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In the field of aliphatic polyesters there is a great interest in building novel macromolecular structures that may effectively feature the requiredproperties for specific applications. For this reason, it is extremely important to understand the correlations between chemical structure and final performance. Monomers based on the 1,4-cyclohexylene unit are interesting as they are potentially bio-based and rigid enough to improve glass transition and melting temperatures. The present paper describes the preparation of samples of poly(1,4-cyclohexylenedimethylene adipate), characterized by different cis/trans isomeric ratio of the cyclic units, the analysis of their thermal properties and the comparison with the properties of similar polymers such as poly(butylene adipate), poly(butylene-1,4-cyclohexanedicarboxylate) and poly(1,4-cyclohexylenedimethylene-1,4- cyclohexanedicarboxylate). The effect of the rigidity and of the stereochemistry of the 1,4-cyclohexylene unit on the thermal properties was analysed. Such an effect reaches its maximum level when the cyclic-containing monomers are the diacid or the diester and when the trans isomers predominate. Starting from such a result, the combination of specific cyclic building blocks with the correct cis/trans ratiomakes it possible to build macromolecular structures with the required final properties.

Nowadays the development of sustainable polymers, with convenient properties to substitute the traditional petroleum-based materials, is one of the major issues for material science. The utilization of renewable resources as feedstock for biopolyesters is a challenging target.The research work described in the present thesis is strictly connected to these urgent necessities and is focused mainly in finding new biopolymers, in particular biopolyesters, which are obtainable from biomass and characterized by a wide range of properties, in order to potentially substitute polyolefins and aromatic polyesters (for example, poly(ethylene terephthalate))

Degradability or, on the contrary, durability of polymers are very important features affecting the performances of the materials in their shelf-life and their impact on the environment. The degradation can be due to different environmental factors, including light exposure, very important for polymers used in outdoor applications. The knowledge of the photo-degradation mechanisms and the possibility to modify them is a very important topic, especially for the novel biopolymers, as their durability with respect to the petro-plastics is yet an open question. Among the biopolymers aliphatic polyesters are an emerging class of materials, thanks to the possibility of preparing them from renewable resources and their potential environmental degradability. In this study two aliphatic molecular structures, containing 1,4-cyclohexylene units, have been analysed and used as matrixes for composites. PBCHD and PCCD were exposed to UV irradiation in an accelerated photo-ageing device and the modifications in their chemical structures were analysed by rheology, UV and IR spectroscopies. It results that the photo durability of PBCHD, containing only one cycle per monomeric unit, is higher than that of PCCD. Moreover, in order to increase the durability, substances can be incorporated into the polymer. Among all the particles and nanoparticles which can be used, titanium dioxide (TiO2) is known for its capability of absorbing UV radiation. This photo-catalytic effect is strictly connected to its crystalline phases. Therefore, composites containing different amount of TiO2, in the anatase and rutile crystalline phases separately, have been prepared by using a Brabender mixer. The well dispersion of the particles and the good adhesion between TiO2 and polymer have been checked by SEM observations. The composites result to have a photo stability higher than those of the homopolymers. The protection of TiO2 against the photo-oxidation increases with the particle content and results higher for the anatase crystalline phase. As a conclusion, a good increment of the photo-durability of the studied aliphatic polyesters has been obtained by preparing composites with titanium oxide. This result could be particularly significant for outdoor applications of these polymers.

Aliphatic polyesters containing 1,4-cyclohexylene rings are an interesting class of materials, not yet fully investigated. They potentially have the good characteristics typical of biopolyesters (for example, polyalkylene dicarboxylates and polyhydroxy alkanoates), such as sustainability and biodegradability. Indeed, renewable biomass resources can be used as feedstock to prepare the monomers and some preliminary tests of biodegradation suggest that the aliphatic rings do not hinder the microorganism attack.1 Moreover, the presence of cyclohexyl groups into the main chain provides rigidity to macromolecular chains, raises Tg, and imparts desirable physical-mechanical properties. In this way, the problem of the poor mechanical properties generally found in aliphatic polyesters can be solved. Finally, the 1,4-cyclohexylene unit shows the other remarkable peculiarity that it can have two possible configurations, cis and trans. In a polymer containing the 1,4-cyclohexylene rings, it will suffice to slightly modify the cis/trans isomeric ratio to obtain materials whose phase behavior changes from fully amorphous to semicrystalline.2 Therefore, the final properties of these materials can be easily tailored according to the specific applications. In this work diols with different chain length were tested as monomers for novel polyesters and the effects of the molecular characteristics on final properties were analyzed.

The development of biobased polymers that bring unique properties desired by consumers at acceptable prices is a major challenge and opportunity. Recently, Gross and collaborators reported the development of an engineered Candida tropicalis strain capable of producing commercially viable yields of ω-hydroxyfatty acids. This required the identification and elimination of 16 genes from the diploid yeast Candida tropicalis genome. After reintegration of a P450 and process optimization, volumetric yields higher than 150 g/L of 14-hydroxytetradecanoic acid (14HA) was produced using methyl myristate as substrate.1 In this work, 14HA was used in two-step polycondensations to obtain novel copolyesters with 1,4-cyclohexylene units or terephthalate moieties along chains. The introduction of aliphatic or aromatic rings into the main chain aims at improving thermal and mechanical performances.

Nowadays the urgency for solving plastic waste problems is inducing academic and industrial research to develop novel environmentally friendly polymers, i.e. materials produced from alternative resources, with low energy consumption, non-toxic to the environment, and biodegradable. These biopolymers should have also good physical performances. In the field of aliphatic polyesters, novel (co)polymers, containing 1,4-cyclohexylene units, appear very promising materials, which are obtainable from biomass, potentially biodegradable and characterized by good mechanical properties. Moreover, these polyesters have the interesting peculiarity that their phase behavior is strictly connected to the ratio of the two possible configurations, cis and trans, of the cyclic units. Indeed, the trans isomer is more rigid and symmetric than the cis. Highly symmetrical units tend to improve the chain packing with a consequent increment in crystallinity and crystalline perfection. On the other hand, the cis isomer introduces kinks into the main chain, which hinder the formation of stable crystals. Thus, at high trans content the polyesters are characterized by relative high degree of crystallinity, whereas at low trans content the polymers are amorphous. Therefore, accordingly to the final cis/trans ratio, the phase behavior of the homopolymers and copolymers significantly changes and the stereochemistry of the cycloaliphatic units result to be a key factor to tailor the final thermal properties of the material. In this paper the properties of some homopolymers and copolymers, containing the 1,4-cyclohexylene units with different cis/trans ratio, are discussed just in terms of the correlations between stereochemistry and phase behavior.

Novel aliphatic, random copolyesters, containing co-units derived from a poly(alkylene dicarboxylate) and a poly(butylene 1,4-cyclohexanedicarboxylate), have been synthesized and characterized in terms of molecular structure and thermal properties. In particular, the effects of the molar composition, the length of the aliphatic sequences, and the cis/trans ratio of the 1,4-cyclohexylene units on the characteristics of the crystalline and amorphous phases are discussed. Some interesting structure-property relationships have been found. The materials result to be very promising new biopolymers as they are characterized by a potential biodegradability and good physical properties, which can be easily modified, according to the requests of specific applications, by little changes in the Molecular structure.

The aliphatic counterparts of the most used aromatic polyesters (PET, PPT, and PBT) have been synthesized by a two-stage polycondensation process, starting from dimethyl 1,4-cyclohexane dicarboxylate and different diols. The fully aliphatic polyesters are characterized by two cis/trans isomeric ratios (50 and 90 mol%) of the 1,4-cycloaliphatic rings. According to the cis/trans content, the properties of the materials notably change. Indeed, polymers rich in trans isomer are semicrystalline, whereas polymers with low trans content are fully amorphous, due to the presence of kinks along the chain. Trans isomer is characterized by higher rigidity than the cis one and the corresponding polymers have high glass transition temperatures. Moreover, the length of the methylene sequences in the diol has a notable influence on the final thermal and mechanical properties. Therefore, tunable properties can be easily obtained. This characteristic, in association with good mechanical performances, potential sustainability of the monomers and biodegradability, makes these aliphatic polyesters an interesting class of polyesters for some specific applications.

A family of unique aliphatic–aromatic copolyesters was prepared by bulk condensation copolymerizations of bio-derived ω-hydroxytetradecanoic acid (H) with 1,4-butanediol (B) and dimethyl terephthalate (DMT). 1H NMR analysis showed the copolyesters have random repeat-unit sequence distributions. Thermal properties strongly depend on molar composition. Melting temperatures are lower than 70 °C for compositions rich in H-units; Tm varies from about 140 to 180 °C for copolymers with high butylene terephthalate (BT) content. Crystal lattice structures shift from the crystal phase of poly(ω-hydroxytetradecanoate) (PH) to that of PBT with increasing BT copolymer content, while the minor component is trapped in the crystallizable domains as defects. The amorphous phase is homogeneous for all compositions and Tg increases from −21 °C (PH homopolymer) to 61 °C (PBT). Also, mechanical properties vary in a continuous way, according to copolymer composition. Therefore, the combination of aliphatic and aromatic units enables molecular design of partially biobased materials with adjustable thermal and physical–mechanical properties. Thus, by judicious selection of copolymer composition, material properties can be fine-tuned to attain the desired balance of material rigidity, ductility, melting point and biobased content.

International audience; The knowledge of the photodegradation mechanisms and the possibility to modify them is a very important topic, especially for the novel biopolymers, as their durability with respect to the petro-plastics is yet an open question. Among the biopolymers, aliphatic polyesters are an emerging class of materials, thanks to the possibility of preparing them from renewable resources and their potential environmental degradability. In this study two aliphatic molecular structures, containing 1,4-cyclohexylene units, have been used: poly(butylene 1,4-cyclohexanedicarboxylate) (PBCHD) and poly(1,4-cyclohexylenedimethylene 1,4-cyclohexanedicarboxylate) (PCCD). Moreover, in order to increase the durability, titanium dioxide (TiO2), known for its capability of absorbing UV radiation, was incorporated into the polymer. Therefore, composites containing different amount of titania, in the anatase and rutile crystalline phases separately, have been prepared by using a Brabender mixer. Both matrixes and composites were exposed to UV irradiation in an accelerated photo-ageing device and the modifications in their chemical structures were analysed by UV and IR spectroscopies. It results that the photodegradability of PBCHD, containing only one cycle per repeating unit, is lower than that of PCCD and that the composites have a photodegradability lower than those of the homopolymers. The well dispersion of the particles and the good adhesion between TiO2 and polymer have been checked by SEM observations. The protection of TiO2 against the photooxidation increases with the particle content and results higher for the anatase crystalline phase.