Crosslinking of oligomers bearing carbamoyloxyimino groups with their photochemical and thermal reactions

Carbamoyloxyimino (COI) groups are precursors of photochemically base‐generating groups as well as those of thermally isocyanate‐generating groups. In this study, photochemical and thermal reactions of COI groups in oligomers were investigated by spectral analyses and solubility changes. Oligomers bearing three types of COI groups were prepared. COI groups in all oligomer films were photolyzed on irradiation with 254 nm of light and were deblocked to form isocyanato groups on heating. From the IR spectral analyses, the formation of urea linkage was confirmed by the decrease in isocyanato groups and peak generation because of urea groups on postexposure bake (PEB) treatment. For all oligomer films, PEB was effective for the enhancement of insolubilization of the films in tetrahydrofuran. Heating followed by irradiation was also effective for the insolubilization. These results indicated that photochemical and thermal treatments of COI groups afforded highly sensitive crosslinking systems because of photochemically generated basic groups and thermally generated isocyanato groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2612–2620, 2004     

Photochemistry of ketone polymers. XIV. Studies of ethylene copolymers

Studies have been made of the photochemistry of ethylene copolymers with carbon monoxide (CO), methyl vinyl ketone (MVK), and methyl isopropenyl ketone (MIPK) in solid films. Infrared (IR) evidence is presented to show that a variety of unexpected ketone structures is present in these polymers as a result of 1,5-hydrogen transfer or “back-biting” during the high-pressure polymerization reaction. These additional structures complicate the analysis of the quantum yield data. The overall quantum yield for carbonyl disappearance (?-co) which increases from 0.074 to 0.24 to 0.26 in the series PE-1% CO, PE-2% MVK, and PE-20% MIPK reflects the increasing stability of the alkyl radicals produced from the type I process in the respective ketone structures. It is also shown that ketone groups located in the backbone of the polymer, as in the 1% CO copolymer, have lower quantum yields for photochemical reactions, particularly those that produce free radical intermediates. Studies of the gaseous products from extensive photodegradation under nitrogen show that in all three cases carbon monoxide is the major product (46-65% of the total). Acetaldehyde and methane, expected from the type I reaction, are major products only for the MVK and MIPK copolymers. Reaction schemes are presented to explain the major products observed.     

Functional monomers and polymers. XCIII. Photochemical reactions on the acrylic and methacrylic copolymers containing thymine bases

Photodimerization of Polyacrylic and polymethacrylic derivatives with different pendant thymine unit content was studied in dimethylformamide solution. The quantum efficiency of thymine base for the photodimerization increased with increasing thymine content in the copolymers. The quenching study, which used isoprene as the quencher, revealed that the photodimerization resulted from excited singlet state increases with increasing thymine content. The photochemical results were discussed in terms of self-association of thymine bases in the polymer chain.     

Photochemical reactions of polymers containing thiocyanatoacetyl groups and dyeing the resulting polymer films

Poly(styrene-co-4-thiocyanatoacetylstyrene) and poly(4-acetylstyrene-co-4-thiocyanatoacetyl-styrene) were prepared and their photochemical reactions were studied in the solid state. It was found that the thiocyanatoacetyl groups were easily rearranged with the corresponding isothiocyanatoacetyl groups by ultraviolet (UV) irradiation and that the resulting isothiocyanatoacetyl groups underwent intramolecular cyclization when treated with triethylamine or ammonia to yield oxazole-2-thione moieties. The irradiated polymer films could be dyed selectively with cationic dyes in an appropriate dye bath because of the formation of anionic species by keto-enol tautomerization of oxazole-2-thione moieties in an alkaline state.     

Syntheses and crosslinking reactions of self-curable copolymers containing pendant cyclic iminoethers and carboxylic acid groups

Soluble copolymers containing both pendant cyclic iminoethers such as 4,4-dimethyl-2-oxazoline or 4,4,6-trimethyl-4H-dihydro-1,3-oxazine and carboxylic acid were successfully synthesized by radical copolymerizations of 4,4-dimethyl-2-vinyl-2-oxazoline, 4,4-dimethyl-2-isopropenyl-2-oxazoline, or 4,4,6-trimethyl-2-vinyl-4H-dihydro-1,3-oxazine with methacrylic acid and styrene, methyl methacrylate, or ethyl acrylate using AIBN as an initiator in benzene or DMF at 60 or 80°C. The crosslinking reaction of the copolymers obtained did not occur by heating at 70°C. However, these copolymers quantitatively produced gel products by heating at 130°C. The rate of crosslinking reaction of the copolymer increased with increasing pendant cyclic iminoether and carboxylic acid groups. The rate of crosslinking was also affected by the molecular motion of the polymer chain. Our results show that the copolymers of more sterically hindered 2-vinyl-2-oxazolines are more stable and so they can be crosslinked in a controlled manner and at higher temperatures than the previously studied polyoxaziline system.     

Study of photopolymers. XVI. Novel syntheses of the polymers with azidonitrobenzoyl groups and their photochemical and thermochemical reactions

Poly-2-(2-azido-5-nitrobenzoyloxy)ethylmethacrylate (P-II-A) and poly-2-(4-azido-3-nitrobenzoyloxy)ethylmethacrylate (P-II-B) were synthesized from the reactions of 2-hydroxyethylmethacrylate with 2-chloro-5-nitrobenzoic acid and 4-chloro-3-nitrobenzoic acid, respectively, by substitution reactions of sodium azide with the corresponding chloronitrobenzoyl group. In addition, the degradation reaction of the 2-azido-5-nitrobenzoyl group in P-II-A and the transformation of the 4-azido-3-nitrobenzoyl group to 5-carboxylbenzofurazane-1-oxide ring in P-II-B by irradiation with ultraviolet (UV) light or by heating were investigated in detail. In the photochemical reaction the reaction of the azide group in P-II-A was affected by the presence of a spacer in the polymer chain. Moreover, in the thermochemical reaction the rates of the reactions of azide groups in P-II-A and P-II-B were controlled by the facility of molecular motion and the conformation of polymer chains.     

Syntheses and reactions of porphyrin and metalloporphyrin polymers

Various porphyrin functions such as protoporphyrin IX and chlorin a as well as metalloporphyrin functions such as Mg(II)– and Cu(II)–chlorophyllin a and Fe(III)– and Co(II)–protoporphyrin IX were incorporated into vinyl polymers by preparation and polymerization of their p-vinylbenzyl esters. The porphyrin function was also incorporated by reaction of poly-p-chloromethylstyrene with porphyrins or metalloporphyrins or by the reaction of p-aminostyrene polymers with chlorophyll b through Schiff-base formation. Mg(II)–porphyrin polymers were found to be remarkably effective as catalysts in photoredox systems; porphyrin polymers without central metal atoms were also effective to a lesser extent.     

Functional monomers and polymers. LXI. Photochemical reactions on the synthetic polymers containing thymine bases

Photodimerization of N-2-isobutyloxyethyl thymine (T-M), bis[2-(5-methyl-1-primidinyl)-ethyl] glutarate (T-T), poly(N-2-methacryloyloxyethyl thymine) (polyMAOT), and poly(N-2-acryloyloxyethyl thymine) (poly AOT) was studied in dimethylformamide solution. The rate of intramolecular photodimerization of polyMAOT and polyAOT was 5.7 and 7.2 times faster, respectively, than that of T-T. In T-M, however, intermolecular photodimerization did not occur under the reaction condition used. Quenching studies with isoprene suggest that the photodimerization of T-T occurs predominantly in an excited triplet state, whereas that of polyMAOT and polyAOT occur in singlet and triplet states. It was concluded that the photodimers of T-T, polyMAOT, and polyAOT are two syn-fused cyclobutane-type dimers (cis-syn and trans-syn). Quantum efficiencies of thymine base disappearance were determined by ultraviolet (UV) analysis to be 0.0012 for T-T, 0.0084 for polyMAOT, and 0.010 for polyAOT.     

Enhanced dissolution of copolymers bearing photobase- or photoacid-generating groups in polar solvents by photochemical formation of ionic pairs

Solubility changes in the irradiation of copolymers bearing photoacid- or photobase-generating groups and low molecular weight photobase generators (PBGs) or photoacid generators (PAGs) were investigated. Copolymers bearing acyloxyimino (AOI) groups were used as those generating pendant amino groups photochemically. Copolymers bearing o-nitrobenzyloxycarbonyl and imino sulfonate groups were used as those generating carboxy and sulfo groups, respectively. The solubility of copolymers bearing AOI groups into polar solvents was enhanced by added PAGs such as β-keto sulfones or imino sulfonates after irradiation. A similar enhancement was observed in copolymers bearing o-nitrobenzyloxycarbonyl groups in the presence of PBGs such as oxime esters or o-nitrobenzyl carbamates. These results showed that the formation of acid–base pairs on irradiation was effective for dissolution into polar solvents. Copolymers bearing imino sulfonate groups showed a high solubility, and no such enhancement was observed by PBG. Films of copolymers bearing β-keto sulfone groups became insoluble because of crosslinking. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1708–1715, 2001     

Synthesis and photochemical properties of high-impact styrene copolymers containing keto groups

A method for the preparation by suspension polymerization of high-impact styrene copolymers containing built-in keto groups is described. Some of the features of the process are described. Photolysis of these copolymers on irradiation with polychromatic and monochromatic light (λ = 313 and 366 nm) has been investigated. The quantum yields of cleavage of the main chain (ø_cs) in film or solution have been shown to be concentration dependent. It has been concluded that the photoprocesses in these two-phase polymeric systems proceed independently in the polymer matrix and in the dimethylformamide insoluble fraction.     

Syntheses and crosslinking reactions of polymers containing spiroorthoester moieties

The radical copolymerization of unsaturated spiroorthoesters such as 2-methylene-1,4,6-trioxaspiro[4.6]undecane (SOE I) and 2-methylene-9-methyl-1,4,6-trioxaspiro[4,5]decane (SOE II) with vinyl monomers was carried out to find that SOE I and SOE II were copolymerized with electron-poor olefins such as methyl acrylate, acrylonitrile, and methyl methacrylate to obtain the corresponding copolymers containing spiroorthoester moieties, respectively. The obtained copolymers were treated with BF₃.OEt₂ or BzS⁺SbF to afford crosslinked polymers undergoing expansion in volume on crosslinking in those cases of copolymers of SOE I.     

Syntheses and reactions of functional polymers. XLVI. Preparation and reactions of N-benzyloxyisomaleimide–styrene copolymer

Polymerization of N-benzyloxymaleimide(I) was attempted to obtain a polymer with the N-hydroxysuccinimide unit in the chain. In the light of infrared and NMR data the compound reported by Ames as N-benzyloxymaleimide is N-benzyloxyisomaleimide (III). Homopolymerization of III did not give polymer. Copolymerization of III with styrene was carried out in dioxane at 70°C. A strong alternation tendency like that of maleimides was observed. Monomer reactivity ratios and Q-e values were determined. Copolymer having the isoimide structure showed infrared absorptions at 1815 and 1675 cm^?1 in the carbonyl region. The copolymer was isomerized to N-benzyloxymaleimide type copolymer and debenzylated to N-hydroxymaleimide type copolymer. An insoluble copolymer was prepared by using divinylbenzene as a crosslinking agent and was converted to N-acetoxymaleimide type copolymer, which was used as an insoluble acetylating agent.     

New high temperature polymers. VI. Ordered heterocycle copolymers

A new class of linear, thermostable polymers is reported. The compositions are ordered heterocycle copolymers in which two different heterocycles alternate regularly along the polymer chain. Examples of combinations studied are: oxadiazole–benzimidazole, oxadiazole–pyromellitimide, and thiazole–pyromellitimide. The heterocycle copolymers, or alternatively, the corresponding precursor polymers, were prepared by condensing preformed di-or tetrafunctional blocks which contain one type of heterocycle with a second di- or tetrafunctional monomer under such conditions that no rearrangement of bonds occurred. The polymers are characterized in general by neither melting nor decomposing below 500°C. when heated in an inert atmosphere at a rate of about 10°C./min. Some of the copolymers are readily soluble in organic solvents; many, however, are soluble only in solvents such as concentrated sulfuric acid. In the case of the more intractable polymers, soluble precursor polymers can usually be prepared. In such precursor polymers only one of the heterocycles is preformed; the second heterocycle is formed by post-treatment after the polymer has been fabricated into an end product. All of the polymers yielded self-supporting films, some having very high strength; films of several of the polymers were hot-drawable. Drawn film of an ordered oxadiazoleimide copolymer was shown to be well oriented and moderately crystalline.     

Investigation of photophysical and photochemical properties of phthalocyanines bearing fluorinated groups

This study presents synthesis of novel peripherally tetrasubstituted Zn(II) and In(III) phthalocyanine complexes bearing 3,5-bis(trifluoromethyl)phenoxy groups. These phthalocyanines were characterized by performing elemental analysis, mass spectrometry, nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and ultraviolet visible spectrophotometric techniques. Aggregation properties of the resulting phthalocyanines were studied in different concentrations of DMSO. Aggregation behavior of the newly synthesized phthalocyanines was investigated in various organic solvents, as well. Photochemical and photophysical characterization of the resulting compounds were carried out to evaluate their photodynamic therapy properties in DMSO. The new metallophthalocyanines have high singlet oxygen quantum yields ranging from 0.72 to 0.88.     

Dendrimers as photochemical reaction media. Photochemical behavior of unimolecular and bimolecular reactions in water-soluble dendrimers

Synthesis and studies of poly(alkyl aryl ether) dendrimers, possessing carboxylic acid functionalities at their peripheries, are reported. 5-Bromopentyloxy methylisophthalate was utilized as the monomer to O-alkylate the phenolic hydroxyl groups of poly(alkyl aryl ether) dendrimers. Dendrimers of first, second, and third generations, possessing 6, 12, and 24 carboxylic acids, respectively, were thus prepared. These dendrimers were soluble in alkaline aqueous solutions, and the ensuing microenvironmental properties of the aqueous solutions were assessed by pyrene solubilization studies. Upon establishing the presence of nonpolar microenvironments within the dendritic structures, solubilizations of few organic substrates were conducted and their photochemical behaviors were assessed. Specifically, the photolysis of 1-phenyl-3-p-tolyl-propan-2-one and benzoin ethyl ether and photodimerization of acenaphthylene were conducted. These studies revealed that the product distribution and the "cage effect" were more distinct and efficient for the third generation dendrimer, than for the first and second generation dendrimers. The photochemical studies of carboxylic acid functionalized dendrimers were compared to that of hydroxyl group terminated poly(alkyl aryl ether) dendrimers.     

Photochemistry of fiber-forming polymers. I. Acrylonitrile copolymers and fibers containing ketone groups

The inclusion of minor amounts of methyl isopropenyl ketone in polyacrylonitrile and its copolymers with methyl acrylate and vinyl acetate causes the polymer to become sensitive to ultraviolet light in the 290–320 nm region. Both films and fibers show decreases in molecular weight on irradiation which are attributable to C? C bond scission by the Norrish type II reaction. In addition to bond cleavage, decarbonylation occurs, presumably by a type I radical process which also leads to the formation of ketonitrile groups. Fibers spun from such polymers lose most of their tensile strength and elongation after a few months outdoor exposure to natural sunlight, whereas control samples not containing carbonyl groups will retain their strength for much longer periods. Quantum yields both for chain scission and for carbonyl loss in these systems are estimated to be of the order of 0.005.