Properties of poly(vinyl alcohol)-graft-polyacrylamide copolymers depending on the graft length. 3. Benzene solubilization by solutions of the copolymer

The peculiarities of poly(vinyl alcohol)-graft-polyacrylamide copolymers (PVA-g-PAA), which are characterized by the equal average number (N=9), but various molecular weight (or length) of graft chains, in comparison with individual PAA and PVA, were investigated in aqueous medium. Sharp rise in benzene solubilization in PVA-g-PAA solutions at M_PAA higher than 4.3·10⁵ has been established. It was shown that such effect is stipulated by the destruction of intramolecular polymer-polymer complex in the copolymer and increasing the benzene binding to separate PVA-g-PAA groups by means of hydrogen bonds. The changes in the PVA-g-PAA solubilizing ability as the function of temperature were also investigated. The obtained results are discussed from the point of view of conformational transitions of intramolecular polymer-polymer complexes (intraPPC), which exist in copolymers, in dependence on the length of graft chains.     

About the compatibility of polymer components in polymer complexes based on poly(acrylamide) and poly(vinyl alcohol)

The issue of applying the usual concepts of polymer compatibility to nonstoichiometric PVA/PAA mixtures of chemically complementary poly(vinyl alcohol) and poly(acrylamide), which form in water solution InterPC (intermolecular polymer complex) stabilyzed by H‐bonds, and PAA to PVA graft copolymers (PVA‐PAA_N) with different grafted chains number N, that are IntraPC (intramolecular polymer complexes) is discussed. PVA and PAA are compatible on molecular level. At the same time PVA/PAA mixture (50/50 W/W) is characterized by heterogeneous structure consists of InterPC with ϕ_char=9g_PVA/g_PAA and the excess of unconnected PAA. In the case of IntraPC, yet, only PVA‐PAA_N, where N=25, is characterized by a single glass transition temperature (Tg). At larger values of N separate PAA domains form giving rise to the corresponding Tg. These results are discussed in view of IntraPC structure peculiarities as a function of N investigated by IR spectroscopy.     

Novel Polymer Clusters with a Uniform Chain Density

The thermal decomposition of polystyrene clusters prepared by using 4‐methacryloyloxy‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl as a branching agent was studied. The weight‐average molar mass (M̄_w) and the radius of gyration (R_g) of the resultant clusters can be scaled as M̄_w ∝︁ R_g^{3.0 ± 0.1}, revealing that these clusters have a uniform chain density. Moreover, the dynamic properties of such clusters converge unexpectedly faster than the static properties as the molar mass decreases.     

Conformational changes in poly(vinyl alcohol)-graft-polyacrylamide in aqueous solutions vs graft content

Conformational changes have been studied in intramolecular polymer-polymer complexes (intraPC) of graft copolymers of poly(acrylamide) and poly(vinyl alcohol) (PVA-g-PAA) with various numbers of grafts (4-42) per molecule as a function of temperature and copolymer concentration. It is shown that the magnitude of conformational change depends on the grafts content while the temperature range over which the conformation changes occur is essentially determined by copolymer concentration. The conformational changes are reversible on heating and cooling.     

Narrow-polydispersity polystyrene/poly[styrene-co-(butyl methacrylate)] block copolymers by an N-oxyl mediated free radical polymerization process

Polystyrene/poly[styrene-co-(butyl methacrylate)] block copolymers with controlled molecular weights and with polydispersities generally below M̄_w/M̄_n = 1,45 and partially as low as M̄_w/M̄_n = 1,19 were synthesized by a free radical bulk copolymerization using a 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO)-capped polystyrene macroinitiator. The influence of the macroinitiator concentration on the block copolymerization was studied. The polymerization rates are independent of the macroinitiator concentration and are close to that of thermally self-initiated styrene/butyl methacrylate copolymerizations showing the important role of self-initiation for N-oxyl mediated free radical polymerizations.     

Preparation of polysulfone‐g‐poly(N‐isopropylacrylamide) graft copolymers through atom transfer radical polymerization and formation of temperature‐responsive nanoparticles

Polysulfone‐g‐poly(N‐isopropylacrylamide) (PSf‐g‐PNIPAAm) graft copolymers were prepared from atom transfer radical polymerization of NIPAAm using chloromethylated PSf as a macro‐initiator. The chain lengths of PNIPAAm of the graft copolymers were controllable with polymerization reaction time. The chemical structures of the graft copolymers were characterized with FTIR, NMR, and elemental analysis and their amphiphilic characteristics were examined and discussed. The PSf‐g‐PNIPAAm graft copolymers and the nanoparticles made from the graft copolymers exhibited repeatable temperature‐responsive properties in heating–cooling cycles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4756–4765, 2008     

Studies on the self-assembly behavior of the amphiphilic block copolymer of PSt-b-PAA in apolar solvents with polar fluorescent probe

The block copolymer of polystyrene-b-poly(butyl acrylate) (PSt-b-PBA) with a well-defined structure was synthesized by atom transfer radical polymerization (ATRP); its structure was characterized, and the living polymerization was also validated by gel permeation chromatography, Fourier transform infrared, and ¹H NMR measurements. Then, the amphiphilic block copolymer of polystyrene-b-poly(acrylic acid) (PSt-b-PAA) has been prepared by hydrolysis of PSt-b-PBA, and copolymers of PSt-b-PAA with longer PSt blocks and shorter PAA blocks were obtained by controlling the conditions of ATRP polymerization. The reversed micelle solution of PSt-b-PAA in toluene was prepared by using the single-solvent dissolving method, and the reverse micellization behavior of PSt-b-PAA in toluene was mainly investigated in this paper. The fluorescent probe technique was used by using polar fluorescence compound N-(1-Naphthyl)ethylenediamine dihydrochloride (NEAH) as a polar fluorescent probe to study the reverse micellization behavior of PSt-b-PAA. It was found that the reverse micellization behaviors of PSt-b-PAA in toluene can be clearly revealed by using NEAH as a polar fluorescence probe, and the critical micelle concentrations (cmcs) can be well displayed. The experimental results showed that the self-assembling behavior of PSt-b-PAA in toluene depends apparently on the microstructure of the macromolecules and is also influenced by the temperature. For the copolymers of PSt-b-PAA with the same length of hydrophobic PSt blocks, the copolymer with a longer hydrophilic block PAA has lower cmc, and at higher temperature, the copolymer has lower cmc.     

Synthesis,characterization, and swelling behaviors of chitosan‐g‐poly(acrylic acid)/poly(vinyl alcohol) semi‐IPN superabsorbent hydrogels

A series of granulated semi‐interpenetrating polymer network (semi‐IPN) superabsorbent hydrogels composed of chitosan‐g‐poly(acrylic acid) (CTS‐g‐PAA) and poly(vinyl alcohol) (PVA) were prepared by solution polymerization using ammonium persulfate (APS) as an initiator and N,N′‐methylenebisacrylamide (MBA) as a crosslinker. The effects of reaction conditions such as the concentration of MBA, the weight ratio of AA to CTS, and the content of PVA on water absorbency were investigated. Infrared (IR) spectra and differential scanning calorimetry (DSC) analyses confirmed that AA had been grafted onto CTS backbone, and PVA semi‐interpenetrating into CTS‐g‐PAA networks. SEM analyses indicated that CTS‐g‐PAA/PVA has improved porous surface and PVA was uniformly dispersed in CTS‐g‐PAA network. The semi‐IPN hydrogel containing 10 wt% PVA shows the highest water absorbency of 353 and 53 g g^?1 in distilled water and 0.9 wt% NaCl solution, respectively. Swelling behaviors revealed that the introduction of PVA could improve the swelling rate and enhance the pH stability of the superabsorbent hydrogel. Copyright © 2009 John Wiley & Sons, Ltd.     

Swelling behavior of thermosensitive polyvinyl alcohol-graft-N-isopropylacrylamide copolymer membranes containing carboxyl groups and properties of their polymer solutions

The thermosensitive polyvinyl alcohol-graft-N-isopropylacrylamide–methacrylic acid (PVA-g-NIPAAm–MAc) terpolymer membranes containing carboxyl groups were prepared. The swelling ratios of the membranes were measured at various temperatures. The temperature dependence of the swelling ratios of the terpolymer membranes was different from that of PVA-g-NIPAAm copolymer membranes. The swelling ratios of PVA-g-NIPAAm–MAc (5–15) (wt % in feed) increased with increasing temperature up to 35–38°C, then decreased. However, the swelling ratio of PVA-g-NIPAAm–MAc (30–50) terpolymer membranes did not depend on temperature in the temperature range of 10–48°C. To clarify the swelling behavior of the PVA-g-NIPAAm–MAc terpolymer membranes, the swelling ratios of the PVA-g-NIPAAm–Acrylic acid (AAc) terpolymer membranes, the viscosity, and optical density of various polymer solutions were measured. The different swelling behavior of PVA-g-NIPAAm–MAc (or AAc) terpolymer membranes from that of PVA–NIPAAm copolymer membranes was thought to be due to hydrogen bonding between amide groups in NIPAAm moieties and carboxyl groups in MAc (or AAc) moieties in the terpolymer membranes and the difference of swelling behavior between PVA-g-NIPAAm–MAc and PVA-g-NIPAAm–AAc terpolymer membranes was thought to be brought about by hydrophobic interaction due to methyl groups in PVA-g-NIPAAm–MAc terpolymer membranes. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3097–3106, 1998     

Synthesis and characterization of polytulipalin‐g‐polylactide copolymers

Graft copolymers of poly(tulipalin A) (PT) and poly(DL‐lactide) (PDLLA) (PT‐g‐PDLLA) having various graft lengths and ratios were synthesized by free‐radical copolymerization of α‐methylene‐γ‐butyrolactone (MBL) and PDLLA macromonomers (HEMA‐PDLLA) terminated by 2‐hydroxyethyl methacrylate (HEMA)‐terminated. HEMA‐PDLLA were synthesized by ring opening polymerization (ROP) of DL‐lactide in the presence of HEMA. Both HEMA‐PDLLA and the copolymers were characterized by NMR spectroscopy and gel permeation chromatography (GPC). The thermal properties of the graft copolymers were found to depend on the graft length and the ratio. The copolymers consisting of PDLLA side chains of M_n = 500 Da showed a single T_g between T_gs of the two component polymers, suggesting a miscible state of PT and PDLLA. In contrast, the copolymers consisting of PDLLA side chains of M_n = 1100, 2000, and 7000 Da showed two isolated T_g, suggesting two segregated domains. The AFM phase images of the copolymers supported the single and phase‐separated morphologies for the former and latter systems, respectively. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Controlled polymerization of ϵ-caprolactone -from macromolecules to microspheres

Pseudoanionic polymerization of ϵ-caprolactone (CL), initiated with dialkylaluminum alkoxides, was used for the tailored synthesis of poly(CL) with M̄_n ≤ 100 000 and M̄_w /M̄_n < 1. 20. Macromolecules with functional groups at one or at both ends were obtained in this way. Controlled polymerization of CL allowed to prepare poly(dodecyl acrylate)-g-poly(ϵ-caprolactone) (poly(DAC)-g-poly(CL)) with well defined poly(CL) grafts. These copolymers were used as the surface active agents for the direct synthesis of poly(CL) microspheres. The number average diameter (D̄_n ) of poly(CL) microspheres varied from 0.628 μm to 0.94 μm and the diameter polydispersity (D̄_v /D̄_n ) varied from 1.038 to 1.26, depending on the composition of poly(DAC)-g-poly(CL). Human serum albumin (HSA) and human gamma globulins (_γ G) were attached to the poly(CL) microspheres. The maximal surface concentrations of HSA and _γ G adsorbed onto the microspheres were equal to 9·10⁻⁴ g/m² and 2.0·10⁻³ g/m² respectively.     

Synthesis and characterization of maleimide polymers with pendant pyrazole groups. IV. Copolymerization of pyrazole-modified maleimides with vinyl ethers

The synthesis of maleimides that have pyrazolic or bipyrazolic pendant groups is described. Their homopolymerization and their copolymerization with 2-chloroethyl vinyl ether (CEVE) is reported. The homopolymerizations of such maleimides were performed under various conditions and led to low molecular-weight polymers. However, alternating copolymers were obtained from CEVE as comonomers whatever the monomers feed compositions. A similar behavior was also observed for maleimides that do not exhibit any spacer, whereas for bulky vinyl ethers, random copolymers were produced. A comparison of the thermal behavior between these copolymers (glass transition temperatures, T_g, and decomposition temperatures) and other copolymers having different spacers between the nitrogenated cycles and the chain are related. Thus, an important decrease of T_g, was observed when C₃H₆CO₂CH₂ groups were used as the spacer instead of methylene groups. Moreover, the thermal weakness of these copolymers may come from the substituents of the vinyl ether and is discussed. © 1994 John Wiley & Sons, Inc.     

Radical copolymerization of N-alkylmaleimides with isobutene and the properties of the resulting alternating copolymers

Radical copolymerization of N-methylmaleimide (MeMI) as well as other N-alkylmaleimides (RMI) and isobutene (IB) was carried out with 2,2′-azobis(isobutyronitrile) as an initiator at 60°C. The initial rate of the copolymerization (R_p) was dependent on the monomer composition and was maximum at the 40 mol % of MeMI in the feed. A solvent effect on the R_p and the monomer reactivity ratio was observed in this copolymerization system, i.e., copolymerization in chloroform produced a higher R_p and an alternating tendency compared with those in dioxane (r_MeMI = 0.14, r_1B = 0 in chloroform and r_MeMI = 0.47, r_1B = 0 in dioxane). The alternating copolymer of RMI and IB shows a high glass transition temperature (T_g) and excellent thermal stability, e.g., the T_g and the thermal decomposition temperature (T_d) were 152 and 363°C, respectively, for the alternating copolymer of MeMI and IB. Both the T_g and T_d increased as the concentration of the MeMI unit in the copolymers increased. Colorless transparent sheets were obtained from press molding the alternating copolymers. They showed excellent mechanical and optical properties. © 1996 John Wiley & Sons, Inc.     

Compacting of poly(acrylamide)‐poly(vinyl alcohol) grafted copolymers in aqueous solution of phenol and its effect in the copolymers films structure

The interaction of phenol with graft copolymers of poly(acrylamide) to poly(vinyl alcohol) (PVA‐PAA_N) forming intramolecular polycomplexes (Intra PC), and also with PAA, is investigated by the methods of gel chromatography, viscometry, UV and IR spectroscopy. It is shown, that phenol connection with polymers is weak and carried out on the equilibrium mechanism. Under phenol influence the effect of compacting of polymer macromolecules is observed. It is revealed, in particular, by change of the ratio between different H‐bonds structures in polymer films obtained at phenol presence. PVA‐PAA_N connect phenol more effectively, than PAA; the quantity of bound phenol grows with N.     

Glass Transition Temperatures of Poly[(methyl methacrylate)‐co‐(butyl acrylate)]s Synthesized by Atom‐Transfer Radical Polymerization

Glass transition temperatures T_g of methyl methacrylate/butyl acrylate copolymers obtained by means of atom‐transfer radical polymerization are measured using differential scanning calorimetry. Due the nature of this polymerization method an increase in molecular weight is produced as the reaction progresses, which gives rise to an increase in T_g. Simultaneously, a composition gradient with the enrichment of butyl acrylate causes a decrease in T_g. These opposite effects almost compensate each other and, therefore, no influence on the molecular weight at M̄_n < 10000 is found. This fact allows the application of the Johnston's equation and the Mayo‐Lewis terminal model to describe and predict the variation in T_g with copolymer conversion for the copolymers and under the experimental conditions investigated.     

Synthesis and characterization of amphiphilic block–graft MPEG‐b‐(PαN3CL‐g‐alkyne) degradable copolymers by ring‐opening polymerization and click chemistry

A straightforward strategy is proposed for the synthesis of novel, amphiphilic block–graft MPEG‐b‐(PαN₃CL‐g‐alkyne) degradable copolymers. First, the ring‐opening polymerization of α‐chloro‐ε‐caprolactone (αClCL) was initiated by hydroxy‐terminated macroinitiator monomethoxy poly(ethylene glycol) (MPEG) with SnOct₂ as the catalyst. In a second step, pendent chlorides were converted into azides by the reaction with sodium azide. Finally, various kinds of terminal alkynes were reacted with pendent azides by copper‐catalyzed Huisgen's 1,3‐dipolar cycloaddition, and thus a “click” reaction. These copolymers were characterized by differential scanning calorimetry (DSC), ¹H NMR, IR, and gel permeation chromatography. By fixing the length of the MPEG block and increasing the length of PαClCL (or PαN₃CL) block, an increase tendency in T_gs was observed. However, the copolymers of MPEG‐b‐PαClCL and MPEG‐b‐PαN₃CL were semicrystalline when the M_n of MPEG was above 2000 g mol^?1. The block–graft copolymers formed micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 1.4–12.0 mg L^?1 depending on the composition of polymers. The lengths of hydrophilic segment influence the shape of the micelle. The mean hydrodynamic diameters of the micelles from dynamic light scattering were in the range of 90–160 nm. In vitro hydrolytic degradation of block–graft copolymers is faster than the corresponding block copolymers. The drug entrapment efficiency and the drug loading content of micelles depending on the composition of block–graft polymers were described. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4320–4331, 2008     

ATNRC and SET‐NRC synthesis of PtBA‐g‐PEO well‐defined amphiphilic graft copolymers

A series of new well‐defined amphiphilic graft copolymers containing hydrophobic poly(tert‐butyl acrylate) backbone and hydrophilic poly(ethylene oxide) side chains were reported. Reversible addition‐fragmentation chain transfer homopolymerization of tert‐butyl 2‐((2‐bromopropanoyloxy)methyl)acrylate was first performed to afford a well‐defined backbone with a narrow molecular weight distribution (M_w/M_n = 1.07). The target poly(tert‐butyl acrylate)‐g‐poly(ethylene oxide) (PtBA‐g‐PEO) graft copolymers with low polydispersities (M_w/M_n = 1.18–1.26) were then synthesized by atom transfer nitroxide radical coupling or single electron transfer‐nitroxide radical coupling reaction using CuBr(Cu)/PMDETA as catalytic system. Fluorescence probe technique was employed to determine the critical micelle concentrations (cmc) of the obtained amphiphilic graft copolymers in aqueous media. Furthermore, PAA‐g‐PEO graft copolymers were obtained by selective acidic hydrolysis of hydrophobic PtBA backbone while PEO side chains kept inert. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

The grafting of acrylamide onto poly(ε‐caprolactone) and poly(1,5‐dioxepan‐2‐one) using electron beam preirradiation. II. An in vitro degradation study on grafted poly(ε‐caprolactone)

Acrylamide was graft polymerized onto the surface of a biodegradable semicrystalline polyester, poly(ε‐caprolactone). Electron beam irradiation at a dose of 5 Mrad was used to generate initiating species in the polyester. The degradation in vitro at pH 7.4 and 37°C in a phosphate buffer solution was studied for untreated, irradiated and acrylamide‐grafted polymers. In the case of poly(ε‐caprolactone), all materials showed similar behavior in terms of weight loss. No significant decrease in weight was observed up to 40 weeks, after which the loss of weight accelerated. The main differences in degradation behavior were found for the average molecular weights, M̄_n and M̄_w. Virgin poly(ε‐caprolactone) maintained M̄_n and M̄_w up to about 40 weeks, whereas the irradiated and grafted poly(ε‐caprolactone) showed similar continuous declines in M̄_n and M̄_w throughout the degradation period. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1651–1657, 1999     

Polyurethanes containing sulfur. I. New thermoplastic polyurethanes with benzophenone unit in their structure

New thermoplastic nonsegmented thiopolyurethanes were obtained from the low-melting aliphatic–aromatic thiodiols 4,4′-bis(2-hydroxyethylthiomethyl)benzophenone (BHEB), 4,4′-bis(3-hydroxypropylthiomethyl)benzophenone (BHPB), and 4,4′-bis(6-hydroxyhexylthiomethyl)benzenophenone(BHHB) as well as hexamethylene diisocyanate (HDI), both by melt and solution polymerization with dibutyltin dilaurate as the catalyst. The effect of various solvents on molecular-weight values was examined. The polymers with the highest reduced viscosities (0.63–0.88 dL/g) were obtained when the polymerization was carried out in a solution of tetrachloroethane, N,N-dimethylacetamide, and N,N-dimethylacetamide or N,N-dimethylformamide for BHEB-, BHPB-, and BHHB-derived polyurethanes, respectively. These polymers with a partially crystalline structure showed glass-transition temperatures (T_g) in the range of −1 to 39 °C, melting temperatures (T_m) in the range of 107 to 124 °C, and thermal stabilities up to 230 to 240 °C. The BHEB-derived polyurethane is a low-elasticity material with high tensile strength (ca. 50 MPa), whereas the BHPB- and BHHB-derived polyurethanes are more elastic, showing yield stress at approximately 16 MPa. We also obtained segmented polyurethanes by using BHHB, HDI, and 20 to 80 mol % poly(oxytetramethylene) glycol (PTMG) of M̄_n = 1000 as the soft segment. These are high-molecular thermoplastic elastomers that show a partially crystalline structure. Thermal properties were investigated by thermogravimetric analysis and differential scanning calorimetry. The increase in PTMG content decreases the definite T_g and increases the solubility of the polymers. These segmented polyurethanes exhibit the definite T_g (−67 to −62 °C) nearly independent of the hard-segment content up to approximately 50 wt %, indicating the existence of mainly phase-separated soft and hard segments. Shore A/D hardness and tensile properties were also determined. As the PTMG content increases, the hardness, modulus of elasticity, and tensile strength decrease, whereas elongation at break increases. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4140–4150, 1999     

Characterization and degradation of the poly(methylphenylsiloxane)–poly(methyl methacrylate) graft copolymer

Poly(methylphenylsiloxane)–poly(methyl methacrylate) graft copolymers (PSXE-g-PMMA) were prepared by condensation reaction of poly(methylphenylsiloxane)-containing epoxy resin (PSXE) with carboxyl-terminated poly(methyl methacrylate) (PMMA), and they were characterized by gel permeation chromatography (GPC), infrared (IR), and ²⁹Si and ¹³C nuclear magnetic resonance (NMR). The microstructure of the PSXE-g-PMMA graft copolymer was investigated by proton spin–spin relaxation T₂ measurements. The thermal stability and apparent activation energy for thermal degradation of these copolymers were studied by thermogravimetry and compared with unmodified PMMA. The incorporation of poly(methylphenylsiloxane) segments in graft copolymers improved thermal stability of PMMA and enhanced the activation energy for thermal degradation of PMMA. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2521–2530, 1998