Communications
DOI: 10.1002/anie.201005456
Smart Polymers
Thermally Induced Structural Transformation of Bisphenol-1,2,3-
triazole Polymers: Smart, Self-Extinguishing Materials**
Beom-Young Ryu and Todd Emrick*
In modern organic polymer chemistry, step- and chain-growth
polymerization methods are critically important for the
fabrication of high-volume and specialty plastics, foams,
gels, and rubbery materials. Such materials have enabled
new applications that have transformed society.[1] Despite the
many advances realized through polymer chemistry, many
imperfections remain problematic, often associated with
aging and cracking of the material, and leaching of additives.[2]
Environmental contamination and bioaccumulation of addi-
tives, such as plasticizers, anti-oxidants, and flame-retardants,
are particularly problematic.[3] Added inorganic salts com-
promise the physical and mechanical properties of polymers,
while halogenated flame retardant additives are bio-accum-
luative, and thus threaten the environment and human
health.[4] Organic/polymer chemistry advances that address
this additives problem are needed urgently, and will be
beneficial in terms of both materials performance and safety.
Specific to the area of polymer flammability is the need
for novel polymers that exhibit non-flammable properties in
the absence of additives. Key to discovering inherently non-
flammable polymers is a mechanistic organic understanding
of polymer decomposition. Structurally simple hydrocarbon
polymers like polyethylene combust readily and completely.
Other polymers, especially aromatic structures, possess
decomposition mechanisms that prevent complete combus-
tion. For example, polymers based on bisphenol C (BPC)[5]
lose Cl2 to generate a carbene, then rearrange to diphenyla-
cetylenes that, at high temperature, aromatize and char. We
adapted this concept to totally halogen-free materials, by
developing a new class of deoxybenzoin polymers, which at
high temperature undergo dehydration, conversion to diphe-
nylacetylenes, and aromatization/char.[6] The charring event is
critically important for precluding further oxidative combus-
tion, by providing a self-extinguishing mechanism.
We recently took interest in the insights reported by
Gilchrist and co-workers on the conversion, by flash vacuum
pyrolysis, of bisphenyl-1,2-3-triazoles to phenylindoles and
nitrogen gas (Scheme 1).[7,8] This organic structural rearrange-
ment provides a new opportunity in polymer synthesis and
Scheme 1. Thermally induced structural rearrangement of diphenyl-
1,2,3-triazole.
materials applications, but to our knowledge there is no prior
report on the synthesis of polymers containing BPT in the
backbone. Here we describe the synthesis of BPT-containing
aromatic polyesters by step-growth polymerization, giving
para- and meta-linked structures. Characterization of the
BPT-polymers produced in this work revealed exceptional
examples of high performance materials, thus representing
new opportunities in additive-free, non-flammable macro-
molecular materials chemistry.
Scheme 2 shows our preparation of BPT-containing
aromatic polyesters from the corresponding BPT monomer
precursors. The phenyl azide and trimethylsilylethynyl
(TMSE) precursors to monomers 1 and 2 were connected
by copper catalyzed click cycloaddition,[9] using CuBr and
2,2’-bipyridyl, in polar solvents such as DMF, to give the
desired bis-phenolic triazole structures. Recrystallization
from acetic acid/water gave 4-BPT (1) and 3-BPT (2) in 60–
70% yield, in sufficiently pure form to use directly in
polymerization chemistry.
BPT-containing polymers were prepared by interfacial
polycondensation of BPT monomers 1 or 2 with isophthaloyl
dichloride as the difunctional comonomer, benzyltriethylam-
monium chloride as the phase-transfer catalyst, and CH2Cl2 as
the organic phase. Typical of interfacial polymerization, a film
was seen to develop in the stirring heterogeneous reaction
mixture during the course of the polymerization, indicating
successful polymer formation at the fluid–fluid interface. The
4-BPT aromatic polyesters isolated from this reaction (65%
yield on ca. 1-gram scale) were found to be poorly soluble in
common solvents (e.g., THF, DMF, and NMP), making
spectroscopic characterization difficult. Thus, we performed
the interfacial polymerization experiments using bisphenol A
(BPA) as a comonomer with BPT and isophthaloyl chloride,
[*] Dr. B.-Y. Ryu, Prof. Dr. T. Emrick
Polymer Science and Engineering
University of Massachusetts
120 Governors Drive, Amherst, MA 01003 (USA)
Fax: (+1)413-545-0082
E-mail: tsemrick@mail.pse.umass.edu
[**] The authors acknowledge the financial support of the Federal
Aviation Administration (FAA-09-G-013), and the member compa-
nies and organizations of the Center for UMass-Industry Research
on Polymers (CUMIRP) that support anti-flammable polymer
research, including Boeing, Sabic-Innovative Polymers, Kydex, Inc.,
and the U.S. Army. Facilities support from the NSF Materials
Research Science and Engineering Center (DMR-0820506) is also
acknowledged.
Supporting information for this article is available on the WWW
9644
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2010, 49, 9644 –9647