NMR depth profiles as a non-invasive analytical tool to probe the penetration depth of hydrophobic treatments and inhomogeneities in treated porous stones

Hydrophobic treatment is one of the most important interventions usually carried out in the conservation of stone artifacts and monuments. The analytical study reported in this paper was aimed at answering general questions such as the penetration depth of a hydrophobic treatment into a porous material, its capability to impair the water absorption, how the presence of a treatment may change the open porosity available to the water, and how a treatment may affect the diffusion of water inside a porous structure. Also, inhomogeneities in treated stones due to sharp variations of the amount of the absorbed product in the porous material were evidenced and scaled. The results of this fully non-invasive analytical study were rationalized in terms of new parameters obtained by a suitable process of nuclear magnetic resonance data. These analytical parameters reported here for the first time, namely the hydrophobic efficiency, the penetration depth, and angles describing changes in slope in depth profiles, gave important information in assessing the performance of a treatment.     

Mechanochemical Friedel–Crafts Alkylation—A Sustainable Pathway Towards Porous Organic Polymers

This study elucidates an innovative mechanochemical approach applying Friedel–Crafts alkylation to synthesize porous covalent triazine frameworks (CTFs). Herein, we pursue a counterintuitive approach by utilizing a rather destructive method to synthesize well-defined materials with intrinsic porosity. Investigating a model system including carbazole as monomer and cyanuric chloride as triazine node, ball milling is shown to successfully yield porous polymers almost quantitatively. We verified the successful structure formation by an in-depth investigation applying XPS, solid-state NMR and FT-IR spectroscopy. An in situ study of pressure and temperature developments inside the milling chamber in combination with two-dimensional liquid-state NMR spectroscopy reveals insights into the polymerization mechanism. The versatility of this mechanochemical approach is showcased by application of other monomers with different size and geometry.     

A key factor in modern protection of historic buildings: the assessment of penetration of water-repellent polymers into porous stone-materials

From the 1960s on, the conservation of monuments and stone masonry has witnessed an increasing use of polymeric products during restoration interventions. Actual penetration depths reached by different polymers within the porous stone matrix are supposed to be key factors in determining the efficacy of the treatments themselves (besides, of course, the chemical-mineralogical nature of the stone and the chemical-physical characteristics of the various polymers). This work presents some preliminary results obtained on specimens of Noto calcarenite treated with various polymeric protective products. Samples were investigated with direct analytical methods (micro-ATR spectroscopy, SEM) in order to assess penetration depths reached by polymers inside the stone while reducing to a minimum the necessary manipulation of specimens. The obtained results highlighted the following trend in penetration depths for the various products tested: siloxane product > partially fluorinated acrylic resin > acrylic resin. Moreover, data obtained allowed to establish direct correlation between long term efficacy of products and relative penetration depths.     

Mechanochemical Friedel–Crafts Alkylation—A Sustainable Pathway Towards Porous Organic Polymers

This study elucidates an innovative mechanochemical approach applying Friedel–Crafts alkylation to synthesize porous covalent triazine frameworks (CTFs). Herein, we pursue a counterintuitive approach by utilizing a rather destructive method to synthesize well‐defined materials with intrinsic porosity. Investigating a model system including carbazole as monomer and cyanuric chloride as triazine node, ball milling is shown to successfully yield porous polymers almost quantitatively. We verified the successful structure formation by an in‐depth investigation applying XPS, solid‐state NMR and FT‐IR spectroscopy. An in situ study of pressure and temperature developments inside the milling chamber in combination with two‐dimensional liquid‐state NMR spectroscopy reveals insights into the polymerization mechanism. The versatility of this mechanochemical approach is showcased by application of other monomers with different size and geometry.     

In situ polymerization of 3-glycidoxypropyl trimethoxysilane (GLYTS) as a new tool for stone conservation

The effectiveness, as stone restoration materials, of a series of polymers obtained by "in situ polymerization" of the epoxy derivative 3-glycidoxypropyltrimethoxysilane (GLYTS) with the primary amine 3-aminopropyltriethoxysilane (ATS), at various molar ratios and concentrations, has been explored through selected preliminary tests. The experiments carried on a low-porosity quartzite show that, independently from concentration and molar ratio, all of the mixtures fail to significantly affect the porosimetric and hydric properties of this stone while inducing not negligible chromatic alterations. As it concerns high porosity stones, such as Comiso calcarenite, the 2:1 15% mixture only has been selected for further experiments since preliminary tests show that it acts as an excellent barrier against water penetration either by capillarity as by total immersion while showing only negligible chromatic alterations.     

Frontal copolymerization synthesis and property characterization of starch-graft-poly(acrylic acid) hydrogels

Recently, a considerable amount of research has centered on uniquely structured polymers synthesized through self-propagating frontal polymerization. The obtained polymer materials have better features than those obtained by using the classical batch route. The additional advantages are short reaction times and low cost. This work describes the first frontal polymerization synthesis of a graft copolymer superabsorbent hydrogel of acrylic acid onto starch at high monomer and initiator concentration. The effects of varying the relative amounts of the reaction components on the most relevant parameters relating to frontal polymerization were explored. The front velocity dependence on initiator concentration could be fit to a power function. The temperature profiles were found to be very sharp with a maximum temperature below 150 degrees C, which was responsible for high monomer conversion. The ultimate properties of the product appear to depend on the polymerization front velocity and the temperature. The high-temperature and rapid temperature increase at the polymerization front led to products with interconnected porous structures caused by the evaporation of water. So, a fast-swelling, highly absorbing hydrogel with respect to batch polymerization was obtained.     

Controlled polymerization in mesoporous silica toward the design of organic-inorganic composite nanoporous materials

Free-radical polymerization inside mesoporous silica has been investigated in order to open a route to functional polymer-silica composite materials with well-defined mesoporosity. Various vinyl monomers, such as styrene, chloromethyl styrene, 2-hydroxyethyl methacrylate, and methacrylic acid, were polymerized after impregnation into mesoporous silicas with various structures, which were synthesized using polyalkylene oxide-type block copolymers. The location of the polymers was systematically controlled with detailed structures of the silica framework and the polymerization conditions. Particularly noteworthy is the polymer-silica composite structure obtained by in situ polymerization after the selective adsorption of monomers as a uniform film on silica walls. The analysis of XRD data and the N(2) adsorption isotherms indicates the formation of uniform polymer nanocoating. The resultant polymer-silica composite materials can easily be post-functionalized to incorporate diverse functional groups in high density, due to the open porous structure allowing facile access for the chemical reagent. The fundamental characteristics of the composite materials are substantiated by testing the biomolecule's adsorption capacity and catalytic reactivity. Depending on the structure and composition of polymers, the resultant polymer-silica composite materials exhibit notably distinct adsorption properties toward biomolecules, such as proteins. Furthermore, it is demonstrated that the nanocoatings of polymers deposited on the mesopore walls have remarkably enhanced catalytic activity and selectivity, as compared to that of bulk polymer resins. We believe that, due to facile functionalization and attractive textural properties, the mesoporous polymer-silica composite materials are very useful for applications, such as adsorption, separation, host-guest complexes, and catalysis.     

Well-defined protein-polymer conjugates via in situ RAFT polymerization

Biotechnology, biomedicine, and nanotechnology applications would benefit from methods generating well-defined, monodisperse protein-polymer conjugates, avoiding time-consuming and difficult purification steps. Herein, we report the in situ synthesis of protein-polymer conjugates via reversible addition-fragmentation chain transfer polymerization (RAFT) as an efficient method to generate well-defined, homogeneous protein-polymer conjugates in one step, eliminating major postpolymerization purification steps. A water soluble RAFT agent was conjugated to a model protein, bovine serum albumin (BSA), via its free thiol group at Cys-34 residue. The conjugation of the RAFT agent to BSA was confirmed by UV-visible spectroscopy, matrix-assisted laser desorption ionization--time of flight (MALDI-TOF), and 1H NMR. BSA-macroRAFT agent was then used to control the polymerization of two different water soluble monomers, N-isopropylacrylamide (NIPAAm) and hydroxyethyl acrylate (HEA), in aqueous medium at 25 degrees C. The growth of the polymer chains from BSA-macroRAFT agent was characterized by size exclusion chromatography (SEC), 1H NMR, MALDI-TOF, and polyacrylamide gel electrophoresis (PAGE) analyses. The controlled character of the RAFT polymerizations was confirmed by the linear evolution of molecular weight with monomer conversion. The SEC analyses showed no detectable free, nonconjugated polymer formation during the in situ polymerization. The efficiency of BSA-macroRAFT agent to generate BSA-polymer conjugates was found to be ca. 1 by deconvolution of the SEC traces of the polymerization mixtures. The structural integrity and the conformation-related esterase activity of BSA were found to be unaffected by the polymerization conditions and the conjugation of the polymer chain. BSA-poly(NIPAAm) conjugates showed hybrid temperature-dependent phase separation and aggregation behavior. The lower critical solution temperature values of the conjugates were found to increase with the decrease in molecular weight of poly(NIPAAm) block conjugated to BSA.     

Solvent effect on TEOS film formation in the sandstone consolidation process

Alkoxysilanes, low-viscosity monomers capable of polymerizing into the porous network of stone by a sol-gel process, are widely used as consolidants in the restoration of stone monuments. However, since consolidation is a non-reversible application capable of causing serious harmful side effects to the original material, stone consolidation is almost always considered a very risky intervention. Alkoxysilanes are insoluble in water, so co-solvented systems are very often used, but even knowing that the solvent is a determinant parameter for sol-gel reactions, there is still a lack of information regarding how it can influence the stone-alkoxysilane affinity. For two different tetraethoxysilane-acidic co-solvented systems we are reporting both the morphological characteristics showed by gels formedin situ and the affinity reached with the stone in the sandstone consolidation process. Aqueous solutions of ethanol and methyl-ethyl-ketone (MEK) were the solvents compared. SEM and ²⁹Si Solid State NMR were used todetermine the alkoxysilane performance on these silicic-based materials. It was found that using MEK solutions resulted in appreciable sandstone-alkoxysilane interaction, forming a more homogeneous film. On the other hand, ethanol does not promote alkoxysilane-sandstone compatibility. A brittle film is obtained when ethanol is used.     

Trimethoxysilylpolymethacrylate as new material for stone conservation. Porosimetric and colorimetric investigations

Aimed to obtain new materials for the conservation of stone substrates, we report here on the synthesis of a polymer which has been obtained by inducing polymerization on a methacrylate monomer functionalized by alchoxysilane groups. Two lithotypes, the Comiso calcarenite and Mistretta quartzite, stones largely used in artworks of north-eastern Sicily, were treated with the above polymer and its conserving efficacy evaluated in terms of porosimetric features, hydric properties and appearance. The collected data were compared to those provided, under the same experimental conditions, by an ethylmethacrylate/methylmethacrylate copolymer and an alkylalchoxysilane, products widely employed in the protection of stones. Experiments aimed to test the durability of the above polymer against UV artificial ageing are also reported.     

溶胶-凝胶法制备丙烯酸树脂/TiO2有机-无机杂化材料及其结构表征

通过预水解的二氧化钛(TiO2 )溶胶与丙烯酸树脂共混或原位聚合的方法制备了均匀透明的丙烯酸树脂 TiO2 有机 无机杂化材料.考察了TiO2 溶胶制备方法、聚合物中—COOH官能团含量和杂化材料制备方法对杂化材料结构的影响.索氏抽提实验表明聚合物中的羧酸官能团和无机TiO2 相间发生了交联反应,且随着—COOH官能团含量的增加,交联程度增大.小角X射线散射(SAXS)结果发现,杂化材料中TiO2 为疏松的三维网状结构,且在纳米尺度范围内,但这种三维网状结构随着TiO2 溶胶制备中水或酸的用量增加,其致密度增加,尺寸增大.同原位聚合法相比,共混法可制备出更均匀的杂化体系,且TiO2 为单分散.     

Synthesis of poly(ω‐pentadecalactone)‐b‐poly(acrylate) diblock copolymers via a combination of enzymatic ring‐opening and RAFT polymerization techniques

Herein the first reported preparation of diblock copolymers of the polyethylene‐like polyester poly(ω‐pentadecalactone) (PPDL) via a combination of enzymatic ring‐opening polymerization (eROP) and reversible addition‐fragmentation chain‐transfer (RAFT) polymerization techniques is described. PPDL was synthesized via eROP using Novozyme 435 as a catalyst and a bifunctional initiator/chain transfer agent (CTA) appropriate for the eROP of ω‐pentadecalactone (PDL) and RAFT polymerization of acrylic and styrenic monomers. Chain growth of the PPDL macro‐CTA was performed to prepare acrylic and styrenic diblock copolymers of PPDL, and demonstrates a facile, metal‐free, and “greener” alternative to preparing acrylic diblock copolymers of polyethylene (PE). Diblock copolymer architecture was substantiated via analysis of ¹H NMR spectroscopic, UV‐GPC chromatographic, DSC onset crystallization (T_c), and MALDI‐ToF mass spectrometric data. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3326–3335     

Synthesis of snowman‐like polymer‐silica asymmetric particles by combination of hydrolytic condensation process with γ‐ray radiation initiated seeded emulsion polymerization

We report on a facile route to synthesize snowman‐like asymmetric composite particles via γ‐ray initiated seeded emulsion polymerization after a hydrolytic condensation process on the surface of second monomer swollen poly(styrene‐divinylbenzene‐acrylic acid) seeds. Effects of the amounts and kinds of second monomer and inorganic precursor, different radiation polymerization conditions including dose rates and absorbed doses on the morphology of the obtained particles were investigated. The obtained asymmetric particles can serve as ideal solid surfactants to stabilize the water‐in‐oil emulsions, and soap‐free hierarchical materials were obtained by polymerization of monomers in water or oil phase. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 339–348     

Block Copolymerization of Lactide and an Epoxide Facilitated by a Redox Switchable Iron‐Based Catalyst

A cationic iron(III) complex was active for the polymerization of various epoxides, whereas the analogous neutral iron(II) complex was inactive. Cyclohexene oxide polymerization could be “switched off” upon in situ reduction of the iron(III) catalyst and “switched on” upon in situ oxidation, which is orthogonal to what was observed previously for lactide polymerization. Conducting copolymerization reactions in the presence of both monomers resulted in block copolymers whose identity can be controlled by the oxidation state of the catalyst: selective lactide polymerization was observed in the iron(II) oxidation state and selective epoxide polymerization was observed in the iron(III) oxidation state. Evidence for the formation of block copolymers was obtained from solubility differences, GPC, and DOSY‐NMR studies.     

前线聚合研究及应用进展(下)

综述了单体性质、压力、引发剂、反应容器等因素对前线聚合的影响,并对影响前线稳定性的诸多因素进行了讨论,简要介绍了光引发前线聚合近年来最新发展,综述了前线聚合在制作梯度材料、聚氨酯合成、不饱和聚酯及环氧固化、双环戊二烯开环异位聚合、互穿网络结构制备及微孔材料填充固化保护等方面的应用状况。     

PMMA-TiO2有机无机杂化玻璃的制备与表征

有机无机杂化材料是随着对溶胶凝胶方法的广泛研究而发展起来的，有时它们被称为ORMOSILS（OrganicallyModifiedSilicates）[1,2]或ORMOCERS（OrganicallyModifiedCerandcs）[2]．溶胶凝胶过程通过溶液化学（WetChemistry）的途径来形成无机骨架，在过去的几十年里，被广泛应用     

Graft polymerisation of ethyl acrylate/methyl methacrylate copolymers: A tool for the consolidation of paper-based materials

Grafting polymerisation of acrylic monomers onto cellulose chains represents a useful method of restoration for both artificially and naturally aged paper-based materials. In this paper, some results concerning the grafting polymerisation of ethyl acrylate/methyl methacrylate 75/25 wt.% copolymer onto several paper grades are reported, highlighting how the presence of fillers in the raw materials reduced the grafting yields. The consolidating and protective effects have been investigated by evaluating the mechanical properties and the wetting behaviour of the grafted samples, and comparing them with the original and aged substrates.     

Synthesis,characterization and stimuli-sensitive properties of novel linear and crosslinked polybetaines based on acrylic acid and ethyl 3-aminocrotonate

Novel linear and crosslinked polybetaines based on acrylic acid (AA) and ethyl 3-aminocrotonate (CRO) have been synthesized by a Michael addition reaction followed by radical polymerization. The polymerization of AA and CRO was carried out in bulk, water and organic solvents. The dependence of polymer yield on the molar ratio of monomers and water content was found. Primary attention was paid to linear and crosslinked polybetaines synthesized at equimolar ratio of monomers in the feed. The composition and structure of linear polybetaines was determined by elemental analysis, potentiometric titration, FTIR and NMR spectroscopy. The isoelectric points of linear and crosslinked polybetaines determined by electrophoresis, viscometry and swelling experiments corresponded to pH 2.0-2.2. The stimuli-sensitive properties of amphoteric gels were studied as a function of pH, ionic strength, water-organic solvent mixture, electric, and combined electric and magnetic fields. Appearance of pH gradient within the polyampholyte gel matrix under the externally imposed DC electric field was observed.     

In situ monitoring of solid-state polymerization reactions in sodium chloroacetate and sodium bromoacetate by 23Na and 13C solid-state NMR spectroscopy

The thermally induced solidstate polymerization reactions in sodium chloroacetate and sodium bromoacetate, leading to poly(hydroxyacetic acid) (polyglycolide) and NaCl and NaBr, respectively, were studied by isothermal in situ solid-state NMR spectroscopy at 120, 130 and 140 degrees C with a time resolution of the order of 5 to 25 min. The nuclei probed were 23Na and 13C, allowing the parent compounds (sodium halogenoacetates) and both reaction products (polymer and alkali halide) to be monitored. For sodium chloroacetate, there is no evidence for the involvement of intermediate phases during the reaction whereas this cannot be excluded for sodium bromoacetate. The crystal structure of sodium bromoacetate was determined directly from powder diffraction data by the Monte Carlo method, and was found to be isostructural with sodium chloroacetate. The topochemical reaction mechanism proposed previously for sodium chloroacetate is thus also applicable for the polymerization reaction in sodium bromoacetate. The mechanistic and kinetic information obtained from our in situ solid-state NMR investigations is compared and contrasted with information obtained from other in situ probes of the polymerization reactions in these materials.     

端羟基聚丙烯酸酯改性水性聚氨酯

将丙烯酸丁酯(BA)、甲基丙烯酸甲酯(MMA)通过溶液自由基聚合,用巯基乙醇作为链转移剂调控合成了一定分子量的端羟基聚丙烯酸酯(PA),再与聚氨酯(PU)预聚体反应,在水中分散得到PA-PU-PA三嵌段共聚复合乳液。 采用FTIR和¹HNMR测试技术对共聚物结构进行了表征。 结果表明,随着PU与PA质量比的降低,共聚物中丙烯酸酯含量随之增加;PU软硬链段之间的氢键化作用减弱。 TEM显示,复合乳胶粒子形态均匀规整,并呈现明显的核壳结构。改性后的乳胶膜耐水、耐热性能均随着PU/PA质量比的减小而提高,吸水率由25%降低至5%,最大热失重温度由369 ℃提高至432 ℃。