Crystallographic studies of nylon 4. II. On the β and δ polymorphs of nylon 4

Abstract

In addition to the α polymorph, two crystalline forms of nylon 4, the β and δ polymorphs, have been observed and studied. The β polymorph of nylon 4, which has not been found in a pure condition, appears to be similar to the β polymorph of nylon 6. The extended planar zigzag conformation of chains, found in the α polymorph, is present also in the β polymorph. Three models have been proposed to explain the observed data. In model 1, the staggered shear of van der Waals bonded sheets found in the α polymorph is abandoned; in model 2, the sheets are displaced by 1/2 the b axis, and in model 3 the chains are arranged in a parallel array. The β polymorph is converted to the α form in air upon heating for 11 min. at 227°C. and upon immersion in water for 2 hr. Models 1 and 2 would be converted to the α polymorph by a slippage of the van der Waals bonded sheets while the conversion from model 3 would involve a rupture of hydrogen bonds, a rotation of the chains through 90°, and the reformation of hydrogen bonds. The δ polymorph is formed by rapidly quenching extruded nylon 4 against chilled rolls. It is a metastable form which has only been observed in an unoriented condition. Upon orientation it is completely converted to the α polymorph. In addition to this, its conversion to the α form occurs under conditions similar to the β–α transition. The observed diffraction pattern can be indexed on the basis of a hexagonal packing of chains. High‐temperature x‐ray diffraction studies of the α polymorph suggest that the δ form, or a structure similar to it, is the high‐temperature form of nylon 4.

One-pot low temperature synthesis and characterization of hybrid poly(2-pyrrolidone) microparticles suitable for protein immobilization

“…In similitude with the PA6 patterns deconvolutions and in accordance with the findings in Ref. [28] MP the content of the a-polymorph is very high, the a/b ratio being greater than 11, while the presence of payloads, especially Cu and Fe drastically decreases the ratio to 1e2. Apparently, these metals are strong b-nucleating agents.…”

“…The a-PA4 with extended planar zig-zag conformation of chains and monoclinic unit cell similar to the a-PA6 was found to predominate in highly crystalline and oriented filaments [27]. Two less perfect crystalline forms designated as band d-polymorphs with hexagonal packing of chains were detected at temperatures close to the melting point or after quenching [28], but no unit cell parameters or d-spacing values were reported. It is important to note, that according to refs.…”

“…It is important to note, that according to refs. [27,28] the said band d-polymorphs do not co-exist with the more thermodynamically stable and perfect a-PA4. Three decades later, Bellinger et al [29] have revisited the PA4 crystalline structure in single crystals confirming the monoclinic crystalline cell of the a-PA4 with d a½200 ¼ 0.44 nm and d a½020 ¼ 0.37 nm.…”

Polymer-Assisted Biocatalysis: Polyamide 4 Microparticles as Promising Carriers of Enzymatic Function

“…All example deconvolutions in Figure 8 show that excellent fits with regression coefficients R 2 ≥ 0.99 were only possible if along with the two peaks of α−PA4 and the two amorphous halos AH 1 and AH 2 two more crystalline peaks were considered that should be assigned to an additional monoclinic phase designated by β-PA4. It was first described in the early work of Frederiks et al [43] and later on shown to co-exist with α-PA4 [24]. Table 6 shows that the values of the long spacings of these two PA4 phases almost coincide.…”

Three Directional Crystal Structure Changes of Nylon 6-ran-Nylon 4 Copolymer Films by Drawing Ratio and Elevating Temperature

“…β-형 결정은 순수 한 조건에서는 찾아보기 힘들며, 주로 nylon 6의 β-구조와 유사하게 나타난다. δ-형 결정은 냉각 롤에서 배출된 nylon 4를 급속하게 냉각시킬 때 나타나며 이것은 무배향 조건에 서만 관찰된다 [9]. 일반적으로 필름을 연신하면 면배향이 생기기 때문에 X-선을 조사하는 방향에 따라 필름 표면에 수직인 방향(ND, through), 필름 표면에 평행하면서 연신 방향과 수직한 방 향(TD, edge), 필름 표면에 평행하면서 연신방향과 평행한 방향(OD, end)의 정보를 얻을 수 있다 [10].…”