Fixation carbon dioxide into polymer is a feasible proposal to construct high value-added biodegradable plastic. These polymers are environmentally friendly and energy-saving owing to that the raw material is waste gas and finally they decompose back into CO₂. This review mainly focuses on our group work of recent advancements on CO₂-based copolymers, especially for poly (propylene carbonate) (PPC). We also extensively introduce the improvements on thermal and mechanical performances of PPC by physical and chemical modifications. Meanwhile, their practical application is further discussed in detail as well to replace the conventionally non-biodegradable plastics. The commercial PPC has already been found an enormous application prospect in versatile packaging industry.

Itaconic anhydride (IAn) was firstly used for the modification of poly(propylene carbonate) (PPC) by solution blending following with the direct heating treatment, producing end-capped and cross-linkable PPC (PECPPC) with high performance. The reaction of PPC with IAn was detailed investigated and the structure of PECPPC was identified by FTIR and ¹H NMR. A facile strategy including end-capping and cross-linking can be developed to improve the performance of PPC. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) measurements revealed that the glass transition temperature (T_g) and thermal decomposition temperature (T_d) of PECPPCs are all much higher than those of PPC and increased with the increasing content of IAn. Tensile tests also showed the huge enhancement on the mechanical properties of PPC with the end-capping and cross-linking techniques, and the highest tensile strength of PECPPC4 is 37.5 MPa. Furthermore, ECPPC4 exhibits high hydrolysis rate in phosphate buffer solution (PBS) than that of PPC. It is demonstrated that the strategy with the combination of end-capping and cross-linking is efficient for the perfect modification of PPC with IAn.

Poly (butylene furandicarboxylate) based poly (ether ester), with poly (ethylene glycol) (PEG) molecular weight from 600 to 20 K g mol⁻¹ and mass fraction of hard segments fixed at 50%, are synthesized through transesterification and melt polycondensation. When M_n (PEG) is less than 1500 g mol⁻¹, the copolymers tend to be homogeneous. The tendency of microphase separation is facilitated by the increasing M_n (PEG). The mechanical properties and water swelling are influenced by M_n (PEG), equilibrium water-uptake and PEG crystals. Elastic modulus of samples with no PEG crystals vary from 34 to 64 MPa, with elongation at break exceeding 1000%. The hydrolytic degradation is strongly affected by M_n (PEG), degradation medium and alkalinity. The degradation of copolymers with short PEG (<1500 g mol⁻¹) could be accelerated by ions and increasing alkalinity in medium. For copolymers with M_n (PEG) from 2 K to 6 K g mol⁻¹, the degradation rate is relatively slow, due to relatively long PBF segments and improved PBF crystals hindering the hydrolysis of ester bond. For copolyesters of PBF50-PEG10K and 20 K, the oxidation of PEG dominates the degradation behavior while the PBF segments can hardly be damaged. The drastic degradation of these samples takes place in the solutions of pH = 12, suggesting the high alkalinity can break the long PBF segments. The distinct degradation behavior of the copolymers conduces to realize tuned hydrolysis for different biomedical applications.

The copolymerization of CO₂/propylene oxide (PO)/cyclohexene oxide (CHO) was carried out using a Zn-based heterogeneous catalyst, namely a supported multi-component zinc dicarboxylate. The monomer reactivity ratios of PO (r_PO) to CHO (r_CHO) were estimated using the Fineman-Ross and Kelen-Tudos graphical methods. The results showed that the r_PO values were significantly higher than the corresponding r_CHO values in all cases, indicating that the incorporation of CHO into the polymer was kinetically unfavorable. The influence of the reaction temperature and pressure on the monomer reactivity ratios was also discussed. It was found that raising either the reaction temperature or pressure led to an increase in r_CHO. In contrast, r_PO decreased upon increasing the reaction temperature, but exhibited a small fluctuation upon increasing the reaction pressure.

As carbon dioxide (CO₂) is an inexpensive, abundant, sustainable and green carbonyl resource, its utilization to produce value-added chemicals and polymeric materials has attracted much more attention. In this work, a novel CO₂ route polyurea (PUa) was synthesized. The chemical composition, molecular structure, and aggregation structure of polyurea has been confirmed by ¹H-NMR, HMBC-NMR, DSC, TG, MALDI-TOF MS and POM. The result from POM shows that polyurea gives out a spherulitic morphology, exhibited a typical black cross pattern formed by many concentric circles with different light and shade. Moreover, shape memory polymers of polyurea-multiblock-poly(propylene carbonate) (PUa-mb-PPCs) with a M_n nearly 4.72 × 10⁴ Da and a polydispersity index (PDI) of 1.51–1.64 were synthesized by chain extension of the polyurea with CO₂ derived poly(propylene carbonate) diols (PPC-OH). The PUa-mb-PPCs possess high strength and elasticity because the crystallinity formed by polyurea and amorphous region from PPC. Notably, excellent shape memory effect (SME) is observed in shape thermomechanical testing. The present work provides a simple and renewable process for the synthesis of CO₂-copolymer with multiblock structure, opening a new route for preparation of functional polymeric materials from carbon dioxide conversion.

Here, the internal structure and mechanical properties of the hydroxyapatite/polycaprolactone scaffolds, prepared by fused deposition modeling (FDM) technique, were explored. Using hydroxyapatite (HA) and polycaprolactone (PCL) as raw materials, nano-HA/PCL and micro-HA/PCL that composite with 20 wt% HA were prepared by melt blending technology, and HA/PCL composite tissue engineering scaffolds were prepared by self-developed melt differential FDM 3D printer. From the observation under microscope, it was found that the prepared nano-HA/PCL and micro-HA/PCL tissue engineering scaffolds have uniformly distributed and interconnected nearly rectangular pores. By observing the cross-sectional view of the nano-HA/PCL scaffold and the micro-HA/PCL scaffold, it is known that the HA particles in the nano-HA/PCL scaffold are evenly distributed and the HA particles in the micro-HA/PCL scaffold are agglomerated, which attribute nano-HA/PCL scaffolds with higher tensile strength and flexural strength than the micro-HA/PCL scaffolds. The tensile strength and flexural strength of the nano-HA/PCL specimens were 23.29 MPa and 21.39 MPa, respectively, which were 26.0% and 33.1% higher than those of the pure PCL specimens. Therefore, the bioactive nano-HA/PCL composite scaffolds prepared by melt differential FDM 3D printers should have broader application prospects in bone tissue engineering.