Modern Day Alchemy: Computational Investigations Into the Molecular Mechanisms of
Kevlar® & Spectra® Fiber
James Lagasca
Molecular Modeling Using Computational Chemistry Methods
Summer Ventures In Science and Mathematics- UNC at Charlotte
Dr. Lewis Acampora
Abstract
The polymers Kevlar® (Poly-Paraphenyleneterephtalamide) and Spectra®
(Ultra-High Molecular Weight Polyethylene) are renowned for their astounding low
weight to high tenacity ratios. Investigated in this study were their heat of reactions and
the transition states involved in these molecules’ polymerization processes. Results in
Kevlar’s analysis displayed its heat of reaction at -862,074.7602 kcal/mol, and its profiles
showed that in the constrained (1-5 Å) hydrogen bond between the original monomers of
the Kevlar system (terephthaloyl chloride and p-phenylenediamine) there produced a
critical structural morph (2.5-2.6 Å); and in the initial bond (1-5 Å) between the HCl
catalyst and the carbonyl oxygen system, displayed was an “excited” state not seen in the
other energy profiles; instead of having the first calculated value as the highest of
energies (1.16 Å), the calculations showed that the molecule jumped up in energy (1.33
Å) before plummeting (caused by a more transient linear bonding state). Results from
Spectra’s analysis displayed the heat of reactions for its 2, 4, and 6 polyethylene branches
as the following: 2= -197.8303369, 4= -249.619571, 6= -279.71986 in kcal/mol.). The
Di-branched polyethylene chain was also constrained in its ethylene bridge (double
carbon bond at 2-5 Å), and in its bond between its zirconium atom and the polyethylene
component (1-5 Å) for energy profiles. Generally, as the bond lengths increased for these
bonds the energy of the Spectra® system would rapidly increase then, in the ethylene
bridge profile, level out, or, in the more irregular zirconium-polyethylene connection,
skyrocket. The structures, mechanisms of transitions, heats of reactions, and other
properties for the Kevlar® and Spectra® fibers were examined using the PC Spartan Pro
Software Program (v.5.1).
In medieval times, alchemy was defined as the process of transforming ordinary
substances such as iron and copper, into the refined and valuable materials of gold and
silver. However, in today’s world, modern day alchemy has evolved into the field of
polymers. Kevlar® and Spectra® (the trade names for Poly-Paraphenyleneterephtalamide
and Ultra-high Molecular Weight Polyethylene) are the silver and gold of today’s
industry. The polymers (fibers), created from simple monomers, demonstrate astounding
strength compared to their low weight, and thus have been used in a widespread of
protective, armor, outdoor, and structural products and
materials.
Kevlar® was invented in 1966 by Stephanie Louise
Kwolek and Herbert Blades. While working for Dupont,
Kwolek and Blades were pioneers in the development of high
strength polymers utilizing low temperature polycondensation
processes.1 One of the results was Kevlar, a polyaramide that is five times stronger than
steel and one half the density of fiberglass.2
In 1990 the U.S. companies of Dornsife & Associates and Allied Signal worked
together to develop the material Spectra® fiber. However, more importantly was their
utilization of the metallocene catalysis polymerization in the process. The metallocene
catalysis process was able to create extensive high tenacity materials, as opposed to the
original Zieglar-Natta polymerization used for simpler polymers. The latter was able to
increase the molecular weight of its polymers by 6 to 7 million times more than the
1
2
What is Kevlar? <http://www.dupont.com/kevlar/whatiskevlar/htm>
Kevlar. About.com <http://inventors.about.com/science/inventors/library/inventors/blkevlar.htm>
former!3 The ultra-high molecular weight polyethylene is twelve times stronger than
steel, yet it floats on water and in some versions is RADAR transparent.4
The structures and relative properties of the fibers Kevlar® and Spectra® were
investigated in this study. Effects of constrained bond lengths between the interactions in
their catalysts, during their polymerization processes, upon the energy of their systems
were found. The heats of reactions and other interesting features were recorded and
discussed. Calculations and visible interactions were all used with the PC Spartan Pro
(v5.1) software program. Research of this project primarily was composed of Internet
resources.
The first step for this project involved calculating the reaction energies (heat of
reaction) for Kevlar® and Spectra®. As mentioned, Kevlar® (PolyParaphenyleneterephthalamide) is produced through a low temperature polycondensation
process involving an acidic catalysis (usually hydrochloric or sulfuric). Using the Spartan
program the monomers of Kevlar®, terephthaloyl chloride and p-phenylenediamine, and
the catalysis hydrochloric acid are created individually on a Semi-Empirical PM3
3
Kevlar :poly(p-phenyleneterephthalamide) <http://www.umr.edu/~wlf/Synthesis/kevlar.html>
calculation state and were optimized (energy).5 This state was chosen due to time
constraint, and all other energies were recorded using this level. Using the same
parameters, the actual structure of Kevlar® was then created, optimized, and then
inserted with a hydrochloric acid molecule as the other end product. Thus, the energy of
the reactants subtracted from the finalized Kevlar® molecule and its hydrochloric
molecule resulted in the energy given of from the reaction.
ΔHORxn =Σ (Energy of Products) – Σ (Energy of Reactants)
ΔHORxn =Σ (Energy of Kevlar & HCL) – Σ (Energy of
terephthaloyl chloride, p-phenylenediamine, and HCL)
ΔHORxn =Σ (Energy of Spectra & Zirconocene Complex) – Σ
(Energy of n-Ethyne chains, and Zirconocene Complex)
Likewise, Spectra® (Ultra-High Molecular Weight Polyethylene) is produced
through metallocene catalysis polymerization which utilizes a zirconocene catalysis
complex. The catalyst was thus built: a tetrahedral molecule with a Zirconium cation
center from which two cyclopentendinaial ligands, a methyl branch, and an ethylene
bridge are attached. The heat of reactions were calculated and compared for the varying
4
History of Dornsife & Associates <http://www.dornsife.com/overview/D&A.history.html>
“Studies on the Semirigid Chain Polyamide-Poly (1,4 Phenyleneterephthalamide)
<http://www.umr.edu/~wlf/Synthesis/../Experimental/BeijingKevlar.html>
5
lengths of polyethylene branches: two, four, and six
The values were then compared and a relation/average heat reaction was determined.
The second method used in this project involved the actual polymerization
transition state demonstrations for the Kevlar® and Spectra® fibers. Kevlar® when
involved in the low temp. polycondensation polymerization, initiated with a proton,
donated from the hydrochloric catalyst to the carbonyl oxygen of the terephthaloyl
chloride component. In return, a nitrogen of the p-phenylenediamine attracted to the
carbon of the affected branch in the chloride and became positively charged. Thus, HCl
and Chlorine gas were given off along with the end product of Kevlar®.6 Thus, the
constrained bond lengths taken into consideration for the transition process were the
hydrogen bond connecting the monomers together (1.00 Å to 5 Å), and the end distance
between where the HCl catalyst initiated with the carbonyl oxygen system in the
terepthaloyl chloride.
For Spectra® Fiber and the metallocene catalysts polymerization, the electrons
shift to form several different bonds as shown below:
the zirconium-methyl carbon bond shifts to become a bond between the methyl carbon
and one of the ethylene carbons; and a bond connecting the zirconium cation to one of the
methyl hydrogens, becomes a bond between the zirconium cation and the other ethylene
carbon.7 Thus, an unlimited amount of ethylene chains can continue to bond and activate
at the zirconium complex. The proposed constrained bond lengths for energy profiles for
a two ethylene branched polyethylene were between the zirconium center and the
6
Making Nylons <http://www.psrc.usm.edu/macrog/nysyn.htm>
polyethylene chain (2.00 Å to 5.00 Å, set to 25 steps) and upon the double carbon bond
ethylene bridge of the zirconocene catalyst (1.00 Å to 5 Å, set to 25 steps).
As shown from the calculations below, the results displayed that Kevlar’s
synthesis resulted in the release of 862,074.7602 kcal/mol. Spectra’s synthesis for its
multi-branches involved the release of 197.8303369 kcal/mol for di-polyethylene chain,
249.619571 kcal/mol for quartet-polyethylene chain, and 279.71986 kcal/mol for the sixpolyethylene chain. Thus, the longer and heavier the polyethylene chain, the greater the
energy released.
Table 1: Heat of Reaction for Kevlar ®
Energy of Reactants (kcal/mol)
Energy of Products (kcal/mol)
Terephthaloyl chloride= -862,130.376
Combined Kevlar, HCl, and Cl2 gas=
p-phenylenediamine= 19.6643568
- 56.4161629
hydrochloric acid= -20.4647184
Heat of Reaction (kcal/mol)
ΔHORxn =Σ (Energy of Products) – Σ (Energy of Reactants)
- 56.4161629 - -862,131.1764= -862,074.7602
Table 2: Heat of Reaction for Spectra ®
Energy of Reactants (kcal/mol)

7
Zirconocene Catalysis Complex
Energy of Products (kcal/mol)
Spectra= -99.4530284
Metallocene Catalysis Polymerization <http://www.psrc.usm.edu/macrog/nysyn.htm>
W/ ethylene branch= 98.3773085

Zirconocene Catalysis Complex
Spectra= -110.051420
W/ two ethylene branches= 139.568331

Zirconocene Catalysis Complex
Spectra= -120.826528
W/ three ethylene branches= 158.893332
Heat of Reaction (kcal/mol)
ΔHORxn =Σ (Energy of Products) – Σ (Energy of Reactants)
One Ethylene Branch> Di-Polyethylene Chain
-99.4530284 – 98.3773085= -197.8303369
Two Ethylene Branches> Quartet-Polyethylene Chain
-110.051240 – 139.568331= -249.619571
Three Ethylene Branches>Six-Polyethylene Chain
-120.826528 – 158.893332= -279.71986
The transition results for the Spectra® system displayed that the constrained
double bond of the ethylene bridge in the zirconocene catalysis complex, when expanded,
would rapidly increase the energy of the system, and then level at 5Å. The energy profile
for the constrained bond between the zirconium atom and the polyethylene chain
demonstrated an irregular pattern; as the bond would increase, energy would increase, yet
then sharply decrease. However, as shown in the profile, the energy of the polyethylene
system skyrocketed as the bond proceeded over 4.875 Å, even further. Critical features of
the zirconium-polyethylene profile were the two large morphs of its structure (between
2.00 Å and 2.25 Å; at 4.875 Å and 5.000 Å).
Energy Profile- Constrained Double carbon bond in the ethylene bridge
Energy Profile- Constrained Bond involving the zirconium atom and the polyethylene chain at 2.00 Å
Energy Profile- Constrained Bond involving the zirconium atom and the polyethylene chain
at 2.25 Å
Energy Profile- Constrained Bond involving the zirconium atom and the polyethylene chain at 4.875
Energy Profile- Constrained Bond involving the zirconium atom and the polyethylene chain at 5.00 Å
For the Kevlar® system, the profile results demonstrated that for the
hydrogen bond, connecting the original monomers, there was a relevant morph
when the bond expanded from 2.5 Å to 2.6 Å. On basis of energy, the magnitude
for this profile was highest at the 1.00 Å constraint (111.975621 kcal/mol),
dramatically decreased, then rose again. For the profile of Kevlar’s bond between
its HCl catalyst and the carbonyl oxygen system, the energy dramatically
decreased after the bond exceeded 1.333 Å (energy range from 1.333 Å to 1.667
Å was approximately –50 to –60 kcal/mol); this did not seem like an extreme
change, but when compared to the rest of the profile it was the most significant
difference. However, the most interesting feature rested on the “excited state” of
the profile as when expanded from its first calculated value, 1.16 Å, to its next
1.33 Å, the energy “jumped” before plummeting, due to a transient, more linear
bonding state with the catalyst. Afterwards, the energy profile gradually increased
as the bond lengthened from 1.8 Å.
Energy Profile- Constrained Hydrogen bond, connecting the two previous monomers
Energy Profile- Constrained Hydrogen Bond, connecting the two previous monomers at 2.5 Å
Energy Profile- Constrained Hydrogen Bond, connecting the two previous monomers at 2.6 Å
Energy Profile- Constrained Bond between the HCl catalyst and the carboxyl oxygen
In conclusion, the investigation of Kevlar® (Poly-paraphenleneterphthalamide)
and Spectra® (Ultra-High Molecular Weight Polyethylene) revealed several interesting
findings. Both fibers, particularly Kevlar® (-862,074.7602 kcal/mol) gave off large
amounts of energy in their heat of reactions. In the comparisons of Spectra’s two, four,
and six polyethylene composed branches, no numerical relations could be found, though
releases in energy increased as more chains were added (as expected). However, the
energy profiles of constrained bonds for the fibers were very intriguing. As mentioned,
from the double carbon bond (ethylene bridge) in the first Spectra® profile, and as
exemplified in the hydrogen bond in the second Kevlar® profile, there were large
differences in energy (energy released) when the length would only change by tenths of
an Å. However, the most interesting features of the profiles were the structural morphs
involved in the Kevlar-Hydrogen bond and in the Spectra-Zirconium Polyethylene bonds,
which also involved little deviations in distances.