Nomenclature, Classification And Flame Retardants of Polyamides

Nomenclature, Classification And Flame Retardants Of Polyamides

I. Introduction

Polyamide (polyamide, referred to as PA) commonly known as nylon (nylon), is a class of multi-species polymer materials, of which polyamide 66 is the earliest industrialized varieties, 1939 by the U.S. DuPont began production, more than 70 years of history.

Polyamide refers to a class of polymers containing amide group (-CONH-) in the main chain of the molecule has two main structures, one is a ring-opening polymerization of lactam or ω-amino acid self-condensation resin structure, the other is an organic dibasic acid and dibasic amine condensation of the resin structure, its structural formula are as follows:

Generally R and R' are hypromethyl ( - CH2 - ), or aromatic (containing a benzene ring).

II. Naming of Polyamides

The naming methods of polymers include the customary naming method and the systematic naming method. Polyamides are generally named according to the following rules.

• Naming of Aliphatic Polyamides

1. The polymers prepared by self - polycondensation of ω - amino acids or ring - opening polymerization of lactams are called polyamide n, which can also be called nylon n, denoted as PA n. Here, n represents the number of carbon atoms in the repeating unit. Its general formula is:

2. For polyamides obtained by the polycondensation of dibasic acids and diamines, the number of atoms of both monomers should be marked simultaneously. It is called polyamide mn, which can also be called nylon mn, denoted as PAmn. Here, m represents the number of atoms of the diamine and is marked in front, and n represents the number of carbon atoms of the dibasic acid. The general formula is:

• Naming of Semi - aromatic Polyamides

For semi - aromatic polyamides, if the diamine or dibasic acid is aromatic, they are represented by their ISO 1874 - 1 abbreviation codes. Then, the naming is combined according to the above - mentioned principle. That is, the number of carbon atoms or the abbreviation code of the diamine in the repeating unit is placed in the front, and the number of carbon atoms or the abbreviation code of the dibasic acid is placed in the back to form the name of the polyamide.

For example, the polyamide obtained by the polycondensation of hexamethylenediamine and terephthalic acid is called nylon 6T. The poly(m - xylylene adipamide) synthesized by the polycondensation of m - phenylenediamine (abbreviation code MXD in ISO 1874 - 1) and adipic acid can be denoted as PAMXD6.

The common names, Chemical Abstracts Service (CAS) names and registration numbers, ISO 1874 - 1 abbreviation codes, corresponding symbols, and synthetic raw materials of the commonly used monomers in polyamide synthesis are summarized in Table 1 - 1.

Table 1-1  CAS Names, Designations and Registry Numbers of Commonly Used Polyamide Monomers

• Naming of Copolyamides

The naming of copolyamides usually requires indicating the code of each polyamide, with the codes separated by slashes, and the main component placed in the front. For example, a copolymer of nylon 6 and nylon 66 with nylon 6 as the main component is expressed as nylon 6/66 (PA6/66); while nylon 66/6 (PA66/6) represents a copolymer of nylon 66 and nylon 6 with nylon 66 as the main component.

For polyamides polymerized from a mixture of isomers, except those with designated codes in the ISO 1874 - 1 standard, it is required to mark the code of each isomer simultaneously. For example, a polyamide prepared by the polycondensation of trimethylhexamethylenediamine [a mixture of 2,2,4 - trimethyl - 1,6 - hexanediamine (ND) and 2,4,4 - trimethyl - 1,6 - hexanediamine (IND)] and terephthalic acid can be denoted as NDT/INDT. At the same time, due to the differences in the position of methyl groups and the bonding form, there are also various isomeric structures such as head - to - head (H - H), head - to - tail (H - T), and tail - to - tail (T - T). For the sake of simplicity, it can be abbreviated as TMDT according to the ISO 1874 - 1 code shown in Table 1 - 1.

• Naming by Scientific Name

In principle, all polyamides can be named by their scientific names. For example, polyamide 6 can be called polycaprolactam, and polyamide 66 can also be called poly(hexamethylene adipamide).

For wholly aromatic polyamides, they are generally named by their scientific names or represented by the first - letter abbreviations of their English names. For example, the polymer obtained by the polycondensation of p - phenylenediamine and terephthalic acid is called poly(p - phenylene terephthalamide) or PPTA.

III. Classification of Polyamides

There are many types and varieties of polyamide resins. In order to have a basic understanding of various polyamide resins as a whole, this section will classify the currently commonly - used polyamide resins.

According to the preparation chemical reactions, they can be divided into two categories: one category is prepared by the polycondensation of amino acids or the ring - opening polymerization of lactams (also known as AB - type nylons), and the other category is prepared by the polycondensation of diamines and dibasic acids (also known as AABB - type nylons).

According to the special groups contained in the repeating structure of the molecular chain, they can be classified into four categories: aliphatic, semi - aromatic, aromatic, and copolyamides. Figure 1 shows the classification of polyamides.

IV. Properties of Polyamides

The rapid development of polyamides is inseparable from their unique structures: The molecular main - chain of polyamides contains a large number of polar amide groups. This leads to strong intermolecular forces among polyamide molecules and enables the formation of hydrogen bonds (generally, the higher the hydrogen - bond density, the better the mechanical strength; the more carbon atoms, the worse the strength). At the same time, it also makes the polyamide molecules arrange neatly and exhibit crystallinity. The molecular main - chain segments of polyamides also contain methylene groups, which endow polyamides with a certain degree of flexibility and can affect the melting point and glass - transition temperature ( T_g ) of polyamides. In addition, the ends of the macromolecular main - chains of polyamides contain amino groups and carboxyl groups, which have certain reactivity under certain conditions and are easily modified. These polyamides with amide - group ( -CONH- ) structures have a series of excellent properties compared with other materials. The properties of several polyamides are listed in Table 1 - 2.

Table 1-2 Mechanical Properties of Several Polyamides

Although polyamide resin is a material with excellent comprehensive properties, it also has obvious drawbacks, such as its physical properties being sensitive to temperature, large water - absorption affecting dimensional stability, and poor low - temperature toughness. Its properties can be greatly improved through chemical or physical modification methods. For example, the addition of glass - fiber materials can greatly improve water - absorption and dimensional stability, and can also enhance the strength and toughness of the resin; blending and copolymerizing with other polymers can be used to prepare various alloys to replace traditional materials such as metals and woods. Table 3 summarizes the commonly used modification methods and purposes of polyamides.

Table 3 Common Modification Methods and Purposes for Polyamides

With the continuous progress of science and technology and the rapid development of material science, we have higher and higher requirements for the safety and functionality of materials. Especially in the wide application of plastic products, flame retardant performance has become one of the important indexes to measure the safety of materials.

Guangzhou Yinsu Flame Retardant Company has developed a series of flame retardants suitable for polyamides (nylons). These products include traditional red phosphorus flame retardants such as red phosphorus FRP-950-1, FRP-750A, and FRP-302H, organic phosphorus YS-200 etc. In addition to halogen free products, the company also supplies bromine-antimony flame retardants and more environmentally friendly bromine-antimony alternatives. These flame retardants are designed to meet various industrial requirements while ensuring environmental friendliness and cost-effectiveness.

The flame retardants from Yinsu Flame Retardant Company are tailored to enhance the fire safety of polyamides, which are widely used in industries such as automotive, textile, and engineering plastics. By incorporating these flame retardants, polyamides can achieve better compliance with fire safety regulations and are suitable for applications where flame resistance is critical. These efforts by Yinsu Flame Retardant Company contribute significantly to the safety enhancement and sustainable development of polyamide-based materials.