Pub Date : 2026-02-07DOI: 10.1021/acs.macromol.5c03473
Jian Song, Shanshan Xu, Chenxuan Sun, Bao Wang, Ying Zheng, Jian Zhou, Junfeng Liu, Chengtao Yu, Pengju Pan
Post-stretching of polymers often starts from a low-crystallized state in real processing. Unlike the glassy or fully crystallized polymers, the stretch-induced structural evolutions of low-crystallized polymers are much more complex due to the interplay between the pre-existing crystals and the surrounding glassy phase. Herein, we use stereocomplex (SC)-containing poly(lactic acid) (PLA) as a model low-crystallized system and investigated its structural evolutions and deformation mechanism during near-Tg stretching. A low amount of SCs was introduced into glassy PLA through the SC crystallization of l- and d-configured PLAs, and these SCs form physical networks in the polymer matrix. Both the glassy and SC-containing PLAs show rubber-like deformation behavior under stretching, while the presence of the SC network improves the strength, modulus, and toughness of the PLA matrix. In the near-Tg stretching process, the glassy PLA shows slower chain orientation kinetics, delayed formation of homocrystals (HCs) or a mesophase, and the later initiation of cavitation. With the introduction of the pre-existing SC network in glassy PLAs, the chain orientation kinetics and formation of HCs or a mesophase are highly accelerated, and cavitation is more significant under stretching. Such unique structural evolution behavior offers the strengthening and toughening effects of the pre-existing SC network on the PLA matrix. This study provides deep molecular insights for the post-stretching processing of glassy and partially crystallized polymers.
{"title":"Mechanical Strengthening, Facilitated Crystallization, and Microstructural Evolutions of Poly(lactic acid) during Near-Tg Stretching Induced by a Stereocomplex Crystal Network","authors":"Jian Song, Shanshan Xu, Chenxuan Sun, Bao Wang, Ying Zheng, Jian Zhou, Junfeng Liu, Chengtao Yu, Pengju Pan","doi":"10.1021/acs.macromol.5c03473","DOIUrl":"https://doi.org/10.1021/acs.macromol.5c03473","url":null,"abstract":"Post-stretching of polymers often starts from a low-crystallized state in real processing. Unlike the glassy or fully crystallized polymers, the stretch-induced structural evolutions of low-crystallized polymers are much more complex due to the interplay between the pre-existing crystals and the surrounding glassy phase. Herein, we use stereocomplex (SC)-containing poly(lactic acid) (PLA) as a model low-crystallized system and investigated its structural evolutions and deformation mechanism during near-<i>T</i><sub>g</sub> stretching. A low amount of SCs was introduced into glassy PLA through the SC crystallization of <span>l</span>- and <span>d</span>-configured PLAs, and these SCs form physical networks in the polymer matrix. Both the glassy and SC-containing PLAs show rubber-like deformation behavior under stretching, while the presence of the SC network improves the strength, modulus, and toughness of the PLA matrix. In the near-<i>T</i><sub>g</sub> stretching process, the glassy PLA shows slower chain orientation kinetics, delayed formation of homocrystals (HCs) or a mesophase, and the later initiation of cavitation. With the introduction of the pre-existing SC network in glassy PLAs, the chain orientation kinetics and formation of HCs or a mesophase are highly accelerated, and cavitation is more significant under stretching. Such unique structural evolution behavior offers the strengthening and toughening effects of the pre-existing SC network on the PLA matrix. This study provides deep molecular insights for the post-stretching processing of glassy and partially crystallized polymers.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"9 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2026-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146135531","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-02-06DOI: 10.1021/acs.macromol.5c02416
Soumyadeep Chowdhury, Swagata Pahari, Biswanath Guria, Amit Kumar Sen, Kanhaiya Lal Anjana, Prasenjit Ghosh, Rabindra Mukhopadhyay
Understanding how sulfur crosslinking architecture influences the properties of styrene–butadiene rubber (SBR) is critical for optimizing tire performance and durability. Our study employs all-atom molecular dynamics (MD) simulations and experimental validations to systematically investigate the impact of crosslinking density and sulfur crosslink types (monosulfide, disulfide, and polysulfide) on the structural, thermodynamic, dynamical, mechanical, and thermal properties of SBR. The computational framework is designed to enable precise control over network architecture, allowing the effects of crosslink length and density to be isolated─an approach not readily achievable in experimental settings. The models are validated by comparing simulated glass-transition temperatures (Tg) and densities with experimental data. An increase in Tg with crosslinking density and sulfur chain length was observed, consistent with reduced chain mobility. Thermodynamic properties such as thermal expansion coefficient, isothermal compressibility, adiabatic bulk modulus, and specific heat capacity were determined, revealing that higher crosslinking densities generally enhance thermal stability and mechanical rigidity, with subtle differences among crosslink types. Notably, the presence of intrachain crosslinks in polysulfide systems introduced additional constraints, affecting both thermal conductivity and chain dynamics. Stress–strain simulations indicated that mechanical strength primarily depends on crosslinking density, with minimal sensitivity to crosslink type. Our findings provide molecular level insights into how crosslinking architecture governs the macroscopic behavior of vulcanized SBR, offering valuable guidance for the rational design of advanced tire compounds.
{"title":"From Molecular Architecture to Performance: Structure–Property Correlations in Crosslinked SBR Explored through a Combined Experimental and Molecular Simulation Approach","authors":"Soumyadeep Chowdhury, Swagata Pahari, Biswanath Guria, Amit Kumar Sen, Kanhaiya Lal Anjana, Prasenjit Ghosh, Rabindra Mukhopadhyay","doi":"10.1021/acs.macromol.5c02416","DOIUrl":"https://doi.org/10.1021/acs.macromol.5c02416","url":null,"abstract":"Understanding how sulfur crosslinking architecture influences the properties of styrene–butadiene rubber (SBR) is critical for optimizing tire performance and durability. Our study employs all-atom molecular dynamics (MD) simulations and experimental validations to systematically investigate the impact of crosslinking density and sulfur crosslink types (monosulfide, disulfide, and polysulfide) on the structural, thermodynamic, dynamical, mechanical, and thermal properties of SBR. The computational framework is designed to enable precise control over network architecture, allowing the effects of crosslink length and density to be isolated─an approach not readily achievable in experimental settings. The models are validated by comparing simulated glass-transition temperatures (<i>T</i><sub>g</sub>) and densities with experimental data. An increase in <i>T</i><sub>g</sub> with crosslinking density and sulfur chain length was observed, consistent with reduced chain mobility. Thermodynamic properties such as thermal expansion coefficient, isothermal compressibility, adiabatic bulk modulus, and specific heat capacity were determined, revealing that higher crosslinking densities generally enhance thermal stability and mechanical rigidity, with subtle differences among crosslink types. Notably, the presence of intrachain crosslinks in polysulfide systems introduced additional constraints, affecting both thermal conductivity and chain dynamics. Stress–strain simulations indicated that mechanical strength primarily depends on crosslinking density, with minimal sensitivity to crosslink type. Our findings provide molecular level insights into how crosslinking architecture governs the macroscopic behavior of vulcanized SBR, offering valuable guidance for the rational design of advanced tire compounds.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"83 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2026-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146122185","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-02-06DOI: 10.1021/acs.macromol.5c02926
Hongbing Chen, Jian Tang, Quan Chen, Yumi Matsumiya, Hiroshi Watanabe
Nonlinear shear behavior was examined for a representative dually cross-linked elastomer, poly(vinyl alcohol) (PVA)/Borax hydrogel having both permanent and transient cross-links, the former due to covalent bonds and the latter sustained by a complex of the hydroxy group and borate ion. The PVA chain backbone between the transient cross-links behaved as the transient network strand partially relaxing on thermal dissociation and/or mechanical breakage of the transient cross-links. For comparison, the nonlinear behavior was also examined for bulk SI(COOH)S block copolymer having glassy spherical domains of the S block as the permanent end-cross-links for the I blocks and the hydrogen bonds between carboxyl groups as the transient cross-links. The I block backbone between the carboxyl groups served as the transient network strands. Experiments revealed significant shear-softening of the PVA/Borax hydrogel even under a very slow and small shear deformation characterized with the Weissenberg number Wi = 0.2 and the total shear strain γm = 0.03. Namely, the linear viscoelastic (LVE) responses of this gel vanished even under very mild shear conditions. The SI(COOH)S copolymer showed softening of a similar magnitude but under stronger shear conditions, Wi = 4.6 and γm = 2.0. These nonlinear features can be related to the shear-induced breakage of the transient cross-links that results in anisotropy of the population of the network strands reformed in different directions as well as nonequilibrium motion of the strands connected to the broken transient cross-links. The difference between the PVA/Borax hydrogel and the SI(COOH)S copolymer, the nonlinearity much stronger for the former, could be related to the mobility of the transient cross-links (–OH/borate ion complex) along the PVA backbone and lack of the mobility of the carboxyl group along the I block backbone.
{"title":"Nonlinear Rheological Behavior of Dually Cross-Linked Elastomers on Start-Up and Cessation of Shear Deformation","authors":"Hongbing Chen, Jian Tang, Quan Chen, Yumi Matsumiya, Hiroshi Watanabe","doi":"10.1021/acs.macromol.5c02926","DOIUrl":"https://doi.org/10.1021/acs.macromol.5c02926","url":null,"abstract":"Nonlinear shear behavior was examined for a representative dually cross-linked elastomer, poly(vinyl alcohol) (PVA)/Borax hydrogel having both permanent and transient cross-links, the former due to covalent bonds and the latter sustained by a complex of the hydroxy group and borate ion. The PVA chain backbone between the transient cross-links behaved as the transient network strand partially relaxing on thermal dissociation and/or mechanical breakage of the transient cross-links. For comparison, the nonlinear behavior was also examined for bulk SI(COOH)S block copolymer having glassy spherical domains of the S block as the permanent end-cross-links for the I blocks and the hydrogen bonds between carboxyl groups as the transient cross-links. The I block backbone between the carboxyl groups served as the transient network strands. Experiments revealed significant shear-softening of the PVA/Borax hydrogel even under a very slow and small shear deformation characterized with the Weissenberg number <i>Wi</i> = 0.2 and the total shear strain γ<sub>m</sub> = 0.03. Namely, the linear viscoelastic (LVE) responses of this gel vanished even under very mild shear conditions. The SI(COOH)S copolymer showed softening of a similar magnitude but under stronger shear conditions, <i>Wi</i> = 4.6 and γ<sub>m</sub> = 2.0. These nonlinear features can be related to the shear-induced breakage of the transient cross-links that results in anisotropy of the population of the network strands reformed in different directions as well as nonequilibrium motion of the strands connected to the broken transient cross-links. The difference between the PVA/Borax hydrogel and the SI(COOH)S copolymer, the nonlinearity much stronger for the former, could be related to the mobility of the transient cross-links (–OH/borate ion complex) along the PVA backbone and lack of the mobility of the carboxyl group along the I block backbone.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"151 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2026-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146122513","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The broad applicability requires polyethylene (PE) to possess good processability and mechanical properties; direct synthesis of bimodal or multimodal PEs using a well-defined catalyst is therefore of considerable academic and industrial interest. In this paper, a series of dibenzobarrelene-derived α-diimine nickel complexes with a substituted 8-(p-R-phenyl)naphthylamine (R = OMe, Me, CF3) and a naphthylamine were designed and synthesized for ethylene polymerization by unsymmetric and hybrid aniline strategies. At low temperature (<50 °C), bimodal PEs are obtained because of the presence of syn and anti diastereomers of α-diimine nickel catalysts. At high temperatures (>65 °C), multimodal PEs with broad molecular weight distributions are produced, which arises from the cooperative contributions of syn/anti diastereomers of α-diimine nickel catalysts and imine metathesis. The imine metathesis observed for these hybrid α-diimine nickel complexes provides a new mechanistic perspective on their unique ethylene polymerization behavior and a strategy for tailoring PE molecular weight distributions by using well-defined catalysts.
{"title":"Multimodal Polyethylenes Produced by Hybrid and Unsymmetric α-Diimine Nickel Catalysts: The Roles of Syn/Anti Diastereomers and Imine Metathesis","authors":"Zonglin Qiu, Heng Gao, Chunyu Feng, Bo Ning, Cheng Zhang, Handou Zheng, Haiyang Gao","doi":"10.1021/acs.macromol.5c03572","DOIUrl":"https://doi.org/10.1021/acs.macromol.5c03572","url":null,"abstract":"The broad applicability requires polyethylene (PE) to possess good processability and mechanical properties; direct synthesis of bimodal or multimodal PEs using a well-defined catalyst is therefore of considerable academic and industrial interest. In this paper, a series of dibenzobarrelene-derived α-diimine nickel complexes with a substituted 8-(<i>p</i>-R-phenyl)naphthylamine (R = OMe, Me, CF<sub>3</sub>) and a naphthylamine were designed and synthesized for ethylene polymerization by unsymmetric and hybrid aniline strategies. At low temperature (<50 °C), bimodal PEs are obtained because of the presence of syn and anti diastereomers of α-diimine nickel catalysts. At high temperatures (>65 °C), multimodal PEs with broad molecular weight distributions are produced, which arises from the cooperative contributions of syn/anti diastereomers of α-diimine nickel catalysts and imine metathesis. The imine metathesis observed for these hybrid α-diimine nickel complexes provides a new mechanistic perspective on their unique ethylene polymerization behavior and a strategy for tailoring PE molecular weight distributions by using well-defined catalysts.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"384 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2026-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146122514","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-02-05DOI: 10.1021/acs.macromol.5c02656
María del Mar Ramos-Tejada, Alberto Martín-Molina, Daniel Montesinos, Luis Pérez-Mas, Manuel Quesada-Pérez
Nanogels (as well as other polymer networks) can absorb nanoparticles that give them new properties and expand their application possibilities. The resulting hybrid entities constitute a kind of polymer nanocomposites, which have become an emerging area of research. In this work, coarse-grained simulations have been used to study how certain properties of these nanocomposites (size, number of nanoparticles inside, net charge, and surface potential) change with temperature. Four nanocomposites with different values of charge anchored to the polymer network (known as bare charge) were simulated. The degree to which nanocomposites shrink and expel the particles they contain depends strongly on the bare charge, which, in turn, could be related to the pH in pH-sensitive micro- and nanogels. Our results also reveal that nanoparticles are responsible for nanocomposites exhibiting much richer and more complex behavior than nanogels. Furthermore, the strong correlations that nanoparticles experience when the polymer network shrinks should not be ignored in mean-field theories that try to predict how nanocomposites behave.
{"title":"Coarse-Grained Simulations of Thermosensitive Polymer Nanocomposites","authors":"María del Mar Ramos-Tejada, Alberto Martín-Molina, Daniel Montesinos, Luis Pérez-Mas, Manuel Quesada-Pérez","doi":"10.1021/acs.macromol.5c02656","DOIUrl":"https://doi.org/10.1021/acs.macromol.5c02656","url":null,"abstract":"Nanogels (as well as other polymer networks) can absorb nanoparticles that give them new properties and expand their application possibilities. The resulting hybrid entities constitute a kind of polymer nanocomposites, which have become an emerging area of research. In this work, coarse-grained simulations have been used to study how certain properties of these nanocomposites (size, number of nanoparticles inside, net charge, and surface potential) change with temperature. Four nanocomposites with different values of charge anchored to the polymer network (known as bare charge) were simulated. The degree to which nanocomposites shrink and expel the particles they contain depends strongly on the bare charge, which, in turn, could be related to the pH in pH-sensitive micro- and nanogels. Our results also reveal that nanoparticles are responsible for nanocomposites exhibiting much richer and more complex behavior than nanogels. Furthermore, the strong correlations that nanoparticles experience when the polymer network shrinks should not be ignored in mean-field theories that try to predict how nanocomposites behave.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"51 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146122187","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-02-05DOI: 10.1021/acs.macromol.5c03399
Min Wang, Jihang Yu, Yushu Tian, Jiadong Wang, Xuan Qin, Yonglai Lu
Fatigue-induced degradation of polyurethane elastomers (PUEs) significantly affects their long-term performance, yet the effect of the distribution state of hard domains on their fatigue durability remains poorly understood. In particular, the microstructural evolution under compression fatigue, especially when thermal effects are minimized, is scarcely studied. This study investigates how adjusting the hard segment content (HSC) regulates the distribution and hierarchical organization of hard domains. Low-frequency compression fatigue was employed to isolate purely mechanical damage mechanisms. This allows us to elucidate their influence on the fatigue behavior of PUEs. Characterization results show that the high-HSC sample (PU-H25) forms a continuous and highly ordered spherulitic hard segment network that carries most of the compressive load. However, this rigid architecture is susceptible to stress concentration, leading to progressive degradation of the hard network, and pronounced permanent deformation. In contrast, the low-HSC material (PU-H17) contains hard segments dispersed as isolated physical cross-links within the soft-segment matrix. Under cyclic loading, deformation is primarily accommodated by the soft phase, producing a progressive softening behavior. Although PU-H17 exhibits a larger initial strain, it demonstrates superior elastic recovery. The medium-HSC sample (PU-H21) develops a semicontinuous hard domain morphology that enables cooperative load transfer between hard and soft phases, resulting in the highest structural stability and the slowest fatigue-induced damage evolution. Overall, the results demonstrate that HSC is a key factor governing the fatigue response of PUEs by tailoring their microphase-separated morphology. As HSC increases, the dominant fatigue mechanism shifts from soft-phase-controlled stress dissipation, to cooperative load sharing between hard and soft phases, and finally to hard-phase-dominated load bearing and fracture. These mechanistic insights provide a basis for designing PUEs with tailored fatigue resistance for specific service conditions.
{"title":"Mechanical-Fatigue-Driven Hierarchical Structural Evolution in Polyurethane Elastomers with Different Hard Segment Contents","authors":"Min Wang, Jihang Yu, Yushu Tian, Jiadong Wang, Xuan Qin, Yonglai Lu","doi":"10.1021/acs.macromol.5c03399","DOIUrl":"https://doi.org/10.1021/acs.macromol.5c03399","url":null,"abstract":"Fatigue-induced degradation of polyurethane elastomers (PUEs) significantly affects their long-term performance, yet the effect of the distribution state of hard domains on their fatigue durability remains poorly understood. In particular, the microstructural evolution under compression fatigue, especially when thermal effects are minimized, is scarcely studied. This study investigates how adjusting the hard segment content (HSC) regulates the distribution and hierarchical organization of hard domains. Low-frequency compression fatigue was employed to isolate purely mechanical damage mechanisms. This allows us to elucidate their influence on the fatigue behavior of PUEs. Characterization results show that the high-HSC sample (PU-H25) forms a continuous and highly ordered spherulitic hard segment network that carries most of the compressive load. However, this rigid architecture is susceptible to stress concentration, leading to progressive degradation of the hard network, and pronounced permanent deformation. In contrast, the low-HSC material (PU-H17) contains hard segments dispersed as isolated physical cross-links within the soft-segment matrix. Under cyclic loading, deformation is primarily accommodated by the soft phase, producing a progressive softening behavior. Although PU-H17 exhibits a larger initial strain, it demonstrates superior elastic recovery. The medium-HSC sample (PU-H21) develops a semicontinuous hard domain morphology that enables cooperative load transfer between hard and soft phases, resulting in the highest structural stability and the slowest fatigue-induced damage evolution. Overall, the results demonstrate that HSC is a key factor governing the fatigue response of PUEs by tailoring their microphase-separated morphology. As HSC increases, the dominant fatigue mechanism shifts from soft-phase-controlled stress dissipation, to cooperative load sharing between hard and soft phases, and finally to hard-phase-dominated load bearing and fracture. These mechanistic insights provide a basis for designing PUEs with tailored fatigue resistance for specific service conditions.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"88 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146116130","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-02-05DOI: 10.1021/acs.macromol.5c02587
Takeo Hasegawa, Yoshinori Tamai
This study investigated the characteristic dynamics of translational diffusion and reorientational relaxation of substituted benzenes confined within nanoporous channels in the ε form of crystalline syndiotactic polystyrene, employing atomistic molecular dynamics simulations. Reorientational motions were analyzed using the autocorrelation functions of the vectors embedded on the phenyl rings. The motions were classified into two main modes: in-plane motion of the phenyl ring associated with the inversion of the molecular long axis and out-of-plane motion of the ring around the long axis. Interestingly, the former obeys the Arrhenius law, whereas the latter does not. This non-Arrhenius behavior was attributed to temperature-dependent variations in the free energy landscape along the reaction coordinates. It was found that the enhancement of the fluctuation of the nanochannels, which is promoted by thermal expansion, played an important role in this landscape modification. The activation energy of the inversion motion was lower for o-xylene than for toluene. The mechanism of this fast relaxation of bulkier ortho-substituted benzene was interpreted in terms of the activation free energy for the inversion motion, which is specifically associated with the deformation of the host matrix in a confined environment. The fundamental aspects obtained provide crucial information for controlling the functionality of nanoporous materials.
{"title":"Dynamics of Aromatic Molecules in Nanochannels of Crystalline Syndiotactic Polystyrene Studied by Molecular Dynamics Simulation","authors":"Takeo Hasegawa, Yoshinori Tamai","doi":"10.1021/acs.macromol.5c02587","DOIUrl":"https://doi.org/10.1021/acs.macromol.5c02587","url":null,"abstract":"This study investigated the characteristic dynamics of translational diffusion and reorientational relaxation of substituted benzenes confined within nanoporous channels in the ε form of crystalline syndiotactic polystyrene, employing atomistic molecular dynamics simulations. Reorientational motions were analyzed using the autocorrelation functions of the vectors embedded on the phenyl rings. The motions were classified into two main modes: in-plane motion of the phenyl ring associated with the inversion of the molecular long axis and out-of-plane motion of the ring around the long axis. Interestingly, the former obeys the Arrhenius law, whereas the latter does not. This non-Arrhenius behavior was attributed to temperature-dependent variations in the free energy landscape along the reaction coordinates. It was found that the enhancement of the fluctuation of the nanochannels, which is promoted by thermal expansion, played an important role in this landscape modification. The activation energy of the inversion motion was lower for <i>o</i>-xylene than for toluene. The mechanism of this fast relaxation of bulkier ortho-substituted benzene was interpreted in terms of the activation free energy for the inversion motion, which is specifically associated with the deformation of the host matrix in a confined environment. The fundamental aspects obtained provide crucial information for controlling the functionality of nanoporous materials.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"89 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146122186","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-02-05DOI: 10.1021/acs.macromol.5c03088
Noy Cohen
Poly(N-isopropylacrylamide) (PNIPAM) is a temperature-responsive polymer that undergoes large volumetric deformations through a transition from a swollen to a collapsed state at a volume phase transition temperature (VPTT). Locally, these deformations stem from the coil-to-globule transition of individual chains. In this contribution, I revisit the study of Suzuki, A.; Ishii, T. [ J. Chem. Phys.1999, 110, 2289–2296], which demonstrated that a PNIPAM rod can exhibit phase coexistence (i.e., comprise swollen and collapsed domains simultaneously) near the VPTT when subjected to mechanical constraints. Specifically, that paper showed that (1) collapsed domains gradually form in a fixed swollen rod with time and (2) swollen domains can nucleate in a collapsed rod under uniaxial extension. These behaviors originate from the local thermo-mechanical response of the chains, which transition between states in response to the applied mechanical loading. Here, I develop a statistical-mechanics based framework that captures the behavior of individual chains below and above the VPTT and propose a probabilistic model based on the local chain response that sheds light on the underlying mechanisms governing phase nucleation and growth. The model is validated through comparison with experimental data. The findings from this work suggest that in addition to the classical approaches, in which the VPTT is programmed through chemical composition and network topology, the transition can be tuned by mechanical constraints. Furthermore, the proposed framework offers a pathway to actively tailor the VPTT through the exertion of mechanical forces, enabling improved control and performance of PNIPAM hydrogels in modern applications.
{"title":"Phase Coexistence in Thermoresponsive PNIPAM Hydrogels Triggered by Mechanical Forces","authors":"Noy Cohen","doi":"10.1021/acs.macromol.5c03088","DOIUrl":"https://doi.org/10.1021/acs.macromol.5c03088","url":null,"abstract":"Poly(<i>N</i>-isopropylacrylamide) (PNIPAM) is a temperature-responsive polymer that undergoes large volumetric deformations through a transition from a swollen to a collapsed state at a volume phase transition temperature (VPTT). Locally, these deformations stem from the coil-to-globule transition of individual chains. In this contribution, I revisit the study of <contrib-group><span>Suzuki, A.</span>; <span>Ishii, T.</span></contrib-group> [ <cite><i>J. Chem. Phys.</i></cite> <span>1999</span>, <em>110</em>, 2289–2296], which demonstrated that a PNIPAM rod can exhibit phase coexistence (i.e., comprise swollen and collapsed domains simultaneously) near the VPTT when subjected to mechanical constraints. Specifically, that paper showed that (1) collapsed domains gradually form in a fixed swollen rod with time and (2) swollen domains can nucleate in a collapsed rod under uniaxial extension. These behaviors originate from the local thermo-mechanical response of the chains, which transition between states in response to the applied mechanical loading. Here, I develop a statistical-mechanics based framework that captures the behavior of individual chains below and above the VPTT and propose a probabilistic model based on the local chain response that sheds light on the underlying mechanisms governing phase nucleation and growth. The model is validated through comparison with experimental data. The findings from this work suggest that in addition to the classical approaches, in which the VPTT is programmed through chemical composition and network topology, the transition can be tuned by mechanical constraints. Furthermore, the proposed framework offers a pathway to actively tailor the VPTT through the exertion of mechanical forces, enabling improved control and performance of PNIPAM hydrogels in modern applications.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"9 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146116129","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-02-05DOI: 10.1021/acs.macromol.5c03339
Juliana Pretel de Souza, Vicente Lira Kupfer, Hugo Henrique Carline deLima, Jaqueline de Carvalho Rinaldi, Emerson Marcelo Girotto, Marcos Rogério Guilherme, Andrelson Wellington Rinaldi
Hydrogels exhibit excellent permeability for solute transport, with their degree of swelling directly modulating drug diffusion through their polymer network. This dynamic hinders the quantitative prediction of the swelling mechanisms of these materials, owing to a decrease in configurational entropy resulting from the extension of polymer chains during water absorption. This study provides important insights into transport phenomena in a hydroxyapatite (HAp)–poly(vinyl alcohol) (PVA) hydrogel by considering the thermodynamic principles governing molecular diffusion up to equilibrium and elucidating mechanisms relevant to drug delivery. HAp shows a hexagonal phase, and its unit cell volume increases by ∼2% after vinyl functionalization (HAp–π). PVA was converted to a chemically cross-linkable polymer and subsequently reacted with HAp–π to form a hybrid hydrogel network. The resulting system exhibits mechanical robustness resulting not only from chemical cross-links but also from noncovalent network constraints, which cooperatively give rise to a high density of effective cross-linking points. The hydrogel absorbs water and releases the drug slowly due to strong constraints imposed by the polymer structure. Despite these restrictions, molecular diffusion remains thermodynamically spontaneous (ΔG < 0), driven by a low, positive entropy change (ΔS), while enthalpic contributions (ΔH) are unfavorable. During swelling, water penetrates the hydrogel, driven by its higher chemical potential in the initially pure surrounding liquid, migrating into the polymer matrix and inducing network expansion, in a direction opposite to that of drug diffusion out of the hydrogel which further hinders the release dynamics because the solute is already in a high-entropy environment. Mass transport through a water-swellable release system constitutes an entropically driven process, dominated by diffusion within a constrained network. This work provides insight into entropy-regulated drug release, demonstrating that spontaneity is achieved at physiological temperature (∼37 °C) without altering the thermal energy so as to compromise long-term practical applications.
{"title":"Entropy-Regulated Swelling as the Mechanistic Driver of Drug Diffusion in a Mechanically Robust Hydroxyapatite/PVA Hybrid Hydrogel","authors":"Juliana Pretel de Souza, Vicente Lira Kupfer, Hugo Henrique Carline deLima, Jaqueline de Carvalho Rinaldi, Emerson Marcelo Girotto, Marcos Rogério Guilherme, Andrelson Wellington Rinaldi","doi":"10.1021/acs.macromol.5c03339","DOIUrl":"https://doi.org/10.1021/acs.macromol.5c03339","url":null,"abstract":"Hydrogels exhibit excellent permeability for solute transport, with their degree of swelling directly modulating drug diffusion through their polymer network. This dynamic hinders the quantitative prediction of the swelling mechanisms of these materials, owing to a decrease in configurational entropy resulting from the extension of polymer chains during water absorption. This study provides important insights into transport phenomena in a hydroxyapatite (HAp)–poly(vinyl alcohol) (PVA) hydrogel by considering the thermodynamic principles governing molecular diffusion up to equilibrium and elucidating mechanisms relevant to drug delivery. HAp shows a hexagonal phase, and its unit cell volume increases by ∼2% after vinyl functionalization (HAp–π). PVA was converted to a chemically cross-linkable polymer and subsequently reacted with HAp–π to form a hybrid hydrogel network. The resulting system exhibits mechanical robustness resulting not only from chemical cross-links but also from noncovalent network constraints, which cooperatively give rise to a high density of effective cross-linking points. The hydrogel absorbs water and releases the drug slowly due to strong constraints imposed by the polymer structure. Despite these restrictions, molecular diffusion remains thermodynamically spontaneous (Δ<i>G</i> < 0), driven by a low, positive entropy change (Δ<i>S</i>), while enthalpic contributions (Δ<i>H</i>) are unfavorable. During swelling, water penetrates the hydrogel, driven by its higher chemical potential in the initially pure surrounding liquid, migrating into the polymer matrix and inducing network expansion, in a direction opposite to that of drug diffusion out of the hydrogel which further hinders the release dynamics because the solute is already in a high-entropy environment. Mass transport through a water-swellable release system constitutes an entropically driven process, dominated by diffusion within a constrained network. This work provides insight into entropy-regulated drug release, demonstrating that spontaneity is achieved at physiological temperature (∼37 °C) without altering the thermal energy so as to compromise long-term practical applications.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"3 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146122233","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-02-05DOI: 10.1021/acs.macromol.5c02673
Grace E. Castillo, Sarah Karabadjakyan, Aditya V. Singh, Barry C. Thompson
While providing a more sustainable method of conjugated polymer synthesis with advantages over other cross-coupling methods, direct arylation polymerization (DArP) is still reliant on expensive, single-use homogeneous Pd catalysts. Previously, we have demonstrated the compatibility and recyclability of the commercially available heterogeneous catalyst SiliaCat DPP-Pd with DArP for the synthesis of poly[(3,4-ethylenedioxythiophene-2,5-diyl)-(9,9-dioctylfluorene-2,7-diyl)] (PEDOTF). Here, we demonstrate the compatibility of this catalyst across a broader range of monomers, including electron-deficient 2,2′,3,3′,5,5′,6,6′-octafluorobiphenyl and dithienyldiketopyrrolopyrrole (DPP), as well as 3-hexylthiophene and hexyl thiophene-3-carboxylates at 100 °C. Polymers were afforded with molar masses up to 40 kg/mol in yields up to 97%. These reactions also showed good compatibility with SiliaCat, which was able to be recycled up to five times with catalyst recoveries of 80–90%. Investigations of the room-temperature synthesis of PEDOTF using SiliaCat showed reduced reactivity using K3PO4, but using K2CO3, polymers of up to 11.1 kg/mol were achieved, and the catalyst was recycled five times. Investigations of the negative impact of K3PO4 across a range of monomers for polymerizations at 100 °C revealed similar detrimental effects, except for 2-bromo-3-hexylthiophene and 2-bromo-3-hexylesterthiophene, which performed similarly with K3PO4 and K2CO3. These findings provide insight into the compatibility of a broad range of monomers and reaction conditions with heterogeneous catalysis, as relevant to improving the accessibility and scalability of polymerizations using DArP.
{"title":"Elucidating and Expanding the Monomer Scope with Heterogeneous Catalysis in Direct Arylation Polymerization (DArP)","authors":"Grace E. Castillo, Sarah Karabadjakyan, Aditya V. Singh, Barry C. Thompson","doi":"10.1021/acs.macromol.5c02673","DOIUrl":"https://doi.org/10.1021/acs.macromol.5c02673","url":null,"abstract":"While providing a more sustainable method of conjugated polymer synthesis with advantages over other cross-coupling methods, direct arylation polymerization (DArP) is still reliant on expensive, single-use homogeneous Pd catalysts. Previously, we have demonstrated the compatibility and recyclability of the commercially available heterogeneous catalyst SiliaCat DPP-Pd with DArP for the synthesis of poly[(3,4-ethylenedioxythiophene-2,5-diyl)-(9,9-dioctylfluorene-2,7-diyl)] (PEDOTF). Here, we demonstrate the compatibility of this catalyst across a broader range of monomers, including electron-deficient 2,2′,3,3′,5,5′,6,6′-octafluorobiphenyl and dithienyldiketopyrrolopyrrole (DPP), as well as 3-hexylthiophene and hexyl thiophene-3-carboxylates at 100 °C. Polymers were afforded with molar masses up to 40 kg/mol in yields up to 97%. These reactions also showed good compatibility with SiliaCat, which was able to be recycled up to five times with catalyst recoveries of 80–90%. Investigations of the room-temperature synthesis of PEDOTF using SiliaCat showed reduced reactivity using K<sub>3</sub>PO<sub>4</sub>, but using K<sub>2</sub>CO<sub>3</sub>, polymers of up to 11.1 kg/mol were achieved, and the catalyst was recycled five times. Investigations of the negative impact of K<sub>3</sub>PO<sub>4</sub> across a range of monomers for polymerizations at 100 °C revealed similar detrimental effects, except for 2-bromo-3-hexylthiophene and 2-bromo-3-hexylesterthiophene, which performed similarly with K<sub>3</sub>PO<sub>4</sub> and K<sub>2</sub>CO<sub>3</sub>. These findings provide insight into the compatibility of a broad range of monomers and reaction conditions with heterogeneous catalysis, as relevant to improving the accessibility and scalability of polymerizations using DArP.","PeriodicalId":51,"journal":{"name":"Macromolecules","volume":"74 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146122188","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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