Condensation reaction polyimide

The function of the bleeder cloth is to absorb adhesive flash and provide an unrestricted path so that entrained air or reaction volatiles can be removed. In the case of condensation reaction polyimides the bag should be vented to relatively high vacuum conditions. This is critical because it is necessary to depress the boiling point of the high boiling point solvents used to flexibilize the film before gellation of the adhesive occurs. 

Synthesis and Properties. Several methods have been suggested to synthesize polyimides. The predominant one involves a two-step condensation reaction between aromatic diamines and aromatic dianhydrides in polar aprotic solvents (2,3). In the first step, a soluble, linear poly(amic acid) results, which in the second step undergoes cyclodehydration, leading to an insoluble and infusible PL Overall yields are generally only 70—80%. 

Polymer Synthesis and Modification. The condensation reaction between either BTDA or BDSDA and ODA was performed in DMAc at room temperature under a nitrogen atmosphere. ODA (0.004 mole) was added to a nitrogen-purged glass septum bottle with 7 ml DMAc. One of the dianhydrides (0.004 mole) was then added to the diamine solution with an additional milliliter of DMAc resulting in 15-25 wt% solids depending upon the monomer combination. The resulting solution was stirred for 20-24 hours to form the poly(amide acid), a polyimide precursor. For the modified polyimides, anhydrous cobalt(II) chloride (0.001 mole) was added as a solid within one-half hour after the dianhydride. 

Next we consider the dispersion polymerization by polyaddition. In a typical method to prepare polyimide particles, polyamic acid solution is first obtained by coupling of pyromellitic dianhydride and oxy-dianiline, and then by heating the solution. The condensation reaction on heating causes crystallization of polyimide in a spherical form (Fig. 11.2.5, left) (33). However, on the contrary to this conventional method, polyamic acid microspheres could be obtained by dispersion polymerization if an appropriate medium is chosen (34). When a solvent that has a solubility parameter around 17 Mpa is used, submicrometer-sized monodisperse polyamic acid parti-... 

The reaction sequence for the synthesis of polyimides is shown in Scheme I. The imide ring is formed via a thermally initiated condensation reaction from a polyamic acid, a soluble precursor polymer synthesized from... 

Aromatic polyimides have glass transition temperatures in excess of 400 °C, excellent toughness and elongation properties and dielectric constants comparable to that of inorganic dielectrics, about 3.5. An important feature relative to these applications is their ability to planarize the topography when spun on as the soluble precursor polyamic acid. The subsequent intramolecular condensation reaction to form the heterocyclic imide is typically a thermal "curing" process. 

We have been able to measure both the weight average molecular weight and the intrinsic viscosity for equilibrated polyamic acid precursors in NMP, and for stable solutions of the cured polyimide in concentrated sulfuric acid. These measurements were not complicated by either polyelectrolyte effects in the amide solvent or degradation in the acid, as have been reported by other workers for these systems. The results show that molecular weight achieved in the condensation to the polyamic acid is retained in the final polyimide, at least for moderate molecular weights. The condensation reaction appears to follow the expected kinetics and leads to a most probable distribution at equilibrium. 

Polymer 56, soluble in DMF or DMSO, can be prepared by the condensation of amino-substituted [Ru(bpy)3]2+ with glyoxal [112]. This polymer showed weaker emission than the free Ru chromophore that was attributed to less efficient intersystem crossing to the 3MLCT state. Similar condensation reactions with diacid anhydrides to produce polyimides have been reported [113]. These polymers showed long-wavelength emission associated with charge-transfer states. 

The term "condensation polymers" was introduced by W. H. Carothers in his early work on the preparation of polyesters and polyamides to distinguish this class of polymers from vinyl polymers made by addition reactions. Condensation polymers were defined as polymeric molecules that may be converted by hydrolysis, or its equivalent, into monomers that differ from the structural units by one molecule of H2O, HCl, NHj, etc. This broad definition includes many polymers made by ring-opening or addition reactions, for example, lactone and lactam polymers, polyurethanes, polyureas, polyimides, and polyhydrazides, as well as polymers made by true condensation reactions. 

Aromatic polymides made by the condensation reaction of pyromellitic anhydride with aromatic diamines have attracted attention because of their high-temperature properties such as therm.al stability (in air at 811 K, in inert atmosphere at 1005 K) and good mechanical strength, as well as resistance to radiation damage [106, 107]. The generic structure conventionally assigned to these substances is that of a linear polyimide... 

The polyimides and polyamide-imides are produced by condensation reactions which give off volatile low-molecular-weight by-products. The polybismalemimides may however be produced by rearrangement polymerization with no formation of by-products. The starting materials in this case are the bismaleimides, which are synthesized by the reaction of maleic anhydride with diamines (Figure 4.21). 

General Description Polyimides (Pis) are resins produced by the condensation reaction of trimellitic anhydride [OCC6H2C2O3] and various aromatic diamines. Kapton is a transparent, amber-colored... 

Hydrolytic Properties Kapton polyimide film is made by a condensation reaction therefore, its properties are affected by water. Although long-term exposure to boiling water, as shown in the curves in Figs. 22-03 and 22-04, will reduce the level of film properties, sufficient tensile and elongation remain to ensure good mechanical performance. A decrease in the temperature and the water content will reduce the rate of Kapton property reduction, whereas higher temperature and pressure will increase it.t 1... 

The advantage of this one-pot preparation method is that the ehromophores are attached to the polymer backbone at the last stage using a very mild condensation reaction between die hydroxy substituted polyimide and a hydroxy-substituted chromophore. This avoids the harsh imidization process and the necessity of preparing the chromophore-containing diamine monomers. The method also allows a wide variety of polyimide backbones. 

The most important resins available for use as adhesives in high-temperature structural applications are polyimides (Pis) and polybenzimidazoles (PBIs), both of which are described later (see Sections 5.35 and 5.33). These resins are supplied as prepolymers containing open heterocyclic rings, which are soluble and fusible. At elevated temperatures, the prepolymers undergo condensation reactions leading to ring closure and the formation of insoluble and infusible cured resins. 

The sol-gel process performed in low concentrated polymer-solvent solutions is another attractive route to develop hybrid membranes because it allows an in situ dispersion of metal-based nanoparticles within the polymeric matrix, achieving a suitable interfacial morphology between the continuous and the dispersed phase. Silica particles and polyimide have been frequently used to produce these hybrid membranes [107,108]. In general, hydrolysis and condensation reactions are involved in the sol-gel process, when alkoxides are involved in the formation of the dispersed phase. The advantage of using this method is the formation of an inorganic network largely interconnected with the polymeric materials mainly with noncovalent interactions [109]. In Fig. 7.10 a... 

This methodology is quite general and can be utilized to prepare several types of polymers such as polyamides, polyimides, polyurethanes, polyethers etc. The polymer properties depend on the type of functional groups that link the polymer building blocks. Further modulation is achievable by varying the nature of the difimctional monomer within each class of polymers. It is not always necessary to condense two difunctional monomers. Some polymers such as polyethers are prepared by the oxidative coupling of the corresponding phenols. A few examples of polymers that can be prepared by the condensation reactions are shown in Fig. 1.2. 

An example where a simple soruce-based nomendature is not suffident to characterize a polymer is the condensation reaction of a dianhydride - component A - with an amine -component B. The reaction produces first a polyamide-add that can be cydized to a polyimide. Given a simple soruce-based nomendature, both the products would be named as pofy-(A-fllt-B). The ambiguity is easily avoided by incorporating the dass name (generic name) of the couesponding polymer - amide-add, respectivdy imide, in this example. This is even hdpful in cases where there is only one product formed, in particular when the stmcture is complex The simple source-based name pofybutadiene, for example, does not indicate if it is the 1,2-, l,4-cts-, or l,4-tran5 isomer and additional information can be useful. 

Just as simple esters and amides can be made by condensation reactions, polyesters such as Dacron and Mylar are made by reacting diols with dicarboxylic acids (Figure 13.15 A). Similarly, polyamides such as nylon form from amines and carboxylic acids. Starting from anhydrides and amines, polyimides can be formed. These structures tend to be extremely stable, and so are valuable in high temperature applications. 

The most general method for the preparation of high temperature polyimides is based on the reaction between an aromatic diamine and an aromatic dianhydride or tetracarboxylic acid. This proceeds via the formation of the intermediate polyamic acid which in further heating undergoes a ring closure condensation reaction leading to imide formation. The reaction is as follows... 

Another family of aromatic polyimides is produced from the condensation reaction between biphenyl tetra carboxylic dianhydride (BPDA) and aromatic diamines such as ODA and p-phenylene diamine, PDA. The polyimides BPDA-ODA and BPDA-PDA are available from Ube Industries under the Upilex R and S trademarks, respectively. Their T s are reported to be >400°C. Structures appear in Fig. 1.29. 

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