Elsevier

European Polymer Journal

Volume 67, June 2015, Pages 12-20
European Polymer Journal

Hydrogen bonding interactions in poly(ε-caprolactone–dimethyl siloxane–ε-caprolactone)/poly(hydroxyether of bisphenol A) triblock copolymer/homopolymer blends and the effect on crystallization, microphase separation and self-assembly

https://doi.org/10.1016/j.eurpolymj.2015.03.046Get rights and content

Highlights

Abstract

This study investigated the self-assembled microphase separated morphologies that are obtained in bulk, by the complexation of a semicrystalline poly(ε-caprolactone–dimethyl siloxane–ε-caprolactone) (PCL–PDMS–PCL) triblock copolymer and a homopolymer, poly(hydroxyether of bisphenol A) (PH) in tetrahydrofuran (THF). In these blends, microphase separation takes place due to the disparity in intermolecular interactions; specifically, the homopolymer interacts with PCL blocks through hydrogen bonding interactions. The crystallization, microphase separation and crystalline structures of a triblock copolymer/homopolymer blends were investigated. The phase behavior of the complexes was investigated using small-angle X-ray scattering and transmission electron microscopy. At low PH concentrations, PCL interacts relatively weakly with PH, whereas in complexes containing more than 50 wt% PH, the PCL block interacts significantly with PH, leading to the formation of composition-dependent nanostructures. SAXS and TEM results indicate that the lamellar morphology of neat PCL–PDMS–PCL triblock copolymer changes into disordered structures at 40–60 wt% PH. Spherical microdomains were obtained in the order of 40–50 nm in complexes with 80 wt% PH. At this concentration, the complexes show a completely homogenous phase of PH/PCL, with phase-separated spherical PDMS domains. The formation of these nanostructures and changes in morphology depends on the strength of hydrogen bonding between PH/PCL blocks and also the phase separated PDMS blocks.

Introduction

Crystallization behavior and nanostructure formation of block copolymers have gained greater interest in recent years [1], [2], [3]. The microphase structures of semicrystalline block copolymers are determined by two factors: the thermodynamical incompatibility between constituent blocks and the crystallization behavior of crystallizable blocks [4], [5], [6], [7], [8], [9]. It is known that the resulting morphology when crystallization occurs depends on whether the block copolymer crystallizes from a microphase-separated melt or from a disordered melt [10], [11], [12]. There are two possible nanostructures obtained from microphase-separated melts of crystalline–amorphous block copolymers as a result of crystallization; (a) the pre-existing microphase structure is destroyed by crystallization, or (b) crystallization is confined within the pre-existing microdomain and microphase separation is preserved. Generally, such structure development depends on the state (glassy or rubbery) of amorphous blocks during crystallization and also on the segregation strength (χN), where χ is the Flory–Huggins interaction parameter and N is the degree of polymerization [13]. In block copolymers containing crystallizable components, the interplay between crystallization and microphase separation strongly influences the structural changes, morphology, properties, and hence applications, of such materials. In addition, other factors, such as melt morphology, crystallization temperature and the degree of crystallinity, will affect the resulting morphology post-crystallization [4], [5], [6], [7], [8], [9]. The spherulitic structure in semi-crystalline block copolymers can affect the ultimate mechanical properties. In addition, the boundaries between adjacent spherulites are often the weakest point in mechanical performance [14], [15].

It is interesting, and more complicated, to investigate the blends of a crystalline blocks, as both components are capable of crystallization and provide various conditions to study the morphology and crystallization behavior in polymer blends. It has been shown that crystalline–crystalline block copolymers have a significant effect on drug permeability and biodegradation behavior due to their unique properties, such as amphiphilicity, biocompatibility, self-assembly, permeability, and controllable biodegradability [16], [17]. Moreover, the interplay between crystallization and microphase separation in the crystallizable components of the block copolymer influences the structural changes, morphology and properties of these materials [1], [2], [3]. In blends comprising a block copolymer and a homopolymer, the macrophase separation can take place between the block copolymer and homopolymer, while the block copolymer alone can undergo microphase separation and form micro-domains.

Blending of polymers is a convenient route to fabricate functional materials, with property profiles superior to those of the individual components [18], [19], based on non-covalent physical interactions (such as ionic or electrostatic interactions), coordination bonding and hydrogen bonding [20], [21], [22]. The major benefit of this method is that the properties of the materials can be tailored by combining component polymers and changing the blend composition and experimental conditions. The principal advantage of hydrogen bonded mixtures is the ease of processing, compared with the synthesis of covalent analogues, by simply blending a homopolymer that strongly associates with another hydrophilic segment through hydrogen bonding [23], [24], [25], [26], [27]. Therefore, the study of crystallization in blends in connection with intermolecular interactions, such as hydrogen bonding and dipole–dipole interactions, is of great interest.

In this study, the blends of a crystalline PCL–PDMS–PCL triblock copolymer and a homopolymer, PH, where the homopolymer can potentially form hydrogen bonding interactions with PCL blocks, were characterized. Here, the selective association of the homopolymer increases the effective segregation strength, as a result of significantly increased effective interaction parameters in the blend. The self-assembly, hydrogen bonding interaction, crystallization phase behavior, and morphology, of these block copolymer/homopolymer blends are investigated by Fourier Transform Infrared (FTIR) spectrometry, Differential Scanning Calorimetry (DSC), Polarized Optical Microscopy (POM), Small Angle X-ray Scattering (SAXS), Wide Angle X-ray Scattering (WAXS) and Transmission Electron Microscopy (TEM).

Section snippets

Materials and preparation of blends

The poly(hydroxyether of bisphenol A) (PH) sample was obtained from Aldrich Chemical Company, with an average molecular weight Mw = 40,000. The block copolymer, poly(ε-caprolactone)-block-poly(dimethyl siloxane)-block-poly(ε-caprolactone) (PCL–PDMS–PCL) triblock copolymer, was purchased commercially from GoldSchmidt A.G., Germany, under the tradename Tegomer (H–Si 6440). The PCL–PDMS–PCL triblock copolymer has 43 wt% PDMS content and a molecular weight Mn of 6500 ± 600. The average Mn of the PDMS

Hydrogen bonding interactions

FTIR analysis was used to confirm the presence of specific hydrogen bonding interactions of the blends. PH forms self-associated hydrogen bonds due to the presence of its pendent hydroxyl groups in the backbone [28]. Fig. 1 shows the schematic representation of possible hydrogen bonding interaction in the PH/PCL–PDMS–PCL blends.

As shown in Fig. 2 the spectrum of pure PH exhibits two distinct bands in the hydroxyl region. A very broad band, centered at 3435 cm−1, represents the self-associated,

Conclusions

The microphase separation, mediated by hydrogen bonding, in PCL–PDMS–PCL triblock copolymer/PH homopolymer complexes was studied. The PCL–PDMS–PCL/PH blends are not phase-separated over the entire blend composition range; rather, there exists two microphases in the blends. The PDMS block forms a separated microphase, whereas the PH and the PCL blocks, which are miscible, form another microphase. The weakly associated PH/PCL pairs result in composition-dependent microphase separation and the

Acknowledgments

The authors would like to thank Dr. Nishar Hameed, Deakin University for TEM experimental support and the SAXS measurements were carried out on the SAXS beam-line at Australian Synchrotron and we thank Dr. Nigel Kirby for his assistance on the SAXS.

References (40)

  • J.K. Kim et al.

    Prog Polym Sci

    (2010)
  • M.M. Coleman et al.

    Polymer

    (1983)
  • E.J. Moskala et al.

    Polymer

    (1985)
  • M. Vanneste et al.

    Polymer

    (1994)
  • I.H. Lin et al.

    Polymer

    (2009)
  • W.C. Chen et al.

    Polymer

    (2010)
  • T. Gädt et al.

    Nat Mater

    (2009)
  • W.R. Wanga et al.

    Carbon

    (2010)
  • Y.L. Loo et al.

    Macromolecules

    (2001)
  • P. Rangarajan et al.

    Macromolecules

    (1993)
  • R.M. Ho et al.

    Macromol Rapid Commun

    (2005)
  • R.V. Castillo et al.

    Macromolecules

    (2008)
  • F.Y. Tzeng et al.

    Macromolecules

    (2009)
  • Y.L. Loo et al.

    Macromolecules

    (2002)
  • K.C. Douzinas et al.

    Macromolecules

    (1992)
  • P. Rangarajan et al.

    Macromolecules

    (1993)
  • R.E. Cohen et al.

    Macromolecules

    (1990)
  • I.W. Hamley

    The physics of block copolymers

    (1998)
  • E.H. Andrews et al.

    Proc R Soc London, A

    (1971)
  • A. Lustiger et al.

    J Polym Sci, Part B: Polym Phys

    (1998)
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