摘要:

Two series of polyether polyurethane anionomers based on 4, 4-diphenylmethane diisocyanate (MDI) and polytetra-methylene oxide (PTMO) were synthesized and their properties investigated. Ionization proceeded via a bimolecular nucleophilic displacement reaction with sodium hydride, followed by a ring-opening reaction with γ-propane sultone. The lower hard segment content (20 wt% MDI) control material exhibited an initial one-phase morphology that underwent phase separation upon ionization, with subsequent development of hard segment ordering. These changes in morphology were accompanied by dramatic improvements in mechanical properties. The 38 wt% MDI control material possessed a two-phase morphology and well-developed hard segment ordering. Ionization disrupted the hard segment ordering and at low levels decreased the degree of phase separation. Further ionization led to reattainment of the original degree of phase separation and a marked improvement in mechanical strength. The differences in properties of the two series of materials are discussed and compared with properties of other polyurethane ionomers reported in the literature.

ISSN:0022-2348    

DOI:10.1080/00222348408219454

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Four series of polyurethane zwitterionomers based on different soft segment polyols [polyethylene oxide (PEO), polypropylene oxide (PPO), polytetramethylene oxide (PTMO), and polybutadiene (PBD)] were synthesized, and their properties were investigated using differential scanning calorimetry, dynamic mechanical spectroscopy, infrared dichroism, and stress-strain testing. Two different molar ratios of hard segment [4,4′-diphenylmethane diisocyanate (MDI)] to chain extender [N-methyl diethanol-amine (MDEA)] to soft segment polyol, each with three different levels of ionization, were prepared based on the four different polyols. Zwitterionization was accomplished by quaternizing the tertiary amine of MDEA with γ-propane sultone. For the PBD materials, the un-ionized samples exhibited a high degree of phase separation, and ionization served mainly to improve domain cohesion. Increasing ionic content improved material strength while sacrificing extensibility. For the polyether materials the un-ionized samples were not highly phase separated, and ionization improved both the degree of phase separation and hard segment domain cohesion. These morphological changes led to greatly improved mechanical properties. The tensile properties of the ionized PEO and PTMO materials were superior to the tensile properties of the PPO and PBD materials. This was attributed to the ability of the PEO and PTMO segments to crystallize under strain. The effects of segment length (by comparison with a previous study) and hard segment content on mechanical properties are also discussed.

ISSN:0022-2348    

DOI:10.1080/00222348408219455

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

This paper describes how the compensation law can be explained by a linear relation between the activation entropy and enthalpy of a given process in a polymer. These two variables are related by the thermal expansion coefficient and a constant approximately equal to the Rao acoustical parameter. A relation between the activation free energy and some thermodynamic parameters is presented. The activated volumes for the α and β relaxations of polyethylene are shown to vary with temperature and cry-stallinity. The activated volume has also been calculated for some other polymers and is of the order of 1 to 6 molar volumes at 295 K.

ISSN:0022-2348    

DOI:10.1080/00222348408219456

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Temperature-induced solvatochromism in the visible absorption band of 4-dimethylamino-4′-nitroazobenzene (diMANA) dissolved in polystyrene (PS) and poly(vinyl acetate) (PVAc), and in toluene and ethyl acetate used as model liquid solvents was investigated. In all solutions under study the absorption band maximum shifts to blue, and the magnitude of the transition moment slightly diminishes as temperature rises. In polymer solid solution the absorption band maximum is red shifted relative to the position of the band maximum in model liquid solutions. Based on solvatochromism theory, a qualitative interpretation of the changes in the spectrum induced by variation of the temperature, polarity, and rigidity of the medium is given. It is shown that orientational polarization interactions in PVAc play a significant role.

ISSN:0022-2348    

DOI:10.1080/00222348408219457

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Carboxyl-terminated polybutadienes were ionically cross-linked by divalent metal oxide or monovalent metal hydroxide. The thermal, dynamic mechanical, and dielectrical behaviors of these ionomers were examined according to the ratio and the nature of the neutralizing agents. The variations of transition parameters and the classification of the different relaxations could be related to the degree of microphase separation between the elastomeric phase, the multiplet structure, and their associations in clusters.

ISSN:0022-2348    

DOI:10.1080/00222348408219458

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The main purpose of this work is to justify the use of the positions of the maxima of ϵ” versus T curves when calculating the apparent activation energy in secondary dielectric relaxations or in the relaxation associated with the glass transition. To exemplify this, phenomenological models as well as experimental results for methacrylic polymers are discussed.

ISSN:0022-2348    

DOI:10.1080/00222348408219459

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Far-infrared (FIR) spectra of linear and cross-linked polymers have been obtained and analyzed. The relationship of the parameters of these spectra to the characteristics of macromolecules is established. The role of molecular interactions in the formation of potential barriers to libration of polar groups and the low-frequency skeletal motion of the backbone chain of macromolecules is shown. It was found that the chain part participating in low-frequency skeletal motion for polystyrene and poly(methyl methacrylate) is commensurable with the correlation part of the chain for these polymers (the Kuhn segment).

ISSN:0022-2348    

DOI:10.1080/00222348408219460

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor