Design of Mechanically Robust High-Tg Polymers: Synthesis and Dynamic Mechanical Relaxation Behavior of Glassy Poly(ester carbonate)s with Cyclohexylene Rings in the Backbone

Abstract

High-Tg yet mechanically robust polymers are desirable but difficult to realize. To explore whether the insertion of a motionally active molecular entity in the backbone could produce polymers with both high Tg and yet are not brittle, three series of high-Tg glassy polycarbonates/polyesters/poly(ester carbonate)s were designed and synthesized. The secondary relaxation behavior of these polymers was studied by dynamical mechanical analysis (DMA). Incorporation of cyclohexylene groups (C-rings) in the main chain of polymers made from two rigid and bulky monomers, spirobiindane bisphenol (SBI) and trimethylcyclohexylbisphenol (Tmc), respectively, changes the γ relaxation process dramatically in peak shape and position in these polymers. No such change is observed in polycarbonate polymers made from cyclohexylbisphenol (BPAZ), or ZPC for short. Through monitoring the γ relaxation with gradual structural change, C-rings in the main chain backbone are proposed to undergo active ring inversion. The γ relaxation of ZPC is proposed to be mainly due to side-chain C-ring inversion. The narrowing on the high-temperature side of the γ relaxation peak of the polycarbonate of Tmc is proposed to be due to the restricted motion of its axial phenyl rings. A linear correlation between relaxation strength and total C-ring concentration was found for all the polymers.