Radiation initiated grafting on fluoro polymers I. Grafting of N-vinylpyrrolidone on poly(vinyl fluoride) by accelerated electrons

The radiation initiated grafting of N-vinylpyrrolidone on poly(vinyl fluoride) films by means of accelerated electrons using the preirradiation technique in vacuo has been investigated. The time conversion curves showed a steady increase of the initial grafting rate with temperature whereas the saturation grafting yield passes a maximum around 333 K. The Arrhenius plot reveals two straight lines with different slope intersecting around 328 K. Two different overall activation energies are found: 248 kJ mol^?1 for grafting below this temperature and 65 kJ mol^?1 for grafting above this temperature. This behaviour presumably is correlated to a glass transition of the trunk polymer arising from amorphous material under restraint by crystallites. The grafting yield is independent on the dose rate but strongly dependent on the dose. The penetration of the grafting front into the trunk polymer film was quantitatively followed by “Differential Interference Contrast”-microscopy: For any grafting yield the penetration depth of the grafting front increases with decreasing dose. The higher the dose, the higher the grafting yield to achieve grafting through. For a given dose increasing temperature shortens the time to obtain grafting through. On the basis of these experimental results a model was derived to explain the graft kinetics.     

聚偏氟乙烯-b-聚乙烯基吡咯烷酮嵌段共聚物的制备和结构

以C₆F₁₃I为链转移剂,通过碘转移乳液聚合制得碘封端的聚偏氟乙烯（PVDF-I）,再以PVDF-I为大分子链转移剂进行N-乙烯基吡咯烷酮碘转移溶液聚合,得到聚偏氟乙烯-b-聚乙烯基吡咯烷酮（PVDF-b-PVP）两亲性嵌段共聚物;采用NMR、IR、XRD、DSC和AFM等对PVDF-b-PVP嵌段共聚物的分子和相态结构进行了表征。发现PVP能有效嵌入PVDF与末端碘之间,PVDF嵌段PVP后,PVDF分子链的有序度明显降低,产生γ晶型PVDF,同时结晶温度和结晶度降低。PVDF-b-PVP嵌段共聚物表现微相分离结构,相分离尺寸约20 nm,其亲水性也优于PVDF均聚物。     

Grafting poly(vinyl amine-co-acrylic acid)s on poly(vinylidene fluoride) membranes

In this study, N-vinylacetamide (NVA) was graft-polymerized and graft-copolymerized with acrylamide (AAm) onto plasma-activated surfaces. The polymer compositions of the grafted layer were estimated from X-ray photoelectron spectroscopy spectra. N-vinylacetamide was enriched in the grafted polymers in all regions of the monomer compositions. The primary amine groups could be densely introduced on the surface by hydrolyzing the grafted poly(vinylacetamide-co-acrylamide). © 1994 John Wiley & Sons, Inc.     

Radiation initiated grafting of acrylic acid onto tetrafluoroethylene–ethylene copolymers

Hydrophilic carboxyl containing fluoropolymers was obtained by radiation grafting of acrylic acid onto tetrafluoroethylene—ethylene copolymers with different compositions. By using simultaneous (⁶⁰Co) and preirradiation (electron beam) techniques, the effect of the grafting conditions (monomer concentration, dose rate, dose, film thickness, etc.) on the degree of grafting was studied. A considerable effect of the polymer compositions, especially the C? F bonds content, and the batch irradiation on the degree of grafting was found. It was observed by scanning electron microscopy that the grafting took place mainly on the polymeric film surface and developed inward with increasing diffusion of the acrylic acid through the grafted layers. © 1993 John Wiley & Sons, Inc.     

Radiation grafting of vinyl monomers onto wood pulp cellulose. II

The effect of radiation dose rate and beating time on the mutual radiation grafting of styrene to unbleached and bleached kraft wood pulp was studied. Companion studies on the effect of beating time, peroxidation grafting, and order of monomer addition on the preirradiation graft copolymerization of acrylamide and diethylaminoethyl methacrylate were conducted on bleached wood pulp. The grafting rate of styrene increased with dose rate, but the kinetics suggests a significant diffusional resistance to the observed grafting rate. The per cent graft measured at fixed grafting conditions decreased markedly as pulp beating (effected prior to grafting) was increased. It is suggested that the decrease in grafting with beating is due to an increase in the accessibility and swelling of the beaten fibers. Dimethylaminoethyl methacrylate appeared to inhibit the grafting of acrylamide, and double grafting had to be used to graft both hydrophilic polymers to the pulp. The mechanical properties of high-yield pulp and groundwood were improved by the addition of the grafted pulps. The double grafts appeared to show promise as fibrous beaten additives for dry strength improvement. The styrenegrafted pulps were found not to respond at all to the beating process.     

Grafting of vinyl monomers onto wood fibers initiated by peroxidation

Summary The oxidation of chemithermomechanical (aspen) pulp with ruthenium tetroxide followed by peroxidation with hydrogen peroxide was performed to study the graft copolymerization of methacrylic acid, epoxypropyl acrylate and epoxypropyl methacrylate. For epoxy monomers, lower pH (i.e. < 5) is more favorable due to the participation of the epoxy group in the grafting reaction in acidic medium. Moreover, the grafting of epoxy monomers appeared more efficient than methacrylic acid.     

Heat capacity of copolymers of chlorotrifluoroethylene and vinylidene fluoride

The heat capacities of two copolymers of chlorotrifluorethylene and vinylidene fluoride, one 30:70 mol % and the other 44:56 mol % in composition, were measured in an adiabatic calorimeter from 80 to 340 K. The glass-transition points T_g observed at 256 and 269 K for the 30:70 and 44:56 samples, respectively, closely agree with the prediction of the theory of Flory and Fox; the accompanying jump of heat capacities at these points was found to be 2.2 cal/K ‘per bead’ for both samples, in fair agreement with the ‘constant ΔC_p rule’. A small peak was observed immediately above T_g, and interpreted as a time-dependent effect arising from the lack of equilibrium in the region. The data of the heat capacities were analysed in detail in the framework of the Tarasov model and the principle of additivity, and were found to agree well ( 1–3%) with theory up to the respective glass-transition points in all cases, thus giving support to the validity of the previously published segmental values of heat capacity and of characteristic temperature θ₁.     

Controlled grafting of polymer brushes on poly(vinylidene fluoride) films by surface‐initiated atom transfer radical polymerization

Controlled grafting of well‐defined polymer brushes on the poly(vinylidene fluoride) (PVDF) films was carried out by the surface‐initiated atom transfer radical polymerization (ATRP). Surface‐initiators were immobilized on the PVDF films by surface hydroxylation and esterification of the hydroxyl groups covalently linked to the surface with 2‐bromoisobutyrate bromide. Homopolymer brushes of methyl methacrylate (MMA) and poly(ethylene glycol) monomethacrylate (PEGMA) were prepared by ATRP from the α‐bromoester‐functionalized PVDF surface. The chemical composition of the graft‐functionalized PVDF surfaces was characterized by X‐ray photoelectron spectroscopy (XPS) and attenuated total reflectance (ATR)–FTIR spectroscopy. Kinetics study revealed a linear increase in the graft concentration of PMMA and PEGMA with the reaction time, indicating that the chain growth from the surface was consistent with a “controlled” or “living” process. The “living” chain ends were used as the macroinitiator for the synthesis of diblock copolymer brushes. Water contact angles on PVDF films were reduced by surface grafting of PEGMA and MMA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3704–3712, 2006     

Propagation of vinyl polymers on clay surfaces. II. Polymerization of monomers initiated by free radicals attached to clay

The adduct of Kaolin and 2,2′-azobisisobutyramidine hydrochloride has been used to initiate the polymerization of methyl methacrylate, styrene, styrene-butadiene, vinyl acetate, chloroprene, acrylamide, and acrylonitrile. Both extractable and nonextractable polymers are obtained. The adduct of bentonite and 2,2′-azobisisobutyramidine hydrochloride will initiate the polymerization of methyl methacrylate, acrylamide, vinyl acetate, 4-vinylpridine, and styrene. Both extractable and nonextractable polymers are formed. When the bentonite or the hectorite adducts are more than 99% decomposed prior to the addition of methyl methacrylate, essentially no extractable polymer is formed, but an increased quantity of nonextractable polymer is produced. This is probably due to an increased accessibility of the monomer to the clay's interior surface and a decrease in the rate of chain termination. As is the case of the kaolin adduct, the clay surface of bentonite appears to accelerate the chain growth considerably.     

Crosslinking and grafting ethylene vinyl acetate copolymer with accelerated electrons in the presence of polyfunctional monomers

In this study, we have studied the effects of polyfunctional monomers (PFMs) on physical properties of ethylene vinyl acetate (EVA) copolymer crosslinked with electron beam (EB) or peroxides. The PFMs used were triallylcyanurate, triallylisocyanurate, trimethylolpropane trimethacrylate, zinc diacrylate, and ethylene glycol dimethacrylate. Using PFMs has led to (1) optimum cure time t ₉₀ decrease from 19′25″ to 17′30″–18′45″, (2) scorch time increase from 2′ to maximum 3′45″, (3) increasing the crosslink density of peroxide or EB-cured systems by increasing the efficiency of productive radical reactions. The most efficient PFM for EVA copolymer blends has been triallylisocyanurate. Tensile strength and tear strength of samples crosslinked with EB for all irradiation doses are significantly better than those obtained for samples crosslinked with peroxides (differences up to 190%). The results show that EB irradiation gave the best results     

Radiation yield of hydrogen chloride in the poly(vinyl chloride) foils irradiated by accelerated electrons

The G_HCl values of PVC foils, containing 18% of dioctylphthalate, irradiated with accelerated electrons were studied after addition of various amounts of the stabilizers: (I) ethylene glycol bis-β-aminocrotonate, (II) calcium/zinc laurate + epoxy compounds, (III) calcium/zinc stearate, (IV) dioctyltin bis(octylthioglycolate). The effect of stabilization turned out to be very good, especially when stabilizer I was used. In the case of soft PVC foils in contact with water, elution of hydrogen chloride occurs. This creates difficulties in preparing PVC foils sterilized radiatively for medical purposes, especially if the foils are expected to be in contact with water.     

Comparison of gas permeation in vinyl and vinylidene polymers

The gas transport properties of several simple vinyl and vinylidene polymers are compared to examine the effect of pendant group type (H, CH₃, F, Cl) and symmetry of placement. The literature contains extensive information about these polymers, which has been critically reviewed to obtain consistent data for interpretation of the effect of structure on gas permeability. The gas transport data available for many of these polymers are quite variable because of differences in additives, thermal history, and crystallinity. The values used here are from studies where the physical properties of the film were reported along with the transport data. The appropriate data were not available for poly(vinyl fluoride) or poly(vinylidene chloride). For poly(vinyl fluoride), permeability measurements and thermal analysis were done to supply this information. Results for poly(vinylidene chloride) were obtained by extrapolation of copolymer permeation properties. Estimates of the permeability of oxygen in the amorphous phase of each polymer are discussed in terms of the estimated fractional free volume of that phase. In this way, the intrinsic effects of molecular structure on gas permeation exclusive of crystallinity effects have been evaluated.     

Solid state extrusion of vinylidene fluoride (VF2)/vinylidene trifluoride (VF3) copolymers. II: Structure development

Copolymers of vinylidene fluoride (VF2) and vinyltrifluoride (VF3) exhibit Curie transition temperatures well below their melting points. Above these endothermic transitions, they soften and this behavior helps in their solid state extrudability. In this paper, the effects of extrusion speed, temperature, and draw ratio on structure development in 60/40 and 72/28 VF2/VF3 copolymer compositions are presented. With the increase of extrusion draw ratio the Curie transition temperature of the extrudates decreased and melting temperature increased. This behavior suggested that the chains in the crystalline regions contain higher levels of conformational defects while overall crystallinity is increased. Unoriented polymers were optically opaque and extrudates were found to be transparent as a result of breakdown on the superstructural level which decreases the scattering effects in the visible wavelength range. The micro beam WAXS studies on the samples taken from the entrance of the dies revealed that the unoriented core is surrounded by alternating unoriented and oriented layers close to the core. The remainder of the skin layers are found to be oriented with local symmetry axes and main chain orientation being parallel to the die wall surface. The regions that are found to be oriented were also found to be optically translucent and unoriented regions were optically opaque. This structure turns uniformly transparent–and thus oriented?as the polymer enters the die. The existence of layered structure suggests that highly localized yielding occurs during early states of deformation at the converging entrance region of the die. Examination of the radial structural variation in extrudates with micro beam X-ray diffraction technique revealed that the local symmetry axes are tilted away from the extrusion direction and this tilt angle reduces at the sample macro-symmetry axis at the core of the samples. This indicated that the tilted structure developed at the converging entrance region is partially preserved through the die. While the orientation of local symmetry axes varies from skin to core in the extrudates, the orientation of chains with respect to these local symmetry axes remains relatively unaffected.     

Radiation grafting functionalization of poly (vinylidene fluoride) to compatibilize its blends with polyolefin ionomers

Blends of a crystalline vinylidene fluoride copolymer (PVDF) and a polyolefin ionomer were produced by melt mixing and characterized by a variety of techniques to examine the effect of increasing the level of salt formation on morphology. The PVDF component was also grafted with methacrylic acid by irradiating the polymer powder and subsequently treating it with an aqueous monomer solution. The effect of neutralizing the acid in both polymer components to produce the corresponding zinc salt was also investigated. Compatibilization was accomplished by the addition of zinc acetyl acetonate (ZnAcAc) to the mixture. This increased the viscosity of the polyolefin ionomer phase, comparable to that of the PVDF. The viscosity of the grafted PVDF component did not increase appreciably after neutralization with ZnAcAc. The grafted polymer precipitated and formed a particulate dispersion with in a largely graft-free polymer matrix. The addition of ZnAcAc to the blend of grafted PVDF and polyolefin ionomer produced a large enhancement in compatibilization, giving rise to the formation of co-continuous phases that contained encapsulated particles of different size and in various locations.     

Synthesis of permselective membranes by radiation-induced grafting of N-vinylpyrrolidone onto poly(tetrafluoroethylene–hexafluoropropylene–vinylidene fluoride) (TFB) films

The radiation initiated grafting of N-vinylpyrrolidone (NVP) onto poly(tetrafluoroethylene–hexafluoropropylene–vinylidene fluoride) (TFB) films has been investigated using a direct radiation technique. Different solvents were used for diluting the monomer, and it was found that dioxane is suitable for this grafting system. The influence of other grafting parameters, such as inhibitor, monomer concentration and dose rate, on the rate and yield of grafting was studied. The dependence of the grafting rate on the monomer concentration was found to be of the 1.1 order. Some physicochemical properties, such as swelling, thermal behaviour, mechanical and electrical conductivity, were investigated. A study was made to gain a better understanding of the observed water uptake using IR spectroscopy and scanning electron microscope (SEM) analysis. The possibility of some practical uses, e.g. removal of heavy metals from solution by grafted membranes was investigated. © 1999 Society of Chemical Industry     

The role of intumescence on the flammability of vinyl and vinylidene polymers

Thermal stability and flammability properties of six structurally related vinyl and vinylidene polymers fail to show correlation. Instead, it is found that the combustion of these polymers is dominated by their char-forming ability. A remarkable intumescent effect is observed in PVC₂, PVF₂, and PVC which accounts for the high flame extinguence of these polymers.     

Specific heat and thermal diffusivity of vinylidene fluoride/trifluoroethylene copolymers

The specific heat (C) and thermal diffusivity (D) of vinylidene fluoride (VDF)/trifluoroethylene copolymers with 70 and 56 mol % of VDF were measured between 200 and 390 K, and the thermal conductivity (K) was calculated from these data. C, D, and K were rather insensitive to the VDF content but varied significantly with the crystallinity. At room temperature, as the crystallinity increased from about 55 to 85%, C decreased by 17%, and D and K increased by 60 and 40%, respectively. For the copolymer with 70 mol % VDF, C exhibited a broad peak, whereas D showed an abrupt drop at the ferroelectric–paraelectric transition near 370 K on heating. The transition temperature on cooling was about 40 K below that observed in the heating run, thus revealing a large thermal hysteresis. For the copolymer with 56 mol % VDF, the transition temperature was much lower, the transition region was narrower, and the thermal hysteresis was barely observable. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3160–3166, 2003