Network properties: 3. A pulsed n.m.r. study of molecular motions in some AB-crosslinked polymers

This paper presents the results of a pulsed n.m.r. study of molecular motions in poly (methyl methacrylate) (PMMA) and poly (methyl acrylate) (PMA) chains in a series of multicomponent network polymers consisting of poly (vinyl trichloroacetate) (PVTCA) crosslinked with PMMA and with PMA, with emphasis on segmental motions. Results of ancilliary broad line n.m.r. and dilatometric studies are included; the latter demonstrate that in PMA containing polymers microphase separation of the components is complete while in PMMA containing polymers a mixed microphase of PVTCA and PMMA and a pure PMMA microphase are formed. α-Methyl group rotations in PMMA chains and segmental motions in both PMMA and PMA chains are modified with respect to those in the corresponding homopolymers. Modifications to the segmental motions in the crosslinking chains are attributed to the fact that their chain ends are attached to PVTCA chains. It is considered that the comparative rigidity of PVTCA chains (T_g ～ 60°C) reduces segmental motions in at least portions of the PMA chains (T_g ～ 5°C) while the comparative mobility of PVTCA enhances segmental motions in PMMA (T_g ～ 100°C). Thus the molecular mobility of chains of one polymer is to some extent transmitted to chains of another polymer to which it is attached.     

Frozen bound water melting induced cooperative hydration of poly(vinyl methyl ether) in aqueous solution

Summary Poly(vinyl methyl ether) aqueous solution (30 wt.-%) at low temperature has been investigated by DSC and FTIR spectroscopy. Below −20°C, there are two types of ice formed by free water and frozen bound water respectively. When the ice formed by frozen bound water melts, the PVME begins to form hydrogen with water. A cooperative hydration phenomenon is observed in this system between −20 ∼−6°C during heating. FTIR data also show that hydrogen bonds between water molecules and polymer groups are broken completely before the cooperative hydration happens. This indicates that the unfrozen bound might not exist in 30 wt.-% PVME aqueous solution at low temperature. Received: 27 December 2001/Revised version: 4 March 2002/ Accepted: 5 March 2002     

Study of the dielectric relaxation of poly(phenylpropyl acrylate) and poly(phenylpropyl methacrylate): effect of slight differences in chemical structure

A comparative study of the dielectric relaxational behaviour of two structurally close polymers, containing aromatic side groups, was carried out in order to analyse how slight differences in the chemical structure affect the molecular responses to perturbation field. Specifically, poly(phenylpropyl acrylate) (P3Ph1PA) and poly(phenylpropyl methacrylate) (P3Ph1PM) were studied using differential scanning calorimetry and dielectric relaxation spectroscopy in the frequency range 10^?2–10⁶ Hz and temperature window of ?80 to 120 °C. Both techniques show one glass–rubber transition for P3Ph1PA and two for P3Ph1PM, which evidence the great effect of the methyl groups on the segmental motions of the polymer. Phenomenological analysis of the data was carried out in order to establish the strength, width and fragility parameters of the glass–rubber transitions. In the case of P3Ph1PA, the strength is found to be larger than for P3Ph1PM, pointing out that the methyl group disturbs the mobility. Conductive processes dominate the dielectric spectra at high temperatures and low frequencies. © 2015 Society of Chemical Industry     

Lower critical solution temperature (LCST) polymer solution for clear/cloud glazing applications

An aqueous-based clear/cloud solution was developed using poly(vinyl methyl ether) and an antifreeze mixture of ethylene and propylene glycols. The solution has a controllable cloud point from 15 to 90°C, freeze protection to ?46°C, and a density that prevents the precipitated polymer from settling and is fairly stable to UV degradation. A significantly smaller heat gain is achieved through the clear/cloud glazing when compared to a normal double-pane window. © 1994 John Wiley & Sons, Inc.     

A molecular model for tensile shear banding and the brittle-ductile transition in poly(vinyl chloride)

Roetling's adaptation of the Ree-Eyring model to represent tensile shear banding of polymers in terms of two relaxation processes and Mansfield's model to describe alpha and beta relaxation processes in terms of polymer segment mobility are combined with the particulate structure of poly(vinyl chloride) (PVC) to give a more detailed connection between the macroscopic yielding process and the microscopic mobility of polymer segments. Mansfield's model for relaxation processes is cast in terms of intra- and inter-molecular interactions that serve to hinder orientational motions of polymer segments. The viscoelastic beta process in PVC is interpreted in terms of this model to be a hindered rotation of a segment about its main chain axis. About half of the activation energy of the beta process can be estimated from the barriers hindering rotation in simple alkyl halides. According to tensile yield studies it is the beta process that governs the tensile yield behavior of PVC at high loading rates or low temperatures, i.e. the brittle to ductile transition. Viscoelastic measurements were made on milled compression molded powder blends of PVC of differing K-values (55–69), over a frequency range of 0.1 to 500 Rad/sec. and a temperature range of ?140°C to 20°C. The dependence of the complex compliance on frequency and temperature was represented in terms of a five parameter model proposed by Havriliak and Negami to represent the dielectric dispersions of polymers. The five parameters and their dependence on temperature were estimated using the multi-response statistical techniques developed by Havriliak and Watts. The parameters are interpreted in terms of Mansfield segmental jumping model.     

Synthesis and gas permeability of membranes of Poly(vinyl ether)s bearing oxyethylene segments

Cationic copolymerizations of vinyl ether monomers [2-methoxyethyl vinyl ether: MOVE, 2-(2-methoxyethoxy)ethyl vinyl ether: MEEVE, 2-adamantyl vinyl ether: AdVE, 2-(2-vinyloxyethoxy)ethyl methacrylate: VEEM] were performed to obtain three types of vinyl ether copolymers [poly(MOVE-AdVE)s, poly(MEEVE-AdVE)s, and poly(MEEVE-VEEM)s] with different composition rates. Poly(MOVE-AdVE) and poly(MEEVE-AdVE) obtained at monomer feed ratio of 1:1 exhibited the glass transition temperatures (T_g) of 55 and 28 °C, respectively, but the T_g's of copolymers were near or lower than room temperature when the feed ratio of AdVE decreased. Poly(MOVE-AdVE)s and poly(MEEVE-AdVE) with T_g's above room temperature afforded free-standing membranes by casting them from toluene solutions. They exhibited relatively high CO₂ permeability and high CO₂/N₂ separation factors (P(CO₂) = 22–36 barrers, P(CO₂)/P(N₂) = 19–40). The T_g's of poly(MEEVE-VEEM)s were very low and around ?70 °C irrespective of the difference of monomer feed ratio. Methacrylate groups in poly(MEEVE-VEEM)s partially reacted under heating to give crosslinked polymer membranes. The crosslinked membranes showed high CO₂/N₂ selectivity, especially the poly(MEEVE-VEEM) membrane possessing the highest ratio of MEEVE exhibited high CO₂ permeability and high selectivity (P(CO₂) = 120 barrers, P(CO₂)/P(N₂) = 55).     

Binary and ternary blends of poly(vinyl chloride), hytrel,and a polyurethane

Binary blends of poly(vinyl chloride) and a poly(ether urethane) containing 20 and 40 weight percent, respectively, of poly(vinyl chloride) have been prepared by solution blending from tetrahydrofuran and their degree of mixing investigated using dynamic mechanical analysis. In the polyurethane, transitions were found at ?19°C and ?119°C. The former was attributed to the glass transition and the latter to a Schatzki type of motion of the polyether sequences. This latter transition occurred at a temperature which is higher than the literature value for the low temperature transition in poly(tetrahydrofuran), which is equivalent to the polyether sequence in the polyurethane. This discrepancy is attributed to the influence of neighboring hard segments present because of incomplete segmental phase separation of the polyurethane. For the blends only one very broad transition was observed, indicating that there was substantial mixing of these two polymers. Three ternary blends were prepared, also by solution blending, containing poly(vinyl chloride), Hytrel, and the polyurethane in the ratios 1:1:1, 1:2:1, and 2:1:1, respectively. In the first two blends there was clear evidence of phase separation. It was only in the 2:1:1 blend that an apparently significantly compatible material resulted.     

Thermal modification of poly(vinyl chloride) and formation of dehydrochlorinated poly(vinyl chloride)–poly(methyl methacrylate) polymer blend in the process of foaming: Identification and application

Impact resistant plastic foam of dehydrochlorinated poly(vinyl chloride) (DHPVC)—poly(methyl methacrylate) (PMMA) was prepared for cryogenic insulation in space vehicle by the method of compression molding and chemical blowing. Impact resistance was achieved by the formation of the polymer blend, dehydrochlorinated poly(vinyl chloride)-poly(methyl methacrylate), during the process of foaming the mold at the temperature of 200°C. The polymer blend was separated from the plastic foam and the compatibility was investigated by ultraviolet, infrared spectral studies and differential scanning calorimetry (DSC). The compatibility of dehydrochlorinated poly(vinyl chloride) and poly(methyl methacrylate) was highlighted on the basis of allylic activation introduced in the thermally modified poly(vinyl chloride). The thermodynamic views were also correlated. The versatility of the present method for impact-resistant foam was pointed out.     

Preparation, characterization and wettability of porous superhydrophobic poly (vinyl chloride) surface

A porous superhydrophobic poly (vinyl chloride) surface was obtained by a simple approach. The water contact angle and the sliding angle of the superhydrophobic poly(vinyl chloride) surface were 154 ± 2.3o and 7o, respectively. The porous superhydrophobic PVC surface remained superhydrophobic property in the pH range from 1 to 13. When the superhydrophobic PVC surface was immersed in water with the temperatures ranging from 5 °C to 50 °C for 1 h to 30 days, the water contact angle remained higher than 150°. After outdoor exposure for 30 days, the contact angle still remained 150o.     

Novel dielectrics from IPNs derived from castor oil based polyurethanes

Three series of interpenetrating polymer networks (IPNs) based on a polyurethane (castor oil + toluene diisocyanate) with polystyrene, poly(methyl methacrylate), and poly(n-butyl methacrylate) were synthesized and characterized. Dielectric relaxation studies of these IPNs were carried out from ?150 to 100°C in the 100 Hz to 100 kHz range. The effects of structural variables such as composition, type of vinyl monomer, as well as the effect of interaction of the phases on the dielectric properties were studied. A certain degree of phase mixing was observed to exist in all series as detected by the variation of the glass-transition temperatures of the IPNs. Maxwell–Wagner–Sillars polarization at the interface of the two phases was observed. © 1994 John Wiley & Sons, Inc.     

Physicochemical characterization of hydrogels based on polyvinyl alcohol–vinyl acetate blends

Hydrogels made of polyvinyl alcohol–vinyl acetate and its blends with water soluble polymer were studied in terms of swelling behavior, microstructure, and dynamic mechanical properties. Hydrogels prepared by blending polyvinyl alcohol–vinyl acetate with either polyacrylic acid or poly(4‐vinyl pyridine) exhibited a strong pH dependency. When poly(vinyl pyrrolidone) was used for blending, an unusual pH dependency was observed. An increase in the equilibrium water content in all systems resulted in an increase in the freezable water as determined by DSC. Critical point drying led to a striated surface on polyacrylic acid–polyvinyl alcohol–vinyl acetate hydrogels, whereas a porous structure was observed on the freeze‐dried poly(vinyl pyrrolidone)–polyvinyl alcohol–vinyl acetate gels. Hydrogels with elevated storage modulus were obtained when either polyvinyl alcohol–vinyl acetate alone or polyacrylic acid–polyvinyl alcohol–vinyl acetate blends were thermally treated at high temperatures (i.e., 150°C). Low storage modulus was observed for both poly(vinyl pyrrolidone) and poly(4‐vinyl pyridine)‐containing hydrogels. Temperature dependency of storage modulus from 20 to 60°C was observed only for poly(4‐vinyl pyridine)–polyvinyl alcohol–vinyl acetate hydrogels. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3578–3590, 2001     

Influence of diamine structure on the low temperature dielectric relaxation of some poly(ether imide)s

Broadband dielectric relaxation spectra are reported on a range of poly(ether imide) polymers in which the chemical structure of the diamine used to create the polymer is systematically varied with the anhydride structure based on 2,2‐bis‐[4‐(3′,4′‐dicarboxyphenoxy)phenyl]hexafluoroisopropylidine dianhydride. In all the polymers examined, a dipole relaxation was observed below room temperature. The magnitude and activation energy associated with the relaxation process varied with the chemical structure reflecting the effects of steric hindrance on the conformational change associated with the N? C and C? O? C linkages. Values of the activation energies varied between 29 and 34 kJ/mol^?1, and are consistent with the observed relaxation being associated with constrained local oscillatory motions of small elements of the polymer backbone. The glass transition temperatures of these polymers are in the range 195–243°C and are associated with the large scale motion of the polymer backbone. Changes in the backbone structure influence the extent of inter chain–chain interaction and are reflected in the amplitude of the relaxation process and the high frequency limiting dielectric permittivity ε_∞ values which are important when these polymers are used in thin film electronic applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41684.     

Porous SiC ceramics prepared via freeze-casting and solid state sintering

Porous SiC ceramics were prepared by freeze-casting process. In order to enhance the mechanical properties of the porous SiC, poly(vinyl alcohol) (PVA) was added as binder and pore morphology controller in this work. The results indicated that high porosity (>60%) SiC ceramics was obtained although the sintering temperature was over 2000 °C. The pore structure could be divided into two kinds: macropores generated by sublimation of large ice crystals, and micropores in the ceramic matrix caused by sublimating of small ice crystals, stacking of SiC particles, and burning out of PVA. With the increase of the sintering temperature, the specimens exhibited higher density, thus resulted in higher strength. Porous SiC ceramics sintered at 2100 °C showed a good flexural strength of 11.25 MPa with an open porosity as high as 66.46%.     

TSD-Untersuchungen zum Einfluß von Wasser auf die molekularen Beweglichkeiten in Polyamid-6

Molecular motions in nylon 6 are studied by thermally stimulated discharge (TSD) techniques. The effect of absorbed water on the relaxation behaviour of nylon 6 is discussed. The γ relaxation process at ?145°C is attributed to local segmental motions in the amorphous phase. The intensity of the γ relaxation is reduced and broadened by absorbed water. The molecular origin of the β relaxation process in the temperature range between ?80 and ?60°C is associated with localized reorientational motions of chain segments involving nonchain-bonded or weakly bonded amide groups. It is quite likely that also rotational rate processes of water molecules bonded to CO-groups contribute to the β process. The intensity increases are due to added water, since associated water molecules are involved with those molecular motions. The α relaxation process at 70°C is associated with large-scale segmental motions at the glass transition. The chain mobility is increased by added water and gives rise to an α peak near 50°C. The α′ relaxation process in the temperature range between 100 and 110°C may either be associated with reorientational motion of stretched chain segments or with the beginning of a crystalline transformation of the γ phase into the monoclinic α form. The temperatures of TSD-peaks correspond to alternating current loss data at a frequency of 5·10^?2 Hz.     

Effects of the composition ratio,eosin addition,and γ irradiation on the dielectric properties of poly(vinyl alcohol)/glycogen blends

The dielectric relaxation spectra of various poly(vinyl alcohol) (PVA)/glycogen blends and irradiated blend samples with 70 wt % PVA content that were undoped and doped with eosin were measured in extended temperature (30–160°C) and frequency (1 kHz to 1 MHz) ranges. Dielectric relaxation spectroscopy separates different molecular groups of a repeating unit of a polymer with respect to the rate of its orientation dynamics. In the high‐temperature range (>100°C), the σ relaxation, which is associated with the hopping motion of ions in the disordered structure of the biopolymeric material, can be measured. The electric dipole moment and the activation energy of the glass‐transition temperature relaxation process were calculated. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal analysis of complex relaxation processes in poly(desaminotyrosyl-tyrosine arylates)

The goal of this study is to better understand the thermal characteristics and molecular behavior of two poly(desaminotyrosyl-tyrosine arylates). These two polymers were chosen from a combinatorial library of polymers developed by changing the type and size of the two substitutable chain locations. The objective of this work was to describe the origin of the complex relaxation processes that have been observed by thermal analysis methods. DSC, TMA and TSC studies were conducted on poly(desaminotyrosyl-tyrosine dodecyl dodecanedioate), poly(DT 12,10), and poly(desaminotyrosyl-tyrosine ethyl succinate), poly(DT 2,2), in film and fiber form. DSC experiments on poly(DT 2,2) show only a glass transition at about 80 °C which is characteristic of an amorphous polymer. The DSC of poly(DT 12,10) shows multiple thermal events indicative of a more complex internal structure. The thermally stimulated current (TSC) analysis results for poly(DT 2,2) indicate a region of molecular mobility at about 80 °C consistent with the T_g from DSC. For poly(DT 12,10) there is a dipole relaxation process observed at about 40 °C. An additional region of mobility at 60 °C for poly(DT 12,10) fibers is observed. The comparison of conventional TSC with a modified TSC procedure suggests that this process represents a spontaneous reorganization of the internal structure of the solid. The comparison of DSC and TSC results suggests that poly(DT 12,10) has two distinct modes of organization with a transition between these modes at about 60 °C. Previously published results indicate that solid state structure formation is related to two different modes of hydrogen bonding in the internal structure of the solid.     

Influence of change in ether structure on the low temperature dielectric relaxation of some poly(ether imide)

Broad band dielectric relaxation spectra are reported on a range of polymers created by varying the ether segment in a series of poly(ether imide)s. Changes in the structure allow the effects of steric constraints on the local conformational dynamics of the polymer chain to be explored. These changes have a significant effect on the glass transition temperatures of these polymers which range from 245 to over 420°C. In contrast, the low temperature dielectric relaxation behavior of these polymers is very similar and is attributed to cooperative local oscillatory—librational motions. Changes in the stereochemistry effect the amplitude, activation energy for the relaxation process, the packing chain density, and values of the high frequency limiting permittivity, ε_∞′. This latter parameter is sensitive to the extent of dipole induced dipole and π‐π electron interactions and is influenced by the packing density. The magnitude of ε_∞′ is a very important parameter in determining the suitability of poly(imide)s for electrical applications. The magnitude of ε_∞′ increases with the density; however, deviations from this general trend are observed when large nonpolar groups inhibit the interaction of neighboring chains. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41191.     

Thermal Decomposition of Polymer Mixtures Containing Poly(vinyl chloride)

Thermal decomposition of a series of 1 : 1 mixtures of typical polymer waste materials [polyethylene (PE), poly(propylene) (PP), polystyrene (PS), polyacrylonitrile (PAN), polyisoprene, poly(methyl methacrylate) (PMMA), polyamide‐6 (PA‐6), polyamide‐12 (PA‐12), polyamide‐6,6 (PA‐6,6), and poly(1,4‐phenylene terephthalamide) (Kevlar)] with poly(vinyl chloride) (PVC) was examined using thermal analysis and analytical pyrolysis techniques. It was found that the presence of polyamides and PAN promotes the dehydrochlorination of PVC, but PVC has no effect on the main decomposition temperature of polyamides. The hydrogen chloride evolution from PVC is not altered when other vinyl polymers or polyolefins are present. The thermal degradation of PAN is retarded significantly, whereas that of the other vinyl polymers is shifted to a slightly higher temperature in the presence of PVC. Among the pyrolysis products of PAN‐PVC mixture methyl chloride was found in comparable amount to the other gaseous products at 500°C pyrolysis temperature.     

Polymerization of vinyl monomers initiated by zwitterionic polymer in aqueous solution

The polymerization of vinyl monomers, mainly styrene and methyl methacrylate, initiated by zwitterionic poly[3-dimethyl(methacryloyloxy-ethyl)ammonium propane sulfonate], [poly(DMAPS)], in aqueous solution was studied under vacuum at 85°C. An initiation mechanism involving hydrogen atom transfer is proposed. The effects of the efficiency of grafting. pH, water content and betaine polymer content on the polymerization were investigated. The conversion of vinyl monomers in poly(DMAPS) is lower than that in poly [3-dimethyl(acryloyloxyethyl)ammonium propane sulfonate], which may be due to steric hindrance of the methyl group on the α-carbon of the former.     

Water‐soluble esters of biosynthetic poly(γ‐glutamic acid)

Water‐soluble poly(γ‐glutamic acid) (PGGA) esters were prepared by transesterification of poly(α‐methyl‐γ‐glutamate) with mono‐, di‐, and triethylene glycols with one hydroxyl end group blocked as methyl ether. Only the monoglycol appeared to be crystalline with melting at 160°C, and glass‐transition temperatures were found to increase from 10 to 60°C with the length of the oxyethylene side chain. All these poly(γ‐glutamate)s are stable up to temperatures near 250°C. Moisture sorption, surface wettability, and hydrodegradability were evaluated as a function of time. It was found that in overall sensitivity to water increased with the glycol chain length but the behavior at short contact times was critically affected by conformational factors. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2027–2036, 2001