, MALDI TOF and GPC analysis indicated almost quantitative initiation and confirmed the expected structure and molecular masses of the obtained PLAs. The conditions were found in which transesterification process (usually accompanying the cyclic esters propagation) can be avoided. PLAs functionalized with double bond were successfully homopolymerized and copolymerized with butyl acrylate in the presence of AIBN. PLA with triple bond at one chain end was effectively coupled with a model azide by 1,3-dipolar Huisgen cycloaddition (“click” reaction) in order to prove its ability to be further functionalized.
Keywords: Ring-opening polymerization; Cationic polymerization; Polylactide; Functionalization; Macromonomers;

By polymerisation of high internal phase emulsions (HIPEs), containing styrene (STY), divinylbenzene (DVB) and methacrylic acid (MAA) in the continuous phase, highly porous polymers including carboxylic functional groups were prepared. The ratio of methacrylic acid to divinylbenzene was varied in order to obtain polyHIPEs with a different degree of crosslinking which influenced a surface area of the polymers, being substantially higher (185 m2/g) with a higher degree of crosslinking (51% DVB) than with a lower degree of crosslinking (24% DVB, 46 m2/g). Up to 90% porous samples were prepared and the optimum hidrophilicity-lipophilicity balance (HLB) of the surfactant was found to be around 4.8–4.9. Both thermal and photo initiation were used to induce polymerisation. The resulting polymers had an open cellular morphology with cavity diameters between 21.8 μm and 44.2 μm and with interconnecting pores between 2.2 μm and 5.0 μm. Monolithic supports were used for further functionalisation with thionyl chloride and multifunctional amines, namely 1,4-diaminobutane and 1,12-diaminododecane. The functionalisation degree with thionyl chloride was 76%.
Keywords: Poly(methacrylic acid); PolyHIPE; Porous polymers; Emulsions; Functional polymers;

Nanostructured hyperbranched polyurethane elastomer hybrids that incorporate polyhedral oligosilsesquioxane by Sibdas Singha Mahapatra; Santosh Kumar Yadav; Jae Whan Cho (227-232).
Novel thermoplastic hyperbranched polyurethane (HBP) elastomer hybrids containing polyhedral oligomeric silsesquioxane (POSS) have been synthesized using an A2  + B3 approach. Different compositions of these hybrid nanomaterials were obtained from reactions of POSS-diol, triethanolamine, poly(ε-caprolactone)diol, and 4,4′-methylenebis(phenyl isocyanate) with a chain extender. The covalent attachment of POSS molecules to the backbone of the polyurethane chain was characterized with FT-IR and NMR spectroscopies. The non-agglomerated homogeneous dispersion obtained through the covalent attachment of POSS molecules and the HBP matrix was observed by SEM imaging. The mechanical properties, including the tensile and yield strengths, Young’s modulus, and toughness, significantly increased after the introduction of POSS molecules into the hybrids; this increase can be ascribed to the nano-reinforcement effect of the POSS cages and the long-range branched structure of the polymer. Thermogravimetric analyses indicated that the thermal stability of the polymer matrix was improved by the introduction of a small amount of POSS.
Keywords: Hyperbranched polymer; Hybrids; POSS; Mechanical properties;

A novel Hydrogel (1) was prepared from N-isopropylacrylamide, 4-vinylpyridine and potassium acrylate by free radical cross-linking polymerization. Hydrogel (1) showed both thermosensitivity and pH-sensitivity, and exhibited high swelling capacity in water. Because Hydrogel (1) has porous structure in its network and good loading performance with Pd2+, it was used as “microreactor” for immobilization of metal nanoparticles. We chose Heck and Suzuki reaction of aryl halides in water as test reaction to probe the catalytic activity of such Hydrogel (1) supported palladium catalyst. As a result, the Hydrogel (1)-Pd (II) catalyst exhibited good catalytic activity in both Heck and Suzuki reactions. Moreover, the Hydrogel (1)-Pd (II) catalyst was easily recovered and recycled. The reuse experiments showed that it was recycled six times without obviously losing of catalytic activity.
Keywords: Sensitive hydrogel; Palladium; Heck reaction; Suzuki reaction; Aqueous media;

Synthesis of azobenzene-containing polymers and investigation of their substituent-dependent isomerisation behaviour by Ulrike Georgi; Philipp Reichenbach; Ulrich Oertel; Lukas M. Eng; Brigitte Voit (242-251).
A variety of 4,4′-substituted azobenzenes has been synthesised and the kinetics of the thermal cistrans-relaxation of the substances was studied in detail in solution and embedded in a poly(methyl methacrylate) (PMMA) matrix by UV–Vis spectroscopy. Considerable differences in relaxation times were found for the various azobenzenes which interestingly could not be fully explained by simply comparing the substituents with regard to their electron-donating or -withdrawing nature. Any substituents, especially very polar ones, increase the thermal cis–trans-reaction rate. Some of the chromophores were covalently attached to a PMMA-copolymer and we found that this significantly slowed down the isomerisation kinetics compared to the embedding of low molar mass azobenzenes in a polymer matrix. But our study showed also that, even at room temperature, the thermal cis–trans-relaxation of 4,4′-substituted azobenzene chromophores can never be fully suppressed, but only slowed down.
Keywords: Azobenzene; Isomerisation kinetics; Thermal cistrans-relaxation; UV–Vis spectroscopy; Polymer-analogous reaction;

Castor oil-based acid urethane macromers were prepared and employed for obtaining Ag/Au/polymer nanocomposites. Structure and UV induced photopolymerization of the macromers were investigated by spectral methods. The polymerization rate and the degree of conversion decreased with about 10% in the presence of 2.5 wt.% silver nanoparticles (Ag NPs). For the diacid macromer, the surface plasmon intensity increased with irradiation time (the optical density of the absorption maximum (430 nm) attained 2.3 after 600 s), whereas a diminished efficiency was found for Ag NPs in situ generated. Transmission electron microscopy and X-ray photoelectron spectroscopy confirmed uniform distribution of the spherical nanoparticles (0.6 nm (Ag NPs); 5 nm (Au NPs)) and the appearance of Ag 3d3/2, Ag 3d5/2, Au 4f7/2 and Au 4f5/2 peaks corresponding to Ag (0) or Au (0). Environmental scanning electron microscope with energy-dispersive X-ray detector, contact angle and mechanical parameters measurements complemented the above observations.
Keywords: Urethane macromers; Castor oil; Photopolymerization; Ag/Au nanoparticles;

Multilayer approach for tuning the drug delivery from poly(3-hydroxyalkanaoate)s coatings by Gwenaelle Vergnol; Hawaa Sow; Estelle Renard; Ferial Haroun; Valerie Langlois (260-267).
A first feasibility study about the sirolimus release from stent coatings based on degradable poly(3-hydroxyalkanoate)s PHAs is reported. Natural poly(3-hydroxybutyrate-co-3-hydroxyvalerate) PHBHV, poly(3-hydroxyoctanoate) PHO, functional polyesters containing carboxylic groups PHO75COOH25, and diblock copolymer poly((3-hydroxybutyrate-co-3-hydroxyvalerate)-b-(lactic acid)) P(HBHV-b-LA) were sprayed onto metallic stents. Stress behavior and coating integrity studied by scanning electron microscopy on unexpanded and expanded stents were found to be superior for the PHBHV and P(HBHV-b-LA). Release of sirolimus from these coatings showed an important burst effect of drug whatever the nature of PHAs due to their very low glass transition temperatures. However, bilayer systems offered many options for controlling sirolimus release over months.
Keywords: Polyester; Poly(3-hydroxyalkanoate); Functionalized polyester; Stent; Bilayered coating; Degradable polymer; Drug release;

New copolymers graft of α,β-poly(N-2-hydroxyethyl)-d,l-aspartamide obtained from atom transfer radical polymerization as vector for gene delivery by Mariano Licciardi; Gennara Cavallaro; Giovanni Amato; Calogero Fiorica; Gaetano Giammona (268-278).
New cationic α,β-poly(N-2-hydroxyethyl)-d,l-aspartamide (PHEA) graft copolymers were synthesized by ATRP, using diethylamino ethyl methacrylate (DEAEMA) as monomer for polymerization, yielding polycations (PHEA-pDEAEMA) able to condense DNA. Then, consecutive ATRP conditions were set up on PHEA-pDEAEMA to obtain copolymers containing also hydrophilic chains (PHEA-IB-pDMAEMA-pPEGMA) able to improve biocompatibility of polyplexes and to provide them stealth properties. Agarose gel studies showed that the copolymers effectively condensed plasmid DNA to form polyplexes. Light scattering studies were used to analyze the size and the ζ-potential of these polyplexes, showing that copolymers were able to condense the pDNA leading to the formation of nanoscale systems. The copolymers PHEA-IB-pDEAEMA showed high cytocompatibility that was improved with the presence of PEGMA units in the side chain.The transfection efficiency (luciferase) of polyplexes obtained with all copolymers was evaluated on B16F10 cell line obtaining a moderate transfection efficiency in comparison with bPEI that can be explained, supposing a low release of pDNA from polyplexes at endocellular level.
Keywords: ATRP; DEAEMA; Gene delivery; PEGMA; Polyaspartamide;

Reactive modifiers, bearing cyanate and/or alkenyl groups have been shown to improve the thermo-mechanical and water uptake properties of cured bismaleimides and BMI/cyanate ester blends. The allyl-substituted modifiers have been the subject of much study, but the reaction mechanism of the more reactive propenyl analogues (for which lower moisture absorptions have been recorded) have not received much attention until the present study. The synthesis and full characterisation of model maleimide and propenyl-substituted aryl cyanate compounds is reported. Infrared and Raman spectroscopy and thermal analysis techniques are used to examine the thermally initiated co-reaction between blends of the two model compounds. Raman spectroscopy reveals that as the thermal reaction proceeds, there is a pronounced decrease in the alkenyl C=C stretch band at 1655 cm−1 as a function of temperature and this is accompanied by a concomitant decrease in the vinylidene band at 3010 cm−1. In the absence of a dedicated catalyst, the cyanate cyclotrimerization is slow and follows the co-reaction between the alkenyl group and the maleimide ring. Molecular modelling experiments using semi-empirical and ab initio methods support the formation of the trans ene adduct which is consistent with calculated and observed vibrational frequencies.
Keywords: Cyanate ester; Bismaleimide; ene Mechanism; Molecular modelling;

Synthesis and characterization of fluoroquinolone-imprinted polymeric nanoparticles by Pu Xiao; Yves Dudal; Philippe F.-X. Corvini; Priska Spahr; Patrick Shahgaldian (287-293).
Molecularly imprinted polymeric nanoparticles have been prepared by means of the precipitation polymerization method using a fluoroquinolone, levofloxacin, as a template, methacrylic acid as a functional monomer and 2-ethyl-2-(hydroxymethyl)propane-l,3-diol as a crosslinker. The synthesized polymers have been characterized using scanning electron microscopy that revealed that the produced systems are sub-micrometer-sized particles with a diameter ranging from 50 to 100 nm. The study of the interactions of these polymers with selected fluoroquinolones (levofloxacin, ofloxacin, and ciprofloxacin), acetaminophen, diclofenac, aspirin, and sulfamethoxazole has been carried out in acetonitrile and water. It is demonstrated that the amounts of levofloxacin and its structural analogues (ofloxacin and ciprofloxacin) bound to the molecularly imprinted polymeric nanoparticles are higher than those bound to the non-imprinted nanoparticles both in acetonitrile and in water; the binding of acetaminophen, diclofenac, aspirin and sulfamethoxazole onto both the imprinted and non-imprinted nanoparticles are shown to be significantly lower. In water, it has been shown that even if decreased, the imprinted nanoparticles retain a relevant selectivity for the studied fluoroquinolones, and the binding of other studied pharmaceuticals are not enhanced significantly (e.g. acetaminophen) or even suppressed (e.g. diclofenac sodium, aspirin and sulfamethoxazole) by the molecular imprinting.
Keywords: Molecularly imprinted polymers; Precipitation polymerization; Nanoparticles; Fluoroquinolone; Levofloxacin;