Novel High Molecular Weight Aliphatic Polyamide 3X based on 1,3-propanediamine: Synthesis and Side Reaction Mechanism

Abstract

The growing demand for novel sustainable materials has sparked significant interest in material synthesis, which holds great potential for the development of novel polymers. However, synthesizing high-molecular-weight polyamides using 1,3-propanediamine as a monomer is challenging due to its high reactivity. In this study, we synthesized a series of aliphatic polyamides (PA310, PA312, PA314, and PA316) using 1,3-propanediamine and various dicarboxylic acids via melt and solid-state polymerization. PA312 exhibited the highest molecular weight (Mn = 26 kg/mol, Mw = 71 kg/mol, PDI= 2.6). Meanwhile, Side reactions were investigated through the 1H NMR, 13C NMR, GC-MS, LC-ESI-MS, APCI, and MALDI-TOF-MS. Results indicated that the terminal amino group undergoes deamination at high temperatures to form azetidine, and the dehydration of the terminal carboxylic group leads to the formation of 2-oxocycloundecane-1-carbaldehyde-capped oligoamides, which cap the chain ends and inhibit molecular weight growth. Moreover, PA3X exhibited a γ-form crystalline structure and spherulitic morphology. Its thermal properties were favorable, with melting points ranging from 196 to 216 °C. More particularly, Water absorption decreased with increasing dicarboxylic acid chain length, while the water contact angle on the surface increased. This work will offer strong theoretical support for the preparation of novel sustainable polyamides based on the 1,3-propanediamine.