Function Of Degree Research Articles

Epoxy-based azo polymers: synthesis, characterization and photoinduced surface-relief-gratings

Epoxy-based azo polymers with three kinds of backbones, different types of azo chromophores, and selected degrees of functionalization (DFs), were synthesized through a post-polymerization azo-coupling scheme. The T gs of the azo polymers were found to be considerably influenced by the substituents on the 4-positions of the azobenzene units and increased with the increase of the DFs of the polymers. Surface-relief-gratings (SRGs) were induced on the polymer films by interferenced Ar + laser beams. With the same irradiating light intensity and approximately equal film thickness, the rates of SRG formation were found to be significantly dependent on the electron-withdrawing groups on the 4-positions of the azobenzene units. For the polymers with the same type of azo chromophores and backbone structure, the inscription rates increased with the increase of the DFs. Meanwhile, the backbone structure also exhibited some effect on the inscription rates through the ways such as changing chromophore loading density or main-chain rigidity.

Thin layer molecularly imprinted microfiltration membranes by photofunctionalization using a coated alpha-cleavage photoinitiator.

A novel approach towards thin-layer molecularly imprinted polymer (MIP) composite membranes was developed based on using benzoin ethyl ether (BEE), a very efficient alpha-scission photoinitiator. The triazine herbicide desmetryn was used as the template, and a mixture of the functional monomer 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) and the cross-linker N,N'-methylene-bis-acrylamide (MBAA) in methanol was copolymerised via photoinitiation followed by deposition on the surface of either hydrophobic or hydrophilically precoated polyvinylidene fluoride (PVDF) microfiltration membranes. Blanks were prepared under identical conditions, but without the template. Especially, the degree of functionalization (DF) of the PVDF membranes with poly(AMPS-co-MBAA), the membrane permeabilities and non-specific vs. MIP-specific template binding from aqueous solutions during fast filtration were studied in detail to evaluate the effects of the preparation conditions, in particular the coating of the membrane surface with the photoinitiator prior to UV irradiation and the influence of the precoated hydrophilic layer on PVDF. Significant template specificities of the MIP membranes compared with the blanks were only achieved for the preparations including coating the two types of PVDF membranes with BEE. In contrast, a homogeneous photoinitiation of the copolymerisation in the membrane pore volume yielded functional layers with similar DF but with only non-specific desmetryn binding. All data clearly indicate the significant contribution of MIP stabilization by the support material in layers of optimum thickness to the MIP specificity. Main advantages of the novel approach are the potential to synthesize MIP composite membranes by controlled deposition onto any kind of polymer support, and the very fast MIP preparations due to a very efficient photoinitiator and small MIP layer thickness. Due to the mechanical and chemical stability in combination with high permeabilities, thin-layer MIP composite membranes have a large application potential, e.g., in solid phase extraction.

Grafting of diethyl maleate and maleic anhydride onto styrene-b-(ethylene-co-1-butene)-b-styrene triblock copolymer (SEBS)

In this paper a study of the bulk functionalization of styrene-b-(ethylene-co-1-butene)-b-styrene triblock copolymer (SEBS) with diethyl maleate (DEM) or maleic anhydride (MAH) and dicumyl peroxide (DCP) as initiator in a Brabender mixer is described. The determination of the functionalization degree (FD) by NMR analysis indicates that the FD values depend on the feed composition and in particular on the DEM/DCP ratio. All obtained products were fractionated by solvent extraction and characterized by IR, NMR and GPC. The results obtained show that the functionalization takes place with a very large preference at the aliphatic carbons of the polyolefin block. Moreover occurrence of degradation and chain extension reactions gives a functionalized product with a MWD larger than 1. Acetone extraction allows the isolation of styrene rich oligomers, thus the high MW functionalized polymer has a lower content of aromatic units than original SEBS.The results are described with reference to reaction mechanism previously reported in case of the functionalization under similar conditions of polymonoalkenes.

Controlled functionalization of olefin/styrene copolymers through free radical processes

The functionalization of styrene-b-(ethylene-co-1-butene)-b-styrene triblock copolymer (SEBS) and styrene-co-butadiene (SBR) random copolymer by free radical processes is presented. SEBS was functionalized in the melt with diethyl maleate (DEM) and dicumyl peroxide (DCP) as initiator. The functionalization degree (FD) ranges from 0.1 to 1.6% mol and depends on the feed composition and in particular on the DEM/DCP ratio. Such functionalization takes place with a very large preference at the aliphatic carbons of the polyolefin block. The functionalization of SBR was performed by radical addition in solution of two functional thiols (thioglicolic acid and its aliphatic ester), in the presence of free radical initiators. The addition occurs at the vinyl double bonds of the 1-2 butadiene units with high selectivity. FD can be tuned in the range 1-10mol%. These data are rationalized in the frame of the general reaction mechanism of free radical polymerization. A general reaction scheme is proposed which allows the design of proper conditions for favoring functionalization versus degradation and crosslinking depending on the nature of molecules and macromolecules involved.

Preparation and Characterization of Polyoxetane Resins Anchoring the Pendant Spacer-Separated Hydroxamic Acid Residue

Polyoxetane resins, IVa and IVb, anchoring the hydroxamic acid residue were prepared with high degree of functionality (DF) by polymer reactions from aliphatic NH2 groups at pendant spacer-ends of IIa and IIb. The pendant hydroxamic acids adsorbed Cu(II) ions from aqueous solution of Cu(II) acetate at pH 6 to show capacity beyond that calculated for the ordinary Cu(II)-complex chelated with the two pendant ligands, probably due to the formation of uncompleted chelate structures. The corresponding aromatic NH2 groups of IIc and IId showed very low DF in the same polymer reactions. At pH 6, amines of IIc and IId adsorbed Cu(II) ions to a certain extent, although those of IIa and IIb could adsorb no Cu(II) ions. A soft, expansible polyoxetane network, as a supporting matrix, may importantly affect Cu(II)-adsorption at high capacity.

Molecular and mechanistic aspects of the functionalization of polyolefins with ester groups

AbstractIn the present paper the functionalization reaction of polyolefins in the melt with diethylmaleate (DEM) in the presence of peroxide is revisited. The process was analyzed on the basis of several experiments carried out in the Brabender mixer with 30 min residence time and at constant temperature, 190° C for EPR and 200° C for LLDPE samples, while varying the number of branching in the starting polyolefin, the amount of DEM and of dicumyl peroxide (DCP). For reference purposes similar experiments were also examined as performed with EPDM and isotactic polypropylene (PP).At the end of the reaction, the polymeric product was treated with boiling acetone to remove low molecular weight products. In general, the acetone insoluble polymer was soluble in heptane and the functionalization degree (FD) referred to this fraction was in the range 0.2–2.0% mol of DES groups per 100 moles of monomelic units.The contemporary occurrence of the degradation and chain extension, including crosslinking reactions, provides a reasonable explanation of the results obtained. The analysis of the process performed in the present work helps to select proper conditions for controlling the characteristics and FD of the polyolefin and keep undesired secondary reactions under control.