Copolymer irradiation

Changes in M versus radiation dose r for MVK-PS copolymers irradiated under vacuum in solid phase at 35 °C. 

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].

The C NMR analyses supported the FTIR results the irradiated blends showed peaks at 127 and 144 ppm for the blend containing 5 wt% of SB. For the blend with SEP, almost no aromatic groups are detected. Again, this was an indication that the SB is more reactive than the SEP copolymer. Irradiation induced the largest... 

Figure 4. Percent gel vs. irradiation dose for the CL-AGE(6 mol% AGE) copolymers irradiated at room temperature and SO C.

Scanning electron micrographs of the unirradiated copolymer and the copolymers irradiated with 20 Mrad at room temperature and 80°C are shown in Figure 6. All micrographs show spheruiitic structure although the... 

Figure 7. Crystalline melting transitions shown by the first DSC scan for the CL-AGE(6 mol% AGE) copolymer irradiated at (a)room temperature and (b)80 C (A) 0 Mrad (B) 5 Mrad (C) 10 Mrad (D) 20 Mrad (E) 40 Mrad.

A Copolymer before cross-polymerization. B Copolymer irradiated with electron beam (50 Mrads) at 20 C. C Copolymer irradiated at 60 C (Liquid crystalline state) with UV lig t. D Copolymer heated at 100 C (molten state). E Potyester 1 (x=3, y=7) irradiated with UV fight. 

Photolysis is also involved in chain scission of (ethylene-carbon monoxide) copolymers irradiated with UV radiation. 

Stress-strain diagram of polyoxymethylene copolymer, irradiation in vacuum at 15 °C with 1 MeV electrons from a van de Graafgenerator [737]... 

Hexafluoiopiopylene and tetiafluoioethylene aie copolymerized, with trichloiacetyl peroxide as the catalyst, at low temperature (43). Newer catalytic methods, including irradiation, achieve copolymerization at different temperatures (44,45). Aqueous and nonaqueous dispersion polymerizations appear to be the most convenient routes to commercial production (1,46—50). The polymerization conditions are similar to those of TFE homopolymer dispersion polymerization. The copolymer of HFP—TFE is a random copolymer that is, HFP units add to the growing chains at random intervals. The optimal composition of the copolymer requires that the mechanical properties are retained in the usable range and that the melt viscosity is low enough for easy melt processing. 

The ETEE copolymer can be cross-linked by radiation (30), despite the high content of tetrafluoroethylene units. Cross-linking reduces plasticity but enhances high temperature properties and nondrip performance. The irradiated resia withstands a 400°C solder iron for 10 min without noticeable effect. 

Heat stabilizers protect polymers from the chemical degrading effects of heat or uv irradiation. These additives include a wide variety of chemical substances, ranging from purely organic chemicals to metallic soaps to complex organometaUic compounds. By far the most common polymer requiring the use of heat stabilizers is poly(vinyl chloride) (PVC). However, copolymers of PVC, chlorinated poly(vinyl chloride) (CPVC), poly(vinyhdene chloride) (PVDC), and chlorinated polyethylene (CPE), also benefit from this technology. Without the use of heat stabilizers, PVC could not be the widely used polymer that it is, with worldwide production of nearly 16 million metric tons in 1991 alone (see Vinyl polymers). 

Among the preformed polymers cured by minor additions of aHyl ester monomers and catalysts followed by heat or irradiation are PVC cured by diallyl fumarate (82), PVC cured by diallyl sebacate (83), fluoropolymers cured by triaHyl trimeUitate (84), and ABS copolymers cured by triaUyl trimeUitate (85). 

Similar to pure polyglycoHc acid and pure polylactic acid, the 90 10 glycolide lactide copolymer is also weakened by gamma irradiation. The normal in vivo absorption time of about 70 days for fibrous material can be decreased to less than about 28 days by simple exposure to gamma radiation in excess of 50 kGy (5 Mrads) (35). 

Etherification and esterification of hydroxyl groups produce derivatives, some of which are produced commercially. Derivatives may also be obtained by graft polymerization wherein free radicals, initiated on the starch backbone by ceric ion or irradiation, react with monomers such as vinyl or acrylyl derivatives. A number of such copolymers have been prepared and evaluated in extmsion processing (49). A starch—acrylonitrile graft copolymer has been patented (50) which rapidly absorbs many hundred times its weight in water and has potential appHcations in disposable diapers and medical suppHes. 

Copolymers of VDC can also be prepared by methods other than conventional free-radical polymerization. Copolymers have been formed by irradiation and with various organometaHic and coordination complex catalysts (28,44,50—53). Graft copolymers have also been described (54—58). 

The quantum yield of polymerization is 6.72 and for photoinitiation < / = 2.85 x 10 . The polystyrene produced with this initiator shows photosensitivity when irradiated with UV light (A = 280 nm). This polymer, which carries two photosensitive end groups of - SC(S) N(CH3)2, behaves as a telechelic polymer and it is useful for production of ABA block copolymer. 

The cross-sectional area per chain in the hexagonal lattice of irradiated PE varies between 20.6 and 22.0 A. It is, thus, always greater than the cross-sectional area in the rotator phase in paraffins (19.5-20.0 A ), but on average somewhat smaller than that in constrained PE fibers above 7, /, (21.4-22.7 A ). An ethylene-propylene diene copolymer with approximately 64%, 32%, and 4% by weight of each component, respectively, was found to contain hexagonal crystals with a cross-sectional area per chain of 20.3 A". 

The photostabilizing efficiency of polymer-bound HALS in i-PP and E-P copolymers were studied and compared with commercial HALS (i.e., Tinuvin 770 and Chimassorb 944) by measuring the carbonyl index at 1720 cm. Plots of carbonyl index versus irradiation... 

Figure 3 Plot of carbonyl index versus irradiation time in E-P copolymer at 0.2 wt% concentration of stabilizers.

The trapped radicals, most of which are presumably polymeric species, have been used to initiate graft copolymerization [127,128]. For this purpose, the irradiated polymer is brought into contact with a monomer that can diffuse into the polymer and thus reach the trapped radical sites. This reaction is assumed to lead almost exclusively to graft copolymer and to very little homopolymer since it can be conducted at low temperature, thus minimizing thermal initiation and chain transfer processes. Moreover, low-molecular weight radicals, which would initiate homopolymerization, are not expected to remain trapped at ordinary temperatures. Accordingly, irradiation at low temperatures increases the grafting yield [129]. 

---