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  • ORIGINAL PAPER

    On Interaction Characteristics of Polyhedral Oligomeric Silsesquioxane Containing Polymer Nanohybrids

    Sang-Kyun Lim1 • Jae Yun Lee1 • Hyoung Jin Choi1 •

    In-Joo Chin1

    Received: 1 November 2014 / Revised: 20 April 2015 /Accepted: 24 May 2015 /

    Published online: 3 June 2015

    � Springer-Verlag Berlin Heidelberg 2015

    Abstracts A generalized functional group of polyhedral oligomeric silsesquiox- ane (POSS) suitable for various polymer systems, e.g., polyolefins, polyesters and

    polyamides, is presented using theoretical and experimental approaches to examine

    thermodynamic interaction between a polymer and POSS. Both Flory–Huggins

    interaction parameter and maximum difference of the solubility parameter are uti-

    lized to study theoretically specific interaction between polymers and POSS

    nanoparticles. Flory–Huggins interaction parameter was estimated by the melting

    point depression method determined by DSC, while maximum difference of the

    solubility parameter was predicted using the method of Hoftyzer and van Krevelen.

    The interaction characteristics of the polymer/POSS nanohybrids are further tested

    by measuring the activation energy with the Kissinger method, in which the acti-

    vation energy was calculated using the temperature at the maximum degradation

    rate observed TGA. Viscoelastic, dynamic mechanical, thermal and mechanical

    properties of the polymer/POSS nanohybrids were also examined to correlate the

    theoretical and experimental results, finding that the isobutyl group was the most

    suitable functional group of POSS for polyethylene, poly(ethylene terephthalate),

    and Nylon 6.

    Keywords Polyhedral oligomeric silsesquioxane � Thermodynamic interaction � Interaction parameter � Solubility parameter � Activation energy

    Electronic supplementary material The online version of this article (doi:10.1007/s00289-015-1405-5) contains supplementary material, which is available to authorized users.

    & Hyoung Jin Choi hjchoi@inha.ac.kr

    1 Department of Polymer Science and Engineering, Inha University, Incheon 402-751, Korea

    123

    Polym. Bull. (2015) 72:2331–2352

    DOI 10.1007/s00289-015-1405-5

    http://dx.doi.org/10.1007/s00289-015-1405-5 http://crossmark.crossref.org/dialog/?doi=10.1007/s00289-015-1405-5&domain=pdf http://crossmark.crossref.org/dialog/?doi=10.1007/s00289-015-1405-5&domain=pdf

  • Introduction

    For the last decade, the number of investigations on polymer-based nanohybrids,

    derived from the hybridization of inorganic materials and organic polymers at

    molecular scale, has been increased dramatically with the rapid growth of nanoscale

    technologies [1, 2]. Nanohybrids, combining the important properties of inorganic

    materials and organic polymers in general, can show improved properties, such as

    high gas barrier characteristics, solvent resistance, and reduced flammability [3–6].

    Among the various nanoreinforcements, polyhedral oligomeric silsesquioxane

    (POSS) is particularly interesting. The properties of POSS are unique, since one or

    more of the organic groups can be functionalized for polymerization, while the

    remaining unreactive groups can solubilize the inorganic core and at the same time

    control the interfacial interactions occurring between POSS and the polymer matrix

    [7, 8]. Generally, POSS can be incorporated into all types of polymers either by

    chemical tethering to the polymer chains (e.g., grafting and copolymerization

    reactions) [9–16] or physical blending (e.g., solution blending and melt mixing)

    [17–27], which would result in the enhancement of the polymer properties including

    the increase of thermal stability and reduction in flammability and dielectric

    constant [28–32]. Because of their advantageous performance relative to their

    nonhybrid counterparts, POSS-containing nanohybrids can be made with the many

    of the representative polymers such as polyolefins [33–35], polyesters [36–38],

    polyamides [39, 40], styrenics [41–43], acrylates [44–47], polyurethanes [48–51],

    thermosetting polymers [52] and others [53–56].

    While considerable effort has been focused on the thermal properties [2, 26, 29,

    57–61], morphology [13, 23, 62], mechanical properties [63–66] and self-assembly

    of new POSS-containing nanohybrids [67, 68], there were a few studies that dealt

    with the interrelationship between the polymer and POSS by analyzing the

    miscibility and physical properties. However, there have been no studies which

    directly examined the thermodynamic interaction between the polymer and POSS.

    Huang et al. [2] investigated the miscibility and specific interaction behavior of

    the poly(methyl methacrylate) (PMMA)–POSS systems by differential scanning

    calorimetry (DSC) and fourier transform infrared spectroscopy (FT-IR) where

    POSS was substituted with the isobutyltrisilanol group and PMMA with phenolic

    resin. They found that the phenolic/PMMA–POSS blends with a positive q value

    had single glass transition temperatures (Tgs), which were higher than those of the

    phenolic/PMMA blends with a negative q value. The positive deviation of the

    phenolic/PMMA–POSS blends revealed that a strong interassociation interaction

    existed between the POSS siloxane and phenolic hydroxyl groups. FT-IR analysis

    indicated that the PMMA chain of the low molecular weight PMMA (LPMMA,

    Mn = 9800 g/mol)–POSS could not form entanglements with the lower hydrogen

    bonding interaction between the LPMMA and phenolic resin. Furthermore, they

    found a ‘‘screening effect’’ in these phenolic/LPMMA–POSS blends caused by the

    POSS chain end tethered, which has the greater interassociation equilibrium

    constant between hydroxyl and POSS than the interassociations equilibrium

    constant between hydroxyl and carbonyl. On the contrary, the molecular weight

    2332 Polym. Bull. (2015) 72:2331–2352

    123

  • of the high molecular weight PMMA (HPMMA, Mn = 28,900 g/mol)–POSS is

    above its entanglement molecular weight, that is, the hydrogen bonding between

    POSS and the hydroxyl groups becomes less than that between PMMA and the

    hydroxyl groups.

    The structure–property relationships in organic–inorganic nanomaterials based

    on methacryl-POSS and dimethacrylate networks were reported by Bizet et al. [14]

    POSS molecules, acting as the pendant unit on the network backbone, showed

    strong tendency toward aggregation and crystallization, depending on the nature of

    the organic ligands. The POSS–POSS interaction was found to be the main

    parameter governing the network morphology. However, the dynamic mechanical

    properties remained nearly at the same level as those of the neat matrix.

    Multifunctional POSS showed higher miscibility with the dimethacrylate monomer

    and they were dispersed very well in the cured network. As expected, the rubbery

    modulus increased with increasing amount of POSS due to the high functionality of

    these additional cross-links, whereas Tg remained constant. Finally, methacrylate-

    functionalized POSS can be expected to improve the properties of dimethacrylate-

    based networks in the field of surface properties, optical properties and shrinkage,

    rather than in the field of mechanical properties.

    The miscibility behavior and interaction mechanism of PMMA, poly(vinyl

    pyrrolidone) (PVP), and PMMA-co-PVP blends with octa(phenol)octa-silsesquiox-

    ane (OP-POSS) were investigated using the DSC and FT-IR spectroscopy

    techniques [69]. For the OP-POSS/PMMA blends, the value of the association

    constant (KA = 29) was smaller than that in the poly(vinyl phenol) (PVPh)/PMMA

    (KA = 37.4) and in the ethyl phenol (EPh)/PMMA (KA = 101) blend system,

    implying that the spacing between the phenol groups attached to the POSS

    nanoparticles was smaller than those of the other two blend systems, resulting in a

    decrease in the ratio of the interassociation and self-association equilibrium

    constants. In addition, the intermolecular hydrogen bonding became stronger than

    the intramolecular hydrogen bonding after copolymerization with vinyl pyrrolidone

    (VP), because the OH groups preferred to interact with the VP segments.

    Liu and coworkers [70] studied the hydrogen bonding interaction in three

    different types of incompletely condensed silsesquioxanes (POSS-mono-ol, POSS-

    diol and POSS-triol) [70], finding that POSS-diol and POSS-mono-ol could not

    form a dimer in solution and there existed a dynamic equilibrium between the single

    molecule and hydrogen-bonded dimer for POSS-triol.

    Thermal and rheological behavior of polystyrene (PS)-based random copolymers

    were studied, in which POSS was incorporated with three kinds of vertex groups,

    viz. isobutyl (iBu), cyclopentyl (Cp) and cyclohexyl (Cy) [71]. The weak iBuPOSS-

    PS segment interaction resulted in the Tg that monotonically decreased with

    increasing iBuPOSS content. Conversely, the strong CpPOSS/CyPOSS-PS segment

    interaction resulted in the increase of the Tg, through with complex dependence in

    the case of CyPOSS. Wu et al. [71] asserted that the dependence of the Tg of the

    copolymers o

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