Crosslinked PPO

Similarly, the elongation at break and the tensile strength of the crosslinked PPO are lower than those of PCL, which explains the decrease in elongation at break and decrease in tensile strength of the TPVs as shown in Fig. 11. By increasing Tcure, not only the rubber particle size decreases, but also the connectivity increases. 

Typical polyurethanes use a diol extender such as 1,4 butane diol. The NH groups form hydrogen bonds with C=0 groups on neighbouring chains, inside very small, hard blocks. The soft blocks are crosslinked polyethers or polyesters. A typical polyether is poly(propylene oxide) —[—O—CH2— C(CH2)H—] pre-polymerised to a molecular mass Mn of about 6000, a degree of polymerisation n = 140. The PPO has a glass transition temperature of about —60 °C, so the crosslinked PPO is a rubber. This rubbery phase is connected, via the polyurethane molecules, to the crystalline phase. 

Pseudo-IPN s (PDIPN s) Two types of pseudo-IPN s were prepared, one from crosslinked PPO (CPPO)/linear polystyrene (LPS) (PDIPN-1) and the other from a linear PPO (LPPO)/crosslinked polystyrene (CPS (PDIPN-2). The former PDIPN s were prepared from a mixture of PPO solution with ethylene diamine (crosslinking agent) and styrene monomer with AIBN. 1.4 g. of ethylene diamine was added to 40 g. of PPO. The mixture of PPO solution and styrene... 

The effect of UV-radiation on the gas sorption and transport properties of PPO films were reported. The authors have postulated a method for crosslinking of PPO on radiation when a benzylic hydrogen is abstracted from one of the methyl groups on the aromatic ring. In this way radicals are formed that may combine to give crosslinked PPO. Gas transport properties at 2 atmospheric pressure and 35 C for He, H2, O2, N2, CO2 and CH4 were studied. The data are shown in Table 14. 

Attempts to transform both PSU and PPO containing high concentrations of chloromethyl or bromomethyl groups into the corresponding polymers containing pendant vinyl groups led to crosslinked polymers. 

Tg for a linear, high-molecular-mass PPO, which was prepared from a polypropylene glycol precursor (with a molecular mass of 4000 g/mol) using a chain extender with a chemical structure similar to that of the crosslinker, is -62.5 °C. The Tg was determined from DMA measurements performed at 0.215 Hz [43]. 

Fig. 8 a, b. Experimental extension ratio X of crazes as a function of the theoretical maximum extension ratio of a single strand in the network (entanglements and crosslinks) a crosslinked polystyrene (open circles) and poly(pmethylstyrene) (closed circles) and b various entangled homopolymers and copolymers (open circles), and polymer blends of PS and PPO (closed circles)... 

Fig. 9. Plot of the true suain ratio in craze and deformation zones showing the transition from crazing to shear deformation as a function of network strand (entangled + crosslinked) density v. The open squares and open diamonds represent uncrossiinked homopolymers and copolymers, the open triangles and hexagons represent uncrossiinked blends of PS and PPO and the filled triangles and circles represent crosslinked PS (After Ref. courtesy of J. Polym. Sd.-Polym. Phys. (Wiley))...

Three homopolymer (diblock copolymer) phase boundary systems have been studied extensively the system of polystyrene (PS) and poly(2-vinylpyridine) (PVP) reinforced with diblock copolymers ofPS-PVP [22,25,28,31-33], the system of poly(methyl methacrylate) (PMMA) and PS reinforced with diblock copolymers of PMMA-PS [17,24,34,35] and the system of PMMA and poly(phe-nylene oxide) (PPO) reinforced by diblock copolymers of PMMA-PS [ 14,36,37]. Phase boundaries between PS and a crosslinked epoxy (XEp) were reinforced with carboxy-terminated PS chains whose -COOH ends reacted with either excess amines or epoxy to form a grafted brush at the interface [38,39]. In a similar manner, interfaces between rubber-modified PS (HIPS) and XEp reinforced with grafted PS-COOH chains have been investigated [40]. 

Physical hydrogels were formed induced by self-assembled water-insoluble and crystalline polypseudorotaxane domains which act as physical crosslinking points. Such physical hydrogels include the polypseudorotaxane systems of a-CD threading on PEO or its copolymers, a-CD threaded on PEI, PL, or their copolymers, and even 3-CD or y-CD threaded PPO or PEI copolymers. The thermo-reversible and thixotropic properties of these supramolecular hydrogels have inspired their applications as injectable drug delivery systems. Physical hydrogels induced by physical interaction of threaded CD molecules in polyrotaxanes were also developed. 

Sosnik, A., Cohn, D., San Roman, J. S. Abraham, G. A. (2003) Crosslinkable PEO-PPO-PEO-based reverse thermo-responsive gels as potentially injectable materials. Journal of Biomaterials Science - Polymer Edition, 14, 221-2 i9. 

This paper reports what we believe to be the first true IPN, i.e., no grafting between polymers and a single phase morphology (i.e., complete chain entanglement). In order to achieve this, pol3nners of known compatibility were used. Thus, IPN s, pseudo-IPN s (PDIPN s - only one polymer crosslinked), and linear blends of polystyrene (PS), and poly(2,6-dimethyl-l,4-phenylene oxide) (PPO) (whose compatibility has been reviewed elsewhere (14)) were prepared by the simultaneous interpenetrating network (SIN) technique. The polystyrene was crosslinked by incorporating divinylbenzene. Several methods have been reported to synthesize... 

Full IPN s (FIPN s) FIPN s (both pol3rmers crosslinked) were prepared from the mixture of the PPO solution with ethylene diamine and styrene monomer with divinyl benzene and AIBN. The curing conditions and compositions were the same as those for the linear blends. 

The ideal crosslinking reaction of brominated PPO is shown below. To confirm that crosslinking did indeed occur, solubility studies and elemental analyses were performed. The cured polymers did not dissolve in either tetrahydrofuran or trichloroethane (both good solvents for PPO) however, swelling did occur to about twice the initial dimensions. The elemental analyses (N, Br) ... 

Based on the amount of bromine reacted, th number average molecular weight between two crosslink sites (M ) in PPO was 17,000. The theoretical of the crosslinked polystyrene was 7,260. 

If significant phase mixing occurs, a would be expected to be positive or zero (i.e., Tg < Tg(av) as it was (effectively) for these IPN s. For an IPN, a is expected to reach a maximum very close to the maximum in crosslink density (which includes physical entanglement crosslinks resulting from the superposition of the two networks) (17). The maximum value of O is at an IPN of 75% PPO/... 

If the thermal stability of the ether bonds is very low, then their decomposition occurs at temperatures, which are insufficiently high for the subsequent thermal degradation of the polymer. After the decomposition of all the weak bonds, the degradation of the newly formed structure, followed by the release of comparatively high molecular mass oligomers, crosslinking and the thermal decomposition of aromatic nuclei. Such a scheme for the thermal degradation of PPO depends on data on the chemical structure of the initial PPO, and the volatile and final solid products of this process at different temperatures. These data enable determination of the direction of thermal... 

ABS Acrylontrile-butadiene-styrene EVA Ethylene-vinyl acetate PAI Polyamide-imide PC Polycarbonate PE Polyethylene PEEK Polyether ether ketone PES Polyether sulfone PET Polyethylene terephthalate PI Polyimide PMMA Polymethyl methacrylate PPO Polyphenylene oxide PPS Polyphenyl sulfide XLPE Crosslinked polyethylene Source Author s own files ... 

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