Molecular dynamics simulation for polyethylene crystallization: Effect of long chain branches

Document Type : Original research

Authors

1 Shanghai Key Laboratory of Multiphase Material Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China

2 Guangxi Agricultural and Animal Husbandry Engineering School, Guangxi, China

Abstract

The influence of long branches on crystallization behavior has been studied by means of molecular dynamics simulations. Using two systems: polyethylene (PE) with long branches (LCB-PE) and PE without long branches (linear-PE) with the same molecular weight, we have examined the crystallization behavior of the two systems by molecular dynamics simulation. This paper explains the influence of long branches on the isothermal crystallization process and the non-isothermal crystallization process with similar initial interchain contact fraction (ICF) in terms of final ICF, crystal regions, crystallinity, concentration of tie chains and energy. It is found that the crystallization process is classified as two stages: the nucleation stage and the crystal growth stage. The existence of long branches is favorable for the first stage while unfavorable for the second stage. Knots that act as crystalline defects are excluded from the lamella, resulting in decreasing in regularity and crystallinity of molecular chains. From the perspective of potential energy and non-bond energy, LCB-PE has lower energy than linear-PE in the nucleation stage while the energy of linear-PE is lower than that of LCB-PE in the second stage. In short, the long branched chains inhibit the crystallization process.

Keywords

Main Subjects

References

  1. Alt FP, Böhm LL, Enderle H-F, Berthold J (2001) Bimodal polyethylene– interplay of catalyst and process. Macromol Symp 163: 135-144
  2. Alamo RG, McLaughlin KW, Mandelkern L (1989) Changes in the phase structure of the polyethylenes after long-time storage at room temperatures. Polym Bull 22: 299-306
  3. Alamo RG, Chan EKM, Mandelkern L, Voigt­martin IG (1992) Influence of molecular weight on the melting and phase structure of random co­polymers of ethylene. Macromolecules 25: 6381- 6394
  4. Alamo RG, Viers BD, Mandelkern L (1993) Phase structure of random ethylene copolymers: A study of counit content and molecular weight as independent variables. Macromolecules 26: 5740-5747
  5. Failla MD, Mandelkern L (1993) Tensile proper­ties of mixtures of linear polyethylene and ran­dom ethylene copolymers having similar molec­ular weights. Macromolecules 26: 7167-7175
  6. Liu J, Zhang F, He T (2001) Effect of branch con­tent on the transition of crystalline structure and morphology of metallocene-catalyzed branched polyethylene. J Mater Sci 36: 5345-5349
  7. Sworen JC, Wagener KB (2007) Linear low-density polyethylene containing precisely placed hexyl branches. Macromolecules 40: 4414-4423
  8. Giovanni R, Bora I, Yuying W, Wagener KB (2009) Precision polyethylene: Changes in mor­phology as a function of alkyl branch size. J Am Chem Soc 131: 17376-17386
  9. Rojas G, Wagener KB (2009) Precisely and ir­regularly sequenced ethylene/1-hexene copoly­mers: A synthesis and thermal study. Macromol­ecules 42: 1934-1947
  10. Bora I, Wagener KB (2011) Decreasing the al­kyl branch frequency in precision polyethylene: Pushing the limits toward longer run lengths. J Am Chem Soc 133: 11872-118725
  11. Hosoda S, Nozue Y, Kawashima Y, Suita K, Seno S, Nagamatsu T, Wagener KB, Inci B, Zu­luaga F, Rojas G (2011) Effect of the sequence length distribution on the lamellar crystal thick­ness and thickness distribution of polyethylene: Perfectly equisequential admet polyethylene vs ethylene/α-olefin copolymer. Macromolecules 44: 313-319
  12. Nozue Y, Kawashima Y, Seno S, Nagamatsu T, Hosoda S, Berda EB, Rojas G, Baughman TW, Wagener KB (2011) Unusual crystallization be­havior of polyethylene having precisely spaced branches. Macromolecules 44: 4030-4034
  13. Inci B, Lieberwirth I, Steffen W, Mezger M, Graf R, Landfester K, Wagener KB (2012) Decreasing the alkyl branch frequency in precision polyeth­ylene: Effect of alkyl branch size on nanoscale morphology. Macromolecules 45: 3367-3376
  14. Gupta P, Wilkes GL, Sukhadia AM, Krishnas­wamy RK, Lamborn MJ (2005) Does the length of the short chain branch affect the mechanical properties of linear low density polyethylenes? An investigation based on films of copolymers of ethylene/1-butene, ethylene/1-hexene and ethylene/1-octene synthesized by a single site metall. Polymer 46: 8819-8837
  15. Kim MH, Phillips PJ (2015) Nonisothermal melting and crystallization studies of homoge­neous ethylene/α-olefin random copolymers. J Appl Polym Sci 70: 1893-1905
  16. Zhang XB, Li ZS, Lu ZY, Sun CC (2001) Mo­lecular dynamics simulation of the linear low-density polyethylene crystallization. J Chem Phys 115: 3916-3922
  17. Zhang XB, Li ZS, Lu ZY, Sun CC (2002) Roles of branch content and branch length in copoly­ethylene crystallization: Molecular dynamics simulations. Macromolecules 35: 106-111
  18. Ramos J, Martínez-Salazar J (2015) Computer modeling of the crystallization process of single-chain ethylene/1-hexene copolymers from dilute solutions. J Polym Sci Pol Phys 49: 421-430
  19. Sanmartin S, Ramos J, Francisco J, Martinezsala­zar J (2014) Strong influence of branching on the early stage of nucleation and crystal formation of fast cooled ultralong n-alkanes as revealed by computer simulation. Eur Polym J 50: 190-199
  20. Choi P, Wang Q, Vignola E (2014) Molecular dy­namics study of the conformation and dynamics of precisely branched polyethylene. Polymer 55: 5734-5738
  21. Tukur NM, Sharkh BFA, Osei-Twum EY, Hus­sein IA (2010) Impact of short chain branching on conformations of metallocene lldpe melts: NMR, light scattering and MD simulation study. Macromol Symp 263: 121-129
  22. Chunli L, Phillip C, Williams MC (2010) Mo­lecular dynamics study of the melt morphology of polyethylene chains with different branching characteristics adjacent to a clay surface. Lang­muir Acs J Surf Colloids 26: 4303-4310
  23. Haigh JA, Nguyen C, Alamo RG, Mandelkern L (2000) Crystallization and melting of model polyethylenes with different chain structures. J Therm Anal Calorim 59: 435-450
  24. Gao R, He X, Zhang H, Shao Y, Liu Z, Liu B (2016) Molecular dynamics study of the isother­mal crystallization mechanism of polyethylene chain: The combined effects of chain length and temperature. J Mol Model 22: 67
  25. Gao R, He X, Shao Y, Hu Y, Zhang H, Liu Z, Liu B (2016) Effects of branch content and branch length on polyethylene crystallization: Molecu­lar dynamics simulation. Macromol Theor Simul 25: 303-311
  26. Hu Y, Shao Y, Zhen L, He X, Liu B (2018) Effect of short-chain branching on the tie chains and dynamics of bimodal polyethylene: Molecular dynamics simulation. Eur Polym J 103: 312-321
  27. Lai SY, Wilson JR, Knight GW, Stevens JC (1994 Nov 1) Elastic substantially linear olefin polymers. US patent 5278272
  28. Malmberg A, Liimatta J, Lehtinen A, Lofgren B (1999) Characteristics of long chain branching in ethene polymerization with single site catalysts. Macromolecules 32: 6687-6696
  29. Wood-Adams PM, Dealy JM, deGroot AW, Red­wine OD (2000) Effect of molecular structure on the linear viscoelastic behavior of polyethylene. Macromolecules 33: 7489-7499
  30. Malmberg A, Kokko E, Lehmus P, Löfgren B, Seppälä JV (2007) Long-chain branched poly­ethene polymerized by metallocene catalysts Et[ind]2ZrCl2/MAo and Et[ind H4]2ZrCl2/MAO. Macromolecules 31: 8448-8454
  31. Kolodka E, Wang WJ, Zhu S, Hamielec A (2010) Rheological and thermomechanical properties of long-chain-branched polyethylene prepared by slurry polymerization with metallocene cata­lysts. J Appl Polym Sci 92: 307-316
  32. Jiaoyan AI, Zhu F, Lin S (2005) Synthesis and properties of bimodal branched polyethylene by single feed ethylene with α-diimine nickel/ Cp*TiCl3 binary catalysts. Acta Polym Sinica 1: 71-75
  33. Beigzadeh D (2003) Monte carlo simulation of long-chain branched polyethylene chains synthe­sized with dual-site-type catalyst systems. Mac­romol Theor Simul 12: 174–183
  34. Mehdiabadi S, Soares JBP, Dekmezian AH (2010) Simulation of polymerization and long chain branch formation in a semi-batch reactor using two single-site catalysts. Macromol React Eng 2: 37-57
  35. Simon LC, Soares JBP (2015) Polyethylene made with combinations of single-site-type catalysts: Monte carlo simulation of long-chain branch for­mation. Macromol Theor Simul 11: 222-232
  36. Soares J (2015) Mathematical modeling of the long-chain branch structure of polyolefins made with two metallocene catalysts: An algebraic so­lution. Macromol Theor Simul 11: 184-198
  37. Baig C, Alexiadis O, Mavrantzas VG (2014) Advanced monte carlo algorithm for the atomis­tic simulation of short and long-chain branched polymers: Implementation for model h-shaped, A3AA3multiarm (pom-pom), and shortchain branched polyethylene melts. Macromolecules 43: 986-1002
  38. Khonakdar HA, Morsheidan J (2015) Influence of long-chain branching extent in polyethyl­enes on molecular weight and molecular weight distribution predicted via rheological analysis. Polymer Bull 72: 1-15
  39. Jeong SH, Kim JM, Yoon J, Tzoumanekas C, Kröger M, Baig C (2016) Influence of molecular architecture on the entanglement network: Topo­logical analysis of linear, long- and short-chain branched polyethylene melts via monte carlo simulations. Soft Matter 12: 3770-3786
  40. Mayo SL, Olafson BD, Goddard WA (1990) Dreiding: A generic force field for molecular simulations. J Phys Chem 94: 8897-8909
  41. Li C, Choi P, Sundararajan PR (2010) Simulation of chain folding in polyethylene: A comparison of united atom and explicit hydrogen atom mod­els. Polymer 51: 2803-2808
  42. Yu X, Kong B, Yang X (2008) Molecular dy­namics study on the crystallization of a cluster of polymer chains depending on the initial en­tanglement structure. Macromolecules 41: 6733- 6740
  43. Zerze H, Mittal J, McHugh AJ (2013) Ab initio crystallization of alkanes: Structure and kinetics of nuclei formation. Macromolecules 46: 9151- 9157
  44. Nilsson F, Lan X, Gkourmpis T, Hedenqvist MS, Gedde UW (2012) Modelling tie chains and trapped entanglements in polyethylene. Polymer 53: 3594-3601
  45. Moyassari A, Mostafavi H, Gkourmpis T, Heden­qvist MS, Gedde UW, Nilsson F (2015) Simula­tion of semi-crystalline polyethylene: Effect of short-chain branching on tie chains and trapped entanglements. Polymer 72: 177-184
 

Files

Cited by

History

  • Receive Date: 19 January 2021
  • Revise Date: 26 February 2021
  • Accept Date: 02 March 2021
  • First Publish Date: 03 March 2021

Share

How to cite

Statistics