Thermal properties, miscibility and specific interactions in comparison of linear and star poly(methyl methacrylate) blend with phenolic
Introduction
Miscible polymer blends and the strong interaction provide attractive interest in polymer science due to their strong economic incentives arising from their potential application. It has been demonstrated that poly(methyl methacrylate) (PMMA) is able to interact with polymers of a wide variety of structures, such as poly(vinyl phenol) [1], phenoxy [2], poly(ethylene oxide) [3], and poly(vinylidene fluoride) [4]. In blends of two polymer chains, the bulk thermodynamic interaction can vary with blend composition, microstructure [5], tacticity [6], and isotopic labeling [7], [8]. Branched polymer architectures, such as hyperbranched polymers and star polymers have received great attention in recent year [9], [10], because they posses a special structure, with greater number of terminal groups and physical properties different from their linear analogs, such as high solubility and low melt viscosity. Although the effects of branching in polymers have long been recognized as an important area of study [11], [12], the ability to control branching architecture has only recently been achieved. Over the past two decades, dramatic advances in polymer syntheses have provided a means to control polymer architecture on the molecular length scale, thus allowing the creation of a variety of novel macromolecules and the opportunity to experimentally investigate the effects of polymer architecture. The strength and extent of polymer interaction is typically expressed in terms of effective segment–segment-interaction parameter, χeff, which varies with all these molecular particulars. The fluctuation theory of Fredrickson et al. [13] suggests that if one component in a polymer blend is a long-chain branched architecture, the bulk interaction will affect the case of an analogous blend with linear components. This influence in the bulk interaction should manifest itself in an architectural contribution to the value of the χeff parameter, although the architectural effect is intrinsically a non-local effect.
In our previous works [14], [15], [16], we studied the miscibility and the specific polymer–polymer interactions based on linear analogs. Recently, a new synthetic method of well-defined branched polymers has been developed [17]. In this paper, star and linear PMMA were prepared by atom transfer radical polymerization (ATRP) [18] and then blended with phenolic resin. We intend to compare the miscibility and specific interactions between star and linear PMMA. Characterizations were carried out using gel permeation chromatography (GPC), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), and high-resolution solid-state 13C nuclear magnetic resonance (NMR) spectroscopy.
Section snippets
Materials and syntheses
The 4-arm initiator was synthesized as described in our previous paper [18]. To prepare the 4-arm star PMMA, the ATRP with CuBr/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) was carried out. The molecular weight was determined by GPC. In accordance with the controlled polymerization characteristics of ATRP, the polydispersity of this star PMMA is low (PDI=1.21). The linear analog of the PMMA polymer was also prepared by ATRP with methyl dl-2-bromopropionate monofunctional
DSC analyses
In general, the DSC analysis is one of the most convenient methods to determine the miscibility in polymer blends. The glass transition temperatures of these pure polymers synthesized in this study, PMMA and phenolic, are 104 and 50 °C, respectively. Fig. 1 shows the conventional second run DSC thermograms of these homopolymers and linear or star PMMA/phenolic blends with various weight ratios (10/90, 30/70, 50/50, 70/30, 90/10). Essential all these blends have a single Tg. A single Tg strongly
Conclusions
Linear and star PMMA/phenolic blends were investigated by using FT-IR, DSC, and high-resolution solid-state 13C NMR. All these blends are totally miscible in the amorphous phase over entire compositions. The Tg of the star PMMA/phenolic blend is higher than that of the linear ones, both with negative q value. This result indicates that the self-association interaction is stronger than the inter-association interaction between blends of linear or star PMMA with phenolic. Measurements of T1ρH
Acknowledgements
This research was financially supported by the National Science Council, Taiwan, Republic of China, under Contract Nos. NSC-92-2216-E-009-018.
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