Advanced research work on radiation cross-linking of polymers in CIAC

Recent research carried out at the Chinese Institute of Applied Chemistry has contributed significantly to the understanding of the radiation chemistry of polymers. High energy radiation has been successfully used to cross-link fluoropolymers and polyimides. Here chain flexibility has been shown to play an important role, and T-type structures were found to exist in the cross-linked fluoropolymers. A modified Charlesby-Pinner equation, based upon the importance of chain flexibility, was developed to account for the solradiation dose relationship in systems of this type. An XPS method has been developed to measure the cross-linking yields in aromatic polymers and fluoropolymers, based upon the dose dependence of the aromatic shake-up peaks and the F/C ratios, respectively. Methods for radiation cross-linking degrading polymers in polymer blends have also been developed, as have methods for improving the radiation resistance of polymers through radiation cross-linking.     

The Application of Controlled/Living Radical Polymerization in Modification of PVDF-based Fluoropolymer

Fluorinated polymers are important materials that are widely used in many areas as taking the advantage of inertness to chemical corrosion, prominent weather resistance, low flammability, and good thermal stability. Poly(vinylidene fluoride)(PVDF) based fluoropolymers is the most common type of commercial fluoropolymer especially used as dielectric materials. However, there are always some shortcomings in practical applications, so it is necessary to modify PVDF-based fluoropolymers for better a...     

Amorphous fluoropolymers - a new generation of products

Poly(tetrafluoroethylene) (PTFE) already known since 50 years, Is a unique material among plastics due to its chemical inertness, heat resistance, electrical insulation properties and low coefficient of friction. Its high melt viscosity needs special ways of processing. That fact led to the development of melt-processible fluoropolymers such as Perfluoroethylene-propylene (FEP) and Perfluoroalkoxy (PFA). Now we have a third generation which is an amorphous fluorpolymer made by copolymerizing tetrafluoroethylene with 2,2-bis (trifluoromethyl) - 4,5 - difluoro -1,3 - dioxole. The bulky cyclic structure prevents the normal crystallisation as with PTFE polymers. The amorphous fluoropolymers have high clarity and dissolve in selected solvents. Having C-F, C-C and C-O bonds the well known properties as high temperature and chemical resistance are retained. Dielectric constant is in the range 1.83 - 1.93 up to 10.00 MHz the lowest of any plastic material. Optical properties are also very special. Refractive index is very low, in the range 1.29 - 1.32. Transmission is high from UV to IR and the polymer is not photo-degraded. The unique electrical and optical properties, coupled with high chemical and thermal stability, plus the ability to work from solution offers a powerful tool for those working on the frontiers of technology.     

有机氟材料的结构与性能及其在涂料中的应用

高性能、低（无）污染是当今涂料发展的主要趋势，氟树脂独特的结构特点使它具有很高的耐热性，耐化学性和耐候性，独特的电学性能，优良的表面性能和光学特性，从而使其成为可能同时具有这两项要求的材料之一，本文着重介绍了目前几种最主要的氟树脂的结构与性能，如聚四氟乙烯（PTFT），聚偏二氟乙烯（PVDF）、氟烯烃／乙烯基醚共聚树脂（FEVE）及全氟聚醚 （PFPE）等。另外还对当前国内，外含氟高聚物在涂料应用上的研究进展作了一些介绍。     

Plasma Surface Modification of Fluoropolymers Studied by ToF-SIMS

Surface modification by plasma treatment is an efficient way of improving metal adhesion to polymers. Here, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is used to characterize the surfaces of Teflon PFA and Teflon AF1600 films, following plasma treatments in H₂, O₂ and N₂ gases. This work is complementary to our previous study using XPS, and is particularly directed toward the identification of incorporated hydrocarbons which could seriously affect metal adhesion. Plasma treatments strongly modify the surfaces of fluoropolymers, causing the ablation of a part of the fluorocarbon structure, with H₂ being the most effective gas. The hydrocarbon content of such surfaces is not negligible, and a comparison with hydrocarbon levels on untreated surfaces suggests that a substantial fraction of this material was incorporated on plasma treatment; this is particularly so in the case of H₂ plasma treatment. Due to expected strong matrix effects caused by significant changes in surface chemistry and structure following the various plasma treatments, the use of SIMS absolute intensity values is discussed in terms of data treatment artifacts. Moreover, due to the differences in secondary ion yields between characteristic hydrocarbon and fluorocarbon SIMS peaks, the use of peaks normalized to the total intensity is also impractical. Here, positive mode absolute intensities and negative mode peak intensity values, when normalized to I_tot - I(H^–) - I(F^–), give valuable information, as in the comparison of hydrocarbon and N incorporations.     

Controlled Radical Copolymerization toward Well-Defined Fluoropolymers

In the past 80 years, fluoropolymers have found broad applications in both industrial and academic settings, owing to their unique physicochemical properties. Copolymerizations of fluoroalkene feedstocks present an important avenue to obtain high-performance materials by merging intrinsic attributes of fluorocarbons and great versatility of comonomers. Recently, while massive investigations have disclosed the great potentials of precisely synthesized polymers, researchers have made considerable efforts to approach well-defined fluorinated copolymers. This minireview discusses challenges in controlled radical copolymerizations (CRCPs) of fluoroalkenes and provides a concise perspective on recent progress in CRCPs of fluoroalkenes (e.g., tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropene, perfluoroalkyl vinyl ethers) with non-fluorinated vinyl comonomers, which have enabled on-demand preparations of various main-chain fluoropolymers with predefined molar masses, low dispersities, as well as regulable chemical compositions and sequences. The synthetic advantages of CRCPs will promote controlled and facile access to customized fluoropolymers for high-tech applications such as batteries, coatings and so on.     

Microemulsion polymerization for producing fluorinated structured materials

When perfluoropolyether microemulsions are used during polymerization of fluoropolymers, the structure of the reaction environment can be strictly controlled. In particular, the number and size of polymer particles in latexes can be set freely, yielding a number of advantages. First, as a result of radical segregation, terminations can be decreased without reducing polymerization rate: in this way high molecular weights are easily obtained also with poorly reactive monomers. Moreover, in combination with a reversible chain transfer mechanism based on iodine, particle segregation allows establishing pseudo-living polymerization conditions. In this situation formation of long branches in the polymer can be controlled by using bifunctional molecules that are able to link two different polymer chains to each other during polymerization. This is the so-called “branching and pseudo-living” technology. Finally, by co-coagulating latexes of different polymers prepared by microemulsion polymerization, very small particles and, thus, high interface areas are generated. In this way properties of different polymers, such as fluoroelastomers and fluorinated semicrystalline polymers, are matched effectively, generating new nanocomposite materials that exhibit outstanding properties. In this paper these results are reported and an overview of some novel sophisticated fluoropolymers obtained in microemulsion is given.     

利用~1H-NMR研究HDPE/PET/EVA共混体系的酯交换反应

本文在选用EVA作为HDPE/PET共混体系增容剂的基础上 ,通过双螺杆反应挤出熔融加工过程 ,促使EVA侧基上的酯基官能团与PET组分主链上的酯基在适当催化剂———有机金属化合物存在的条件下发生酯交换反应 .1H NMR结果表明 ,酯交换反应的产生在共混体系界面原位形成接枝或交联的PET EVA共聚物 ,且主要是以生成接枝共聚物的反应为主 .     

Polymerized micelles with compartments

Multicompartment micelles with distinct hydrophobic microdomains having different properties have been realized via micellar polymers bearing hydrocarbon and fluorocarbon fragments. In aqueous solution, such polymers can self-organize into coexisting hydrocarbon and fluorocarbon microdomains that selectively solubilize different hydrophobes. The most efficient approach uses block copolymer polysoaps, but simpler designs may be possible.     

Influence of fluorinated substituent and terminal length on phase behavior of mesogen‐jacketed liquid crystalline polymers with a biphenyl mesogen

A series of mesogen‐jacketed liquid crystalline polymers, poly{2,2,3,3,4,4,4‐heptafluorobutyl 4′‐hydroxy‐2‐vinylbiphenyl‐4‐carboxylate} (PF3Cm, where m is the number of carbon atoms in the alkoxy groups, and m = 1, 4, 6, and 8), the side chain of which contains a biphenyl core with a fluorocarbon substituent at one end and an alkoxy unit of varying length on the other end, were designed and successfully synthesized via atom transfer radical polymerization. For comparison, poly{butyl 4′‐hydroxy‐2‐vinylbiphenyl‐4‐carboxylate} (PC4Cm), similar to PF3Cm but with a butyl group instead of the fluorocarbon substituent, was also prepared. Differential scanning calorimetric results reveal that the glass transition temperatures (T_gs) of the two series of polymers decrease as m increases and T_gs of the fluorocarbon‐substituted polymers are higher than those of the corresponding butyl‐substituted polymers. Wide‐angle X‐ray diffraction measurements show that the mesophase structures of these polymers are dependent on the number of the carbon atoms in the fluorocarbon substituent and the property of the other terminal substituent. Polymers with fluorocarbon substituents enter into columnar nematic phases when m ≥ 4, whereas the polymer PF3C1 exhibits no liquid crystallinity. For polymers with butyl substituents, columnar nematic phases form when the number of carbon atoms at both ends of the side chain is not equal at high temperatures and disappear after the polymers are cooled to ambient temperature. However, when the polymer has the same number of carbon atoms at both ends of the side chain, a hexagonal columnar phase develops, and this phase remains after the polymer is cooled. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

由分子间氢键导致的丝素构象转变的FT-IR研究

用FT－IR研究发现，在丙烯腈与丙烯酸甲酯的共聚物（PANMA）与聚L-丙氨酸（PLAL）的共混体系中，丝素（SF）与PANMA的共混体系及SF与聚丙烯酸钠（NA）的共混体系中，含有羰基或其它极性基团的高分子与SF形成强弱不等的氢键．由于氢键的形成,使SF分子不得不调整自身的构象，从而引起其构象转变．讨论了可能的分子间氢键的结构．     

含氟聚合物分子链的构象和柔顺性

通过对含氟聚合物分子链内旋转构象的分析,发现含氟聚合物与其它结构类型的聚合物一样,其玻璃化转变温度Tg与分子链横截面积A和分子链内旋转让阻因子σ之间的关系遵循同样的规律^[1,2]。建议用Tg=973(σ-1.44)来计算含氟聚合物的分子链内旋转位阻因子。内旋转位阻因子相同时,含氟聚合物的玻璃化转变温度较其它结构类型的聚合物为高(图2),可归结为含氟聚合物分子链的紧密堆积。     

Polysulfide Polymers: Synthesis,Blending, Nanocomposites,and Applications

Abstract

Polysulfide polymers as an important class of polymers are used in different applications as sealants, adhesives, etc. They are usually synthesized by reaction of disodium polysulfides with dihalo compounds to yield liquid or solid polymers. Their most important advantages are excellent adhesion to different surfaces, creation of no defect in sealant under stress and pressure, resistance against to fuels and solvents, very low gas and steam permeability, and high resistance to ozone and UV. This article aims to review methods of synthesis, properties, and applications of polysulfide polymers. Also, polysulfide-based nanocomposites and blends are also briefly discussed.     

Pressure dependence of the demixing behaviour in polymer blends: I. Experimental procedure

The most common way to influence the liquid-liquid phase behaviour in partially miscible (co-)polymer blends is changing the blending temperature. Since most extruders can handle pressures, up to 300 bar, pressure may also be used to influence the miscibility of polymers during blending. We have developed equipment and an experimental procedure to study the pressure dependence of the liquid-liquid demixing behaviour of high-viscous polymer blends under equilibrium conditions. Small amounts (1–4 grams) of specially made polymers are blended in the ‘DSM MINI EXTRUDER’. After a chosen mixing time, a small portion of the blend is injected into a small capillary tube and kept at the blending temperature. The phase behaviour of the blends as a function of temperature and pressure is studied via laser light scattering (at a scattering angle of 90°) in a specially made 400 bar/250°C window autoclave, where the capillary cell is placed in a high temperature grade silicon oil.     

Plasmochemical modification of fluorocarbon polymers for creation of new hemocompatible materials

The various plasmochemical technique for the surface functionalization and regulation of the biological characteristics of fluorocarbon polymers aimed at the enhance their blood compatibility are described. The plasmochemical treatment in oxygen and nitrogen containing gases has been used to increase of surface energy and hydrophoby of fluorocarbon polymers. Modification of the surface morphology and chemical structure to improve thromboresistive properties of polymers by plasma etching and deposition of biocompatible materials was demonstrated and discussed. Plasma-assisted immobilization of proteins in combination with other plasma modification methods provides a promising technique for engineering of a new generation of hemocompatible materials.     

Low‐Fouling Fluoropolymers for Bioconjugation and In Vivo Tracking

The conjugation of hydrophilic low‐fouling polymers to therapeutic molecules and particles is an effective approach to improving their aqueous stability, solubility, and pharmacokinetics. Recent concerns over the immunogenicity of poly(ethylene glycol) has highlighted the importance of identifying alternative low fouling polymers. Now, a new class of synthetic water‐soluble homo‐fluoropolymers are reported with a sulfoxide side‐chain structure. The incorporation of fluorine enables direct imaging of the homopolymer by ¹⁹F MRI, negating the need for additional synthetic steps to attach an imaging moiety. These self‐reporting fluoropolymers show outstanding imaging sensitivity and remarkable hydrophilicity, and as such are a new class of low‐fouling polymer for bioconjugation and in vivo tracking.     

The direct fluorination of hydrocarbon polymers

A new technique for direct fluorination has been used to prepare several new fluorocarbon polymers. The direct fluorination of poly-p-xylylene, polyisobutylene, Novolac and a highly crosslinked phenolic resin has produced fluorocarbon polymers which bear a strong structural resemblance to their hydrocarbon polymer precursors, though some crosslinking may occur. The thermal properties of these polymers have been investigated by DSC and TGA techniques.     

Engineering polymer alloys by reactive extrusion

During the last fifty years blending of dissimilar polymers has been a major path to tailor materials with new properties in industry. Since most of the interesting polymer blends are immiscible, the different compatibilisation strategies have received a lot of attention. In the area of engineering plastics, reactive blending is usually used to compatibilise immiscible polymers. The most important polymer alloys prepared by reactive extrusion [Polycarbonate/Polybutyleneterephthalate-alloys (PC/PBT), Polyamide/Polyphenyleneether-alloys (PA/PPE), Styrenics/Polyamide-alloys (ABS/PA)] have already reached an interesting sales volume. The commercial success of these materials is mainly related to their unique combinations of properties, which enables their use in a multitude of applications.     

High DNA‐Binding Affinity and Gene‐Transfection Efficacy of Bioreducible Cationic Nanomicelles with a Fluorinated Core

During the last two decades, cationic polymers have become one of the most promising synthetic vectors for gene transfection. However, the weak interactions formed between DNA and cationic polymers result in low transfection efficacy. Furthermore, the polyplexes formed between cationic polymers and DNA generally exhibit poor stability and toxicity because of the large excess of cationic polymer typically required for complete DNA condensation. Herein, we report the preparation of a novel class of bioreducible cationic nanomicelles by the use of disulfide bonds to connect the cationic shell to the fluorocarbon core. These bioreducible nanomicelles form strong interactions with DNA and completely condense DNA at an N/P ratio of 1. The resulting nanomicelle/DNA polyplexes exhibited high biocompatibility and performed very effectively as a gene‐delivery system.     

Characterisation and morphology of biodegradable chitosan / synthetic polymer blends

Chitosan has been used to form miscible, biodegradable blends with hydrophilic synthetic polymers as PVA and PEO. Characterisation of the blends by DSC, IR and microscopy analysis was made giving much attention to possible interactions of molecular polar group in the polymer chains. PVA/chitosan are found to be amorphous in the whole range of composition having one glass transition temperature. Molecular interactions in the pair of polymers are connected with amide group of chitosan and hydroxyl groups of PVA. PEO/chitosan blends stay amorphous up to 0.2 weight fraction of PEO. For a higher amount of PEO that polymer crystallises forming a spherulite crystalline structure. We correlate the overall kinetics of crystallisation and melting behaviour of solid, semicrystalline blends PEO/chitosan in the form of thin films for a set of PEO species of different blend composition with a morphological structure of the blends. Negative values of the Flory-Huggins interaction parameter due to specific interactions by hydrogen bonding through ether group of PEO and hydroxyl group of chitosan were evaluated. Amide groups do not participate in the molecular interaction between PEO and chitosan molecules. Avrami equation was applied to describe kinetics of crystallisation of pure PEO and PEO/chitosan blends of various compositions.