Carolus H. R. M. Wilsens

Synthesis, kinetics, and characterization of bio-based thermosets obtained through polymerization of a 2,5-furandicarboxylic acid-based bis(2-oxazoline) with sebacic acid

The synthesis of renewable 2,5-furandicarboxylic acid-based cross-linked poly(ester amide)s via the polymerization of a 2,5-furandicarboxylic acid based bis(2-oxazoline) monomer (2,5-bis(4,5-dihydrooxazol-2-yl)furan, 2,5-FDCAox) with sebacic acid is reported in this work. It is demonstrated that the amide groups in the 2,5-furandicarboxamide moiety are susceptible to participation in a branching reaction with 2-oxazoline rings. The corresponding enhanced reaction rate decreases the curing times for the preparation of cross-linked polymers compared to systems containing the isophthalic acid based alternative, 1,3-bis(4,5-dihydrooxazol-2-yl)benzene (IAox). The increased tendency to form branches or cross-links in 2,5-FDCAox based systems is attributed to the occurrence of intra-molecular hydrogen bonding of the 2,5-furandicarboxamide moiety. Such an intra-molecular hydrogen bond increases the nucleophilicity of the furanic amide group and makes it more susceptible to participation in an addition reaction with a 2-oxazoline ring. Furthermore, it is demonstrated that the rate of the branching reaction can be enhanced by the addition of triphenyl phosphite as catalyst, resulting in a further decrease of the curing times of the poly(ester amide)s synthesized in this study. Preliminary coating studies indicate that 2,5-furandicarboxylic acid based cross-linked poly(ester amide)s synthesized via the 2-oxazoline ring opening addition reactions with dicarboxylic acids are good candidates for the development of fully renewable cross-linked poly(ester amide)s.

Self-assembling process of Oxalamide compounds and their nucleation efficiency in bio-degradable Poly(hydroxyalkanoate)s

One of the key requirements in semi-crystalline polyesters, synthetic or bio-based, is the control on crystallization rate and crystallinity. One of the limiting factors in the commercialization of the bio-based polyesters, for example polyhydroxyalkanoates synthesized by bacteria for energy storage purposes, is the slow crystallization rate. In this study, we show that by tailoring the molecular structure of oxalamide compounds, it is possible to dissolve these compounds in molten poly(hydroxybutyrate) (PHB), having a hydroxyvalerate co-monomer content of less than 2 mol%. Upon cooling the polymer melt, the homogeneously dispersed oxalamide compound crystallizes just below the melting temperature of the polymer. The phase-separated compound reduces the nucleation barrier of the polymer, thus enhancing the crystallization rate, nucleation density and crystallinity. The findings reported in this study provide a generic route for the molecular design of oxalamide-based compounds that can be used for enhancing nucleation efficiency of semi-crystalline bio-based polyesters.

Effect of Self-Assembly of Oxalamide Based Organic Compounds on Melt Behavior, Nucleation, and Crystallization of Isotactic Polypropylene

We report on the effect of an aliphatic oxalamide based nucleating agent (OXA3,6) on the melt and crystallization behavior of isotactic polypropylene (iPP) under defined shear conditions. Through polarized optical microscopy, we demonstrate that OXA3,6 self-assembles from the iPP melt into rhombic crystals whereas their size and distribution proved highly dependent on the employed cooling rates. The presence of 0.5 wt % of OXA3,6 in iPP results in a significant suppression in iPP melt viscosity, which could not be explained via molecular modeling. A possible cause for the drop in viscosity in the presence of OXA3,6 is attributed to the interaction (absorption) of high molecular weight iPP chains with the nucleating agent, thereby suppressing their contribution to the viscoelastic response of the melt. This proposed mechanism for the suppression in melt viscosity appears similar to that encountered by the homogeneous distribution of nanoparticles such as CNTs, graphene, and silica. Shear experiments, performed using a slit flow device combined with small-angle X-ray diffraction measurements, indicate that crystallization is significantly enhanced in the presence of OXA3,6 at relatively low shear rates despite its lowered sensitivity to shear. This enhancement in crystallization is attributed to the shear alignment of the rhombic OXA3,6 crystals that provide surface for iPP kebab growth upon cooling. Overall, the suppression in melt viscosity in combination with enhanced nucleation efficiency at low as well as high shear rates makes this self-assembling oxalamide based nucleating agent a promising candidate for fast processing.

Renewable (Bis)pyrrolidone Based Monomers as Components for Thermally Curable and Enzymatically Depolymerizable 2-Oxazoline Thermoset Resins

In this study we describe the synthesis of bis(pyrrolidone) based dicarboxylic acids from itaconic acid and their application in 2-oxazoline resins for fully renewable thermoset materials. The monomers are obtained using a bulk aza-Michael addition of a diamine and two itaconic acid molecules using a catalytic amount of water. The monomers can be isolated in high purity after recrystallization, though their yield proved to be highly dependent on the selected diamine spacer length: In general, only the dicarboxylic acids containing diamines with an even number of methylene spacers are isolated in high yields. Through NMR, GPC, and FTIR analysis we demonstrate that these bis(pyrrolidone) based dicarboxylic acids exhibit significantly enhanced curing rates in 2-oxazoline resins compared to resins containing aliphatic dicarboxylic acids such as sebacic acid. Overall, we demonstrate that the rate of 2-oxazoline ring-opening addition with carboxylic acid functionalities is determined by the used dicarboxylic acid, whereas the ring-opening addition of the 2-oxazoline functionality with amide groups is determined by the used bis(2-oxazoline) compound. The thermosets obtained after curing proved to be readily plasticized by water, opening up possibilities for enzymatic degradation.