Photochemistry of polymeric systems. VI. Photocrosslinking of basic polymers and copolymers dyeing

Poly(N-vinylamine) (PVAm) and methylmethacrylate/dimethylaminoethylmethacrylate copolymers (MMA/DMAEMA) were prepared and then substituted by cinnamic or cinnamylidene photosensitive groups. The photosensitivity of these materials was determined using the so-called photoresist test in various experimental conditions. A comparison was made between MMA/DMAEMA and methylmethacrylate/4-vinylpyridine (MMA/4VP) photosensitized copolymers. The best results were obtained with MMA/DMAEMA on textile support. A photosensitization study was carried out by adding some compounds such as thioxanthone (10% in bulk). It showed that the multiplicity factor can be 10 with MMA/DMAEMA copolymers and even up to 64 for photosensitive PVAm. The addition of anionic dyes on the polymers emphasized that a better fixation occured for aliphatic amines than for pyridinic ones.     

Photocrosslinking of chlorinated polydimethylsiloxanes

Photocrosslinking behavior of chlorinated polydimethylsiloxanes (C-PDMS) has been studied. It was found that the viscous C-PDMS were readily crosslinking to form the rubberlike materials on irradiation from a high pressure mercury lamp. The crosslinking mechanism was proposed on the basis of infrared spectroscopy. It was suggested that the photolysis of the carbon—chlorine bond induced by the ultraviolet irradiation is a primary step for crosslinking, and is followed by mutual combination of SiCH_2· radicals, eventually, to form the crosslinked C-PDMS. The effect of halogens and atmosphere on the crosslinking was also discussed.     

Photochemistry of polymeric systems. V. Photocrosslinking of polymers and copolymers containing pyrazine mono-and di-N-oxide groups

Pyrazine mono- and di-N-oxide chromophores included in a polymeric chain induce its photoreticulation. Photosensitivity is higher for dioxidized samples than for monoxidized ones. The mechanism of photocrosslinking is different from the one which proceeds photoreticulation of polymeric chains containing pyridine N-oxide groups.     

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。     

Photochemistry of polymeric systems. III. Photocrosslinking of polymers and copolymers including cyanocinnamylydene–pyridinium groups

Photocrosslinkable polymers were obtained by reacting esters of cinnamic acid or cyanocinnamylideneacetic acid onto pyridine units of a homopolymer or onto a suitable copolymer. These photosensitive polymers were characterized by conventional analysis and spectrometry. The photocrosslinking was studied on thin films measuring the threshold of insolubilization together with UV and IR spectrometry.     

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 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。     

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 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.     

Photocrosslinking of functionalized rubbers. X. Butadiene–acrylonitrile copolymers

The photocrosslinking of polyacrylonitrile‐block‐polybutadiene‐block‐polyacrylonitrile (ABA) was shown to proceed within seconds at ambient temperature upon UV exposure in the presence of an acylphosphine oxide photoinitiator. The curing process was followed by infrared spectroscopy, insolubilization, and hardness measurements. Complete insolubilization could not be achieved with the neat ABA rubber because of the poor reactivity of the 2‐butene double bond and the low vinyl content of the polybutadiene chain. The addition of multifunctional acrylate monomers (20 wt %) causes a substantial increase of both the reaction rate and the crosslink density of the polymer, which becomes completely insoluble in toluene in less than 1 s upon UV irradiation. An even greater effect was observed by using small amounts (1 wt %) of a trifunctional thiol crosslinker. Both the thiol and the photoinitiator concentrations were shown to affect the kinetics of the thiol–ene polymerization and the polymer network crosslink density. A direct relationship was found to exist between the swelling degree of the UV‐cured rubber and the interchain molecular weight of the network. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2204–2216, 2001     

PP／EPDM热塑性弹性体动态光交联制备法研究

采用动态光交联法制备了3种不同类型的PP/三元乙丙橡胶(EPDM)热塑性弹性体,探讨了PP的结构及化学组成、动态光交联时间对PP/EPDM热塑性弹性体性能的影响。力学性能、扫描电镜、动态力学热分析、熔体流动速率等测试结果表明,PP的结构及化学组成对体系性能的影响显著,H_2P/EPDM热塑性弹性体的综合性能最佳。而动态光交联能明显提高体系的相容性,进而大幅度提高体系的力学性能。H_2P_(70)V_0的拉伸强度为17．3 MPa,缺口冲击强度为34．9 kJ/m~2,而H_2p_(70)V_(60)的拉伸强度为21．2 MPa,缺口冲击强度为66．3 kJ/m~2,拉伸强度提高20％,缺口冲击强度提高近1倍。     

Photocrosslinking reactions of polyfunctional monomers with vinyl ether or propargyl ether groups

Photocrosslinking reactions of di(2-vinyloxy)ethyl ether of bisphenol-A (BPAEVE), dipropargyl ether of bisphenol-A (BPAPE), and diglycidy ether of bisphenol-A (BPAGE) were carried out using various cationic photoinitiators in 1,2-dichloroethane. The reaction of BPAEVE occurred with high conversion to give the gel products, and the reaction rate of BPAEVE was higher than that of BPAGE. While, the photocrosslinking reaction of BPAPE did not take place under the same conditions. Photoinitiated Michael addition reactions of BPAEVE, BPAPE, and other dipropargyl ethers or ester with pentaerythritol (2-tetramercapto)propionate (PETMP) also proceeded very smoothly to give the gel products by using benzophenone as a photosensitizer in THF. Although the rate of addition reaction of BPAEVE was strongly influenced by the photosensitizer concentration, the addition reaction of BPAEVE with PETMP propagated effectively to give the gel products even without the presence of photosensitizer when irradiated with UV light in THF or toluene solution.     

可注射性骨修复材料不饱和聚磷酸酯的光引发交联聚合

通过凝胶含量的测定，研究了紫外光引发不饱和聚磷酸酯（UPPE）与N-乙烯基吡咯烷酮的共聚交联反应，结果表明：加入光引发剂能够显著增加凝胶含量，安息香乙醚（BE），安息香（BN），2，2-二乙氧基苯乙酮的引发活性较高,光引发剂浓度较低时，增加光引发剂的含量能够显著提高单位时间内的凝胶生成率，但含量过大反而降低凝胶生成率．BN、BE的适宜浓度分别为2．4E^-5（mol／gUPPE）及0．6E^-5（mol／gUPPE）,光照较短时间内，UPPE分子量为5960g／mol的体系具有最高的凝胶生成率，但由于粘度的影响，光照2min后其凝胶生成率低于UPPE分子量为4040 g／mol的体系,表层对紫外光的吸收降低了光能量，导致深层交联聚合反应速度降低，1.5mm厚试样通过延长曝光时间，凝胶含量可与1.0mm厚试样接近，6.0mm试样曝光24min后底层仍不能固化。     

A Targeted Releasable Affinity Probe (TRAP) for In Vivo Photocrosslinking

A protein TRAP : The in vivo photocrosslinking of TRAP after its intracellular targeting to a binding sequence on the bait protein stabilizes protein interactions. Because the crosslinker is releasable, simple mass spectrometry can be used to identify the protein binding sites after purification.

     

Synthesis and Characterization of Injectable Photocrosslinking Poly (ethylene glycol) Diacrylate based Hydrogels

The poly (ethylene glycol) diacrylate (PEGDA)-based hydrogels were prepared by UV radiation under nitrogen, using PEGDA and 2-hydroxyethyl methacrylate (HEMA) as precursors. The PEGDA and HEMA precursors were respectively added into distilled water at a predetermined feed ratio. 2-Hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone (Irgacure2959) was used as a photoinitiator. The PEGDA-based hydrogels were characterized by FT-IR spectra, interior morphology, equilibrium swelling ratio, and Dynamic contact angle (DCA). The results showed: (1) -C=C- bonds of PEGDA and HEMA disappeared after photocrosslinking, which indicated hydrogel formation by consuming -C=C- bonds; (2) swelling ratio of the hydrogels were greatly influenced by the additive precursor ratios and microporous net; (3) with HEMA content increasing in PEGDA-based hydrogels, equilibrium water content (EWC) increased and the contact angle decreased, which resulted from the strong H-bonding interactions of HEMA between the polymer and water.     

Photochemistry of polymeric systems. IV. Photocrosslinking of copolymers including pyridinium dicyanomethylide groups

Photocrosslinkable polymers were obtained by reacting tetracyanoethylene oxide with pyridine units of suitable copolymer. Copolymers of styrene and 4-;vinylpyridine dicyanomethylide were synthetized and studied. The methods used for characterization of photocrosslinked films were a “photoresist test” or the measurement of the insolubilization ratio. The reaction is favored by triplet-;state sensitizers such as Michler's ketone. The photosensitivity of the copolymers was determined as a function of the wavelength of the radiation used.     

Photocrosslinking of solvent-based acrylic pressure-sensitive adhesives (PSA) by the use of selected photoinitiators type I

This study investigated the photocrosslinking of solvent-based acrylic pressure-sensitive adhesives (PSA) containing selected photoinitiators type I, known as α-cleavage photoinitiators. Photocrosslinking of PSA, especially of acrylic PSA, is well established crosslinking process using the UV radiation technology. UV-initiated crosslinking of acrylic PSA allows the synthesis of the wide range of UV-crosslinkable PSA with the interesting features. Especially, the important balances of properties such as adhesive and cohesive strength which are typically critical for the application performance can be achieved by this technology. The selection of suitable photoinitiator plays an important role to obtain the optimum properties of acrylic PSA including tack, peel adhesion, and shear strength. In this study, the investigations on different saturated conventional photoinitiators of type I for solvent-based PSA were carried out. The effects of photoinitiator concentration, UV crosslinking time and UV dose on the tack, peel strength, and shear strength were explored in detail for guiding the choice of photoinitiators to fabricate advanced PSA for industrial usage.     

Adhesion of glow discharge polymers to metals and polymers

Adhesion of glow discharge polymers to metals and polymers in an adhesive joint was measured by lap-shear test and immersion in hot water of 70°C °C for an extended time. A glow discharge polymer was deposited onto polymers [polyethylene and poly(tetrafluoroethylene)] and metals (aluminum and stainless steel) prior to when the polymer and metal were joined. It is found that the lap-shear strength is enhanced by coating the surfaces of these substrates with plasma film produced from methane, ethylene, and acetylene, and that deterioration of the adhesive bonding part, when immersed in hot water of 70°C, is strongly dependent on the gas used as well as operational conditions where a polymer film is formed. The adhesion of a polymer produced from methane on the polymer and metal is strong enough to apply for durable, adhesive joints.     

Toughenability of polymers

We demonstrate that all solid polymers are intrinsically brittle and will undergo a ductile to brittle fracture transition based on the nature of their bonding alone. The most effective way of avoiding a ductile to brittle transition is to reduce the plastic resistance to delay reaching the brittle strength which in unoriented polymers is governed by intrinsic cavitation. While a number of possibilities for this exist, the most widely used techniques involve incorporation of rubbery particles that can cavitate or rigid particles that can debond prior to plastic flow. In both approaches the continuous homo-polymer is transformed into a quasi-regular cellular solid that is much more capable of undergoing large local plastic flow by ligament stretching between cavitated particles and is less susceptible to the propagation of brittle cracks under the usual conditions of tensile straining. Under impact conditions, however, in a notched sample which concentrates the strain rate at the notch root, the plastic resistance of the stretching ligaments rises sharply due to two separate but related effects. First, by an increase in the shear modulus due to the high frequency nature of the Izod impact test to fracture, viewed as a quarter cycle oscillation, which directly elevates the flow resistance and second, by the further effect of increase due to the much increased plastic strain rate. At the notch root then, the plastically stretching and strain hardening ligaments are left with a much reduced capacity to strain further before the cavitation stress is reached. While rubber particle-modified polymers can still exhibit considerable toughening, rigid-particle-modified polymers suffer severely from clustering of rigid particles into super critical flaws that trigger brittle response, much like what is encountered in structural steels.Based on their known mechanical response in neat form six, semi-crystalline polymers have been analyzed in detail to evaluate their potential for toughening under impact conditions. The results correlate very well with the experimental findings.