POLYMERS

Background and Summary of the Invention

The instant invention relates to poly-p-xylylene (Parylene) polymers, and more particularly to a plurality of unique, low dielectric constant α-perfluoro-p-xylylene polymers which are formed from their associated cyclic α-perfluoro-di-p-xylylenes.

The outstanding physical properties of the poly-p-xylylene (Parylene) polymer family, including their ability to conformally coat objects of varied geometric shape, have prompted extensive coating applications within the automotive, electronics, and medical industries. Parylene is a generic term used to describe a class of poly-p-xylylene polymers which are derived from a dimer having the structure:

wherein X is typically a hydrogen. Parylene conformal polymer coatings are obtained from their associated parylene dimers by means of a well-known vapor deposition process in which the dimer is vaporized, pyrolized, i.e. cleaved into a monomer molecules deposit and polymerize into a thin film onto a substrate disposed within the vacuum chamber. The process occurs according to the following reaction:

.

J U . -

Although thee polymers have excellent thermal and chemical stability, the presence of -CH ₂ - groups adjacent to the aromatic ring provide potentially vulnerable sites for atmospheric attack. In order to strengthen these weak molecular bonds, it has been found desirable to replace the active hydrogen atoms with a more stable substituent group, such as fluorine, resulting in α-perfluoro-di-p-xylylene, otherwise referred to as Parylene AF4 dimer. The AF4 dimer has the structure:

It is known that Parylene AF4 polymer coatings which are derived from the AF4 dimer by the vapor deposition process have a very high melting temperature (about 500 ^° C), and a relatively low dielectric constant (about 2.3). These characteristics make parylene AF4 ideally suite for a variety of applications within the electronics industry. While Parylene AF4 has a relatively low dielectric constant, which is desirable in almost all electronics applications, thee is nevertheless a continuing need in the electronics industry for coating and/or dielectric materials having still lower dielectric constants.

Accordingly, the instant invention provides a plurality of cyclic α-perfluoro-di-p- xylylenes which are believed to be effective in producing parylene polymer films having equal, if not better, dielectric characteristics, i.e. lower dielectric constant, than the basic AF4 polymer, More specifically, the instant invention provides a first group of cyclic α-perfluoro-di-p- xylylenes having the structure:

wherein G is an aromatic nuclear substituent group selected from the group consisting of fluorine and chlorine, and further wherein m=4.

The invention still further provides a second group of cyclic α-perfluoro-di-p-xylylenes having the structure:

wherein G is an aromatic number substituent group selected from the group consisting of perfluoroalkyl groups having the formula C _n F _2n+ ι for n=l, 2, 3 . . . , and further wherein m=l to 4. The selected substitute groups are believed to provide the resulting polymer films with desirable dielectric characteristics.

Accordingly, among the objects of the instant invention are the provision of cyclic α- perfluoro-di-p-xylylenes for use in the formation of α-perfluoro-p-xylylene polymer films having highly desirable dielectric properties, i.e. low dielectric constant. Other objects, features and advantages of the invention shall become apparent as the description thereof process when considered in connection with the accompanying illustrative drawings.

Description of the Preferred Embodiment

As will hereinafter be more fully described, the instant invention provides cyclic α- perfluoro-di-p-xylylenes which are effective for producing α-perfluoro-di-p-xylylene polymer film having highly desirable dielectric properties, i.e. low dielectric constants.

More specifically, the instant invention provides a first group of cyclic α-perfluoro-di-p- xylylenes having the structure:

wherein G is an aromatic nuclear substituent group selected from the group consisting of chlorine and fluorine, and further wherein m=4.

The invention further provides a second group of cyclic α-perfluoro-di-p-xylylenes having the structure:

wherein G is an aromatic nuclear substituent group selected from the group consisting of perfluoroalkyl groups having the formula C _n F _{2n+ l} , for n=l, 2, 3, . . ., and further wherein m=l to 4, inclusive.

The basic cyclic α-perfluoro-di-p-xylylene, i.e. the parylene AF4 dimer, is well known in the art, and can be readily produced by methods known in the art. For example, the U.S. Patent to Dolbeir No. 5,210,341 describes a method for producing the AF4 dimer. The methods of producing the above-described, ring-substituted AF4 dimers are not critical to the instant invention, as such methods could be implemented by those skilled in the art.

The ring-substituted cyclic α-perfluoro-di-p-xylylenes as described above are readily converted into their polymer forms by the above-described vapor deposition process resulting in

polymer chain films having the structure:

wherein G is a nuclear substituent group selected from the group consisting of chlorine and fluorine (m=4), and perfluoroalkyl groups having the formula C„F _2n+1 , for n=l, 1, 3 (m=l to 4, inclusive), and x is an integer greater than 1.

It is believed that the selected nuclear substituent groups as defined above, will provide highly desirable physical and electrical properties to the polymer films. One such desirable property comprises an expected lower dielectric constant than the currently available parylene materials. Such low dielectric constant materials are highly desirable in the art, and will provide a new generation of materials for the preparation of electronic circuit structures, and coatings for such structures.

It can therefore be seen that the instant invention provides highly desirable cyclic α- perfluoro-di-p-xylylenes which are effective for the production of a-perfluoro-p-xylylene polymer films having low dielectric constants. For these reasons, the instant invention is believed to represent a significant advancement in the art which has substantial commercial merit.

While there is described herein certain specific structures embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein described except insofar as indicated by the scope of the appended claims.