Microwave synthesis of polyamides, polyesters, and...

Details Microwave synthesis of polyamides, polyesters, and... Microwave synthesis of polyamides, polyesters, and...

2000-08-17

2003-02-04

Berman, Susan W. (Department: 1711)

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

Synthetic resins

Compositions to be polymerized by wave energy wherein said...

C522S168000, C522S173000, C522S176000, C522S179000, C522S001000, C264S489000, C264S490000, C264S496000

Reexamination Certificate

active

06515040

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates generally to methods of polymerization and the polymers formed thereby. In particular, this invention relates to methods using pulsed microwave polymerization for the synthesis of polymers such as polyamides, polyesters, and polyamideesters.
Despite extensive research and development directed to methods for the manufacture of polymers, there are still areas where improvement would result in significant economic benefit. Examples include shortening the time required for polymerization, and maximizing the efficiency of the energy input required for polymerization. There is also a continuing need for improved methods for the manufacture of three-dimensional molded parts having fine-scale features, especially those having close tolerances.
One approach to reducing times and input energies required for polymerization reactions is to employ microwave radiation as a heat source. As an alternative to conventional heating techniques, microwave irradiation provides an effective, selective, and fast synthetic method by heating the molecules directly through the interaction between the microwave energy and the molecular dipole moments of the starting materials. Microwave radiation has been employed in polymer synthesis and curing; see, for example, F. Parodi,
Chim. Ind. (Milan
), volume 80, number 1, pages 55-61 (1998); and U.S. Pat. No. 5,317,081 to Gelorme et al. A publication by Albert et al. describes microwave-activated polymerization of epsilon-caprolactone with titanium tetrabutylate catalyst, but this process appears to offer no advantages in reaction times or product molecular weights compared to the corresponding thermal synthesis; see P. Albert, H. Warth, R. Muelhaupt, and R. Janda,
Macromol. Chem. Phys
., volume 197, number 5, pages 1633-1640 (1996). In Great Britain Patent No. 1,534,151, Dolden et al. describe a microwave process for synthesis of polyamides from amino acids, lactams, or mixtures of organic diacids and organic diamines. While the method of Dolden et al. appears to enable reduced reaction times, it does not allow precise control of reaction temperature, and does not produce high molecular weight polymers in high yield. There accordingly remains a need for an efficient and highly reproducible process for microwave synthesis of polyamides, polyesters, and polyamideesters.
BRIEF SUMMARY OF THE INVENTION
A time-saving and reproducible polymer synthesis is provided by a method, comprising:
irradiating a reaction mixture with microwaves, wherein
the microwave radiation is characterized by
a varying frequency of about 2.4 to about 7 GHz;
a frequency sweep rate of about 0.1 to about 10 GHz/sec;
a forward power input of about 200 to about 10,000 Watts per total moles of reactant; and
the forward power input of the microwave radiation is adjusted to maintain a known temperature in the composition; and further wherein
the reaction mixture comprises aliphatic lactones having from 4 to 12 carbon atoms; aliphatic lactams having from 4 to 12 carbon atoms; amino acids having from 4 to 12 carbon atoms; omega-hydroxyacids having from 4 to 12 carbon atoms; mixtures of aliphatic dicarboxylic acids having from 4 to 12 carbon atoms and aliphatic diamines having from 2 to 12 carbon atoms; mixtures of aliphatic dicarboxylic acids having from 4 to 12 carbon atoms and aliphatic diols having from 2 to 12 carbon atoms; or mixtures of aliphatic lactones having from 4 to 12 carbon atoms and aliphatic lactams having from 4 to 12 carbon atoms.
Use of microwave frequency sweeping and temperature control via microwave forward power setting and on/off forward power control enables synthesis of polymer having higher molecular weights and lower dispersities compared to polymers prepared by previously known methods.
The method enables substantial time savings compared to conventional thermal polymerizations. The method also enables solvent-free polymerizations and is suitable for directly producing molded articles by polymerizing monomer mixtures in article-shaped molds.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A method for synthesizing polyamides, polyester, and polyamideesters comprises:
irradiating a reaction mixture with microwaves, wherein
the microwave radiation is characterized by
a varying frequency of about 2.4 to about 7 GHz;
a frequency sweep rate of about 0.1 to about 10 GHz/sec;
a forward power input of about 200 to about 10,000 Watts per total moles of reactant; and
the forward power input of the microwave radiation is adjusted to maintain a known temperature in the composition; and further wherein
the reaction mixture comprises aliphatic lactones having from 4 to 12 carbon atoms; aliphatic lactams having from 4 to 12 carbon atoms; amino acids having from 4 to 12 carbon atoms; omega-hydroxyacids having from 4 to 12 carbon atoms; mixtures of aliphatic dicarboxylic acids having from 4 to 12 carbon atoms and aliphatic diamines having from 2 to 12 carbon atoms; mixtures of aliphatic dicarboxylic acids having from 4 to 12 carbon atoms and aliphatic diols having from 2 to 12 carbon atoms; or mixtures of aliphatic lactones having from 4 to 12 carbon atoms and aliphatic lactams having from 4 to 12 carbon atoms.
The method is suitable for the synthesis of polyesters from lactones. Suitable lactones include aliphatic lactones having from 4 to 12 carbon atoms, preferably from 5 to 10 carbon atoms. Preferred lactones may be represented by the formula
wherein n=3-11. A highly preferred lactone is epsilon-caprolactone (n=5).
The method is also suitable for the synthesis of polyesters from omega-hydroxycarboxylic acids having from 4 to 12 carbon atoms. Preferred omega-hydroxycarboxylic acids are represented by the formula
wherein n=3-11. A highly preferred hydroxycarboxylic acid is epsilon-hydroxycaproic acid (n-5)
The method is suitable for the synthesis of polyesters from mixtures comprising aliphatic dicarboxylic acids having 4-12 carbon atoms and aliphatic diols having 2-12 carbon atoms. Preferred aliphatic dicarboxylic acids are represented by the formula
wherein n=2-10. A highly preferred aliphatic dicarboxylic acid is adipic acid (n=4). Preferred aliphatic diols are represented by the formula
HO—(CH
2
)
n
—OH
wherein n=2-12. Highly preferred organic diols include ethylene glycol and 1,4-butanediol. It is preferred that the molar ratio of the dicarboxylic acid to the diol be about 0.8:1.2 to about 1.2:0.8, more preferably about 0.9:1.1 to about 1.1:0.9, yet more preferably about 0.98:1.02 to about 1.02:0.98.
The method is suitable for the synthesis of polyamides from organic lactams having from 4 to 12 carbon atoms. Preferred lactams are represented by the formula
wherein n=3-11. A highly preferred lactam is epsilon-caprolactam (n=5).
The method is suitable for the synthesis of polyamides from amino acids having from 4 to 12 carbon atoms. Preferred amino acids are represented by the formula
wherein n=3-11. A highly preferred amino acid is epsilon-aminocaproic acid (n=5).
The method is suitable for the synthesis of polyamides from aliphatic dicarboxylic acids having from 4 to 12 carbon atoms and aliphatic diamines having from 2 to 12 carbon atoms. Suitable and preferred aliphatic dicarboxylic acids are the same as those described above for the synthesis of polyesters. Preferred aliphatic diamines are represented by the formula
H
2
N—(CH
2
)
n
—NH
2
wherein n=2-12. A highly preferred aliphatic diamine is hexamethylenediamine (H
2
N(CH
2
)
6
NH
2
). It is preferred that the molar ratio of the dicarboxylic acid to the diamine be about 0.8:1.2 to about 1.2:0.8, more preferably about 0.9:1.1 to about 1.1:0.9, yet more preferably about 0.98:1.02 to about 1.02:0.98.
The method is also suitable for the synthesis of polyamideesters from aliphatic lactones having from 4 to 12 carbon atoms and aliphatic lactams having from 4 to 12 carbon atoms. The aliphatic lactones are the same as those described above for polyester synthesis, and the aliphatic lactams are the

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