Simultaneous determination of primary and secondary amino groups in polyamide with 1‐fluoro‐2,4‐dinitrobenzene

Abstract

In order to determine chemically the amino end groups present in a polyamide, the polymer was treated with a solution of 1‐fluoro‐2,4‐dinitrobenzene (FDNB) in 2,2,2‐trifluoroethanol (TFE). The resulting Nω‐[2,4‐dinitrophenyl‐(1)]‐(DNP‐) polyamide was precipitated in water at pH 3, washed free of excess reagent, redissolved in TFE, and the optical density of the solution measured at λmax = 350 nm (ε350: 17300 [1000 cm2/mole]). Both the primary and secondary amino groups could be simultaneously determined by this method, since the absorption maximum of dinitrophenylated secondary amino groups is shifted to 390 nm (ε390: 18000 [1000 cm2/mole]). Using this spectroscopic phenomenon a two‐component analytical procedure was developed. With known concentrations of dinitrophenylated primary amines, secondary amines, and nylon‐6 and nylon‐6,6 oligomers, the following analytical equations were derived: (c1: concentration of primary amino groups in mole/l; c2: concentration of secondary amino groups in mole/l; D350, D390: optical density at 350 nm and 390 nm resp.). The coefficients of variation for four different commercially available nylon‐6 fibres (unmodified and modified for dyeability) were in the range of 2.7 to 6.0%. The limiting concentration detectable was 6 × 10−7 mole DNP‐amino groups/l TFE. A kinetic analysis was performed for the reaction of FDNB with nylon‐6 and with a model compound, ε‐aminocaproic acid. Using the “absolute rate theory of Eyring”, it was found that the polymer and monomer both fulfilled the “principle of equal reactivity”. The activation parameters for the reaction were: ΔH≠ : 15.9 ± 0.9 kcal/mole, ΔG≠: 22.9 ±0.3 kcal/mole, and ΔS≠: −22.1 ± 1.9 e.u./mole.

Essential role of chain ends in the nylon‐6/poly(ethylene terephthalate) exchange

“…The amounts of end groups for the Ny6 and PET samples used in this work were accurately determined. The amine and carboxyl chain‐end concentrations for the Ny6 samples were measured by the procedure described in the literature,32, 33 and the specific values we are: [NH 2 ] = 36 mmol/Kg and [COOH] = 10 mmol/Kg.…”

Exchange Reactions Occurring through Active Chain Ends. MALDI−TOF Characterization of Copolymers from Nylon 6,6 and Nylon 6,10

“…The concentration of amino terminal groups, and carboxylic chain ends in Ny6,6 and Ny6,10 samples were determined by the procedure described in the literature. 29,30 a (∆Hm)tot is the sum of the ∆Hm determined at each melting processes observed in the DSC curves. b The % of crystallinity of the homopolymers were calculated using specific heats of fusion for 100% crystalline Ny6,6 (∆H°m ) 200.35 J/g) and Ny6,10 (∆H°m ) 205.75 J/g) samples.…”

“…Detection of Amino and Carboxylic End Groups. The concentration of amino terminal groups, and carboxylic chain ends in Ny6,6 and Ny6,10 samples were determined by the procedure described in the literature. , Specific values (mmol/kg) for the samples used in this study are as follows: for Ny6,6, [NH 2 ] = 37, [COOH] = 9; for Ny6,10, [NH 2 ] = 15, [COOH] = 42; for Ny6,6-COOH, [NH 2 ] = 0.5, [COOH] = 310.…”

Essential Role of Chain Ends in the Ny6/PBT Exchange. A Combined NMR and MALDI Approach

“…In Table are reported the amounts of end groups for the Ny6 and PBT samples used in this work. The amine and carboxyl chain end concentrations for Ny6 samples were measured by the procedure described in the literature, , and specific values are reported in Table . The concentration of carboxyl end groups in the PBT samples was determined by titration method used by Jabarin et al The amount of hydroxyl end groups in the PBT samples was determined by FT-IR and confirmed by 1 H NMR analysis in C 2 D 2 Cl 4 at 60 °C.…”