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Significance Statement
Hyperbranched polymers are densely branched structures with high number of end groups stemming from a central core. Their architectural structure is of interest in several industrial applications because of their achievable intrinsic viscosity, better chemical reactivity, conformable branching degrees and solubility as well as admirable mechanical properties. These unique features characterized by hyperbranched polymers have shown positive results when used in biomedical applicationsand conjugated functional materials.
A new research led by Professor Amar Mohanty at the Bioproducts Discovery and Development Centre – University of Guelph in Canada and published in the journal, Macromolecules reported a new method for designing multifunctional hyperbranched polymers by simple using “active” glycidyl ether as a co-monomer agent during the polymerization between glycerol and succinic acid. Herein, the butyl glycidyl ether has been chosen as model molecule to mimic the introduction of this “agent” in the poly (glycerol-succinate) architecture. The work also included verification of their features by taking measurements on their molecular weight, viscosity, stress relaxation, thermal response and branching degrees.
The epoxidized ring-opening reaction characterized by butyl glycidyl ether when observed with Nuclear Magnetic Resonance (NMR) indicated a complete reaction of butyl glycidyl ether on the poly (glycerol-succinate) architectures when added for a period of two hours.
Outcomes observed from Heteronuclear Single Quantum Coherence (HSQC: 2D NMR sequence) spectra showed that butyl glycidyl ether which acted as a grafting agent also functioned as a branching agent between two functional groups of carboxylic acid and hydroxyl group, generated by the epoxide opening ring.
The authors also observed that the regioselectivity against the primary alcohol and the in situ stoichiometry balance modification between the alcohol and carboxylic acid led to a delay in the gelation process with an increase in polyesterification conversion following the complete reaction of butyl glycidyl ether.
Comparison between the molecular weights and molecular number of poly (glycerol-succinate) and that of synthesized poly (glycerol-succinate-co-butyl glycidyl ether) before gelation proved that the grafting of the comonomer agent had less effect on polymerization as increase in molecular weights of the two polymers were quite higher compared to their molecular number. This leads to a reaction between glycerol and succinate as major contributors to the extent of polymerization.
The authors also observed a lower glass transition temperature of -16°C for the synthesized poly (glycerol-succinate-co-butyl glycidyl ether) when compared to poly (glycerol-succinate) having a glass transition temperature of -3.9°C. This shows the effect of butyl glycidyl ether on architectures of poly (glycerol-succinate). Results also showed that the branching degree has little effect on the overall glass transition temperature in this particular case, comparing the spacer effect of the butyl glycidyl ether.
The effective activation energy variation of poly (glycerol-succinate) and poly(glycerol-succinate-co-butyl glycidyl ether) during their respective glass transition temperatures indicates that the relaxation process in polymers was largely influenced by the hydrogen bonded network. The hyperbranched polymers of poly (glycerol-succinate-co-butyl glycidyl ether) exhibit a higher relaxation time, which was attributed to higher free volume and butyl tail motion.
In the study the authors were able to design hyperbranched polymers with enhanced functional properties which are well compatible with modern biomedical applications.
Reference
Pin, J.M., Valerio, O., Misra, M., Mohanty, A. Impact of Butyl Glycidyl Ether Comonomer on Poly(glycerol−succinate) Architecture and Dynamics for Multifunctional Hyperbranched Polymer Design, Macromolecules 50 (2017) 732−745.
Bioproducts Discovery and Development Centre, Department of Plant Agriculture, and School of Engineering, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
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