Method of preparing polymers with low melt viscosity

Details Method of preparing polymers with low melt viscosity Method of preparing polymers with low melt viscosity

1996-06-18

2001-02-20

Truong, Duc (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From carboxylic acid or derivative thereof

C528S332000, C428S473500, C264S045100, C264S232000

Reexamination Certificate

active

06191252

ABSTRACT:

ORIGIN OF THE INVENTION
The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.
BACKGROUND OF THE INVENTION
The present invention relates generally to high performance polymeric materials. The present invention relates particularly to a series of poly(arylene ether)s (PAEs) that are useful as adhesives, composite matrices, moldings, films and coatings. The present invention also relates particularly to a series of polyimides (PIs) that are useful as adhesives, composite matrices, moldings, films and coatings.
DESCRIPTION OF RELATED ART
Poly(arylene ether)s (PAEs) are a class of high performance, aromatic polymers that display excellent thermal stability, good mechanical properties, good chemical resistance and good processability. Some commercially available PAEs include Udel Polysulfone (Amoco), PEEK Polyetheretherketone (ICI), PEK Polyetherketone (BASF) and PES Polyethersulfone. These materials have very good properties, but improvements need to be made in mechanical properties, chemical resistance and processability to take advantage of certain aerospace applications requiring high performance at relatively high temperatures for long times.
Some work has been reported that describes the preparation of PAEs with terminal and/or pendent reactive groups which improves mechanical properties and chemical resistance but the processing requirements still remain relatively high and, therefore, certain techniques to prepare composites are not available for these materials.
Polyimides (PIs) are a class of high performance, aromatic polymers that display excellent thermal stability, mechanical properties and chemical resistance but only fair processability. Overall, these materials have very good properties, but improvements need to be made in mechanical properties, chemical resistance and processability to take advantage of certain aerospace applications requiring high performance at relatively high temperatures for long times.
Some work has been reported that describes the preparation of PIs with terminal and/or pendent reactive groups which improves mechanical properties and chemical resistance but the processing requirements still remain relatively high and, therefore, certain techniques to prepare composites are not available for these materials.
A primary object of this invention is to provide polymers (PAEs and PIs) with lower melt viscosities [so that techniques such as Resin Transfer Molding (RTM) and Resin Film Infusion (RFI) can be used or so that lower pressures and/or temperatures can be used in autoclave processing], improved chemical resistance and improved mechanical properties.
Another object is to provide polymers (PAEs and PIs) with lower melting points, larger processing windows (time at the low viscosities), improved solubility (of the uncured form for materials containing reactive groups) and higher crosslink density in the cured polymer.
SUMMARY OF THE INVENTION
According to the present invention, PAEs and PIs were synthesized such that mixtures of branched, linear and star shaped molecules were obtained. Since the resulting material is a mixture of many different structures, some of which are branched and star shaped, the materials exhibit lower melting points as well as lower melt and solution viscosities than their linear counterparts. The lower melting point and lower melt viscosity provides a larger processing window. These materials are endcapped with either reactive endgroups which produce thermosets or on-reactive endgroups which produce thermoplastics. The synthesis of these mixtures of materials is accomplished by using a small amount of a trifunctional monomer (a bisphenol, for example 1,3,5-trihydroxybenzene, for PAEs or a triamine, for example triamino pyrimidine or melamine, for PIs), along with the conventional difunctional monomers in the polymerization. It is recognized that triamino pyrimidine and melamine are slow reacting triamines and, as a result, may produce lower molecular weight materials until higher temperatures are employed in synthesis or processing. This lower reactivity may, in fact, be very beneficial for certain types of processing which require low solution or melt viscosities. It is also recognized that the lower reactivity in one or more of the amine groups on the triamine could be used to control the final polymer architecture or ratio of linear to branched to star-shaped molecules. As long as the amount of trifunctional monomer is small, the materials remain only branched and therefore soluble. Higher concentrations of trifunctional monomer during synthesis would produce crosslinked, network systems which would be much less soluble. Solubility would be important if future processing techniques required solutions but would be unimportant in future processing techniques required only a melted system. Techniques such as RTM and RFI require a melted system with low melt viscosity and large processing windows (long times at low melt viscosities). As shown in Table 1, materials synthesized using small amounts of 1,3,5-trihydroxybenzene or triamino pyrimidine display lower melting points, lower melt and solution viscosities, and large processing windows. As shown in Table 2, materials synthesized using a small amount of triamino pyrimidine (Example 16) display higher glass transition temperatures (T
g
s), higher tensile strengths and higher tensile moduli at both room temperature and 177° C. As shown in Table 3, these materials also display excellent adhesive strengths when bonded under mild conditions (Example 20).
The advantage of these non-reactive endcapped polymers to linear polymers is the lower melt viscosities at the same molecular weights thereby allowing other processing techniques such as RTM or RFI or lower pressures and temperatures with techniques such as autoclave processing. The advantage of these reactive endcapped polymers to linear reactive endcapped polymers of the same molecular weight is the lower melt viscosities before curing and the higher crosslink densities after curing (where branching in the uncured systems would become crosslinking in the cured systems) leading to improved chemical resistance and mechanical properties.


REFERENCES:
patent: 5055249 (1991-10-01), Schmid
patent: 5223584 (1993-06-01), Lenke et al.

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