Structure and Mechanical Properties of Polymers
Using molecular mechanics and molecular dynamics methods structure,
energetic and thermal behavior and mechanical properties of various
polymers were studied.
- isolated polymer chains: Polyethylene,polyfuran, polyparaphenylene,
polythiophene, DNA strands, Polypeptides
- dendrimers: PAMAM, Ph-O, dendritic box.
- crystalline polymers: Polyethylene, oriented polyimides,
polyesthers, PTFE, Nylons.
- amorphous bulk polymers: Polyethylene, polycarbonate.
In molecular mechanics studies: the objective was to study the structure, energetics,
and mechanical properties of bulk polymers. Volumetric and structural properties of
polymers were obtained by optimizing internal energy(enthalpy) and structure at zero
pressure and temperature.
In mechanical property determinations three different methods are used.
In second derivative calculations, using harmonic theory, thermodynamic
state functions were also computed.
- Constant stress minimization to obtain induced strain components
- Constant strain minimization to obtain internal stress components
- One point calculation: using second derivatives for Born terms.
Molecular dynamics studies, thermal behavior of the polymers were explored.
Isolated polymers were investigated for conformational behavior.
In molecular dynamics studies of mechanical property determination c-Polyethylene is
used as a test example. This was the first time that the fluctuation expressions  for
elastic constants are used to evaluate elastic constants of a polymer at elevated
- T. Cagin, N. Karasawa, S. Dasgupta and W. A. Goddard, III,
"Thermodynamic and Elastic Properties
of Polyethylene at Elevated Temperatures,"
Computational Methods in Materials Science, pp 61-66, 1992.
- T. Cagin, W. A. Goddard, and M. L. Ary,
"Canonical Dynamics Simulation of
Single Chain Polyethylene,"
Comp. Polym. Sci. 1, 241 (1991).
- J. R. Ray, Phys. Rep. 8, 1, (1988) and references therein.
- P.Q. Qian, T. Cagin and Z.M. Chen, "Characterization of Polyesther
properties by Molecular Simulation Technique",
Proceedings of American Chemical Society, pp 92-3; 1993.
- C.F. Fan, T. Cagin, Z.M. Chen and K.A. Smith,
"Molecular Modeling of
Polycarbonate: Force Fields, Structure and Mechanical Properties,"
Macromol. 27, 2383 (1994);
- P.Q. Qian, T. Cagin and Z.M. Chen, "Characterization of highly oriented
polyimides using Molecular Simulations,"
Proceedings of American Chemical Society, pp 96-7; 1993.
- C.F. Fan, T. Cagin, W. Shi, and K.A. Smith,
"Local Chain Dynamics of a Model Polycarbonate Near Glass-Transition
Temperature - A Molecular Dynamics Study," Macromol. Theo. and Simul. ,
6, 83-102 (1997).
- P. Miklis, T. Cagin, W. A. Goddard, III,
Dynamics of Bengal Rose Encapsulated in the Meijer
Dendrimer Box, J. Amer. Chem. Soc., in press.
Drs. C. F. Fan, P. Qian, Z. M. Chen, N. Karasawa, S. Dasgupta,
M.L. Ary ;
Professors J.R. Ray and W. A. Goddard, III.
High performance polymers
Stiff Chain Aromatic Heterocyclic Polymers
Light weight, high strength fibers and films produced from stiff chain aromatic heterocyclic
polymers are good candidates for use as structural materials in advanced technological
applications. Some examples of this kind of polymers we studied are
Molecular mechanics and molecular dynamics methods used in studying the structure,
dynamics, thermodynamics and mechanical properties of these high performance polymers.
Semi-empirical solid state quantum mechanics programs are used in studying the elctronic
structures of the same polymers.
- ABPBO poly-2,5-benzoxazole
- ABPBT poly-2,6-benzothiazole
- ABPBI poly-2,5-benzobimidazole
- PBT poly-paraphenylene-benzothiazole
- PBO poly-paraphenylene-benzoxazole
- PBI poly-paraphenylene-benzobimidazole
Structure of PBZT Crystal.
- We subjected these polymers moderate incremental tension and
compression to compute the finite difference elastic properties. 
- Second, Extreme tensions and compressions are applied to investigate the structural
- Hessians for single crystals were computed using Dreiding Force field to obtain
elastic constants at a single point. 
- Harmonic theory is used to study the structural and thermodynamic stability as a
function of temperature. [1, 2]
- Molecular dynamics simulations on the isolated chains and in the bulk state are
performed to investigate the rigidity, thermal behavior and mechanical properties.
Electronic structures and band gaps of PBO, PBI, and PBT are also studied using
semi-empirical quantum mechanical methods. 
- T. Cagin,
"Mechanical Response of High Performance Polymers,"
in Materials Theory and Modeling, pp 321-4, 1993.
- T. Cagin and W. A. Goddard, III,
- B. L. Farmer, T. Cagin, D. S. Dudis, W. W. Adams, "Molecular Modeling of Rigid Rod Polymers,"
in Deformation, Yield and Fracture of Polymers, 1991.
- T. Cagin and D. S. Dudis, unpublished.
Collaborators Drs. W. W. Adams, D. S. Dudis, and Profs. B. L. Farmer and
W. A. Goddard, III.