1. How to synthesis of polyimides and what is the application of Polyimides (PIs)?
Solution:
Polyimides are synthesized by the reactions of dianhydrides with diamines, for
example, the polymerization of pyromellitic anhydride with p-phenylenediamine to
form poly(pyromellitimido-1,4-phenylene). Solubility considerations sometimes result
in using the half acid-half ester of the dianhydride instead of the dianhydride.
The direct production of high-molecular weight aromatic polyimides in a one-stage
polymerization cannot be accomplished because polyimides are insoluble and infusible.
The polymer chains precipitate from the reaction media before high molecular weights
are obtained. Polymerization is accomplished by a two-stage process. The first step
involves the condensation of aromatic dianhydrides and aromatic diamines in a
suitable solvent, such as dimethylacetamide, to form a soluble precursor or poly(amic
acid). This is followed by the dehydration of the intermediate poly(amic acid) at
elevated temperature.
At the first stage involves an amidation reaction carried out in a polar aprotic solvent
such as NMP or N; N-dimethyl- acetamide (DMAC) to produce a high-molecular-weight
poly(amic acid). Processing of the polymer can be accomplished only prior to the second
stage, at which point it is still soluble and fusible. It is insoluble and infusible after the
second stage of the process. The poly(amic acid) is formed into the desired physical form
of the final polymer product (example, film, fiber, laminate, coating) and then the second
stage of the process is performed. The poly(amic acid) is cyclodehydrated to the
polyimide by heating at temperatures above 150°C.
Solution:
Polyimides are synthesized by the reactions of dianhydrides with diamines, for
example, the polymerization of pyromellitic anhydride with p-phenylenediamine to
form poly(pyromellitimido-1,4-phenylene). Solubility considerations sometimes result
in using the half acid-half ester of the dianhydride instead of the dianhydride.
The direct production of high-molecular weight aromatic polyimides in a one-stage
polymerization cannot be accomplished because polyimides are insoluble and infusible.
The polymer chains precipitate from the reaction media before high molecular weights
are obtained. Polymerization is accomplished by a two-stage process. The first step
involves the condensation of aromatic dianhydrides and aromatic diamines in a
suitable solvent, such as dimethylacetamide, to form a soluble precursor or poly(amic
acid). This is followed by the dehydration of the intermediate poly(amic acid) at
elevated temperature.
At the first stage involves an amidation reaction carried out in a polar aprotic solvent
such as NMP or N; N-dimethyl- acetamide (DMAC) to produce a high-molecular-weight
poly(amic acid). Processing of the polymer can be accomplished only prior to the second
stage, at which point it is still soluble and fusible. It is insoluble and infusible after the
second stage of the process. The poly(amic acid) is formed into the desired physical form
of the final polymer product (example, film, fiber, laminate, coating) and then the second
stage of the process is performed. The poly(amic acid) is cyclodehydrated to the
polyimide by heating at temperatures above 150°C.
