中国改革开放以来的高分子物理和表征研究

本综述介绍了改革开放四十多年来中国大陆学者在高分子物理和表征领域所取得的部分成就.按照时间顺序,分别从概念的突破、理论的发展和技术的创新三个方面选取具有代表性研究成果进行简短的介绍,以期展示当代中国学者在这一基础研究领域所表现出来的拼搏意志和创新精神,激励新一代学者共同努力,勇攀科学高峰,为国民经济和社会发展作出更大的贡献.

Creating super-tough and strong PA6/ABS blends using multi-phase compatibilizers

Polyamide/acrylonitrile-butadiene-styrene copolymer(PA/ABS) blends have drawn considerable attention from both academia and industry for their important applications in automotive and electronic areas. Due to poor miscibility of PA and ABS, developing an effective compatibilization strategy has been an urgent challenge to achieve prominent mechanical properties. In this study, we create a set of mechanically enhanced PA6/ABS blends using two multi-monomer melt-grafted compatibilizers, SEBSg-(MAH-co-St) and ABS-g-(MAH-co-St). The dispersed domain size is significantly decreased and meanwhile the unique "soft shell-encapsulating-hard core" structures form in the presence of compatibilizers. The optimum mechanical performances manifest an increase of 36% in tensile strength and an increase of 1300% in impact strength, compared with the neat PA6/ABS binary blend.

Investigation of Hydrolysis in Poly(ethylene terephthalate) by FTIR-ATR

The hydrothermal aging of poly（ethylene terephthalate） （PET） was investigated at 70-95 ℃. A new method to investigate the hydrolysis degree of PET by Fourier transform infrared spectroscopy （FTIR） was proposed. The spectra during the hydrothermal aging were measured using attenuated total reflection accessory （ATR）. Peak resolving of carbonyl regions was performed, and the ratio of two groups of bands representing carboxylic acids and esters respectively were calculated to show the hydrolysis degree of ester groups in PET. The acid/ester ratio shows exactly the same trend as the average chain scission number per unit mass at various temperatures and thus can be used as a parameter to characterize the hydrolysis and random chain scission of PET. This method related to the hydrolysis mechanism directly, is simple, fast and convenient compared to the traditional methods such as viscometry, end-group titration and size exclusion chromatography （SEC）. It may also be useful in hydrolysis characterization of other polyesters.

Correlation of Morphology Evolution with Superior Mechanical Properties in PA6/PS/PP/SEBS Blends Compatibilized by Multi-phase Compatibilizers

In this study, the maleic anhydride （MAH） and styrene （St） dual monomers grafted polypropylene （PP） and poly[styrene-b- （ethylene-co-butylene）-b-styrene] （SEBS）, i.e. PP-g-（MAH-co-St） and SEBS-g-（MAH-co-St） are prepared as multi-phase compatibilizers and used to compatibilize the PA6/PS/PP/SEBS （70/10/10/10） model quaternary blends. Both PS and SEBS are encapsulated by the hard shell of PP-g-（MAH-co-St） in the dispersed domains （about 2 μm） of the PA6/PS/PP-g-（MAH-co-St）/SEBS （70/10/10/10） quaternary blend. In contrast, inside the dispersed domains （about 1 μm） of the PA6/PS/PP/SEBS-g-（MAH-co-St） （70/10/10/10） quaternary blend, the soft SEBS-g-（MAH-co-St） encapsulates both the hard PS and PP phases and separates them. With increasing the content of the compatibilizers equally, the morphology of the PA6/PS/（PP＋PP-g-（MAH-co-St））/（SEBS＋SEBS-g-（MAH-co-St）） （70/10/10/10） quaternary blends evolves from the soft （SEBS＋SEBS-g-（MAH-co-St）） encapsulating PS and partially encapsulating PP （about 1 μm）, then to PS exclusively encapsulated by the soft SEBS-g-（MAH-co-St） and then separated by PP-g-（MAH-co-St） inside the smaller domains （about 0.6 μm）. This morphology evolution has been well predicted by spreading coefficients and explained by the reaction between the matrix PA6 and the compatibilizers. The quaternary blends compatibilized by more compatibilizers exhibit stronger hierarchical interfacial adhesions and smaller dispersed domain, which results in the further improved mechanical properties. Compared to the uncompatibilized blend, the blend with both 10 wt% PP-g-（MAH-co-St） and 10 wt% SEBS-g-（MAH-co-St） has the best mechanical properties with the stress at break, strain at break and impact failure energy improved significantly by 97%, 71% and 261%, respectively. There is a strong correlation between the structure and property in the blends.

Tough superabsorbent poly(acrylic acid) nanocomposite physical hydrogels fabricated by a dually cross-linked single network strategy

In this work, we report a facile method for the preparation of tough and highly stretchable physical hydrogels by dual cross-linking composed of vinyl-hybrid silica nanoparticles（VSNPs） as multivalent covalent cross-linking and hydrogen bonding as physical cross-linking. Poly（acrylic acid） nanocomposite physical hydrogels（NCP gels） are obtained without adding any organic chemical cross-linkers. When the content of VSNPs is 0.7 wt%（relative to the monomer）, the NCP gels exhibit good mechanical properties（fracture strength = 370 k Pa, elongation at break = 2200%） and a high swelling capacity in both deionized water（2300 g/g） and saline（220 g/g）. Meanwhile, the NCP gels have good recovery ability.

A simple and green route to transparent boron nitride/PVA nanocomposites with significantly improved mechanical and thermal properties

A simple and green method is developed to prepare hexagonal boron nitride （h-BN）/poly（vinyl alcohol） （PVA） nanocomposites by using water as a common solvent ofh-BN nanosheets and PVA. The obtained h- BN/PVA nanocomposites are highly transparent, and have significantly improved mechanical and thermal properties. They may outperform nano-clay and nano-alumina/PVA nanocomposites as flexible optoelectronic devices, optical windows and heat-releasing materials operated in oxidative or corrosive environment.

Super-tough and rapidly self-recoverable multi-bond network hydrogels facilitated by 2-ureido-4[1H]-pyrimidone dimers

Multi-bond network(MBN) hydrogels contain hierarchical dynamic bonds with different bond association energy as energy dissipation units,enabling super-tough mechanical properties.In this work,we copolymerize a protonated 2-ureido-4[1 H]-pyrimidone(UPy)-contained monomer with acrylic acid in HCl solution.After removing excess HCl,UPy motifs are deprotonated and from dimers,thus generating an UPy-contained MBN hydrogel.The obtained MBN hydrogels(75 wt% watercontent) exhibit super-tough mechanical properties(0.39 MPa to 2.51 MPa tensile strength),with tremendous amount of energy(1.68 MJ/m^(3) to 11.1 MJ/m^(3)) dissipated by the dissociation of UPy dimers.The introduction of ionic bonds can further improve the mechanical properties.Moreover,owing to their dynamic nature,both UPy dimers and ionic bonds can re-associate after being dissociated,resulting in excellent self-recovery ability(around 90% recovery efficiency within only 1 h).The excellent self-recovery ability mainly originates from the re-association of UPy dimers based on the high dimerization constant of UPy motifs.

Polyolefin-functionalized graphene oxide and its GO/HDPE nanocomposite with excellent mechanical properties

To prepare GO/Polyolefin nanocomposites with enhanced mechanical, electrical, or thermal properties is still a challenge due to the poor interfacial adhesion between GO and non-polar polyolefins. In this study, we report an effective strategy for the polyolefin-functionalized graphene oxide （fGO） using two-step methods GO was firstly modified by using glycidyl methacrylate （GMA） and styrene （St） dual monomers grafting method, thus GO-g-（GMA-co-St） with numerous epoxide groups is obtained. Then through the reaction between the epoxide group of GMA and anhydride group of maleic anhydrides （MAH） of the prepared HDPE-g-（MAH-co-St）, GO-g-HDPE-g-（MAH-co-St） could be obtained. The successful prepara- tion of the GO-g-HDPE-g-（MAH-co-St） was confirmed by AFM, TEM, FTIR, XRD, DSC, and TGA characterization. The results show the grafting ratios of the poly（GMA-co-St） and HDPE-g-（MAH-co-St） being up to 50.4 wt% and 70.4 wt%, respectively. The functionalized GO shows homogeneous dispersion in the nanocomposites with HDPE, and the stress at break and strain at break of the nanocomposite is increased by 28.7% and 130% respectively with only 0.2 wt% fGO loading. The approach of the polyolefin- functionalized GO paves a new way to develop not only polyolefin/graphene nanocomposites but also excellent nanocomposites of polyolefin/engineering plastic blends with graphene.

Transparent h-BN/polyacrylamide nanocomposite hydrogels with enhanced mechanical properties

In this study, a facile way has been proposed to prepare transparent, tough and flexible polyacrylamide （PAM） hydrogels which is composed of a dually crosslinked single network by chemical crosslinking of N,N＇-methylenebisacrylamide （BIS） and physical crosslinking of hydrophilic hexagonal boron nitride （h- BN） nanosheets. The resulting h-BN/PAM nanocomposite hydrogels are highly transparent, and exhibit significantly enhanced mechanical properties compared to the dark （GO）/PAM nanocomposite hydrogels or chemical crosslinking PAM hydrogels. Thus it opens up new opportunities for developing next- generation transparent, tough and flexible hydrogels that hold great promise in such important applications as light responsive soft robot and liquid microlenses.

Stretchable alkaline quasi-solid-state electrolytes created by super-tough, fatigue-resistant and alkali-resistant multi-bond network hydrogels

Hydrogel-based quasi-solid-state electrolytes(Q-SSEs) swollen with electrolyte solutions are important components in stretchable supercapacitors and other wearable devices. This work fabricates a supertough, fatigue-resistant, and alkali-resistant multi-bond network(MBN) hydrogel aiming to be an alkaline Q-SSE. To synthesize the hydrogel, a 2-ureido-4[1H]-pyrimidone(UPy) motif is introduced into a poly(acrylic acid) polymer chain. The obtained MBN hydrogels with 75 wt% water content exhibit tensile strength as high as 2.47 MPa, which is enabled by the large energy dissipation ability originated from the dissociation of UPy dimers due to their high bond association energy. Owing to the high dimerization constant of UPy motifs, the dissociated UPy motifs are able to partially re-associate soon after being released from external forces, resulting in excellent fatigue-resistance. More importantly, the MBN hydrogels exhibit excellent alkali-resistance ability. The UPy Gel-10 swollen with 1 mol/L KOH display a tensile strength as high as ~1.0 MPa with elongation at break of ~550%. At the same time, they show ionic conductivity of ~17 m S/cm, which do not decline even when the hydrogels are stretched to 500% strain.The excellent mechanical property and ionic conductivity of the present hydrogels demonstrate potential application as a stretchable alkaline Q-SSE.

Super Tough Hydrogels with Self-adaptive Network Facilitated by Liquid Metal

Liquid metals(LM)refer to Ga-based alloys with low melting points such as Eutectic GaInSn alloys(EGaInSn),which have excellent fluidity,flexibility and low toxicity at room temperature.In this work,by incorporating EGaInSn into poly(acrylic acid)(PAA)hydrogels as dynamic crosslinkers and effective energy-dissipating units,tough and strong PAA-LM hydrogels are prepared through the interactions between the oxide layers on the surface of LM and carboxyl groups of PAA chains.Moreover,owing to the fluidity of LM,one LM droplet as a cross-linking point may change its shape or break into more and smaller droplets in the hydrogels upon stretching.Then hydrogels with self-adaptive networks can be fabricated by mechanical training through cyclic stretch at a certain elongation.Thus,the networks of the hydrogels are further homogenized,and the hydrogels are significantly toughened during the training due to the increased cross-linking density from the larger number of smaller LM droplets.After a 5-cycle training at the maximum strain of 500%and 24 h recovering,the tensile strength and initial modulus of the PAA-LM hydrogels can be increased from 355 kPa to 597 kPa and 71 kPa to 166 kPa,respectively,while the elongation at break only decreases from 1491%to 1034%.

A facile route to the hierarchical assembly of Au nanoparticles on carbon nanotubes through Cu^(2＋) coordination for surface-enhanced Raman scattering

We report the hierarchical assembly of Au nanoparticles on carboxylized carbon nanotubes（c-CNTs）through Cu^（2＋） coordination. This route is facile and green, and can easily control the loading density of Au nanoparticles. The c-CNT matrix ensures uniform distribution of Au nanoparticles, which is particularly important for the enrichment of hot spots while preventing their serious agglomeration. Moreover, the cCNT matrix also contributes to the electromagnetic enhancement due to its surface plasmon resonance,and the chemical enhancement due to the adsorption of the target molecules. The resulting Au@c-CNT nanohybrids exhibit a remarkable synergy in SERS compared to neat Au nanoparticles.