Ionic π‐Conjugated Polyelectrolytes by Catalyst Free Polymerization of Bis(pyridyl)acetylenes and Bis[(pyridyl)ethynyl]benzenes

The spontaneous, catalyst free polymerization of four monomers of the bis(pyridyl)acetylene and bis[(pyridyl)ethynyl]benzene types containing either 2‐pyridyl or 4‐pyridyl groups via activation with benzyl bromide leads to ionic π‐conjugated polyacetylene‐type polyelectrolytes (CPEs). All polymers are characterized by means of NMR, IR, UV/vis and photoluminescence spectroscopies, thermogravimetric analysis (TGA) and matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI‐TOF MS). The position of the pyridyl groups in the monomer influences the degree of quaternization and the extent of conjugation of CPEs. Monomers with 4‐pyridyl groups provide CPEs with a low extent of quaternization [N⁺/(N⁺ + N) = 0.27–0.34] and high extent of conjugation. On the other hand, the CPEs derived from 2‐pyridyl‐containing monomers are highly quaternized [N⁺/(N⁺ + N) = 0.77–1.00], however, possess lower conjugation of the main chains. The mechanism assuming quaternization and polymerization as competitive reactions is proposed to explain the difference in the extent of quaternization of CPEs. Prepared CPEs i) are well soluble in polar solvents, e.g., water, methanol, dimethyl sulfoxide, and dimethylformamide, ii) exhibit photoluminescence (emission in the violet to yellow region), and iii) possess high thermal stability.

     

Amphiphilic PEG‐b‐PMCL‐b‐PDMAEMA Triblock Copolymers: From Synthesis to Physico‐Chemistry of Self‐Assembled Structures

A synthetic route toward a new family of amphiphilic mPEG‐b‐PMCL‐b‐PDMAEMA triblock copolymers is reported. Chemical structures and compositions are confirmed by ¹H NMR and SEC. Polydispersity indices are typically <1.4, indicating good control of the reactions. The physicochemical parameters associated with mPEG‐b‐PMCL‐b‐PDMAEMA self‐assembled structures are investigated. Nanoparticles are prepared via a co‐solvent method, and parameters such as nanoparticle $\overline {M} _{{\rm w}} $ , N_agg, A₂, and R_h are calculated based on static and dynamic light scattering data. Critical aggregation concentrations for the polymers are determined by measuring surface tensions of polymer solutions. TEM is employed to visualize the morphology of the assemblies.

     

Morphology Transition of Dual‐Responsive ABC Terpolymer in Water: Effect of Hydrophobic Block

To reveal the importance of hydrophobic block in morphology transition of responsive copolymers, four well‐defined ABC terpolymers with the same poly(dimethylamino ethyl methacrylate) (PDMAEMA) and PEG segments are synthesized by sequential RAFT polymerization. Poly (n‐hexyl methacrylate) (PnHMA), poly(n‐butyl methacrylate) (PnBMA), poly(ethyl methacrylate) (PEMA), and poly(methyl methacrylate) (PMMA), with glass transition temperatures of ?5, 20, 65, and 100 °C, respectively, are selected as hydrophobic segments. The structures and compositions of four terpolymers, that is, mPEG₄₅‐b‐PnHMA₂₉‐b‐PDMAEMA₂₈(EHD), mPEG₄₅‐b‐PnBMA₂₈‐b‐PDMAEMA₃₂ (EBD), mPEG₄₅‐b‐PEMA₃₁‐b‐PDMAEMA₃₀ (EED), and mPEG₄₅‐b‐PMMA₃₀‐b‐PDMAEMA₂₉ (EMD), are confirmed by gel permeation chromatography and ¹H NMR. Their morphology transitions in water are investigated via a combination of UV‐vis spectroscopy, light scattering, zeta potential measurements, and cryogenic transmission electron microscopy. All terpolymers can form spherical micelle by direct dissolution in acidic water. However, the spherical micelles of EBD and EHD progressively switch to cylinders and vesicles upon variations of external pH and temperature. In contrast, the spherical micelles of EMD and EED reversibly form larger aggregates when the temperature is above the cloud point of PDMAEMA in basic water. This study demonstrates the importance of hydrophobic block on the morphology transition of responsive copolymers.     

EDC‐Mediated Grafting of Quaternary Ammonium Salts onto Chitosan for Antibacterial and Thermal Properties Improvement

The present study provides antibacterial and thermal improvements of chitosan‐based systems through chemical modification with different quaternary ammonium salts using 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide (EDC) as mediator. Three different ammonium salts with a carboxylic acid end group are synthesized through a quaternization reaction between bromohexanoic acid and the respective tertiary amines (quinoline, N,N‐dimethylbenzylamine and pyridine). They are then chemically grafted along the chitosan backbone using EDC as a carboxyl activating agent for the coupling with the primary amine groups. This allows three different chitosan derivatives to be obtained: Quinolinium‐Chitosan (QA‐Cs), Benzalkonium‐Chitosan (BK‐Cs), and Pyridinium‐Chitosan (PA‐Cs), respectively. The chemical structures are characterized by ¹H NMR analysis. The thermal stability is analyzed by thermogravimetric analysis. Antibacterial efficiencies of chitosan derivatives against Pseudomonas aeruginosa and Staphylococcus aureus strains are determined. All the chitosan derivatives show negligible antibacterial activity against Gram‐positive S. aureus strain. However, the antibacterial activity against Gram‐negative P. aeruginosa strain is significantly improved.     

Synthesis and Ring‐Opening Metathesis Polymerization (ROMP) Reactivity of endo‐and exo‐Norbornenylazlactone Using Ruthenium Catalysts

Summary: Norbornenylazlactone ( NBAz ) was prepared by a Diels‐Alder cycloaddition between cyclopentadiene and 2‐vinyl‐4,4‐dimethyl‐5‐oxazolone. The stereoselectivity of this pericyclic reaction was in favour of endo isomers. The ring‐opening metathesis polymerization (ROMP) of NBAz was carried out in presence of ruthenium catalysts [(PCy₃)₂(Cl)₂Ru?CHPh 1 ; (SIMes)(PCy₃)(Cl)₂Ru?CHPh 2 (SIMes: 1,3‐dimesityl‐4,5‐dihydroimidazol‐2‐ylidene); (PiPr₃)₂(Cl)₂Ru?CH? S? Ph 3 ; (PiPr₃)(Cl)₂Ru?CH? (CH₂)₂? C, N‐2‐C₅H₄N 4 ]. It was found that the exo isomer is much more reactive than the corresponding endo isomer. Some hypotheses of mechanism are suggested to justify the low polymerization rate of endo isomer using the results of NBAz derivatives as the hydrolyzed NBAz , 5 , and the coupling product between NBAz and glycine methyl ester hydrochloride, 6 . For exo ‐ NBAz , the propagating rate constant, k_p, was determined with the four Ru‐initiators and their activity decreases in the order 2 > 1 > 3 > 4 . Complementary kinetic measurements with 1 and 2 were given as k_p/k_i ratio. The ROMP of exo isomer was faster with 2 than 1 in spite of a worse control of the chains size. The azlactone ring survived intact during the polymerization and may be used for further reactions with nucleophiles.

ROMP of NBAz by ruthenium initiators.     

Microwave‐Assisted Direct Synthesis and Polymerization of Chiral Acrylamide

Summary: Chiral (R)‐N‐(1‐phenylethyl)‐acrylamide ( 3 ) was synthesized directly from acrylic acid ( 1 ) and (R)‐1‐phenylethylamine ( 2 ) via microwave irradiation without any further activation and in a solvent‐free medium. The kinetic measurements performed show high selectivity and conversion to the amide after only few minutes of reaction time. It was possible to obtain optically active polymers containing both acrylamide and imide structural units in a one‐pot reaction starting from acrylic acid ( 1 ), amine ( 2 ) and AIBN as a free radical initiator. The same reactions were evaluated by classical thermal heating in an oil bath and the results are compared.

The condensation reaction between acrylic acid and (R)‐1‐phenylethylamine by MW irradiation in the presence and absence of AIBN as a free radical initiator.     

Synthesis and Spectral Properties of Novel Poly(disubstituted acetylene)s

The synthesis of mostly new acetylenes, R₁C?CR₂, (R₁ = 4‐t‐butylphenyl; R₂ = 4‐t‐butylphenyl; 4‐[(t‐butyl)(diphenyl)silyloxy]phenyl; 1‐naphthyl; 2‐naphthyl; 9‐anthryl) is reported. Their UV‐vis characteristics are discussed in comparison to the results of TD‐DFT calculations. R₁C?CR₂ (except for R₂ = 9‐anthryl) give polyacetylenic polymers—[C(R₁) = C(R₂)]‐_n, insoluble if R₁ = R₂ and well soluble if R₁ ≠ R₂ in polymerization with TaCl₅/SnBu₄. Polymerizability increases with increasing monomer triple bond accessibility for the catalyst. The photoluminescence yield of the soluble polymers rises in the R₂ order: 1‐naphthyl < 2‐naphthyl < 4‐[(t‐butyl)(diphenyl)silyloxy]phenyl.

     

Poly(ε‐caprolactone)‐graft‐poly(2‐(dimethylamino)ethyl methacrylate) Amphiphilic Copolymers Prepared via a Combination of ROP and ATRP: Synthesis,Characterization, and Self‐Assembly Behavior

Poly(ε‐caprolactone)‐graft‐poly(2‐(dimethylamino) ethyl methacrylate) (PCL‐g‐PDMAEMAs), a kind of amphiphilic graft copolymer, was prepared by combination of ROP and ATRP. The FTIR, ¹H NMR, and GPC results indicate that well‐defined polymers with controlled graft density and length of side chain were successfully synthesized. We prepared PCL‐g‐PDMAEMA nanoparticles by employing a nanoprecipitation technique. The pH‐ and thermosensitive properties of PCL‐g‐PDMAEMA nanoparticles were investigated by ¹H NMR, TEM, and DLS. It was found that the nanoparticles with an average size of 120 nm presented core–shell structure in aqueous dispersion. Furthermore, the nanoparticles are sensitive to temperature in base while not in an acidic environment.

     

Quaternization of poly(acrylonitrile-co-2-methyl-5-vinylpyridine) and properties of the products in N,N-dimethylformamide solution

The kinetics of quaternization of poly(acrylonitrile-co-2-methyl-5-vinylpyridine) ( 1 ) by methyl iodide was investigated. The rate constant k was shown to be independent of the degree of quaternization τ and the second order is valid for the reaction, independent of τ. From the dependence of k on the temperature, the thermodynamic parameters of the reaction were deduced and compared with literature data. Under the conditions to obtain τ = 1 in N-methylpyrrolidone as solvent, a low charge polyelectrolyte was produced, soluble in DMF without decrease of the average molecular weight. The viscosimetric behaviour of the copolymer in DMF as solvent (in presence or absence of external KI salt) was studied, dependent on the charge density controlled by τ, and the ageing depends on the presence of oxygen, on the basicity of the solvent, on the degree of quaternization, and on the nature and concentration of the external salt. A mechanism is proposed, which implies the oxidation of the I^? counterions to IO₃^?, initiating an intramolecular cyclisation of the nitrile groups.     

Tailoring Linear and Nonlinear Optical Properties of a Side‐Chain Liquid Crystalline Azo‐Polymethacrylate

The molecular orientation in a side‐chain liquid crystalline azopolymer with push–pull chromophores ( Pol‐PZ‐CN ) is studied by UV‐vis spectroscopy, refractive index and second harmonic generation measurements. Fresh films show homeotropic arrangement, but irradiation with polarized light induces “in‐plane” birefringence, which is enhanced by subsequent thermal annealing up to values as high as 0.34. The nonlinear response of Corona poled films with “in‐plane” anisotropy is governed by three independent NLO d_ij coefficients, evidencing symmetry different from the usual (C_∞v). For irradiated films, stable values d₃₁ = 1.4, d₃₂ = 0.9 and d₃₃ = 11 pm·V^?1 are measured at 1.9 µm. A noticeable higher d₃₁/d₃₂ ratio is obtained for preirradiated and annealed films. The proposed two‐step method consisting of light irradiation and heating is an effective strategy to tailor the polar molecular orientation of nonlinear liquid crystalline azopolymers.

     

The Influence of Hydrogen Bonding on the Propagation Rate Coefficient in Free‐Radical Polymerizations of Hydroxypropyl Methacrylate

The propagation rate coefficient k_p was determined for hydroxypropyl methacrylate by applying pulsed laser initiated polymerizations and subsequent analysis of the polymer by size‐exclusion chromatography. k_p data were derived for polymerizations in bulk and in several solvents: toluene, tetrahydrofuran (THF), benzyl alcohol, and supercritical CO₂. With the exception of THF, no solvent influence on k_p was observed. For polymerizations in THF k_p values 40% below the corresponding bulk data were obtained. In addition, the activation energy of k_p for polymerizations in THF is higher than for the other systems. The results are explained by a complexation of the OH group contained in the ester group with THF. As a consequence, H bonds between OH groups and carbonyl O atoms, which occur in the other systems, are not formed in the presence of THF. This explanation is supported by Raman spectra, which show that association of carbonyl groups does not occur for systems containing THF, whereas for all other systems the occurrence of two peaks at 1 703 cm^?1 and 1 720 cm^?1 is indicative of the vibrations of two different – associated vs. not associated – types of carbonyl groups. Based on the change in activation energy it is suggested that a true kinetic solvent effect occurs.

Temperature dependence of k_p for HPMA polymerizations in bulk and in solution of THF. The literature data for bulk polymerizations are taken from ref. 22 . Open symbols refer to ν_rep = 10 Hz and filled symbols to ν_rep = 25 Hz.     

Copolymers of N-vinyl-2-pyrrolidone and 2-(dimethylamino)ethyl methacrylate, 1. Synthesis,characterization, quaternization

2-(Dimethylamino)ethyl methacrylate (DMAEM) — N-vinyl-2-pyrrolidone (VP) copolymers were synthesized and characterized. The copolymerization parameters were determined: r_VP = 0,61, r_DMAEM = 11,41. The tacticity of DMAEM sequences and the distribution of monomer units were estimated. Then, the experimental conditions for the quaternization of the copolymers with alkyl bromides were defined. The modified copolymers were characterized and the mechanism of the quaternization reaction was studied via potentiometry.     

Cationic Bottlebrush Polymers from Quaternary Ammonium Macromonomers by Grafting‐Through Ring‐Opening Metathesis Polymerization

Cationic bottlebrush homopolymers are polymerized using a grafting‐through approach by ring‐opening metathesis polymerization (ROMP) to afford well‐defined polymers. Quaternary ammonium macromonomers (MMs) are prepared by quaternizing tertiary amine MMs synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization. The quaternary ammonium MMs undergo ROMP to target molecular weights (M_n = 30 000–100 000 g mol^?1) and a low dispersity (? = 1.10–1.30). Halide‐ligand exchange between the third generation Grubbs catalyst (G3) and halide counter ions (bromide and iodide ions) of MMs changes the catalyst activity throughout ROMP, causing it to deviate from pseudo‐first order kinetic behavior; however, the polymerization still follows controlled behavior without significant catalyst termination. Increasing steric bulk of the MMs decreases the polymerization rate as well. Amphiphilic block copolymers are synthesized by sequential polymerization of quaternary ammonium MMs and polystyrene (PS) MMs. Using a PS macroinitiator affords block copolymers with lower ? values as compared to the less active cationic macroinitiator.     

Asymmetrically Substituted Poly(diitaconates) Obtained by Reversible Addition‐Fragmentation Chain Transfer (RAFT) Polymerization: Synthesis,Copolymerization Parameters,and Antimicrobial Activity

Asymmetrically substituted poly(diitaconate) copolymers are synthesized from 1‐((N‐tert‐butoxycarbonyl)‐2‐aminoethyl)‐4‐propyl diitaconate (PrIA) and different comonomers (N,N‐dimethyl‐acrylamide, DMAA; acrylic acid; or ((N‐tert‐butoxycarbonyl)‐2‐aminoethyl)methacrylate) by reversible addition–fragmentation chain transfer polymerization (RAFT). The RAFT copolymerization parameters of PrIA and DMAA are r_DMAA = 0.49 and r_PrIA = 0.17, compared to r_DMAA = 0.52 and r_PrIA = 0.54 obtained by free radical copolymerization (FRP). Thus, the RAFT process has a stronger trend to alternating polymerization than the FRP process. The polydispersity index of the RAFT copolymers is around 1.2–1.8, compared to 2.8–2.9 for the corresponding FRP copolymers. After removal of the tert‐butoxycarbonyl protective groups, antimicrobially active synthetic mimics of antimicrobial peptides are obtained. The thus activated poly(PrIA‐co‐DMAA) copolymers (repeat unit ratio 1:1) have an increasing activity against Escherichia coli and Staphylococcus aureus with increasing molar mass. The RAFT copolymers are slightly more active and less toxic than comparable FRP polymers, leading to a higher selectivity for bacteria over mammalian cells. Higher molar fractions of PrIA in poly(PrIA‐co‐DMAA) copolymers (up to 80 mol%) do not increase their antimicrobial activity; reduction of the BuIA content in poly(BuIA‐DMAA) (down to 10 mol%) leads to a loss of activity against both E. coli and S. aureus.     

Novel Features of 9‐Methylene‐9H‐thioxanthene (MTAE) in Living Anionic Polymerization

For this study, a new epithio‐1,1‐diphenylethylene (DPE) derivative, namely, 9‐Methylene‐9H‐thioxanthene (MTAE), is synthesized, and its copolymerization reactions are investigated, showing distinctive features in living anionic copolymerization. At room temperature and hydrocarbon solvents, MTAE cannot be copolymerized with styrene (St) but can be copolymerized with 1,4‐divinylbenzene (DVB), forming a linear alternating copolymer. Based on this finding, ter‐polymerization of MTAE, DVB and St is conducted to generate a special alternating structure. Additionally, MTAE is found to exhibit fairly high reactivity in copolymerization with Isoprene (Ip) under the same conditions. An alternating sequence of alt‐MTAE/Ip containing high trans‐geometric Ip content (76% of trans‐1,4) and a di‐block sequence of alt‐MTAE/Ip‐b‐Ip are easily obtained. Its experimental reactivity ratio with Ip is investigated via the in situ ¹H NMR method (r_Ip = 0.28), and the corresponding kinetic behaviors and sequence structure are elucidated. Finally, the origin of the effect of MTAE on the isomerism of Ip during chain propagation is investigated by density functional theory (DFT) calculations, and it is found that the bridge sulfur atom in MTAE interacts strongly with living species. This special finding provides a novel approach for the sequence regulation, precise functionalization, and stereo‐structure control in living anionic polymerization originating from monomer structure design.     

Direct Observation of a Cyclic Vinyl Polymer Prepared by Anionic Polymerization using N‐Heterocyclic Carbene and Subsequent Ring‐Closure without Highly Diluted Conditions

A 1:1 adduct of methyl sorbate (MS) and 1,3‐di‐tert‐butylimidazol‐2‐ylidene (NHCtBu) initiates anionic polymerization of a nonconjugated polar alkene, allyl methacrylate (AMA) in toluene at ?20 °C. After the monomer is consumed quantitatively using a bulky aluminum Lewis acid, methylaluminum bis(2,6‐di‐tert‐butyl‐4‐methylphenoxide) (MAD), as an additive, successive ring‐closure occurs without highly dilute conditions to give a cyclic poly(AMA) containing α‐terminal MS unit, and an M_n of 8.8 × 10³?58.5 × 10³ with a narrow molecular dispersity index (M_w/M_n = 1.1₄–1.3₇). The lack of a need for dilution is due to the fact that an α‐terminal NHCtBu group is acting as the counter cation for the propagating center in the polymerization. From ¹H NMR and matrix assisted laser desorption/ionization (MALDI‐TOF) mass spectra, combined with transmittance electron microscope (TEM) observation of a synthesized poly(AMA) with longer alkyl side chains prepared via a thiol‐ene click reaction, it is concluded that once the monomer is consumed, nucleophilic attack at the neighboring methine of the α‐terminal NHCtBu residue by the propagating anionic center causes ring‐closing to cyclic poly(AMA).     

Synthesis and Characterization of Wide‐Bandgap Conjugated Polymers Consisting of Same Electron Donor and Different Electron‐Deficient Units and Their Application for Nonfullerene Polymer Solar Cells

Substantial development has been made in nonfullerene small molecule acceptors (NFSMAs) that has resulted in a significant increase in the power conversion efficiency (PCE) of nonfullerene‐based polymer solar cells (PSCs). In order to achieve better compatibility with narrow‐bandgap nonfullerene small molecule acceptors, it is important to design the conjugated polymers with a wide bandgap that has suitable molecular orbital energy levels. Here two donor–acceptor (D–A)‐conjugated copolymers are designed and synthesized with the same thienyl‐substituted benzodithiophene and different acceptors, i.e., poly{(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)‐alt‐(1,3‐bis(2‐octyldodecyl)‐1,3‐dihydro‐2H‐dithieno[3′,2′:3,4;2″,3″:5,6]benzo[1,2‐d]imidazol‐2‐one‐5,8‐diyl) } ( DTBIA , P1 ) and poly{(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)‐alt‐(2‐(5‐(3‐octyltridecyl)thiophen‐2‐yl)dithieno[3′,2′:3,4;2″,3″:5,6]benzo[1,2‐d]thiazole‐5,8‐diyl)} ( TDTBTA , P2 ) (and their optical and electrochemical properties are investigated). Both P1 and P2 exhibit similar deeper highest occupied molecular orbital energy level and different lowest unoccupied molecular orbital energy level. Both the copolymers have complementary absorption with a well‐known nonfullerene acceptor ITIC‐F. When blended with a narrow‐bandgap acceptor ITIC‐F, the PSCs based on P1 show a power conversion efficiency of 11.18% with a large open‐circuit voltage of 0.96 V, a J_sc of 16.89 mA cm^?2, and a fill factor (FF) of 0.69, which is larger than that for P2 counterpart (PCE = 9.32%, J_sc = 15.88 mA cm^?2, V_oc = 0.91 V, and FF = 0.645). Moreover, the energy losses for the PSCs based on P1 and P2 are 0.54 and 0.59 eV, respectively. Compared to P2, the P1‐ based PSCs show high values of incident photon to current conversion efficiency (IPCE) in the shorter‐wavelength region (absorption of donor copolymer), more balanced hole and electron mobilities, and favorable phase separation with compact π–π stacking distance.     

Aliphatic Hyperbranched Copolyesters by Combination of ROP and AB2‐Polycondensation

Summary: Hyperbranched aliphatic copolyesters have been prepared by the copolymerization of ε‐caprolactone and 2,2‐bis(hydroxymethyl)butyric acid (AB₂‐monomer), catalyzed by (i) HfCl₄(THF)₂ and (ii) diphenylammonium trifluoromethanesulfonate (DPAT), respectively. In both cases, copolymerization by combined ROP/AB₂‐polycondensation was achieved. The degree of branching (DB) and consequently the density of functional groups of the resulting copolyesters were controlled by the comonomer ratio in the feed. Molecular weights in the range = 22 000–166 000 g · mol⁻¹ (GPC, PS standards) were obtained, with apparent polydispersity indices of 1.20 to 1.95. The DB was in the range 0.03–0.35. Remarkably, HfCl₄(THF)₂ appeared to cause no transesterification of the ester bonds in the hyperbranched polymer formed. Further esterification or functionalization of the hydroxyl end groups of the hyperbranched polymers is therefore possible in a convenient two step/one pot process. The prepared hyperbranched polycaprolactones can be used as multifunctional initiators for the ROP of ε‐caprolactone, which is also catalyzed by HfCl₄(THF)₂, resulting in multi‐arm star polymers. Diphenylammonium trifluoromethanesulfonate (DPAT) was also found to catalyze the combination of ROP and AB₂ polycondensation. However, the applicability of this system is restricted due to side reactions that can lead to crosslinking.

Synthesis of hyperbranched copolyesters by combined ROP/polycondensation.     

In Situ Forming Poly(ethylene glycol)‐ Poly(L‐lactide) Hydrogels via Michael Addition: Mechanical Properties,Degradation, and Protein Release

Chemically crosslinked hydrogels are prepared at remarkably low macromonomer concentrations from 8‐arm poly(ethylene glycol)‐poly(L ‐lactide) star block copolymers bearing acrylate end groups (PEG‐(PLLA_n)₈‐AC, n = 4 or 12) and multifunctional PEG thiols (PEG‐(SH)_n, n = 2, 4, or 8) through a Michael‐type addition reaction. Hydrogels are obtained within 1 min after mixing PEG‐(PLLA₄)₈ ‐AC and PEG‐(SH)₈ in phosphate buffered saline, quickly reaching a high storage modulus of 17 kPa. Lysozyme and albumin are released for 4 weeks from PEG‐(PLLA₁₂)₈‐AC/PEG‐(SH)₈ hydrogels. Lysozyme release from PEG‐(PLLA₁₂)₈‐AC/PEG‐(SH)₂ and PEG‐(PLLA₁₂)₈‐AC/PEG‐(SH)₄ hydrogels is significantly faster with complete release in 3 and 12 d, respectively, as a result of a combination of degradation and diffusion.     

Surface Functionalization of Polypropylene Film via UV‐Induced Photografting of N‐Vinylpyrrolidone/Maleic Anhydride Binary Monomers

Summary: A polymeric surface with desirable wettability and versatile reactivity was facilely fabricated by UV‐induced surface photografting of N‐vinylpyrrolidone (NVP)/maleic anhydride (MAn) binary monomers, with polypropylene (PP) film as a model substrate. It was found that the photografting process of NVP/MAn is much faster than that of individual NVP or MAn; both the grafting efficiency (E_g) and grafting yield (Y_g) reach a maximum at around 1:1 molar feed ratio of NVP to MAn. These results indicate that the electron donor‐acceptor monomers can synergistically promote surface photografting by a known charge‐transfer‐complex (CTC) mechanism. Moreover, the grafted NVP and MAn units cooperatively enhance the surface hydrophilicity; the water contact angle of the modified surface drastically decreases from the original 99.4° to less than 36° within 30 s of irradiation time. Subsequently, we demonstrated that the surface‐grafted succinic anhydride groups could readily perform a variety of organic reactions such as acidic/alkaline hydrolysis and esterification, which is expected to facilitate further surface functionalizations. Besides, the complexing reaction of surface pyrrolidone groups with iodine was investigated, which was followed by UV‐vis spectroscopy. The antimicrobial activity against Escherichia coli, Staphylococcus aureus and Candida albicans show that this unique iodine‐complexated surface has desirable antimicrobial property.

Surface photografting of NVP/MAn and post reactions of surface‐grafted anhydride groups and pyrrolidone groups.