Applications and future prospects dynamic covalent cross⁃linking networks in thermoplastic polymers， A review

doi:10.19491/j.issn.1001-9278.2024.12.002

Abstract

Abstract:

This paper reviewed the research progress in the applications of dynamic covalent cross⁃linking networks in several major thermoplastic polymers， including polyolefins， polystyrene， poly（methyl methacrylate）， and polyesters. Through introducing dynamic covalent bonds， the resultant materials obtained an enhancement in melt strength， mechanical properties， heat resistance， and solvent resistance along with well maintainability of their inherent characteristics. However， there still have some challenges such as complex fabrication processes， high costs， and insufficient research on long⁃term stability and degradation in spite of significant advancements. Future research was suggested to focus on optimizing the preparation methods， enhancing the material properties， and investigating the long⁃term stability under various environmental conditions to promote the large⁃scale industrial applications of the dynamic covalent cross⁃linking technology.

Key words: dynamic covalent cross?linking, thermoplastic polymer, mechanical property, thermal stability, reprocessability

CLC Number:

TQ325.1/TQ323.4

WEI Ce, CHEN Tianyu, ZHANG Xiutao, ZHANG Yiyao, ZHANG Sibo, ZHANG Xiaoyu, HUANG Jing, DONG Weifu. Applications and future prospects dynamic covalent cross⁃linking networks in thermoplastic polymers， A review[J]. China Plastics, 2024, 38(12): 8-18.

Figures/Tables 11

Fig.1. Schematic illustration of two types of CANs［4］

Fig.2. Comparison of viscous flow behavior between an epoxy vitrimer， silica and polystyrene［15］

Fig.3. （a） Schematic diagram of a one⁃step method for preparing PE vitrimer by mixing boronic ester bonds with dynamic crosslinking agents and PE；（b） Creep resistance of PE⁃HD vitrimer and PE⁃HD at 80 ℃ ［24］；（c） Comparison of mechanical properties between PE vitrimer and PE ［25］

Fig.4. Schematic diagram of interpenetrating network structure formed by adding PE vitrimer to PE and corresponding 3D printed item photos ［29］

Fig.5. （a） The preparation process and chemical structure of PP vitrimer；（b） Diagram of network rearrangement of PP vitrimer through ester exchange reaction；（c） Stress⁃strain curves of pure PP， PP vitrimer， and PP vitrimer after 5 repeated processing cycles；（d） 3D printing wires and items prepared from PP vitrimer［31］

Fig.6. （a） Preparation process and chemical structure of PS vitrimer；（b） Photos illustrating the recycling of PS vitrimer （c） Changes in stress⁃strain curves of PS vitrimer before and after recycling；（d） Changes in dielectric constant of PS vitrimer before and after recycling［34］

Fig.7. （a） Preparation process and chemical structure of PMMA CANs；（b） Colorless and transparent characteristics of HUB⁃Cx PMMA CANs；（c） The stress⁃strain curves of PMMA CANs with different contents of crosslinking agents；（d）Water vapour adsorption⁃desorption isotherms for PMMA and HUB⁃C0.1 PMMA CAN［38］

样品编号	T_g/℃	T_c/℃	ΔH_c/J·g^-1	T_m/℃	ΔH_m/J·g^-1	σ/MPa	ε/%	E/MPa	G_f/%
PET	80.5	205.6	38.6	252.2	39.5	56.0±0.8	618±47	891.00±38.62	0
PET⁃0.1	81.5	197.4	38.1	251.3	38.9	54.3±1.4	753±96	809.52±81.09	0
PET⁃0.3	81.8	183.7	36.0	249.4	37.2	56.3±1.0	703±65	868.31±51.08	0
PET⁃0.5	82.1	184.9	31.8	248.8	33.2	62.3±1.1	338±40	1095.41±29.02	2.52
PET⁃0.7	82.7	185.8	34.9	248.5	35.9	64.5±2.6	6±1	1240.94±110.42	66.18
PET⁃1.0	83.0	185.2	36.0	248.0	37.5	63.4±2.5	6±1	1241.22±58.41	68.91
PET⁃1.2	83.3	179.4	33.7	247.0	34.0	59.9±1.2	5±1	1262.24±135.88	76.29
PET⁃1.5	84.4	178.4	32.2	245.1	33.0	50.9±2.3	4±1	1239.73±162.03	71.35
PET⁃2.0	85.3	175.6	29.6	244.9	30.5	43.6±7.0	2±1	1273.22±396.00	69.54

Tab.1. Summary of thermal parameters， mechanical properties and gel content of PET and PET vitrimer with different TGDDM content［44］

Fig.8. （a） Chemical structures and sketches of BIS⁃TRIS， PMDA， and PET；（b） Reactions of pristine materials in the internal mixer：（1） transesterification reaction；（2） chain extension and crosslinked reactions；（c） Illustration of the topological network structure of the vitrimer. In vitrimer molecules， the green solid spheres represent carbonyl groups and green hollow spheres represent the neighboring group of the ester group， the yellow solid dots represent the tertiary amines， the red arcs represent hydroxyl groups， the combination of red arcs and green solid dots represent ester groups， and the gray lines represent the PET macromolecular chain. In PMDA， the combination of green solid spheres and green hollow spheres represent the anhydride groups. Foamability of the PET⁃based vitrimer by environmentally friendly scCO2 foaming technology：（d） the solid PET⁃based vitrimer sample；（e） foamed PET⁃based vitrimer sample；（f） PET⁃based vitrimer foam morphology observed by SEM， and （g） ultra⁃light foam supported by hairs［45］

Fig.9. （a） Angular frequency dependence of storage modulus G′（filled symbol） and loss modulus G″（open symbols） at 250 ℃ for PBT （circles）， compound 4d （squares）. （b） Appearance of PBT and compound 4d disks after 3 min in an oven at 250 ℃. （c） Appearance of PBT and compound 4d disks after 30 min in an oven at 250 ℃［48］

Fig.10. （a） Photos of the film⁃blowing process for （a） neat PLA⁃175 and （b） ESO 0.8⁃185； Transmittance and haze spectra of the blown films of neat PLA and PLA vitrimer ESO 0.8 （c）， and their stress⁃strain curves in the take⁃up direction （MD） and transverse direction （TD）［52］

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