0-Scission, methacrylate copolymers

Poly(acrylates) and (alkyl acrylates). - Structured nanopore films of poly(styrene-block-methyl methacrylate) copolymers have been made with controlled spectral sensitivity, such that each block is sensitive to a specific degradation wavelength. In copolymers of 2,2,2-trifluoroethyl methacrylate with vinyl ethers, the photosensitivity is controlled by the vinyl ether units. Photodegradation occurs at the tertiary positions of the ether units followed by lactone formation and chain scission processes. Furthermore, the fluorinated side chains have been found to inhibit cyclization reactions. 

Chain-Scission Yields of Methacrylate Copolymers Under Electron Beam Radiation... 

Fig. 17. Dependence of rates of crosslinking and scission on the composition of methyl methacrylate copolymers irradiated in the form of films and A chain scission, crosslinking [reproduced from Ref. 89].

Hepuzer et al. [91] have used the photoinduced homolytical bond scission of ACPB to produce styrene-based MAIs. These compounds were in a second thermally induced polymerization transferred into styrene-methacrylate block copolymers. However, as Scheme 24 implies, benzoin radicals are formed upon photolysis. In the subsequent polymerization they will react with monomer yielding nonazofunctionalized polymer. The relatively high amount of homopolymer has to be separated from the block copolymer formed after the second, thermally induced polymerization step. 

Consideration of the relationship between the effects of radiation on homopolymers and copolymers raises the question of the variation from homopolymer behaviour with sequence length. Every copolymer has a distribution of sequence lengths for each comonomer. At what minimum sequence length does methyl methacrylate not show the high scission of PMMA The future will probably see the development of processes for making polymers with controlled mini-block sequences to maximize a number of properties such as scission yield, adhesion, flexural strength, Tg.. 

Copolymer of ethylene and 15 wt% of methacrylic acid neutralized with 60 % sodium cations. b Typical use rate is 1.2% (can cause chain scission of PET chains). 

Another interesting positive-tone polyacrylate DUV resist has been reported by Ohno and coworkers (82). This material is a copolymer of methyl methacrylate and glycidyl methacrylate. Such materials are negative e-beam resists, yet in the DUV they function as positive resists. Thermal crosslinking of the images after development provides relief structures with exceptional thermal stability. The reported sensitivity of these copolymers is surprising, since there are no obvious scission mechanisms available to the system other than those operative in PMMA homopolymer, and the glylcidy side-chain does not increase the optical density of the system. 

In the poly(methyl methaerylate)-styrene system, less than 7% of the original polymer remained as homopolymer at total conversion (77). Over 85% of the product was non-branched, single-segment block copolymer. The difference for these two systems is in part due to the higher molecular weight of the initial poiy(methyl methycrylate) (2900000 versus 495000) and in part to the preferential scission of the poly(methyl methacrylate) chain. This point was confirmed by running tests on a mixture of the two homopolymers in the presence of a radical acceptor to prevent macroradical recombination, and on the isolated block copolymers. 

If a mechanical degradation of a solution of two polymers is carried out by high speed stirring, the formation of a block copolymer is not probable as the scission of polymer molecules at low concentration is not caused mainly by intermolecular interaction, such as by collision of molecules and through entanglements, but by displacements due to hydrodynamic forces in velocity gradients. Nakamo and Minoura (98) did obtain reaction by stirring a benzene solution of polyethylene oxide and poly(methyl methacrylate). 

PVC, another widely used polymer for wire and cable insulation, crosslinks under irradiation in an inert atmosphere. When irradiated in air, scission predominates.To make cross-linking dominant, multifunctional monomers, such as trifunctional acrylates and methacrylates, must be added. Fluoropolymers, such as copol5miers of ethylene and tetrafluoroethylene (ETFE), or polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), are widely used in wire and cable insulations. They are relatively easy to process and have excellent chemical and thermal resistance, but tend to creep, crack, and possess low mechanical stress at temperatures near their melting points. Radiation has been found to improve their mechanical properties and crack resistance. Ethylene propylene rubber (EPR) has also been used for wire and cable insulation. When blended with thermoplastic polyefins, such as low density polyethylene (LDPE), its processibility improves significantly. The typical addition of LDPE is 10%. Ethylene propylene copolymers and terpolymers with high PE content can be cross-linked by irradiation. ... 

On fractionation, two maxima can be taken in evidence, one corresponding to the-graft copolymer, the second to the homopolymethyl methacrylate initiated by the OH radicals resulting from the hydroperoxide scission ... 

In addition to the polarity change, the tone of certain resist materials may be reversed simply by changing the wavelength of exposure. For example, copolymers of methacrylonitrile and methacrylic acid undergo main-chain scission when exposed to DUV radiation to provide positive-tone im-... 

In some instances, the macromonomers synthesized by CCT can be copolymerized with acrylics to form comb copolymers. While /1-scission predominates in copolymerizations with methacrylates, acrylates and styrene give both incorporation to yield comb copolymers and /1-scission.492 Products of this type have been thoroughly characterized by a variety of spectroscopic techniques. When high levels of CCT macromonomers are employed, it is possible to go beyond the comb structure and obtain more highly branched polymers.493... 

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