Motional heterogeneity of segmented polyurethane-polymethacrylate mixtures: an influence of functional groups concentration

The motional heterogeneity in the polymer mixtures of segmented polyether polyurethane (PU) with carboxylic groups and methacrylic copolymer (PM) with tertiary amine groups was studied by the electron spin resonance (ESR)—spin probe and spin label methods. Pure polymer components containing varying amounts of functional groups and their 1:1 mass ratio mixtures have been analysed. The results of motional heterogeneity and polymer interaction were complemented with the glass transition temperatures, structural and morphological characteristics. Spin probed PU/PM mixtures indicate that the probe motion and the phase separation deduced from the temperature-dependent ESR spectra are sensitive to a free volume determined by the polymer-polymer interactions. The interaction between the two components in PU/PM mixture with the highest functional groups concentration disorganizes hard segment domains with spherulitic character at the microscopic level as compared with the ordered hard phase in the corresponding pure PU sample. The influence of PU hard and soft segments on the motional dynamics of PM chains is analysed from the ESR spectra of spin labelled PM chains in the mixtures with unlabelled PU components. The fractional amount of the PM fast motion depends on the temperature and concentration of functional groups.     

Motional heterogeneity and phase separation of semi-interpenetrating networks and mixtures based on functionalised polyurethane and polymethacrylate prepolymers

Semi-interpenetrating polymer networks (SIPNs) and polymer mixtures (1:1 mass ratio) based on segmented polyester polyurethane (PU) with carboxylic groups and methacrylic copolymer (PM) with tertiary amine groups were studied by the electron spin resonance (ESR) spin label method. The concentration of functional groups varied from 0 to 0.45 mmol g⁻¹ in both prepolymers. The ESR spectra of spin labelled PM component were used to characterise the heterogeneity of segmental motion and transitions due to the additional polymer interactions imposed by complementary functional groups. The results were deduced from the temperature dependent ESR spectra. Two component spectra reflect the effect of PU chains on segmental motion of the PM component below the macroscopic glass transition temperature, T_g. The ratio of the fast and slow component was related to the complex polymer-polymer interaction or extent of miscibility. Restrictions of segmental motion of PM chains increase with functional groups concentration and above certain concentration (0.25 mmol g⁻¹) PM segments in the network assess faster motion suggesting a change in the local packing density and domain structure. An increased miscibility and disorganisation of the ordered domains are confirmed by the loss of spherulitic morphology and crystallinity at higher functional groups concentration. PU/PM mixtures reveal similar motional behaviour as SIPNs of the same composition. However, the differences in the fractional amount of fast and slow motions confirm better interpenetration and interaction of the two polymers in the SIPNs. The results of motional heterogeneity and polymer interactions were complemented with the T_gs.     

Preparation of ketoprofen‐loaded high‐molecular‐weight poly(vinyl alcohol) gels

High‐molecular‐weight atactic poly(vinyl alcohol) (a‐PVA) gels loaded with (R,S)‐2‐(3‐benzoylphenyl)propionic acid (ketoprofen) were prepared from 5, 6, 7, and 8 g/dL solutions of a‐PVA with a number‐average degree of polymerization of 4000 in an ethylene glycol/water mixture with an aging method to identify the effect of the initial polymer concentration on the swelling behavior, morphology, and thermal properties of a‐PVA gels. Then, the release behavior of ketoprofen from a‐PVA gels was investigated. As the polymer concentration decreased, the ability for network formation decreased, and the degree of swelling of the a‐PVA gels increased. In addition, the enthalpy increased with an increase in the a‐PVA concentration, but the melting temperatures of the gels prepared at different initial polymer concentrations were the same; this indicated that tighter gel networks would be formed by a higher polymer chain density. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

The study of poly(styrene-co-p-(hexafluoro-2-hydroxylisopropyl)-α-methyl-styrene)/poly(propylene carbonate) blends by ESR spin probe and Raman

Different hydroxyl content poly(styrene-co-p-(hexafluoro-2-hydroxyisopropyl)-α-methylstyene) [PS(OH)] copolymers were synthesized and blends [noted for PP-X] with poly(propylene carbonate) [PPC] were prepared by casting from chloroform solution. The miscibility, micro heterogeneity and hydrogen bonding interaction of the component polymers were investigated by Differential Scanning Calorimetry (DSC), Electron Spin Resonance (ESR) spin probe method and Micro Raman spectroscopy. DSC results showed that the PP-2, PP-5, PP-8, PP-12 blends exhibited two distinct T_gs, indicating immiscibility, while the PP-20 and PP-27 blends were miscible with the existence of a single T_g. ESR results indicated that the probe molecule: Tempo couldn't give clear micro phase separation or miscibility information and thus was not sensitive to the investigated polymer blends system. On the contrary for all the blends spin probed with the probe molecules: Tempol and Tamine, two spectral components with different rates of motion: ‘fast’ and ‘slow’ motion were observed in different temperature range, which indicated the existence of micro heterogeneity on the molecular level; the more mobile PPC-rich micro phase and the more rigid PS(OH) rich micro phase. In addition, the scale of miscibility was progressively enhanced due to the increasing hydrogen bonding interaction between the hydroxyl in PS(OH) and the oxygen atoms in PPC. Meanwhile it was found that the degree of the probe molecule rotation detectable in the ESR spectrum was dependent on the polymer matrix rigidity and the strength of the hydrogen bonding between the probe molecule and the polymer matrix. Micro Raman substantiated the existence of the PS(OH)-rich micro phase and the PPC-rich micro phase. The hydrogen bonding strength between PS(OH) and PPC and the mixing level of the component polymers were increased gradually with the increase of hydroxyl content in the PS(OH) copolymer.     

Synthesis of poly(vinyl butyral)s in homogeneous phase and their thermal properties

The condensation reaction of butyraldehyde (BA) with poly(vinyl alcohol) (PVA) to give poly(vinyl butyral) (PVB) was studied in detail using N‐methyl‐2‐pyrrolidone (NMP) as solvent for PVA and PVBs. PVBs having various degrees of acetalization were obtained. The acetalization reaction under a variety of conditions gave at best a polymer with 97% acetalization. The extent of modification and the structure of the polymer, i.e., the ratio of acetal units from meso and racemic dyads of PVA, were determined by ¹H‐NMR. The acetalization degree was reflected in the solubility of PVB; all products were soluble in NMP. PVBs were characterized by IR spectroscopy and ¹H and ¹³C‐NMR. The glass transition temperatures of PVBs, determined by DSC, increased as vinyl alcohol units increased and displayed a positive departure from linearity. Thermal degradation of PVBs was studied using differential thermal analysis (DTA) and thermogravimetry (TGA) under dynamic conditions in nitrogen. The content of hydroxyl groups had an effect on the thermal stability of PVBs; the thermal stability of PVBs decreased as vinyl alcohol units increased. The apparent activation energy of the decomposition was determined by the Kissinger and Flynn–Wall methods, which agree well. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5007–5017, 2006     

Optical characteristics of responsive biopolymers; co-polycondensation of tri-functional amino acids and Cy-3 bis-amine with diacylchlorides

The synthesis and fluorescence behaviour of a range of amphiphilic poly(l-lysine co-bis-amine-Cy-3 iso-phthalamide) polymers that incorporate low levels of Cy-3 dye co-monomer (0.5-2.1% (w/w)) in their backbone have been investigated in aqueous solution over a range of pH values. The desired functionality of these biocompatible, hydrophobically modified polyelectrolytes was achieved by incorporating pendant hydrophilic carboxyl groups along the polymer backbone, via the l-lysine moiety, balanced by a degree of hydrophobicity introduced via the iso-phthaloyl moiety. Thus, the polymer changes from an extended conformation at high degrees of ionisation to a compact conformation stabilised by hydrophobic association at low degrees of ionisation and eventually precipitates from solution. At intermediate degrees of ionisation, such polymers exhibit amphiphilic properties. A bis-functional cyanine fluorophore derivative, co-polymerised within the polymer backbone, is demonstrated to act as a fluorescent reporter on the conformational state of the polymer. The materials have higher intrinsic fluorescence intensity per fluorophore monomer over a broad range of concentrations than bis-amine Cy-3 and their maximum fluorescence intensity is up to eight fold higher than the maximum intensity of bis-amine Cy-3, which is limited by quenching. It is also shown that the free fluorophore can be used to probe the conformation of unlabelled poly(l-lysine iso-phthalamide) through electrostatic interaction with the polymer. The technique allows rapid spectrophotometric determination of polymer conformation and offers the potential of an environmentally sensitive molecular pH probe for in vivo use.     

Stabilization of photo-induced radicals in hematoporphyrin-IX-doped chitosan film

Induction and stabilization of free radicals were investigated in hematoporphyrin-IX (Hp)-doped chitosan (Hp-Ch) film by electron spin resonance (ESR) following photo-irradiation. Induced radicals were more stable in chitosan and 6-O-carboxymethyl chitin films than in carboxymethyl cellulose and sodium alginate films. Hydroxyl groups on D-glucosamine residues in chitosan are suggested as participating in accepting radicals, since spin trapping was absorbed in ESR spectra of Hp-Ch film by the use of oxygen sensitive spin trapping reagent. An induced circular dichroism spectrum was observed only for Hp-doped chitosan film over a range 360–450 nm among seven pairs of polymers and dyes; it is suggested that Hp molecules are arranged parallel along the carbohydrate backbone of chitosan, resulting in the highest acceptance of photo-induced radicals in the polymer film.     

Functional polymers for colloidal applications. IV. Aggregate formation of lipophile-grafted water-soluble copolymers in aqueous solutions

A water-soluble styrene–maleic anydride copolymer (SMA) is derivatized with different lipophilic groups, butylamine and dodecylamine, with different degrees of substitution (5, 15, and 30%). These lipophile-grafted SMAs are water-soluble, and their solutions are transparent. A plot of I₁/I₃ as a function of polymer concentrations indicates the extent of aggregate formation. Surface tension methods also verify the existence of aggregates. It is found that the aggregates begin to form at concentrations below that of the polymer transfer to the air–water interface. The plots of I₁/I₃ as a function of polymer concentrations for SMAs of different molecular weights derivatized with different lipophile with varying degrees of substitution show that the polymers with a higher degree of substitution and lower molecular weights aggregate at lower concentrations. Polymers substituted by butylamine form aggregates at a very high concentration, independent of the degree of sub-stitution. These phenomena are interpreted in terms of hydrophobic interactions as in micelles formed from surfactants. The higher degree of dodecyl-substituted SMA solubilizes pyrene at higher concentrations, and these pyrene solubilized solutions show pyrene excimer emission spectra. These emission spectra are used to characterize the relative size and hydrophobicity of aggregates. © 1993 John Wiley & Sons, Inc.     

Preparation and study of functionalized polymers containing pendent pesticide-active groups

A number of pesticide monomers containing pentachlorophenol as active group attached to vinyl groups, through oxyethylene as spacer group, have been prepared. The resulting monomers were homopolymerized under free-radical conditions and also copolymerized with styrene and 2-(2-hydroxyethoxy)ethyl methacrylate to introduce hydrophobic and hydrophilic nature to the resulting polymers. In addition, crosslinked copolymers were prepared by using different ratios of divinylbenzene. Data on the pentachlorophenol released through hydrolysis show that the degree of crosslinking, the hydrophilicity and the spacer group, as determined by the chemical structure and the polymer composition, as well as the pH, time and temperature appear to be major factors governing the rate at which a given polymer undergoes hydrolysis.     

Main chain and segmental dynamics of semi interpenetrating polymer networks based on polyisoprene and poly(methyl methacrylate)

Main chain and segmental dynamics of polyisoprene (PI) and poly(methyl methacrylate) (PMMA) chains in semi IPNs were systematically studied over a wide range of temperatures (above and below T_g of both polymers) as a function of composition, crosslink density, and molecular weight. The immiscible polymers retained most of its characteristic molecular motion; however, the semi IPN synthesis resulted in dramatic changes in the motional behavior of both polymers due to the molecular level interpenetration between two polymer chains. ESR spin probe method was found to be sensitive to the concentration changes of PMMA in semi IPNs. Low temperature spectra showed the characteristics of rigid limit spectra, and in the range of 293-373 K, complex spectra were obtained with the slow component mostly arising out of the PMMA rich regions and fast component from the PI phase. We found that the rigid PMMA chains closely interpenetrated into the highly mobile PI network imparts motional restriction in nearby PI chains, and the highly mobile PI chains induce some degree of flexibility in highly rigid PMMA chains. Molecular level interchain mixing was found to be more efficient at a PMMA concentration of 35 wt.%. Moreover, the strong interphase formed in the above mentioned semi IPN contributed to the large slow component in the ESR spectra at higher temperature. The shape of the spectra along with the data obtained from the simulations of spectra was correlated to the morphology of the semi IPNs. The correlation time measurement detected the motional region associated with the glass transition of PI and PMMA, and these regions were found to follow the same pattern of shifts in α-relaxation of PI and PMMA observed in DMA analysis. Activation energies associated with the T_g regions were also calculated. T_50G was found to correlate with the T_g of PMMA, and the volume of polymer segments undergoing glass transitional motion was calculated to be 1.7 nm³. C-13 T_1ρ measurements of PMMA carbons indicate that the molecular level interactions were strong in semi IPN irrespective of the immiscible nature of polymers. The motional characteristics of H atoms attached to carbon atoms in both polymers were analyzed using 2D WISE NMR. Main relaxations of both components shifted inward, and both SEM and TEM analysis showed the development of a nanometer - sized morphology in the case of highly crosslinked semi IPN.     

Some surface properties of plasma polymers prepared from hexamethyldisilazane and diethylaminotrimethylsilane

Plasma polymers from some silyl amines were produced by the radio frequency of 13.56 MHz, and the surface properties were investigated. The polymers were revealed to be as hydrophobic as a plasma polymer from tetramethylsilane, which does not contain nitrogen. The hydrophobicity became effective at around 50 Å thicknesses of these polymer layers deposited on micro-slide glass. These polymers have gradually become comparatively hydrophilic with the aging. The change of wettability is probably due to the oxidation of these surface layers to form oxides and peroxides, which are more hydrophilic. The hydrophobic character of silyl amine plasma polymers could be explained by the lack of amines and/or amides in these polymers, as observed with ATR-IR and ESCA spectra. These spectroscopic observations also suggest that nitrogen is a more fragile element in plasma than carbon or silicon in the silyl amines.     

Enhancement of water barrier properties of cassava starch-based biodegradable films using silica particles

Biodegradable films are used in a variety of applications, including packaging. However, their use is limited due to their high moisture and water sensitivity. In this work, cassava starch (CS) was blended with poly(vinyl alcohol) (PVA). Silica particles (SiO₂) were incorporated to increase the hydrophobicity of the blend by intermolecular interaction through hydrogen bonding between the three components. Instead of a plasticizer or crosslinker, a small amount of triethylamine was added to eliminate residual acetate groups in PVA. The miscibility of CS and PVA phases was confirmed by smooth fracture surfaces and a single glass transition temperature. When SiO₂ content was below 5% (wt), the particles were well dispersed in a continuous phase of polymer matrix. At this loading of SiO₂, the increase in tensile strength was as high as 170% and in elongation-at-break, 250%. All loadings of SiO₂ increased thermal stability of the blend films because silanol groups on the surface of SiO₂ particles formed effective interfacial interactions with hydroxyl groups of the polymers. These interactions also prevented the ingress of water molecules, significantly increasing the hydrophobicity of the films. The water contact angle increased as high as 113° and moisture absorbency and water solubility were low. These highly hydrophobic, photodegradable, biodegradable CS/PVA/SiO₂ films show great potential as a low-cost, eco-friendly material.

     

Nanoconjugates of methacrylic polymers: Synthesis,characterization, and immobilization to leather

Imparting superhydrophobicity to surfaces has direct implications for developing water-repellent materials. Most hydrophobic materials cannot be applied directly to specific surfaces like leather because of noncompatibility. Although methacrylic polymers are compatible to leather, their inherent hydrophilic characteristics make it challenging to use for introducing hydrophobicity or superhydrophobicity. In this article, we present a strategy of introducing hydrophobicity in various degrees as well as superhydrophobicity to different surfaces, particularly leather and glass surfaces by using conjugates of methacrylic polymers and various carbon nanomaterials. The covalent functionalization of methacrylate polymers with carbon nanotubes and fullerenes was performed by radical polymerization in the presence or absence of chain transfer agents (CTAs). CTA was used during polymerization to introduce carboxylic acid group, necessary for chromium-assisted binding to leather to avoid leaching. A balance between the compatibility of the polymer nanoconjugates with the leather and the amount necessary for coating stabilization was studied by a rheometer. While water contact angle measurement indicated the mild hydrophobicity in most cases, we were delighted to observe superhydrophobicity in one case presumably due to increased roughness because of the presence of specific nanomaterial to overcome inherent hydrophilicity of methacrylic polymers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48627.     

Effect of thermal oxidative ageing on the morphology of natural rubber networks as viewed by ESR

The change of network morphology of unfilled sulfur crosslinked natural rubber exposed to thermal oxidative ageing has been studied. Three model networks with different sulfur contents (efficient network, semi‐efficient and conventional vulcanizate) have been analysed by applying spin probe ESR, equilibrium swelling measurements and mechanical measurements. By combining the density distribution deduced from the complex ESR spectra and the equilibrium swelling density, it is shown that the major network changes occur in the networks with predominantly polysulfidic bonds (conventional network) after 96 h of ageing at 373 K. The effect of ageing on the network with predominantly monosulfidic bonds is much less pronounced. Both effects (main chain scission and additional local crosslinking) have been analysed in the course of prolonged ageing up to 240 h. A correlation between network structure and its mechanical performance is established. © 2000 Society of Chemical Industry     

Synthesis of poly(vinyl benzal) from poly(vinyl alcohol) in nonaqueous medium

Poly(vinyl alcohol) (PVA) is soluble only in water and so some important derivatives like esters cannot be prepared from PVA. The 100% conversion of PVA to acetal is also elusive as there is strong intermolecular and intramolecular hydrogen bonding. However, PVA can be dissolved in a nonaqueous medium in the presence of a small amount of C₂H₅NO₃ · DMSO(EN · DMSO) and so a maximum extent of conversion may be possible. Here, we report the preparation of poly(vinyl benzal) (PVB) by acid-catalyzed homogeneous acetalization of PVA with benzaldehyde in a nonaqueous medium. The formation of PVB was confirmed by IR and ¹H-NMR spectra. The molecular mass of the polymer was determined by the GPC method. The PVB prepared had a degree of acetalization of 95 mol%. The glass transition temperature, T_g was measured from differential scanning calorimetric (DSC) thermograms. Thermal stabilities were checked by thermogravimetric analysis (TGA) and differential thermogravimetry (DTG). A possible mechanism of three-step thermal decomposition of PVB is proposed. © 1996 John Wiley & Sons, Inc.     

An inelastic electron tunnelling spectroscopy (IETS) study of poly(vinylacetate) poly(methyl methacrylate) and poly(vinylalcohol) adsorbed on aluminium oxide

IETS is used to investigate the adsorption of poly(vinylacetate) (PVA), poly(methylmethacrylate) (PMMA), and poly(vinylalcohol) (PVOH) on aluminium oxide. These polymers are of interest in the field of adhesion science, and until now synthetic macromolecules have not been studied in this way. Both commercially available polymers and those synthesized in our laboratory have been used. On the basis of IET spectra presented here, and existing i.r. spectra it is believed that PMMA and PVA undergo ester cleavage at the oxide surface leading to their subsequent adsorption. For PMMA this is thought to be via carboxylate anions generated on the polymer side groups, while PVA is expected to be adsorbed as PVOH. Bonding of PVOH to the oxide is not fully understood, but may occur by the formation of an AlOC bridge. Another possibility for the above polymers, that of intermolecular hydrogen bonding between polar polymer side groups, and adsorbed hydroxyl species present on the oxide surface, cannot be ruled out.     

Permeable domains of segmented polyurethanes studied with paramagnetic spin probe

Studies on the permeable regions of the dense polyurethane-based membranes were performed by electron spin resonance spectroscopy (ESR) using TEMPO spin probe incorporated into the membrane via diffusion from the vapour phase. The ESR spectra were measured as a function of temperature and microwave power for polyurethanes (PU) varying in the molecular structure and morphology. It was found that the TEMPO spin probe exhibited anisotropic rotation whose anisotropy increased as temperature decreased and was more pronounced for PU with shorter soft segments. The simplified method was used to obtain apparent correlation time τ_c enabling the comparison of the polyurethanes studied. This approach was based on the Arrhenius relation of τ_c vs. 1/T determined from motionally narrowed ESR spectra and on the assumption that this behaviour prevails over a broader temperature range at temperatures generally greater than T_g of a given polymer.     

Thermal,mechanical, and surface properties of poly(vinyl alcohol) (PVA) polymer modified cementitious composites for sustainable development

This study aimed to investigate the effect of poly(vinyl alcohol) (PVA) polymer on the thermal, mechanical, and surface properties on cementitious composites for sustainable development. Thermal properties of the PVA‐modified cement paste, including thermal insulation and energy absorption ability, were first studied and correlated with the porosity and microstructures. The experimental results indicated that the thermal conductivity of cement paste can be greatly reduced by 42.9% with 2.0 wt % addition of PVA due to the more porous structure. However, at the same time, more thermal energy can be captured and concentrated at the surface of cement paste with the increasing amount of PVA, causing an increased thermal load and a negative effect on thermal insulating efficiency of cement paste. The contradictory effect of PVA on thermal properties of cement paste should be balanced before it is used as a foaming modifier to fabricate cementitious composites with thermal insulation. In addition, the contact angle measurement revealed that PVA can be used as an effective additive to improve the hydrophobicity of cement‐based materials. Only 3.0% PVA can turn the surface nature from hydrophilicity to hydrophobicity for cement paste, which benefited to the development of self‐cleaning cementitious composites. Finally, the mechanical properties of the PVA‐modified cement paste, especially for the tensile strength that has been rarely reported, were investigated and correlated with its thermal and surface properties. Due to the compensative effects of irregular packing, formation of PVA films and microcracks, tensile strength of cement paste can be improved by 23.5% with a small scarifying of the compressive strength by adding 2.0% of PVA. In conclusion, the PVA‐modified cement‐based materials with lower thermal conductivity, hydrophobic surface nature and enhanced mechanical properties have a great potential to satisfy the high requirements in developing sustainable infrastructure. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46177.     

Polyisoprene matrix inhomogeneity studied by nitroxide spin probe motion

Summary The spin probe ESR method was applied to study natural rubber and synthetic polyisoprenes with different content of cis-configuration over a wide temperature range. The ESR spectra of natural rubber near and above the glass transition indicate the existence of two distinctly different mobilities as a consequence of the spin probe distribution in sol and gel phase. The results show that the spin probe method can yield information about the inhomogeneity of the polyisoprene matrix and the character of gel phase.     

Thermal properties of hydrophobically modified methacrylic acid–ethyl acrylate copolymer solutions

The thermal behavior of a water‐soluble associating polymer system, hydrophobically modified alkali‐soluble emulsion (HASE) polymer, was investigated. This polymer contains a methacrylic acid–ethyl acrylate copolymer backbone with 1 mol % of pendant hydrophobic groups grafted to it. The thermal behavior of the HASE polymer exhibits different trends compared to the hydrophobic ethoxylated urethane (HEUR) system. The lifetime of the hydrophobic junction of the HASE polymer increases with temperature due to the increase in the entropy of the system. However, the structural relaxation time decreases with temperature, caused by the enhanced Brownian dynamics of polymer chains. The relaxation behavior of HASE polymers is either governed by the lifetime of the hydrophobic junction, the structural relaxation time, or a combination of both, depending on the degree of network formation and temperature. Temperature studies indicated that the transient network theory proposed by Tanaka and Edwards is inadequate for describing the activation process of hydrophobic junctions in the HASE associative polymer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 604–612, 2004