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Inverse emulsion polymerization technique was employed to synthesize hydrophobically modified polyacrylamide polymers with hydrophobe contents near to feed composition. Three different structures were obtained: multisticker, telechelic, and combined. N-Dimethyl-acrylamide (DMAM), n-dodecylacrylamide (DAM), and n-hexadecylacrylamide (HDAM) were used as hydrophobic comonomers. The effect of the hydrophobe length of comonomer, the initial monomer, and surfactant concentrations on shear viscosity was studied. Results show that the molecular weight of copolymer increases with initial monomer concentration and by increasing emulsifier concentration it remained almost constant. Shear viscosity measurements results show that the length of the hydrophobic comonomer augments the hydrophobic interactions causing an increase in viscosity and that the polymer thickening ability is higher for combined polymers.

Composite mats based on submicron biopolyester fibers, such as poly(3-hydroxyalkanoate)s, and zinc oxide (ZnO) nanoparticles have been exploited in medicine and environmental areas, as antibacterial wound dressings or filters. Generally, the resulting mats have to be subjected to UV irradiation in order to promote the formation of reactive oxygen species, thus activating the antimicrobial or photocatalytic effect of ZnO. Therefore, investigation related to the influence of ZnO on poly(3-hydroxyalkanoate)s photo-degradation is required. In this context, the present paper addresses the long-term photo-degradation of nanofibrous poly(3-hydroxybutyrate) (PHB)/ZnO composites derived from two complementary electro-hydrodynamic techniques, namely electrospinning or electrospinning/electrospraying tandem processes. A thorough investigation of the as-obtained PHB/ZnO fibrous composites implying the utilization of ATR-FTIR, SEC, and SEM analysis pre- and post-aging under UV irradiation (313 nm) for a period of time of 500 h to study the effect of electro-hydrodynamic technique utilized and the ZnO content on the UV shielding properties of PHB mats.

Herein, we report a novel type of symmetrical trithiocarbonate chain transfer agent (CTA) based diphenylmethyl as R groups. The utilization of this CTA in the Reversible Addition-Fragmentation chain Transfer (RAFT) process reveals an efficient control in the polymerization of methacrylic monomers and the preparation of block copolymers. The latter are obtained by the (co)polymerization of styrene or butyl acrylate using a functionalized macro-CTA polymethyl methacrylate (PMMA) previously synthesized. Data show low molecular weight dispersity values (Đ < 1.5) particularly in the polymerization of methacrylic monomers. Considering a typical RAFT mechanism, the leaving groups (R) from the fragmentation of CTA should be able to re-initiate the polymerization (formation of growth chains) allowing an efficient control of the process. Nevertheless, in the case of the polymerization of MMA in the presence of this symmetrical CTA, the polymerization process displays an atypical behavior that requires high [initiator]/[CTA] molar ratios for accessing predictable molecular weights without affecting the Đ. Some evidence suggests that this does not completely behave as a common RAFT agent as it is not completely consumed during the polymerization reaction, and it needs atypical high molar ratios [initiator]/[CTA] to be closer to the predicted molecular weight without affecting the Đ. This work demonstrates that MMA and other methacrylic monomers can be polymerized in a controlled way, and with “living” characteristics, using certain symmetrical trithiocarbonates.

The synthesis of linear and branched hydrophobically water soluble (co) polymers composed of acrylamide (AM), lauryl acrylate (LA) and N,N ′-methylenebis (acrylamide) was carefully carried out via a one-pot process using the reversible addition-fragmentation chain transfer (RAFT) polymerization in aqueous media. The polymerization reactions were triggered out by sequential addition of monomers in the absence of surfactant through thermal initiation using 4,4′-azobis(4-cyanopentanoic acid)-ACPA as initiator. For understanding the influence of both hydrophobic and crosslinking agent on the structure and rheological properties thus the synthesized polymers were thoroughly characterized. Size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) and dynamic light scattering (DLS) analyses demonstrated the insertion of hydrophobic block inside the polymeric chains. Further, the rheological studies confirmed the influence of both crosslinking agent and hydrophobic block inserted within the backbone polymers on the thickening properties of copolymers obtained in each step.

SummaryThe effect of stirring speed (SS) on the kinetics of styrene emulsion polymerization at 70 °C, using SDS as surfactant and KPS as initiator, was studied. The conversion (x) and weight average molecular weight (Mw) results are higher in the optimum SS range, which seems to be strongly dependent on the hydrodynamic characteristics of the reactor and the polymerization conditions. Above the optimum SS range, the number of particles and Mw are lower, therefore limited coagulation lead to a decrease in Mw caused by the increment of the free-radical entry frequency. These radicals not only come from the aqueous phase (oligomeric radicals), but also come from the radicals contained in the particles subject of coagulation (coagulative entry).

The rise of antibiotic-resistant microorganisms has become a critical issue in recent years and has promoted substantial research efforts directed to the development of more effective antimicrobial therapies utilizing different bactericidal mechanisms to neutralize infectious diseases. Modern approaches employ at least two mixed bioactive agents to enhance bactericidal effects. However, the combinations of drugs may not always show a synergistic effect, and further, could also produce adverse effects or stimulate negative outcomes. Therefore, investigations providing insights into the effective utilization of combinations of biocidal agents are of great interest. Sometimes, combination therapy is needed to avoid resistance development in difficult-to-treat infections or biofilm-associated infections treated with common biocides. Thus, this contribution reviews the literature reports discussing the usage of antimicrobial polymers along with nanomaterials or other inhibitors for the development of more potent biocidal therapies.

The effect of poly N-isopropylacrylamide (PNIPAM) blocks on the thermoresponsive behavior of multiblock copolymers with polyacrylamide (PAM) backbones synthesized via RAFT polymerization in aqueous solution is examined. These multiblock copolymers (or multistickers) were prepared by the sequential polymerization of acrylamide and N-isopropylacrylamide. Initially, a hydrophilic macro-RAFT PAM is synthesized using acrylamide (AM), [S, S′-bis(α,α′-dimethyl-α″-acetic acid)-trithiocarbonate (DMAT)] as a chain transfer agent, and 4,4′-azobis(4-cyanopentanoic acid) (ACPA) as an initiator. Chain extensions were carried out by the sequential polymerization of N-isopropylacrylamide (NIPAM) or acrylamide (PAM). Multiblock copolymers (tri-, penta-, hepta- and nonablock) were acquired by the insertion of 1, 2, 3 or 4 NIPAM blocks, respectively. The resultant copolymers were characterized by nuclear magnetic resonance (NMR) spectroscopy, size-exclusion chromatography (SEC), dynamic light scattering (DLS), ultraviolet-visible (UV-vis) spectroscopy and rheometry. Rheological analyses were performed at different temperatures from 25 to 70 °C, and the data showed an increase in the apparent viscosity of the copolymers from the macro-chain transfer agent to the nonablock copolymer. The lower critical solution temperature (LCST) was measured for each polymer, and the resulting values were found fluctuate as a function of the number of thermoresponsive blocks incorporated into the thermoresponsive copolymers.

The use of 2,5-di-(2-ethylhexanoylperoxy)-2,5-dimethylhexane (T141) as difunctional radical initiator in Reverse Iodine Transfer Polymerization (RITP) was studied at 80 °C ( k d,T141  = 9.6 × 10 −5  s −1 ) for styrene (St), methyl methacrylate (MMA) and butyl acrylate (BuA). Firstly, the apparent efficiency coefficients α and β were determined by RITP of St, MMA and BuA using monofunctional initiators such as dilaurylperoxide (LYP) at 73 °C ( k d,LYP  = 9.6 × 10 −5  s −1 ) and bis(4-tert-butylcyclohexyl)peroxydicarbonate (P16S) at 59 °C ( k d,P16S  = 9.6 × 10 −5  s −1 ). The decomposition of the monofunctional initiators LYP and P16S generates free radicals with similar structures as those produced during the homolysis of T141. Once the polymerization reactions were performed, monomer conversions were determined by proton nuclear magnetic resonance and the molecular weights M n,exp were obtained by size exclusion chromatography. Thus, the following apparent efficiency coefficients were calculated: α = 0.41 and β = 1.00 for St, α = 0.14 and β = 0.75 for MMA and α = 0.07 and β = 0.14 for BuA. Afterwards, these values were successfully tested in RITP using an asymmetric initiator such as tert -amyl peroxy-2-ethylhexanoate (T121). In addition, the RITPs were performed for all three monomers using T141 as difunctional initiator. The results prove that the calculated values for α and β were consistent, since the theoretical molecular weights in all polymeric samples match well with the M n,exp .