Poly(benzoxazole-amide-imide) copolymers for interlevel dielectrics: interchain hydrogen bonding, molecular arrangement and properties

Temperature-Controlled Chain Dynamics in Polyimide Doped with CoCl2 Probed Using Dynamic Mechanical Analysis

Cobalt(II) chloride (CoCl2) being in the vicinity of polyimide chains entails modifications in terms of the molecular dynamics, which are mainly governed by the possible presence of amic acid residual groups, by the transition-metal-type characteristics of cobalt and by the CoCl2 content. Polyimide was synthesized using poly(amic acid) according to the reaction of 2,2'-bis(3,4-dicarboxylphenyl)hexafluoropropane dianhydride (6FDA) with 3,3'-dimethyl-4,4'-diaminodiphenylmethane (MMDA) in N,N-dimethylacetamide. CoCl2 was added before the thermal imidization of the poly(amic acid). An experimental approach was designed to establish the interaction between the polyimide and CoCl2 and whether the interaction depends on the quantity of the salt. Evidence for the existence of residual amic acid groups was obtained using second derivative Fourier Transform Infrared Spectroscopy (FTIR) and with the help of 2D correlation spectroscopy (2D-COS). Moreover, FTIR, along with X-ray photoelectron spectroscopy (XPS), revealed the interaction between the polymer and CoCl2, primarily in the form of Co(II)-N coordinated bonds. Nevertheless, the coordination of cobalt with suitable atoms from the amic acid groups is not precluded. The results of dynamic mechanical analysis (DMA) featured a specific relaxation assigned to the presence of CoCl2 in the polymeric film and demonstrated that its (non)reinforcing effect depends on its content in the polyimide.

The Thermal Properties and Degradability of Chiral Polyester-Imides Based on Several l/d-Amino Acids

Eight kinds of chiral diacid monomers were prepared with amino acids with different side groups or configurations. Polyester-imides (PEIs) were synthesized from these diacid monomers and diphenol monomers through polycondensation reaction, and the performances and properties were compared with the chiral polyamide-imides (PAIs) previously synthesized by our work group. Their thermal properties were analyzed by thermo gravimetric analysis (TGA) and dynamic thermomechanical analysis (DMA), and it was found that the glass transition temperature (Tg) of PEI was mainly affected by the volume of side groups. Their degradability was studied through buffer degradation experiments, and the changes in their water contact angle, molecular weight, structure and appearance during the degradation process were characterized by contact angle tester, gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). With degradation, the hydrophilicity of PEI was improved, and when amino acids with larger side groups or D configuration were introduced into the backbone of PEI, the degradability decreased.

Structural evolution from poly(amic acid) to polyimide fibers during thermal imidization process

In this study, poly(amic acid) (PAA) precursor fiber was prepared via a two-step wet spinning method and subsequently heat-treated to obtain the polyimide fiber by thermal imidization. The structural evolution of the PAA precursor during the imidization was traced using various measurements. The imidization degree of the PAA fibers treated at different temperatures was calculated by Fourier transform infrared analysis, and the cyclization reaction occurred accompanied by the decomplexation of the H-bonded N, N′-dimethylacetamide (DMAc). The thermogravimetry test illustrated that the residual solvent evaporation took place prior to imidization. Moreover, in situ wide-angle X-ray diffraction and small-angle X-ray scattering measurements were employed to investigate the development of the aggregation structure and microvoids in PAA fibers. The results indicated that molecular chains were thermally extended during the thermal imidization, resulting in the increase of Hermans’ orientation factor and the increased strain. The thermal imidization process also led to the orientation and elongation of microvoids along the molecular chains.