The Role Of Unsaturations In The Gamma Irradiation Of Crosslinkable Polymers (original) (raw)
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Gamma-irradiated metallocenic polyethylene and ethylene-1-hexene copolymers
Journal of Applied Polymer Science, 2010
The aim of this work is to present a detailed study of the changes introduced by gamma radiation on several metallocenic polyethylene copolymers. Therefore, metallocenic polyethylene and copolymers with 3.3, 9.2, and 16.1 mol % of hexene comonomer content were synthesized and irradiated with 60 Co gamma radiation under vacuum at room temperature with radiation doses ranging from 0 to 100 kGy. Size Exclusion Chromatography data show that crosslinking reactions predominate over scission, even for the copolymer with the highest tertiary carbon content. Over a certain critical dose, which depends on the molecular weight and molecular structure of the initial polymer, an insoluble gel forms. The irradiated polymers also exhibit complex rheological behavior with increasing melt viscosity and elasticity, consistent with long chain branching and/or crosslinking. FTIR confirms depletion of terminal vinyl groups and increase of trans unsaturations with dose. The rate at which these two reactions evolve seems to depend on the comonomer content of the irradiated copolymers. Differential scanning calorimetry and Raman spectroscopy analyzes indicate less crystallinity and thicker interphases in irradiated materials. A mathematical model, which accounts for scission and crosslinking reactions, fitted well the evolution with radiation dose of the measured molecular weight data.
Radiation Physics and Chemistry, 2010
Two different post reactor processes were compared, 60 Co vacuum gamma irradiation and chemical modification with 2,5-dimethyl-2,5-di(tert-butylperoxy)-hexane (DBPH), on two metallocenic copolymers. These copolymers have a similar molecular weight and crystallinity, but different side chain lengths and concentration of end vinyl groups. The influence of the crosslinking agents on the structure of the samples was studied using gel extraction, size exclusion chromatography (SEC), FTIR spectroscopy and differential scanning calorimetry (DSC). The analysis of the data indicates that crosslinking reactions predominated over scission reactions in all cases. At the same conversion, peroxide modified samples show higher crosslinking levels than irradiated samples. The modified polymers show a complex rheological behavior and an increment in their rheological properties due to crosslinking. FTIR data demonstrated a depletion of vinyl terminal groups with the increment of the absorbed dose and the peroxide concentrations applied. This depletion was more significant in the peroxide crosslinked samples. A mathematical model that accounts for scission and crosslinking reactions fitted well the experimental data.
Radiation crosslinking and scission parameters for poly(vinyl methyl ether) in aqueous solution
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003
In oxygen-free aqueous solutions, poly(vinyl methyl ether) (PVME) was subjected to gamma irradiation. In such conditions PVME radicals recombine by way of crosslinking. The major result of crosslinking is an increase in the average molecular weight of the polymer, which close to the gelation point tends to infinity. Further irradiation increases the amount of formed gel, while the soluble fraction-sol decreases. The basic parameters related to the radiation processing are gelation doseD g , as well as radiation yield of intermolecular crosslinking and scission, G X and G S , respectively. There are three general approaches for estimation of those parameters. The first method is based on the study of molecular weight changes before the gelation point. The second method combines the gel-sol as well as the swelling analysis results. The third one allows one to calculate the yield of crosslinking from the value of D g. All of these methods of calculation were used in this work for determination of radiation parameters and results obtained are discussed.
Crosslinking of metallocenic α-olefin propylene copolymers by vacuum gamma irradiation
Radiation Physics and Chemistry, 2012
c Vacuum gamma irradiation of metallocenic isotactic propylene copolymers. c We examine the radioinduced changes in rheological properties and molecular weights. c Radioinduced crosslinking in the copolymers, without the presence of additives. c Dependence of crosslinking with copolymer 0 s length and amount of short branches.
Journal of Applied Polymer Science, 2011
Anionic ring-opening polymerization (AROP) was employed for the controlled synthesis of linear model block copolymers of 1,3,5,7-tetrametil-1,3,5,7-tetravinyl(cyclotetrasiloxane) (V 4) and 1,3,5-dimethyl(cyclotrisiloxane) (D 3) monomers by using sec-butyl lithium (sec-Bu À Li þ) as initiator, and high-vacuum anionic polymerization techniques. V 4 copolymerization was promoted by employing D 3 and sec-Bu À Li þ producing living silanolates that open the stable V 4 ring. For this purpose, two strategies were applied: (a) sequential addition of monomers, and (b) onestep copolymerization at different reaction temperatures. According to the experimental results, higher levels of V 4 incorporation ($ 18.14 mol %) were obtained by mixing both co-monomers and performing the reaction at high temperature (80 C). This strategy allowed the control of the V 4 incorporation into the copolymer structure, giving the opportunity of synthesizing model vinyl-siloxane polymers. The gamma radiation of these materials showed that lower doses are needed to achieve the same gel content as in a model poly(dimethylsiloxane) (PDMS). In such a sense, these results constitute one of the first reports regarding the effect of gamma radiation on vinyl-containing silicon polymers, and may be of fundamental importance if a biomedical cross-linked rubber-type PDMS is needed at earlier doses of sterilization. V
Polymer Bulletin, 2008
Due to their new combination of properties and shortage of the experimental data, the radiolysis of a new class of materials, cyclo-olefin copolymers (COC), which are polymerized from norbornene and ethylene using metallocene catalysts, is of great interest to the study of radiation chemistry and physics of polymeric systems. Ethylene-norbornene copolymer, bare and containing 0.45 wt % of the hindered phenolic type of an antioxidant (IRGANOX 1010) was subjected to gamma irradiation (100, 200 and 500 kGy) in the presence of air and in water. The irradiated copolymer was studied using FTIR, UV-vis spectrophotometric and gel content analysis. The insoluble fraction was formed in copolymer irradiated in water with 500 kGy, in bare 36% and in copolymer with an antioxidant 23%. The radiation induced changes in the molecular structure were correlated to the specific heat capacity and the glass transition temperature measured by DSC method.
Radiation Physics and Chemistry, 1998
Radiation-induced crosslinking of homogeneous glassy polyvinyltrimethylsilane was carried out either by the girradiation of the polymeric ®lms containing 3±20 wt% of ethylene glycol dimethacrylate or by the radiationinduced grafting of allyl methacrylate from vapour phase onto ®lms made of pure polymer. The dependence of grafting value on the absorbed g-irradiation dose and ®lm thickness was investigated. The modi®ed ®lms were analyzed for the sol/gel content and the dependence of gel fraction yield of crosslinked polymer on absorbed dose, concentration of the crosslinking agents and ®lm thickness.
Crosslinking of poly(ethylene-co-1,9-decadiene) by electron beam irradiation
Polymer, 2000
The response to electron beam irradiation of poly(ethylene-co-1,9-decadiene) was examined and compared to a reference polyethylene. The polymers were produced in a low-pressure process using a chromium-based catalyst giving relatively high levels of inherent unsaturations through thermal termination of the polymerisation. The copolymerisation with 1,9-decadiene gave an additional 63% vinyl end groups. A dramatic improvement in the crosslinking response was observed for the decadiene polymers and consequently considerably smaller radiation doses were needed to obtain a certain degree of crosslinking. The reason for the improved response was the overall higher amount of vinyl groups as well as the placement of vinyl groups along the molecular weight distribution; the longer molecules contained more vinyls than the shorter ones. A certain amount of vinyls remains after irradiation. It is likely that the restricted mobility due to the crystalline structure makes these vinyls less accessible for reaction. Elongation at break data at room temperature exhibited significant differences between the reference and decadiene materials, although M c determinations showed little difference in actual crosslinking density. This is likely to depend on the changes in the amorphous part of the material where the crosslinks are formed whereas the M c calculation is based on the same concentration of crosslinks but they are instead spread in the whole material. Therefore, larger differences could be seen in the solid state.
Structural changes induced by γ-rays on model linear ethylene-butene copolymers
International Journal of Radiation Applications and Instrumentation. Part C. Radiation Physics and Chemistry, 1988
Well characterized model copolymers are used to study the effects of ionizing radiation Linear copolymers of ethylene and butene-1 with uniform chemical mlcrostructure and vary narrow molecular weight distributions are Irradiated at room temperature with 3'-rays from a 60Co source Changes in the molecular hydrodynamic volume can be readily detected by GPC Changes in molecular weight averages M n and M w are measured by membrane osmometry and light scattering Cross linking seems to he the main effect of radiation and chain selsslon is neghglble up to the gel point The very uniform molecular structure and size in the non-irradiated polymer allows for the usa of a completely general model to correlate changes in molecular weight averages and branching. The model is suitable for linear polymers with reactive groups randomly distributed along the chain, and contains no simplifying approximations