Elsevier

Polymer

Volume 46, Issue 19, 8 September 2005, Pages 8410-8415
Polymer

Reaction kinetics study of asymmetric polymer–polymer interface

https://doi.org/10.1016/j.polymer.2005.07.003Get rights and content

Abstract

In this study, the reaction kinetics of asymmetric polymer–polymer interface was experimentally and theoretically studied. A new rheological method correlating the change of rheological property of reactive system with the conversion of the in situ formed copolymers was applied to study the reaction kinetics of PBT/epoxy reactive system. Then, the new method was proved to be useful by comparing its results with that obtained from the conventional endgroup determination method. Moreover, the conversion of PBT/epoxy reactive system from rheological method could be well fitted by the numerical analysis, from which the kinetic constant and the diffusion constant of epoxy in PBT could be determined simultaneously.

Introduction

Reactive blending of two or more polymers with in situ reactive compatibilizers has been extensively employed for developing new materials with desirable mechanical properties [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], which provided an attractive alternative to costly developments of new copolymer syntheses. However, most of the present studies were motivated principally by industrial applications and focused on the improvement of physical properties of the blend systems [5], [6], [7], [8], [9], [10], [11]. Only a few studies [12], [13], [14], [15] were reported on the examination of the reaction kinetics in the reactive blend, which was probably due to the complexity of the reaction and restricted methods for monitoring the process of reaction.

Fredickson [16], [17] and O'Shaughnessy [18], [19], [20] theoretically studied the reaction at a planar interface between two polymers. They showed that with increasing reaction time the reaction became mean-field type at initial time. As the interface became saturated with in situ formed copolymers, the reaction rate decreased markedly and the reaction became diffusion-controlled. Although the theoretical frameworks of the reactions were presented in these reports, there were no experimental supports. Oyama and Inoue [21], [22], [23] proposed pseudo-first-order kinetics for PA6/PSU-MAH blends on a planar interface by employing the assumption that reaction rate was proportional to the area density change investigated by X-ray photoelectron spectroscopy (XPS). Since, they assumed that this reaction was similar to the kinetics of a gas/solid system in surface science, the reaction rate was dependent on the number of vacant sites available for the reaction at the interface. The first-order kinetics of reactive blends on a planar interface might be unexpected since the interface reaction was usually taken as second-order kinetics because of the reaction of two different reactive groups. As the rheological properties are related to the amount of in situ formed graft (or block) copolymers for a reactive blend, Kim and co-workers [24], [25] evaluated the kinetics of the reaction between the reactive polymer–polymer interface by using PS-mCOOH/PMMA-GMA reactive system. The results showed that there were three distinct stages during the change of complex viscosity as a function of time and the apparent reaction kinetics in stage I was a first-order reaction. However, they did not give a very clear physical explanation for correlating the change of rheological property with the conversion of the in situ formed copolymers.

Other theoretical and experimental studies [26], [27], [28] have also addressed these interfacial reaction kinetics, but these studies focused on the reactions at the interface between two thermodynamically immiscible polymers. In the simplest situation, these authors considered a flat, symmetric interface between two polymer melts with same degree of polymerization N. However, the molecular weights of components of reactive systems were always different from each other in real industrial processes. In some situations, the added compatibilizers with relative lower molecular weights might be miscible with one of the components and the asymmetric polymer–polymer interface would be formed. These situations were much different from those assumptions for reactions at immiscible symmetric polymer–polymer interface. So, a number of basic questions are begged. How do the molecules diffuse and react at asymmetric interface? How rapidly do copolymers build up at the interface?

In this paper, experimental studies on the reaction kinetics of PBT/epoxy reactive system were carried out by a new rheological method. PBT is a kind of engineering thermoplastic polymer, and the epoxy resin with relative low molecular weight is often used as reactive modifier for the PBT blends. The reaction between the carboxyl acid in PBT and the epoxy group in epoxy resin occurs at the asymmetric interface easily, giving the in situ copolymers which usually as the compatibilizer for the PBT reactive blends [6], [8], [11]. Then, a theoretical study was presented and a simple numerical mode for reaction kinetics of asymmetric polymer–polymer interface was established.

Section snippets

Materials

The poly(butylene terephthalate) (PBT, 1097, Mn=20,000, density: 1.31±0.02 g/cm3; intrinsic viscosity: 0.97±0.02 cm3/g; melting point: 222–226 °C) used in this study was a natural grade product from Nantong XinChen Synthetic Material Co. Ltd, China, and the content of carboxylic acid is 0.03 mol/kg determined by potentiometric titration method. The epoxy resin used was E12, a bisphenol A diglycidyl ether-based resin made by Shanghai Synthetic Resin Co. Ltd, China. Its average molecular weight is

Rheological analysis of reaction conversions

The plot of complex viscosity (η*) at 240 °C with time for PBT/epoxy blends is shown in Fig. 1. The changes of the storage and loss modules (G′ and G″) with time are similar to the change of η*. For a reactive system consisting of PBT and epoxy, η* increased quickly, which is attributed to the coupling reaction between the carboxyl group of PBT and the epoxy group at interfacial region [9]. When the couple reaction occurs, copolymer, which have longer chains, is produced, which lead to the

Conclusions

In the present study, a new rheological method, which correlates the change of rheological property of reactive system with the conversion of the in situ formed copolymers, was used to experimentally study the reaction kinetics of asymmetric polymer–polymer interface. This method was proved to be useful through studying the reaction kinetics of PBT/epoxy reactive system by conventional endgroup determination method. Then a simple numerical analysis was used to theoretically study the reaction

Acknowledgements

The authors thank financial support for this work from the National Science Foundation of China (NSFC No. 50390090).

References (33)

  • P. Martin et al.

    Polymer

    (2003)
  • P. Martin et al.

    Polymer

    (2004)
  • S.C. Jana et al.

    Polymer

    (2001)
  • S. Parnell et al.

    Polymer

    (2005)
  • F. Burel et al.

    Polymer

    (2005)
  • C. Liu et al.

    Polymer

    (2003)
  • H. Koriyama et al.

    Polymer

    (1999)
  • H.K. Jeon et al.

    Polymer

    (2001)
  • G.H. Hu et al.

    Polymer

    (1997)
  • H. Yang et al.

    J Appl Polym Sci

    (2002)
  • P. Martin et al.

    J Appl Polym Sci

    (2004)
  • E. Lievana et al.

    Macromol Symp

    (2003)
  • A. Arostegui et al.

    J Appl Polym Sci

    (2004)
  • D. Dharaiya et al.

    Polym Eng Sci

    (2003)
  • K. Chiou et al.

    J Polym Sci, Part B: Polym Phys

    (2000)
  • Y. Shieh et al.

    J Appl Polym Sci

    (2001)
  • Cited by (13)

    • Enhancement in interfacial reactive compatibilization by chain mobility

      2014, Polymer
      Citation Excerpt :

      The plasticizer effectively reduces the viscosity of the PA phase at all shear rates without modifying the shear thinning exponent. The rheological tracking of the reaction between two polymers is typically studied using disks of the different polymers, one on top of the other [31–34]. The disks are sheared for over an hour under small amplitude dynamic oscillatory shear (DOS) conditions.

    • Study on degradation and crosslinking of impact polypropylene copolymer by dynamic rheological measurement

      2010, Polymer
      Citation Excerpt :

      Among these, dynamic oscillation rheology, especially under the low frequency, was found to be one of the most efficient techniques for detecting chemical reactions and microstructural transformation of polymers due to chain scission and recombine, because different polymer chains could behave diagnostic viscoelastic response in long time regime due to the difference of relaxation rate [16–22]. In addition, another excellence of dynamic oscillate rheological measurement is that its strain is too small to damage the structure of a polymer [16,17,19,21,22]. Impact polypropylene copolymer(IPC), also so-called polypropylene catalloys (PP-cats) or polypropylene impact copolymer, is an in situ polypropylene copolymer prepared by two-step polymerization: bulk polymerization of propylene and then gas-phase copolymerization of ethylene and propylene with a spherical superactive TiCl4/MgCl2 based catalyst systems [23–26].

    • Rheological testing on shear enhanced chemical reaction at SMA/PA6 interface

      2011, Gaofenzi Cailiao Kexue Yu Gongcheng/Polymeric Materials Science and Engineering
    View all citing articles on Scopus
    View full text