Synthesis of Polymandelide:  A Degradable Polylactide Derivative with Polystyrene-like Properties

Abstract

Polymandelide, an aryl analogue of polylactide, was synthesized by the ring-opening polymerization of mandelide, the cyclic dimer of mandelic acid. The poor solubility of rac-mandelide limited the synthesis of polymandelide via solution polymerization, but polymerization of mandelide at 70 °C as a heterogeneous slurry in acetonitrile yielded first-order kinetic plots and polydispersities <1.2. High molecular weight polymer prepared by melt polymerizations at T > 150 °C exhibit properties that mimic those of polystyrene. Polymandelide is a glassy amorphous polymer with a T g of 100 °C, with rheological properties comparable to polystyrene, and thermal gravimetric analyses under nitrogen show that the polymer is stable to ∼300 °C. Racemization during polymerization precluded formation of a crystalline polymer. Degradation of polymandelide in pH 7.4 buffer at 55 °C is consistent with a bulk erosion model and, due to its high T g , proceeds at ∼1/100 the rate of polylactide under similar conditions.

Preparation of Stereoregular Isotactic Poly(mandelic acid) through Organocatalytic Ring‐Opening Polymerization of a Cyclic O‐Carboxyanhydride

“…[12] Recently, in an intriguing report, Baker et al demonstrated the first synthesis of high-molecular-weight poly(mandelic acid) (PMA) through a tin-catalyzed ROP of mandelide, the cyclic dimer of mandelic acid (an aryl analogue of lactide; Scheme 1). [13] They demonstrated that polymandelide shares many physical and mechanical properties with polystyrene, including a high T g (95-100 8C), but is available from renewable resources and degradable as PLA. However, the synthesis of mandelide requires extended reaction times and high-boiling solvents and results in poorly soluble monomers in poor to moderate yields.…”

Synthesis of Poly(lactide)s with Modified Thermal and Mechanical Properties

“…In an attempt to increase the relatively low T g values (<60 °C) of these alkyl‐functional cyclic diesters, Baker and coworkers reported the synthesis of cyclohexyl‐, isopropyl‐, and phenyl‐substituted glycolides 84, 85. 3,6‐Diphenyl‐1,4‐dioxan‐2,5‐dione (mandelide, 9 ) is readily prepared from rac ‐mandelic acid by dimerization in the presence of acidic catalyst as a statistical mixture of LL ‐, DD ,‐ and meso ‐diastereomers 85. While the rac ‐ and meso ‐isomers could be readily separated based on their solubility, the ready racemization of the benzylic methine proton under polymerization conditions made their isolation unnecessary.…”

Controlled Ring‐Opening Polymerization of O‐Carboxyanhydrides Using a β‐Diiminate Zinc Catalyst

“…[12] One drawback of these base catalysts is deprotonation of the a-methine hydrogen of OCAs during the ROPprocess. [14] It is therefore crucial to develop aviable catalyst that has enhanced control over the ROPo fO CAs leading to PA HAs with controlled molecular weights (MWs) and stereoregularity.A na lternative to the use of organocatalysts for the ROPo fO CAsi nvolves the use of organometallic catalysts, [6,15] such as metal alkoxides that have been shown to polymerize lactones in al iving, highly controlled manner. [14] It is therefore crucial to develop aviable catalyst that has enhanced control over the ROPo fO CAs leading to PA HAs with controlled molecular weights (MWs) and stereoregularity.A na lternative to the use of organocatalysts for the ROPo fO CAsi nvolves the use of organometallic catalysts, [6,15] such as metal alkoxides that have been shown to polymerize lactones in al iving, highly controlled manner.…”