Impact of Butyl Glycidyl Ether Comonomer on Poly(glycerol–succinate) Architecture and Dynamics for Multifunctional Hyperbranched Polymer Design

An original strategy is proposed to easily design functional materials from poly­(glycerol–succinate) (PGS). This approach consists in the introduction of an epoxidized functional agent during the polyesterification between the glycerol and succinic acid. In order to model the effect of this epoxide group on the polymerization process and its resulting hyperbranched architecture, the butyl glycidyl ether (BGE) has been selected as comonomer agent. The theoretical potential reactions have been confronted with the topological units revealed by 2D NMR correlations. The regioselectivity against the primary alcohol and the stoichiometric balance of the system have been modified <i>in situ</i> by the kinetic control of parallel reactions. This had the effect to delay the gelation and increase the polyesterification conversion. The resulting hyperbranched polymers (HBPs) obtained just after gelation exhibit a temperature of glass transition (<i>T</i>_g) of −3.9 °C for PGS and −16.1 °C for poly­(glycerol–succinate-<i>co</i>-butyl glycidyl ether) (PGS-<i>co</i>-BGE). This difference was explained by the BGE butyl tails effect which plays the role of dynamic spacer between the polymer chains during the relaxation process. The relaxation processes were investigated by the computation of the effective activation energy (<i>E</i>_α) through the <i>T</i>_g using the advanced isoconversional method and by the estimation of the β-relaxation activation energy (<i>E</i>_β) by means of annealing experiments. The variation of <i>E</i>_α and <i>E</i>_β values was discussed in terms of competition between the cooperative/noncooperative segment motions and the hindrance effect of the hydrogen-bonded network. The dynamic behavior of this system can be potentially generalizable to all the plastic glass containing a critical amount of secondary interactions

Synthesis of Glycerol-Based Biopolyesters as Toughness Enhancers for Polylactic Acid Bioplastic through Reactive Extrusion

The synthesis of polyesters based on glycerol, succinic acid [poly­(glycerol succinate), PGS] and/or maleic anhydride [poly­(glycerol succinate-<i>co</i>-maleate), PGSMA] was investigated aiming to produce a green product suitable for toughening of polylactic acid (PLA) using melt blending technologies. The molar ratio of reactants and the synthesis temperature were screened to find optimum synthesis conditions leading to the highest toughness enhancement of PLA. It was found that a molar ratio of reactants of 1:1 glycerol/succinic acid increases the effectiveness of PGS as a toughening agent for PLA, which correlates with the achievement of a higher molecular weight on the synthesis of PGS. The introduction of maleic anhydride as a comonomer for the synthesis of the partial replacement of succinic acid was advantageous for making PGS suitable for reactive extrusion (REX) mediated by free radical initiators. The tensile toughness of the REX PLA/PGSMA blends was improved by 392% compared with that of neat PLA, which was caused by the simultaneous cross-linking of PGSMA within the PLA matrix, and the in situ formation of PLA-<i>g</i>-PGSMA graft copolymers acting as interfacial compatibilizers. Two-dimensional nuclear magnetic resonance and Fourier transform infrared analysis confirmed the formation of PLA-<i>g</i>-PGSMA species on REX experiments. This in turn caused a decrease in the diameter of the PGS particles dispersed within the PLA matrix from >10 μm to approximately 2 μm as observed using scanning electron microscopy. A further increase of 1600% in the toughness of the blends was achieved by lowering the synthesis temperature of PGSMA from 180 to 150 °C. The optimum synthesis conditions for PGSMA leading to the highest increase in the toughness of 80/20 PLA/PGSMA blends were found to be 1:0.5:0.5 mol glycerol/succinic acid/maleic anhydride synthesized at a temperature of 150 °C for 5 h

In Situ Cellulose Nanocrystal-Reinforced Glycerol-Based Biopolyester for Enhancing Poly(lactic acid) Biocomposites

Biobased, elastomeric polymer poly­(glycerol succinate-<i>co</i>-maleate) (PGSMA) was produced using a “green” synthesis with added cellulose nanocrystals (CNCs) to create a novel PGSMA–CNC material. PGSMA–CNC was synthesized with the aim of developing a new strategy for successfully dispersing CNCs within a poly­(lactic acid) (PLA) matrix for optimal reinforcement of tensile strength and modulus while having the added benefit of the proven toughness enhancements of PLA/PGSMA blends. Optical microscopy and fractionation in tetrahydrofuran showed that CNCs agglomerated during PGSMA–CNC synthesis and remained in agglomerates during PLA/PGSMA–CNC reactive blending. Fourier transform infrared, differential scanning calorimetry, and dynamic mechanical analyses also showed that PGSMA–CNC inhibited the formation of PGSMA crosslinks and PLA-<i>g</i>-PGSMA during reactive blending. These two effects resulted in loss of impact strength and only a 4% increase in tensile modulus over PLA/PGSMA at the highest CNC content. Further work in preventing CNC aggregation could help improve mechanical properties of the final blend