Polyimide siloxane segmented copolymers

Arnold CA, Summers JD, Bott RH, Taylor L T, Ward TC, McGrath JE (1987) Structure property behavior of polyimide-siloxane segmented copolymers. SAMPE Proceedings 32 586... 

Yoon TH, Arnold-McKenna CA, McGrath JE (1992) Adhesion behavior of thermoplastic polyimides and poly(imide siloxane) segmented copolymers influence of test temperatures J Adhes 39(100) 15... 

Polyimides are of particular interest for many engineering applications due to their excellent thermal and mechanical properties in the aerospace and microelectronics industries. Many important applications have been developed (1,2 The poiyimide siloxane segmented copolymers have been of particular interest since incorporation of amine functionalized polysiioxanes into polyimides have resulted in improved solubility and processability, decreased water absorption, atomic oxygen resistance (3), lower dielectric constants (4) and enhanced adhesion (5). The copolymers are generally synthesized as shown in Scheme 1 from a combination of a dianhydride and... 

One of the major goals of this endeavor was to solubilize the normally intractable polyimides by the incorporation of siloxane segments, and, optionally, by solution imidization. Solubilities of a series of siloxane-modified polyimide copolymers were evaluated in a variety of solvents as indicated in Table I. Copolymer solubility was found to be a function of the siloxane oligomer concentration... 

Thus, N-pyrimidine phthalimide reacted with hexylamine at room temperature to form an amide-amide. The initial amide-amide formation proceeded more rapidly in chloroform as compared to dimethylsulfoxide (DM SO). However, the ring closure reaction to the imide was favored by the more polar, aprotic DMSO solvent, yielding the imide in nearly quantitative yield after 3 hours at 75 °C. The authors were able to utilize this synthetic approach to prepare well-defined segmented poly(imide-siloxane) block copolymers. It appears that transimidi-zation reactions are a viable approach to preparing polyimides, given that the final polyimide has a Tg sufficiently low to allow extended excursions above the Tg to facilitate reaction without thermal decomposition. Additionally, soluble polyimides can be readily prepared by this approach. Ultimately, high Tg, insoluble polyimides are still only accessable via traditional soluble precursor routes. 

The earlier sections of this review have attempted to review the synthesis and characterization of the segmented copolymer materials as well as to highlight fundamental efforts related to a number of structure-property relationships. Polyimide-siloxane copolymers are high performance materials that have been driven by applications frequently identified with aerospace. However, this section will also include surface phenomena which are critical for certain electronic applications and high performance blends utilizing imide-siloxane copolymers. 

Yoon TH, Arnold CA, McGrath JE (1989) Titanium 6/4 single lap shear adhesive performance of polyimide homopolymers and poly(siloxane imide) segmented copolymers. Mater Res Soc Symp Proc 153 (Interfaces Polym Met Ceram) 211... 

Chen DH, Chen YP, Arnold CA, Hedrick JC, Graybeal JD, McGrath JE (1989) Compatible blends of segmented polyimide siloxane copolymers with engineering thermoplastics I polybenzimidazole (PBI). 34th International SAMPE Symposium 1247... 

Arnold CA, Summers JD, Chen YP, Yoon TY, McGrath BE, Chen D, McGrath JE (1989) Soluble polyimide homopolymers and poly (siloxane imide) segmented copolymers with improved dielectric behavior polyimides In Feger C, Khojasteh MM, McGrath JE (eds) Materials chemistry and characterization. Elsevier, Amsterdam... 

PERFECTLY ALTERNATING SEGMENTED POLYIMIDE SILOXANE COPOLYMERS... 

The polyimide siloxane copolymers are generally synthesized, as shown in Scheme 1, from a combination of a dianhydride and diamine monomer and an aminopropyl terminated polysiloxane to form the segmented polyamic acid. The polyamic acid is then cyclodehydrated by either thermal or solution imidization to give randomly segmented polyimide siloxane copolymers (4). This is indeed the classical approach of reacting one flexible oligomer with two monomers which form the "hard segment (9). 

Scheme 1. Synthesis of Randomly Segmented Polyimide Siloxane Copolymers...

Fig. 18. Density vs. PDMS content for a homopolyimide and the polyimide/poly(dimethyl-siloxane) perfectly alternating block copolymers with the 11,000 g/mol polyimide segments...

Segmented polyimide-polydimethylsiloxane copolymers have been successfully synthesized both in laboratory and industrial quantities to produce multiphase siloxane-modified polyimides. The siloxane detracts somewhat from the otherwise excellent thermo oxidative stability of the polyimide, but it does produce a number of important properties. These include multiphase behavior, improved adhesion to many substrates, improvements in fire resistance and enhanced gas and liquid separation membranes, where one wishes not only to maximize the contribution of the siloxane to permeability, but also to utilize the imide to re-... 

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