Star-shaped poly(2,6-dimethyl-1,4-phenylene ether)

The properties of star-shaped poly(2,6-dimethyl-1,4-phenylene ether) (PPE) as prepared by the redistribution of PPE and tyrosine-modified poly(propylene imine) dendrimers, are studied in solution and in 50/50 wt% blends with linear polystyrene. Star polymers with constant armlength but increasing number of arms show the same hydrodynamic volume as measured by Size Exclusion Chromatography (SEC), but decreasing hydrodynamic radius as measured by Dynamic Light Scattering (DLS). This is caused by the restricted mobility of the more densely packed chains at high numbers of arms, also leading to a decrease in intrinsic viscosities. These solution properties are also reflected in the miscibility behaviour in polymer blends. Star-shaped polymers with a high number of PPE arms (16,32 or 64 respectively) give inhomogeneous blends with linear polystyrene, in contrast to the miscible combination of linear polystyrene with linear PPE or starshaped polymers with a low number (4 or 8) of PPE arms

Reactive compatibilization of blends of poly(2,6-dimethyl-1,4-phenylene ether) and poly(butylene terephthalate)

This paper deals with the development of a compatibilized polymer blend based on poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and poly(butylene terephtalate) (PBT). Blending of PET with PPE, with PET as the continuous phase, could yield materials which are mutually incompatible, and the phase morphologies obtained during blending of these polymers are generally unstable. When PPE is functionalized selectively, in situ compatibilization during processing is feasible. Due to the formation of segmented copolymers, which act as compatibilizing agents, stabilization of the morphology obtained during blending is feasible. Different types of reactive PPE polymers were investigated, e.g. PPE with hydroxyalkyl, carboxylic acid, methyl ester, amino and t-BOC protected amino endgroups. These groups are positioned either in the middle of the chain or as the endgroup. All these reactive PPE polymers result in better compatibilization after mixing with PET versus unfunctionalized PPE. PPEs with carboxylic acid endgroups proved to be the most efficiently compatibilized with PET, for the PET type employed in this study. Promoters, which catalyze or take part in the coupling between PET and/or functionalized PPEs, such as triphenyl phosphite (TPP), sodium stearate, titanium (IV) isopropoxide and epoxy resins, were used in order to improve compatibilization of the PPE/PBT blends. The use of these promoters proved to give synergetic compatibilization in combination with functionalized PPEs. (C) 2001 Elsevier Science Ltd. All rights reserved

Supramolecular polymers from linear telechelic siloxanes with quadruple- hydrogen- bonded units

Telechelic oligo- and poly(dimethylsiloxanes) with two ureidopyrimidone (UPy) functional groups and 2 (I) and 100 (II) dimethylsiloxy repeating units, were prepd. via hydrosilylation reaction of poly(dimethylsiloxane). The compds. were characterized in soln. by 1H NMR and viscometry and in the solid state by 1H NMR and 13C NMR, FTIR, and rheol. measurements. The measurements show that the UPy groups of the polymers are assocd. via quadruple hydrogen bonds in a donor-donor-acceptor-acceptor (DDAA) array. In many aspects, the materials behave like entangled, high mol. wt. polymers. Compd. II has a Tg of -119 Deg and shows melting of microcryst. domains of assocd. UPy units at -25 Deg. Compd. I has a cryst. form (Tm = 112 Deg) and an amorphous modification with a Tg of 25 Deg. Solid-state NMR was used to study the mobility of these phases; wide-line sepn. [WISE] spectra show a higher mobility of the UPy groups in the amorphous phase than in the crystals of I. Amorphous I and II behave like entangled polymers. The mech. behavior is characterized by a rubbery plateau and a relatively high activation enthalpy for stress relaxation (DH = 127 kJ/mol for I; DH = 54 kJ/mol for II), which was derived from the temp. dependence of the zero-shear viscosity. Ests. for the d.p. of I and II, based on the mech. properties, give DP > 100 for I and approx. 20 for I. Like in condensation polymn., the DP of reversible supramol. polymers is presumably limited by the presence of small amts. of monofunctional impuritie