Loris Giorgini

Poly(glycidyl methacrylate): a highly versatile polymeric building block for post-polymerization modifications

The treatment of poly(glycidyl methacrylate) with nucleophilic agents yielded new linear homo/co-polymers. The materials obtained have different physicochemical properties depending upon the nucleophiles utilized and thus, by this way, water soluble polymers are easily accessible. This approach is also very convenient for the synthesis of amphiphilic block copolymers. Additional chemical modifications can further transform the obtained polymers after the post-polymerization treatment. Starting from RAFT pre-synthesized/pre-functionalized polymers, the described procedures allow us to obtain a wide variety of chemically diverse materials characterized by controlled structure and specific functions.

Photomodulation of the chiroptical properties of new chiral methacrylic polymers with side chain azobenzene moieties.

We have investigated the photoinduced optical properties of a new class of chiral methacrylic polymers characterised by the presence in the side chain of an optically active pyrrolidinyl ring linked to a trans-azoaromatic system. The homopolymers are enantiomerically pure and their strong optical activity indicates that the macromolecules assume, both in solution and in solid thin films, highly homogeneous conformations with a prevailing chirality. As expected, the studied polymers exhibit reversible linear dichroism and birefringence when irradiated with linearly polarised light. By irradiating with circularly polarised light, we have discovered that it is possible to photomodulate the chiroptical properties of the polymer films. After irradiation with L-polarised light, the CD spectra of the films show a net inversion of their relative sign. The effect is reversible and the original shape of the CD spectra can be restored by pumping with R-polarised radiation. This unexpected new phenomenon can be explained in terms of the ability of the L-polarised radiation to invert the prevailing helicity of the polymeric chains. The observed effect seems to open new possibilities for the use of azobenzene-containing materials as chiroptical switches.

Synthesis, chiroptical properties and photoresponsive behaviour of optically active poly[(S)-4-(2-methacryloyloxypropanoyloxy)azobenzene]

Abstract A novel optically active monomer containing a photochromic chromophore, such as trans-(S)-4-(2-methacryloyloxypropanoyloxy)azobenzene and its low molecular weight model compound trans-(S)-4-(2-pivaloyloxypropanoyloxy)azobenzene were prepared. Free radically initiated homopolymerization of the methacrylic monomer afforded in fairly high yield a rather high molecular weight polymer which was molecularly and structurally characterized. The molecular mobility of the polymer in all trans configuration, as well as chiroptical properties, photoisomerization kinetics and photochromic behaviour were investigated and compared with those of the low and high molecular weight related compounds. The polymer photoresponsive properties were evaluated by circular dichroism measurements at various extents of photoisomerization. All the results are discussed in terms of structural requirements of the macromolecules.

Methacrylic polymers bearing side-chain permanent dipole azobenzene chromophores spaced from the main chain by chiral moieties: synthesis and characterization

Abstract Novel optically active polymethacrylates bearing in the side chain a chiral group of one prevailing absolute configuration linked to the trans -azoaromatic chromophore, have been synthesized by radical homopolymerization of the corresponding optically active monomers, prepared in turn from optically active precursors by synthetic methods avoiding any racemization of the chiral center. These polymeric derivatives, namely poly[( S )-3-methacryloyloxy-1-(4′-X-4-azobenzene) pyrrolidine], with X=CN, CHO, CHC(SO 2 CH 3 )(CN), CHC(CN) 2 , are characterized by the presence of the 3-hydroxy-pyrrolidinyl ring as the chiral moiety and the azoaromatic donor-acceptor conjugated system as the moiety with permanent dipole moment. The polymers display optical activity in solution much higher than that afforded by the corresponding low molecular weight models, representative of the monomeric repeating unit, purposely synthesized. Owing to the substantially stereoirregular structure of the main chain, this suggests that the overall optical activity is mainly due to conformational dissymmetry of the macromolecules. Spectroscopic evidence suggests the presence in the above mentioned polymeric derivatives of dipole–dipole interactions between the side-chain azoaromatic chromophores, occurring as a consequence of their anchorage to the polymer backbone, which favors their aggregation.

Synthesis and chiroptical properties of optically active photochromic methacrylic polymers bearing in the side chain the (S)‐3‐hydroxypyrrolidinyl group conjugated with the trans‐azoaromatic chromophore

Novel optically active polymethacrylates, namely poly[(S)-3-methacryloyloxy-1-(4-azobenzene)pyrrolidine] and poly[(S)-3-methacryloyloxy-1-(4′-nitro-4-azobenzene)pyrrolidine], have been synthesized by radical polymerization of the corresponding monomers, prepared in turn through a synthetic route preserving the asymmetric center by any racemization reaction. These homopolymers are characterized by the presence in the side chain of an optically active pyrrolidinyl ring linked to the trans-azoaromatic system through the nitrogen atom. The optical activity of the polymers in solution appears much higher than that observed with the low molecular weight models, purposely synthesized for comparison. Circular dichroism spectra of the synthesized products demonstrated that, in solution, the macromolecules assume highly homogeneous conformations with a prevailing chirality to a larger extent with respect to analogous systems previously investigated.

Dimethyl carbonate and switchable anionic surfactants: two effective tools for the extraction of polyhydroxyalkanoates from microbial biomass

The availability of green and cheap technologies to recover polyhydroxyalkanoates (PHAs) from microbial biomass is crucial for the development of a reliable and sustainable production chain. Here, two novel protocols are proposed to extract PHAs from Cupriavidus necator. The first method is based on PHA-extraction with dimethyl carbonate (DMC), a green solvent that is completely biodegradable and less harmful to humans and the environment than most solvents. The procedure can be applied directly to concentrated microbial slurries or to dry biomass, affording very high polymer recovery (>85%) and excellent purity (>95%). No degradation/decomposition of the polymer is observed in both cases. The second protocol uses fatty acid carboxylates as surfactants, which disrupt cell membranes, providing excellent polymer recovery (>99%) and high purity (>90%). Ammonium laurate can be successfully used and easily recycled (98%) by lowering the pH through CO2 addition. Therefore, both protocols reported here are effective and sustainable: the recovery and purity of the obtained PHAs are very high, the use of toxic chemicals is avoided, and the recycling of various solvents/surfactants used in the processes is optimal.

Photoinduced chiroptical bistability in new chiral methacrylic azobenzene-containing polymers

The photoinduced chiroptical properties of an optically active methacrylic polymer bearing in the side-chain a conjugated trans-azoaromatic chromophore linked to the main chain through a chiral cyclic pyrrolidine moiety of one prevailing absolute configuration have been investigated. The polymeric film is characterized by a strong optical activity that can be amplified and reversibly modulated by irradiation with circularly polarized (CP) light at 488 nm. A remarkable modification of the shape of the circular dichroism (CD) spectrum after the initial irradiation steps is observed, with an amplification of the CD signal upon increasing the total irradiation fluence. The most important results are connected with the handedness of the CP radiation: left circularly polarized (CP-L) light is able to reverse the relative sign of the CD spectra, whereas by pumping with right circularly polarized (CP-R) radiation, it is possible to recover the original shape of the signal. This well reproducible and reversible effect suggests the possibility to use the investigated material for chiroptical switching.

Synthesis and chiroptical properties of optically active methacrylic polymers bearing the (S)‐ and/or (R)‐2‐hydroxysuccinimide moiety linked to the trans‐azobenzene group in the side chain

The synthesis of novel optically active monomers, namely (S)-(+)- and (R)-(-)-2 methacryloyloxy-N-(4-azobenzene) succinimide, is described. The monomers have been radically polymerized to afford the corresponding optically active homopolymers, characterized by the presence of an optically active rigid succinimide ring in the side chain linked to the trans-azoaromatic system through the imide nitrogen atom. A series of copolymers containing both the enantiomeric monomers in different molar amounts, have also been prepared in order to observe possible effects on the optical activity of the resulting deritatives. The chiroptical and conformational properties of the polymers in solution have been investigated by circular dichroism measurements and compared with those of low molecular weight model compounds, purposely synthesized, with the aim to verify the existence of cooperative interactions between chromophoric groups disposed along the macromolecular chain according to dissymmetric conformations.

Extraction of polyhydroxyalkanoates from mixed microbial cultures: Impact on polymer quality and recovery.

Polyhydroxyalkanoates (PHAs) can be extracted from mixed microbial cultures (MMCs) by means of dimethyl carbonate (DMC) or combination of DMC and sodium hypochlorite (NaClO). The protocol based on DMC, a green solvent never used before for the extraction of PHAs from MMC, allows an overall polymer recovery of 63%; also the purity and the molecular weight of the recovered polymers are good (98% and 1.2 MDa, respectively). The use of NaClO pretreatment before DMC extraction increases the overall PHA recovery (82%) but lowers the mean molecular weight to 0.6-0.2 MDa. A double extraction with DMC results to be the method of choice for the recovery of high quality PHAs from attractive but challenging MMCs.

Optically active polymethacrylates with side-chain L-lactic acid residues connected to push-pull azobenzene chromophores

Abstract Novel optically active methacrylic homopolymers with side-chain l -lactic acid moieties interposed through ester bonds between the main chain and trans -4-azobenzene chromophores bearing in the 4′-position electron withdrawing groups, such as the cyano and nitro residues, have been synthesized and structurally characterized. Investigation by circular dichroism of the chiroptical and conformational properties of the polymers in solution indicates a much higher optical activity of these latter with respect to that of the corresponding low molecular weight model compounds, purposely prepared, due to the presence of dissymmetric conformations of one prevailing handedness. The trans to cis photoisomerization kinetics of the azoaromatic double bond has been measured in solution for polymers and models and the resulting data compared with those of previously reported similar photochromic derivatives. The influence of the nature of the electron withdrawing group in the 4′-position of the azobenzene chromophore on the chiroptical properties of the polymers is also discussed.