PA1212: A New Breakthrough in the Green Synthesis of High-Performance Long-Chain Nylon (Polymers 2026, 18, 101)
PA1212: A new breakthrough in the green synthesis of high-performance long-chain nylon (Polymers 2026, 18, 101)
The latest research findings by a team at the National Technical University of Athens in Greece have opened up a completely new avenue for the industrial production of highly hydrophobic long-chain polyamides.
The aim of this study is to synthesise polyamide 1212 (PA 1212) via direct solid-state polymerisation (DSSP) using solid-state salt precursors as raw materials. Previous studies have shown that the direct solid-state polymerisation of aliphatic polyamide salts involves a molten intermediate state, which is consistent with the solid-melt transition (SMT) mechanism well documented in the literature. However, due to their strongly hydrophobic nature, PA 1212 salts are expected to deviate from this model. This study first explored the reaction on a micro-scale within a thermogravimetric analysis (TGA) chamber, before scaling it up to laboratory scale. The effects of reactor design, reaction temperature and residence time were investigated. The DSSP products were characterised in terms of molecular weight and morphological properties. Concurrently, a novel method based on Fourier-transform infrared spectroscopy–attenuated total reflection (FTIR-ATR) analysis was developed for the qualitative monitoring of the polymerisation process. The final morphology of the products was examined primarily via scanning electron microscopy (SEM imaging). Although it was confirmed that the DSSP underwent a quasi-solid-melt transition, significant differences were observed compared with the classical mechanism established in the literature. This paper reveals that the limited surface softening or agglomeration observed is primarily related to the hydrophobic structure of the PA 1212 salt. This paper reveals that the limited surface softening or agglomeration observed in the experiments is primarily related to the hydrophobic structure of the PA 1212 salt.
PA1212 is an important member of the long-chain aliphatic polyamide family. Its molecular structure features a low density of amide groups and a high proportion of long methylene chains, giving it a unique combination of properties:
✤ Extremely low moisture absorption — far superior to PA6 and PA66; it retains dimensional stability and mechanical properties even when exposed to water
✤ Excellent thermal and dimensional stability
✤ Good flexibility and processability
✤ Can be used as a substitute for PA12 in 3D printing and selective laser sintering (SLS), whilst offering superior bio-based properties
The Core Scientific Hypothesis of the Paper
Scientific hypothesis
PA1212 has an extremely long salt-carbon chain and a very low proportion of polar amide groups; it is highly hydrophobic and exhibits minimal hydration effects. Consequently, the DSSP process deviates from the classical SMT mechanism and does not result in complete melting, offering potential for resolving the problem of industrial caking.
Established a process for the preparation of PA1212 using the PA1212 salt DSSP;
Scaled up from the micro-scale (TGA) to two different laboratory-scale reactors, comparing the effects of three key parameters: reactor configuration, temperature and residence time;
Establish a new FTIR-ATR method for the quantitative monitoring of polymerisation progress;
Combining SEM morphology, terminal group titration, viscosity and thermal analysis to reveal a novel reaction mechanism, and to compare differences with the traditional SMT model.
(1) Basic Physical Properties of PA1212 Salt
Structure and Polarity: FTIR confirms an ionic salt structure (characteristic peaks of \(NH_3^+\) and \(COO^-\)); strong peaks at 2918/2850 cm⁻¹ for the long alkyl chains indicate high hydrophobicity; completely insoluble in water at room temperature.
Particle Size: The average size of virgin particles is 2.2 μm, with a specific surface area of 1.30 m²/g; the high specific surface area of the small particles facilitates the removal of condensation water; laser diffraction D(v,0.9) = 29.9 μm, with only minimal agglomeration.
Thermal Properties: Melting point \(T_m\) = 190 ℃; TGA: two weight-loss stages: 185–200 °C for the loss of condensation water (theoretical 8.4%, measured approximately 11%, including the volatilisation of diamine); 449 °C is the thermal decomposition temperature of PA1212.
Terminal group balance: the concentrations of amine and carboxyl groups are close to theoretical values, and the ratio of salt monomers is balanced.
(2) Micro-scale TGA single-factor experiment (effect of temperature)
Temperature range: 160–170 °C. Pattern:
The reaction rate increases significantly with temperature: as the temperature rises, the half-life \(t_{1/2}\) decreases substantially; at 160 °C, the half-life is 21.2 h, whereas at 170 °C it is only 4.4 h; a temperature increase of just 2 °C is sufficient to significantly accelerate the reaction.
The loss of diamine due to volatilisation follows a ‘V-shaped’ pattern:
At 160 °C, evaporation is at its highest (the reaction is slow, and prolonged purging removes a large amount of diamine); at 165 °C, evaporation is at its lowest (the reaction rate and evaporation reach equilibrium); at 170 °C, a rise in temperature once again accelerates the evaporation of diamine.
No complete melting, only slight surface softening:
At 160–165 °C, the product is loose and brittle; at 170 °C, it becomes only slightly sticky, in contrast to the SMT phenomenon observed with PA612 and PA66, which melt and form lumps under the same conditions.
Mechanistic explanation: 12,12-diamine has a high boiling point and an extremely low vapour pressure, and crystal defects form slowly; consequently, the overall reaction rate is relatively low. Its hydrophobic structure contains little water and is therefore unable to form a large, molten hydration layer.
(3) Laboratory-scale upscaling: Comparison of reactor designs (R1 vs R2, 170 °C/24 h)
A comparison of the two reactors was carried out under the following conditions: 170 °C, 24 hours, and a nitrogen flow rate of 100 mL/min:
Key conclusion: The solid state can only be maintained in the R2 reactor, demonstrating the efficiency of this reactor design for DSSP. The higher gas flow rate in R2 is more conducive to the removal of by-products such as water and amines.
SEM images provided further confirmation: the edges of the R1 product particles had become rounded and cracks were visible, indicating the formation of a quasi-melt intermediate state; the R2 product, by contrast, showed no obvious agglomeration or cracking.
The reaction performance in the R2 reactor was investigated under conditions of 160–170 °C, 24 h and 100 mL/min: the effect of temperature on the reaction was extremely significant. From 162 °C to 165 °C, the polymer content increased by 103%; from 165 °C to 170 °C, [η] increased further.
(4) The revised PA1212 DSSP reaction mechanism (core innovation)
Experiments were carried out at 170 °C with varying residence times (0.5–24 h) to elucidate the reaction mechanism:
Key findings: A 277 per cent increase in molecular weight was achieved between 6 and 8 hours, accompanied by the most significant morphological changes. This confirms that the DSSP of PA 1212 salts follows a ‘nucleation–growth’ mechanism.
Traditional three-step SMT for short-chain polyamides:Induction → Complete melting → Re-solidification; PA1212 hydrophobic salt quasi-solid-to-melt transition (quasi-SMT) two-step mechanism:
Induction phase:At low temperatures in the solid phase, the volatilisation of diamines creates lattice defects, causing the polycondensation to commence slowly and resulting in the formation of trace amounts of water;
Gentle Reunification / Near-Melting Stage:A small amount of water causes only localised softening of the particle surfaces, without overall melting; polymerisation proceeds rapidly, resulting in slight adhesion and agglomeration of the particles; No secondary curing step is required: the melting points of PA1212 salt and the resulting PA1212 are virtually identical (both ≈190 °C); there is no significant increase in melting point with rising molecular weight. The material remains in a solid state, loose and brittle, and does not form large solidified lumps upon cooling, thereby resolving the pain points associated with traditional DSSP industrial processes.
PA1212 salt can be successfully synthesised into long-chain fatty polyamides via the DSSP process, without the need for high-temperature melting, resulting in an environmentally friendly process with low degradation;
The highly hydrophobic nature of the substrate causes the process to deviate entirely from the classical SMT mechanism; only localised surface softening and mild agglomeration occur, with no overall melting or subsequent re-solidification. The material remains loose throughout the process, making it suitable for industrial application;
Reaction temperature, the efficiency of water vapour removal from the reactor, and residence time are the three key parameters: at 170 °C, in fixed-bed reactor R2, and over 24 hours, complete conversion of the salt can be achieved, yielding PA1212 with the highest molecular weight;
The fixed-bed reactor R2 outperforms the conventional autoclave R1, preventing localised melting and agglomeration, and resulting in better product flowability;
An FTIR-ATR internal standard quantification method has been established, enabling rapid, non-destructive monitoring of the degree of solid-phase polymerisation conversion solely through infrared peak ratios, without the need for destructive sample analysis via titration or viscosity measurement;
The volatilisation of long-chain diamines is an irreversible side reaction; a reaction temperature of 165 °C strikes a balance between the reaction rate and diamine loss, thereby optimising both conversion rate and feedstock utilisation;
This work provides comprehensive process and mechanistic support for the low-cost, sustainable solid-phase synthesis of bio-based long-chain polyamides.
Through research on the direct solid-phase polymerization of PA1212 salts, a team from the National Technical University of Athens has successfully developed a green synthetic route that is entirely melt-free, requires no stirring, and operates at low temperatures with low energy consumption. This process completely avoids the equipment damage and process instability caused by solid-to-melt transitions in traditional solid-phase polymerization, paving the way for the clean industrial production of long-chain hydrophobic polyamides. It holds significant academic value and industrial application potential.
Highlights of the Achievements
Material Type
PA1212 — A long-chain aliphatic polyamide that combines the strength of nylon with the hydrophobicity of polyethylene
Synthesis Process
Direct Solid-Phase Polymerization (DSSP) — No melting required; environmentally friendly
Key Breakthrough
Successfully avoids the "solid-to-melt transition" (SMT) issue associated with traditional solid-phase polymerization, maintaining a solid state throughout the entire reaction.
Molecular weight
The number-average molecular weight is 3,700 g/mol, and the intrinsic viscosity is 0.50 dL/g.
Reaction Temperature
At just 170°C (20°C below the salt’s melting point), energy consumption is significantly reduced
Source of Raw Materials
Dodecanedioic acid can be derived from bio-based sources or produced through biological processes, and has the potential to be labeled as renewable or green.
Based on the findings of this study, the direct solid-phase polymerization technology for PA1212 is expected to play a significant role in the following areas:
3D Printing and Additive Manufacturing— A more environmentally friendly, high-performance powder material that replaces PA12
High-Performance Engineering Plastics — Can be used in the manufacture of automotive parts and electronic and electrical components
Fishing Nets / Outdoor Gear — Its low moisture absorption ensures long-term stability during outdoor use
Thermoplastic elastomer matrix — Can be combined with polyurethane, carbon nanofibers, and other materials to develop high-performance advanced materials
Sustainable Materials Solutions — Combining bio-based raw materials with green solid-phase polymerization processes to achieve low-carbon manufacturing across the entire supply chain for sustainable materials — By combining bio-based raw materials with green solid-phase polymerization processes, low-carbon manufacturing can be achieved across the entire supply chain. For example, Hengxing New Materials has established a collaborative R&D platform for green synthesis technologies, and its Shandong facility has entered the project approval stage for synthesis technologies based on bio-based natural products. These technologies will be commercialized in the future, providing a practical model for the implementation of such solutions.
Reference: This study was published in *Polymers* 2026, 18(1), 101, under the title: “Direct Solid-State Polymerization of Highly Aliphatic PA 1212 Salt: Critical Parameters and Reaction Mechanism Investigation Under Different Reactor Designs”
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