Copolymerization photoinitiated

Thus, BP-aniline may serve as the photoinitiator in the establishment of some new methods of block copolymerization. 

Copolymerization of methacrylic acid with butadiene and isoprene was photoinitiated by Mn2(CO)io without any halide catalyst [28,29]. The po]ymerization system is accompanied by a Dieis-Alder additive. Cross propagation reaction was promoted by adding trieth-y]aluminum chioride. 

The primary aim of most studies on Lewis acid controlled copolymerization has been the elucidation of mechanism and only low conversion polymerizations are reported. Sherrington et al.m studied the high conversion synthesis of alternating MMA-S copolymers in the presence of Lewis acids on a preparative scale. Many Lewis acids were found lo give poor control (i.e. deviation from 50 50 composition) and were further complicated by side reactions including cross-linking. They found that the use of catalytic BCI- as the Lewis acid and photoinitiation gave best results. 

Two methods for modification of polymer surfaces by photoinitiated graft copolymerization have been developed a discontinuous method (1) with vapor phase transfer of initiator and monomer and a continuous method (2) with presoaking of a film strip or a fiber bundle in a solution of initiator and monomer. Both methods have been applied to polyelefins and linear polyester. 

Difunctional vinvl ether/difunctional N-maleimide. Up until this point, our results have centered on the reactivity of monofunctional maleimide divinyl ether mixtures. From Kloosterboer s26 work for acrylate polymerization, it is known that the rate of polymerization of a free-radical process is increased dramatically as the functionality of the acrylate is increased. In order to enhance the polymerization rates of maleimide divinyl ether systems, it was decided to synthesize difimctional maleimides for copolymerization with difunctional vinyl ethers. The results in Table V indicate that the photoinitiated TTDBM [bismaleimide made from maleic anhydride and 4,7,10-... 

The best evidence for the photolytic decomposition of mercaptans and disulfides into free radicals involves photoinitiation of polymerization of olefins. Thus, photolysis of disulfides initiates the copolymerization of butadiene and styrene,154 as well as the polymerization of styrene207 and of acrylonitrile.19 Thiophenol and other thiols promote polymerization upon ultraviolet irradiation.19 Furthermore, the exchange of RS-groups between disulfides and thiols is greatly accelerated by light. Representative examples are benzothiazolyl disulfide and 2-mercapto-thiazole,90 tolyl disulfide and p-thiocresol, and benzyl disulfide and benzylmercaptan.91 The reaction probably has a free radical mechanism. Similar exchange reactions have been observed of RS-groups of pairs of disulfides have been observed.19... 

Polyfructan (inulin) of MW 30-50 million was synthesized from sucrose with fructosyltransferase (FTF, inulin sucrase from Streptococcus mutans) immobilized by photoinitiated graft copolymerization with poly(2-aminoethyl methacrylate) in the pores of a 3.0 pm microfiltration membrane (Hicke, 1999). 

Similar to the above discussed processes, the photoinitiation of the copolymerization between cyclohexene and AN in the presence of pyromellitic dianhydride or phthalic anhydride is based on the sequence of PET and proton transfer [30]. Consequently, the copolymerization rate with the former acceptor (Rp = 1.6x 10-4moll-1 s-1) is higher than this of the latter (Rp = 1.4x 10-4moll-1 s-1 [AN] = 4.5 mol l-1, 30°C). Interestingly, the average-molar weights of the alternating copolymers lie between 1000-2000 g mol- The reason for this very small value is possibly an efficient primary radical termination due to the formation of the two radicals IV and V see Eq. (4). Exact polymer characterization data are not available, so far. 

In conclusion, on the basis of the collected results, polymeric photoinitiators bearing side-chain benzophenone moieties show, at least under nitrogen atmosphere, a large improvement of activity as comjMred with low-molecular-weight structural models. Pol)rmeric systems having even higher activity can easily be prepared by introducing in the macromolecules, via a copolymerization route. 

Polymeric systems based on side-chain acyloxime moieties and prepared by copolymerization of 1,2-diphenyl-l,2-ethanedione-2-0-acryloyloxime with men-thyl acrylate [poly(BMOA-co-MtA)], have been used as photoinitiators in the UV curing, under nitrogen, of the HDDA/BA equimolar mixture and their activity compared with that of the corresponding low-molecular-weight structural model compound 1,2-diphenyl-l,2-ethanedione-2-0-acetyloxime (BMOAc) [61,84]. 

The reaction of glycidyl acrylate with a-(2-carboxyethyl)benzoin methyl ether has allowed one to obtain [101] the corresponding acrylic monomer which, upon copolymerization with different amounts of MMA, butyl methacrylate and 2-(V, V-dimethylamino)ethyl methacrylate, gives rise to polymeric photoinitiators, containing side-chain benzoin methylether moieties, for photocurable coatings ... 

An inverted sequence of the same procedure has also been used [139] to prepare the same three-block copolymers. Indeed, thermal polymerization of MMA by ABME gives rise to a polymer mainly containing only one benzoin methyl ether moiety per macromolecule, since growing MMA radicals terminate mostly by disproportionation. Thus, terminally photoactive poly(MMA) is used to obtain the photoinitiated block copolymerization of styrene. In this case, a 90% yield of block copolymers is obtained, appreciably higher than in the preceding method, fully consistent with the usual assumption that the termination in styrene polymers occurs by combination. In fact, coupling of the growing styryl radicals with the less reactive poly(MMA)-bound methoxy benzyl radicals also contributes to the formation of block copolymers. 

A further interesting feature of the polymeric photoinitiators is based on the possibility of anchoring different photosensitive moieties to the same macromolecule in order to provide a synergistic effect on activity due to their interaction along the polymer chain. In this context, the synthesis of several copoly-meric photoinitiators bearing side-chain thioxanthone and hydroxyalkylphenone or morpholino ketone moieties has been reported recently [156]. In particular, the free radical copolymerization of 2-[2-(acryloyloxy)ethylthio] thioxanthone (AETX) with either [4-(2-acryloyloxyethoxy)phenyl]-2-hydroxy-2-propyl ketone (HPA) or [4-(2-acryloyloxyethylthio)phenyl]-2-(iV-morpholino)-2-propyl ketone (APMK) [poly(AETX-co-HPA) and poly(AETX-co-APMK), respectively] and of 4-[2-(methacryloyloxy)ethoxycarbonyl] thioxanthone (METX) with APMK [poly(METX-co-APMK)] has been performed. 

M. Sangermano, et al., Cationic photoinitiated copolymerization of 1-propenyl-vinyl ether systems. Eur. Polym. J. 2002, 38(4), 655-659. 

The role of sulphur-containing compounds in photopolymerization appears to have attracted some interest. Bis(j -methylpyridazinyl)-3,3 -disulphide has been found to initiate the photopolymerization of styrene but inhibits the thermal polymerization. The role of thiyl radicals (PhS-) in photoinitiated polymerization of vinyl monomers by aromatic thio-compounds has been postulated by several workers. In one study, flash photolysis was used to identify the nature of the radical. Sulphur-containing monomers such as 4-methyl-2-(vinylthio)thiazole and thiocyclanes have been photopolymerized and copolymerized with other vinyl monomers. Luca et al. have devised a mathematical model for the photopolymerization of 2,3-dimethylbutadiene and thiourea. 

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