Dynamics of Poly(cyclohexene carbonate) as a Function of Molar Mass

Abstract

Stereoregular poly­(cyclohexene carbonate) (PCHC) homopolymers were prepared via copolymerization of cyclohexene oxide and carbon dioxide (CO2) using (R,R)-(salcy)-CoCl and bis­(triphenylphosphine)­iminium chloride as a catalyst. The homopolymers had molar masses in the range of 4800–33,000 g mol–1 and relatively narrow dispersity after careful fractionation, as required for the molecular dynamics investigation. We employed differential scanning calorimetry and dielectric spectroscopy, the latter as a function of temperature and pressure, for investigating the thermal properties and the molecular dynamics, respectively. The segmental dynamics in the vicinity of the liquid-to-glass temperature was very complex. The dual segmental processes were inseparable by decreasing the temperature or by increasing the pressure. Based on DFT calculations of the dipole moment, they were ascribed to different stereo sequences of the PCHC backbone. The limiting glass temperature, T g, for very high molar masses was ∼125 °C. The high T g value obtained herein well justifies its application as a CO2-based alternative for polystyrene (PS) in a variety of materials based on block copolymers. Moreover, fragility increased with increasing molar mass with values intermediate to poly­(styrene) and poly­(cyclohexyl methacrylate). The flexible cyclohexyl group in PCHC undergoing intramolecular chair-to-chair conversion increases the packing ability and consequently decreases the fragility. PCHC is a brittle material because it lacks entanglements even for the higher molar masses investigated herein, which is relevant for application as a PS substitute. Within the investigated range of molar masses, the dependences of the terminal relaxation times, τΝΜ, and of the zero-shear viscosity, ηο, on the molar mass, M, are τΝΜ/τSM ∼ M 3.2 and ηο ∼ M 1.4, revealing an intermediate behavior between Rouse and entangled chains.

High Molar Mass Polycarbonates as Closed-Loop Recyclable Thermoplastics

“…All the samples are amorphous plastics showing high glass transition temperatures ( T g ) with values, as determined by DSC, in the range 85–126 °C, which are dependent on the ring-size and alkyl-substituents (Figure S27a). As such, the T g for PCHC, featuring the 6-membered ring ( T g,DSC = 126 °C, which is at the limit predicted by the Fox–Flory equation), was ∼40 °C higher than for PCPC, which features the 5-membered ring ( T g,DSC = 85 °C) . Substituted rings show greater segmental motion compared to nonsubstituted ones, i.e., added pendant alkyl chains resulted in a slight reduction of the T g values.…”

“…The comparison of this series of polymers reveals that the cyclohexyl ring polymers, PCHC and PvCHC, both show M e values that are >10 times higher (∼54–56 kg mol –1 ) than the cyclopentyl ring-substituted polymer, PCPC ( M e ∼ 4.0 kg mol –1 ). Due to the high molar masses and narrow dispersity values of the polymers described in this work, values of M e obtained for PCHC are 4 times greater than those previously estimated. , Intriguingly, ethyl-substituted PeCHC displays a somewhat intermediate value of M e ∼ 15 kg mol –1 between these two extremes. It is clear from these results that ring-size and alkyl substitution directly influence the molecular dynamics, including the distance between entanglements.…”

“…The data are also fully consistent with the difficulties in processing and testing brittle PCHC: almost all prior investigations used samples that were below the critical molar mass or chain entanglement thresholds. 43,45,46,54,56 Certainly, the steep frequency dependence of the G′ data in the rubbery plateau region makes the evaluation of M e still somewhat challenging, and more refined estimates from the value of ∼56 kg mol −1 might still be possible in the future. In contrast, the much less widely investigated PCPC shows an order of magnitude lower M e , with entanglement being of the same magnitude as other strong thermoplastics, e.g., BPA-PC M e = 1.6−4.8 kg mol −1 , and is considerably lower than brittle thermoplastics, e.g., PLLA, M e = 8−10 kg mol −1 ; 82 PS, M e = 13−18 kg mol −1 .…”

“…In 2022, Frey and Floudas investigated, both experimentally and computationally, the chain dynamics of moderate molar mass PCHC (5 < M n < 33 kg mol −1 ) produced using a [(R,R-salcy)CoCl]/PPNCl catalyst system, estimating an M e of 16 kg mol −1 . 46 It is also relevant to note that PCHC has been successfully applied as a "rigid" block in various phase separated copolymers (T g of PCHC ∼ 110−120 °C), producing adhesives, elastomers, and plastics, depending on the comonomers and overall molar mass values. 15,18,43,51−53 Beyond CHO as comonomer in ROCOP, the teams of Rieger and Greiner independently focused on related 6-membered ring, biobased poly(limonene carbonate), developing routes to high molar mass and terpolymers with PCHC.…”

Solid-State Chemical Recycling of Polycarbonates to Epoxides and Carbon Dioxide Using a Heterodinuclear Mg(II)Co(II) Catalyst

“…Cyclohexene oxide/CO 2 ROCOP is the benchmark for catalyst comparisons and PCHC shows a high glass transition temperature (∼120 °C) and tensile modulus (3600 MPa) . It has a broad processing temperature range (>100 °C), and thermal degradation begins at temperatures of >240 °C. − PCHC-containing block polymers show promise as toughened plastics, elastomers, and adhesives . Thus, achieving its chemical recycling to monomer is important; earlier this year, we reported a Mg­(II)­Mg­(II) catalyst, applied in para -xylene solution, which delivered very high CHO selectivity (98 %) and a turn-over-frequency (TOF) of 150 h –1 (0.33 mol % catalyst, 120 °C, [PCHC] 0 = 1 M) (Figure ).…”