Biobased step-growth polymers : chemistry, functionality and applicability

Inspired by the opportunity to obtain materials with interesting new properties and further stimulated by the increasing oil prices and the augmenting environmental concerns, renewed interest in biobased polymers has recently arisen. Extensive efforts are being invested in extracting useful starting materials from renewable resources and to use these molecules to synthesize novel polymers. The aim of this study was to investigate the potential of several biobased monomers as starting compounds to synthesize polycondensate resins suitable for coating or toner applications. An in-depth study of the chemistry, functionality and the structure-property relations of such polymers was performed. Step-growth polymers with specific characteristics with respect to molecular weight (distribution), end-group structure and thermal properties were targeted. This part of the project included a detailed study of the suitable reaction conditions to polymerize the biobased starting materials, which often have limited reactivity and thermal stability. Polyesters were prepared by reacting the 1,4:3,6-dianhydrohexitols (DAHs, i.e. isosorbide, isoidide and isomannide) with dicarboxylic acids such as succinic acid. The bicyclic structures of the DAHs introduce sufficient chain rigidity and, thus, already for the relatively low molar masses required for coating resins sufficiently high glass transition temperatures (Tg) were obtained. Series of linear and branched terpolyesters were synthesized, of which the average number of reactive end-groups per polymer chain could be adjusted by varying the amount of polyols present in the reaction mixture. It was shown that the exo-oriented hydroxy-groups present in isoidide and isosorbide are more reactive in melt polycondensation reactions, using non-activated dicarboxylic acids, than their endo-oriented counterparts present in both isomannide and isosorbide. In addition, we found that the anhydro ether rings of isomannide are susceptible to ring-opening at elevated temperatures, in contrast to the ether rings of isosorbide and isoidide, which appear to be stable under these conditions. When using isoidide or isomannide to synthesize polyesters, semi-crystalline polymers are obtained, while polymerization of isosorbide with dicarboxylic acids yields amorphous materials. To obtain carboxylic acid-functional polyesters, linear hydroxy-functional polyesters were reacted with citric acid in the melt. Model reactions were carried out to investigate the chemistry of this modification reaction and the resulting end-group structures. Interestingly, citric acid is transformed into a more reactive anhydride species close to its melting temperature of 153 ºC. Therefore, the modification of hydroxy-functional polymers with the thermally labile citric acid can be performed at relatively low temperatures. In addition, the modified products can be cured with conventional cross-linkers (vide infra) at moderate temperatures, which is probably partly due to anhydride formation at the polyester chains ends, accelerating the curing reaction. Aliphatic, biobased polycarbonates were prepared by polymerization of the DAHs, in combination with other diols and/or polyols, using several types of carbonyl sources such as triphosgene, diphenyl carbonate and bis(ethyl/phenyl carbonate) species derived from the DAHs. It proved to be difficult to control the end-group structures of the polycarbonates when using the highly reactive phosgene derivatives, whereas the interchange reactions of the biobased diols with diphenyl carbonate required high reaction temperatures to achieve sufficient conversion. Thermal degradation occurred through an unzipping mechanism and decarboxylation. To prevent these detrimental side reactions, the hydroxy-groups of the DAHs were first converted to carbonate linkages using chloroformates, followed by melt interchange reactions of the resulting molecules with primary diols and/or polyols. These polymerizations do not require too high reaction temperatures, thereby limiting degradation and resulting in the desired hydroxy-functional copolycarbonates with satisfactory Tgs and molecular weights. Another route to functionalized, aliphatic polycarbonates was investigated, involving alcoholysis of high molecular weight poly(cyclohexene carbonate) by polyol species such as trimethylolpropane and 1,3,5-cyclohexanetriol. The obtained polycarbonates have significantly enhanced functionalities as well as reduced molecular weights and Tgs, all suitable for coating applications. The various hydroxy-functional polymers were mixed with free or e-caprolactam-blocked polyisocyanate curing agents and applied as coatings by either solution casting or powder coating. Polymers with carboxylic acid end-groups were cured using epoxy-compounds or ß- hydroxyalkylamides. The resulting polyester and poly(ester/carbonate urethane) coatings were tested for chemical, mechanical and UV stability. In addition, the rheological properties of these materials were investigated. Networks obtained by curing branched polymers perform better than those prepared from linear polymers, which is mainly due to the enhanced crosslink density of the former systems. Solvent and impact resistant coatings were prepared from linear and branched, biobased polycondensates. In addition to the conventional curing agents used in this study, several novel, biobased, e-caprolactam-blocked diisocyanates proved efficient in cross-linking branched polyesters and polycarbonates, leading to fully biobased, chemically and mechanically stable, glossy coatings with very promising properties

Polyuretanes, polyurethaneureas and polyureas and use thereof

The present invention is to a chain extended polyurethane, polyurethaneurea and/or polyurea segmented copolymer wherein the polyurethane, polyurethaneurea or polyurea segment contain a chain extender having an amide segment, an ester segment or a combination of amide and ester segments

Hydrophobic, self-replenishing coatings for polar substrates

Abstract only

Polyesters, polycarbonates and polyamides based on renewable resources

In this chapter, we have given an overview of a range of biomass-based polymers prepared through polycondensation chemistry. This is by no means an exhaustive summary of available starting materials and polymers. Still, it is clear that this rapidly expanding field of research opens up new synthetic pathways to performance polymers with exciting novel properties. Some of these biobased polycondensates can rival conventional polymers from petro-chemistry in terms of mechanical and chemical performance and a limited number have already found their way to the market place. Further development of bio-refining processes is expected to improve the availability and economics of the discussed starting materials and polymers. Several of the presented polymers can be produced in existing process equipment with only minor adjust ments. Typically, improved temperature control and an inert atmosphere are required to prevent degradation and discoloration of the bio-based products. In addition, more sustainable and milder synthetic routes as well as more effective catalysis are necessary to make optimal use of biomass, constituting stimuli for new research into the field of step-growth polymerization

Polyesters, polycarbonates and polyamides based on renewable resources

In this chapter, we have given an overview of a range of biomass-based polymers prepared through polycondensation chemistry. This is by no means an exhaustive summary of available starting materials and polymers. Still, it is clear that this rapidly expanding field of research opens up new synthetic pathways to performance polymers with exciting novel properties. Some of these biobased polycondensates can rival conventional polymers from petro-chemistry in terms of mechanical and chemical performance and a limited number have already found their way to the market place. Further development of bio-refining processes is expected to improve the availability and economics of the discussed starting materials and polymers. Several of the presented polymers can be produced in existing process equipment with only minor adjust ments. Typically, improved temperature control and an inert atmosphere are required to prevent degradation and discoloration of the bio-based products. In addition, more sustainable and milder synthetic routes as well as more effective catalysis are necessary to make optimal use of biomass, constituting stimuli for new research into the field of step-growth polymerization

Aromatic thermotropic polyesters based on 2,5-furandicarboxylic acid and vanillic acid

This paper addresses a route to synthesize bio-based polymers with an aromatic backbone having a liquid crystalline (LC) phase in the molten state. The LC phase is employed to achieve uniaxial orientation during processing required in e.g. fiber spinning. For this purpose 2,5-furandicarboxylic acid (2,5-FDCA) and O-acetylvanillic acid (AVA), obtained from natural resources, are used as monomers. Similar to the 2,6-hydroxynapthoic acid used to perturb the crystalline packing of poly(oxybenzoate) in the Vectran® series, these bio-based monomers are used to lower the crystal to liquid crystal transition temperature. Considering that the poly(oxybenzoate) can also be obtained from natural resources, the adopted route provides the unique possibility to synthesize bio-based polymers that can be used for high performance applications. To obtain the desired polymers, a synthetic route is developed to overcome the thermal instability of the 2,5-FDCA monomer. Experimental techniques, such as optical microscopy, FTIR spectroscopy, DSC, and TGA are employed to follow the polymerization, phase transitions and evaluate thermal stability of the synthesized polymers

Polyurethane elastomers with amide chain extenders of uniform length

Toluene diisocyanate based polyurethanes with amide extenders were synthesized poly(propylene oxide) with a number average molecular weight of 2000 and endcapped with toluene diisocyanate was used as the polyether segment. The chain extenders were based on poly(hexamethylene terephthalamide): hexamethylene diamine, bisamine-diamide and bisamine-tetra-amide. The linear poly(ether bisurethane-bisurea-amide)s (PUA) were colorless transparent thermoplastic elastomers with a high molecular weight. The polymers were analyzed by IR and DSC, the morphology studied by TEM, the mechanical properties studied by DMTA and the tensile, the elastic properties by compression and tensile set and thermal stability by melt rheology.\ud \ud The phase separation with these amide extenders was by crystallization. Increasing the length of the amide chain extender increased the modulus and the melting temperature of the PUA without changing the good low temperature properties. Also the elastic properties improved with amide segment length. The fracture stress increases with amide extender length. At 200 °C, the melt stability of the PUA with the bisamine-diamide chain extender was good