Effects of alkali metal catalysts on the melt fluidity of polycarbonates with different degrees of polymerization

Abstract

The melt fluidity of polycarbonate (PC) significantly influences the processing, while the melt viscosity depends on the molecular structure. Specifically, the melt viscosity increases sharply with the increase of polymerization degree.However, the influence mechanism of alkali metal catalysts on the fluidity by affecting the molecular structure remains unclear. Herein, high and low concentrations of NaOH catalysts were used to synthesize PC with different polycondensation degrees. The effect of NaOH catalyst content on the molecular structure and thus melt fluidity of PC were systematically characterized and discussed employing NMR spectroscopy, absolute and relative molecular weight, intrinsic viscosity, melt flow index, and thermal analysis. The results show that a random branched structure of the PC molecular chain caused by excess NaOH improves the melt flowability. However, the residual NaOH promotes the degradation of carbonate bonds during thermal processing, resulting in poor PC stability. Based on the above discussion, empirical fitting equations are proposed to describe the relationship between molecular structure and flow properties, which provides a new way to judge PC performance.

Alkali Metal/Quaternary Ammonium Salt Synergistic Catalytic System for the Efficient Synthesis of Biobased Poly(Isosorbide Carbonate)

“…The curves were shown in Figure , and the results were summarized in Table . According to the DSC curves, PICs prepared by different catalysts were amorphous with glass transition temperature ( T g ) in the range of 167 and 171 °C, higher than that of BPA-PC (140–150 °C) . The asymmetric structure of ISB broke the regularity of polymer chains, making the polymer hard to crystallize.…”

“…Intrinsic viscosity [η] was determined by using Ubbelohde viscometer at 20 ± 0.5 °C with CH 2 Cl 2 as the solvent, and it was calculated according to eq : ,, [ η ] = 2 ( η s p − ln ⁡ η normalr ) / C where C is the concentration of the PIC solution, C = 0.005 g/mL, η r is the relative viscosity, and η sp is the specific viscosity. Viscosity-average molar mass ( M η ) was calculated by the following eq [ η ] = K M η α where the constants K = 0.0111 mL/g and α = 0.82. ,, …”

“…According to the DSC curves, PICs prepared by different catalysts were amorphous with glass transition temperature (T g ) in the range of 167 and 171 °C, higher than that of BPA-PC (140−150 °C). 43 The asymmetric structure of ISB broke the regularity of polymer chains, making the polymer hard to crystallize. And the adjacent furan rings hindered the movement of the polymer chains, which resulted in higher T g .…”

Synthesis, Characterization, and Application of High-Molecular-Weight Polyethylene-like Polycarbonates: Toward Sustainable and Recyclable Fibers

“…23,34 The polymerization process undergoes an transesterification process at 180 °C and a polycondensation process at 230 °C (Figure 2a). NaOH (1 × 10 −4 mol %) and PPh 4 OPh (2.5 × 10 −3 mol %) were chosen as a catalytic system, which shows as excellent catalytic performance as the polycondensation of DPC and bisphenol A in our previous work, 43 producing highquality polycarbonates. The presence of PPh 4 OPh can enhance the reactivity in the transesterification and reduce the usage of NaOH, the residual of which reduces the thermal stability of product polycarbonates.…”

“…Notably, the usage of a small amount of NaOH catalyst is still necessary as using PPh 4 OPh alone is difficult to drive the later-stage polycondensation reaction. 43 The resultant PLPCs are characterized by 1 H NMR, 13 C NMR, and gel permeation chromatography (GPC). As an overview for all the resultant PLPCs, >99% carbonate linkages, weight-average molecular weight (M w ) around 10 5 g/mol, narrow molecular weight distribution (Đ, 1.69−1.80), and moderate to high crystallinity (38−64%) were observed (Table 1).…”