Photocrosslinking of stilbene-modified polymers

The reactions of trans-2,5-dimethoxy-4′-aminostilbene with poly(maleic anhydride-co-methylvinyl ether) and trans-2,5-dimethoxy-4′-isocyanatostilbene with poly(oxy-1,4-phenyleneisopropylidene:1,4-phenyleneoxy-2-hydroxytrimethylene) yield polymeric systems which undergo rapid crosslinking upon short exposure to ultraviolet light. The extent of photocrosslinking as a function of exposure time was determined by the decrease of the trans-stilbene ultraviolet absorption at 350 nm.     

SBS的光交联研究

利用测凝胶含量的方法对SBS热塑性弹性体在紫外光辐照下的光交联反应进行了研究;并分析了光交联的影响因素。实验表明：采用安息香二甲醚（BDK）作为引发剂、三聚异氰酸三烯丙酯（TAIC）作为交联剂,能使SBS快速有效地发生交联,且凝胶含量达到90％以上。在此基础上,对不同的交联环境（空气、N2）、温度、样品厚度进行了对比,而且初步研究了蒙脱土（MMT）的加入对交联体系的影响。     

Supramolecular association of acid terminated polydimethylsiloxanes

Summary. Benzoic acid terminated polydimethylsiloxanes (PDMS) have been synthesized by hydrosilylation of allyloxybenzylbenzoate with SiH terminated precursors followed by deprotection. These oligomers have been characterized by ¹H, ¹³C and ²⁹Si NMR, by FTIR and by SEC in tetrahydrofurane. Because of the flexibility and low polarity of the siloxane backbone, they are ideally suited to study the effect of hydrogen bonding on macromolecular properties. Received: 17 July 1997/Revised: 22 July 1997/Accepted: 6 August 1997     

Interfacial reactions and self-adhesion of polydimethylsiloxanes

Polydimethylsiloxane (PDMS) oil and crosslinked rubber react with hydroxylated surfaces, when heated at 250-300°C. PDMS is thus chemically bound to silicate glass sheets and to iron hydrous oxide particles. As a result, stable and adherent PDMS coatings may be obtained over glass, by heating silicone oil spread over glass sheets. Glass-PDMS-glass adhesive joints can also be obtained by heating preformed, crosslinked silicone sheets between glass parts. Also, PDMS rubber is heat-stabilized by in situ-generated iron hydrous oxide particles. These results are explained by considering that active Si-O chain ends, formed by chain scission, bind to surface hydroxyl groups, in a reaction competitive with the formation of cyclic oligomers. PDMS can thus be seen as a thermally-activated, reactive adhesive.     

Photocrosslinking in ruthenium-labelled duplex oligonucleotides

The formation of a photoadduct between a [Ru(1,4,5,8-tetraazaphenanthrene)(2)4,7-diphenylphenanthroline](2+) complex chemically attached to a synthetic oligonucleotide, and a guanine moiety in a complementary targeted single-stranded DNA molecule was studied for ten 17-mer duplexes by denaturing gel electrophoresis. This photoadduct formation leads to photocrosslinking of the two strands. The percentage quenching of luminescence of the complex by electron transfer was compared to the resulting yield of photocrosslinked product. This yield does not only depend on the ionisation potential of the guanine bases, which are electron donors, but also on other factors, such as the position of the guanine bases as compared to the site of attachment of the complex. The photocrosslinking yield is higher when the guanine moieties are towards the 3' end on the complementary strand as compared to the tethering site. Computer modelling results are in agreement with this preference for the 3' side for the photoreaction. Interestingly, the photocrosslink is not alkali labile. Moreover, a type III exonuclease enzyme is blocked at the position of photocrosslinking.     

Photocrosslinking of a maleimide functionalized polymethacrylate

A polymethacrylate bearing pendent maleimide (MI) groups has been crosslinked by UV irradiation of the photoinitiator‐free functionalized polymer. The reaction was followed in situ by real‐time IR spectroscopy and shown to proceed with an initial quantum yield of two maleimide double bonds polymerized per photon absorbed, the value expected for a photocycloaddition mechanism. A twofold increase of the reaction rate was achieved by performing the UV irradiation in the presence of a thioxanthone photosensitizer (1 wt%). Insolubilization of the photoresist requires the reaction of at least 18 MI double bonds per polymer chain, thus implying the occurrence of an intramolecular coupling process between neighbouring MI groups located on the same polymer chain. In the presence of an electron donor monomer, like the divinylether of triethyleneglycol used, the cycloaddition reaction gives way to a radical‐induced copolymerization of maleimide and vinyl ether double bonds, which becomes the only crosslinking process in a stoichiometric mixture of the two components. Copyright © 2003 Society of Chemical Industry     

Industrial applications of the surface activity of polydimethylsiloxanes

The surface properties of silicones are responsible for many of their varied applications. An explanation in basic terms is given in this paper for this surface activity together with some insight into several of the applications that result from this surface activity.     

Model study of the crosslinking of polydimethylsiloxanes by peroxides

The decompositions of di-t-butyl peroxide (TBP) and diaroyl peroxides in permethylated silicone oil (47V20) have been studied by differential scanning calorimetry (DSC). Results show the importance of the solubility of the peroxide in the silicone on their rate of disappearance. For the diaroyl peroxides, according to the nature of the substituents on the phenyl ring and the concentration of the peroxide, the decomposition occurs in solution and/or in the solid phase. Decomposition in solution began at a lower temperature than in the solid phase, which took place immediately after melting and was quite instantaneous. Decomposition of these peroxides was also performed in octamethylcyclotetrasiloxane (D₄) and decamethyltetrasiloxane (DMTS). According to DSC results, D₄ seems to be a better model of the silicone than the linear one. Analyses of the products of the decomposition of TBP and dibenzoyl peroxide (BP) in this model showed that the dehydrodimer of D₄ was produced in low yield relative to peroxide. The main compounds obtained were high molecular weight compounds, which were apparently different for the two peroxides. The free radical origin of these products has been proven in the case of TBP by the addition of TEMPO in the reaction medium.     

Electrospinning and Photocrosslinking of Highly Modified Fungal Chitosan

The main focus of this study is to elucidate and optimize the electrospinning process for highly modified fungal chitosan. An efficient one-step process for functionalization of chitosan with arylazide and other desired functional groups via amidation is used for synthesis. Critical electrospinning process parameters, namely, molecular weight, concentration, and ratio of chitosan and additive poly(ethylene oxide) as well as degree of substitution of chitosan are identified by systematic parameter variation following design-of-experiment guidelines. Their influence on the viscoelastic properties of spinning solutions is studied and attributed to changes in chain entanglements. These changes result in drastic shifts in the electrohydrodynamic jet behavior and the resulting fiber morphologies. When the viscosity is increased above a critical limit, complete cancellation of whipping instabilities is observed, resulting in a stable linear jet and highly aligned but partly coalescing microfibers. It is shown how this process conditions can be avoided and how the production of uniform and defect-free nanofibers from highly functional chitosan can be carried out. In addition, a new photocrosslinking method for generation of water and acid stable chitosan nanofiber meshes is established.     

Photocrosslinking kinetics of polymer blends undergoing spinodal decomposition process

Photocrosslinking reaction kinetics of poly(2-chlorostyrene) performed inside the spinodal region of poly(2-chlorostyrene)/poly(vinyl methyl ether) (P2CS/PVME) blends was investigated by means of ultraviolet (UV)-visible absorption spectroscopy. The reaction was performed via photodimerization of anthracene moieties chemically labeled on the P2CS chains. The crosslinking kinetics of (P2CS/PVME) blends submitted to a temperature jump from the one-phase into the spinodal regions was observed by monitoring the irradiation time dependence of the absorbances of anthracene as well as of the blend in two regions of wavelengths. One is inside and the other is outside the absorption range of anthracene. The contribution of the sample cloudiness to the absorbance of anthracene was subtracted from the absorption data by using an empirical power law experimentally established between the incident wavelengths and the absorption of the blends. It was found that the reaction kinetics approximately follows the mean-field kinetics inside the spinodal region, resembling the behavior of the crosslinking reaction performed in the miscible region at relatively low crosslinking densities. On the other hand, the method described here fails to estimate the crosslinking densities when the phase separation proceeds rapidly, overcoming the reaction. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:885–893, 1998     

光交联对HDPE凝胶量的影响

用安息香二甲醚和三(丙烯酰氧乙基)异氰尿酸酯(TAEIC)作为PE的光敏剂和助交联剂,研究了它们的用量、光照时间、交联温度,紫外光光强对PE交联度的影响。结果表明,安息香二甲醚是一种有效的光敏剂,引发效率较高;助交联剂可以提高交联效率;光照时间、紫外光光强和交联温度等对PE的交联度均有明显的影响。     

Miscibility of PVC with chlorinated PE and chlorinated PVC

Miscibility of PVC with chlorinated PE and chlorinated PVC was reviewed. The miscible region of chlorine content ranged from 44 wt% to 65 wt%, which was not symmetric to the chlorine content of PVC, 56.7 wt%. Two group contribution methods were used to calculate solubility parameters of polymers. The results of solubility parameters showed a more symmetric miscible region with respect to the value of PVC. However, the ranges of miscibility were different. It was 2.3 (J/cm 3 ) 0.5 in a three-dimensional method and was 1.5 (J/cm 3 ) 0.5 in the Fedors method.     

Telechelic polydimethylsiloxanes with terminal acetylenic groups prepared by phase-transfer catalysis

Telechelic, hydroxyalkyl terminated polydimethylsiloxanes were obtained under mild conditions via hydrosilylation of allyl alcohol or ethylene glycol monoallyl ether by oligomeric αω-hydride terminated polydimethylsiloxanes, with the use of a platinum catalyst. They were subsequently modified in a phase transfer catalyzed reaction by propargyl bromide, to give telechelic polysiloxanes terminated by acetylenic groups. The synthetic pathway is described and the characterization of the obtained products is presented.     

Synthesis and Photocrosslinking Reaction of N-Allylcarbamoylmethyl Cellulose Leading to Hydrogel

Summary The reaction of the carboxymethyl cellulose sodium salt (Na-CMC) (degrees of substitution (DS) = 1.2) with N-hydroxysuccinimide (Su-OH) in the presence of 1-hydroxybenzotriazole and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) was carried out in water to obtain the Su-OH ester of carboxymethyl cellulose, Su-CMC, with the DS values of 0.19 – 1.04. N-Allylcarbamoylmethyl cellulose (Allyl-CMC), which was prepared from the reaction of Su-CMC with an excess amount of allylamine, was crosslinked by UV-irradiation. In addition, the photocrosslinked Allyl-CMC film was swollen with water to form a hydrogel having a relatively high water-swelling property, e.g., the degree of swelling (ds) was ca. 360% for Allyl-CMC with the DS of 0.93.     

Photocrosslinking Polymerization of Methacrylate Modified Triethoxysilanes Polycondensates and Multifunctional Methacrylates

Densely crosslinked polymer networks were prepared by fast, visible light‐induced polymerization at 20–22 °C. The two methacrylate functionalized triethoxysilanes polycondensates (MSiP) either alone, or in a mixture with methacrylate modified oxozirconium clusters, were polymerized separately and as comonomers to multimethacrylate monomers in a weight ratio of 1:0.9. Pure organic networks based on 1,6‐bis(2‐hydroxy‐3‐methacryloyloxyethoxycarbonylamino)‐2,2,4‐trimethylhexane (UDMA) were used for comparison in the same ratio to other comonomers. The networks based on organic bifunctional monomers showed high, around 85% conversion of double bonds. Nevertheless the non‐reacted monomer that migrates to the toluene amounts from 5.6 to 11.65 wt.‐%. Copolymerization of UDMA with tetrafunctional components resulted in networks with higher residual unsaturation up to 27.7%. This result points out the important role that functionality and the spacer structure between the monomer double bonds play in the extent of reaction. Based only on modified inorganic Si? O? Si nano‐structures the networks are characterized by nearly complete building up of MSiP in the network, extreme crosslinks density, and mostly less than 1 wt.‐% of soluble substances. However, residual unsaturations exceeded 22%. The advantage of copolymerization of MSiP with proper organic comonomers as potential solvent free matrices for dental composites was demonstrated by a network consisting of MSiP II and UDMA. The 13.7% of unreacted double bonds and 99.65 wt.‐% gel content approximated efforts to minimize residual unsaturation and maximize monomer conversion in cured networks.

Monomers used for the synthesis of the densely crosslinked polymer.     

氯化聚丙烯的乳化

对氯化聚丙烯的乳化作了初步探索。实验表明,用十二烷基硫酸钠和磺化蓖麻油作乳化剂,可以把氯化聚丙烯制咸水性乳液涂料。从粘附力和拉伸剪切强度测定结果可以看出,用水性氯化聚丙烯代替溶剂型氯化聚丙烯是可行的。     

含氯荧光素的合成

以2,4-二羟基苯甲酸甲酯为原料,经过氯代反应、水解反应、脱羧反应合成2,4-二氯间苯二酚.在甲基磺酸作用下,以2,4-二氯间苯二酚和3,6-二氯-4-羧基邻苯二甲酸酐为原料缩合得到重要的含氯荧光素.目标产物及中间体的结构通过IR、1HNMR、MS和元素分析表征.     

Emissivity of chlorinated polyethylene

The emissivity of chlorinated polyethylene containing varying amounts of combined chlorine has been investigated. It was found that the emissivity of these compounds increases significantly with increase in chlorination.     

Photocrosslinking of poly(ethylene terephthalate) copolymers containing photoreactive comonomers

Poly(ethylene terephthalate) (PET) copolymers containing 4,4′-, 3,5-, and 2,4-benzophenone dicarboxylate chromophores have been synthesized by transesterification of PET with benzophenone 4,4′-dicarboxylic acid (4,4′-BDA), dimethyl benzophenone 4,4′-dicarboxylate (4,4′-BDE), dimethyl benzophenone 3,5-dicarboxylate (3,5-BDE) and dimethyl benzophenone 2,4-dicarboxylate (2,4-BDE). The benzophenone segments in the backbone induce photocrosslinking upon UV irradiation in the solid state most probably by a hydrogen atom abstraction mechanism. The crosslinking rate depends upon the concentration and the structure of chromophores as evidenced by gel content measurements. The photocrosslinking efficiency of 4,4′-benzophenone dicarboxylate containing polymers is higher than for 2,4- or 3,5-benzophenone dicarboxylate containing polymers. Photocrosslinked PET copolymers show increased glass transition temperatures and broadening of melting transitions.