Polymer Chemistry最新文献

The synthesis of novel tertiary polythioamide copolymers, analogues of poly(2-ethyl-2-oxazoline) (PEtOx), is reported. Firstly, the direct synthesis of poly(2-methyl-2-thiazoline) was attempted via the cationic ring-opening polymerization of 2-methyl-2-thiazoline, in analogy to the well-known 2-alkyl-2-oxazoline monomers. Since no conversion was monitored under several conditions – which was investigated in parallel by density functional theory calculations – the post-polymerization modification of PEtOx using Lawesson's reagent was successfully achieved, yielding poly(2-ethyl-2-thiazoline)-co-(2-ethyl-2-oxazoline) copolymers with up to 95 mol% of the thioamide unit. The newly synthesized copolymers exhibited significantly lower water solubility and thermal stability than the pristine PEtOx, as demonstrated during cloud point temperature determination and thermal gravimetric analysis, respectively. Moreover, the glass transition temperature of the copolymers increases linearly with increasing oxygen–sulfur exchange.

Secondary interactions, such as hydrogen bonding or phase separation, can enhance the stability of dynamic covalent materials without compromising on desired dynamic properties. Here, we investigate the combination of multiple secondary interactions in dynamic covalent materials based on acylsemicarbazides (ASCs), with the aim of achieving tunable material properties. The effects of different ASC substituents on the dynamic covalent and hydrogen bonding capabilities were investigated in a small molecule study using a combined experimental and theoretical approach, and revealed the presence of cooperative hydrogen-bonding interactions in 2 directions in one of the derivatives. The different motifs were subsequently incorporated into polymeric materials. Combining ASC motifs capable of strong, multiple hydrogen bonding with a polydimethylsiloxane backbone introduces structure-dependent, ordered nanophase separation in polymeric materials. The thermo-mechanical properties of the materials reveal a strong dependance on the hydrogen-bonding structure and exact nature of the ASC bond. The dynamic behavior in bulk shows that bond exchange depends on the dissociation rate obtained from ASC model compounds, as well as the strength of the secondary interactions in these materials. Differences in hydrogen-bonding structures of the ASC motifs also cause differences in creep resistance of the materials. Interestingly, the materials with strong, ordered and cooperative hydrogen-bonded clusters show the highest creep resistance. Our results demonstrate that tuning both the dissociation rate and the secondary interactions by molecular design in dynamic covalent materials is important for controlling their thermal stability and creep resistance.

With the aim of efficiently converting the microscopic second-order nonlinear optical (NLO) effect of chromophore moieties into macroscopic NLO performance as high as possible, this work focused on the connection groups between the chromophore moieties of NLO polymers, in which alkoxy chains with different lengths and positions were systematically incorporated. The ignorable difference of the alkoxy chain from the normally utilized alkyl one directly resulted in improved macroscopic NLO performance, and d₃₃ values increased gradually from 105 to 131/157, then to 165 pm V⁻¹ with increasing contents of alkoxy chains, and further reached up to 178 pm V⁻¹ with the prolonged lengths of alkoxy chains. This was mainly due to the lower rotational barriers of ether bonds than those of the commonly used alkyl chains with carbon–carbon bonds, and the isolated effect of alkoxy chains with larger sizes. This work provides a new way to achieve a high second-order NLO effect from efficient modulation of chromophore orientations by adjustment of energy barriers.

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Direct arylation polymerization conditions can be classified into phosphine-assisted and “ligandless” conditions. We compared the outcomes of five poly[thiophene-derivative-alt-EDOT]s and PEDOTF polymerized under two kinds of conditions. The results revealed that the “ligandless” conditions led to higher polymerization efficiency compared to phosphine-assisted conditions when employing n-hexyl functionalized EDOT as an arylative substrate and various dibromoarenes as oxidative substrates. Computational studies revealed that the phosphine-assisted conditions follow the standard concerted metalation–deprotonation (CMD). In contrast, the amide-assisted conditions follow electrophilic CMD. This mechanistic difference provides a reasonable explanation for the preference of “ligandless” conditions towards the activation of electron-donating arenes. Additionally, the use of sterically hindered amide solvents and dibromoarenes helps reduce branching defects, preserving the desired linear polymer structure.

According to the theory established by Carothers and Flory, stoichiometric control of monomers is necessary for efficient step-growth polymerization of AA-type and BB-type monomers in a single-phase solution. This review examines recent progress in synthesizing high-molecular-weight polymers via atypical nonstoichiometric step-growth polymerization (NSSP). The reactive intermediate mechanism (RIM) and intramolecular catalyst transfer (ICT) systems are essential for efficient NSSP, generating polymers with much higher molecular weights than theoretically predicted. NSSP systems provide many advantages in fine synthetic technologies for producing complex multifunctional polymers suitable for specific applications.

Pelvic floor disorders (PFD) are common among women, causing dysfunction, incontinence, and discomfort. Surgeries to repair the descended tissues can result in complications due to implant material design, particularly from the hardness and mechanical mismatch to native tissue. A more flexible implant could reduce complications, such as exposure and tissue erosion. This work seeks to characterize a 3D-printed double-crosslinked hydrogel tissue scaffold consisting primarily of polyvinyl alcohol (PVA). It also compares its static/dynamic/thermal/biological properties to existing commercial products used in PFD therapies, showing our pelvic mesh's biodegradability/robustness advantages over the commercial ones. Tensile tests revealed that the hydrogel scaffold was more compliant than the commercial alternatives. Dynamic mechanical testing has shown that these polymers are durable enough to support organs with specific weight above the pelvic floor. In vivo mouse studies demonstrated low inflammation and good biocompatibility over a 28-day period. The development of this scaffold offers a promising alternative for more effective, long-lasting PFD treatments with fewer post-operative complications, advancing personalized medicine.

To avoid sequence bias in the chain growth process of multicomponent periodic polymers, we reported an indirect method for the synthesis of strictly periodic polymers using nonpolar monomers. Using 1,1-diphenylethylene (DPE) as the comonomer, the precise sequence was achieved through living anionic polymerization (LAP) and hydrogenation. Four dienes (isoprene (Ip), 2,3-dimethylbuta-1,3-diene (DMBD), 2,3-diphenylbutadiene-1,3-diene (DPB), and 1-phenyl-1,3-butadiene (1-PB)) and an olefin with cyclic tension 1-cyclobutylvinylbenzene (CBVB) were copolymerized with DPE to prepare the alternating precursors. The periodic sequences of DPE–styrene–propylene (pd-DSP), DPE–propylene–propylene (pd-DPP), DPE–ethylene–styrene (pd-DES), DPE–styrene–styrene (pd-DSS) and DPE–ethylene–styrene–styrene (pd-DESS) were successfully synthesized with hydrogenation of these alternating precursors, and the nonpolar olefin units were successfully introduced into the periodic polymer. The results showed that the modification of the backbone carbon framework structure caused a consistent change in the thermal properties of the polymers. Moreover, the steric hindrance and arrangement density of the side chain substituents could significantly affect the performance of the periodic copolymers. This study provides a feasible method for the synthesis of non-polar periodic copolymers with precise periodic arrangements.

Most elastomers are formed using solvent-based processes which result in an environmental burden. Consequently, elastomers formed using water-based nanoparticle dispersions are highly desirable. Here, we investigate elastomer-like films based on water-dispersible carboxylic acid-containing core–shell (CS) nanoparticles. The nanoparticles contain a poly(n-butylacrylate) (PBA) core and a poly(BA-co-acrylonitrile-co-methacrylic acid) shell. We react the –COOH groups of the shell with a di-epoxide (1,4-butanediol diglycidyl ether, BDDE) which replaces dissipative hydrogen bonds in the nanoparticle elastomer films with covalent bonds. The reaction with BDDE enables the transformation of a stretchable dissipative film (shear modulus of 9.0 MPa with 20% strain energy recovery) into a predominantly elastic film (shear modulus of 0.20 MPa with almost 100% energy recovery). Our optimum system, CS-0.5, has a shear modulus of 0.40 MPa, an impressive strain-at-break of greater than 300% and an energy recovery of 80%. The strain-at-break is increased to more than 450% using a monofunctional epoxide. We further explore the inter- and intra-nanoparticle nature of the di-epoxide reaction and how the mechanical properties can be tuned by varying the method of film formation. The facile approach introduced here enables the tuning of the mechanical properties of elastomeric core–shell nanoparticle films from dissipative to predominantly elastic on demand.

Surface modification of nanoparticles involves numerous types of active molecules such as DNA, antibodies, enzymes, or carbohydrates. These modifications usually require reactive handles like amines, carboxylic acids, azides, etc. on the nanoparticles. In this work, utilizing poly-benzyl methacrylate based nanoparticles as a model nanoparticle system, the number of functional groups was tuned with functional comonomers, amino ethyl methacrylate for the amino groups or methyl methacrylate for the carboxylic groups. Herein a systematic study is presented where the functional groups in the nanoparticles are differentiated between total, visible and accessible functional groups. The concentration of each type of functional group is compared using various methods. Polymers synthesized using free radical polymerization were analyzed using ¹H-NMR spectroscopy to obtain the total number of functional groups. Via a miniemulsion–solvent evaporation technique, these polymers were used to synthesize the nanoparticles. Zeta potential, pH value and particle charge detection measurements were used to determine the number of visible functional groups. The number of accessible functional groups was quantified by conjugating small dyes and fluorescence measurements were directly executed on the system under investigation, hence eliminating errors associated with indirect measurements and detecting very low concentrations (e.g. 80 nM). Lastly, human serum albumin was conjugated to investigate the effect of a bulky molecule on the accessibility of these reactive handles.